XRD Peak Shift Research Articles

New structural features and pinning-evolved coercivity mechanism: A potential route for developing high coercivities in anisotropic Sm-Fe-N material

Sm-Fe-N material holds immense promise as new material for developing next generation permanent magnets. However, the achievement of high coercivity in this material remains a big challenge, and moreover new coercivity theories beyond the commonly considered nucleation-type mechanism needs exploration. This study describes both the yielding of anisotropic Sm-Fe-N powders with high coercivities and the discovery of new coercivity mechanism by a systematic study using a designed milling preparation method. As a result, a random-direction cleavage behavior with unexpected XRD peak shifts and formation of new micron-sized flower-like particles were found in the yielded Sm-Fe-N powders. The grain sizes of the powders are of nanoscale dimension and they refine gradually as the milling time increases. The measured coercivity is up to 15.0 kOe, which is a substantial increase of approximately 36.4% compared to the original commercial powders and among the highest reported values via the milling preparation method (commonly below 13 kOe). The yielded powders also demonstrate a new dual-type coercivity mechanism (combing both nucleation-type and pinning-type control effect), and the improved pining effect contributes to the high coercivities. This study opens the door of utilizing pinning effect for achieving high coercivities in anisotropic Sm-Fe-N material.

Reverse strain effects in the defect states in aluminium doped ZnO

ZnO was synthesised by the sol–gel method using zinc nitrate as the precursor. ZnO was doped with Al. Stress in the lattice was evident from the XRD peak shifts. A higher concentration of Al+3 showed a reverse strain effect also causing a reverse effect in the optical properties. An increase in crystallite size due to increased Al+3 was observed. A variation in absorption intensity based on the defect energy levels was observed. A difference in energy of the emission and absorption spectra resulting from defects in the material and non-radiative decay was seen. A change in the band gap was observed with changes in different dopant concentrations. These findings are useful for photocatalytic as well as antibacterial and anticancer treatments.

Synthesis of W/Fe co-doped g-C3N4 decorated with Au nanoparticles for photocatalytic performance

Water pollution is one of the important issues in the world. It was reported that the lack of drinking water would be one of the important problems for many countries in the future. Therefore, finding new materials for the decontamination of water from different kinds of toxins is of great importance. In the present study, W/Fe co-doped g-C3N4 decorated with Au nanoparticles was prepared via a facile thermal treatment method. The synthesized specimens were used as a photocatalyst for water decontamination. The XRD findings revealed that crystalline g-C3N4 was formed after heat treatment. The addition of W and Fe to the g-C3N4 led to an XRD peak shift to the lower angles. XPS analysis confirmed the successful doping of W and Fe elements into the g-C3N4. TEM image showed that gold particles with an average size of 100 nm were uniformly dispersed on the surface of layered g-C3N4. The band gap energy of samples decreased from 2.69 eV to 2.59 eV by the addition of tungsten and iron to g-C3N4, whereas the deposition of gold nanoparticles did not have an important effect on band gap and improved the light-harvesting via the SPR phenomenon. The W/Fe co-doped g-C3N4 decorated with Au had a higher photocatalytic yield compared to other specimens. The possible mechanisms of dye removal and the role of reactive species on photocatalytic activity via the produced samples were discussed.

