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The properties of artificially grown thin films are strongly affected by surface processes during growth. Coherent X-rays provide an approach to better understand such processes and fluctuations far from equilibrium. Here we report results for vacuum deposition of C$_{60}$ on a graphene-coated surface investigated with X-ray Photon Correlation Spectroscopy in surface-sensitive conditions. Step-flow is observed through measurement of the step-edge velocity in the late stages of growth after crystalline mounds have formed. We show that the step-edge velocity is coupled to the terrace length, and that there is a variation in the velocity from larger step spacing at the center of crystalline mounds to closely-spaced, more slowly propagating steps at their edges. The results extend theories of surface growth, since the behavior is consistent with surface evolution driven by processes that include surface diffusion, the motion of step-edges, and attachment at step edges with significant step-edge barriers., Comment: 14 pages and 7 figures

In this study, a strontium doped lanthanum cobalt ferrite thin film with 30% Sr on A-site, denoted as La 0.7 Sr 0.3 Co 0.2 Fe 0.8 O 3-δ or LSCF-7328, is investigated before and after annealing at 800 °C under CO 2 containing atmosphere for 9 h. The formation of secondary phases on surface of post-annealed LSCF-7328 is observed using atomic force microscope (AFM) and scanning electron microscope (SEM). The extent of Sr segregation at the film surface is monitored using the synchrotron-based total reflection X-ray fluorescence (TXRF) technique. The bonding environment of the secondary phases formed on the surface is investigated by synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). Scanning transmission electron microscopy (STEM) and related spectroscopy techniques are used for microstructural and quantitative elemental analyses of the secondary phases on surface. These studies reveal that the secondary phases on surface consist of SrO covered with a capping layer of SrCO 3 . The formation of Co-rich phases is observed on the surface of post-annealed LSCF-7328.

Strontium-doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, and reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as surface segregation of Sr during solid oxide fuel cell (SOFC) operation, which can adversely affect the electrochemical performance. Thus, understanding the nature of the Sr surface segregation phenomenon and how it is affected by the composition of LSCF and strain are critical. In this research, heteroepitaxial thin films of La1–x SrxCo0.2Fe0.8O3−δ with varying Sr content (x = 0.4, 0.3, 0.2) were deposited by pulsed laser deposition (PLD) on single-crystal NdGaO3, SrTiO3, and GdScO3 substrates, leading to different levels of strain in the films. The extent of Sr segregation at the film surface was quantified using synchrotron-based total-reflection X-ray fluorescence (TXRF) and atomic force microscopy (AFM). The electronic structure of the Sr-rich phases formed on t...

The properties of artificially grown thin films are often strongly affected by the dynamic relationships between surface growth processes and subsurface structure. Coherent mixing of X-ray signals promises to provide an approach to better understand such processes. Here, we demonstrate the continuously variable mixing of surface and bulk scattering signals during real-time studies of sputter deposition of a-Si and a-WSi2 films by controlling the X-ray penetration and escape depths in coherent grazing-incidence small-angle X-ray scattering. Under conditions where the X-ray signal comes from both the growth surface and the thin film bulk, oscillations in temporal correlations arise from coherent interference between scattering from stationary bulk features and from the advancing surface. We also observe evidence that elongated bulk features propagate upwards at the same velocity as the surface. Furthermore, a highly surface-sensitive mode is demonstrated that can access the surface dynamics independently of the subsurface structure. Defects affect materials’ properties. A method is now presented for studying dynamic processes during the growth of thin films — specifically, the evolution of defects — based on the coherent mixing of bulk and surface X-ray scattering signals.

We present a systematic synchrotron radiation photoemission spectroscopy study of the interaction of O2 with defective La0.8Sr0.2Co0.2Fe0.8O3 − δ(100) surfaces at low temperatures. First, the surface chemical evolution during low energy Ar+ ion sputtering is investigated and is found to create oxygen vacancies. Subsequently, the interaction of the O2 molecules with La0.8Sr0.2Co0.2Fe0.8O3 − δ(100) surface is observed to create an insulating phase. We performed a detailed core-level peak-fitting analysis to identify the chemical nature of this phase and to probe the role of vacancies in the formation of this phase.

