In-plane X-ray Diffraction Measurements Research Articles

C-axis texture of high-rate-sputtered Nd2Fe14B thin films: independence of sheet texture of Mo underlayer

In this study, we investigated the effects of the sheet texture of the Mo underlayer on the c-axis texture of the high-rate-sputtered Nd2Fe14B phase. The magnetic properties revealed that the squareness of the Nd–Fe–B magnetic layer did not depend on the sheet texture of the Mo underlayer but on the substrate temperature: large squareness was obtained when the magnetic layer was sputtered at high substrate temperature above 500 °C. In-plane X-ray diffraction measurements indicated that the intensity of diffraction from the Nd2Fe14B (410) plane did not depend on the sheet texture of the Mo underlayer but on the substrate temperature: high intensity was obtained when the magnetic layer was sputtered at above 500 °C, which was consistent with magnetic properties. These results support that the c-axis texture of the high-rate-sputtered magnetic layer was driven by the c plane with the lowest surface energy among the crystal planes in the Nd2Fe14B phase.

Depth-Resolved Phase Analysis of Expanded Austenite Formed in Austenitic Stainless Steel

Expanded austenite γN formed after nitrogen insertion into austenitic stainless steel and CoCr alloys is known as a hard and very wear resistant phase. Nevertheless, no single composition and lattice expansion can describe this phase with nitrogen in solid solution. Using in situ X-ray diffraction (XRD) during ion beam sputtering of expanded austenite allows a detailed depth-dependent phase analysis, correlated with the nitrogen depth profiles obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) or glow discharge optical emission spectroscopy (GDOES). Additionally, in-plane XRD measurements at selected depths were performed for strain analysis. Surprisingly, an anomalous peak splitting for the (200) expanded peak was observed for some samples during nitriding and sputter etching, indicating a layered structure only for {200} oriented grains. The strain analysis as a function of depth and orientation of scattering vector (parallel/perpendicular to the surface) is inconclusive.

Modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO2 thin films using ultrathin interfacial layers

In this study, tailoring the microstructures and ferroelectric(FE)/antiferroelectric(AFE) properties of nanoscale ZrO2 thin films is demonstrated with an intentional introduction of sub-nanometre interfacial layers. The ferroelectricity of ZrO2 thin films is significantly enhanced by the HfO2 interfacial layers, while the TiO2 interfacial layers lead to a dramatic transformation of ZrO2 from ferroelectricity into antiferroelectricity. The HfO2 and TiO2 interfacial layers boost the formation of the polar orthorhombic phase with (111)-texture and the non-polar tetragonal phase with (110)-texture in the FE/AFE ZrO2 thin films, respectively, as evidenced by grazing incidence, out-of-plane, and in-plane X-ray diffraction measurements. Furthermore, the modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO2 thin films by the HfO2/TiO2 interfacial layers can be achieved without high-temperature annealing, which is highly advantageous to process integration. The findings demonstrate the important role of the interfaces in the effective tuning of FE/AFE properties of nanoscale thin films.

Effect of sputtering pressure on stacking fault density and perpendicular magnetic anisotropy of CoPt alloys

We report the effects of Ar sputtering pressure on perpendicular magnetic anisotropy in disordered CoPt alloys via the modulation of stacking fault density. The coercivity and anisotropy field of CoPt alloys are gradually enlarged with an increase in Ar sputtering pressure from 3 mTorr to 30 mTorr. Structural analyses using transmission electron microscopy, atomic force microscopy and x-ray reflectivity show that the structural properties of the samples, such as roughness or grain size, are not significantly changed by variations in Ar sputtering pressure. On the other hand, in-plane x-ray diffraction measurements reveal that the stacking fault density is reduced in films grown under higher pressure, and instead favors HCP stacking. Our results suggest that perpendicular magnetic anisotropy in CoPt alloys can be enhanced by the growth of the sample under a high Ar sputtering pressure, which decreases stacking fault density.

