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Ultrathin VO2 films with insulator-metal transition (IMT) were successfully fabricated on sapphire (001) substrates by utilizing radio frequency-biased reactive sputtering. We realized a 6 nm-thick VO2 film that shows resistance change over 2 orders of magnitude. Microscopic observations combined with energy dispersive x-ray analyses revealed characteristic networking morphology in VO2 films with thickness up to around 10 nm. It was found through micro-Raman analyses that a 30 nm-thick film possessed flat surface and ordered lattice with strong in-plane tensile stress. We evaluated the thickness dependence of optical switching performance for infrared-light. The results suggest that the thickness of the VO2 films should be carefully selected for realizing required performances of optical switching, which depends on not only IMT but also characteristic morphological aspects., Part of this work was carried out under the Cooperative Research Project Program of the Research Institute of Electrical Communication, Tohoku University. XRD, SEM, AFM, and EDX analyses were performed in the Future Science and Technology Joint Research Center of Tokai University.

Novel methods for the deposition of thin functional coatings, such as hybrid physical vapor deposition-chemical vapor deposition (CVD) technologies, have the potential to become an important means of overcoming the limitations of current processes, such as low deposition rates, associated with some sputtering processes, or limited material/precursor choices, associated with CVD processes. This work explores the potential of addressing these issues through the development of a hybrid system, which combines the latest magnetron sputtering technology, high power impulse magnetron sputtering (HiPIMS), with plasma enhanced chemical vapor deposition (PECVD) technology. This system seeks to overcome the limitations of each technique and provide a new, flexible deposition tool for functional films, such as transparent conductive oxides. In this system, the plasma generated by the magnetron provides a source of electrons to drive the CVD precursor decomposition and reaction chemistry in the PECVD process. Consequently, only one power supply is required. Thus, niobium-doped titania coatings were deposited on glass and Si wafer substrates by this hybrid HiPIMS-CVD technique. The TiO2 coatings were deposited by CVD from a titanium (IV) tetraisopropoxide precursor via the vapor drawn method. The HiPIMS process provided not only the source of the Nb metal dopant to the functional films but also sustained the low temperature CVD process by supplying energetic plasma particles. Furthermore, since HiPIMS deposition rates are very sensitive to magnetic field strength and the degree of unbalance, by using a magnetron with variable magnetic field strength, it was possible to adjust the dopant content of the film without adjusting the power applied to the magnetron target. The effect of processing parameters (pulse frequency, peak powers, precursor flow rates, operating pressure, etc.) on generating a stable HiPIMS discharge across the process envelope has been studied. The composition and microstructure of the deposited coatings have been investigated, in respect to variable process parameters, such as substrate temperature and operating pressure.

La1−xSrxVO3 (0 ≤ x ≤ 1) films can be transparent conducting oxides such as n-type SrVO3 and p-type La2/3Sr1/3VO3 films. They also show a semiconductor-to-metal transition (SMT) near x = 0.2. The optical and electrical properties of La1−xSrxVO3 (0 ≤ x ≤ 1) films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates using RF sputtering deposition were investigated. Resistivities of La1−xSrxVO3 showed SMT near x = 0.2. La1−xSrxVO3 films grown on LSAT substrates were found to have high crystallinity using θ−2θ scan and grazing incidence x-ray diffraction measurements. Dielectric functions of La1−xSrxVO3 films were measured using spectroscopic ellipsometry. The evolution of optical spectra of La1−xSrxVO3 films from LaVO3 to SrVO3 was compared to the electronic band structures as a function of Sr composition, which was either experimentally observed or theoretically calculated in the literature. With increasing Sr composition, the interband transition energies of O 2p to V 3d states near 4 eV changed linearly as a function of Sr content.

The demand for ion beam sputtering-coated substrates is growing. In order to introduce ion beam sputter deposition (IBSD) technology into new fields of application, the deposition area must be further increased. In this context, the ion species applied for the sputtering process is an important parameter. In the present investigation, an industrial scale IBSD process was characterized with respect to productivity and layer quality by varying the ion species. Ar, Kr, or Xe broad ion beams at an ion energy of 1.8 keV were used, and the evaluation was carried out on the basis of Ta2O5 layers. The dielectric films were produced in a reactive process through the sputtering of a metallic Ta target, and their two-dimensional distributions of the coating rate R, the refractive index [Formula: see text], and the extinction coefficient [Formula: see text] were determined over a planar area of 0.9 × 1.0 m2 above the target by the collection method. R served as a measure of productivity, while [Formula: see text] and [Formula: see text] were quality parameters. Additionally, the layer composition was determined for selected samples on the collector by an electron probe microanalyzer (EPMA). As expected, the different ion-solid interaction mechanisms resulted in significant differences with regard to productivity. Linear scaling of productivity as a function of ion mass was observed. Calculations of the sputtering yield with semiempirical models or SRIM-2013, a binary collision Monte Carlo simulation program, did not confirm the observed linearity. Furthermore, the configuration with the highest productivity, Xe, led to a locally occurring and significant reduction in layer quality, more precisely, an increase of [Formula: see text]. Additionally, the layer compositions determined with EPMA confirmed that ions originating from the ion source were implanted in the thin films during their formation. A detailed evaluation of the angle-resolved energy distributions of the involved particles, simulated with SRIM-2013, was performed. However, the determination of the energies carried away from the target by backscattered ions and sputtered target atoms does not explain the observed degradation mechanism. This concludes that for the realization of future large-area coatings with IBSD, not all relevant mechanisms are yet understood in sufficient detail.

The Bi 4Se 3 system is an intrinsic superlattice of two topological materials, a 2D Bi 2 sheet and a quintuple layer (QL) slab of Bi 2Se 3. Both the QL slab and 2D sheet host distinct topologically protected states; this, in turn, allows for the selection of the topologically protected electronic state with the choice of surface layer termination. The Bi 4Se 3 films were grown by direct current magnetron sputtering under an additional external magnetic field to further confine the plasma region. We developed a recipe to transition from an atomically smooth layered growth to a smooth faceted granular growth. We characterized the morphology, composition, and local crystal orientation of grown films via scanning electron microscopy, energy dispersive x-ray spectroscopy, and electron backscattered diffraction. Additionally, characterization by scanning tunneling microscopy/spectroscopy confirmed the presence of the topologically protected surface states in these films. This work buttresses the commercial scalability of sputtering materials with tunable Bi 4Se 3 morphology, which provides the option of tuning the surface topological state and thus expanding the possibilities for the production of devices with this material systems.

Boron-containing materials exhibit a unique combination of ceramic and metallic properties that are sensitively dependent on their given chemical bonding and elemental compositions. However, determining the composition, let alone bonding, with sufficient accuracy is cumbersome with respect to boron, being a light element that bonds in various coordinations. Here, we report on the comprehensive compositional analysis of transition-metal diboride (TMBx) thin films (TM = Ti, Zr, and Hf) by energy-dispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), time-of-flight elastic recoil detection analysis (ToF-ERDA), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). The films are grown on Si and C substrates by dc magnetron sputtering from stoichiometric TMB2 targets and have hexagonal AlB2-type columnar structures. EDX considerably overestimates B/TM ratios, x, compared to the other techniques, particularly for ZrBx. The B concentrations obtained by XPS strongly depend on the energy of Ar+ ions used for removing surface oxides and contaminants prior to analyses and are more reliable for 0.5 keV Ar+. ToF-ERDA, RBS, and NRA yield consistent compositions in TiBx. They also prove TiBx and ZrBx films to be homogeneous with comparable B/TM ratios for each film. However, ToF-ERDA, employing a 36-MeV 127I8+ beam, exhibits challenges in depth resolution and quantification of HfBx due to plural and multiple scattering and associated energy loss straggling effects. Compared to ToF-ERDA, RBS (for the film grown on C substrates) and NRA provide more reliable B/Hf ratios. Overall, a combination of methods is recommended for accurately pinpointing the compositions of borides that contain heavy transition metals. Funding agencies: The SwedishResearch Council VR (Grant Nos. 2021-00357, 2018-03957, and642-2013-8020); the Knut and Alice Wallenberg (KAW) Foundation for project funding (No. KAW 2015.0043), the Swedish Energy Agency under Project No. 51201-1, Carl Tryggers Stiftelse (Contract Nos. CTS 15:219, CTS 20:150, and CTS 14:431); the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO Mat LiU No. 2009 00971), the Swedish Research Council VRRFI (No. 2017-00646_9) for supporting the Accelerator based ion technology center; the Swedish Foundation for StrategicResearch (Contract No. RIF14-0053)

