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Gold–germanium (Au[Formula: see text]Ge[Formula: see text]) solid solutions have been demonstrated as highly sensitive thin film thermometers for cryogenic applications. However, little is known regarding the performance of the films for thicknesses less than 100 nm. In response, we report on the resistivity and temperature coefficient of resistance (TCR) for sputtered films with thicknesses ranging from 10 to 100 nm and annealed at temperatures from 22 to 200 [Formula: see text]C. The analysis is focused upon composition [Formula: see text], which demonstrates a strong temperature sensitivity over a broad range. The thinnest films are found to provide an enhancement in TCR, which approaches 20% K[Formula: see text] at 10 K. Furthermore, reduced anneal temperatures are required to crystallize the Ge matrix and achieve a maximum TCR for films of reduced thickness. These features favor the application of ultra-thin films as high-sensitivity, on-device thermometers in micro- and nanolectromechanical systems.

There has been increasing interest in the fabrication of thin film materials with mixed dimensions, in particular, 2D to 3D and 3D to 2D heterostructures. Often, if the interface interaction is weak, the lattice matching criterion between the substrate and overlayer can be lifted. If the overlayer lattice is completely relaxed, it can form an incommensurate film on the mismatched substrate. In this work, we show that domain boundaries are inherent in the incommensurate epitaxial films due to random nucleation sites of domains in an overlayer. The nature and origin of the incommensurate domain boundaries are different from the conventional dislocation boundaries that come from the relaxation of strain due to film–substrate lattice mismatch. We propose that the formation of such domain boundaries can be studied through Voronoi tessellation. Using a case study of monolayer WS2 on sapphire (2D on 3D), we show the formation of domain boundaries that compared well with a recent experiment reported in the literature. In the Voronoi tessellation, we also show quantitatively that the average domain size depends on the density of nucleation sites. The conclusion of this case study may be generalized to any incommensurate epitaxial films when the interface interaction is weak.

We investigate the effects of surface tunneling on electrostatics and transport properties of two-dimensional electron gases (2DEGs) in undoped Si/SiGe heterostructures with different 2DEG depths. By varying the gate voltage, four stages of density-mobility dependence are identified with two density saturation regimes observed, which confirms that the system transitions between equilibrium and nonequilibrium. Mobility is enhanced with an increasing density at low biases and, counterintuitively, with a decreasing density at high biases as well. The density saturation and mobility enhancement can be semiquantitatively explained by a surface tunneling model in combination with a bilayer screening theory.

Many diffraction and imaging techniques have been developed and used to measure the strains in epitaxial films with different degrees of accuracy. In this tutorial, we will focus on measurements of strains in epitaxial films using electron diffraction techniques. These include reflection high-energy electron diffraction (RHEED), azimuthal reflection high-energy electron diffraction, low-energy electron diffraction (LEED), and high-resolution low-energy electron diffraction techniques. These diffraction techniques are surface sensitive and are suitable for in situ measurements of strains in ultrathin epitaxial films quantitatively. In particular, RHEED and LEED are simple to operate and readily available in many laboratories. We discuss the instrument limit of strain measurement in each technique. A nominal definition of the resolving power of an instrument to resolve a strain state is given as the percentage of intrinsic instrumental broadening in the reciprocal unit with respect to the first reciprocal Brillouin zone (2π/lattice constant) of a sample. It is shown that the resolving power of these diffraction techniques ranges from 2% to 0.2%. Experimental strategies without modifying the instrument and to achieve a strain detection capability beyond the definition of the nominal resolving power of these techniques are presented.