Impact of mechanical stress on ferroelectricity in (Hf0.5Zr0.5)O2 thin films

To investigate the impact of mechanical stress on their ferroelectric properties, polycrystalline (Hf0.5Zr0.5)O2 thin films were deposited on (111)Pt-coated SiO2, Si, and CaF2 substrates with thermal expansion coefficients of 0.47, 4.5, and 22 × 10−6/ °C, respectively. In-plane X-ray diffraction measurements revealed that the (Hf0.5Zr0.5)O2 thin films deposited on SiO2 and Si substrates were under in-plane tensile strain and that their volume fraction of monoclinic phase decreased as this strain increased. In contrast, films deposited on CaF2 substrates were under in-plane compressive strain, and their volume fraction of monoclinic phase was the largest among the three kinds of substrates. The maximum remanent polarization of 9.3 μC/cm2 was observed for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2, while ferroelectricity was barely observable for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2/CaF2. This result suggests that the in-plane tensile strain effectively enhanced the ferroelectricity of the (Hf0.5Zr0.5)O2 thin films.

Effect of vanadium doping on amorphization of ZnO thin films on c-plane sapphire substrate

The effect of vanadium (V) doping on amorphization of zinc oxide (ZnO) thin films deposited on c-plane sapphire substrate at room temperature by RF magnetron sputtering was investigated. From the in-plane X-ray diffraction measurements, the diffraction intensity from 30° rotated domains observed in the ZnO film weakened with increasing V concentration. Faint diffractions from both the 30° rotated and normal domains were seen in the V-doped ZnO (VZO) film of 1.7-at.%V, and relatively strong diffractions only from the normal domain were observed at 2.1-at.%V while the 30° rotated domains diminished. There were only weak normal domains for VZO over 2.4-at.%V. Concerning the c-axis orientation, the broad (0002) diffraction peaks were observed in all VZO films, and the peak was the widest for the 3.8-at.%VZO film. From the dependence of crystallinity on thickness for the highly-doped VZO (V: 3.8at.%) films, the c-axis orientation deteriorated with increasing film thickness and no diffraction signal was seen for the VZO films over 35-nm thick. This means that the VZO film aligned by the c-plane sapphire grew only at the initial stage, but an accumulation of disordered layers worsened the crystallinity with thickening the film. From the above-mentioned results, even in the ZnO film in which the grains tend to align to the c-axis orientation preferentially, the doping of transition metals, like V in this study, plays an effective reaction to form the pseudo-amorphous thin film. It is considered that this phenomenon is attributed to the feature of transition metal in which the transition metal atoms can take a state of various valence or coordination numbers.

Néel temperature of Cr2O3 in Cr2O3/Co exchange-coupled system: Effect of buffer layer

The lattice parameter dependence of the Néel temperature TN of thin Cr2O3 in a Cr2O3/Co exchange-coupled system is investigated. Lattice-mismatch-induced strain is generated in Cr2O3 by using different buffer layers. The lattice parameters are determined from out-of-plane and in-plane X-ray diffraction measurements. The Néel temperature is detected by direct temperature-dependent magnetization measurement as well as the temperature-dependent interface exchange coupling energy. It is observed that in-plane lattice contraction can enhance TN in Cr2O3, which is consistent with theoretical calculations.

Semi-Epitaxial SmB6 Thin Films Prepared by the Molecular Beam Epitaxy

We grow thin films of SmB6 by molecular beam epitaxy under ultra-high vacuum better than 1×10−6Pa. Sm and B were evaporated independently by Knudsen cells with the deposition rate ratio of B and Sm as B/Sm in between 4.0 and 5.7 on an MgO (100) substrate with the substrate temperature of 1000 ∘C. Reflection high energy electron diffraction patterns show spotted ones indicating a relatively flat film surfaces. This is in good agreement with the surface roughness measured by the atomic force microscope. Interplane and inplane X-ray diffraction measurements represent the preference growth of c-axis oriented SmB4 thin films with the ratio B/Sm = 4.0. We obtained SmB6 thin films with the ratio B/Sm in between 4.9 and 5.7. X-ray diffraction measurements clarify that our SmB6 thin films show evidence of partial epitaxial growth as major domains orienting along [100]SmB6 ∥ [100]MgO. Crystallinity of inplane alignment is improved with approaching the stoichiometric deposition rate of B/Sm = 6. The electrical resistivity increases with decreasing temperature as a semiconductor, and becomes constant at low temperatures. These features well reproduce the tendency observed for the resistivity of bulk samples.

