X-ray Pole Figure Analysis Research Articles

Heterogeneous microstructure development in additive friction-stir deposited Al-Mg-Si alloy

Aluminum alloy 6061-T6511 was printed by additive friction stir deposition onto a cast aluminum A206-T4 plate. Metallography, X-ray powder diffraction, X-ray pole figure analysis, and electron backscatter diffraction of the center, advancing side, and retreating side of the 6061 deposit reveals different texture and grain structure characteristics across the transverse direction and through each layer. These distinct microstructural domains are indicative of spatially varied temperature, strain rate, and strain accumulation during deposition, and consequently of regions differing in the fraction of dynamic recovery and dynamic recrystallization during deposition. Hardness mapping over the complete cross section at 0.75 mm resolution shows the alloy continues to age after active deposition, and hardness increases over the 5 mm nearest the final printed layer. Additional mapping at 0.10 mm resolution shows intralayer hardness variations of the deposit on the retreating side. These observations demonstrate that complex and non-uniform thermal-mechanical transients occur during additive friction stir deposition, resulting in spatially non-uniform microstructure and properties.

Surface scattering-dependent electronic transport in ultrathin scandium nitride films

With the constant miniaturization of device technologies, it has become essential to understand and engineer the electronic properties of semiconductors in nanoscale dimensions. Scandium nitride (ScN), an emerging rock salt indirect bandgap semiconductor, has attracted significant interest for its interesting thermoelectric, plasmonic, neuromorphic computing, and Schottky barrier device applications. However, an in-depth understanding of the electronic transport, carrier scattering mechanism, and optical properties in ultrathin ScN films is still missing. Here, we show surface-scattering dominant electronic transport in epitaxial ScN films at nanoscale thicknesses. At the ultrathin dimensions, surface scattering increases significantly due to the large surface-to-volume ratio and growth-induced texturing. As a result, mobility decreases, and resistivity increases drastically with decreasing film thickness. Temperature-dependent electronic transport shows that the mobility of the ultrathin films decreases with increasing temperature due to the ionized-impurity and dislocation scattering. Electronic transport properties are further rationalized with x-ray diffraction and pole-figure analysis that shows that while the ultrathin films maintain their predominant 002 texture, their quality degrades with decreasing thickness. However, no significant changes are observed in the electronic structure of the films, as evidenced by x-ray photoelectron spectroscopy, photoemission measurements, and first-principles density functional theory calculations. Our results elucidate the impact of surface scattering on the ultrathin ScN films and would lead to miniaturized devices with improved efficiencies.

Growth and optical properties of NiO thin films deposited by pulsed dc reactive magnetron sputtering

NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 °C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111)∥Al2O3(0001) and NiO[11¯0]∥Al2O3[101¯0] or NiO[1¯10]∥Al2O3[21¯1¯0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content.

X-ray Pole figure analysis for orienting TGSM grown bulk ZnTe crystal for Terahertz device applications

X-ray Pole figure analysis for orienting TGSM grown bulk ZnTe crystal for Terahertz device applications

The effect of orientation and pore size on nano mechanical behaviour of Ag thin films: a comparison between experiment and atomistic simulation

ABSTRACT This paper describes the thickness-dependent texture evolution during annealing in Ag thin films, commonly used in micro and nano-devices. The effect of porosity and crystal orientation on mechanical properties for the films deposited by the magnetron sputtering method is particularly addressed using nano-indentation experiment and atomistic simulation. X-ray pole figure analysis revealed that the films exhibited sharp fibre texture with a major <1 1 1> component accompanied by minor twin components of <5 1 1> and <5 7 13> and a weak component of <1 0 0>. The mechanical behaviour of the films was investigated experimentally using a Berkovich tip to measure the hardness (H) and modulus of elasticity (E) at each individual grain and porous region. The average Young’s modulus of strongly oriented [1 1 1] grain at porous and non-porous regions is estimated to be 44 ± 7 and 67 ± 5 GPa. Molecular Dynamics simulations have been performed on (1 1 1), (1 1 0), (0 0 1), (5 1 1), and (5 7 13) surfaces of Ag single crystal using a spherical indenter to investigate the anisotropic nature of hardness and elastic modulus from the Load∼Indentation depth curves. The mechanical properties of [1 1 1] oriented single crystal in the presence of a sub-surface void have been studied. Our results have demonstrated that the void acts as an efficient absorber of dislocation limiting the extension of the plastic zone. The simulated modulus of elasticity (E: 54.2 GPa) results obtained at a temperature of 300 K in the presence of a void are compared with experimentally measured values with a variation of around 6%.

