Ion channeling, high resolution x-ray diffraction and Raman spectroscopy in strained quantum wells

Influence of initial growth stages on AlN epilayers grown by metal organic chemical vapor deposition

We directly demonstrate quantum-confined direct band transitions in the tensile strainedGe/SiGe multiple quantum wells grown on silicon substrates by room temperaturephotoluminescence. The tensile strained Ge/SiGe multiple quantum wells withvarious thicknesses of Ge well layers are grown on silicon substrates with a lowtemperature Ge buffer layer by ultrahigh vacuum chemical vapor deposition.The strain status, crystallographic, and surface morphology are systematicallycharacterized by high-resolution transmission electron microscopy, atomic forcemicroscopy, x-ray diffraction, and Raman spectroscopy. It is indicated that thephotoluminescence peak energy of the tensile strained Ge/SiGe quantum wellsshifts to higher energy with the reduction in thickness of Ge well layers. Thisblue shift of the luminescence peak energy can be quantitatively explained bythe direct band transitions due to the quantum confinement effect at theΓ point of the conduction band.

Multiferroic Bismuth Ferrite (BiFeO3) thin films with varying excess bismuth (Bi) concentration were grown by chemical solution deposition technique. Room temperature multiferroic properties (ferromagnetism, ferroelectricity, and piezoelectricity) of the deposited BiFeO3 thin films have been studied. High resolution X-ray diffraction and Raman spectroscopy studies reveal that the dominant phases formed in the prepared samples change continuously from a mixture of BiFeO3 and Fe2O3 to pure BiFeO3 phase and, subsequently, to a mixture of BiFeO3 and Bi2O3 with increase in the concentration of excess Bi from 0% to 15%. BiFeO3 thin films having low content (0% and 2%) of excess Bi showed the traces of ferromagnetic phase (γ-Fe2O3). Deterioration in ferroic properties of BiFeO3 thin films is also observed when prepared with higher content (15%) of excess Bi. Single-phased BiFeO3 thin film prepared with 5% excess Bi concentration exhibited the soft ferromagnetic hysteresis loops and ferroelectric characteristics with remnant polarization 4.2 μC/cm2 and saturation magnetization 11.66 emu/g. The switching of fine spontaneous domains with applied dc bias has been observed using piezoresponse force microscopy in BiFeO3 thin films having 5% excess Bi. The results are important to identify optimum excess Bi concentration needed for the formation of single phase BiFeO3 thin films exhibiting the improved multiferroic properties.

ABSTRACTPerovskite structured mixed metal fluorides containing manganese/sodium or potassium have been synthesized in pure form by a greener precipitation route and characterized by high-resolution powder X-ray diffraction and Raman spectroscopy techniques. While all the reflections in the powder X-ray diffraction pattern of potassium manganese fluoride could be indexed in cubic symmetry with a = 4.1889 Å, sodium manganese fluoride showed reflections at positions typical of orthorhombic symmetry (Pnma space group) with a = 5.751, b = 8.008, and c = 5.548 Å. Potassium manganese fluoride in powder form showed bands at 209, 291, 386, 558, 621, and 733 cm−1 in the Raman spectrum at room temperature. All these bands disappeared and second-order band at 1151 and 1298 cm−1 emerged when the powders were compacted under pressure ranging between 1 and 4 tons (uniaxial). A similar change was noticed for sodium manganese fluoride in which bands at 1099, 1149, 1203, and 1286 cm−1 were observed for the compacted samples. The response of the vibrational modes of these compounds to uniaxial pressure revealed the existence of large structural disorder in them. Additionally, the need for the extreme care to collect and interpret Raman data of polycrystalline samples of these systems has been illustrated through this study.

Although the AlxGa1−xAs alloy system has been extensively investigated, there are still considerable uncertainties in measuring the value of x. Here a new AlxGa1−xAs calibration structure, grown by molecular beam epitaxy, has been used to establish unambiguous alloy compositions. Such “standard’’ AlxGa1−xAs layers were measured by high-resolution x-ray diffraction, photoluminescence, and Raman spectroscopy to determine the compositional variations of the measured physical parameters. The phenomenological equations derived from these measurements can now be used to establish the Al content of unknown alloys with confidence. In addition, the results show that Vegard’s law does not hold for the variation of the AlxGa1−xAs lattice constant with x. The small quadratic term has very important implications for a correct analysis of x-ray results.