The ultra-high vacuum surface preparation of heteroepitaxial lanthanum strontium cobalt ferrite thin films has been studied using soft X-ray photoelectron spectroscopy. Specifically, the effect of annealing the films at low temperatures in low partial pressures of oxygen and argon has been investigated. We find that atmospheric surface carbon contamination of the films can be removed in select anneal temperature regimes in argon, but remains bound to the surface with oxygen annealing at any temperature. Irrespective of the gas used, an insulating phase transition occurs near 300 °C due to strontium segregation at the surface. The surface develops more insulating character if annealed with oxygen. Different species are proposed to be responsible for the discrepancy in insulating character.

Synchrotron based hard x-ray photoelectron spectroscopy (HAXPES) technique has been utilized to measure the oxidation states of the associated ions on the surface of strontium doped lanthanum cobalt iron oxide (LSCF), as a function of strontium dopant concentration and gas composition. LSCF is a widely used cathode material for solid oxide fuel cells (SOFCs), which are ideally suitable for environmentally benign electricity generation. However, LSCF suffers from long term stability issues by surface segregation phenomena under typical SOFC working conditions. Leveraging the capability of HAXPES to overcome surface contamination issues and obtaining information from tunable penetration depth, depth dependence information about changes in the electronic structure were obtained, which helps better understand the segregation phenomena. Surface chemistry of both as-deposited and post-annealed LSCF thin films with different Sr concentrations are discussed.

This paper explores the effects of different plasma treatments on low dielectric constant (low-k) materials and the consequences for the growth behavior of atomic layer deposition (ALD) on these modified substrates. An O2 and a He/H2 plasma treatment were performed on SiCOH low-k films to modify their chemical surface groups. Transmission FTIR and water contact angle (WCA) analysis showed that the O2 plasma changed the hydrophobic surface completely into a hydrophilic surface, while the He/H2 plasma changed it only partially. In a next step, in situ X-ray fluorescence (XRF), ellipsometric porosimetry (EP), and Rutherford backscattering spectroscopy (RBS) were used to characterize ALD growth of TiO2 on these substrates. The initial growth of TiO2 was found to be inhibited in the original low-k film containing only Si-CH3 surface groups, while immediate growth was observed in the hydrophilic O2 plasma treated film. The latter film was uniformly filled with TiO2 after 8 ALD cycles, while pore filling was delayed to 17 ALD cycles in the hydrophobic film. For the He/H2 plasma treated film, containing both Si-OH and Si-CH3 groups, the in situ XRF data showed that TiO2 could no longer be deposited in the He/H2 plasma treated film after 8 ALD cycles, while EP measurements revealed a remaining porosity. This can be explained by the faster deposition of TiO2 in the hydrophilic top part of the film than in the hydrophobic bulk which leaves the bulk porous, as confirmed by RBS depth profiling. The outcome of this research is not only of interest for the development of advanced interconnects in ULSI technology, but also demonstrates that ALD combined with RBS analysis is a handy approach to analyze the modifications induced by a plasma treatment on a nanoporous thin film.

Synchrotron-based X-ray fluorescence (XRF) is introduced as a promising in situ technique to monitor atomic layer deposition cycle-per-cycle. It is shown that the technique is greatly suitable to study initial nucleation on planar substrates. The initial growth of TiO2 from tetrakis(dimethylamino)titanium (TDMAT) and H2O is found to be linear on thermally grown SiO2, substrate-inhibited on H-terminated Si and substrateenhanced on atomic layer deposited Al2O3. Furthermore, in situ XRF is employed to monitor the Ti uptake during deposition of TiO2 in nanoporous silica films. In mesoporous films, the Ti content varied quadratically with the number of cycles, a behavior that is attributed to a decreasing surface area with progressing deposition. In microporous films, the XRF data suggest that 1−3 ALD cycles shrunk the pore diameters below the kinetic diameter of the TDMAT molecule.