Oblique angle co-deposition of nanocolumnar tungsten thin films with two W sources: Effect of pressure and target current

Two series of tungsten thin films are sputtered on silicon and glass substrates by oblique angle co-deposition technique with an original configuration. Two opposite distinct tungsten targets are simultaneously used, both tilted with an oblique angle of 80°. The growth is performed at low (0.33 Pa) and high (1.5 Pa) argon sputtering pressure and the current intensity applied to the targets varies between 50 and 250 mA. The effect of these deposition parameters on the films microstructure and electrical properties is investigated by scanning and transmission electron microscopy, X-ray diffraction and pole figures, and van der Pauw method. Due to self-shadowing effect, all tungsten sputtered thin films are porous and columnar. At low pressure, the columnar tilt angle β can be tuned with the target current intensity until obtaining vertical columns. X-ray diffraction and pole figure analyses point out a A15 crystal structure (β-W) and a uniaxial fiber texture with a <100> growth direction. In contrast, tungsten thin films deposited at high pressure present a cauliflower structure and are poorly crystallized. Both deposition parameters also affect the films electrical resistivity and anisotropy. These behaviors are discussed and linked to the microstructure and crystallography.

Thermal conductivity across the van der Waals layers of α-MoO3 thin films composed of mosaic domains with in-plane 90° rotations

α-Molybdenum trioxide (α-MoO3) is a typical two-dimensional metal oxide material, in which the covalently bonded layers are bonded by van der Waals forces. Herein, the thermal conductivities across the van der Waals layers of α-MoO3 thin films with nominal thicknesses of 50, 100, and 125 nm were investigated. The α-MoO3 thin films were fabricated on the (100) plane of a single-crystalline SrTiO3 substrate heated up to 400 °C by DC reactive magnetron sputtering using a Mo metal target. The b-axis-oriented α-MoO3 thin films epitaxially grown on the SrTiO3 (100) plane were confirmed by x-ray diffraction and x-ray pole figure analyses. Electron diffraction patterns and plane-view transmission electron micrographs revealed that the α-MoO3 thin films were composed of mosaic domains with a diameter of ∼2 nm, with each domain rotated in-plane by 90° with respect to the neighboring one. The mean thermal conductivity across the van der Waals layers of the three α-MoO3 thin films was evaluated to be 1.2 ± 0.3 W m−1 K−1, which is comparable to the reported thermal conductivities of layered cobalt oxide thin films. The reduced thermal conductivity is mainly due to phonon scattering at domain boundaries lying in the in-plane direction.

Uniaxial and Mixed Orientations of Poly(ethylene oxide) in Nanoporous Alumina Studied by X-ray Pole Figure Analysis

The orientation of polymers under confinement is a basic, yet not fully understood phenomenon. In this work, the texture of poly(ethylene oxide) (PEO) infiltrated in nanoporous anodic alumina oxide (AAO) templates was investigated by X-ray pole figures. The influence of geometry and crystallization conditions, such as pore diameter, aspect ratio, and cooling rates, was systematically examined. All the samples exhibited a single, volume-dependent crystallization temperature (Tc) that is much lower than that exhibited by bulk PEO, indicating “clean” microdomains without detectable heterogeneous nucleation. An “orientation diagram” was established to account for the experimental observations. Under very high cooling rates (quenching), crystallization of PEO within AAO was nucleation-controlled, adopting a random distribution of crystallites. Under low cooling rates, growth kinetics played a decisive role in the crystal orientation. A relatively faster cooling rate (10 °C/min) and/or smaller pores lead to the ⟨120⟩*||pore axis (n⃗) mode (uniaxial orientation). When the cooling rate was lower (1 °C/min) and/or the pores were larger, a mixed orientation, with a coexistence of ⟨120⟩*||n⃗ and ⟨010⟩*∥n⃗, was observed. The results favor the kinetic model that the fastest growth direction tends to align parallel to the pore axis.

