We investigated with synchrotron x-ray diffraction and reflectometry the formation of structural domains in the near-surface region of single crystalline SrTiO3 (001) substrates with Y0.6Pr0.4Ba2Cu3O7 / La2/3Ca1/3MnO3 superlattices grown on top. We find that the antiferrodistortive cubic-to-tetragonal transition, which occurs at T_STO = 104K in the bulk and at a considerably higher temperature of at least 120K in the surface region of SrTiO3, has only a weak influence on the domain formation. The strongest changes occur instead in the vicinitiy of the tetragonal-to-orthorhombic transition in SrTiO3 around 65K, where pronounced surface facets develop that reach deep (at least several micrometers) into the SrTiO3 substrate. These micrometer-sized facets are anisotropic and tilted with respect to one another by up to 0.5deg along the shorter direction. Finally, we find that a third structural transition below 30K gives rise to significant changes in the spread of the c-axis parameters. Overall, our data provide evidence for a strong mutual interaction between the stuctural properties of the SrTiO3 surface and the multilayer grown on top.
New perspective cubic quasi-alloys CdO/MgO short period superlattices were grown on sapphire substrates by plasma assisted molecular beam epitaxy. Their crystal quality was characterized using High Resolution X-ray Diffraction (HRXRD) and Transmission Electron Microscopy (TEM) techniques. The thickness and growth rate of MgO and CdO individual layers have been extracted. Small angle X-ray diffraction peaks corresponding to the period of the superlattices ranging from 0.6 to 5 nm were clearly observed. From the XRD measurements we obtain 65% relaxation to the substrate of superlattice (SL) in S…
Single-crystal Heusler atomic-scale superlattices that have been predicted to exhibit perpendicular magnetic anisotropy and half-metallicity have been successfully grown by molecular beam epitaxy. Superlattices consisting of full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers with high cobalt or high iron concentrations for samples grown near room temperature on GaAs (001). Superlattice structures grown with an exce…
The unique topology and physics of chiral superlattices make their self-assembly from nanoparticles a holy grail for (meta)materials. Here we show that tetrahedral gold nanoparticles can spontaneously transform from a perovskite-like low-density phase with corner-to-corner connections into pinwheel assemblies with corner-to-edge connections and denser packing. While the corner-sharing assemblies are achiral, pinwheel superlattices become strongly mirror-asymmetric on solid substrates as demonstrated by chirality measures. Liquid-phase transmission electron microscopy and computational models s…
Comprehensive investigation on the correlation of growth, structural and optical properties of GaN nanowires grown on Si(111) substrates by plasma assisted molecular beam epitaxy technique
Monte Carlo Simulation of Sinusoidally Modulated Superlattice Growth
利用蒙特卡罗模拟研究了在非均匀磁通分布下旋转衬底代替连续关闭和打开源光闸生长ZnSe/ZnTe超晶格的过程。据发现，每种化合物的浓度是正弦调制沿生长方向，所造成的不均匀到达的Se和Te原子在样品的一个给定的点，并通过在该点的Te/Se比的变化，由于旋转的衬底。以这种方式，我们获得了ZnSe $_{1-x}$ Te $_x$合金，其中组分$x$沿生长方向正弦变化。调制的周期由衬底旋转的速率直接控制。成分调制的幅度对于衬底旋转的小角速度是单调的，但是其本身对于大的角速度是调制的。调制图案的平均振幅随着衬底旋转的角速度增加和测量位置接近旋转中心而减小。模拟结果与以前发表的实验测量结果吻合得很好，以这种方式制造的超晶格。