We studied the role of hydrogen-containing species (OH and/or H) in promoting photoluminescence (PL) from 1 at. % Eu3+ ions doped in ZnO thin films. The hydrogen concentration in the films was systematically changed by varying the substrate temperature and the vapor pressure of H2O gas supplied during sputter deposition. The correlation between the PL spectra via bandgap excitation and the degree of oxidization/hydrogenation was investigated by x-ray diffraction and Fourier-transform infrared spectroscopy. Films deposited at room temperature under H2O partial pressures higher than 10−2 Pa were sufficiently hydroxylated, as confirmed by the appearance of diffractions peaks from Zn(OH)2 coexisting with ZnO(002). Eu3+ emissions were observed after post-annealing in a vacuum or O2 atmosphere. When the H2O pressure was lower than 10−2 Pa, the ZnO:Eu films were so oxygen-deficient as to exhibit a metallic character, which deactivated the Eu3+ emission. Deposition at temperatures above 200 °C reduced the OH and/or H species incorporated in the ZnO films and only a faint Eu3+ emission was observed. The H2O pressure under which a sharp Eu3+ emission could be obtained was between 1.0 and 2.5 × 10−2 Pa if subsequent post-annealing was done in a vacuum. For more oxidized films deposited at 3.5 × 10−2 Pa, reduction by post-annealing in an H2 atmosphere was effective to generate a sharp and intense Eu3+ emission signal through reduction and hydrogenation, confirming that a moderate oxidization/hydrogenation state is a necessary condition. Codoped hydrogen species will facilitate substituting Zn2+ sites with emission-active Eu3+ ions and stabilize them.

This work is devoted to the problem of the formation of titanium monoxide and dioxide by magnetron sputtering. Sputtering titanium in constant flows of oxygen and argon and constant magnetron power leads to the creation of equilibrium partial pressures of oxygen and titanium vapors. The conditions for the synthesis of nanocrystalline titanium monoxide at low temperatures were determined experimentally and substantiated by the thermodynamic method. An analysis is made by the method of minimizing the Gibbs free energy. We have obtained an expression for the ratio of the oxygen flow and the gas discharge power, the analysis of which makes it possible to determine the conditions for the formation of titanium oxide with a certain stoichiometric composition. The developed method for the analysis of equilibrium in the deposition chamber can be used to identify the conditions for the synthesis of other compounds that are important for practice, including oxides and chalcogenides, and the horizons of their use in nanoelectronics are constantly growing at the present time.

We report the direct deposition of model sodium sulfide films by RF magnetron sputtering from Na2S and Na2S2 deposition targets. Analytical characterization and electrochemical cycling indicate that the deposited films are amorphous with stoichiometries that correspond to Na2S3 and Na2S2 formed from the Na2S and Na2S2 targets, respectively. We propose that the loss of Na in the case of the Na2S target is due to preferential sputtering of Na resulting from the higher energy required to break the Na–S bonds in Na2S. The development of thin film sodium sulfides opens a new route to understanding their fundamental properties, such as Na+ transport, conductivity, and reactivity.

We insert a silver (Ag) layer between zinc oxide (ZnO) and graphene films of a bilayer structure to create trilayer transparent conductive oxide films with improved conductivities due to the bridge provided by the Ag layer to transport free electrons. To construct trilayer ZnO/Ag/graphene transparent conductive films, the Ag and ZnO layers are deposited successively on a graphene/glass substrate by magnetron sputtering from solid Ag and powder ZnO targets. The results show that the electron concentration in the trilayer films increases one order of magnitude to 1021 cm−3 upon inserting dispersed Ag dots and three orders of magnitude to 1023 cm−3 upon adding a relatively continuous 10.5-nm-thick Ag layer. However, the electron mobility drops dramatically from 10−1 to 10−2 cm2 V−1 s−1 because the dispersed Ag dots of a thin Ag layer form narrow bridges, which limit electron transport. The continuous 10.5-nm-thick Ag layer not only acts as a wide bridge but also provides electrons; therefore, the resistivity of the ZnO/Ag(continuous)/graphene trilayer decreases significantly, while the mobility of the trilayer film remains of the same order of magnitude as that of the continuous Ag layer. Of course, the transparency of the trilayer film decreases slightly upon inserting the Ag layer. To create frontier electrodes, the ZnO/Ag/graphene multilayer structure must be built up to form transparent conductive oxide films.

A magnetron sputtering discharge with a positively biased anode in argon gas is investigated by Langmuir probe diagnostics and by energy-resolved mass spectrometry. The discharge is operated in continuous (direct current) and in pulsed (high power impulse magnetron sputtering, Hi) mode with a Ti target and in Ar gas. Singly-charged Ar +, Ti +, and Ar 2 + and doubly-charged Ar 2 + and Ti 2 + ions are observed. A novel approach is to bias the magnetron anode. Application of a positive anode voltage shifts the kinetic energies of plasma ions by q e 0 V a, where V a is the anode voltage and q e 0 is the ion charge. It allows for an effective control of plasma ion energies.

International audience; A high power impulse magnetron sputtering (HiPIMS) discharge process is analyzed numerically and experimentally so that one may better understand and explain the effect of the pressure and pulse width on HiPIMS discharges and the deposited thin films. For this reason, a time-dependent global plasma model is developed for the ionization region in a HiPIMS discharge of a Cr target in Ar gas. It is based on the solving of a nonlinear equation system composed of the continuity equations of neutral and charged species in the ionization region considered in the reaction scheme. The pulse widths are about tens of microseconds for a frequency cycle of 1KHz. The simulations are performed for a 150W average power and 5-30mTorr pressure range. In these average power and pressure ranges, a double peak of the electron temperature is observed. The high first peak is due to a high rapid increase of negative voltage during the rising time of pulses, while the second one is due to a diminution of the injected gas Ar in the ionization region. On the other hand, gas rarefaction characterized by the diminution of the Ar density during time-on is due to the high ionization degree and the sputtering wind effect. During plasma off, the density of Ar returns to the stationary state corresponding to the initial pressure. In addition, the simulations reveal that the Cr+ population is more important than that of Ar+ caused by the high ionization degree of Cr compared with Ar. This confirms the high ionization degree during time-on, leading to a high efficiency of sputtering of Cr material. However, Cr2+ is still weak. In addition, a good agreement is shown between the calculated time current evolution and the measured one.

In this study, we investigate the residual stress gradient of aluminum nitride thin film deposited by reactive pulse DC magnetron sputtering technique on a 200 mm diameter silicon wafer with a 1 μm layer of plasma enhanced chemical vapor deposition tetraethylorthosilicate. Stress measurements are obtained using in situ fabricated rotational beam microstructures. The rotating beam moves in response to relief of the residual stress on the connecting arms that experience lengthening or shortening due to compressive or tensile residual stresses, respectively. Various arm-beam connecting joints, separation gaps between the arms, and arm lengths are considered to determine the optimum microstructure for localized residual stress evaluation of the sputtered aluminum nitride. The displacement of the rotating beams with four different arm-beam connecting-joint designs is analytically modeled using COMSOL multiphysics finite element method simulation. The results of the analytical model were found to be in agreement with the results observed through experiments. The stress gradient measurements obtained using the microstructures are compared to the Stoney stress evaluated using a wafer bow technique. Although the predicted Stoney stress shows a 220 MPa tensile residual stress, the observed trend in localized stress values shows that the maximum stress is 280 MPa at the center of the wafer and reduces to about 100 MPa at the edge of the wafer.