Analyses of orientational superlattice domains in epitaxial ZnTe thin films grown on graphene and mica

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//[11¯]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//[21¯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.

Van der Waals epitaxial ZnTe thin film on single-crystalline graphene

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 systematically investigates the optoelectronic properties of this epitaxial ZnTe film on graphene using temperature-dependent Raman spectroscopy, steady-state and time-resolved photoluminescence spectroscopy, and fabrication and characterization of a ZnTe-graphene photodetector. The research suggests an effective approach towards graphene-templated flexible electronics.

Van der Waals epitaxy of SnS film on single crystal graphene buffer layer on amorphous SiO2/Si

Conventional hetero-epitaxial films are typically grown on lattice and symmetry matched single crystal substrates. We demonstrated the epitaxial growth of orthorhombic SnS film (∼500 nm thick) on single crystal, monolayer graphene that was transferred on the amorphous SiO2/Si substrate. Using X-ray pole figure analysis we examined the structure, quality and epitaxy relationship of the SnS film grown on the single crystal graphene and compared it with the SnS film grown on commercial polycrystalline graphene. We showed that the SnS films grown on both single crystal and polycrystalline graphene have two sets of orientation domains. However, the crystallinity and grain size of the SnS film improve when grown on the single crystal graphene. Reflection high-energy electron diffraction measurements show that the near surface texture has more phases as compared with that of the entire film. The surface texture of a film will influence the growth and quality of film grown on top of it as well as the interface formed. Our result offers an alternative approach to grow a hetero-epitaxial film on an amorphous substrate through a single crystal graphene buffer layer. This strategy of growing high quality epitaxial thin film has potential applications in optoelectronics.

Van der Waals epitaxy of Ge films on mica

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 Ge1¯10 and mica[100] of (20n)°, where n = 0, 1, 2, 3, 4, 5. A superlattice area mismatch model was used to account for the likelihood of the in-plane orientation formation and was found to be qualitatively consistent with the observed dominant orientations. Our observation of Ge epitaxy with one out-of-plane growth direction through van der Waals forces is a step toward the growth of single crystal Ge films without the constraint in the lattice and symmetry matches with the substrates.

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.

(Invited) Contacts in Advanced CMOS: History and Emerging Challenges

Silicide materials used as contacts in CMOS devices have evolved over many technology nodes. This article traces the often forgotten defectivity related reasons that were the primary drivers for a change in materials or process flow – evolving from Ti to Co and Ni silicides, and the more recent return to Ti-based liner silicides. The criteria used for the selection of these metal silicides have undergone a dramatic change with the advent of 3-D transistors and trench silicide contacts, and is now primarily guided by the value of interfacial contact resistivity (ρc). Furthermore, using results from synchrotron X-ray diffraction and pole-figure analysis, we present how phase formation and microstructure of contacts vary with Ti thickness, alternative annealing treatments, and substrate composition and orientation. We show that microstructure in very thin films can change from amorphous to epitaxial, a factor likely to become important for the contacts in upcoming generations of devices.

Formation of nickel germanides from Ni layers with thickness below 10 nm

The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleation-controlled for Ni thicknesses &amp;lt;5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.

Preferred orientation of BaSi&lt;sub&gt;2&lt;/sub&gt; thin films fabricated by thermal evaporation

Thermal evaporation is a simple and high-speed method to grow a BaSi2 thin film, which is an emerging candidate for an absorber-layer material of thin-film solar cells. In this study, we have investigated the preferred orientation of BaSi2 films grown at substrate temperatures of 600–700 °C by thermal evaporation using X-ray diffraction. 2θ–ω scans show that peaks derived from (100) orientation grow steadily with increasing substrate temperature. By X-ray pole figure analysis, the (100)-oriented crystals are proven to be epitaxially grown on Si(100) with two variants. The reason of epitaxial growth is discussed from the epitaxial temperature.

