Superlattice Diffraction Peaks Research Articles

Growth of high material quality InAs/GaSb type-II superlattice for long-wavelength infrared range by molecular beam epitaxy

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.

Electronic structure and magnetic properties of a full-Heusler Mn2NiSb: Cu2MnAl type structure

Manganese (Mn) based full-Heusler alloys have been shown to be the most promising materials due to their excellent magnetic behaviors for applications in magneto resistance, magnetic tunnel devices, spin valve and spin injection devices. Here, we report the study of crystal structure, electronic structure and magnetic properties of Mn2NiSb full-Heusler alloy. XRD investigation of Mn2NiSb followed by Rietveld refinement reveals the material to be successfully crystallized in a well-ordered Cu2MnAl prototype structure manifested by the existence of super-lattice diffraction peaks of (111) and (220). The experimental lattice parameter is estimated to be 6.01 Å which is larger than the available reports. Magnetic measurement (M-H) performed by applying external magnetic field up to 1.8 Tesla reveals the saturated magnetic moment (MS) of 4.07μB/formula unit and 2.50μB/formula unit at temperature 5 K and 300 K respectively which is the highest value reported so far at 5 K for Mn2NiSb stabilized in Cu2MnAl type structure. Further, magnetization versus temperature (M-T) curve with zero-field cooled (ZFC) and field-cooled (FC) up to 300 K indicates that Mn2NiSb crystallized in a single phase. However, the square of magnetization and temperature curve was best fitted with linear fitting supporting to Stoner like ferromagnetism. In order to have a better understanding of magnetic behavior, the First principal calculation has also been performed. Interestingly, our experimental observations were found to be well corroborated with the theoretically estimated magnetic behavior.

Formation of L10-ordered CoPt during interdiffusion of electron-beam-deposited Pt/Co bilayer thin films on Si/SiO2 substrates by rapid thermal annealing

Preparation of ordered CoPt on Si substrates is significant for expanding future applications of spintronic devices. In this study, ordered CoPt alloys including the L10 phase with a maximum coercivity of 2.1 kOe are formed in electron-beam-deposited 11.4 nm thick Pt/Co bilayer thin films on Si/SiO2 substrates via interdiffusion during rapid thermal annealing (RTA). The effects of RTA temperature on the magnetic properties, crystal structures, cross-sectional elemental profiles, and surface morphologies of the films are analyzed by vibrating sample magnetometer (VSM), grazing incidence x-ray diffraction (GI-XRD), energy-dispersive x-ray spectroscopy (EDX), and scanning electron microscope (SEM), respectively. For the as-deposited film, polycrystalline Pt was confirmed by uniform Debye–Scherrer rings of Pt. At 200 °C, interdiffusion between Co and Pt atoms in the film started to be observed by EDX elemental maps, and at 300 °C, alloying of Co and Pt atoms was confirmed by diffraction peaks corresponding to A1-disordered CoPt. At 400 °C, the in-plane coercivity of the film began to increase. At 700 °C, ordered CoPt alloys were confirmed by superlattice diffraction peaks. At 800 °C, a graded film containing L10-ordered CoPt was found to be formed and a maximum coercivity of 2.1 kOe was observed by VSM, where the easy axis of magnetization was oriented along the in-plane direction. At 900 °C, deformation of the ordered CoPt alloys was observed by GI-XRD, and the grain size of the film reached a maximum.

Correlations between microwave dielectric properties and crystal structures of Sb-doped Co0.5Ti0.5NbO4 ceramics

Co0.5Ti0.5Nb1-xSbxO4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics with low dielectric losses were fabricated by the conventional solid-state reaction method. A single-phase tetragonal rutile structure with a superlattice diffraction peak was observed. The temperature coefficient of resonant frequency (τf) decreased with an increase in oxygen octahedron distortion. The quality factor (Q×f) was increased owing to the enhanced cation ordering, which reduced the lattice energy and internal stress of the oxygen octahedron. Sb3+ was transformed into Sb5+, while the transformation of Co2+ to Co3+ was inhibited. The as-prepared Co0.5Ti0.5Nb0.5Sb0.5O4 ceramic exhibited εr of 38, Q × f of 32,047 GHz, and τf of 32.6 parts-per-million/°C.