The cathode deposit produced by carbon arc discharge was studied by scanning electron microscopy, high resolution electron microscopy, x-ray diffraction and Raman spectroscopy. The results indicate that the stacking of hexagonal carbon layer in the discharged graphite is different from the ABAB stacking sequence in graphite, and that carbon nanotube is a kind of graphite-like micro-crystal with a low-dimensional structure.

Effect of temperature and carrier gas on the properties of thick [formula omitted]N layer

Organometallic vapor phase epitaxy (OMVPE)

In recent years, it is urgent and challenging to fabricate highly sensitive and selective gas sensors for breath analyses. In this work, Sr-doped cubic In2O3/rhombohedral In2O3 homojunction nanowires (NWs) are synthesized by one-step electrospun technology. The Sr doping alters the cubic phase of pure In2O3 into the rhombohedral phase, which is verified by the high-resolution transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy, and is attributable to the low cohesive energy as calculated by the density functional theory (DFT). As a proof-of-concept of fatty liver biomarker sensing, ethanol sensors are fabricated using the electrospun In2O3 NWs. The results show that 8 wt % Sr-doped In2O3 shows the highest ethanol sensing performance with a high response of 21-1 ppm, a high selectivity over other interfering gases such as methanol, acetone, formaldehyde, toluene, xylene, and benzene, a high stability measured in 6 weeks, and also a high resistance to high humidity of 80%. The outstanding ethanol sensing performance is attributable to the enhanced ethanol adsorption by Sr doping as calculated by DFT, the stable rhombohedral phase and the preferred (104) facet exposure, and the formed homojunctions favoring the electron transfer. All these results show the effective structural modification of In2O3 by Sr doping, and also the great potency of the homojunction Sr-doped In2O3 NWs for highly sensitive, selective, and stable breath ethanol sensing.

以蔗糖为碳源，Ni-Fe层状双金属氢氧化物为模板和催化剂制备了高度石墨化的介孔炭材料。采用透射电子显微镜(HRTEM)、X射线衍射仪(XRD)和拉曼光谱法(Raman)对产物的形貌和结构进行表征。结果显示该材料具有较高的石墨化程度。采用循环伏安法和脉冲伏安法研究了对苯二酚和邻苯二酚在修饰电极上的电化学行为。结果表明该修饰电极对对苯二酚和邻苯二酚的电化学反应具有显著的催化效果。 Highly graphitic mesoporous carbon was synthesized using sucrose as carbon precursor and Ni-Fe layered hydroxide as template and catalyst. High-resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the morphology and structure of the material. The results indicated that the graphitic mesoporous carbon has high degree of graphitization. Moreover, the electrochemical properties of the modified electrode were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The graphitic mesoporous carbon modified electrode has excellent electrocatalytic activity for the oxidation of hydroquinone (HQ) and catechol (CC), as the result has proved.

The authors report a simple chemical technique to prepare a hybrid nanostructure of single wall carbon nanotubes (SWCNT) with CdS nanocrystals. By chemical reaction of cadmium acetate and sodium sulphide in the sodium dodecyl sulphate (SDS) solution containing SWCNT, cadmium sulphide quantum dots (QDs) of average size 5.5 nm are decorated onto the walls of SWCNT bundles. The hybrid material has been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and Raman spectroscopy. Characteristic optical properties of the hybrid structure have been identified through UV-Vis and photoluminescence (PL) spectroscopy.