Cation Diffusion in Non-Stoichiometric (La, Sr)MnO3/CeO2 Nano-Composite Cathode

Co-sintering of stacks or cells containing electrodes, electrolytes, and separators is essential fabrication technology to improve power density per unit volume significantly. Generally, cathode materials have low heat-resistant temperatures, and they are easily decomposed or degraded by sintering at a high temperature. (La0.8Sr0.2) MnO3 (LSM) shows relatively high resistance and preferable low-reactivity with fluorite electrolytes during sintering at a high temperature. But it shows lower cathodic properties than lanthanum strontium cobaltite or lanthanum strontium cobalt ferrite because of poor oxygen diffusion. Thus, we have investigated LSM/ceria nanocomposite to improve oxygen diffusion.Nanocomposite precursor powder containing LSM and ceria was synthesized by glycine method. The composite ratio of LSM and ceria was fixed at 9:1 (molar ratio). The dense composite compact was obtained by sintering the powder at 1200oC for 5 h in air, and fine ceria particles were homogeneously dispersed with LSM. Electrical conductivity and oxygen diffusion coefficient were estimated with these dense composites. Oxygen diffusion coefficients were estimated by electrical conductivity relaxation method. The amount of cation dissolved in ceria was investigated from XRD peak shifts. The defect of La or Sr in LSM formed by sintering with ceria was estimated with magnetic properties of LSM and LSM/ceria nanocomposite. The defect was also investigated using the relationship between activation energy and composition of a-site defect LSM or La-defect LSM.LSM showed a low oxygen diffusion coefficient, and the coefficient of LSM/ceria nanocomposite was much improved even though ceria composite ratio is 10%. However, LSM/ceria composite showed much lower conductivity than LSM since a-site cation of LSM, La or Sr, may be easily diffused into ceria. XRD peaks derived from only ceria were shifted toward lower angle for LSM/ceria nanocomposite prepared under various sintering conditions. The shift revealed that 2-5% La in LSM was diffused into ceria, assuming that only La is diffused. Diffusion of La into ceria increases in oxide ionic conductivity and the diffusion would benefit the composite's cathodic properties in terms of oxygen diffusion. However, if the diffusion would bring about La defect LSM and deviations from the optimum composition, the diffusion would be detrimental in terms of electrical conductivity.Then we investigated the effects of the diffusion on the defect structure of LSM in LSM/ceria nanocomposite by magnetic properties and electrical conductivities. Assuming that only La of LSM was diffused into ceria, the loss amount of La from LSM was estimated with magnetic phase transition temperatures for LSM and LSM/ceria nanocomposite. The temperatures were measured by SQUID. The overall loss amount of La from LSM was increased according to solid solution of La in ceria. But, the loss amount was slightly different from the solution amount to ceria.The ionic radius of Sr2+ is similar to that of La3+. Dissolution of Sr in ceria also leads to XRD peaks shift toward lower angle as well as that of La. Then, we investigate whether the loss from LSM was derived from only La (La-defect LSM) or both La and Sr ( a-site-defect LSM). La-defect and a-site-defect LSM dense ceramics with various defect concentrations were prepared by glycine method. Activation energy of these LSM ceramics was estimated from the temperature dependence of electrical conductivity measured in air. That of La-defect LSM was monotonically decreased with increasing defect concentration. A-site-defect LSM showed no significant change in activation energy within the defect concentration less than 8%. The relationship between activation energy of LSM/ceria nanocomposite and the defect concentration of LSM was measured using various sintering conditions. The relationship showed the activation energy of LSM/ceria was almost independent of the defect concentration. Therefore, Sr would simultaneously diffuse from LSM to ceria during sintering LSM/ceria nanocomposite. Electrical degradation of LSM/ceria nanocomposite would be derived from Sr defect of LSM as well as La.

Single-step hydrothermal synthesis of nitrogen-doped ZnO nanostructures and an insight into its electrochemical properties

Zinc oxide (ZnO) nanostructures have been extensively used as electrochemical sensing material for the development of biosensors and bioimplantable devices. It is important to evaluate their electrochemical performance while developing materials with rapid response time and higher sensitivity. Herein, we present a novel one-step low-temperature hydrothermal technique for simultaneous nitrogen doping and growth of ZnO (N-ZnO) nanostructures. Nitrogen addition is expected to enhance the electron mobility and hence the electrical conductivity of ZnO. The nanostructures were characterized by X-ray diffraction, UV–Vis spectroscopy and field emission scanning electron microscopy. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry using an N-ZnO/Ag/Glass symmetric two-electrode system. The nitrogen addition to ZnO lattice is suggested by XRD peak shift, changing lattice parameters and dislocation density as compared to pristine ZnO. A substantial increase in the electrochemical response and conductivity can be attributed to nitrogen incorporation into ZnO lattice.