Simulated x-ray diffraction from pseudomorphic GaAs/In0.3Ga0.7As superlattice high electron mobility transistor heterostructures on GaAs (001) substrates

In this paper, the authors report a study of the simulated dynamical x-ray diffraction from GaAs/In0.3Ga0.7As superlattice high electron mobility transistor heterostructures on GaAs (001) substrates both with (metamorphic) and without (pseudomorphic) dislocations. The analysis of dynamical x-ray diffraction for 004, 115, 026, and 117 reflection profiles was conducted for the case of Cu kα1 radiation. The authors show that the threading dislocation density may be estimated from nondestructive x-ray rocking curve measurements, using the rocking curve peak intensity ratios or widths for superlattice diffraction peaks. Despite the complexity of these multilayered device structures and the resulting x-ray diffraction profiles, analysis of the 004 x-ray diffraction profile allows characterization of the pseudomorphic–metamorphic transition in them and is of considerable practical importance for device realization.

Strain Effects on Redox Reaction in Li-Rich Layered Oxide Electrode

It has been conventionally understood that constituent transition metals mainly contribute to the charge compensation that accompanies Li insertion/extraction in oxide-electrode materials for lithium ion batteries (LIBs). However, such understanding is no longer sufficient in Li-rich layered electrode materials, which is a quasi solid solution of Li2 M 1O3 and LiM2 O2 (M 1 = Mn, Ru, Sn, M 2 = Mn, Co, Ni) because their practical capacities are larger than the capacities predicted from the valence changes of the constituent transition metals. This electrode family frequently exhibits the domain structures of Li2 M 1O3 and LiM2 O2 phases1. It would induce significant strain in the structure due to a lattice mismatch of each phase during the Li insertion/extraction, which facilitates an orbital hybridization between oxygen and transition metal. Such strong hybridization is expected to eventually unlock the limited capacity beyond that predicted by the valence changes of the constituent transition metals. It is, therefore, of great importance to reveal the local strain in the domain structures of the electrode during Li insertion/extraction in order to expedite the development of this electrode family. In this study, the local structure of transition metal and its evolution in a Li-rich layered oxide electrode upon charge/discharge were investigated using a combination of X-ray diffraction spectroscopy (XDS)2,3, with which phase-selective X-ray absorption fine structure (XAFS) can be obtained, and X-ray absorption spectroscopy (XAS). The active material of Li[Li0.2Ni0.2Mn0.6]O2 (LNMO) was synthesized by well-established procedure of the solid-reaction method followed by the coprecipitation technique4. Charged and discharged samples in the first two cycles for the X-ray analyses were prepared by the electrochemical Li insertion/extraction at 50 °C using a plastic bag cell. Both XDS and XAS measurements around Mn and Ni K-edges were performed at BL28XU in SPring-8. For the phase-selective XAFS analysis, resonant X-ray diffraction intensities were measured at the superlattice-diffraction peak near 003 diffraction of the layered rock-salt structure and its fundamental diffraction peaks, i.e., 003 and 104. The XDS study on superlattice diffraction of LNMO revealed that this material exhibits composite structure of Mn- and Ni-rich domains. Long-range order of the Mn-rich domain vanishes during the first charge. However, the XAFS analyses indicates that the local honeycomb ordering of Mn in this domain, which is also seen in Li2MnO3, remains in subsequent charge/discharge cycles. Little change in Mn-O bond length indicates little contribution to the charge compensation of this domain accompanies with Li insertion/extraction. In contrast, the drastic change in Ni-O bond length indicates the intensive redox reaction of Ni-rich domain, the magnitude of which is beyond that expected by the valence change of Ni from +II to +IV. The crystalline structure of this domain is constrained within the transition-metal layer by electrochemically inactive Mn-rich domain, which induces the trigonal distortion of the octahedral NiO6cluster by the in-plane strain when shortening the bond length of Ni-O that accompanies Li extraction. Such distortion would facilitate the orbital hybridization between an atomic d-orbital of transition metal and p-orbital of oxygen, and eventually allow us to utilize the deeper redox reaction of the transition-metal oxide electrodes. Evaluation and design of the domain structure of the electrode will pave the way to bring out the unseen potentials of the layered oxide electrodes.

