High Resolution X-ray Diffraction Spectra Research Articles

Influence of low-temperature cap layer thickness on the structure and luminescence of InGaN/GaN multiple quantum wells

In order to effectively regulate the luminescence performance of MQW and enhance its optical quality, it is crucial to investigate the InGaN/GaN MQW's structure and luminescence properties. In this study the focus is how they are affected by low-temperature cap (LT-cap) layer's thickness which is grown above each InGaN well layer during growth process of InGaN/GaN multiple quantum well (MQW) samples in MOCVD system. This was achieved by analyzing high resolution X-ray diffraction (HRXRD) spectra, electroluminescence (EL) spectra, temperature-dependent photoluminescence (TDPL) spectra, and micro-area fluorescence imaging of these samples. The results show that changes in LT-cap layer's thickness even have no significant impact on some structural parameters of MQW, such as the thickness of the well layer, but have an influence on the In component of the well layer. Due to the existence of LT-cap layer, dissociation of InGaN can be effectually reduced. In addition, the augmentation of LT-cap layer's thickness will make polarization effect of the QW sample more remarkable, so that the blue shift of the EL peak with the augmentation of current injection increases. The change of LT-cap layer's thickness will also influence distribution of the tail states of the quantum wells, which leads to a different localization states for injected carriers. As LT-cap layer becomes getting thicker, the material's internal quantum efficiency (IQE) tends to decrease, which may result from an increase in non-radiative recombination centers.

Subsurface damage evolution of β-Ga2O3 (010) substrates during lapping and chemical mechanical polishing

For semiconductor single crystal substrates, subsurface damage (SSD) is an important factor for device failure. For β-Ga2O3 with two cleavage planes, the SSD is the key issue that needs to be addressed. In this work, β-Ga2O3 (010) substrates were lapped and polished precisely. The formation and evolution mechanisms of SSD were analyzed by cross-section transmission electron microscopy and wet chemical etching techniques. The linear distribution of scratches was found on the substrates after lapping. After chemical mechanical polishing (CMP), the surface scratches were eliminated. However, the SSD layer may still exist under the surface. Chemical etching was developed to identify the "invisible damage" to the CMP-finished (010) substrate. The SSD including nanocrystalline, tilt boundary, twist boundary, and high-density dislocations in β-Ga2O3 was first reported. Distinctively, there was no slip occurrence in the SSD of the (010) plane different from the (100) and (001) planes. The Schmid factor of multiple slip systems was calculated to analyze the cause of no slip on the subsurface. The formation mechanism of SSD was believed that when the slip system could not be activated, the stress was released through rotation and distortion of the crystal plane. The accumulation of grain boundary dislocations at twist grain boundary junctions provided a driving force for the formation of nanovoids. The relationship of substrate damage evolution and crystal strain with different machining parameters was established by high-resolution X-ray diffraction and Raman spectra. A non-damaging β-Ga2O3 (010) substrate with a surface roughness of less than 0.2 nm was obtained by the optimized CMP process. The research results had guiding significance for damage control of β-Ga2O3 and other brittle crystals in ultra-precision machining.

A new sesquiterpene from Syringa oblata

In this study, the chemical components of ethanol extract from the aromatic parts of Syringa oblata were systematically separated and purified by silica gel column chromatography, thin layer plate preparation and liquid phase preparation. Combined with ultraviolet analyzer(UV), infrared analyzer(IR), nuclear magnetic resonance analyzer(NMR), high resolution mass spectrometer(HR-ESI-MS), X-ray diffraction and other spectrum technology as well as literature physicochemical data comparison methods for structural identification, a total of 10 compounds were identified. They were identified as oblatanoid D(1),(-)-T-muurolol(2), oblatanoid E-G(3-5), 14-noreudesma-3-hydroxy-3-en-2,9-dione(6), 1-isopropyl-2,7-dimethylnaphthalene(7), isocoradiol(8), α-calacorene(9), cadin-4-en-1-β-ol(10). Compound 1 is a new sesquiterpene compound that has not been reported, and the other 9 compounds are isolated from S. oblata for the first time. The compound 1 has a significant protective effect on the LPS-induced inflammatory injury model of RAW264.7 cells.