Mechanical Property and Heat Treatment Behaviour of Ti-Zr-Fe Alloys

The element of zirconium (Zr) belongs to the same group 4 as Ti in the periodic table. Therefore it possesses similar chemical properties. The Ti-Zr binary system forms a continuous solid solution for both high temperature β phase with the body centered cubic (BCC) structure and low temperature α phase with the hexagonal close-packed (HCP) structure throughout the entire range of composition. As is well known, on the other hand, the element of iron (Fe) is not only inevitable but also effective element in Ti.By incorporating Fe at the stage of alloy design, off-grade sponge titanium can be employed. Both elements seem to be effective in strengthening the titanium alloys. The purpose of this work was to prepare Ti-Zr-Fe alloys and then mechanical property and heat treatment behaviours were investigated as a fundamental research. Ti-x mass% Zr-1mass% Fe alloys (x=0, 5, 10) were melted in a laboratory-scale arc furnace under a high purity argon atmosphere from the sponge Ti, the sponge Zr and the Fe wire. The resulting ingots were hot forged and rolled at approximately 1120 K to obtain plates of approximately 2 mm in thickness. Well-mixed and homogeneous samples could be obtained, oxygen contaminations were less than 0.09 %. Solid solution of Zr into Ti was confirmed by the XRD peak shift in α phase. Vickers hardness and proof stress increased with Zr content. No remarkable changes could be observed in the microstructures after the solution treatment at 1173 K. However, Young’s modulus increased at x=10 by the treatment.

Synthesis and physical property of GaN:Mn nanoparticles

The GaN:Mn nanostructure was prepared using direct current (DC) arc discharge plasma method. No catalysts or templates are involved in the experiment. The test of energy dispersive x-ray spectroscopy (EDXS) detected the signals of Ga, N, Mn, and the Mn signal strength is slightly stronger with the increasing Mn content. The X-ray diffraction peak (XRD) is sharp, and there is a clear XRD peak shift towards larger angle with the increase of doping concentration. It is indicated that GaN:Mn nanoparticles have good crystallinity, and the introduced Mn has changed the lattice parameter. Photoluminescence (PL) shows that the absorption of visible light is a relatively broad range. The Mn doped induced the energy levels in the band gap, leading to the increasing of yield of electron-hole pair, and the optical property enhanced with the increasing of Mn concentration. Meanwhile the complicated magnetic transition has been found due to the quantum tunneling of magnetization. The magnetism is from the doped Mn, and its concentration impacts the strength of magnetic coupling.

Superior sunlight photocatalytic of N/La codoped ZnO nanostructures synthesized using different chelating agents

N/La codoped ZnO exhibited high sunlight activity, good reusability and rapid photodegradation for Congo red, malachite green and methylene blue dyes. Pure and N/La codoped ZnO were synthesized by sol gel using different chelating agents. All XRD patterns are fully indexed to hexagonal wurtzite structure of ZnO. The XRD peak shift and the increases in unit cell volume confirm the effective incorporation of N/La ions into ZnO. N/La blend extended the absorption ability of ZnO nanostructures to visible light region. Pure and N/La codoped ZnO synthesized by citric acid showed homogenous spherical nanoparticles distribution. Oxalic acid induced the formation of nanosheets and fine nanoparticles in N/La codoped ZnO. The adsorption capacity of pure and N/La codoped ZnO powders toward CR, MG and MB was less than 8%. The degradation of CR, MG and MB dyes under sunlight without catalyst is very weak. N/La codoped ZnO nanostructures exhibited superior sunlight photocatalytic activity for organic dyes degradation. N/La codoped ZnO–C and N/La codoped ZnO–O samples displayed remarkable photodegradation activities within 92–97% for CR, MG and MB in 60 min. N/La codoped ZnO–C showed a perfect photostability and reusability for four cycles. N and La enhance the charge carriers’ separation and the visible light absorption in ZnO which increase the photocatalytic activity.

Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1−x)O2 thin films

Polymorphic (HfxZr1−x)O2 (HZO) thin films exhibit ferroelectric, dielectric, and antiferroelectric properties across a wide compositional range due to the existence of orthorhombic, monoclinic, and tetragonal phases. To better understand the phase stability across the HfO2–ZrO2 compositional range, we investigate the structural evolution of HZO thin films in situ via high-temperature x-ray diffraction (HTXRD) for five different compositions [ZrO2, (Hf0.23Zr0.77)O2, (Hf0.43Zr0.57)O2, (Hf0.67Zr0.33)O2, and HfO2]. The real-time monitoring of HZO crystallization reveals a competing driving force between the tetragonal and monoclinic phase stabilities for HfO2-rich vs ZrO2-rich compositions. Additionally, we confirm an XRD peak shift toward lower 2θ with increasing temperature in ZrO2, (Hf0.23Zr0.77)O2, and (Hf0.43Zr0.57)O2 films, which we ascribe to the appearance of a metastable orthorhombic phase during heating. A monotonic trend for the onset crystallization temperature is reported for five compositions of HZO and reveals an increase in onset crystallization temperature for HfO2-rich compositions. Relative intensity fraction calculations suggest a higher fraction of monoclinic phase with increasing annealing temperature for (Hf0.67Zr0.33)O2. This study of phase stability and onset crystallization temperatures offers insight for managing the thermal budget for HZO thin films, especially for temperature-constrained processing.

Giant photostriction of CaCu3Ti4O12 ceramics under visible light illumination

Ferroelectrics with a perovskite structure, exhibiting strong coupling between photons, carriers, and phonons, have been demonstrated to show a strong photostrictive response. Limited by the optical bandgap, most of the reported ferroelectric perovskites respond only to UV light or weakly respond to visible light below 550 nm. Herein, the photostrictive performance of CaCu3Ti4O12 (CCTO) ceramics, with a low bandgap of ∼1.5 eV (ideal for solar spectrum absorption), is comprehensively investigated. Although the compound presents no ferroelectricity, in general, a giant photostriction of ∼10−3 with a large photostrictive efficiency of ∼10−11 m3/W in CCTO ceramics is observed by applying purple (405 nm), green (520 nm), and red (655 nm) laser illumination. Evidenced by the XRD peak shifts under external laser illumination and the phonon mode shifts via the power-dependent Raman spectrum, the light-induced non-thermal deformation in CCTO is attributed to the enhanced stretching of O–Ti–O chains and the distortions of TiO6 octahedrons. The excellent and uniform photostrictive performance of CCTO ceramics in the visible-light region makes them potential candidates for practical applications in next-generation photo-driven electromechanical devices.

Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites

AbstractLead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX3 (X=I, Br) perovskite nanocrystals with size control achieved by varying the concentration of a cysteammonium halide ligand. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX3 nanocrystals undergo a lattice expansion due to partial replacement of Cs+ with larger cysteNH3+ cations into their lattice. We successfully dope Mn2+ into the CsGeX3 lattice for the first time with incorporation of up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn2+ is doped into the lattice. Our results introduce a new member to the lead‐free halide perovskite family and set the fundamental stage for their use in optoelectronic devices.

Characterization investigations of the mechanically alloyed and sequentially milled Al-12.6 wt.% Si eutectic alloy powders

This study reports on the detailed microstructural characterization of Al-12.6 wt.% Si eutectic alloy powders synthesized from Al and Si elemental starting materials via mechanical alloying (MA) for 4, 6, and 8 h, and subsequent cryomilling (CM). Mechanically alloyed (MA’d) powders were cryomilled (CM’d) for 10, 20, and 30 min in a freezer/mill using liquid N2 gas circulated externally around the polycarbonate milling vial containing stainless steel rods. SEM/EDS and TEM/EDS mapping analyses revealed the presence of some Si embedded in the Al-rich particles and some existed as free Si. As expected, with increasing MA and sequential milling (MA + CM) duration, strain values increased and crystallite sizes decreased. Si solubility in α-Al was enhanced with increasing MA durations and utilizing MA and CM consecutively (sequential milling) as indicated by DSC endothermic and XRD peak shifts. A maximum solubility of 2.25 at.% Si in α-Al or Si solid solubility extension of 0.65 at.% was estimated for the Al12.6Si eutectic alloy powders MA’d for 8 h.