Effects of calcining temperature on crystal structures, dielectric properties and lattice vibrational modes of Ba(Mg1/3Ta2/3)O3 ceramics

Ba(Mg1/3Ta2/3)O3 ceramics were synthesized via a conventional solid-state sintering technique, calcined at 1200 °C (Y1), 1250 °C (Y2), and 1280 °C (Y3) for 2 h, separately, and next sintered at 1490 °C for 3 h. The main phase of BMT ceramics is a hexagonal structure \(\upsilon (\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r} )\) (164) with 1:2 ordered structure. The intensities of the superlattice diffraction peaks (001) and (100) decrease with the increase in the calcining temperature, and the diffraction peaks’ intensities of the main phase also decrease, accordingly. The baseline of Y1 and Y2 are smooth, while that of Y3 is wavily, even some new modes appear, which is due to lower ordering degree. All in all, 1200 °C (Y2) and 1250 °C (Y3) are the better calcining temperatures because they possess better dielectric properties. Ten far-infrared modes are observed for Y2 sample, which are divided into three sections, including I section: the modes below 160 cm−1 being related to the vibration between Ba2+ and the (MgTa)O6 octahedron; II section: the modes between 180 and 300 cm−1 being mostly concerned with the (MgTa)-O and (WTa)-O stretching modes; III section: the modes above 500 cm−1 being related to the O-(MgTa)-O bending modes.

Absence of Magnetic Field Dependence of the Anomalous Bond-Stretching Phonon in YBa2Cu3O6.6

Superlattice diffraction peaks have been recently observed in underdoped YBa2Cu3O6.6. They have been interpreted to originate from a charge density wave (CDW) formation. It is believed that strong phonon anomalies previously observed near the same wavevectors are related to the CDW. Competition with superconductivity is a salient feature of the CDW peaks. We investigated if the same is true of anomalous bond-stretching phonons around 60 meV by measuring the spectrum of this phonon at 10 K with and without an applied magnetic field of 10 T. Applying the field had no effect on the phonon within the experimental uncertainty.

Study on lattice symmetry of sputtered Co–Cu–Pt metastable ordered thin films

The lattice symmetry and atomic stacking sequence of Cu-doped metastable L11 Co50Pt50 (Co50−xCuxPt50) films with thicknesses varied from 5 to 50nm were examined by X-ray diffraction along the (10.1) diffraction rod. Replacement of Co with Cu significantly decreases the linewidth of the (111) superlattice diffraction peak, revealing reduced defect density. The crystal symmetry of CoPt L11 is identified as face-centered. After the addition of Cu (x≥23), it evolves into rhombohedral, which is the thermodynamically equilibrium structure of CuPt. Furthermore, the decrease in film thickness results in the modification of structure in CoPt binary films, forming pseudo-hexagonal phase. As the film thickness is decreased from 10 to 5nm, the component of pseudo-hexagonal phase increases from 7.1vol.% to 13.6vol.%. However, such a phase evolution disappears in the films with x=23. The stabilization of rhombohedral L11 promotes the alignment of magnetic easy-axis, yielding a high perpendicular remanence ratio and negligible in-plane magnetic component, even in the 5nm-thick sample. The presented results provide detailed information for the understanding of the relation between structure and magnetic properties of metastable CoPt-based L11 films.

Facile synthesis of superparamagnetic Ni–Fe ultrafine nanoalloy nanoparticles with equilibrium ordered phase structure via a sol–gel process

Ni-Fe nanoalloy nanoparticles with an average grain size of 4 nm in diameter have been prepared by a sol-gel method under a hydrogen atmosphere where ethanol and oleic acid have been used as solvent and surfactant, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) examinations of the nanoparticles show the occurrence of (111), (200), (220) and (311) diffraction peaks and rings, meaning that the nanoparticles have a face-centered-cubic phase structure. Moreover, a superlattice diffraction peak and a diffraction ring/spot can also be observed in XRD and SAED results, indicating the formation of an equilibrium ordered L1(2) phase structure. The as-prepared Ni-Fe nanoalloy particles show typical superparamagnetic behavior at room temperature and the blocking temperature of the nanoparticles is determined to be about 50 K.