Intense luminescence emission and lattice damage of the implanted Eu ions in KTiOPO4 crystals

The doping of rare earth elements revolutionized applications of optoelectronic devices. Europium (Eu) ions acting as activators can provide the fundamental effect on luminescence of host materials. We investigate photoluminescence, lattice damage formation of Eu-implanted potassium titanyl phosphate (KTiOPO4) crystals using 400-keV Eu ions with a fluence of 5 × 1015 ions / cm2 at room temperature. Effective doping is achieved in the depth range of about 50 to 200 nm from the surface of KTiOPO4 crystal, and the luminescent activity of Eu ions is inhibited due to significant implantation damage. However, the samples showed intense luminescence emission at room temperature through the lattice recovery after annealing at 600°C and 700°C. The lattice damage of as-implanted and annealed samples was investigated by Rutherford backscattering spectrometry in channeling configuration. Furthermore, the relative strain depth curves of Eu implanted KTiOPO4 samples at different annealing temperatures were studied using the high resolution x-ray diffraction and Raman spectra. The present research reveals that Eu implanted KTiOPO4 samples have great prospects in the field of optical applications and waveguide quantum reservoirs.

Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

A study on characterization of microstructures in ammonothermal grown GaN wafers at different stages of device fabrication is conducted using synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron X-ray rocking curve topography (SXRCT) as well as high resolution X-ray diffraction (HRXRD). Synchrotron monochromatic beam X-ray topographs reveal the various dislocation types and their distribution in the GaN wafer at different processing stages remains the same except that the contrast of threading dislocations is enlarged or darkened. HRXRD spectra of the ion implanted wafer reveals satellite peak and fringes from lattice damage. Rocking Curve Analysis by Dynamical Simulation (RADS) that fits the spectra gives a depth profile of strain correlated well to the designed implantation profile. This damage is completely healed after annealing process at 1225 ℃. Strain and tilt maps generated from SXRCT show an improvement in lattice bending level during annealing.

Growth temperature effect on physical and mechanical properties of nitrogen rich InN epilayers

A set of N-polar InN epilayers has been grown at different temperatures by plasma–assisted molecular beam epitaxy (PA-MBE) on GaN/AlN/Al2O3(0001) templates. The purpose is to understand how the variation of crucial factor, such as the temperature, impacts the growth process and the resulting samples’ properties. The characterization of these InN samples using atomic force microscopy and scanning electron microscopy showed different island distributions and shapes by varying the growth temperature. High resolution-X-ray diffraction (HRXRD) enabled to identify a single crystalline phase (hexagonal wurtzite), whatever the growth temperature. Actually, the increase of growth temperature up to 560 °C has improved the crystalline quality; whereas for high temperature, the crystalline quality degrades. The dislocation density of the epilayer grown at this optimum temperature (around 560 °C) is about 1.9 × 1010 cm−2, which is determined using HRXRD spectra analysis. High compressive residual stress value of 0.54 GPa was derived using Raman spectroscopy. Room temperature photoluminescence (PL) displays a band gap energy around 0.69 eV. Besides, Burstein-Moss effect, the PL band gap energy measured at 10 K is dictated by the biaxial compressive residual stresses. Nanoindentation tests were carried out on InN epilayers. Only, the sample grown at 560 °C exhibited a pop-in event, for which the measured hardness and Young’s modulus are of 4.5 ± 0.5 GPa and of 171 ± 8 GPa, respectively. Accordingly, the growth temperature of InN epilayers influences the resulting physical and mechanical performances, thus a good compromise between physical and mechanical features permits to manufacture efficient devices.

Highly Effective Disinfection of E. coli Using the Nanohybrids Ti1−xNixO2/CNTs

The nanohybrids Ti1−xNixO2/CNTs (x = 0; 0.01; 0.03; 0.06; 0.09) were synthesized by hydrolysis. The samples were characterized by high-resolution transmission electron microscopy (HR-TEM), x-ray diffraction (XRD), and optical absorption spectra (UV–Vis). The XRD analysis shows that the Ni-doped TiO2 exists mainly in the form of the anatase phase. The average size of TiO2 nanoparticles attached on the surface of the carbon nanotubes (CNTs) was found to be around 8 nm (based on the results from the XRD and HR-TEM images). The UV–Vis spectra of the Ti1−xNixO2/CNTs reveal not only a redshift due to the Ni-doping, but also an increase in the absorbance in the visible range due to nanohybridization of CNTs. The photocatalytic activity of the samples was tested by antibacterial activity against Escherichia coli. The results show that almost 100% of E. coli was destroyed, indicating a significantly much higher activity than that of pure TiO2.