The manufacturing of multilayer films with improved mechanical and tribological properties has attracted attention recently for enabling their space applications. In this study, we aim to optimize the manufacturing process of WSx/a-C multilayer films by alternately depositing WS2, amorphous carbon (a-C), and Al metal on silicon substrates through magnetron sputtering. The microstructure and morphology of the multilayer films were investigated by x-ray diffractometry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The mechanical and tribological properties of the films were evaluated in vacuum using a nanoindentation tester, ball-on-disk tribometer, and scratch tester. The results showed that the addition of an Al layer with an optimal thickness refined the microstructure of the films. The tribological properties of the films deteriorated with increasing thickness of the Al single layer. When the thickness of the Al film was 1 nm, the tribological properties of the films were optimal, and the adhesion was maximum (49.1 N). Hardness of the films gradually decreased with an increase in the thickness. Wear rate of the films decreased initially and then increased, and the wear rate was lowest when the thickness of the Al single layer was 2 nm (1.41 × 10−15 m3 N−1 m−1). By manufacturing films with optimal thickness, suitable tribological properties for vacuum applications can be achieved.

Indium tin oxide (ITO) thin films were grown by Ar ion beam sputter deposition under systematic variation of ion energy, geometrical parameters, and O 2 background pressure and characterized with regard to the film thickness, growth rate, crystalline structure, surface roughness, mass density, composition, electrical, and optical properties. The growth rate shows an over-cosine, forward-tilted angular distribution with a maximum, which increases with increasing ion energy, increasing ion incidence angle, and decreasing O 2 background pressure. ITO films were found to be amorphous with a surface roughness of less than 1 nm. Mass density and composition show only small changes with increasing scattering angle. The electrical resistivity behavior in dependence on the process parameters is complex. It is not only driven by the O 2 background pressure but also very much by the scattering angle. The observed behavior can be understood only if competing processes are considered: (i) reduction of the number of oxygen vacancies due to the presence of O 2 background gas and (ii) defect generation and preferential sputtering of oxygen at the surface of the growing films due to the impact of high-energy scattered particles. Even though absolute numbers differ, optical characterization suggests a similar systematics.

We report on a comprehensive analysis of titanium boride thin films by x-ray photoelectron spectroscopy (XPS). Films were grown by both direct current magnetron sputtering and high-power impulse magnetron sputtering from a compound TiB2 target in Ar discharge. By varying the deposition parameters, the film composition could be tuned over the wide range 1.3 ≲ B / Ti ≲ 3.0, as determined by elastic recoil detection analysis and Rutherford backscattering spectrometry. By comparing spectra over this wide range of compositions, we can draw original conclusions about how to interpret XPS spectra of TiBx. By careful spectra deconvolution, the signals from Ti–Ti and B–B bonds can be resolved from those corresponding to stoichiometric TiB2. The intensities of the off-stoichiometric signals can be directly related to the B/Ti ratio of the films. Furthermore, we demonstrate a way to obtain consistent and quantum-mechanically accurate peak deconvolution of the whole Ti 2p envelope, including the plasmons, for both oxidized and sputter-cleaned samples. Due to preferential sputtering of Ti over B, the film B/Ti ratio is best determined without sputter etching of the sample surface. This allows accurate compositional determination, assuming that extensive levels of oxygen are not present in the sample. Fully dense films can be accurately quantified for at least a year after deposition, while underdense samples do not give reliable data if the O/Ti ratio on the unsputtered surface is ≳ 3.5. Titanium suboxides detected after sputter etching is further indicative of oxygen penetrating the sample, and quantification by XPS should not be trusted.

We report the results of the design, simulation, fabrication, and cold-test measurements of millimeter-band 2D planar microstrip slow-wave structures (SWSs) on dielectric substrates. Such structures have a high slow-wave factor, which allows for low-voltage operation and reduction in the size and weight of the device. A low-cost and flexible fabrication technology based on magnetron sputtering and subsequent laser ablation has been developed and is reported in the paper. Microstrip meander-line SWS circuits at V-, W-, and D-bands have been fabricated and characterized. The fabrication of ring-bar planar SWSs by the photolithographic method is also discussed. Experimental measurement of S-parameters of the fabricated structures reveals good transmission properties. Return loss (S11) does not exceed −10 dB and attenuation is about 2 dB/cm in the V-band, 10 dB/cm in the W-band, and 8.5 dB/cm in the D-band.

Fe2O3-WO3 nanosystems have been grown on metallic Ti substrates by a hybrid chemical vapor deposition (CVD) / Radio Frequency (RF)-sputtering route. The obtained specimens have been characterized in their structure, morphology and chemical composition by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). Herein, a detailed XPS investigation of a representative sample is proposed. In addition to the wide scan spectrum, particular attention is dedicated to the analysis of O 1s, Fe 2p, W 4f, and W 4d core levels. The obtained results suggested the formation of pure Fe2O3-WO3 composites, in which each oxide maintained its chemical identity.

Large-area, flexible, two-dimensional transition metal dichalcogenide semiconductor materials (MoS2 and WSe2) were synthesized via magnetron sputtering of amorphous stoichiometric precursor materials on polydimethylsiloxane polymer substrates. Purely amorphous precursor materials and amorphous materials with pre-existing nanocrystalline regions observed via transmission electron microscopy were grown for the studies presented here. The MoS2 and WSe2 material precursors were then illuminated with a pulsed 532 nm laser to induce crystallization to their semiconducting hexagonal phases. The laser optics included an axicon lens to shape the Gaussian pulsed laser into a “Bessel beam” characterized by annular ring geometry. The pattern of the beam, with its rings of high-intensity laser light around a higher-intensity core, produced crystalline rings of the material around an ablation zone on the polymer substrate for MoS2 and WSe2 materials. The crystalline structure and density of atomic defects over the crystalline regions decreased as the same sample area was illuminated with additional pulses. The lateral coherence of the crystal lattice increased with the first 4 pulses but decreased with each subsequent pulse. The impact of preexisting nanocrystalline nanoinclusions in an amorphous film on the crystallization rate for WSe2 precursor materials was examined. The presence of nanocrystalline regions in the amorphous materials increased the crystallization rate under the photonic annealing conditions examined here. This approach of direct synthesis and patterning of materials is a route toward the fabrication of inexpensive flexible electronic devices.

Metal-insulator-metal tunnel junctions (MIMTJs) are an enabling technology for future electronics including advanced computing, data storage, sensors, etc. MIMTJs are formed by inserting an ultrathin insulating layer, known as the tunnel barrier (TB), between metal electrodes. Devices based on MIMTJs have advantages of enhanced quantum coherent transport, fast speed, small size, and energy efficiency. The performance of MIMTJs depends critically on the thickness and quality of the tunnel barrier. Specifically, the tunneling current, for example, the superconducting critical current in superconductor-insulator-superconductor Josephson junctions (JJs) or the spin tunneling current in ferromagnetic-insulator-ferromagnetic magnetic tunnel junctions (MTJs), decreases exponentially with the TB thickness. This means thinner TBs would enable stronger coherent tunneling in MIMTJs. In addition, the defects in the TBs can degrade the quantum coherence of electrons (spins) of JJs and MTJs, respectively, resulting in decoherence and degraded performance of the MIMTJs. This justifies the urgent need in research and development of ultrathin (subnanometers to 1 nm) pinhole-free and defect-free TBs beyond the current state-of-the-art TBs of larger thickness (>1–2 nm) and high defect concentration made using thermal diffusion of oxygen or physical vapor deposition (PVD) including magnetron sputtering and molecular beam epitaxy. Atomic layer deposition (ALD) can provide a unique resolution to achieving ultrathin and defect-free dielectric TBs for high-performance MIMTJs for future electronics. In this article, a review on their recent effort in the development of in vacuo ALD for the fabrication of ultrathin TBs for JJs and MTJs is presented. A custom-designed system that integrates high-vacuum/ultrahigh-vacuum PVD, ALD, and scanning probe microscopy was established for in vacuo fabrication of MIMTJs and characterization of the electronic properties of ALD TBs including Al2O3, MgO, and Al2MgO4 on both superconductor metals (Al) and ferromagnetic metals (Fe and FeCoB). Capacitors with ALD dielectric of thickness in the range of 1–5 nm were also constructed for the characterization of the dielectric properties of the ALD TBs. The authors have found that the metal-insulator interface plays a critical role in controlling the quality of the ALD TBs including the tunnel barrier height, dielectric constant, electric breakdown, and uniformity. They have shown that JJs and MTJs with 0.1–1.0 nm thick ALD Al2O3 TBs can be obtained with highly promising performance. The result obtained suggests that the in vacuo ALD may provide a unique approach toward MIMTJs with an atomic-scale control of the device structure required for high-performance future electronics.