(BiFeO3)(1-x)Λ/(LaFeO3)xΛ superlattices (SLs) with varying x have been grown by pulsed laser deposition on (111) oriented SrTiO3 substrates. In order to obtain good epitaxy and flat samples a conducting SrRuO3 buffer has been deposited prior to the superlattices to screen the polar mismatch for such (111) SrTiO3 orientation. X-ray diffraction reciprocal space mapping on different family of planes were collected and evidenced a room temperature structural change at x=0.5 from a rhombohedral/monoclinic structure for rich BiFeO3 to an orthorhombic symmetry for rich LaFeO3. This symmetry change ha…
Enhanced high-temperature performance of GaN light-emitting diodes grown on silicon substrates
我们比较了在硅和蓝宝石衬底上生长的市售GAN发光二极管（LED）的光学和电气特性对温度的依赖性。与传统预期相反，生长在硅衬底上的LED（通常称为GaN-on-Si LED）在较高温度下显示出较小的效率下降，即使具有更多的穿透位错。结温的分析表明，尽管与生长在蓝宝石衬底上的LED相比共享相同的外延结构和封装，但GaN on Si LED具有较冷的结。我们还观察到理想因子随着环境温度的增加而降低，这表明理想二极管电流随着温度的增加而增加。应变和温度系数测量的分析表明，与生长在蓝宝石上的LED相比，Si上GaN LED的有源区内的空穴传输效率增加，这导致了较少的温度依赖性效率下降。
Ordered atomic-scale superlattices on surface hold great interest both for basic science and for potential applications in advanced technology. However, controlled fabrication of superlattices down to atomic scale has proven exceptionally challenging. Here we demonstrate the segregation-growth and self-organization of ordered S atomic superlattices confined at the interface between graphene and S-rich Cu substrates. Scanning tunneling microscope (STM) studies show that, by finely controlling the growth temperature, we obtain well-ordered S (sub)nanometer-cluster superlattice and monoatomic sup…
X-ray nanodiffraction is applied to study the formation and correlation of domain boundaries in mesocrystalline superlattices of PbS nanocrystals with face-centered cubic structure. Each domain of the superlattice can be described with one of two mesocrystalline polymorphs with different orientational order. Close to a grain boundary, the lattice constant decreases and the superlattice undergoes an out-of-plane rotation, while the orientation of the nanocrystals with respect to the superlattice remains unchanged. These findings are explained with the release of stress on the expense of specifi…
Co40Fe40B20 layers were grown on the Pb0.71Sn0.29Te topological insulator substrates by laser molecular beam epitaxy (LMBE) method, and the growth conditions were studied. The possibility of growing epitaxial layers of a ferromagnet on the surface of a topological insulator was demonstrated for the first time. The Co40Fe40B20 layers obtained have a bcc crystal structure with a crystalline (111) plane parallel to the (111) PbSnTe plane. The use of three-dimensional mapping in the reciprocal space of reflection high electron diffraction (RHEED) patterns made it possible to determine the epitaxia…
Here, we report on the characterization of {CdO/ZnO}m superlattice structures (SLs) grown by plasma assisted molecular beam epitaxy. The properties of as-grown and annealed SLs deposited on m-oriented sapphire were investigated by secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) in cathodoluminescence (CL) and energy dispersive X-ray modes. The deformation of the crystallographic structure of SLs was observed after rapid thermal annealing at 900°C in oxygen flow due to migration and segregation of Cd atoms. SIMS measurements revealed that the distributions of cadmi…
High quality berylium doped InAs layer grown by MBE on GaAs substrate has been examined via magnetotransport measurements and high resolution quantitative mobility spectrum analysis in the range from 5 to 300 K and up to 15 T magnetic field. The layer homogenity and dopant concentration has been proofed via HR-SIMS. The results shew four channel conductivity and essential splitting of the most populated holelike channel below 55 K. The multilayer model concluded from the QMSA results has been compared with nextnano simulation.
