X-ray Pole Figure Measurements Research Articles

Interface structures of Al0.85Sc0.15N-on-Si thin films grown by reactive magnetron sputtering upon post-growth cyclic rapid thermal annealing

Al0.85Sc0.15N thin films, about 920 nm thick, have been deposited on the Si (001) substrate by reactive magnetron sputtering at 600 °C. X-ray diffraction and pole-figure measurements revealed [0002]-oriented texture structures of the nitride films without any phase separations before and after cyclic annealing at 600–900 °C for up to 48 min. Cross-sectional studies by transmission electron microscopy and energy dispersive x-ray analysis revealed an intermediate Al0.85Sc0.15N layer of ∼24.6 nm thick with smaller grains and tilted [0002]-orientations compared to its overlayer, i.e., a nucleation layer (NL), on the Si substrate. After annealing, apparent morphological changes have been observed at the near-interface regions, including the NL, the NL/Si interface, and the Si substrate, rather than in the Al0.85Sc0.15N overlay. Undesired oxygen has been observed in the nitride film and its composition increased during post-growth thermal annealing without forming oxides. These observations shed new light on crystal growth and post-growth thermal annealing of AlScN toward their high-performance piezoelectric applications.

Homoepitaxial growth of β-Ga2O3 by halide vapor phase epitaxy

We demonstrated halide vapor phase epitaxy of β-Ga2O3 on a native substrate, which should be scalable and useful for the formation of vertical fins and trenches with smooth (100)-faceted sidewalls using plasma-free microfabrication techniques, e.g., selective area growth and gas etching, for use in power device applications. No misoriented domains were detected in the epiwafer during x-ray pole figure measurements. The full width at half maximum values of the x-ray rocking curves of the epiwafer were virtually the same as those of the bare substrate. No domain boundaries were found using scanning transmission electron microscopy at the film/substrate interface. The growth rate was as high as 23 μm h−1, which was comparable to the rate for a (001) epilayer that was grown simultaneously.

New Features in Crystal Orientation and Phase Mapping for Transmission Electron Microscopy

ACOM/TEM is an automated electron diffraction pattern indexing tool that enables the structure, phase and crystallographic orientation of materials to be routinely determined. The software package, which is part of ACOM/TEM, has substantially evolved over the last fifteen years and has pioneered numerous additional functions with the constant objective of improving its capabilities to make the tremendous amount of information contained in the diffraction patterns easily available to the user. Initially devoted to the analysis of local crystallographic texture, and as an alternative to both X-ray pole figure measurement and EBSD accessories for scanning electron microscopes, it has rapidly proven itself effective to distinguish multiple different phases contained within a given sample, including amorphous phases. Different strategies were developed to bypass the inherent limitations of transmission electron diffraction patterns, such as 180° ambiguities or the complexity of patterns produced from overlapping grains. Post processing algorithms have also been developed to improve the angular resolution and to increase the computing rate. The present paper aims to review some of these facilities. On-going works on 3D reconstruction are also introduced.

Phase Transformation and Superstructure Formation in (Ti0.5, Mg0.5)N Thin Films through High-Temperature Annealing

(Ti0.5, Mg0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by θ–2θ X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 mΩ·cm, as measured by four-point-probe, and a Seebeck coefficient of −25 µV/K. It is shown that high temperature (~800 °C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.

Growth of high-quality one-inch free-standing heteroepitaxial (001) diamond on (112¯0) sapphire substrate

One-inch free-standing (001) diamond layers on a (112¯0) (a-plane) sapphire substrate with an Ir buffer layer (Kenzan Diamond®) were grown. The full-width at half maximum values of (004) and (311) x-ray rocking curves were 113.4 and 234.0 arc sec, respectively. The dislocation density of the substrates was 1.4 × 107 cm−2, determined by plan-view transmission electron microscopy observation. These values are much lower than the reported values among heteroepitaxial diamonds. Furthermore, x-ray pole figure measurements showed four symmetry of the crystal, showing single crystallinity without any twinning. The curvature radius of diamond was measured to be 90.6 cm, which is much larger than previous values, ca. 20 cm. Surprisingly, a cubic-lattice (001) diamond crystal was epitaxially grown on a trigonal-lattice (112¯0) sapphire substrate. However, we found that the epitaxial relation is diamond (001) [110]//Ir (001) [110]//sapphire (112¯0) [0001]. Now, high-quality one-inch diamond wafers will be available as a substrate used for diamond electronic devices.