Detailed quantitative measurement of surface dynamics during thin film growth is a major experimental challenge. Here x-ray photon correlation spectroscopy with coherent hard x rays is used in a grazing-incidence small-angle x-ray scattering (i.e., Co-GISAXS) geometry as a tool to investigate nanoscale surface dynamics during sputter deposition of a-Si and a-$\mathrm{WS}{\mathrm{i}}_{2}$ thin films. For both films, kinetic roughening during surface growth reaches a dynamic steady state at late times in which the intensity autocorrelation function ${g}_{2}(q,\phantom{\rule{0.16em}{0ex}}t)$ becomes stationary. The ${g}_{2}(q,\phantom{\rule{0.16em}{0ex}}t)$ functions exhibit compressed exponential behavior at all wavenumbers studied. The overall dynamics are complex, but the most surface sensitive sections of the structure factor and correlation time exhibit power law behaviors consistent with dynamical scaling.

The texture of CoSi2 films on Si(001) substrates has been examined using synchrotron based high-resolution pole figure analysis. We find that axiotaxy, a recently recognized type of texture which was observed in NiSi thin films on Si(001), is also occurring in CoSi2 layers. Typical of axiotaxy texturing, the CoSi2 pole figures show symmetrical patterns of lines. Calculations show that these features on the pole figures are created by three off-normal fiberlike texture components. These off-normal fiber orientations are a consequence of the alignment of CoSi2〈110〉 planes with Si〈110〉 planes because of very similar d spacings, which causes a periodic arrangement along Si〈100〉 directions in the plane of the interface. This one-dimensional periodicity may provide a lower interfacial energy; however, the periodic arrangement along the Si〈100〉 directions may also be indicative of growth anisotropy. The influence of Ti alloying has been investigated by using in situ x-ray diffraction measurements, as well as pol...

Atomic ordering in AlGaN films produced by plasma assisted molecular beam epitaxy (PA-MBE) was investigated with X-ray diffraction (XRD) and transmission electron microscopy selected area diffraction (TEM-SAD). Under nitrogen-rich growth conditions, films undergo 1×1 monolayer cation ordering along the [0001] growth direction. This type of ordering is stronger in N-polar films than in Ga-polar films and is sensitive to the growth ratio of group-III to group-V flux. These observations are in qualitative agreement with the first principal calculations by Northrup and co-workers. Under group-III rich growth conditions of Ga-polar films, the XRD data is consistent with the quasi-random stacking of spontaneously formed 14-ML and 12-ML superlattice structures. Reciprocal space mapping shows a small tilt (0.25°) between the crystallographic c-axis of the wurtzite structure and the superlattice axis. This result can be explained by the presence of c-axis oriented superlattice domains with a parallel step translation between neighboring domains. This result is in qualitative agreement with a recently proposed model by Venezuela and co-workers of self-organized superlattice formation during step flow growth of strained alloys on vicinal surfaces.

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (

Texture development in (Ti,Ta)Si2, formed from Ti–Ta alloy (0–6 at. % Ta) thin films sputtered on Si(001) and poly-Si substrates, was studied using both in situ and ex situ x-ray diffraction. The addition of Ta fundamentally changes the C54 texture. At 6 at. % Ta, an effective composition for lowering the C49–C54 transformation temperature, films on both substrates develop a strong (010) texture normal to the film plane. Alloy films on Si(001) also exhibit an in-plane orientational relationship between the final C54 texture and the underlying silicon lattice. A pseudoepitaxial film relationship with the substrate may, therefore, be playing an important role in the C54 transformation process. For 32 nm films on single-crystal substrates, the in situ measurements show that significant evolution of the C54 texture occurs during the growth process, suggesting that those grains well oriented with respect to the Si substrate lattice have higher growth velocities. The possibility of a template effect by the C40 ...