Structural coherence and layer perfection in Fe/MgO multilayers

A series of Fe/MgO multilayers was grown on single-crystal MgO(001) substrates atdifferent temperatures using magnetron sputtering. The structural quality of thesamples was investigated by x-ray reflectometry, x-ray diffraction and transmissionelectron microscopy. The results show a strong dependence of the structural qualityon the growth temperature. Although good epitaxial layers are obtained at165 °C, the sample does not exhibit any superlattice diffraction peaks. This effect is shown to berelated to a continuous variation of the distance between the Fe layers as well as betweenthe MgO layers.

Crystal and magnetic structural study of theLa1−xCaxMnO3compound(x=34)

We studied the crystal and magnetic structure of the ${\mathrm{La}}_{1∕4}{\mathrm{Ca}}_{3∕4}\mathrm{Mn}{\mathrm{O}}_{3}$ compound using ultrahigh resolution synchrotron x-ray and neutron-diffraction techniques. The experimental results revealed that the particular compound undergoes a structural transition at ${T}_{\mathrm{CO}}=220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This transition results in an increase of the orthorhombic splitting and the appearance of superlattice diffraction peaks, which can be indexed assuming a supercell $4a$ ($a$ is the unit cell parameter for $T>{T}_{\mathrm{CO}}$). This transition is reminiscent of those observed for the $x=1∕2$ and $x=2∕3$ stoichiometries where superstructures with $2a$ and $3a$, respectively, have been observed. At ${T}_{N}=160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the neutron-diffraction patterns exhibit additional diffraction peaks, corresponding to antiferromagnetic long-range order with propagation vectors $\mathbf{k}=[\frac{1}{4},0,\frac{1}{2}]$ and $\mathbf{k}=[\frac{1}{2},0,\frac{1}{2}]$. In addition to the structural transition at ${T}_{\mathrm{CO}}$ the synchrotron high resolution x-ray diffraction patterns revealed a three phase coexistence.

Ordered structure formation in the flux-grown Ba(Mg1/3Ta2/3)O3 single crystals

Formation of ordered structure in flux-grown Ba(Mg1/3Ta2/3)O3(BMT) single crystals was studied using x-ray diffraction, electron diffraction, and high-resolution electron microscopy. The low-temperature-grown crystals exhibited no sign of B-site ordering. Annealing at 1500 °C induced the 1:2 ordered phase, and its content increased with the annealing time. The superlattice diffraction peaks were broad initially; they sharpened rapidly with the annealing time. Diffuse superlattice reflections were found in electron diffraction patterns of 1500 °C annealed BMT; they turned into sharp reflections under long annealing time or higher temperature, 1600 °C. The intensity of diffuse reflections was sparsely distributed, but the maximum intensity location was determined in the digitized recording of image plate. The maximum intensity sites of two diffuse reflections in the 〈111〉 direction deviated from the presumed 1/3 and 2/3 positions and shifted towards the center. The diffuse reflection and the deviation from regular positions were interpreted as the composition modulation during B-site cation diffusion.

Atomic Structure of PbZrO3 Determined by Pulsed Neutron Diffraction

The atomic structure of lead zirconate, PbZrO3 (PZ), was studied using Rietveld refinement and atomic pair distribution function analysis of pulsed neutron powder diffraction data for the antiferroelectric, intermediate and paraelectric phases. The symmetry of PZ at T = 20 K in the antiferroelectric phase was determined to be Pbam. The structure was characterized by distortions of the ZrO6 octahedra which are smaller than in previous studies. Locally correlated displacements of Pb in the c direction develop with increasing temperature. The average magnitude was 0.06 Å at room temperature, 0.14 Å at T = 473 K and 0.20 Å in the intermediate phase at T = 508 K. The intermediate phase was characterized by in-plane antiferroelectric Pb displacements which produce 1\over 2{110} superlattice diffraction peaks. Above 473 K the local structure of PZ remains largely unchanged, in spite of the transitions in the long-range order from the antiferroelectric to the intermediate and to the paraelectric phases.

Synchrotron X-ray scattering study of lead magnoniobate relaxor ferroelectric crystals

Results of a synchrotron radiation scattering study of single crystals of relaxor ferroelectric lead magnoniobate (PMN) are presented. It is demonstrated that the diffuse scattering could be separated into two components—longitudinal Huang scattering related to the deformation of lattice and transverse ferroelectric fluctuations (FF) scattering. It is shown that at large q, where q is the deviation in the scattering vector from the reciprocal lattice point, FF scattering follows a q − ga power law. As the temperature is decreased the power exponent α changes from 2.3 to 2.7 through T g = 230 K where the freezing of FF takes place. Strong asymmetry of the lineshape for the transverse scan in the vicinity of the (2 3 0) reciprocal lattice point is observed. This may be explained in terms of the strong linear coupling between the ferroelectric fluctuations and the lattice deformation. In addition two types of diffuse superlattice diffraction peaks, at 1 2 (111) and 1 2 (110) , have been observed for the first time with X-ray diffraction.

