Density Of Nd Research Articles

Structural, Optoelectronic, and Photoelectrochemical Investigation of CdSe NC's Prepared by Hot Injection Method

In this study, we report the synthesis and characterization of CdSe nanocrystals (NC's) by facile Hot injection (HI) method. The formation of CdSe NC's was confirmed by x-ray diffraction (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). The optical properties were analyzed by UV-visible and photoluminescence (PL) spectroscopy shows an excitonic peak at 600 nm in UV-Vis spectra corresponds to the band gap of ~ 2 eV favorable for optoelectronic device applications. The Photoelectrochemical (PEC) performance of CdSe thin film prepared by spin coating demonstrates a rise of photocurrent density (Jsc = 0.081 µAcm-2) after illumination. The Mott-Schottky (MS) and electrochemical impedance spectroscopy (EIS) measurements were further carried out to understand intrinsic properties namely the type of conductivity, flat band potential, charge carrier density (ND), charge transfer resistance, and recombination lifetime. The n-type conductivity, the charge carrier density of ND = 1.292 x 1016 cm-2, and recombination lifetime of 32.4 µs suggest the ideal behavior of CdSe NC's for device quality photoelectrodes.

Quantitative Identification of Constituent Phases in a Nd-Fe-B Sintered Magnet and Temperature-Dependent Change in the Electron Density of Nd <sub>2</sub>Fe <sub>14</sub>B Studied by Synchrotron X-Ray Diffraction

We measure the temperature-dependent XRD profiles of an isotropic Nd-Fe-B-Cu sintered magnet during the annealing process. Through Rietveld refinement, we demonstrate the changes in the volume fractions of the Nd2Fe14B main phase and the other secondary phases as a function of increasing temperature up to 1047 °C. The secondary phases include dhcp-Nd, fcc-NdOx, and hcp-Nd2O3 at room temperature and fcc-Nd at elevated temperatures. The main phase remains relatively stable up to 600 °C and starts melting above 900 °C, while diffraction from the dhcp-Nd phase completely disappears at around 600 °C. Taking advantage of the excellent quality of the XRD profiles in the powdered single-crystal sample, we also investigate the electron density distribution of the main phase by the maximum entropy method (MEM)/Rietveld analysis in order to elucidate the origin of the large magnetic anisotropy. From the subtraction of the electron density distributions recorded above (-123 °C) and below (-173 °C) the spin reorientation transition (-138 °C), we observe an anomalous change of the electron density distribution around the Nd f and g sites of Nd2Fe14B whose electron density distributions are intimately related to the magnetic anisotropy.

Device simulation of Cu(In,Ga)Se2 solar cells by means of voltage dependent admittance spectroscopy

The simulation of solar cell devices is important for the understanding of defect physics and loss mechanisms in real solar cells. On the other hand, voltage dependent admittance spectroscopy delivers essential information for establishing a baseline simulation model of Cu(In,Ga)Se2 (CIGSe) solar cells. Here we give an explanation for the weak temperature dependence of the N1-signal, the latter being not compatible with a bulk defect or with a simple hole barrier at the Mo back contact. Furthermore, we find a Ed,IF – EV ≈ 0.3 eV deep recombination-active acceptor state at the absorber/buffer interface made of air-light exposed CIGSe absorbers. This gives us the ability to explain the reduction of power conversion efficiency of solar cells made from air-light exposed absorbers. From the voltage dependent capacitance step of this interface defect we can deduce the formerly unknown position of the Fermi level at the hetero junction in equilibrium which is close to mid-gap. Simulation of dark J-V curves allows a refinement of the parameter of this absorber/buffer interface defect, resulting in a defect density of Nd,IF ≈ 3.5·1011 cm−2 as well as capture cross sections of σn ≈ 4·10−16 cm2 for electrons and σp ≈ 3·10−11 cm2 for holes.