The transformation from the C49 to the C54 phase in TiSi2 thin films has been studied for more than a decade because of its importance to the semiconductor industry. In previous work we identified three dominant C54 orientations in TiSi2 thin films on Si(001) substrates using x-ray pole figure analysis. In the current study the evolution of the three prominent C54 texture components was further examined using synchrotron based time-resolved in situ x-ray diffraction. The kinetics results show significant differences in the nucleation and growth kinetics of the individual orientations. Simulations suggest that this could be explained by an inhomogeneous nucleation of different texture components in the thin film, but not by simple differences in nucleation and/or growth rates. Classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis of nucleation and growth was applied to model the C49–C54 phase transformation kinetics for each C54 orientation. These results showed a systematic decrease of the Avrami expon...

The texture of blanket C49 and C54 phase TiSi2 films on Si (001) substrates was examined with x-ray pole figure analysis. Textures were studied both in films with initial Ti deposited by sputtering and by low-temperature, plasma assisted chemical vapor deposition. Detailed differences were observed between silicide films grown by subsequently annealing films deposited with the two different methods. However, in both cases, the dominant C49 phase orientational relationships develop with respect to the substrate (001) planes. In contrast, we find that the dominant crystallographic relationships of the C54 phases in both cases are not with the surface (001) plane of the substrate, but instead with the Si (111) planes. Texturing in the case of the sputtered films is particularly complex with one prominent orientation having C54 (11¯0)‖(1¯11) Si with C54 (331)‖(011) Si and a second having C54 (1¯03¯)‖(111) Si with C54 (040)‖(11¯0) Si. These orientations, which suggest local epitaxy of the disilicide with...

The temporal evolution of high quality indium nitride (InN) growth by plasma-assisted atomic layer epitaxy (ALEp) on a-plane sapphire at 200 and 248 °C was probed by synchrotron x-ray methods. The growth was carried out in a thin film growth facility installed at beamline X21 of the National Synchrotron Light Source at Brookhaven National Laboratory and at beamline G3 of the Cornell High Energy Synchrotron Source, Cornell University. Measurements of grazing incidence small angle x-ray scattering (GISAXS) during the initial cycles of growth revealed a broadening and scattering near the diffuse specular rod and the development of scattering intensities due to half unit cell thick nucleation islands in the Yoneda wing with correlation length scale of 7.1 and 8.2 nm, at growth temperatures (Tg) of 200 and 248 °C, respectively. At about 1.1 nm (two unit cells) of growth thickness nucleation islands coarsen, grow, and the intensity of correlated scattering peak increased at the correlation length scale of 8.0 a...

Synchrotron based x-ray fluorescence (XRF) and grazing incidence small angle scattering (GISAXS) are demonstrated to be excellent in situ methods for monitoring atomic layer deposition (ALD) processes. XRF allows to identify and to quantify the amount of material deposited, whereas GISAXS is a powerful technique for monitoring nanoscale morphology. Three case studies are discussed where these in situ techniques are used to investigate specific aspects of ALD processes that are of relevance for applications in micro-electronics: the initial growth of gate oxides, the initial nucleation during metal ALD processes, and the penetration of ALD deposited materials into nanoporous low-k oxides.

Aluminum gallium nitride alloys were grown by molecular beam epitaxy and their film composition, structure and microstructure were investigated by Rutherford backscattering spectroscopy, Atomic Force Microscopy, X-ray diffraction, Transmission Electron Microscopy and High Resolution Electron Microscopy. The kinetics of growth was investigated and the result show that at the growth temperature of 750 °C the sticking coefficient of Ga varies monotonically from practically 0 to 1 as the growth varies from group-III to -V rich regime. Correspondingly, the surface morphology changes from atomically smooth in the group-III regime to relatively rough in the nitrogen-rich regime. The X-ray diffraction and TEM studies revealed the existence of three types of spontaneously formed superlattice structures, along the [0001] direction, with periodicities of 2-, 7- and 12-monolayers. While the two-monolayer ordering is preferred under group-V rich conditions of growth, the 7- and 12-monolayer ordering were observed under group-III rich conditions of growth. Off-axis X-ray diffraction shows the absence of in-plane ordering and that periodic stacking faults are not present in the superlattice structures.