Large Area Plan-View Transmission Electron Microscopy Sample Preparation for Direct-Bonded Interfaces

A focused ion beam (FIB) sample preparation technique is developed to produce large areas of electron transparent material for plan-view transmission electron microscopy measurements from direct-bonded interfaces without thinning the bonded wafers. A FIB cut allows plan-view sample creation from the bonded interface region, and therefore rapid characterization of the defect density as a function of bonding conditions, substrate miscut, or pre-bonding surface treatments. Uniform electron transparent plan-view areas are extracted from the interface region to facilitate observation of the interface reconfiguration. To demonstrate the technique, the electrically active interfaces of a series of bonded III-V structures is studied as a function of substrate miscut as well as in-plane misorientation. Distinct differences in the interface reconstruction are observed and the interface reconstruction produces screw and edge dislocation networks at the III-V interfaces. The degree of twist and tilt is confirmed with both cross section electron microscopy measurements as well as in-plane x-ray diffraction measurements.

Heteroepitaxial growth of ZnO films on Gd3Ga5O12 garnet substrates

ABSTRACTThis study focused on structural and optical properties of ZnO films grown epitaxially on Gd3Ga5O12 substrates. ZnO films (a = 3.2439 Å and c = 5.2036 Å) were deposited on the (001) and (111) planes of Gd3Ga5O12 (GGG: a = 12.383 Å) garnet substrates by a pulsed laser deposition method. From out-of-plane and in-plane X-ray diffraction measurements, the obtained ZnO films showed a single phase with the (0001) orientation on the GGG (001) and (111) substrates. The epitaxial relations between the ZnO film and GGG (001) substrate were [10-10] ZnO ‖ [100] GGG and [10-10] ZnO ‖ [010] GGG, while the epitaxial relations between the ZnO film and GGG (111) substrate were [10-10] ZnO ‖ [11-2] GGG ±21°. Furthermore, transmittance electron microscopy revealed sharp interfaces between ZnO films and GGG substrates. From photoluminescent spectra, the ZnO films showed donor bound emissions superimposed with free excitons at a low temperature of 10 K.

Correlation between strain and the metal–insulator transition in epitaxial V2O3 thin films grown by Molecular Beam Epitaxy

We report on the deposition of high quality epitaxial V2O3 thin films on (0001) oriented Al2O3 substrates with Molecular Beam Epitaxy. Growth of smooth V2O3 films with root mean square roughness values down to 1Å exhibiting both bulk-like and non bulk-like electrical properties has already been reported in a previous contribution. In this work, the lattice parameters and strain state of deposited films are extracted from both out-of-plane and grazing incidence in-plane X-ray diffraction measurements. Resistivity measurements are performed as a function of temperature using the four-point probe method. We observe a correlation between the in-plane tensile strain and the electrical properties, in particular the room-temperature resistivity. We also compare the electrical data of our V2O3 thin films with the features of the V2O3 bulk phase diagram.

Surface morphology and crystalline structure of high-stable polycrystalline transparent conductive zinc oxide films

Surface morphology and crystalline structure of high-stable zinc oxide films were evaluated by atomic force microscopy, scanning electron microscopy and X-ray diffraction (XRD) measurements. AFM measurement revealed that the higher stable samples have smaller roughness (average roughness and root mean square) parameters than the lower stable samples. Furthermore, in-plane XRD measurement showed that the crystallite size of high stable samples is smaller than that of the low stable samples. These results indicate that the larger surface area and lower film density deteriorates the stability of zinc oxide films through the adsorption and reaction of water or oxygen molecules. They also suggest that we can prepare the high stable zinc oxide transparent electrode films by controlling the surface morphology.