High power impulse magnetron sputtering (HiPIMS) of diamond-like carbon coatings is reviewed. Three variations of HiPIMS were used to deposit diamond-like carbon coatings: use of neon as compared to argon for sputtering, very high discharge peak current density in an Ar atmosphere, and the use of bursts of short sputtering pulses. All three variations were able to provide sufficient ion-to-neutral ratios to effectively control the coating quality using substrate bias. The resulting coatings are typically smooth, amorphous, hard (up to 25 GPa), and dense but have low stress (below 2.5 GPa). The coatings exhibit an increased stability at higher temperature (up to 500 °C) compared to the coatings prepared using standard magnetron sputtering. The resulting coatings also exhibited low wear rates in ambient ball-on-disc tests (2.1 × 10−8 mm3 N−1 m−1). These improvements are explained in terms of the rate of sputtered carbon atom ionization in the plasma and material transport to the substrate. However, the chemical bonding in the films is not yet well understood as relatively low sp3 bond content has been observed.

Throughout his career, Dr. Stephen Rossnagel and his co-workers have had a profound influence on thin film deposition. His seminal work includes the development of reactive, collimated, and ionized methods of DC and RF magnetron sputtering, as well as plasma-enhanced atomic layer deposition. Most importantly, his contributions have been widely adopted within the microelectronics community in its efforts to produce finer layers with increased uniformity and functionality. While applications span a very broad range, from complementary metal oxide semiconductor device metallization to DNA sensing, Dr. Rossnagel has also conducted fundamental investigations into microstructural effects on electronic scattering. In this manuscript, the authors will highlight some of Steve’s contributions to these areas and their continued relevance to current and future microelectronic device scaling.

The sideways (radial) deposition rate and ionized flux fraction in a high power impulse magnetron sputtering (HiPIMS) discharge are studied and compared to a dc magnetron sputtering (dcMS) discharge, while the magnetic field strength | B | and degree of balancing are varied. A significant deposition of the film forming material perpendicular to the target surface is observed for both sputter techniques. This sideways deposition decreases with increasing axial distance from the target surface. The sideways deposition rate is always the highest in dc operation, while it is lower for HiPIMS operation. The magnetic field strength has a strong influence on the sideways deposition rate in HiPIMS but not in dcMS. Furthermore, in HiPIMS operation, the radial ion deposition rate is always at least as large as the axial ion deposition rate and often around two times higher. Thus, there are a significantly higher number of ions traveling radially in the HiPIMS discharge. A comparison of the total radial as well as axial fluxes across the entire investigated plasma volume between the target and the substrate position allows for revised estimates of radial over axial flux fractions for different magnetic field configurations. It is here found that the relative radial flux of the film forming material is greater in dcMS compared to HiPIMS for almost all cases investigated. It is therefore concluded that the commonly reported reduction of the (axial) deposition rate in HiPIMS compared to dcMS does not seem to be linked with an increase in sideways material transport in HiPIMS.

Hydrogen behavior in tantalum and tantalum oxide thin films was examined using the in situ oxidation secondary ion mass spectrometry (in situ oxidation SIMS) method previously developed by the authors. Oxidation of Ta films by the introduction of O2 into the sputter deposition chamber immediately after film growth was found to reduce the amount of H absorbed in the Ta films by 2.7 times for samples exposed to lab air at ambient temperature; the difference increased to 4.8 times for samples exposed to air at 300 °C. From these results, it is apparent that Ta absorbs H from H2 or through reaction with H2O in air and that an oxide film “cap” largely stymies H absorption. To investigate the redistribution of hydrogen during oxidation of Ta, sputtered Ta films were implanted with deuterium, and some were subsequently anodized. In situ oxidation SIMS analysis of Ta2O5/Ta bilayer films created by anodization of deuterium (D)-implanted Ta films revealed no deuterium in the upper Ta2O5 portion; however, the total amount of deuterium detected in the underlying Ta layer of the anodized samples was close to the total amount of deuterium measured in the Ta layer of a nonanodized, D-implanted Ta film. These results indicate that during anodization, D is concentrated in the residual metal region as it is excluded from the growing oxide film. Ab initio calculations of H interstitial defects in Ta and Ta2O5 revealed that the heat of formation, ΔH, for H interstitial defects in Ta is 1.31 eV lower than that of Ta2O5; this result is consistent with the observed H blocking property of oxide films and the observed redistribution of D from oxide to metal during anodization.

A new industrial approach for the production of CuInSe2 (CISe) absorber layers in a roll-to-roll process is described. This process is used by Sunplugged GmbH and combines magnetron sputtering with thermal coevaporation. A CISe-based device with a conversion efficiency of more than 10% has been fabricated from absorbers grown on polyimide at low temperature. The characteristic properties of a copper-poor ([Cu]/[In] = 0.73) CISe layer, deposited by Sunplugged's industrial process, are compared to those of a state-of-the-art, more copper-rich ([Cu]/[In] = 0.93) layer, grown in a molecular beam epitaxy system at Helmholtz-Zentrum Berlin. The presence of a so called vacancy-compound in low [Cu]/[In] CISe devices exhibiting an increased bandgap energy is visible by external quantum efficiency measurements, Raman scattering, and scaps simulations.

The authors investigated the relationship between the content of incorporated Ar atoms and the crystalline polarity of polycrystalline Al-doped ZnO (AZO) films and examined the influence of this relationship on the resulting growth rate, crystallographic texture, and electrical properties. They deposited AZO films on glass and c-plane sapphire substrates via radio-frequency magnetron sputtering at substrate temperatures (Ts) of 100 or 200 °C using sintered AZO targets with an Al2O3 content of 2.0 wt. %. The incorporation of a large amount of Ar atoms induced a change in the crystalline polarity from Zn-polar to O-polar, the latter of which is associated with numerous obstacles, such as a lower deposition rate, large residual compressive stress, and increased electrical resistivity. The authors demonstrated that increasing the Ts led to a reduction in the amount of unintentionally retained Ar atoms, thereby affording Zn-polar AZO films with their associated advantages.The authors investigated the relationship between the content of incorporated Ar atoms and the crystalline polarity of polycrystalline Al-doped ZnO (AZO) films and examined the influence of this relationship on the resulting growth rate, crystallographic texture, and electrical properties. They deposited AZO films on glass and c-plane sapphire substrates via radio-frequency magnetron sputtering at substrate temperatures (Ts) of 100 or 200 °C using sintered AZO targets with an Al2O3 content of 2.0 wt. %. The incorporation of a large amount of Ar atoms induced a change in the crystalline polarity from Zn-polar to O-polar, the latter of which is associated with numerous obstacles, such as a lower deposition rate, large residual compressive stress, and increased electrical resistivity. The authors demonstrated that increasing the Ts led to a reduction in the amount of unintentionally retained Ar atoms, thereby affording Zn-polar AZO films with their associated advantages.

In recent years, transparent conductive oxide (TCO) films that can be applied to flexible devices have attracted considerable attention. Among TCOs, indium tin oxide (ITO) is frequently used, but ITO contains the rare metal In and is inflexible. Therefore, the authors focused on an Al-doped ZnO (AZO) transparent conductive film as an alternative material for ITO. The authors prepared films on polyethylene naphthalate (PEN) substrates to prepare flexible electrodes. PEN substrates are sensitive to heat and must be deposited at low temperatures. However, there is a limit to improving the conductivity of AZO film formation at low temperatures. Therefore, the authors focused on the AZO/Ag/AZO multilayer transparent conductive films. The AZO layer was deposited by RF magnetron sputtering, and the Ag layer was deposited by electron beam evaporation. The electrical and optical characteristics were evaluated by changing the deposition conditions during the AZO and Ag deposition. Thus, when the thickness of the Ag layer was changed, the maximum transmittance was obtained at a thickness of 10 nm. Next, the upper AZO film was divided into room temperature/50 °C. When the upper AZO is formed at 50 °C, the already deposited Ag is affected by thermal oxidation. Ag was protected from thermal oxidation by first depositing the upper AZO at room temperature and then applying 50 °C, resulting in improved transmittance and resistivity. Furthermore, the resistivity and transmittance were improved by increasing the deposition rate of the Ag layer due to a decrease in the oxygen content in the Ag layer. Among the formed thin films, the best obtained characteristics were the resistivity of 1.24 × 10−4 Ω cm and the transmittance of 84.8%.