This study investigates Sr surface segregation behavior and phase formation in La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), a commonly used cathode material for solid oxide fuel cells (SOFCs). (100)-oriented LSCF thin films were deposited on (110)-oriented NdGaO3(NGO) substrates by Pulsed Laser Deposition (PLD). The samples were annealed in atmospheres with various CO2partial pressures at 800°C. Using the synchrotron technique of Total Reflection X-ray Fluorescence (TXRF), surface segregation in these thin films were quantified. The morphological changes at the surface were examined by AFM studies. The kinetics and thermodynamics of the segregation are discussed.

A limiting factor for Solid Oxide Fuel Cell (SOFC) performance is the oxygen reduction reaction (ORR) at the cathode surface. Changes in the surface composition and structure on annealing at 800°C has been studied, since these can influence the ORR. Idealized single crystals of cathode materials La0.8Sr0.2MnO3 (LSM) and La1-xSrxCoyFe1-yO3 (LSCF) were grown as heteroepitaxial thin films on lattice matched single crystal substrates. Changes upon heating the films to operating temperature and pressures were characterized using various synchrotron x-ray techniques. Total Reflection X-ray Fluorescence (TXRF) measurements, which probe compositional changes, were made at high temperature in real time. The LSM surfaces were found to develop manganese enrichment when heated. Highly strontium doped LSCF were found to develop strontium-rich surfaces. HArd X-ray PhotoElectron Spectroscopy (HAXPES) was used to investigate the electronic structure of the materials. Highly strontium doped LSCF precipitates a surface strontium phase that contains both oxide and carbonate contributions.

In-situ X-ray diffraction during rapid thermal annealing at rates from 3 to 20°C s −1 was used to study the formation of titanium silicide phases from a thin film of Ti and doped single-crystal or undoped polycrystalline silicon substrates. In all cases, a metal-rich silicide (identified as either Ti 5 Si 4 or Ti 5 Si 3 ) was the first crystalline phase to form between 500 and 550°C, followed by C49-TiSi 2 between 575 and 600°C. The formation of C49-TiSi 2 completely consumed the metal-rich silicide before transforming into the low-resistance C54-TiSi 2 phase at approximately 800°C. These results indicate that while there is sufficient thermodynamic driving forces to nucleate both a metal-rich silicide and C49-TiSi 2 the subsequent growth of C49-TiSi 2 , is kinetically favored over the growth of Ti 5 Si 4 or Ti 5 Si 3 .

Real time grazing incidence small angle x-ray scattering and x-ray fluorescence (XRF) are used to elucidate nanodot formation on silicon surfaces during low energy ion beam irradiation of ultrathin iron-coated silicon substrates. Four surface modification stages were identified: (1) surface roughening due to film erosion, (2) surface smoothing and silicon-iron mixing, (3) structure formation, and (4) structure smoothing. The results conclude that 2.5 x 10(15) iron atoms in a 50 nm depth triggers surface nanopatterning with a correlated nanodots distance of 25 nm. Moreover, there is a wide window in time where the surface can have correlated nanostructures even after the removal of all the iron atoms from the sample as confirmed by XRF and ex-situ x-ray photoelectron spectroscopy (XPS). In addition, in-situ XPS results indicated silicide formation, which plays a role in the structure formation mechanism. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773202]

Atomic layer deposition is demonstrated to be greatly suitable to tune the pore size of ink-bottle mesopores at the atomic level. This is confirmed by quantitative electron tomography, which enable...