Fabrication of Anatase Thin Film with Perfect c-Axis Orientation on Glass Substrate Promoted by a Two-Dimensional Perovskite Nanosheet Seed Layer

Nanointerface engineering using unique two-dimensional (2D) crystals of nanosheets overcomes the difficulty in controlling crystal growth processes on amorphous substrates. Fabrication of highly oriented anatase (001) films on widely used glass substrates has been achieved for the first time utilizing a monolayer film of Ca2Nb3O10 nanosheets. The nanosheet has a 2D-perovskite structure, and the cell parameter (0.386 nm) is very similar to the a-axis of anatase (0.379 nm). The orientation degree and crystallinity of the films are examined by X-ray diffraction (XRD). The χ-rocking curve for the anatase 004 peak reveals a full width at half-maximum of 1.2°, which is virtually the same as that on single-crystal substrate of SrTiO3 (001) (fwhm = 1.0°) deposited under the same conditions. The epitaxial relationship between the anatase layer and the underlying nanosheet is confirmed by cross-sectional high-resolution transmission electron microscopy observations. Synchrotron radiation in-plane XRD measurement is...

Fabrication of perpendicularly magnetized magnetic tunnel junctions with L1-CoPt/Co2MnSi hybrid electrode

Magnetic tunnel junctions (MTJs) of perpendicularly magnetized L10-CoPt/Co2MnSi/MgO/FePt structure were fabricated. In-plane x-ray diffraction measurements and element specific evaluation of magnetic properties using soft x-ray magnetic circular dichroism were carried out to examine quite thin Co2MnSi (CMS) inserted layer between CoPt and MgO interface. Ordered B2-CMS was successfully fabricated onto L10-CoPt as thin as 1 nm thick, and CMS layer shows perpendicular magnetic anisotropy below 3 nm thick via exchange coupling with CoPt layer. In the MTJ-stacking, epitaxial growth was confirmed except for partial misalignment in the upper FePt layer, and coercive field difference clearly appeared between the bottom and the top ferromagnetic electrodes.

Evolution of 2,5-Bis(4-biphenylyl)bithiophene Thin Films and Its Effect on the Weak Epitaxy Growth of ZnPc

Evolution of BP2T films grown at the early stage was investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). The AFM results demonstrate that the BP2T grown on the SiO2 substrate transformed from a layer by layer growth to island growth when the coverage is higher than 3 ML. The out-of-plane and in-plane X-ray diffraction measurements reveal a phase transition from the thin film phase to the bulk phase suddenly occurs as the growth mode changes. A careful analysis of the structure evolution implies that not only the strain but also the soft matter property of the organic thin films are responsible for the thickness dependent evolution. Moreover, the thickness dependent structure and phase of BP2T films result in different morphologies of ZnPc grown on different layers of BP2T. The ZnPc crystals gradually changed from stripe-like to nanofiber-like, concomitantly with the epitaxy relationships from incommensurate epitaxy to commensurate epitaxy. Conversely, the diversity of ZnPc films also reflects different properties of the BP2T films with different numbers of layer, which cannot be obtained from the AFM or XRD. This study supplies a deeper insight into the thickness evolution of organic thin films and to the weak epitaxy growth.

Control of Arrangement for s-Triazine Group in Comb Copolymers by the Langmuir−Blodgett Method and Its Structural Estimation by NEXAFS Spectroscopy

We investigated the molecular orientation of organized molecular films with regard to solid-state structures for newly synthesized comb copolymers with 2-vinyl-4,6-diamino-1,3,5-triazine (VDAT) by surface pressure-area (pi-A) isotherms, in-plane and out-of-plane X-ray diffraction (XRD), atomic force microscopy (AFM), and polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Since VDAT has adsorption ability to an adenine-thymine base pair of a DNA molecule, control of orientation for VDAT units in monolayers is possible to form surface patterning of biomolecules and construct candidates of new biochip materials. In the bulk state, hydrogenated and fluorinated comb copolymers containing VDAT form side-chain crystals for a two-dimensional lattice spacing of 4.2 and 5.0 A, respectively. From the results of the differential scanning calorimetric (DSC) measurements, sharp-shaped melting peaks appear on the relatively lower temperature side of the thermograms. This result supports the formation of side-chain crystals in the synthesized comb copolymers. These monolayers of copolymers on the water surface were extremely condensed, except for the VDAT:OA = 5:1 copolymer. From the in-plane XRD measurement of multilayers on solids, changes in the two-dimensional lattice structure of fluorinated comb copolymer films containing VDAT units, as opposed to their bulk state, were confirmed. It seems that these structural changes are caused by the stronger pi-pi interaction between the s-triazine rings rather than the van der Waals interaction between fluorocarbons. Polarized NEXAFS spectroscopy showed highly ordered orientation of s-triazine groups in the films based on the incident angle dependency of C and N1s-pi*(CN) transitions with synchrotron radiation. These experimental findings relate to well-ordered arrangement of functional groups supporting the side-chain rearrangement caused by the pi-pi interaction between the s-triazine rings.

