Deterioration Of Crystal Quality Research Articles

Trace Al component in ε-(AlxGa1-x)2O3 alloy films and film-based solar-blind photodetectors

ε-(AlxGa1-x)2O3 alloy thin films containing Al fractions of 0, 2.9 at%, and 4.7 at% with ε-Ga2O3 templates were fabricated on (0001) c-sapphire by tin-assisted PLD technique. Sn is a surface-mediated surfactant to stabilize the formation of epsilon phase. XRD reveals that the peak position of ε-(AlxGa1-x)2O3 shifts to a higher diffraction angle and that ε-(AlxGa1-x)2O3 is accompanied by a deterioration of crystal quality when the Al composition increases from 0 to 4.7 at%. With Al content increasing, XPS demonstrates the appearance of more aluminum atoms bound to oxygen atoms and higher oxygen vacancy density in ε-(AlxGa1-x)2O3 films. The optical bandgap for ε-(AlxGa1−x)2O3 thin films with various Al components are 4.97 eV, 5.09 eV and 5.16 eV, respectively. The solar-blind photodetectors were fabricated on ε-(AlxGa1-x)2O3 alloy thin films with various Al fractions. The photo-to-dark current ratio, responsiveness, detectivity and response time (rise time/decay time) for ε-(AlxGa1-x)2O3 (x = 2.9 at%) PDs were 2.7 × 103, 4.2 A/W, 1.23 × 1013 Jones and 2.09 s/0.49 s.

Epitaxial Growth of “Strain-Free” Indium Oxide Films on (111) Yttria-Stabilized Zirconia by Metal-Organic Chemical Vapor Deposition

In this work, In2O3 thin films were grown on (111) yttria-stabilized zirconia (YSZ) by metal-organic chemical vapor deposition (MOCVD) at different temperature. It is found that samples grown at low temperature showed lower residual stress but higher mosaicity while high growth temperatures could also cause deterioration in crystal quality due to increasing lattice mismatch. To obtain high quality In2O3 film with low residual strain, a 30-nm thick layer grown at 530 °C was introduced as buffer layer, considering both stress relaxation and crystalline mosaicity. By using two-step growth method, a 400 nm-thick, high quality, near-strain-free In2O3 thin film with the full width at half maximum (FWHM) values of (222) diffraction peaks being as narrow as 648 arcsec was successfully obtained.

Fastly steady UV response feature of Mn-doped ZnO thin films

Abstract When the conventional zinc oxide film is used as an ultraviolet detector, it has the disadvantages of slow response time, unstable signal. In order to solve this problem, Mn-doped ZnO films (MZO) were prepared by sol-gel method in this work. Results show that Mn doping can cause deterioration of crystal quality, photocurrent and dark current will decrease at the same time, but in low doping mode (1.5 at.%), the response time of the film can be greatly improved (from about 100 s to 10 s), and the photocurrent is very stable. Moreover, since the dark current is simultaneously weakened, the signal-to-noise ratio is not significantly reduced and is still acceptable. Further increasing the doping concentration, the photocurrent and the dark current continue to decrease. Although a faster photoelectric response is obtained, since the photocurrent is too weak, the electrode is extracted more than the rate at which the photocurrent is generated, and the photocurrent has a tendency to decrease.

Physical properties of RF magnetron sputtered GaN/n-Si thin film: impacts of RF power

GaN thin film was successfully produced on $$n{\text{-}}Si\left({100} \right)$$ substrate by RF magnetron sputter under different RF power. Experimental measurement techniques such as UV/Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Micro-Raman Spectroscopy were used to research effects of Radio Frequency power on physical properties of produced thin film. It has been found that produced thin film was polycrystalline structure with (100) and (110) planes of hexagonal $$GaN$$ from X-ray diffraction measurement result. It also proved that increasing RF power gives rise to deterioration in crystal quality of $$GaN$$ thin film. Reason of this deterioration was discussed. It has been achieved that increasing RF power has resulted in decreasing optical band gap energy of $$GaN$$ thin film. Reasons for these changes in optical band gap energy were explained. It was seen that some thin films were grown as layer-plus-island mode (Stranski–Krastanov growth mode) and others were grown as layer-by-layer growth mode (Frank van der Merwe mode) from AFM analysis. It has been found that increasing RF power has resulted in improvement of surface morphology of thin film from field emission scanning electron microscopy analysis. However, reaching RF power to 125 W leads to start to deteriorate of surface of $$GaN$$ thin film. The reasons for this have been discussed. $$E_{1} \left( {TO} \right)$$ transverse optical phonon mode of hexagonal $$GaN$$ with different intensity was detected from Micro-Raman Spectroscopy measurement. The reasons for this difference have been discussed. It was concluded that RF power has played a significant role in growing high quality $$GaN$$ thin film. Morphological, structural, and optical properties of $$GaN$$ thin film were enhanced by controlling RF power, making them a potential candidate for LED, solar cell, diode application.