An X-ray diffraction study of superlattice ordering in lead magnesium niobate

We report a direct observation of the superlattice diffraction peaks, indicating a doubling of unit cell, from lead magnesium niobate (PMN) single crystal using X-ray diffraction technique. The broad width of the superlattice diffraction peaks indicates that the superlattice ordering in PMN is of short range. In the temperature range studied (from 10 K to 355 K) the peak width shows no temperature dependence. The intensity distribution among the observed superlattice peaks suggests that the doubling of unit cell in the superlattice regions involves significant ionic displacements in addition to a chemical ordering.

Evidence for a deconstructed “even” flat phase on the Pd(110) + K 1 × 2 surface

The existence of a 1 × 2 missing row reconstruction on fcc metal (110) surfaces leads to a particularly rich variety of possible disordered phases. Five distinct disordering scenarios have been predicted for the 1 × 2 missing row reconstruction, differentiated by the relative energy cost to generate the different types of defects that can form on this surface. In this work we present high resolution LEED data for the alkali coverage driven 1 × 2 → 1 × 1 transition on Pd (110) + K. Superlattice and integer diffraction peaks as a function of potassium coverage have been analyzed. The width and shift of the superlattice diffraction peaks are found to be consistent with a transition to the deconstructed “even” phase. This transition is driven by the formation of bound steps. No evidence of isolated step formation is found in the coverage range 0 < θ < 0.4.

150% magnetoresistance in sputtered Fe/Cr(100) superlattices

We report the epitaxial growth of Fe/Cr(100) superlattices onto MgO(100) single-crystal substrates by magnetron sputtering. Superlattices that are epitaxially oriented within 1° both in-plane and out-of-plane with the MgO substrate are achieved by initial growth of a Cr base layer at high temperature. Multiple superlattice diffraction peaks are observed in the low- and high-angle x-ray diffraction spectra. Three peaks are observed in the magnetoresistance associated with the oscillatory antiferromagnetic interlayer magnetic coupling as a function of Cr thickness. A maximum magnetoresistance of 150% at 4.2 K (28% at room temperature) is observed for a Cr(100 Å)/[Fe(14 Å)/Cr(8 Å)]50 superlattice.

Structural characterization of GaAs/GaP superlattices

Powder and double-crystal X-ray diffraction were used to study the structural properties of highly strained (GaAs)N/(GaP)M short-period superlattices grown on GaAs (001) substrates. In spite of the large lattice mismatch (f=3.6%) between GaAs and GaP and the competition for incorporation between As and P, high-quality short-period superlattices of GaAs/GaP have been grown by a development of conventional molecular beam epitaxy named atomic layer molecular beam epitaxy. The in-plane lattice parameter (a/sub ///) of the different superlattices was measured and studied as a function of the GaP content. The authors found that, for a given total superlattice thickness of 4000 AA, the critical lattice mismatch is fc approximately=0.5% (corresponding to an average GaP content of 13.6% in the superlattice). This means that for an average misfit or lattice mismatch above fc the superlattice starts to relax. This experimental result is compared with predictions of critical thickness theories based on energy criteria. A clear relation of the degree of relaxation with peak width of the superlattice zeroth-order diffraction peak is found. High-resolution transmission electron microscopy has been performed to analyse the type of dislocations that relax the mismatched layers.

Resonant magnetic soft x-ray diffraction at Ni L III edge: ferro- and antiferromagnetism in Ag-Ni multilayers

Resonant enhancement of the X-ray magnetic scattering allowed to evidence the antiferromagnetic coupling between the Ni layers in an Ag/Ni multilayer through the appearance at small angles of a magnetic superlattice diffraction peak. The magnetic moments are found to be oriented perpendicular to an applied magnetic field weaker than the saturation field. Moreover, we observed a large magnetization dependent amplitude of 2.5 electrons.