Study of uniaxial deformation behavior of 50 nm-thick thin film of gold single crystal using in situ X-ray pole figure measurements

In this paper, in situ measurements of synchrotron x-ray pole figure have been performed during incremental uniaxial deformation test on a single-crystal gold foil. The 50 nm thick Au thin film was elaborated by ion sputtering at 400 °C on NaCl single crystal as a template. The resulting film consists of a single-crystal gold foil containing a small density of thin and small {111} growth twins (few nm thick and few tens of nm long) revealed by x-ray pole figure measurement. The as-deposited gold single crystal was then transferred onto flexible polyimide substrates for deformation test. This work focuses on the relative evolution of the diffracting volume related to growth twins during a loading-unloading tensile test. Macroscopic applied deformations and x-ray pole figures were measured in situ during a uniaxial tensile test in the Au [110] direction. X-ray pole figures clearly evidenced the relative evolution of the diffracting volumes related to the (111) and 1¯1¯1 twins which exhibit a huge increase of about 450% at a uniaxial applied true strain of about 4%. The concomitant variation of diffracting volumes related to the two other twin variants (namely 1¯11 and 11¯1 twins) shows a relatively low decrease of 25%. The results open out onto a true strain-twinning volume hysteresis curve, indicative of the deformation mechanisms of gold thin films that can be interpreted as a twinning-detwinning mechanism.

Evidence of adaptive modulation and magnetic field induced reorientation of variants in epitaxially grown Ni-Mn-Ga thin film on Al2O3[formula omitted] substrate

Epitaxial Ni-Mn-Ga thin films with a room temperature martensite phase were fabricated on single crystal Al2O3(112¯0) substrate using direct current (DC) magnetron sputtering. The X-ray pole figure measurements confirm the epitaxial relationship of Ni-Mn-Ga (101)7M || Al2O3(112¯0) and Ni-Mn-Ga [101¯]7M || Al2O3[11¯01] between the film and substrate. Transmission electron microscopy reveals the presence of (220) micro-twins at an angle of 62.5° and 56.3° with respect to (202) growth plane. Coexistence of non-modulated martensite phase (aNM = 5.45 Å and cNM = 6.56 Å) and seven modulated martensite phases (a14M=6.26Å,b14M=5.89Åandc14M=5.56Å) has been observed in the film. The in-situ high-temperature X-ray diffraction indicates reversible thermal phase transformation in the film with a very low thermal hysteresis. The magnetic field induced reorientation (MIR) effect is displayed by the film.

New insights into microstructural evolution of epitaxial Ni–Mn–Ga films on MgO (1 0 0) substrate by high-resolution X-ray diffraction and orientation imaging investigations

In this work, a detailed investigation has been performed on hetero-epitaxial growth and microstructural evolution in highly oriented Ni–Mn–Ga (1 0 0) films grown on MgO (1 0 0) substrate using high-resolution X-ray diffraction and orientation imaging microscopy. Mosaicity of the films has been analysed in terms of tilt angle, twist angle, lateral and vertical coherence length and threading dislocation densities by performing rocking curve measurements and reciprocal space mapping. Density of edge dislocations is found to be an order of magnitude higher than the density of screw dislocations, irrespective of film thickness. X-ray pole figure measurements have revealed an orientation relationship of || (1 0 0)MgO; || [0 0 1]MgO between the film and substrate. Microstructure predicted by X-ray diffraction is in agreement with that obtained from electron microscopy and atomic force microscopy. The evolution of microstructure in the film with increasing thickness has been explained vis-à-vis dislocation generation and growth mechanisms. Orientation imaging microscopy observations indicate evolutionary growth of film by overgrowth mechanism. Decrease in coercivity with film thickness has been explained as an interplay between stress field developed due to crystal defects and magnetic domain pinning due to surface roughness.