Insights into the C Distribution in Si:C/Si:C:P and the Annealing Behavior of Si:C Layers

Si:C and Si:C:P alloys are potential candidates for source-drain stressor applications in n-type Fin Field Effect Transistors (FinFETs). Increasing the C content to achieve high strain results in the arrangement of C atoms as third nearest neighbors (3nn) in the Si:C lattice. During thermal annealing, the presence of C atoms as 3nn may promote clustering at the interstitial sites, causing loss of stress. The concentration of C atoms as 3nn is reduced by the incorporation of a small amount of Ge atoms during the growth, whereas in-situ P doping does not influence this 3nn distribution [J Solid State Sci. Technol vol 6, p 755, 2017]. Small amounts of Ge are provided during low temperature selective epitaxial growth scheme, which are based on cyclic deposition and etching (CDE). In this work, we aim to provide physical insights into the aforementioned phenomena, to understand the behavior of 3nn C atoms and the types of defects that are formed in the annealed Si:C films. Using ab-initio simulations, the Ge-C interaction in the Si matrix is investigated and this insight is used to explain how the Ge incorporation leads to a reduced 3nn distribution of the C atoms. The interaction between C and P in the Si:C:P films is also investigated to explain why the P incorporation has not led to a reduction in the 3nn distribution. We then report on the Raman characterization of Si:C layers subjected to post epi annealing. As the penetration depth of the laser is dependent on the wavelength, Raman measurements at two different wavelengths enable us to probe the depth distribution of 3nn C atoms after applying different annealing conditions. We observed a homogeneous loss in 3nn C throughout the layer. Whereas in the kinematic modeling of high resolution X-ray diffraction spectra, a gradient in the substitutional C loss was observed close to the epitaxial layer/substrate interface. This gradient can be due to the out diffusion of C atoms into the Si substrate or to the formation of interstitial C clusters, which cannot be distinguished in HR-XRD. Deep Level Transient Spectroscopy indicated that the prominent out-diffusing species was interstitial CO complex while the interstitial C defects were also prevalent in the epi layer.

Ultrasensitive zinc magnesium oxide nanorods based micro-sensor platform for UV detection and light trapping

A cost effective unique approach has been employed to realize high quality zinc magnesium oxide (Zn1-xMgxO) based nanostructures which can replace conventional material i.e. Zinc oxide (ZnO) in detector and sensor applications. High resolution structural studies showed the formation of vertically aligned hexagonal and truncated hexagonal nanorods on RF sputtered ZnO and Zn1-xMgxO seed layer. Single crystal Zn1-xMgxO and ZnO nanorods with dominant c-axis growth along (002) crystal axis and d-spacing of 0.262 and 0.266 nm, respectively were obtained from high resolution transmission electron microscopy, selective area diffraction pattern and high resolution X-ray diffraction spectra. The high external quantum efficiency of 12.054% with narrow full width half maxima of 12.63 nm was achieved from photoluminescence spectroscopy (Zn1-xMgxO nanorods) performed at room temperature. Approximately two order of enhancement in current density was observed from photodetector fabricated using Zn1-xMgxO nanorods. A state of art peak responsivity of 62.19 A/W at 350 nm attributed to near band edge emission peak and high current rectification capability with a maximum internal gain of 185 was measured from Zn1-xMgxO detector. Zn1-xMgxO detector exhibited temporal response with reasonable rise and fall time constants along with three order higher detectivity values in comparison to ZnO detector. A DC current based humidity sensor was fabricated and characterized using sample synthesized for longer growth duration. High sensitivity of 1.612 /% RH was achieved and low recovery time was observed as the sample was subjected to annealing treatment.

Controlled synthesis of manganese tungstate nanorods for highly selective NH3 gas sensor

In this paper, single-crystalline MnWO4 nanorods were prepared through a facile single-step hydrothermal approach and used for gas sensing. The morphology and phase of the products were characterized in detail through transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and elemental dispersive spectrum analyses. Results showed that the as-prepared MnWO4 nanorods possess uniform shape with their length of 250–300 nm and width of 20–30 nm. The nanorods were used to fabricate sensors for detecting reducing gases such as NH3, H2 and CO and evaluate gas sensing properties. The sensors exhibit not only good response and fast response time, but also almost full recovery and good stability, to NH3 gas.