Evaluation of super-critical thickness strained-Si on insulator (sc-SSOI) substrate

Crystal quality and strain distribution in SOI layer of conventional strained-Si on insulator (SSOI) and super-critical thickness strained-Si on insulator (sc-SSOI) were evaluated by in-plane X-ray diffraction (XRD), Raman spectroscopy, and other techniques. The surface defect distribution measured by wafer inspection system shows pit-type and line defects in both SSOI layers. More specifically, the sc-SSOI material has more line defects than conventional SSOI layers. Cross-hatched pattern defects were observed using X-ray topography (XRT) measurements. Raman mapping of 300 mm wafers shows the strain at the center of the wafer is larger than at the edge. In magnified close-up mapping, cross-hatched contrasts corresponding to misfit dislocations are observed, while the surface morphology is completely smoothed out. In-plane XRD measurements show the strain depth variations are quite uniform along the depth direction. The full width at half maximum (FWHM) of in-plane XRD peaks obtained from strained-Si layers is much larger than for un-strained SOI and bulk Si, reflecting poor crystal quality. SSOI was fabricated by the layer transfer of strained-Si on a virtual SiGe substrate. Therefore, we believe the crystal quality and strain distribution originate in the donor strained Si when virtual SiGe substrate is the starting material.

Control of arrangement for carbazole group in fluorinated comb copolymers by method of organized films

Control of orientation for functional carbazole groups in comb copolymer was carried out by co-polymerization with long-chain vinyl compound and method of organized molecular films. Further, their structural estimation was performed by in-plane X-ray diffraction (XRD) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In the bulk state, fluorinated comb copolymers form side-chain crystal for a two-dimensional lattice spacing of 5.0Å. From the in-plane XRD measurement of multilayers on solids, changes in the two-dimensional lattice structure of fluorinated comb copolymer films containing NVCz units, as opposed to their bulk state, were confirmed. In this case, polarized NEXAFS measurement showed that highly ordered orientation of carbazole groups was attained in the films. It is considered that this well-ordered arrangement of functional groups is caused by enhancement of π–π interaction between the carbazole rings.

X-ray analysis of ZnO nanorods grown by microwave irradiation heating on ZnO films

Utilizing microwave irradiation heating, 100-nm-diameter ZnO nanorods were grown from aqueous solution on sputtered ZnO films on glass substrates. Its out-of-plane X-ray diffraction (XRD) measurement indicated that the ZnO nanorods were grown with c-axis orientation, similar with the underlying ZnO films. In the in-plane XRD measurement, intensity of the ( 11 2 ¯ 0 ) diffraction was comparable with that of the ( 10 1 ¯ 0 ) one, suggesting their intensity ratio would contain useful information on nanorods density.

Ga2O3 Thin Film Growth on c-Plane Sapphire Substrates by Molecular Beam Epitaxy for Deep-Ultraviolet Photodetectors

(201)-oriented β-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. In-plane X-ray diffraction measurements revealed the inclusion of α-Ga2O3 and rotational domains. However, the film grown under the optimized growth conditions exhibited a sharp absorption edge at around 5.0 eV, which is in the deep-ultraviolet region. An ohmic-type metal–semiconductor–metal photodetector showed a high resistance of around 6 GΩ with a small dark current of 1.2 nA at the 10 V bias voltage. Under 254 nm light illumination and 10 V bias voltage, the photoresponsivity was 0.037 A/W, which corresponded to a quantum efficiency of 18%.