Impact of sputter deposition parameters on the microstructural and piezoelectric properties of CrxAl1 −xN thin films

In the field of MEMS, aluminum nitride (AlN) in the wurtzite phase is an important functional material due to its piezoelectricity. To further enhance device performance, transition metal alloying of AlN is proposed to achieve a higher piezoelectric response. In this work, the effect of moderate chromium (Cr) doping (up to x=(5.0±0.6) at.%) as well as the influence of changing deposition pressures and gas composition are investigated, focusing on the microstructure, morphology and piezoelectric response of sputter deposited CrxAl1−xN thin films. X-ray diffraction analyses reveal a wurtzite type structure with highest degree in c-axis orientation for lowest deposition pressures and Cr concentrations. With increasing deposition pressure, a deterioration in crystal quality and the formation of other crystal orientations within the films are observed. The presence of crystallite orientations away from the 〈002〉 orientation is linked to the presence of randomly oriented, conical-shaped grains which are embedded in the fine grainy thin film surface topography as indicated by atomic force microscopy. By using piezo force microscopy, these grains are identified to cause a reduction in the effective piezoelectric response. Furthermore, we show that combining both the analysis of orientation distribution and surface morphology, is by far more reliable for estimating the piezoelectric response of thin films than the sole use of one method.

Strong red emission and catalytic properties of ZnO by adding Eu2O3 shell

The structural, optical properties and catalytic activity of ZnO@Eu2O3 core-shell nanostructutres have been investigated systematically. Sharp intense red emissions in the range of 580–650 nm due to the intra-4f transition of Eu3+ ions are observed from the sample. It is found that some of the Eu3+ ions are in the Eu2O3-like state located at the surface of ZnO and others are doped into ZnO host. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. Adding the Eu2O3 layer increased the number of excited carriers within ZnO, thus enhancing the luminescence and photocatalysis properties. Our findings not only open an avenue for synthesis sophisticated ZnO@Eu2O3 core-shell nanostructutres but also pave a way towards improving red emission and photocatalysis properties in ZnO nanostructures.

Growth and Characterization of InAs1–xSbx with Different Sb Compositions on GaAs Substrates**Supported by the Aeronautical Science Foundation of China under Grant No 20132435, the National High-Technology Research and Development Program of China under Grant No 2013AA031903, the National Natural Science Foundation of China under Grant Nos 61106013 and 61275107, and the China Postdoctoral Science Foundation under Grant No 2014M560936.

InAs1–xSbx with different compositions is grown by molecular beam epitaxy on (100)-oriented semi-insulating GaAs substrates. The increase of Sb content in the epilayer results in the deterioration of crystal quality and surface morphology. Hall measurements show that the carrier concentration increases with the composition of Sb. The electron mobility decreases initially, when Sb composition exceeds a certain value, and the mobility increases slightly. In this work, we emphasize the comparison of crystal quality, surface morphology and electrical properties of epilayers with different Sb compositions.

Crystallization rate control for alkali halide crystal growth by the VGF technique with a skull layer

This study describes the ability to use the melt‐level control for stabilization of the crystallization rate during NaI crystal growth by the VGF technique with a skull layer. It is shown that a conventional linear decrease of the heater temperature leads to a nonuniform crystallization rate and deterioration of crystal quality. A method and algorithm of temperature control for the stabilization of the crystallization rate during crystal growth is proposed. The series of growth experiments with NaI(Tl) crystals proved the efficiency of this approach and ability to obtain scintillators with high registration efficiency, about 6.3% energy resolution for a 137Cs (662 keV) source.