A class of artifacts manifesting as soft magnetic components are revealed from magnetometry measurements of rare earth-transition metal (TbFe) thin films prepared by magnetron sputtering. They are not inherent to TbFe, but are a direct result of the manner in which the substrates are mounted prior to sample fabrication, with a material deposited at the substrate sides giving rise to a significant magnetic moment. The authors find the same artifacts to also be present in rare earth-free [Co/Pt] multilayers. Trying to supress the appearance of this type of artifact has an influence on the coercivity and, in some cases, on the shape of the reversal curves. Care needs to be taken during fabrication to ensure reliable and reproducible samples so that sensitive magnetic parameters, such as coercivity and compensation points, can be extracted accurately and that data are not misinterpreted for even more complex systems. This type of artifact is not limited to samples prepared by sputtering but can extend to other conventional thin-film deposition methods.

The authors developed a microparticle simulation for low-pressure plasma environments occurring in certain plasma coating systems. The simulation is based on a theoretical model for the forces and currents acting on microparticles and takes place in a 3D geometry modeled after the coating chamber. As a test case, the Enhanded Optical Sputtering System was used, and the resulting size distribution functions for two different microparticle species were compared with experimental size distributions, showing a qualitative agreement and yielding some explanations for the experimental results.The authors developed a microparticle simulation for low-pressure plasma environments occurring in certain plasma coating systems. The simulation is based on a theoretical model for the forces and currents acting on microparticles and takes place in a 3D geometry modeled after the coating chamber. As a test case, the Enhanded Optical Sputtering System was used, and the resulting size distribution functions for two different microparticle species were compared with experimental size distributions, showing a qualitative agreement and yielding some explanations for the experimental results.

Journal of vacuum science & technology : JVST / A 38(2), 023401 (2020). doi:10.1116/1.5138248 special issue: "Festschrift Honoring Dr. Steve Rossnagel", Published by American Institute of Physics, New York, NY

Copper oxides (CuO, Cu2O) have promising application potential in sensors or solar cells. In this study, copper oxide thin films were prepared by reactive DC magnetron sputtering using helicon plasma. A pure copper target was sputtered with Ar gas in an O2 atmosphere with a DC sputtering power in the range of 10–40 W, while the other fabrication conditions were kept constant. X-ray diffraction and x-ray photoelectron spectroscopy were used to investigate the effect of the sputtering power on the structure and the chemical state of the fabricated films. Atomic force microscopy was used to determine the relationship between the film's surface morphology and its structure. Hall effect measurements were employed to measure the semiconductor's properties, and the optical bandgap was determined by UV-Vis spectroscopy. The copper oxide film could be continuously tuned from n-type CuO to p-type Cu2O by changing the DC magnetron sputtering power.Copper oxides (CuO, Cu2O) have promising application potential in sensors or solar cells. In this study, copper oxide thin films were prepared by reactive DC magnetron sputtering using helicon plasma. A pure copper target was sputtered with Ar gas in an O2 atmosphere with a DC sputtering power in the range of 10–40 W, while the other fabrication conditions were kept constant. X-ray diffraction and x-ray photoelectron spectroscopy were used to investigate the effect of the sputtering power on the structure and the chemical state of the fabricated films. Atomic force microscopy was used to determine the relationship between the film's surface morphology and its structure. Hall effect measurements were employed to measure the semiconductor's properties, and the optical bandgap was determined by UV-Vis spectroscopy. The copper oxide film could be continuously tuned from n-type CuO to p-type Cu2O by changing the DC magnetron sputtering power.

Nitrogen-containing diamondlike carbon (N-DLC) films are excellent surface protection films with high wear resistance and low electrical resistivity. In this paper, N-DLC/tungsten (W) and N-DLC/tungsten carbide (WC) multilayer films with low-electrical-resistance layers formed between N-DLC layers are presented. W or WC layers were formed as a low-electrical-resistance layer using unbalanced magnetron sputtering methods at a low substrate temperature. N-DLC layers were fabricated by the T-shape filtered arc deposition method. The N-DLC/WC multilayer films showed higher polishing resistance compared with the N-DLC single-layer films, and the electrical resistivity of the multilayer films was about half compared with single-layer films. The high polishing resistance of the multilayer films was considered to be due to the WC layers acting as a hard layer and the N-DLC layers acting as a cushion layer to absorb the film load.Nitrogen-containing diamondlike carbon (N-DLC) films are excellent surface protection films with high wear resistance and low electrical resistivity. In this paper, N-DLC/tungsten (W) and N-DLC/tungsten carbide (WC) multilayer films with low-electrical-resistance layers formed between N-DLC layers are presented. W or WC layers were formed as a low-electrical-resistance layer using unbalanced magnetron sputtering methods at a low substrate temperature. N-DLC layers were fabricated by the T-shape filtered arc deposition method. The N-DLC/WC multilayer films showed higher polishing resistance compared with the N-DLC single-layer films, and the electrical resistivity of the multilayer films was about half compared with single-layer films. The high polishing resistance of the multilayer films was considered to be due to the WC layers acting as a hard layer and the N-DLC layers acting as a cushion layer to absorb...

In this work, the relationships between bottom electrode/substrate configuration, crystalline microstructure, and electrical performances of BaTiO3 (BTO) thin films were investigated. The films were fabricated via RF magnetron sputtering on (Sr0.5La0.5)CoO3 (LSCO) buffered (110)-, (111)-SrTiO3 (STO) and SrRuO3 (SRO) buffered (110)-, (111)-MgO (MGO) substrates. The x-ray diffractometer results show that the LSCO/STO substrate resulted in films with high-quality epitaxial orientation, whereas the SRO/MGO substrate resulted in films having a strong (110) texture. The electrode/substrate configurations were designed to control the crystalline microstructure, which in turn affects the electrical performances of the films. The electrical performances were studied by employing a metal/ferroelectric/metal model. The J-V characteristics show obvious asymmetry with bias, which is mainly due to the varying transport state of oxygen vacancies. BTO films grown on LSCO/STO substrates exhibit large dielectric frequency dispersion, while those grown on SRO/MGO substrates display a nearly frequency independent response. All electrical parameters of these films were strongly affected by the polarization-tilting angle and the preferred orientation degree. Epitaxial and textured (110)-oriented films show higher permittivity but lower loss tangent, free-carrier concentration, built-in voltage, and leakage current density as compared to the epitaxial (111)-oriented film.

Thin layers containing lithium oxide (Li2O), lithium sulfide (Li2S), or lithium selenide (Li2Se) are relevant for many electrochemical processes in lithium-based batteries. As a step toward understanding the electrochemical properties of such layers, this work demonstrates the growth of dense single-phase films by both sputter deposition (for Li2O and Li2S) and thermal evaporation (for Li2S and Li2Se). The dependence of morphology and grain size on the growth conditions is characterized. Reactive deposition is found to be faster and more practical than direct deposition, and both sputtered S8 and heated SnS2 are shown to be viable sulfur precursors for growing sulfides. These results enable the preparation of Li2O, Li2S, and Li2Se films suitable for future electrochemical studies. An initial set of conductivity data from an evaporated Li2S film is also presented.