Low-pressure solid-state bonding technology using fine-grained silver foils for high-temperature electronics

A solid-state bonding technique using fine-grained silver (Ag) foils is presented. The Ag foils are manufactured using many runs of cold rolling and subsequent annealing processes to achieve the favorable microstructure. X-ray diffraction and pole figure measurement are performed to examine the crystal structure and grain orientations. Si chips are bonded to bare Cu substrates using the Ag foil as the bonding medium at 300 °C in 0.1 torr vacuum assisted by 6.9 MPa static pressure, which is much lower than that used in conventional thermal compression bonding. Cross sections prepared by focus ion beam show clear bonding interfaces with only a few voids smaller than 100 nm. The bonded structures do not crack after cooling down to room temperature, indicating that the ductile Ag layer is able to manage the strain induced by the large coefficient of thermal expansion mismatch between Si and Cu. The average shear strength of as-bonded samples is 29 MPa. High-temperature storage tests are conducted, and slight increase in strength can be observed after 300 °C aging. Fracture analyses show that the breakage occurs within the Ag foil rather than on the bonding interface. Transmission electron microscopy and energy-dispersive spectroscopy (TEM/EDX) are conducted for Ag/Cu interface after 200-h aging, and the result shows that slight diffusion proceeds during the aging. Since Ag has the highest electrical and thermal conductivities among metals, therefore the bonded structures reported in this paper probably represent the best possible design for high-temperature and high-power electronic packaging applications.

X-ray pole figure analysis of catalyst free InAs nanowires on Si substrate

We present crystallographic analysis of InAs nanowires by X-ray pole figure measurements and reciprocal space mapping in this report. The InAs nanowires have been grown on Si (111) substrates by a catalyst free approach using molecular beam epitaxy technique. The pole figure measurement of InAs nanowires for (111) and (220) reflections reveals important details such as the nanowire crystal structure, orientation, presence of twin defects and the epitaxial relation of the nanowires with the substrate. Angular relationship between several set of twin planes in each pole figure reflection is analyzed and the twin direction in each case is determined using a quantitative approach. Possibility of presence of mixed zinc blende /wurtzite phases in the nanowires is explored from an analysis of pole figure measurement for the (311) and (10−15) reflections and an asymmetric reciprocal space map (RSM) measurement.

Impact of laser anneal on NiPt silicide texture and chemical composition

We have combined synchrotron X-ray pole figure measurements and transmission electron microscopy (TEM) nano-beam diffraction to study the impact of millisecond laser anneal on the texture and microstructure of NiPt silicide thin films. The powerful use of nano-beam diffraction in plan-view geometry allows here for both a mapping of grain orientation and intra-grain measurements even if these crystalline grains become very small. With this unique combination of local and large-scale probes, we find that silicide formation on n and p doped substrates using laser annealing results in smaller grains compared with the films processed using standard rapid thermal annealing. The laser annealed samples also result in grains that are more epitaxially oriented with respect to the Si substrate. For n-type substrate, the film is dominated by (020) and (013) oriented fibers with significant levels of intra-grain bending (transrotation) observed in both types of grains. For p-type substrates, mostly epitaxially aligned grains are detected. TEM coupled with energy-dispersive X-ray analysis was also used to study the elemental distribution in the silicide samples. Here, we confirm that laser anneal leads to a larger accumulation of platinum at the silicide-substrate interface and modifies the distribution of dopants throughout the film.