ZnTe has a favorable band alignment with CdTe and is an ideal buffer between CdTe and metal contacts used in photovoltaics. Using metalorganic chemical vapor deposition, we report epitaxial growth of ZnTe thin films on 2D substrates, namely, single crystal graphene on amorphous SiO2/Si and freshly cleaved mica(001). Despite the large in-plane lattice mismatches between ZnTe and graphene (∼75%) and between ZnTe and mica(001) (∼17%), X-ray pole figure analyses show preferred epitaxial alignments with the out-of-plane orientation along [111] for ZnTe films on both substrates. For ZnTe on graphene, besides the primary in-plane orientation of [ 1 ¯ 10 ] ZnTe / / [ 1 1 ¯ ] graphene, two secondary in-plane orientations rotating ±25.28° away from the primary domain are found. A geometrical superlattice area mismatch (GSAM) model is implemented to explain the existence of the primary and secondary domains in ZnTe on graphene. For ZnTe on mica(001), only one in-plane orientational domain is found experimentally with the epitaxial relationship of [ 1 ¯ 10 ] ZnTe / / [ 100 ] mica (or [ 1 ¯ 10 ] ZnTe / / [ 2 1 ¯ 1 ¯ 0 ] mica if four-index notation is used for mica). However, the prediction of domain orientation between ZnTe and mica(001) based on the GSAM model slightly deviates from that observed experimentally. Furthermore, it should be noted that multiple order twinning domains of the primary domain are observed in both ZnTe films. While coexisting with the primary domain, each of the twinning domains is still epitaxially aligned with respect to the substrate. The in-depth understanding of ZnTe's epitaxial behaviors on graphene and mica(001) provides a valuable guidance for future studies on epitaxy of 3D zinc-blende overlayers on 2D hexagonal substrates.

Graphene template has long been promoted as a promising host to support van der Waals flexible electronics. However, van der Waals epitaxial growth of conventional semiconductors in planar thin film form on transferred graphene sheets is challenging because the nucleation rate of film species on graphene is significantly low due to the passive surface of graphene. In this work, we demonstrate the epitaxy of zinc-blende ZnTe thin film on single-crystalline graphene supported by an amorphous glass substrate. Given the amorphous nature and no obvious remote epitaxy effect of the glass substrate, this study clearly proves the van der Waals epitaxy of a 3D semiconductor thin film on graphene. X-ray pole figure analysis reveals the existence of two ZnTe epitaxial orientational domains on graphene, a strong X-ray intensity observed from the ZnTe [ 1 ¯ 1 ¯2] ǁ graphene [10] orientation domain, and a weaker intensity from the ZnTe [ 1 ¯ 1 ¯2] ǁ graphene [11] orientation domain. Furthermore, this study systematical...

Vanadium thin films were deposited on sapphire substrates by DC magnetron sputtering and then oxidized in a tube furnace filled with oxygen under different temperatures and oxygen flow rates. The significant influence of the oxygen flow rate and oxidation temperature on the electrical and structural properties of the vanadium oxide thin films were investigated systematically. It shows the pure vanadium dioxide (VO2) state can only be obtained in a very narrow temperature and oxygen flow rate range. The resistivity change during the metal-insulator transition varies from 0.2 to 4 orders of magnitude depending on the oxidation condition. Large thermal hysteresis during the metal-insulator phase transition was observed during the transition compared to the results in literature. Proper oxidation conditions can significantly reduce the thermal hysteresis. The fabricated VO2 thin films showed the potential to be applied in the development of electrical sensors and other smart devices.

To date, many materials have been successfully grown on substrates through van der Waals epitaxy without adhering to the constraint of lattice matching as is required for traditional chemical epitaxy. However, for elemental semiconductors such as Ge, this has been challenging and therefore it has not been achieved thus far. In this paper, we report the observation of Ge epitaxially grown on mica at a narrow substrate temperature range around 425 °C. Despite the large lattice mismatch (23%) and the lack of high in-plane symmetry in the mica surface, an epitaxial Ge film with [111] out-of-plane orientation is observed. Crystallinity and electrical properties degrade upon deviation from the ideal growth temperature, as shown by Raman spectroscopy, X-ray diffraction, and Hall effect measurements. X-ray pole figure analysis reveals that there exist multiple rotational domains in the epitaxial Ge film with dominant in-plane orientations between Ge 1¯10 and mica[100] of (20n)°, where n = 0, 1, 2, 3, 4, 5. A supe...