Polyoxymethylene dimethyl ether 3 (PODE3) is a polymerized ether with multiple C-O-C chains, distinguished by higher oxygen and less carbon content, making it an eco-friendly and cost-effective alternative fuel. This study explores the synergistic effects of varying PODE3 amounts on soot characteristics in isooctane inverse diffusion flames, utilizing optical diagnostics and sampling techniques. Optical diagnostic was used to measure flame temperature and the KL factor, while quartz sampling was employed to analyze soot particle behaviors through transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and Raman spectroscopy. The results showed that small proportions of PODE3 (2–5%) led to slight increases in flame height, maximum flame temperature, and mean KL factor. In contrast, a 20% PODE3 addition produced a smaller flame height, lower luminous intensity, and reduced maximum flame temperature, along with a lower mean KL factor, indicating enhanced combustion performance and reduced soot concentration. Moreover, small amounts of PODE3 resulted in chain-like liquid morphologies in soot particles, characterized by slightly longer fringe lengths, decreased tortuosity, and increased crystallite sizes. On the other hand, higher PODE3 ratios caused soot particles to adopt film-like liquid morphologies, with reduced fringe length, increased tortuosity, and more disordered structures. Therefore, soot particles generated from a 20% PODE3/isooctane mixture exhibited a more film-like liquid morphology, characterized by a turbostratic structure with shorter fringe lengths, greater tortuosity, and a lower degree of graphitization. These structural changes highlight the significant influence of PODE3 addition on both soot formation and overall combustion dynamics.

For the first time, we report the synthesis of turbostratic carbon derived from tire waste with high surface area and its utilization as an electrode material in vanadium redox flow batteries (VRFBs). The tire waste carbon was initially subjected to acid demineralization followed by KOH activation wherein the carbon to KOH ratio was varied (1:1, 1:2, and 1:5), and the electrochemical performance toward VO2+/VO2+, V3+/V4+, and V2+/V3+ redox reactions was investigated. The turbostratic nature of carbon derived from tire waste was confirmed by high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Brunauer–Emmett–Teller (BET) measurements revealed the surface area was as high as 875 m2·g–1 for the 1:5 KOH activated sample. The electrochemical performance of pretreated carbon (TW) and turbostratic carbon (1:1, 1:2, and 1:5) was compared by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge methods. Our results indicated that the...

The AlxGa1 − xN/AlyGa1 − yN multiple quantum well (MQW) structure for deep ultraviolet emission has been grown on sapphire by metal organic chemical vapor deposition (MOCVD). High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and cathodoluminescence (CL) are used to characterize the structural and optical properties of MQWs, respectively. Clear step flows can be observed in the AFM image indicating a two-dimensional growth model. There are many cracks on the surface of the MQW structure because of the high tensile stress. HRXRD shows multiple satellite peaks to the 2nd order. The HRXRD simulation shows that the MQW period is about 11.5 nm. The emission peak of AlxGa1 − xN/AlyGa1 − yN MQWs is about 295 nm in the deep ultraviolet region from the CL spectra.

Following a study of implantation enhanced interdiffusion of InGaAs∕InP multiple quantum well (MQW) structures by cross-sectional scanning tunneling microscopy (XSTM), the techniques of low temperature photoluminescence spectroscopy, high-resolution x-ray diffraction (HRXRD), and grazing incidence x-ray analysis (GIXA) are used to independently investigate the suitability of a square well model for the interdiffused MQW profiles, and the observed dependence of strain development as a function of the implanted ion range relative to the MQW stacks. In agreement with previous XSTM findings, when ions are implanted through the MQWs, HRXRD measurements indicate equivalent extents of interdiffusion occurring on both sublattices, while GIXA measurements further indicate the compositional profiles to be non-Fickian and compatible with uniformly broadened square well distributions. Following shallow ion implants (where ions are deposited between the MQWs and the sample surface), (004) HRXRD measurements indicate preferential group V interdiffusion. Dynamical simulations of the superlattice envelope in the (004) HRXRD rocking curves show the compositional profiles to be non-Fickian and compatible with a square well model for the broadened compositional profiles. Additional analysis of the (001) bilayer spacing from previously published XSTM linescan data for this structure is also consistent with this finding. Results of a preliminary photoluminescence and HRXRD investigation of disordering induced by indium implants and the effects of extended annealing on a series of MQW samples (with and without implantation) are presented. Implications for the implantation enhancement of interdiffusion in the InGaAs∕InP material system are discussed. The interpretation of quantum well interdiffusion experiments in this material system in terms of Fickian diffusion models warrants revision in light of the present findings.