Effect of C/Si Moore Ratio on the Morphology and Crystallinity of 3C-SiC/Si(100) by the Modified Two-Step Carbonization Process

A modified two-step carbonization process was used to growth high oriented 3C-SiC films on Si(100) substrates by using SiH4 and C3H8 as precursors. The investigation revealed that the C/Si Moore ratio has important influences on the SiC nucleation model on Si substrates and the crystal quality of 3C-SiC films. The effect of C/Si Moore ratio on the SiC/Si(100) were evaluated by Microscopy and SEM. This indicates that the growth model of the individual nuclei gradually changed from vertical to lateral growth as the C/Si Moore ratio increased. High-resolution X-ray diffraction and Raman spectra were used to analyze the crystalline quality of 3C-SiC films grown at 1385 °C under different C/Si ratios. The results showed that the optimum C/Si Moore ratio for high oriented and high crystal quality 3C-SiC films was 1.6. The mirro-like high-crystallinity 3C-SiC films on the Si(100) was grown with a 1.6 C/Si ratio at 1385 °C for 1hr. The surface roughness was 3.6nm.DOI: http://dx.doi.org/10.5755/j01.ms.23.3.16323

Upconversion photoluminescence of core-shell structured SiO2@YVO4:Yb3+, Er3+, Eu3+ nanospheres.

Core-shell structured SiO2@YVO4:Yb3+, Er3+, Eu3+ nanospheres were prepared by a simple solgel method followed by a subsequent heat treatment. The as-prepared composites were characterized by a scanning electron microscope, high-resolution transmission electron microscope, x-ray diffraction, and photoluminescence spectra. The influences of different coating numbers were also studied. To sum up, the composites are spherical shaped with an average diameter of 200 nm, and the YVO4:Yb3+, Er3+, Eu3+ luminescent particles are successfully coated on the surface of SiO2 nanospheres. Under the near-infrared irradiation at 980 nm, the composites can emit strong green lights (at 525 nm, 550 nm) attributed to the H11/22→I15/24, S3/24→I15/24 transitions of Er3+ ions, and slight red lights (at 590 nm, 620 nm) attributed to the D05→F17, D05→F27 transitions of Eu3+ ions. Given the above, due to the regular core-shell structure, the uniform distribution of nanoparticles, and the colorful emissions, the SiO2@YVO4:Yb3+, Er3+, Eu3+ nanospheres may have great potential for some biological applications, such as biological tracers, bio-labeling, and so on.

Investigation on crystalline perfection, optical transmittance, birefringence, temperature-dependent refractive index, laser damage threshold and pyroelectric characteristics of inversely soluble lithium sulfate monohydrate single crystals

Bulk prismatic lithium sulfate monohydrate (LSMH) single crystals were grown by seed rotation with slow heating method from aqueous solution. Small FWHM obtained from high-resolution X-ray diffraction spectrum shows that the crystals grown by this method have less defects and absence of low-angle grain boundaries. The high transmittance and low reflectance nature of the grown crystal was observed using UV–Vis–NIR spectrometer. The principal refractive indices of a LSMH crystal have been measured by a prism coupling method for the wavelengths of 0.407, 0.532, 0.828, 1.064 and 1.551 µm at room temperature, and Sellmeier equations are determined from the fitting of the data point. The refractive index data confirm that LSMH crystal is negative biaxial and the optic axis lies in YZ plane with an angle (2Vy) of 51.74° with respect to y axis at 532 nm wavelength. The thermo-optic coefficients were determined from the temperature-dependent refractive indices measured in the range of 30–125 °C for the wavelengths of 532 and 1064 nm. The surface laser damage threshold studies reveal the higher optical radiation stability against 532-nm laser. The pyroelectric coefficients and pyroelectric figure of merit were determined from the pyroelectric current measurement by the Byer and Roundy method.

Effects of growth temperature on the properties of InGaN channel heterostructures grown by pulsed metal organic chemical vapor deposition

Pulsed metal organic chemical vapor deposition (P-MOCVD) is introduced into the growth of high quality InGaN channel heterostructures. The effects of InGaN channel growth temperature on the structural and transport properties of the heterostructures are investigated in detail. High resolution x-ray diffraction (HRXRD) and Photoluminescence (PL) spectra indicate that the quality of InGaN channel strongly depends on the growth temperature. Meanwhile, the atomic force microscopy (AFM) results show that the interface morphology between the InGaN channel and the barrier layer also relies on the growth temperature. Since the variation of material properties of InGaN channel has a significant influence on the electrical properties of InAlN/InGaN heterostructures, the optimal transport properties can be achieved by adjusting the growth temperature. A very high two dimension electron gas (2DEG) density of 1.92 × 1013 cm−2 and Hall electron mobility of 1025 cm2/(V⋅s) at room temperature are obtained at the optimal growth temperature around 740 °C. The excellent transport properties in our work indicate that the heterostructure with InGaN channel is a promising candidate for the microwave power devices, and the results in this paper will be instructive for further study of the InGaN channel heterostructures.