We have studied, in real time, the evolution of a thin (less than 200A) copper film deposited onto an oxidized silicon surface using reflection high-energy electron diffraction. We show that quantitative measurements of island size and shape as functions of time are possible and the results are presented. While the film texture is initially random, texture competition leads to an absence of the low-energy (111) and (200) oriented grains for later times. It is also found that the film surface is composed of facets that increase in size with time. This behavior is explained in terms of facet coalescence.

The residual stress in thin films is a major limiting factor for obtaining high quality films. We present a strategy for stress reduction in sputter deposited films by using a nanostructured compliant layer obtained by the oblique angle deposition technique, sandwiched between the film and the substrate. The technique is all in situ, does not require any lithography steps, and the nanostructured layer is made from the same material as the deposited thin film. By using this approach we were able to reduce stress values by approximately one order of magnitude in sputter deposited tungsten films. These lower stress thin films also exhibit stronger adhesion to the substrate, which retards delamination buckling. This technique allows the growth of much thicker films and has enhanced structural stability. A model is developed to explain the stress relief mechanism and the stronger adhesion associated with the presence of the nanostructured compliant layer.

A continuum equation for the shadowing growth of individual nanostructures by oblique angle deposition is proposed and numerically integrated. The radius R of rotationally symmetric columns is calculated as a function of height z. Before the radius R saturates at its final value Rsat, column shapes obey the power law R∼zp with the exponent value p∼0.37±0.02. The results are compared to those of an experimental study of Si columns grown on a template (p∼0.39±0.03), and on a flat surface (p∼0.32±0.01). The model additionally predicts that the saturated radius should depend on column separation d as Rsat∼d1.20±.01. This relation implies that the gap between the surfaces of adjacent columns can be optimized by altering the column separation.

A low dielectric constant polyarylether (PAE) polymer was investigated for resistance to copper drift. Positive bias-temperature stressing (BTS) of metal/PAE/SiO2/Si capacitors led to large initial flat-band voltage shifts toward the left-hand side in the capacitance–voltage curve for all gate metals investigated (Pt, Al, and Cu). Upon triangular voltage sweep (TVS) testing, Pt/PAE/SiO2/Si capacitors exhibited no peak, whereas a single peak (indicative of mobile ions) was seen for Cu/PAE/SiO2/Si capacitors. The results indicate that an intrinsic polymer instability source, such as polarization (under bias), was the major cause for the BTS instability of the polymer. From TVS studies, Cu+ ion drift could be characterized in the temperature range of 150–250 °C, and mobility of Cu+ in PAE was extracted from Hillen’s analysis. A combination of BTS and TVS techniques is thus more useful for characterization of copper drift, and helps to resolve the intrinsic polymer effect from that of metal drift-related instability.

An experimentally verified analytical model for pulsed dc reactive sputtering of tantalum oxide films is described. The influences of important process variables, like oxygen flow rate and sputtering ion current, on the oxygen partial pressure in the chamber, deposition rate, as well as film breakdown and leakage characteristics, are predicted using this model. The experimentally established existence of multiple oxygen partial pressures at a given oxygen flow rate (hysteresis loop) is theoretically explained using steady state analysis. The partial pressure of oxygen during deposition can be used to correlate and predict the critical oxygen flow rate required to achieve insulating dielectric films (with no metallic tantalum) for a specified sputtering ion current. The experimental results suggest that in order to ensure the electrical reliability of tantalum oxide films, deposition should be done at oxygen flow rates more than that required to go beyond the hysteresis region in partial pressure versus fl...

A retarding field analyzer is used to obtain a measure of the energy of the ions extracted from a direct current discharge driven by a low-frequency (100–100 kHz) asymmetrically pulsed bias. Measurements are made to illustrate the effects of the pulse’s shape (frequency and duty) on the distribution in the energies of the ions extracted from the plasma. Ion energy distributions are computed by a quasistatic treatment of the ion’s response to the measured wave form of the pulsed electrode. Comparisons are made between the measured and calculated ion energy distributions to demonstrate the effectiveness of the technique used to calculate the ion energy distribution. Expressions are then produced for the time scales in which the quasistatic treatment of the sheath remains a valid approximation to predict the energy distribution of the ions.