A semiconductor optical amplifier comprising highly stacked InAs quantum dots fabricated using the strain-compensation technique

A semiconductor optical amplifier was fabricated by incorporating highly stacked InAs quantum dots (QDs) as a gain media. Twenty InAs QD layers were successfully stacked through the strain-compensation technique, without any deterioration of crystal quality. A wide-range 1.55 µm band gain was observed, and maximum gain reached 25 dB at 1530 nm when the input power was below −40 dBm.

Laser ablation for protein crystal nucleation and seeding

With the recent development in pulsed lasers with ultrashort pulse widths or wavelengths, spatially precise, low-damage processing by femtosecond or deep-UV laser ablation has shown promise for the production of protein single crystals suitable for X-ray crystallography. Femtosecond laser processing of supersaturated solutions can shorten the protein nucleation period or can induce nucleation at low supersaturation, which improves the crystal quality of various proteins including membrane proteins and supra-complexes. In addition to nucleation, processing of protein crystals by femtosecond or deep-UV laser ablation can produce single crystalline micro- or macro-seeds without deterioration of crystal quality. This tutorial review gives an overview of the successful application of laser ablation techniques to nucleation and seeding for the production of protein single crystals, and also describes the advantages from a physico-chemical perspective.

Sn-Modified ZSM-5 As Support for Platinum Catalyst in Propane Dehydrogenation

Sn modified ZSM-5 was hydrothermally synthesized and this kind of zeolite was used as the support for platinum catalyst in propane dehydrogenation. In this tin-doped material, XRD results established the presence of highly crystalline and the analysis of SEM showed the deterioration in crystal quality. The incorporation of Sn into the framework of ZSM-5 zeolite introduced the strong interactions between Sn species and the support, thus more amounts of tin could exist in oxidized form. Moreover, on the Sn-containing PtNa/Sn-ZSM-5 catalyst, the substitution of Sn changed the interfacial character between Pt and the support, which in consequence promoted the occurrence of spillover hydrogen and facilitated the reduction of Pt species. Compared with the conventional impregnated PtNa/HZSM-5 and PtSnNa/HZSM-5 catalysts, the Sn-modified ZSM-5-based Pt catalyst exhibited higher reaction activity and stability. It showed the lowest deactivation parameter (6.2%) and exhibited a selectivity to propene higher than 98...

Forming Gas Annealing Induced Degradation in Nanoscale Electrical Homogeneity of Bismuth Ferrite Thin Films

In this study, 60 nm-thick BiFeO3(BFO) thin films with (h00) orientation were successfully grown on LaNiO3(LNO)-buffered Pt/Ti/SiO2/Si(100) substrates. The effects of the temperature (300–500°C) of forming gas (7% H2 + 93% Ar) annealing (FGA) on the physical properties of the BFO thin films were investigated. The x-ray diffraction results show that the higher FGA temperature results in a larger degree of deterioration in crystal quality of the BFO thin films. This change can be attributed to a loss of oxygen from the BFO thin films and the incorporation of hydrogen atoms into the lattice of the film during FGA. FGA produces an increase in surface roughness for the BFO thin films. The current maps obtained by conductive atomic force microscopy demonstrate that the leakage behaviors of BFO thin films, with and without FGA, at various temperatures under the breakdown electric field, are different. The leakage currents are detected mostly in areas surrounding large crystallites in BFO thin films with or without FGA at 300°C. In contrast, large crystallites in the BFO thin films with FGA at 400–500°C are electrically leaky and the detected currents are high compared to those of BFO thin films with and without FGA at 300°C.