Ruthenium thin films were prepared by DC magnetron sputtering on silicon (111) substrates. Samples were subjected to different temperature conditions (300, 400, 500, and 600 °C) under a flow of hydrogen and carbon dioxide with a 4:1 molar ratio to emulate the atmosphere of the methanation reaction. Each treatment was performed in situ. X-ray photoelectron spectroscopy was used to examine the surface chemical changes on Ru thin films before and after the treatments. Survey spectra, Ru 3d, and O 1s core level spectra were measured for each sample. Results showed that the O 1s spectra presented significant changes in all samples; before the thermal treatments, this signal has four different oxygen species, where it can be appreciated the existence of nonstoichiometric oxidized ruthenium. The latter disappears after the first heat treatment due to the high reducibility of ruthenium. Subsequently, in the following treatments, ruthenium oxide reappears, in smaller quantities when compared with the film without treatments. However, the highest amount of oxidized ruthenium can be observed in the temperature range (400–500 °C) during the treatments, in which the conversion of CO2 is maximum for Ru supported catalysts.Ruthenium thin films were prepared by DC magnetron sputtering on silicon (111) substrates. Samples were subjected to different temperature conditions (300, 400, 500, and 600 °C) under a flow of hydrogen and carbon dioxide with a 4:1 molar ratio to emulate the atmosphere of the methanation reaction. Each treatment was performed in situ. X-ray photoelectron spectroscopy was used to examine the surface chemical changes on Ru thin films before and after the treatments. Survey spectra, Ru 3d, and O 1s core level spectra were measured for each sample. Results showed that the O 1s spectra presented significant changes in all samples; before the thermal treatments, this signal has four different oxygen species, where it can be appreciated the existence of nonstoichiometric oxidized ruthenium. The latter disappears after the first heat treatment due to the high reducibility of ruthenium. Subsequently, in the following treatments, ruthenium oxide reappears, in smaller quantities when compared with the film without ...

Ion irradiation is a key tool for controlling the nanostructure, phase content, and physical properties of refractory ceramic thin films grown at low temperatures by magnetron sputtering. However, in contrast to gas-ion bombardment, the effects of metal-ion irradiation on properties of refractory ceramic thin films have not been extensively studied due to (i) low metal-ion concentrations (a few percents) during standard direct-current magnetron sputtering (DCMS) and (ii) difficulties in separating metal-ion from gas-ion fluxes. Recently, the situation has changed dramatically, thanks to the development of high-power impulse magnetron sputtering (HiPIMS), which provides highly-ionized metal-ion plasmas. In addition, careful choice of sputtering conditions allows exploitation of gas-rarefaction effects such that the charge state, energy, and momentum of metal ions incident at the growing film surface can be tuned. This is possible via the use of pulsed substrate bias, synchronized to the metal-ion-rich portion of each HiPIMS pulse. In this review, the authors begin by summarizing the results of time-resolved mass spectrometry analyses performed at the substrate position during HiPIMS and HiPIMS/DCMS cosputtering of transition-metal (TM) targets in Ar and Ar/N2 atmospheres. Knowledge of the temporal evolution of metal- and gas-ion fluxes is essential for precise control of the incident metal-ion energy and for minimizing the role of gas-ion irradiation. Next, the authors review results on the growth of binary, pseudobinary, and pseudoternary TM nitride alloys by metal-ion-synchronized HiPIMS. In contrast to gas ions, a fraction of which are trapped at interstitial sites, metal ions are primarily incorporated at lattice sites resulting in much lower compressive stresses. In addition, the closer mass match with the film-forming species results in more efficient momentum transfer and provides the recoil density and energy necessary to eliminate film porosity at low deposition temperatures. Several novel film-growth pathways have been demonstrated: (i) nanostructured N-doped bcc-CrN0.05 films combining properties typically associated with both metals and ceramics, (ii) fully-dense, hard, and stress-free Ti0.39Al0.61N, (iii) single-phase cubic Ti1−xSixN with the highest reported SiN concentrations, (iv) unprecedented AlN supersaturation in single-phase NaCl-structure V1−xAlxN, and (v) a dramatic increase in the hardness, due to selective heavy-metal ion bombardment during growth, of dense Ti0.92Ta0.08N films deposited with no external heating.Ion irradiation is a key tool for controlling the nanostructure, phase content, and physical properties of refractory ceramic thin films grown at low temperatures by magnetron sputtering. However, in contrast to gas-ion bombardment, the effects of metal-ion irradiation on properties of refractory ceramic thin films have not been extensively studied due to (i) low metal-ion concentrations (a few percents) during standard direct-current magnetron sputtering (DCMS) and (ii) difficulties in separating metal-ion from gas-ion fluxes. Recently, the situation has changed dramatically, thanks to the development of high-power impulse magnetron sputtering (HiPIMS), which provides highly-ionized metal-ion plasmas. In addition, careful choice of sputtering conditions allows exploitation of gas-rarefaction effects such that the charge state, energy, and momentum of metal ions incident at the growing film surface can be tuned. This is possible via the use of pulsed substrate bias, synchronized to the metal-ion-rich port...

Photoluminescence (PL) from defect-rich ZnO thin films was investigated in relation to transparent conductive properties. By varying the sputter deposition and post-treatment conditions, the correlation between deep-level luminescence and changes in the optical and electrical properties was examined, and the defects that were the origin of the donors and acceptors were identified. Slightly oxygen-deficient and transparent conductive films deposited on glass substrates without a supply of oxygen source gas had a resistivity of 3 × 10−3 Ω cm; these films exhibited only band edge emissions peaking at 380 nm in the PL spectra. Abundant defects were introduced through postannealing in an H2 atmosphere at 300−400 °C. The permeating H2 reacted with the O and Zn atoms constituting the crystal network, and the resulting PL spectra exhibited a continuous defect-emission band ranging from violet to red. The spectra included transitions of the conduction band (CB) → zinc vacancies (VZn) (400 nm), zinc interstitials (Zni) → valence band (VB) (440 nm), CB → oxygen vacancies (VO) (560 nm), and CB → oxygen interstitials (Oi) (620 nm). Similar PL spectra from disordered crystals were obtained by sputter deposition at 300 and 400 °C under a reducing atmosphere. The films deposited on the sapphire substrate above 300 °C were nonemissive because they were strongly oxygen deficient compared to those on the glass substrate. When the films on sapphire were postannealed, only emissions from the CB → VO transition appeared. Thus, VO is the primary defect in films on sapphire, whereas every type of intrinsic defect (Zni, Oi, VO, and VZn) builds up in ZnO films on glass. Electronically excited modifications induced by argon plasma irradiation were investigated in order to discriminate the influence from that of thermal processes. After prolonged plasma exposure, emissions corresponding to CB → VO (540 nm) and Zni → VB (420−470 nm) transitions predominated as a result of preferential sputtering of oxygen atoms. The improvement in electric conduction by the plasma treatment is attributed to hydrogen atoms trapped at newly created VO sites.

TiZrN thin films were prepared by DC magnetron sputtering on silicon (111) substrates. Samples were subjected to different temperature conditions (200, 400, and 600 °C) under a flow of carbon dioxide to emulate a corrosive atmosphere. Each treatment was performed in situ. X-ray photoelectron spectroscopy was used to examine the surface chemical changes on TiZrN thin films before and after the treatments. Survey spectra and C 1s, O 1s, N 1s, Ti 2p, and Zr 3d core level spectra were measured for each sample. Results show remarkable differences in all spectra when the sample was heated over 400 °C. At these temperatures, it is evident that the coating undergoes the greatest chemical change since metals cease to be nitrides and oxidize.TiZrN thin films were prepared by DC magnetron sputtering on silicon (111) substrates. Samples were subjected to different temperature conditions (200, 400, and 600 °C) under a flow of carbon dioxide to emulate a corrosive atmosphere. Each treatment was performed in situ. X-ray photoelectron spectroscopy was used to examine the surface chemical changes on TiZrN thin films before and after the treatments. Survey spectra and C 1s, O 1s, N 1s, Ti 2p, and Zr 3d core level spectra were measured for each sample. Results show remarkable differences in all spectra when the sample was heated over 400 °C. At these temperatures, it is evident that the coating undergoes the greatest chemical change since metals cease to be nitrides and oxidize.