Pole figure measurement of the initial growth of GaN nanoneedles on GaN/Si(111) by using hydride vapor phase epitaxy

We report on crystallographic analyses of one-dimensional GaN nanoneedles grown on a n-GaN epilayer by using hydride vapor phase epitaxy. The nanoneedles were grown with a HCl:NH3 gas flow ratio of 1:38 at 600 °C. The growth time of the GaN nanoneedles affected their morphologies. As time progressed, GaN dots nucleated and then evolved as nanoneedles. The vertical growth rate of GaN nanoneedles was higher than the lateral growth rate under optimized growth conditions. X-ray pole figure measurements were carried out using a four-axis diffractometer. For the sample grown for 20 min, we obtained discrete patterns with six strong dots and weak dough-nut and cotton swab patterns, indicating that most of the nanoneedles were grown ideally, but partially, in the x-y plane with an azimuthal rotation angle ϕ = 15 ~ 45° rotated to the substrate, and a few GaN nanoneedles were tilted by ±4° or by more than 32° from the vertical c-axis.

Inhomogeneous Spin Diffusion in Thickness-Controlled La 0 . 6 7 Sr 0 . 3 3 MnO 3 /YBa 2 Cu 3 O 7 − δ /La 0 . 6 7 Sr 0 . 3 3 MnO 3 Trilayers

La0.67Sr0.33MnO3/YBa2Cu3O7 − δ /La0.67Sr0.33 MnO3 (LSMO/YBCO/LSMO) trilayers are prepared on single-crystal LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) with the thicknesses of LSMO layers fixed at 50 nm, and the thickness of YBCO sandwich varied from 10 to 40 nm. X-ray diffraction (XRD) and pole figure measurements disclose that all the trilayers are c-oriented and there is little change in the textures of YBCO layer for both in-plane and out-of-plane. Based on inductive, transport, and magnetic measurements, obvious suppression of superconductivity with a decrease in YBCO thickness is observed, particularly at thickness below 20 nm. Importantly, there are great disparities in the superconducting transition temperature (T c) and transition width (ΔT c) values for both inductive and transport measurements. The T c values from an inductive method are much smaller than those from transport measurements, with ΔT c in the opposite direction. The results are explained by the nonuniform diffusion of spin-polarized quasiparticles due to the comparable length scales of the spin diffusion length and the superconducting film thickness.

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

Texture of Ge on SrTiO3 (001) substrates: Evidence for in-plane axiotaxy

We report the first experimental evidence of the formation of an axiotaxial texture in a semiconductor/oxide structure, namely Ge deposited by molecular beam epitaxy on a SrTiO3 substrate. The texture of the deposit is carefully analyzed based on X-ray pole figure measurements. We show in particular that the axiotaxial texture is not random, but that the deposit presents a limited number of well defined crystal orientations along axiotaxy locus. We also evidence the presence of twinned zones in the Ge crystal, and we discuss their experimental signature regarding that of the axiotaxy texture. In the end, we show that interface dangling bonds are the main parameter driving Ge crystal orientation, and we compare their influence to that of epitaxial misfit.

Effects of Heat-Treatment Temperature and Binder Content on the Microstructure and Thermal Conductivity of Graphite Flake-Carbon Composites

In this work, graphite flake-carbon composites were fabricated from natural graphite flake and spinning pitch by a hot-pressing technique at 500°C and 10 MPa. The X-ray pole figure measurements show that the orientation degree of graphitized composite is higher than that of hot-pressed and carbonized composite and presents a descending tendency from 74.4 to 71.2% when the pitch content increases from 4 to 14 wt.%. A reducing trend of d002 and an increasing tendency of the average crystallite diameter (La), crystallite stack height (Lc) and degree of graphitization (g) can also be observed when pitch fraction increases from 4 to 16 wt.%. The apparent density and thermal conductivity in the direction perpendicular to the hot-pressing direction of graphitized composite with 16 wt.% of binder all achieve maximum values, 1.930 g/cm3 and 485 W/m K, respectively.