Atomic layer deposition (ALD) is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. The self-limiting nature of the chemical reactions ensures precise film thickness control and excellent step coverage, even on 3D structures with large aspect ratios. At present, ALD is mainly used in the microelectronics industry, e.g. for growing gate oxides. The excellent conformality that can be achieved with ALD also renders it a promising candidate for coating porous structures, e.g. for functionalization of large surface area substrates for catalysis, fuel cells, batteries, supercapacitors, filtration devices, sensors, membranes etc. This tutorial review focuses on the application of ALD for catalyst design. Examples are discussed where ALD of TiO(2) is used for tailoring the interior surface of nanoporous films with pore sizes of 4-6 nm, resulting in photocatalytic activity. In still narrower pores, the ability to deposit chemical elements can be exploited to generate catalytic sites. In zeolites, ALD of aluminium species enables the generation of acid catalytic activity.

The initial growth of HfO2 was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO2 was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H2O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

The structure of GaN films grown by electron‐cyclotron‐resonance‐assisted molecular beam epitaxy on Si(111), Si(001), basal‐plane sapphire, a‐plane sapphire, and r‐plane sapphire substrates was studied with four‐circle x‐ray diffractometry. Phase content, domain size, inhomogeneous strain, and in‐plane and out‐of‐plane domain misorientations were measured and compared for films grown on each type of substrate. Wurtzite and zinc blende polymorphs were found to coexist in films grown on Si(111). The two structures grow in the (0002) and (111) orientations, respectively, so that they may transform into each other via stacking faults on close‐packed planes. Smaller amounts of zinc blende material were also found in predominately (0002) wurtzitic films on a‐plane sapphire and (1120) wurtzitic films on r‐plane sapphire.

The first observation of atomic long range ordering in AlxGa1−xN thin films grown by electron cyclotron resonance assisted molecular beam epitaxy on sapphire and 6H-SiC substrates is reported. The phenomenon was investigated by studying the superlattice peaks (0001), (0003), and (0005) using x-ray diffraction. The relative intensity of these peaks was found to be largest for Al content in the 30%–50% range in qualitative agreement with expectations for an ordered structure of ideal Al0.5Ga0.5N stoichiometry. The average size of the ordered domains in the films was found to be within a factor of 4 of the films’ thicknesses. The degree of ordering depends on the III/V flux ratio and exhibits a weaker dependence on Si doping.

High quality films of YBa2Cu3O7−δ on LaAlO3 have been grown by pulsed‐laser deposition at oxygen pressures of 3.4–54 Pa (25–400 mTorr). X‐ray diffraction reveals the coexistence of grains that align with the substrate axes (axial grains) and grains that are rotated by 0.4° from the substrate axes (diagonal grains). The axial grains are tetragonal while the diagonal grains achieve lattice parameters close to bulk YBa2Cu3O7. The relative proportion of axial grains accounts for the measured variations of normal‐state conductance and superconducting critical current density from film to film, based on a simple two‐dimensional model of randomly positioned, insulating axial grains.

We examine how the substrate temperature during Ti film sputter deposition influences the subsequent texture formation in TiSi2 thin films. Titanium films of 32 nm thickness were sputtered onto Si(001) at elevated substrate temperatures varying between 100 °C and 900 °C. After the depositions, in situ x-ray diffraction (XRD) measurements were performed to study the thin film reactions in real time, as the samples were annealed. The XRD results show that the substrate temperature significantly influences the texture of the initial Ti film as well as the texture of the resulting C54-phase TiSi2. The preferred Ti orientation gradually changes from (002) to (101) fiber texture as the deposition temperature increases up to 500 °C. Films deposited at 600 °C transformed into the C49 phase during deposition while films deposited at 700 °C and higher temperatures transformed into the C54 phase during deposition. The series of deposited films was annealed up to 1000 °C in He to complete the C54 phase formation while monitoring the texture evolution in situ using a position sensitive x-ray detector. The XRD results show that the final C54 phase texture changes from a dominant (311) orientation normal to the substrate to a (010) orientation for substrate temperatures between 600 °C and 700 °C. The C49-C54 phase transformation temperature is also lowered for these deposition temperatures. Ex situ pole figure analysis of the film deposited at 700 °C confirms the dominant C54 (010) texture and shows an in-plane orientation with C54 [001] ∥ Si [110]. For substrate temperatures between 800 °C and 900 °C, the C54 texture changes dramatically. In this case, θ - 2 θ scans do not show a preferred C54 orientation, but pole figure analysis indicates weak inplane orientations.