THE THERMAL PROCESSING INFLUENCE ON CURRENT-VOLTAGE CHARACTERISTIC AND INJECTION PROPERTIES OF HETEROJUNCTIONS

Context. Nowadays the research and development of heterojunctions are carried out to search new metal-gallium arsenide compositions, the development of technological regimes which could ensure the microwave devices with Schottky barriers parameters reproducibility. Comparing to gold, silver has a large thermal and electrical conductivity, a relatively small diffusion coefficient to gallium arsenide, which makes it possible to reduce the transition layer thickness. The transition to silver-based metallization should improve the products technical characteristics. The technological regimes development for manufacturing improved silver-based heterojunctions to GaAs is relevant from scientific and practical points of view. Objective. The goal of the work is to determine the heat treatment influence on real current-voltage characteristics and the injection coefficient value of the Ag/n-n+GaAs heterojunction. Method. The heterojunctions manufacturing method is vacuum thermal evaporation. The calculation of the heterojunction parameters was made by the current-voltage characteristics method. Results. The GaAs-substrate chemical treatment regime is recommended. The heat treatment effect on the Ag/n-n+GaAs heterojunctions parameters and characteristics is studied. The barrier height influence on the injection coefficient value was investigated. Various methods for determining the Schottky barrier height and the nonideality factor for the current-voltage characteristics have been examined and tested. Conclusions. It is established that the annealing temperature increase up to 803 K gives the highest barrier height for the Ag/n-n+GaAs heterojunction with a donor density of ND=2 1016 cm–3 into epitaxial layer. It has been established that the most accurate method for the heterojunction parameters determining using the current-voltage characteristic is the direct approximation method, which takes into account the effect of the series resistance in determining the nonideality factor and the Schottky barrier height. The calculated injection coefficients for heterojunctions with different Schottky barrier heights, obtained at different annealing temperatures, have very small values, therefore, hole injection can be neglected.

Properties of Ce3+ -Doped Y3Al5O12 Phosphor Nanoparticles Formed by Laser Ablation in Liquid

Y3Al5O12: Ce3+ (YAG: Ce) nanoparticles were generated by the laser ablation from the micron-size YAG: Ce particles suspended in deionized water as a target suspension. The mean diameter of nanoparticles observed by a scanning electron microscopy were about 15–300 nm, and the morphology showed a dependence on an average energy density of Nd: YAG laser. The photoluminescence spectra exhibited peaks at 510 and 560 nm which are attributed to the 5d→4f transition of the Ce3+ activator. The luminescence intensity for the nanoparticles generated by the suspension increased with increasing the average energy density of Nd: YAG laser, and the intensity of 510 nm peak also exhibited higher than that for the nanoparticles generated by the micron-size particles precipitated on a bottom of vial. It was found that the laser ablation in liquid using the suspension was effective to generate the YAG: Ce phosphor nanoparticles.

Effect of fibre laser process on in-vitro degradation rate of a polycaprolactone stent a novel degradation study method

In this paper, the authors present the effect of input energy density of Nd:YAG fibre laser upon the degradation rate of the polycaprolactone. The degradation study were carried out with a novel in-vitro method closer to body conditions and were compared with the traditional in-vitro method. This approach was not presented in the available literature. The degradation rate of biodegradable stents is one of the most importance factor upon making these devices, due to it is the property in charge to provide the appropriate period of time to heal the atherosclerosis. The research for a degradable material that shows mechanical properties similar to the current permanent stents in the market and an appropriate degradation rate is still an open challenge. The literature has shown the degradation rate of some biodegradable materials before stent manufacturing's process employing in-vitro degradation methods in static flow conditions which does not match properly with the real body conditions where the blood flow circulate by the vessel. The laser cut samples were analysed by Scanning Electron Microscopy (SEM), Optical Microscopy, and weighing in order to study the effect of laser process, and degradation method over the degradation rates, surface morphology changes, and geometric pattern changes in the stent. Results have shown the influence of the laser process over the degradations rate, accelerating it according the input energy density increases. The dynamic method has increased the weight of samples, fact that will accelerate the degradations rate in a medium period of time that prove the differences that will exist in body conditions.

Thermal, defects, mechanical and spectral properties of Nd-doped GdNbO4 laser crystal

A Nd-doped GdNbO4 crystal was grown successfully by Czochralski method. Its monoclinic structure was determined by X-ray diffraction; the unit-cell parameters are a = 5.38 A, b = 11.09 A, c = 5.11 A, and β = 94.56°. The morphological defects of Nd:GdNbO4 crystal were investigated using the chemical etching with the phosphoric acid etchant. For a new crystal, the physical properties are of great importance. The hardness and density of Nd:GdNbO4 were investigated first. Thermal properties of Nd:GdNbO4, including thermal expansion coefficient and specific heat, were measured along a-, b-, and c-crystalline axes. Thermal properties indicate that the Nd:GdNbO4 pumped along c-axis can reduce the thermal lensing effect effectively. The specific heat is 0.53 J g−1 K−1 at 300 K, indicating a relatively high damage threshold of Nd:GdNbO4. The transmission and emission spectrum of Nd:GdNbO4 were measured, and the absorption peaks were assigned. The strongest emission peak of Nd:GdNbO4 is located at 1065.3 nm in the spectral range of 850–1420 nm excited by 808 nm laser. The refractive index of Nd:GdNbO4 was calculated with the transmission spectrum and fitted with Sellmeier equation. All these obtained results is of great significance for the further research of Nd:GdNbO4.