Correlation between structural and luminescent properties of Eu3+-doped ZnO epitaxial layers

We have studied the epitaxial growth and photoluminescent (PL) properties of Eu3+-doped ZnO layers in correlation with structural analyses. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. The spectral structure of Eu3+ emission revealed that Eu3+ ions were located at site symmetries lower than the original C3v of the Zn2+ ion sites in a hexagonal wurtzite structure of ZnO, which allowed for efficient red luminescence based on the electric dipole transitions. Moreover, we have found an anticorrelation of PL intensity between the excitonic and Eu3+ emissions, related to energy transfer from the ZnO host to the Eu3+ ions. The excitonic structure at the band edge was obscured upon doping with Eu3+ ions due to the formation of a band tail around 3.2 eV. This correlated with a reduction in excitonic emissions, leading to enhancement of Eu3+ emission. Strong PL emission from Eu3+ ions was only observed at low temperatures, and was remarkably suppressed with increasing temperature due to two types of nonradiative energy transfer paths. For the energy transfer process to Eu3+ ions, we suggest that the recombination energy of an electron–hole pair at the band tail near the band edge is close to that of high-lying excited levels in the Eu3+ 4f shell, providing an efficient energy pathway for the excitation of Eu3+ ions in the ZnO system.

Microstructure and photoluminescence study of vanadium-doped ZnO films

Zn1−xVxO films (x = 0, 1.3, 1.9, 2.6, 3.5, 4.3 and 6.2 at%) were prepared on glass substrates via the direct current reactive magnetron co-sputtering method. The microstructure, band gap, photoluminescence and Raman scattering of these films have been systematically investigated. The structural and chemical state characterizations indicate that the crystallinity of Zn1−xVxO films (x ⩽ 2.6 at%) can be improved by V incorporation into the ZnO wurtzite lattice, but excess V will precipitate as V clusters when x ⩾ 4.3 at%, resulting in the deterioration of crystal quality. The defects in Zn1−xVxO films (x ⩽ 2.6 at%) can be suppressed by V doping, which induces the enhancement of the near band edge (NBE) emission. However, when x ⩾ 4.3 at%, defects adjacent to the V dopant quench the NBE emission. On the other hand, the band gap of the films gradually increases with the increase in V concentration, which is accompanied by the blue shift of the NBE emission.

Room temperature ferromagnetism of GaN:Mn thin films grown by low pressure metal-organic chemical vapor deposition by mn periodic delta-doping

Epitaxial films of GaN:Mn have been grown on c-sapphire substrates by low pressure metal-organic chemical vapor deposition (LP-MOCVD) by Mn periodic delta-doping. The samples showed ferromagnetic behavior at room temperature with hysteresis curves showing a coercivity of 170 Oe. No ferromagnetic second phases and no significant deterioration in crystal quality with the incorporation of Mn were detected by high-resolution X-ray diffraction (XRD). The Mn concentrations of the layers were determined to be 0.227% by proton induced X-ray emission (PIXE).

Phasing on Rapidly Soaked Ions

Publisher Summary There are three basic ways of solving macromolecular crystal structures: (1) the molecular replacement method, (2) direct methods, and (3) the heavy-atom method. Molecular replacement involves the use of a known search model, closely similar to the macromolecule being investigated. Direct methods are routinely used to solve structures of small molecules, where the diffraction data extend to atomic resolution. As a consequence, these two methods cannot be used to solve novel structures with crystals diffracting to lower than atomic resolution. The heavy atoms, providing the initial phase information, can be present in the original macromolecule, such as certain transition metals in metalloproteins, sulfur in proteins, and phosphorus in nucleic acids. However, most general is the derivatization before or after crystallization. The classic derivatization approach involves prolonged soaking of the native crystals in diluted solutions of various heavy-metal salts and coordination compounds. Such soaking procedures are time consuming and are often unsuccessful owing to the lack of heavy-atom binding or the deterioration of crystal quality. The rapid soak approach uses this property of protein crystals that allows small ions to diffuse within a short time to the solvent regions surrounding the protein molecules and adopt ordered sites at their surfaces.

Substitutional versus interstitial carbon incorporation during pseudomorphic growth of Si1−yCy on Si(001)

Molecular beam epitaxial growth of Si1−yCy alloys pseudomorphically strained on the (2×1) reconstructed Si(001) has been investigated as a function of growth conditions. An important question concerns the relation between substitutional and interstitial carbon incorporation, which has a large impact on electrical and optical properties of these layers. We show that the interstitial-to-substitutional carbon ratio is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. Both reduction in growth temperature and increase of the overall growth rate lead to an increase in the substitutional-to-interstitial carbon ratio. However, these changes in growth conditions can also cause some deterioration in crystal quality. The carbon incorporation behavior is well described by first order kinetics.