Mechanisms of atmospheric pressure plasma treatment of BOPP

Surface energy increase of polymers with plasma treatment is an industrially significant process. The mechanisms behind this process are little understood, with work addressing the water contact angle decrease with treatment and changes in surface chemistry. Work presented here addresses the mechanism of this surface energy increase, by using crystalline biaxially orientated polypropylene (BOPP) films to identify plasma induced structural changes. Increased crystallinity of the BOPP films were observed by ATR‐FTIR spectroscopy, indicating preferential oxidation of amorphous regions of the BOPP films by the plasma. This crystal structure change correlates with XRD peak shifts, implying relaxation of crystal regions into regions previously occupied by amorphous BOPP. The trend in surface energy increases also correlates with the effective increase in crystallinity.

Electrochemical Property of LiCoMnO4 Cathode Thin Film Prepared By PLD and Oxygen Post Annealing

Introduction Lithium ion batteries used in electric vehicles and high power/energy storage systems are required to improve their high voltage and capacity. Spinel structured lithium manganese cobalt oxide (LiMnCoO4) is a potential cathode material to solve these problems. Since, its operating potential (about 5V) is very high compared to other cathode materials. [1]. Moreover, its theoretical discharge capacity is 740 Wh/kg, which is 1.3 times higher than LiCoO2: the most popular cathode material at present. However, previous reports on cyclic voltammetry studies on LiCoMnO4 revealed an unexpected peak around 4V, in addition to the main peak at 5V corresponding to the Co3+/4+ redox couple. This electrochemical reaction at 4V reduces the capacity of LiCoMnO4 above 5V. [2]. This peak at 4V is associated with the Mn3+/4+ redox couple in the spinel structure. Pasero et al. reported that Mn3+/4+ redox peak is due to the loss of oxygen content in the LiCoMn1-2δ +4Mn2δ +3O4-δ structure where the oxygen loss increases the Mn3+ content [3]. They reported that the control of oxygen content is effective to increase the capacity above 5V. In this study, we tried to control the loss of oxygen content in LiCoMnO4thin films by post annealing process and to improve its capacity around 5V. Experiment LiCoMnO4 was prepared by solid-state reaction method using mixtures of Li2CO3, Co3O4 and MnCO3. All starting materials were ground thoroughly in an gate mortar, treated in a muffle furnace at 850℃ for 24 hour at a rate of 100℃/h. Following this, the samples were ball milled in a planetary mill for 2 hours and calcined at 600℃ for 12 h. The process was repeated thrice. A PLD target of LiCoMnO4was prepared by hydrostatic pressing at 75 MPa for 15 min and 90 MPa for 15 min followed by sintering at 600℃ for 24 h. LiCoMnO4 thin-films were grown by pulsed laser deposition (PLD) at room temperature with an oxygen partial pressure of 0.1Pa. After preparing the films were treated by post annealing condition to study the difference in structural change and electrochemical property by post annealing condition. After preparing the thin films, the samples were heated in atmospheric pressure of O2 at 500, 600, and 700℃ for 1 ~ 72 h at a rate of 800℃/h in a tube furnace and then cooled rapidly to room temperature. An electrochemical cell was assembled with the LiCoMnO4 thin film as positive electrode on a Pt/Cr/SiO2 glass substrate, Li metal as the negative electrode and reference electrode, and 1 mol/L LiPF6 in ethylene carbonate (EC:DMC, 1:1 volume,) as the electrolyte. Cyclic voltammetry (CV) was performed on the cell in the potential range of 3.0 - 5.3 V vs. Li/Li+at a scan rate of 0.5 mV/s. Results & Discussion The results of post annealing of LiCoMnO4 suggests that the optimum temperature is 600℃. Fig.1 shows the XRD peak profile for LiCoMnO4/Pt/Cr/SiO2 heated at 600℃ for 0h~72h. The as-prepared sample shows no peak corresponding to LiCoMnO4, confirming its amorphous structure. Upon annealing a peak appeared at 2θ value of 18° which is attributed to the (111) Bragg reflection of LiCoMnO4. Similarly, the XRD peaks of (311), (400), (333) and (400) are observed after post-annealing, which shows the formation of spinel structure of LiCoMnO4. Fig.2 shows the enlarged XRD spectra in the (311) reflection region as shown in Fig.1. The peaks were fitted with voigt profiles. All peaks are found to shift toward lower 2θ against the LiCoMnO4 target peak, which is shown the black line in Fig.2. These shifts are caused by oxygen deficiency in LiCoMnO4 thin-films. Oxygen deficiency is related to the crystal spacing and hence XRD peak shift. This result confirms that the post-anneal time strongly affects the oxygen deficiency amount in the LiCoMnO4 thin films. The CV of LiCoMnO4 ­thin films are shown in Fig.3. This result confirm that the post-annealing increases the capacity of LiCoMnO4 at 5V region due to the decrease in oxygen loss. However, the 4V region increases if the annealing time is longer than 6h. Thus, this study shows that the optimum condition for post-annealing is found to be at 600℃ for 6 h in 1 atm O2.