The coating system (Cr,Al)ON can enhance the wear and corrosion resistance of tools applied in technical applications. It is possible that, under different loading conditions, the oxygen content of the coating could influence the performance of the coated tools. The aim of the present work is to study the influence of the oxygen content of the coating system (Cr,Al)ON on its elastic-plastic deformation and cracking behavior under static and dynamic loading conditions. For these purposes, three (Cr,Al)ON coatings with different oxygen contents were deposited on a quenched and tempered tool steel substrate AISI 420. The coatings were deposited using a hybrid technology combining direct current and high power pulse magnetron sputtering techniques in an industrial coating unit. The investigations were carried out by applying static loadings using nanoindentation and Rockwell tests as well as dynamic loading conditions using nanoscratch tests. Qualitative investigations were carried out using confocal laser scanning microscopy. The analyses of Rockwell imprints and nanoscratch tracks were conducted through scanning electron microscopy. Test results show that an improved understanding of possible crack formation in the coatings can be achieved through the analyses of nanoindentation force-displacement curves. Differences in the crack resistance of oxynitrides are more noticeable under dynamic loadings. Furthermore, coatings with a moderate value of oxygen content appear most promising in terms of mechanical and tribological behavior as well as crack resistance among the oxynitrides under investigation.

Time-resolved optical emission spectroscopy was carried out during controlled reactive high-power impulse magnetron sputtering of ZrO 2 films in argon–oxygen gas mixtures. The effects of increased target power density (up to 3.0 kW cm − 2) applied in voltage pulses shortened from 200 to 50 μs were studied at a nearly constant deposition-averaged target power density (close to 50 W cm − 2) and a fixed repetition frequency of 500 Hz. The trends in time evolution of the local ground-state densities of Zr, Ar, and O atoms and that of the Zr +, Zr 2 +, Ar +, and O + ions during a voltage pulse were deduced from the time evolution of the corresponding excited-state populations and the excitation temperature. It was found that the sputtered Zr atoms are much more ionized (with a high fraction of Zr 2 + ions) and the Ar atom density is more decreased near the target during the shorter (50 μs) high-power pulses. These shorter pulses produce a four times higher pulse-averaged target power density oscillating between 1.7 and 2.1 kW cm − 2 during deposition. Under these conditions, much higher densities of O atoms and Zr 2 + ions were measured in the plasma bulk. The higher backward flux of the Zr + and Zr 2 + ions onto the target during this high-power discharge regime contributed significantly to a 34% decrease in the efficiency of the magnetron sputter deposition of ZrO 2 films.Time-resolved optical emission spectroscopy was carried out during controlled reactive high-power impulse magnetron sputtering of ZrO 2 films in argon–oxygen gas mixtures. The effects of increased target power density (up to 3.0 kW cm − 2) applied in voltage pulses shortened from 200 to 50 μs were studied at a nearly constant deposition-averaged target power density (close to 50 W cm − 2) and a fixed repetition frequency of 500 Hz. The trends in time evolution of the local ground-state densities of Zr, Ar, and O atoms and that of the Zr +, Zr 2 +, Ar +, and O + ions during a voltage pulse were deduced from the time evolution of the corresponding excited-state populations and the excitation temperature. It was found that the sputtered Zr atoms are much more ionized (with a high fraction of Zr 2 + ions) and the Ar atom density is more decreased near the target during the shorter (50 μs) high-power pulses. These shorter pulses produce a four times higher pulse-averaged target ...

Pd(111) thin films, ∼245 nm thick, are deposited on Al2O3(0001) substrates at ≈0.5Tm, where Tm is the Pd melting point, by ultrahigh vacuum dc magnetron sputtering of Pd target in pure Ar discharges. Auger electron spectra and low-energy electron diffraction patterns acquired in situ from the as-deposited samples reveal that the surfaces are compositionally pure 111-oriented Pd. Double-axis x-ray diffraction (XRD) ω-2θ scans show only the set of Pd 111 peaks from the film. In triple-axis high-resolution XRD, the full width at half maximum intensity Γω of the Pd 111 ω-rocking curve is 630 arc sec. XRD 111 pole figure obtained from the sample revealed six peaks 60°-apart at a tilt angles corresponding to Pd 111 reflections. XRD ϕ scans show six 60°-rotated 111 peaks of Pd at the same ϕ angles for 11 2¯3 of Al2O3 based on which the epitaxial crystallographic relationships between the film and the substrate are determined as (111)Pdǁ (0001)Al2O3 with two in-plane orientations of [112¯]Pdǁ [112¯0]Al2O3 and [21¯1¯]Pdǁ [112¯0]Al2O3. Using triple axis symmetric and asymmetric reciprocal space maps, interplanar spacings of out-of-plane (111) and in-plane (11 2¯) are found to be 0.2242 ± 0.0003 and 0.1591 ± 0.0003 nm, respectively. These values are 0.18% lower than 0.2246 nm for (111) and the same, within the measurement uncertainties, as 0.1588 nm for (11 2¯) calculated from the bulk Pd lattice parameter, suggesting a small out-of-plane compressive strain and an in-plane tensile strain related to the thermal strain upon cooling the sample from the deposition temperature to room temperature. High-resolution cross-sectional transmission electron microscopy coupled with energy dispersive x-ray spectra obtained from the Pd(111)/Al2O3(0001) samples indicate that the Pd-Al2O3 interfaces are essentially atomically abrupt and dislocation-free. These results demonstrate the growth of epitaxial Pd thin films with (111) out-of-plane orientation with low mosaicity on Al2O3(0001).Pd(111) thin films, ∼245 nm thick, are deposited on Al2O3(0001) substrates at ≈0.5Tm, where Tm is the Pd melting point, by ultrahigh vacuum dc magnetron sputtering of Pd target in pure Ar discharges. Auger electron spectra and low-energy electron diffraction patterns acquired in situ from the as-deposited samples reveal that the surfaces are compositionally pure 111-oriented Pd. Double-axis x-ray diffraction (XRD) ω-2θ scans show only the set of Pd 111 peaks from the film. In triple-axis high-resolution XRD, the full width at half maximum intensity Γω of the Pd 111 ω-rocking curve is 630 arc sec. XRD 111 pole figure obtained from the sample revealed six peaks 60°-apart at a tilt angles corresponding to Pd 111 reflections. XRD ϕ scans show six 60°-rotated 111 peaks of Pd at the same ϕ angles for 11 2¯3 of Al2O3 based on which the epitaxial crystallographic relationships between the film and the substrate are determined as (111)Pdǁ (0001)Al2O3 with two in-plane orientations of [112¯]Pdǁ [112¯0]Al2O3 and ...

Metastable Ti1-xAlxN (0

This paper presents the results of the optical characterization of inhomogeneous thin films of polymer-like SiO x C y H z and non-stoichiometric silicon nitride SiN x. An efficient method combining variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied at the near-normal incidence based on the multiple-beam interference model is utilized for this optical characterization. The multiple-beam interference model allows us to quickly evaluate the values of ellipsometric parameters and reflectance of the inhomogeneous thin films, which exhibit general profiles of their optical constants. The spectral dependencies of the optical constants of the inhomogeneous SiO x C y H z and SiN x thin films are determined using the Campi–Coriasso dispersion model. The profiles of the optical constants of these films can also be determined. Furthermore, the transition layers at the lower boundaries of the characterized films are also taken into account. Spectral dependencies of the optical constants of these transition layers are also determined using the Campi–Coriasso dispersion model.This paper presents the results of the optical characterization of inhomogeneous thin films of polymer-like SiO x C y H z and non-stoichiometric silicon nitride SiN x. An efficient method combining variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied at the near-normal incidence based on the multiple-beam interference model is utilized for this optical characterization. The multiple-beam interference model allows us to quickly evaluate the values of ellipsometric parameters and reflectance of the inhomogeneous thin films, which exhibit general profiles of their optical constants. The spectral dependencies of the optical constants of the inhomogeneous SiO x C y H z and SiN x thin films are determined using the Campi–Coriasso dispersion model. The profiles of the optical constants of these films can also be determined. Furthermore, the transition layers at the lower boundaries of the characterized films are also taken into account. Spectral dependencies o...