Measurements of the electrical resistivity of thin copper films sputtered onto silicon dioxide, in real time, are reported. The electrical resistivity is shown to strongly depend on the film’s thickness for thicknesses below the bulk mean free path of copper (39 nm). Model fits to the electrical resistivity combined with ex situ atomic force microscopy and transmission electron microscopy suggest that the average grain size plays a dominant role in the resistivity during growth. Furthermore, observations are made on the relaxation of the electrical resistivity after the growth (by sputtering) is terminated, at room temperature. Both the magnitude and the time scale of change in the electrical resistivity are observed to be a function of the film’s thickness.

Calculations of the transient charging currents to an insulating surface exposed to a dc discharge after the application of a pulse bias to the insulating surface are made based on a quasistatic treatment of the sheath’s impedance as a nonlinear dc resistance. Measurements of these transient charging currents are shown to correlate with the calculated transient currents for the experimental conditions used in this study. Discussion is then provided to indicate the limits on the pulse, plasma, and coupling conditions in which this quasistatic, dc treatment of the sheath’s response to the applied pulse remains valid.

The effects of charge accumulation during bias sputtering of copper onto an insulating material are studied. To eliminate the effects of charge accumulation, we periodically apply a pulse bias to the electrode. Microstructure and electrical properties of the sputtered copper films grown on silicon dioxide are measured as a function of the pulse bias frequency. By comparing the observed properties of these films grown under a pulse bias to those grown under a dc bias (with a conducting path to the electrode), the effectiveness of the pulse bias in controlling the ion energy distribution is demonstrated.

We present a detailed study of the surface roughness of a computer hard disk using atomic force microscopy and light scattering. The power spectrum density analysis showed that the surface possesses an anisotropic scaling behavior and has both random roughness and periodic roughness components. Quantitative anisotropic correlation length (ξ) and roughness exponent (α) for the directions parallel and perpendicular to the grooves are obtained. A novel in-plane (measurement parallel to the sample surface) light scattering technique is shown to be particularly useful for the analysis of the rough surface parallel to the grooves.

Bubbles in organic light-emitting diodes can be formed from gas release due to Joule heating effect at localized electrical shorts during operation, which could be simulated by a rapid thermal annealing. The gases in the bubbles consist of not only adsorbed moistures but also the decomposed organic species, which are detected in situ in an ultrahigh vacuum chamber. In the device of Al/tris-(8-hydroxyquinoline) aluminum (Alq/N,N′-diphenyl-N.N′-bis-{3-methylphenyl}{1,1′biphenyl}-4,4′-diamine/indium tin oxide (ITO), the gases released from ITO surface were mainly of adsorbed moistures, while those released from the organic layers were of both the decomposed products from Alq and the trapped moistures. The decomposition of Alq could not be easily avoided if there were severe localized electrical shorts in the devices.

Room temperature deposition of tantalum oxide films on metallized silicon substrates was investigated by reactive pulsed magnetron sputtering of Ta in an Ar/O2 ambient. The dielectric constant of the tantalum oxide ranged from 19 to 31 depending on the oxygen percentage [P(%)=PO2/(PO2+PAr)] used during sputtering. The leakage current density was less than 10 nA/cm2 at 0.5 MV/cm electric field and the dielectric breakdown field was greater than 3.8 MV/cm for P=60%. A charge storage as high as 3.3 μF/cm2 was achieved for 70-A-thick film. Pulse frequency variation (from 20 to 200 kHz) did not give a significant effect in the electrical properties (dielectric constant or leakage current density) of the Ta2O5 films.