Growth, structure, spectral properties and crystal-field analysis of monoclinic Nd:YNbO4 single crystal

A Nd:YNbO4 single crystal was successfully grown by Czochralski (Cz) method, its structural and spectroscopic properties were investigated. The X-ray rocking curve of the (010) diffraction face of Nd:YNbO4 crystal was measured, the full width at half maximum (FWHM) of this diffraction peak is 0.05°, which indicates a high crystalline quality of the as-grown crystal. Its lattice parameters, atomic coordinates and so on were obtained by Rietvield refinement to X-ray diffraction data. According to the Archimedes drainage method, the crystal density of Nd:YNbO4 is calculated to be 5.4g/cm3. The Mohr′s hardness value along (010) face was determined to be 6.0. The transmission spectrum along (010) face at room temperature was recorded and the excitation and emission spectra at 8K were measured. Photoluminescence peaks of Nd:YNbO4 were assigned, and the crystal-field splitting of Nd3+ in YNbO4 was obtained. The fluorescence lifetime of the 4F3/2→4I11/2 transition of Nd3+ in YNbO4 is fitted to be 152μs These spectroscopic and energy splitting data give an important reference for the research of laser property of Nd:YNbO4 crystal.

Characterisation of intrinsic silicon oxide absorber layers for use in silicon thin film solar cells

The use of a wide bandgap absorber layer in the top cell of a multi-junction silicon thin film solar cell is necessary to achieve a high-conversion efficiency. A higher bandgap of the absorber results in a higher open-circuit voltage (Voc) of the cell. In this work, intrinsic hydrogenated amorphous silicon oxide (i)a-SiO:H films have been prepared by using 13.56 MHz radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) at a substrate temperature of 195 °C. The carbon dioxide (CO2) to silane (SiH4) ratio rc was varied and the influence of the ratio rc on the optoelectronic film properties was investigated. These thin films have been studied in detail in terms of their dark (σd) and photo (σph) conductivity and photoresponse PR (σph/σd). The defect density Nd and Urbach energy EU were determined by constant photocurrent method (CPM). The optical bandgap Eg,Tauc was derived from Tauc plots. Optical constants were determined by spectroscopic ellipsometry measurements in the range between 300 and 1000 nm. It was found that the increase in the CO2 to SiH4 ratio rc not only leads to a higher optical bandgap, but also higher defect density Nd and Urbach energy EU and on the other hand to a lower photoresponse PR. A suitable photoresponse PR = 8.64 × 105 at a high bandgap of Eg,Tauc = 1.91 eV and a defect density of Nd = 1.7 × 1016 cm−3 was achieved. The refraction index and extinction coefficient were lowered with increasing rc. The analysis of light-induced degradation in the (i)a-SiO:H layers showed a smaller increase of deep defects Nd and a higher increase of the Urbach energy EU in terms of the light soaking time with respect to the (i)a-Si:H reference layer.

Growth and thermal properties of Nd 3+:YbVO 4 crystal

New crystal Nd 3+:YbVO 4 has been successfully grown by using the Czochralski method. The rocking curves from (0 0 4) and (4 0 0) diffraction planes of as-grown Nd 3+:YbVO 4 crystal were measured by the high-resolution X-ray diffractometer (HRXRD) D5005, and the full-width values at half-maximum were 19.80″ for (0 0 4) face and 70.92″ for (4 0 0) face, respectively. The measured effective segregation coefficients were 0.545 for Nd 3+ and near 1 for V 3+ and Yb 3+ by using the X-ray fluorescence method. The density of Nd 3+:YbVO 4 crystal is also measured. The measured thermal expansion coefficients are α 1=2.6×10 −6 K –1, α 2=2.5×10 −6 K –1, α 3=8.7×10 −6 K –1 from 298.15 to 573.15 K along its crystallographic a, b and c axes, respectively. The measured specific heat is 0.45–0.65 J/g·K in the temperature range from 298.15 to 573.15 K. The thermal diffusion coefficients of Nd:YbVO 4 were measured and the thermal conductivities were also calculated.

Carrier concentration dependence of optical Kerr nonlinearity in indium tin oxide films

Optical Kerr nonlinearity (n2) in n-type indium tin oxide (ITO) films coated on glass substrates has been measured using Z-scans with 200-fs laser pulses at wavelengths ranging from 720 to 780 nm. The magnitudes of the measured nonlinearity in the ITO films were found to be dependent on the carrier concentration with a maximum n2-value of 4.1 x 10-5 cm2/GW at 720-nm wavelength and an electron density of Nd = 5.8 x 1020 cm-3. The Kerr nonlinearity was also observed to be varied with the laser wavelength. By employing a femtosecond time-resolved optical Kerr effect (OKE) technique, the relaxation time of OKE in the ITO films is determined to be ~1 ps. These findings suggest that the Kerr nonlinearity in ITO can be tailored by controlling the carrier concentration, which should be highly desirable in optoelectronic devices for ultrafast all-optical switching.