Scaling like behaviour of resistivity observed in LaNiO_3 thin films grown on SrTiO_3 substrate by pulsed laser deposition
本文讨论了用脉冲激光淀积技术在SrTiO_3衬底上生长的高度取向的LaNiO_3薄膜（厚度为d）的电阻率随温度变化的原因。发现在整个温度区间（20 K <T<300 K），所有实验数据都坍缩成一条普适曲线[T/ T_{sf}（d）]^{3/2}，其中T_{sf}（d）是LaNiO_3/SrTiO_3异质结中自旋涨落引起传导电子共振散射的起始温度。
XPS studies on AlN thin films grown by ion beam sputtering in reactive assistance of N+/N2+ ions: Substrate temperature induced compositional variations
Room-temperature magnetoelectric multiferroicity has been observed in c-axis oriented GaFeO$_3$ thin films (space group $Pna2_1$), grown on economic and technologically important (100)Si substrates by pulsed laser deposition technique. Structural analysis and comprehensive mapping of Ga:Fe ratio across a length scale range of 10$^4$ reveal coexistence of epitaxial and chemical strain. It induces formation of finer magnetic domains and large magnetoelectric coupling - decrease in remanent polarization by $\sim$21\% under $\sim$50 kOe. Magnetic force microscopy reveals presence of both finer ($<…
Magnetic skyrmions have been suggested as information carriers for future spintronic devices. As the first material with experimentally confirmed skyrmions, B20-type MnSi was the research focus for decades. Although B20-MnSi films have been successfully grown on Si(111) substrates, there is no report about B20-MnSi films on Si(100) substrates, which would be more preferred for practical applications. In this letter, we present the first preparation of B20-MnSi on Si(100) substrates. It is realized by sub-second solid-state reaction between Mn and Si via flash-lamp annealing at ambient pressure…
Two-dimensional electron gases (2DEGs) at the ZnO/ZnMgO interface are promising for applications in spintronics and quantum computing due to the combination of low spin-orbit coupling and high electron mobility. Growing high mobility 2DEGs requires high quality substrates with low impurity densities. In this work we demonstrate a ZnO substrate sample treatment combining high temperature rapid thermal annealing and chemical etching to improve the surface quality for the subsequent growth of 2DEGs. This process enables the growth of a 2DEG with low-temperature mobility of $4.8\times10^4$~cm$^2$V…
We report on structural and optical properties of InGaN/GaN thin films, with a 0.46o misalignment between the surface and the (0001) plane, which were grown by metal-organic chemical vapor deposition (MOCVD) on 0.34o miscut sapphire substrates. X-ray diffraction and X-ray reflectivity were used to precisely measure the degree of miscut. Reciprocal space mapping was employed to determine the lattice parameters and strain state of the InGaN layers. Rutherford backscattering spectrometry with channeling was employed to measure their composition and crystalline quality with depth resolution. No st…
Thin crystalline layers of TaAs Weyl semimetal (9 and 18 nm thick) are grown by molecular beam epitaxy on GaAs(001) substrates. The (001) planes of the tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the corresponding in-plane crystallographic directions of the substrate and the layer are rotated by 45°. In spite of a substantial lattice mismatch (about 19%) between GaAs(001) substrate and TaAs epilayer no misfit dislocations are observed at the GaAs(001)/TaAs(001) interface. Only stacking fault defects in TaAs are detected with transmission electron microscopy. Thorough X…
Structural, magnetic and superconducting properties of pulsed-laser-deposition-grown $\rm{La_{1.85}Sr_{0.15}CuO_{4}/La_{2/3}Ca_{1/3}MnO_{3}}$ superlattices on $\rm{(001)}$-oriented $\rm{LaSrAlO_{4}}$ substrates
Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi2Se3, a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. This discovery paves the way toward gro…
Varying the substrate temperature changes structural and magnetic properties of spinel ferrite NZFO thin films. XRD of films grown at different temperature display only 004 reflections, without any secondary peaks, showing growth orientation along the c axis. We find an increase in crystalline quality of these thin films with the rise of substrate temperature. The surface topography of the thin films grown on various growth temperatures conditions reveal that these films are smooth with low roughness, however the thin films grown at 800 C exhibit lowest average and rms roughness among all thin…
(111)NiO epitaxial layers are grown on c-sapphire substrates by pulsed laser deposition (PLD) technique. Structural and morphological properties of the films are studied using in-plane as well as out-of-plane high resolution X-ray diffraction and atomic force microscopy techniques as functions of growth temperature, oxygen pressure and the pulses count of the laser. The study shows that continuous epitaxial films of thickness as low as 3 nm with high crystalline quality, smooth surface and interface morphology can be grown by this technique. The study also reveals the co-existence of 60°-rotat…
On the high accuracy lattice-parameters determination by n-beam diffraction: Theory and application to the InAs quantum dots grown over GaAs(001) substrate system