The reciprocal space structures of Si backside rough surfaces were studied using an in-plane light scattering technique. A diode array detector was used to collect the angular distribution of the scattered intensity. The diffraction profiles are interpreted based on the theory of diffraction from a self-affine rough surface. Roughness parameters such as interface width, lateral correlation length, and the roughness exponent, are extracted from the profiles and are compared to that obtained by real space imaging techniques such as atomic force microscopy and stylus profilometry. Factors that limit the accuracy of light scattering measurements are discussed.

Reflection x-ray pole figure analysis techniques were used to study the heteroepitaxial relationships of the cobalt germanide CoGe2 to GaAs(100). The alloy films were grown using the partially ionized beam deposition technique, in which low energy Ge+ ions are employed to alter the heteroepitaxial orientation of the CoGe2 deposits. The CoGe2[001](100)∥GaAs[100](001) orientation, which has the smallest lattice mismatch, was found to occur for depositions performed at a substrate temperature around 280 °C and with ∼1200 eV Ge+ ions. Lowering the substrate temperature or reducing the Ge+ ion energy leads to CoGe2(100) orientation domination with CoGe2[100](010)∥GaAs[100](001) and CoGe2[100](001)∥GaAs[100](001). Substrate temperature alone was seen to produce only the CoGe2(100) orientation. For CoGe2(001) films, additional energy was required from Ge+ ions in the evaporant stream.

It is shown that a peel strength of larger than 70 g/mm adhesion can be achieved between Cu and Parylene‐N surfaces using the partially ionized beam (PIB) deposition technique while the conventional deposition techniques such as thermal evaporation, e‐beam evaporation, and sputtering give no measurable adhesion. With the PIB process, neither an adhesion enhancement layer nor substrate pretreatment is required. In the PIB deposition, up to 5% of self‐ions and 3 kV substrate bias were used during deposition. Secondary‐ion‐mass spectroscopy revealed a Cu–Parylene‐N intermixed layer located at the Cu/Parylene‐N interface. It is proposed that the mechanical interlocking provided by the graded interface region may play a role for the observed adhesion enhancement.

Nonlinear optical films were vapor deposited onto Si(100) and indium‐tin‐oxide‐coated glass. These films are guest‐host‐type polymer and showed electrooptical (EO) properties after poling. The host polymer is Teflon AF 1600 (AF) and the guest is dimethylaminonitrostilbene (DANS). Deposition is done by coevaporation. EO effects were found in films containing 5–25 vol % DANS. The EO coefficient r33, is found to be a function of composition, poling temperature, and cooling rate during poling. The highest EO coefficient obtained is 2.4 pm/V from a film with 10 vol % DANS and poled at a temperature of 130 °C. Very little or no EO effects were found for films with ≳25 vol % DANS. This is found to be a result of phase separation and subsequent crystallization of DANS. A decrease of EO effect at higher poling temperature is possibly a result of thermal disorder which was ‘‘frozen’’ during cooling. DANS was also found to react with Teflon AF 1600 at a higher DANS concentration.

The room temperature growth of 1000–1500 A Ag films on HF‐dipped Si substrates is studied as a function of self‐ion (Ag+) energy during deposition. In all cases the films contained a mixture of epitaxial grains and randomly oriented (111) grains. The orientations observed were Ag(111)/Si(111) with both type A (Ag〈110〉//Si〈110〉) and type B (Ag〈110〉//Si〈114〉) twins; Ag(110)/Si(110) with Ag〈001〉//Si〈001〉; and Ag(100)/Si(100) with Ag〈011〉//Si〈011〉. All three constructions match three Si atomic rows with four Ag rows. As judged by the ratio of epitaxial to nonepitaxial grains, the strength of the epitaxy was seen to decrease in the order (111)≳(110)≳(100). Increasing the Ag+ ion energy during the deposition was generally seen to decrease this ratio. Annealing of the Ag/Si(100) films induced preferential (100) grain growth.