Ex-situ X-ray diffraction analysis of electrode strain at TiO2 atomic layer deposition/α-MoO3 interface in a novel aqueous potassium ion battery

The effect of thin film TiO2 atomic layer deposition (ALD) coating on induced material strain is investigated utilizing ex-situ XRD analysis of a layered-structured α-MoO3 anode. Electrode material lattice expansion is quantified by the examination of ex-situ XRD peak shift, and is performed on both potassiated and potassium-deficient electrodes. Observations of TiO2 ALD coated electrodes reveal significant strain reduction of the electrode material resulting in an increase in the life-cycle of the aqueous cells. The presence of the 10 nm thick amorphous TiO2 ALD layer is found to withhold considerable lattice strain at the thin-film/electrode interface, reducing lattice deformation by 68.2% and exhibits a capacity retention 2.5 times greater than that of the pristine electrode after 20 cycles of operation. The influence of the ALD coating on charge/discharge kinetics and cell capacity is also examined.

Microstructure and magnetic properties of equiatomic FeNiCo alloy synthesized by mechanical alloying

Equiatomic FeNiCo alloy was prepared by mechanical alloying using high energy planetary ball mill for 25 h. Structural properties of as-milled powders were characterized using X-ray diffraction technique (XRD), field emission scanning electron microscope and transmission electron microscope (TEM). The crystallite size and the % lattice strain obtained after 25 h of milling was found to be 19.26 nm and 0.43 % respectively. XRD analysis confirmed the dissolution of Co and Ni into Fe lattice and forming Fe (Co, Ni) supersaturated solid solution. XRD peak shift corresponding to (110) plane of major phase confirmed decrease in the lattice parameter from 0.288 to 0.286 nm after 25 h of milling. The initial powder morphology was irregular in shape which continued to reduce in size forming platelets after 25 h of milling. TEM study confirms the synthesis of nanocrystalline material. Magnetic properties of powder samples with milling time were evaluated using vibrating sample magnetometer (VSM). The maximum saturation magnetic flux density Bs obtained from VSM was 10.75 kilogauss which is comparatively higher than that of common soft ferrites and 80 % of Ni Permalloy.