The growth and perfection of organic non-linear optical crystals: N-methyl urea (NMU) from methanol solution. II. Morphological instability

Studies of the anisotropy of the kinetics of growth of N-methyl urea (NMU) crystals have shown that the dominant influence on the growth process is volume diffusion rather than solvent—surface interactions. The consequence of this is that even at low supersaturations the crystals become morphologically unstable with the ready inclusion of solvent and consequent deterioration of crystal quality. This paper reports on studies of the development of this instability in order to define the conditions for the stable growth of crystals of this material for non-linear optical devices.

Dose dependence of crystallinity and resistivity in ion beam synthesised CoSi 2 layers

Epitaxial CoSi 2 layers have been fabricated in silicon by implanting 200 keV cobalt ions to doses of 2 × 10 17–7 × 10 17 Co + cm −2. For the lower doses (2 × 10 17 and 3 × 10 17 Co + cm −2) the synthesised layers, after implantation, are silicon-rich and consist of A- and B-type CoSi 2 precipitates interwoven by silicon. For the medium doses (4 × 10 17 and 5 × 10 17 Co + cm −2) an epitaxial aligned layer of CoSi 2 is formed after implantation, with any excess cobalt being incorporated in small CoSi inclusions at the peak of the distribution. For the highest doses (6 × 10 17–7 × 10 17 Co + cm −2) preferential sputtering of the silicon at the surface of the synthesised layer means that this region is cobalt-rich and grains of CoSi form above the epitaxial CoSi 2 layer. As the dose is increased up to 5 × 10 17 Co + cm −2, the crystallinity of the layer improves, after which it deteriorates again as the thickness of the layer of CoSi grains increases. The degradation in crystallinity is accompanied by a rise in resistivity and this can be correlated to the value of x in CoSi x . When x ≠ 2 then the resistivity of the layer increases and there is a corresponding deterioration in crystal quality. After annealing the resistivity of the CoSi 2 layer decreases and the crystallinity improves as the ratio of Co: Si approaches that in the stoichiometric compound (CoSi 2).

1990 C R burch prize-joint award: Ion beam synthesis of epitaxial CoSi 2 layers

Epitaxial CoSi 2 have been layers fabricated by implanting 200 keV cobalt ions, to doses between 1.5×10 17 and 7×10 17 Co + cm −2, into (100), (110) and (111) single crystal silicon substrates. The experimental results after implantation are in close agreement with those obtained from computer simulations using single crystal targets. The as implanted structures for the lower doses (1.5×10 17→3×10 17 Co + cm −2) are silicon rich and consist of a mixture of A- and B-type CoSi 2 precipitates interwoven by silicon. For the medium doses (4×10 17→5×10 17 Co + cm −2) an epitaxial layer of CoSi 2 is formed with any excess cobalt being incorporated in small CoSi inclusions, at the peak of the implanted distribution. For the highest doses (6×10 17→7×10 17 Co + cm −2) preferential sputtering of silicon at the surface of the silicide causes this region to become increasingly rich in cobalt. To accomodate this cobalt excess, grains of CoSi form above the epitaxial CoSi 2 layer. As the dose is increased up to 5×10 17 Co + cm −2 the crystallinity of the synthesised layer improves and there is a corresponding decrease in resistivity, after which any further increase in dose causes the crystallinity to deteriorate again and the resistivity to increase. These changes can be correlated with the value of x in CoSi x , i.e. when the layer is either rich in cobalt or silicon (2>×>2) the resistivity increases and there is a corresponding deterioration in crystal quality. For all doses, furnace annealing (at 1000°C, 30 min) causes a decrease in resistivity and a corresponding improvement in crystallinity as the ratio of Co:Si approaches the value for the stoichiometric compound (CoSi 2). After rapid thermal annealing (RTA) at 1000°C for 5 s. the resistivity and crystal quality of the synthesised layer for the medium dose specimen (5×10 17 cm −2) are close to those achieved by conventional furnace annealing. For the higher and lower doses the crystal quality is slightly worse and the resistivity slightly higher than those for analogous samples which have been furnace annealed.