We have studied the formation of titanium silicides in the presence of an ultra-thin layer of Ta, interposed between Ti and Si. In-situ x-ray diffraction (XRD), resistance measurements and elastic light scattering were used to study the thin film reactions in real time during ramp anneals to 1000°C. On poly-Si substrates the Ta thickness was varied from 0 to 1.5 nm while the Ti thickness was held constant at ∼27 nm. The time-resolved XRD shows that the volume fraction of C40 and metal-rich silicide phases grows with increasing Ta layer thickness. Increased Ta layer thicknesses also delay the growth of the C49 disilicide phase to higher temperatures. Among the Ta thicknesses we examined, 0.3 nm is the most effective in lowering the C49-C54 transformation temperature. Films with Ta layers thicker than 0.5 nm do not completely transform into the C54 phase. The texture of the C54 phase is also sensitive to the Ta thickness. The C54 disilicide film is predominantly (010) textured for the Ti / 0.3 nm Ta sample. The final C54 texture is significantly different for Ta layers thinner or thicker than the optimal 0.3 nm. This suggests that the most effective thickness for lowering the C54 formation temperature is related to the development of a strong (010) texture. The possibility of a template effect by the C40 or metal-rich Ti5Si3 phases is also discussed on the basis of texture considerations.

The structural and electrical quality of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grown on ion-etched substrates by a variety of techniques was investigated. Co-evaporated YBa/sub 2/Cu/sub 3/O/sub 7- delta / films deposited and postannealed on etched LaAlO/sub 3/ substrates have substantially higher room-temperature resistivities and wider c-axis rocking curve widths than films on unetched substrates. Annealing of the etched substrate prior to evaporation narrows the c-axis rocking curve width and restores resistivity and critical current densities to values comparable to those of the unetched controls. Laser-ablated films on etched substrates show a smaller absolute magnitude of rocking curve broadening and no change in DC electrical properties. An increase of the inhomogeneous strain was also observed in coevaporated postannealed and laser-ablated films on etched substrates. >

Atomic layer deposition (ALD) is a thin film deposition technique that has been studied with a variety of in situ techniques. By exploiting the high photon flux and energy tunability of synchrotron based x-rays, a variety of new in situ techniques become available. X-ray reflectivity, grazing incidence small angle x-ray scattering, x-ray diffraction, x-ray fluorescence, x-ray absorption spectroscopy, and x-ray photoelectron spectroscopy are reviewed as possible in situ techniques during ALD. All these techniques are especially sensitive to changes on the (sub-)nanometer scale, allowing a unique insight into different aspects of the ALD growth mechanisms.

This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (112¯0) A-plane parallel to the (11¯02) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (112¯0) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (112¯6) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut (∼0.5°) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects i...

Structures with incommensurate ordering along the [0001] direction are observed in wurtzite Al0.72Ga0.28N alloys grown by plasma-assisted molecular beam epitaxy on c-plane sapphire. Films grown in environments with group-III/N ratios greater than 1 exhibit ordered superlattice structures that are incommensurate with the wurtzite crystal lattice. In contrast, films grown under nitrogen-rich conditions exhibit ordered structures with a periodicity of four cation-N monolayers. The increasing complexity of the ordering with increasing Ga-rich growth environment suggests that the ordering is related to the presence of a Ga overlayer believed to exist on the surface of the growing film.