The electrical and structural properties of sputter-deposited W Schottky contacts with Au overlayers on n-type Ga2O3 are found to be basically stable up to 500 °C. The reverse leakage in diode structures increases markedly (factor of 2) for higher temperature annealing of 550–600 °C. The sputter deposition process introduces near-surface damage that reduces the Schottky barrier height in the as-deposited state (0.71 eV), but this increases to 0.81 eV after a 60 s anneal at 500 °C. This is significantly lower than conventional Ni/Au (1.07 eV), but W is much more thermally stable, as evidenced by Auger electron spectroscopy of the contact and interfacial region and the minimal change in contact morphology. The contacts are used to demonstrate 1.2 A switching of forward current to −300 V reverse bias with a reverse recovery time of 100 ns and a dI/dt value of 2.14 A/μs. The on/off current ratios were ≥106 at −100 V reverse bias, and the power figure-of-merit was 14.4 MW cm−2.

Transparent conductive oxides are a class of materials that combine high optical transparency with high electrical conductivity. This property makes them uniquely appealing as transparent conductive electrodes in solar cells and interesting for optoelectronic and infrared-plasmonic applications. One of the new challenges that researchers and engineers are facing is merging optical and electrical control in a single device for developing next-generation photovoltaic, optoelectronic devices and energy-efficient solid-state lighting. In this work, the authors investigated the possible variations in the dielectric properties of aluminum-doped ZnO (AZO) upon gating by means of spectroscopic ellipsometry (SE). The authors investigated the electrical-bias-dependent optical response of thin AZO films fabricated by magnetron sputtering within a parallel-plane capacitor configuration. The authors address the possibility to control their optical and electric performances by applying bias, monitoring the effect of charge injection/depletion in the AZO layer by means of in operando SE versus applied gate voltage.

Group 4 metal oxides TiO2, ZrO2, and HfO2 were deposited on glass substrates at substrate temperatures ranging from 100 to 800 °C by reactive direct current magnetron sputtering using an Ar and O2 mixture as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the homologous substrate-temperature dependence of the film structure and properties for the sputter-deposited metal oxide thin films are discussed. The x-ray diffraction measurements show the diffraction patterns characteristic of the anatase (tetragonal) structure at substrate temperatures below 400 °C and those of the rutile (tetragonal) structure at substrate temperatures above 600 °C for TiO2 thin films and the patterns attributable to the monoclinic structure with 〈−111〉 orientation for ZrO2 and HfO2 thin films. Scanning electron microscopy (SEM) observations show voided columnar structures with rough surfaces for TiO2 thin films and fine columnar structures with smooth surfaces for ZrO2 and HfO2 thin films, which is supported by the results obtained from atomic force microscopy (AFM) analysis. The quantitative data on the lattice strain, crystallite size, surface roughness, and refractive index are plotted against the homologous substrate temperature, Tsub/Tm (Tsub: substrate temperature and Tm: melting point of thin film materials). The lattice strain reaches approximately zero at Tsub/Tm = 0.3–0.35, suggesting that the residual stress is relaxed at this point, and the crystallite size reaches a plateau at the same range of Tsub/Tm. The surface roughness increases sharply after passing Tsub/Tm = 0.25–0.30, and the refractive index shows a rise at Tsub/Tm = 0.30–0.35. The images obtained by SEM and AFM are categorized based on the property transition observed in the quantitative property changes. The data obtained in this work are utilized to systematically study the effectiveness and appropriateness of the homologous (normalized) substrate temperature to explain the changes in structure, morphology, and properties of oxide thin films. Furthermore, it is suggested that the structure zone model, which is normally applied to sputtered metal films, is also applicable to sputtered oxide thin films.

The Pb-Ti/MoS2 nanoscale multilayer films are synthesized by unbalanced magnetron sputtering. The effect of bilayer period on the structure, oxidation, and corrosion resistance of the nanoscale multilayer films has been investigated. For the Pb-Ti/MoS2 nanoscale multilayer films, the basal (002) planes of MoS2 are oriented parallel to the substrate, and the crystallite size gradually increases with the bilayer period, obtaining a maximum value when the bilayer period is 17.1 nm. A further increase in the bilayer period results in a decrease in the crystallite size. The oxidation resistance of the Pb-Ti/MoS2 nanoscale multilayer films is systematically evacuated by sliding against the GCr15 pair under humid air. The anticorrosion properties are investigated by electrochemical measurements and sliding against the GCr15 pair after the salt spray tests. The results indicate that oxidation and corrosion resistance of the nanoscale multilayer films first increases with an increase of the bilayer period, and the nanoscale multilayer film with a period of 17.1 nm obtains the best antioxidation and anticorrosion resistance. This benefits us to select the MoS2-based multilayer films for different operating conditions.

This paper introduces a novel TiAlSiN/CrN multilayer film deposited on substrates of silicon Si (100) or tungsten carbide steel using high-power impulse magnetron sputtering. The authors systematically analyzed the effects of N2/Ar flow ratio on the microstructural and mechanical properties of the thin films using TEM, SEM, XRD, and nanoindentation measurements. SEM images revealed that increasing the N2/Ar flow ratio led to corresponding decreases in the thickness of TiAlSiN/CrN multilayer films (from 1.9 to 0.5 μm) and the bilayer (from 21.5 to 6.6 nm). XRD and TEM analysis revealed that under the same conditions, the structure of a TiAlSiN monolayer transformed from amorphous to crystallite. Thus, increasing the N2/Ar flow ratio from 5% to 80% led to a sharp increase in hardness (from 9.8 to 19.6 GPa) and Young's modulus (from 178 to 245 GPa).This paper introduces a novel TiAlSiN/CrN multilayer film deposited on substrates of silicon Si (100) or tungsten carbide steel using high-power impulse magnetron sputtering. The authors systematically analyzed the effects of N2/Ar flow ratio on the microstructural and mechanical properties of the thin films using TEM, SEM, XRD, and nanoindentation measurements. SEM images revealed that increasing the N2/Ar flow ratio led to corresponding decreases in the thickness of TiAlSiN/CrN multilayer films (from 1.9 to 0.5 μm) and the bilayer (from 21.5 to 6.6 nm). XRD and TEM analysis revealed that under the same conditions, the structure of a TiAlSiN monolayer transformed from amorphous to crystallite. Thus, increasing the N2/Ar flow ratio from 5% to 80% led to a sharp increase in hardness (from 9.8 to 19.6 GPa) and Young's modulus (from 178 to 245 GPa).

The number of medical procedures involving the use of cyclotron-produced radionuclides is constantly growing year by year. The design and construction of the cyclotron targets appropriate for the production of the radionuclides of interest are the most challenging issues. The cyclotron targets for the medical radionuclide production suffer from two main corrosion problems: the corrosion due to proton-irradiated water and liquid metal embrittlement. The design of the target for radionuclide production limits the ability to select an ideal material that meets all of the following requirements: machinability or ease of construction, high melting temperature, high thermal exchange performance, excellent chemical inertness, etc. The use of thermally and mechanically suitable substrate materials protected by chemically resistant coatings can be a good compromise. These two corrosion problems can be attributed to the mechanism of diffusion by the aggressive particles through the protective coating. In this research, niobium has been chosen as the principal material for the design of thin film protective coatings. The coating microstructure was correlated to specific deposition parameters to provide chemical resistance to both proton-irradiated water corrosion and liquid metal embrittlement. Film densification and amorphization were pursued to achieve niobium-based thin films efficient as diffusion barriers to proton-irradiated water and liquid metal. The most important conclusions were that the performance of thin films as diffusion barriers varied dramatically based on various deposition parameters and deposition technologies. Among the configurations studied, only three are acceptable as anticorrosion coatings: niobium deposited on axis with unbalanced magnetron sputtering, niobium coated at a high sputtering rate and on a water-cooled sample holder, and the niobium-titanium alloy sputtered at a low argon pressure.The number of medical procedures involving the use of cyclotron-produced radionuclides is constantly growing year by year. The design and construction of the cyclotron targets appropriate for the production of the radionuclides of interest are the most challenging issues. The cyclotron targets for the medical radionuclide production suffer from two main corrosion problems: the corrosion due to proton-irradiated water and liquid metal embrittlement. The design of the target for radionuclide production limits the ability to select an ideal material that meets all of the following requirements: machinability or ease of construction, high melting temperature, high thermal exchange performance, excellent chemical inertness, etc. The use of thermally and mechanically suitable substrate materials protected by chemically resistant coatings can be a good compromise. These two corrosion problems can be attributed to the mechanism of diffusion by the aggressive particles through the protective coating. In this resea...