Van der Waals epitaxy of CdTe thin film on graphene

van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

Structural, magnetic and optical properties of Y bFe2O4 films deposited by spin coating

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their numerous functionalities, such as electronic ferroelectricity, ferrimagnetism, and high infrared absorption. In this paper, nearly monophasic Y bFe2O4 films were prepared on α-Al2O3(001) substrates by the spin coating method using an aqueous-based Y bFe2O4 solution. The solution was composed of a stoichiometric ratio of Y b(CH3COO)3 and Fe(NO3)3 with excess chelating agents. After heat treatment above 800 °C, well-crystallized and highly (001)-oriented Y bFe2O4 started to epitaxially form on the substrate under controlled oxygen partial pressure with H2/CO2 gas mixtures. X-ray pole figure analysis confirmed the following epitaxial relationship: Y bFe2O4[100](001)//α-Al2O3[100](001). Moreover formation of an Fe3O4 interracial layer between Y bFe2O4 and α-Al2O3 was detected by high-resolution transmission electron microscopy. Presence of the Fe3O4 interracial layer seemed to release the lattice misfit with the substrate. The Fe2+/Fe3+ ratio in the obtained Y bFe2O4 films was nearly stoichiometric and the indirect bandgap assigned to Fe2+ → Fe3+ charge transfer excitation was found to be ∼0.4 eV by optical spectroscopy. A clear magnetic transition from the paramagnetic state to the ferrimagnetic state occurred at ∼230 K.

Large Single Crystal SnS2 Flakes Synthesized from Coevaporation of Sn and S

Remarkable properties of layered metal dichalcogenides and their potential applications in various fields have raised intense interest worldwide. We report tens of microns-sized ultrathin single crystal SnS2 flakes grown on amorphous substrates using a simple one-step thermal coevaporation process. X-ray pole figure analysis reveals that a majority of flakes are oriented with the (0001) plane parallel to the substrate and a preferred fiber texture. For few-layer-thick SnS2, Moire patterns of 6-fold and 12-fold symmetries are observed by transmission electron microscopy imaging and diffraction. These patterns result from the relative rotation between SnS2 layers in the ultrathin flake. The 12-fold symmetry is consistent with a known quasicrystal pattern. The photoluminescence spectrum supports that these ultrathin flakes possess a direct bandgap. Carrier lifetime measured by time-resolved photoluminescence of a single flake is a few nanoseconds. These results improve our understanding of the formation and ...

Effect of substrates and surfactants over the evolution of crystallographic texture of nanostructured ZnO thin films deposited through microwave irradiation

In spite of intense research on ZnO over the past decade, the detailed investigation about the crystallographic texture of as obtained ZnO thin films/coatings, and its deviation with growth surface is scarce. We report a systematic study about the orientation distribution of nanostructured ZnO thin films fabricated by microwave irradiation with the variation of substrates and surfactants. The nanostructured films comprising of ZnO nanorods are grown on semiconductor substrates such as [Si(100), Ge(100)], conducting substrates (ITO-coated glass, Cr coated Si), and polymer coated Si (PMMA/Si) to examine the respective development of crystallographic texture. The ZnO deposited on semiconductor substrates yields mixed texture, whereas c-axis oriented ZnO nanostructured films are obtained by conducting substrate, and PMMA coated Si substrates. Among all the surfactants, nanostructured film produced by using the lower molecular weight of polymeric surfactants (polyvinylpyrrolidone) shows a stronger (0002) texture, and that can be tuned to 10-1̅0 by increasing the molecular weight of the surfactant. The strongest basal pole is achieved for the ZnO deposited on PMMA coated Si as substrate, and cetyl-trimethyl ammonium bromide as cationic surfactant. The texture analysis is carried out by X-ray pole figure analysis using the Schultz reflection method.