Led InGaN/GaN Structures with Short-Period Superlattice Grown on Flat and Patterned Sapphire Substrates

The results of studies of blue LED InGaN/GaN heterostructures with a short-period InGaN/GaN superlattice in front of an active region of the structure grown on flat and patterned Al2O3 substrates are presented. In these structures, an increase of the internal quantum efficiency is observed. The high-resolution X-ray diffraction spectra and the integrated PL intensity are measured for two temperatures – 10 and 300 K – at different levels of optical YAG-laser pumping.

Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

We use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellent quantitative match to all important aspects of the x-ray data.

Optical and structural properties of single-crystal lithium niobate thin film

High-refractive-index contrast, single-crystal lithium niobate thin films are emerging as a new platform for integrated optics. Such lithium niobate thin films are prepared using ion implantation and direct-wafer bonding to a SiO2 layer deposited on a LN substrate. However, the ion-implantation process can cause changes in the refractive index and result in lattice damage, and there are few studies on the optical and structural properties of lithium niobate thin film to compensate for this. In this paper, we reported that the refractive index of lithium niobate thin film can reach that of the bulk material by annealing in an oxygen atmosphere at 500°C for 5h. The experimental results of high-resolution X-ray diffraction (HRXRD) and Rutherford back-scattering spectrum (RBS) showed a good crystal lattice arrangement in the LN thin film. These experimental results confirmed that the refractive index and crystal-lattice structural properties of the lithium niobate thin film were similar to that of the bulk material. To demonstrate the application on integrated optics, a 1μm wide photonic wire was fabricated and the near-field intensity profile at 1.55μm wavelength was obtained and compared with the simulation result.

Nano-Crystalline Diamond Films with Pineapple-Like Morphology Grown by the DC Arcjet vapor Deposition Method

A nano-crystlline diamond film is grown by the dc arcjet chemical vapor deposition method. The film is characterized by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and Raman spectra, respectively. The nanocrystalline grains are averagely with 80 nm in the size measured by XRD, and further proven by Raman and HRTEM. The observed novel morphology of the growth surface, pineapple-like morphology, is constructed by cubo-octahedral growth zones with a smooth faceted top surface and coarse side surfaces. The as-grown film possesses (100) dominant surface containing a little amorphous sp2 component, which is far different from the nano-crystalline film with the usual cauliflower-like morphology.

Dual-superlattice calibrations for group-III species in III-V semiconductor epitaxial structure growth

High-resolution x-ray diffraction analysis of superlattice structures is often used to calibrate epitaxial growth systems. In most cases, systematic errors introduce biases that overwhelm the random measurement error, thus requiring a series of calibrations to be completed in order to target a narrow range of materials. Structures consisting of two superlattices grown with a single pair of group-III sources offer significant improvements in calibrating group-III growth rates over conventional single-superlattice structures. It is shown that these dual superlattices avoid pitfalls associated with uncertainty and variability in the lattice constants and elastic constants of the constituent materials as well as those of the substrate. Analyses of the high-resolution x-ray diffraction spectra for several different binary/binary, ternary/binary, and quaternary/binary superlattices provide accurate determination of group-III beam fluxes, leading to the capability of reproducing growth rates with accuracy of within 1%.

Growth of Ge1−xSnx/Ge strained-layer superlattices on Si(1 0 0) by molecular beam epitaxy

Low-temperature molecular beam epitaxy was employed to grow Ge1−xSnx/Ge strained-layer superlattices (SLSs) on Si(100) substrates with a Ge buffer layer. The Ge1−xSnx and Ge layers in the SLSs were deposited at the same temperature as low as 180°C. Surface roughening during the growth was investigated by in situ reflection high-energy electron diffraction (RHEED). The periods, compositions, and quality of the SLSs were characterized by high resolution X-ray diffraction (HR-XRD), random and aligned Rutherford backscattering spectra (RBS), transmission electron microscopy (TEM), and scanning TEM. Besides, a Ge1−xSnx/Ge SLS sample was grown directly on Si(100) for comparison. It’s found that the quality of the Ge1−xSnx/Ge SLSs grown on a Ge buffer was significantly better than that grown directly on Si(100) substrate.