Photocatalytic activity and formation of oxygen vacancies in cation doped anatase TiO2 nanoparticles

We report the influence of iron doping on structure, stoichiometry, and photocatalytic efficiency of single phase anatase TiO2 nanoparticles which were synthesized via the sol gel technique. The XPS and FTIR results reveal the formation of oxygen vacancies and Ti3+ defects following doping with iron which was further confirmed by PL studies. XRD and TEM investigations indicate that the phase structure of TiO2 nanoparticles is preserved after incorporation of iron to the crystallographic lattice. XRD peak shift and broadening, observed in the doped nanoparticles, were attributed to the formation of point defects and the resulted strains. Photocatalytic activity of the samples was examined through measuring the decomposition rate of rhodamine B under ultraviolet illumination. It was found that Fe-doping significantly improves the photocatalytic activity of anatase TiO2. We envisage that a more effective use of the UV photon energy, higher charge carrier mobility, and suppressed charge recombination due to the point defects are the primary reasons behind the enhanced photocatalytic activity.

Structural, FTIR and photoluminescence properties of ZnS:Cu thin films by chemical bath deposition method

ZnS:Cu thin films were deposited on glass substrate using chemical bath by neutral pH solution synthesis route. Cu is varied between 0 and 0.1M%. The XRD measurement shows hexagonal structure with the average crystalline size between 1.67 and 2.47nm (below Bohr diameter). Energy dispersive X-ray spectrum reveals the presence of Cu in the ZnS lattice. The increase of lattice parameters, the reduction of particle size and a small shift in XRD peaks by Cu-doping reveals the substitution of Cu2+ ions into the ZnS lattice. The observed red shift of green emission from 506 to 519nm in photoluminescence spectra confirms the presence of Cu2+ ions that are embedded in the ZnS matrix.

Fabrication of a transparent ultraviolet detector by using n-type Ga2O3 and p-type Ga-doped SnO2 core–shell nanowires

This study investigates the feasibility of synthesizing high-density transparent Ga(2)O(3)/SnO(2):Ga core-shell nanowires on a sapphire substrate at 1000 °C by VLS. The doping Ga concentrations are 0.46, 1.07, 2.30 and 17.53 atomic%. The XRD spectrum and HR-TEM reveal Ga(2)O(3) and SnO(2) as having monoclinic and tetragonal rutile structures, respectively. Experimental results indicate that the XRD peak shift of SnO(2) to a larger angle increases with the increasing amount of Ga doping. According to the CL spectrum, SnO(2) and Ga(2)O(3) peak at approximately 528-568 nm and 422-424 nm, respectively. The maximum quantum efficiency of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 0.362%. The UV light on-off current contrast ratio of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 1066.7 at a bias of 5 V. Moreover, the dynamic response of Ga(2)O(3)/SnO(2):Ga core-shell nanowires has an on-off current contrast ratio of around 16. Furthermore, the Ga(2)O(3) region functions similar to a capacitor and continues to accumulate SnO(2):Ga excited electrons under UV light exposure.

Low Porosity FeSe Preferred Orientation Crystal Growth by Bridgman Method

The new kind of iron-based superconductor FeSe which has being widely studied recently is arsenic-free and has about 8 K of Tc. The less poisonous and simple binary FeSe is interesting for both scientific studies and engineering applications, even though its Tc is lower than that of other iron-based compounds. Recently, the single crystal and thin film technology of FeSe has been studied to realize the anisotropic property. In our study, the highly preferred orientation poly-crystal was grown by the Bridgman method. The vacuum condition during growth affects the porosity of FeSe. It is difficult to produce high density under 1 atmosphere even when maintained at high temperature for a long time. When the pressure is controlled at less than 10-1 torr, ultra low porosity (and high density) crystal can be grown. Polarized optical microscope images show the single crystal domain up to about 5 mm with (110) preferred orientation by XRD analysis. A XRD peak shift is observed between samples grown by furnace-cooling and the Bridgman method, which is supposed to be due to residual stress during growth. It also induced a Tc decrease to 5.9 K in the Bridgman sample, but recovered to 6.8 K after annealing. From the microstructure, considerable columnar precipitation is observed in the Bridgman sample, which is identified as iron-rich phase by energy dispersive spectrum (EDS) analysis.