Effects of reduction methods on the structure and thermal conductivity of free-standing reduced graphene oxide films

In this work, free-standing graphene oxide (GO) films obtained by vacuum filtration were reduced in HI acid or annealed in a confined space to form self-standing reduced graphene oxide (RGO) films. The effects of reduction methods on the reduction degree, microstructure and thermal conductivity of the RGO films were investigated. The RGO films obtained by thermal annealing have higher reduction degree than those treated with HI acid (55%) or treated with the combination of HI acid and 600°C annealing. The X-ray pole figure measurements show that the orientation degree of GO films after reduction is degraded, and the HI acid reduction results in the worst oriented structure. The in-plane thermal conductivities of the RGO films obtained by thermal reduction are higher than those of films reduced by other methods due to their higher reduction degree and the resulting unfolded structure. However, the differences in the thermal conductivity of the RGO films obtained by thermal annealing at different temperatures are minor, even their reduction degree is enhanced with the increasing of annealing temperature, which is probably due to the generated interspaces between the graphene layers during reduction that greatly limit thermal transport.

Low temperature epitaxy of Ge-Sb-Te films on BaF2 (111) by pulsed laser deposition

Pulsed laser deposition was employed to deposit epitaxial Ge2Sb2Te5-layers on the (111) plane of BaF2 single crystal substrates. X-ray diffraction measurements show a process temperature window for epitaxial growth between 85 °C and 295 °C. No crystalline growth is observed for lower temperatures, whereas higher temperatures lead to strong desorption of the film constituents. The films are of hexagonal structure with lattice parameters consistent with existing models. X-ray pole figure measurements reveal that the films grow with one single out-of-plane crystal orientation, but rotational twin domains are present. The out-of-plane epitaxial relationship is determined to be Ge2Sb2Te5(0001) || BaF2(111), whereas the in-plane relationship is characterized by two directions, i.e., Ge2Sb2Te5 [-12-10] || BaF2[1-10] and Ge2Sb2Te5[1-210] || BaF2[1-10]. Aberration-corrected high-resolution scanning transmission electron microscopy was used to resolve the local atomic structure and confirm the hexagonal structure of the films.

Quasi-heteroepitaxial growth of β-Ga2O3 on off-angled sapphire (0 0 0 1) substrates by halide vapor phase epitaxy

We demonstrate the high-speed growth of β-Ga2O3 quasi-heteroepilayers on off-angled sapphire (0001) substrates by halide vapor phase epitaxy (HVPE). (2¯01) oriented β-Ga2O3 layers were successfully grown using GaCl and O2 as source gases. The growth rate monotonically increased with increasing the partial pressures of the source gases, reaching over 250μm/h. This rate is over two orders of magnitude larger than those of conventional vapor phase epitaxial growth techniques such as molecular beam epitaxy or metalorganic vapor phase epitaxy. X-ray pole figure measurements indicated the presence of six in-plane rotational domains, in accordance with the substrate symmetry, plus some minor (310) domains. By the use of off-angled substrates and thick layer overgrowth, one of the in-plane orientations was strongly favored and the (310) residuals effectively suppressed, so that quasi-heteroepitaxial growth was achieved. Therefore, these results indicate the high-potential of the HVPE technique for the growth of thick and thin β-Ga2O3 layers for the cost-effective production of β-Ga2O3 based devices.

Epitaxy from the liquid phase: tuning metastable phases in Fe–Pd thin films by laser-assisted rapid solidification on substrates

Epitaxy by crystallization of thin liquid films on suitable substrates constitutes an alternative approach to molecular beam epitaxy, particularly if metastable phases are required. Employing laser-assisted rapid solidification, we demonstrate for the example of the body-centred-cubic, body-centred-tetragonal, face-centred-tetragonal and face-centred-cubic phases of Fe7Pd3 thin films, how the interplay of cooling rate and substrate-assisted nucleation affects the resulting metastable crystal phase and epitaxial relationship. Exemplarily employing lanthanum strontium aluminium tantalum oxide, MgO, and Si single crystals as substrates, this is experimentally demonstrated by an x-ray diffraction study and pole figure measurements. The underlying solidification kinetics are clarified using finite element calculations on the resulting time–temperature profile. Employing secondary ion mass spectroscopy we additionally demonstrate that the absence of interdiffusion is a central requirement for successful application.