The properties of amorphous BaTiO3 thin films deposited on Si substrates were studied as functions of annealing temperature. The film thickness decreased monotonically as the annealing temperature increased up to 600 °C. This reduction is believed to correlate with the densification process observed in the amorphous films during annealing. After the 500 °C annealing, a partial crystallization process was observed. It was also found that the dielectric constant and the index of refraction of the film showed significant changes as the annealing temperature increased from 400 to 500 °C. Correlations between the film density, index of refraction, and the dielectric constant are discussed. A severe reaction at the interface between the film and Si substrate was observed in the 750 °C annealed sample.

The diffusion characteristics of metal barrier materials in porous films having low dielectric constant are studied using the Rutherford backscattering spectrometry technique. It is shown that barrier materials such as TaN and TiN do not diffuse into the xerogel film with porosity of 70%–75% after 450 °C annealing in N2 ambient for 2 h. This result points to an interesting possibility that one may not require a dielectric liner for a porous film (to prevent the diffusion of metal barrier materials into the porous material) in the Cu porous film interconnect technology.

Polycrystalline thin films (1–10 μm) of the nonlinear material 2‐methyl‐4‐nitroaniline were deposited on Ag, Cu, and Si by conventional and partially ionized beam deposition. The use of ions was seen to promote a highly oriented film, with only the single x‐ray diffraction orientation (112) being observed at reduced temperatures (−50 °C). The effect of the ions on the physical microstructure of the films was to densify the film and reduce the size of the microcrystals. The films had powderlike optical properties and displayed a strong second harmonic from a Nd:YAG laser.

The observation of room‐temperature epitaxy of vapor‐deposited thin Ag films on Si(111) accomplished under conventional vacuum conditions is reported. Epitaxy was also observed at 350 °C. The films were deposited using a partially ionized beam deposition system, and were typically 1500 A thick. Epitaxy was confirmed via pole‐figure analysis. Scanning electron microscopy revealed excellent surface flatness even for the room‐temperature films. Contrary to previous observations, the growth was found to proceed by the layer mode, even at the elevated temperature. This change in morphology is attributed to the enhanced density of nucleation sites due to the energetic ions.

SiO2 film of 1500‐A thickness has been grown by a conventional thermal dry oxidation process on commercial Si(111) and Si(100) wafers. A secondary‐ion mass spectrometry study of the SiO2/Si structure showed that a gettering of Cu atoms, which were present in the Si wafers as residual impurities, has occurred at the SiO2/Si interface due to the thermal dry oxidation process. The areal concentration of the Cu atoms at the interface has been found to depend on the Cu concentration in the Si wafers. Areal concentrations in order of 1×1012/cm2 were measured at the interfaces. Facilitated by the high diffusivity of Cu in SiO2 and Si, the gettering is thermodynamically driven by the low solid solubility of Cu, either in SiO2 at the temperature range up to the oxidation temperature, or in Si at low temperatures as the wafers cool down. The defects generated at the SiO2/Si interface provide the nucleation sites for the Cu gettering.

Cu thin films have been deposited on Si(111) substrate using partially ionized deposition technique in which the self‐ions, i.e., the ions derived from the depositing materials themselves, are being used to concurrently bombard the substrate surface during thin film growth. The ion percentage in the deposition beam is in the range from 0% to 5% with the ion energy varying between a few eV and several keV. The Si(111) substrates are chemically cleaned by a RCA cleaning process before loading into the vacuum chamber of deposition. No in situ cleaning of the substrate surface is performed prior to deposition. A reduction of impurities such as oxygen, carbon, and hydrogen at the Cu/Si interface is observed as a function of the ion bombardment parameters using secondary‐ion mass spectrometry. The estimates of the sputtering cross section of oxygen, carbon and hydrogen at the Cu/Si interface by Cu ions and their energy dependence are discussed in the framework of mechanisms of the impurity sputtering by low‐energy ions.

A new Al(111)/Si(111) orientational epitaxy using x‐ray pole figure analysis is reported. The new structure has a 19° rotation with respect to the parallel epitaxy. The results are explained using a geometrical lattice matching concept.