Growth and characterization of the new laser crystal Nd:LuVO4

The growth, thermal properties, Mohs hardness, density and laser properties of a new laser crystal Nd:LuVO 4 are reported. Nd:LuVO 4 crystal belongs to tetragonal system and its cell parameter was calculated: a =7.0275, c =6.2507 Å. The measured thermal expansion coefficient are α a =1.7×10 −6 , α b =1.5×10 −6 , α c =9.1×10 −6 /K from 50 to 300 °C along its crystallographic axes respectively. The measured specific heat value is 0.45 J g −1 K −1 at 330 K. The highest output power at 1.064 μm is 530 mW at the pumping power of 2.76 W of a laser diode (LD), slope efficiency is 23.1%, and the optical–optical conversion efficiency is 19.3%. The theoretical density of LuVO 4 and measured density of Nd:LuVO 4 are 6.260 and 6.233 g/cm 3 , respectively. And its Mohs hardness is measured to be approximately 6. All these properties show Nd:LuVO 4 is crystal can be used for efficient LD pump lasers system.

Polycrystalline Nd:YAG ceramics lasers

Nd-doped YAG (Y3Al5O12) ceramics that contained from 1.1 to 4.8 at.% Nd additives and exhibited nearly the same optical properties as those of a single crystal was fabricated by a solid-state reaction method using high-purity powders. The average grain size and relative density of Nd:YAG ceramics obtained were about 50 μm and 99.9999%, respectively. Effective laser oscillation was performed successfully for the first time using Nd:YAG ceramics. The laser characteristics of the Nd:YAG ceramics were revealed to be nearly equivalent or far superior to those of high-quality Nd:YAG single crystal fabricated by the Czochralski (Cz) method.

Repair welding of etched tubular components of nuclear power plant by Nd:YAG laser

In this paper the possibility to repair etched tubular components of nuclear power plant by Nd:YAG laser is investigated. Experimental results indicate that the residual stresses of welds increase the sensitivity of stress corrosion cracking. A structure with low restraint and equipment to realize the welding on the inner wall of sleeve are designed. The high energy density of Nd:YAG laser produces deep penetration and can weld sleeve with tube. The microstructures and mechanical properties of welded joint are studied. The base metals of sleeve and tube are not severely affected by the heat of welding. The weld metal is ductile and its tensile shear strength is about 60% of that of Inconel 600 tube. Experiments indicate that it is a suitable method to repair etched tubular components of heat exchanger by Nd:YAG laser.

Development and Prospect of Ceramics Laser Elements.

Transparent polycrystalline YAG ceramics with nearly the same optical characteristics as those of a singlecrystal were fabricated by a sintering method using > 99.99 mass% purity powder. The average grain size andpore density of Nd: YAG ceramics obtained were several ten μm and about 1 ppm, respectively. A cwoscillation experiment using present Nd: YAG ceramics was performed by a diode laser pumping in the regionof 808 nm. The laser performance of the Nd: YAG ceramics was equivalent or superior to those of high-qualitycommercial Nd: YAG single crystal by the Czochralski method.

High critical-current density of Nd(Ba,Nd)2Cu3O7−δ single crystals

We have studied the superconducting properties of Nd(Ba1−xNdx)2Cu3O7−δ (Nd123, x≊0.1) single crystals grown by the traveling-solvent floating-zone method under 0.1% O2 in Ar atmosphere. An anomalous peak effect in the magnetization hysteresis (M–B) loop is observed in the Nd123 single crystals as well as in the Nd123 bulk crystals prepared by the oxygen-controlled melt growth (OCMG) method. The critical current density (Jc) of the Nd123 single crystals is 70 600 A/cm2 in 1.0 T at 77 K for the applied field perpendicular to the a-b plane. Uniform flux density distribution with the same shape as the sample is observed in the field perpendicular to the a-b plane by the magneto-optical flux-density observation. Finely dispersed white regions in the dark-field image due to Nd substitutions for Ba are observed in the Nd123 matrix by the transmission electron microscopy. The high Jc value of the Nd123 single crystals in the applied field is explained by the field-induced pinning centers caused by the Nd–Ba substitutions in the Nd123 matrix.

Characterization of electrochemical photovoltaic cells using polycrystalline CdSe and CdTe electrodes grown by a liquid metal-vapor reaction

Polycrystalline CdSe and CdTe layers were fabricated by putting liquid Cd in contact with Se or Te vapors under constant Ar flow. The crystalline structure, surface properties, and semiconducting properties of these materials have been determined. Both materials were found to be n-type semiconductors. The results show that, under the proper experimental conditions, the liquid metal-vapor reaction enables the synthesis of polycrystalline CdSe photoelectrodes with a 6.9% energy conversion efficiency when used in an electrochemical photovoltaic cell under 80 mW/cm2 of white light illumination. This efficiency rates amongst the highest ones measured under similar conditions using polycrystalline CdSe. These CdSe layers have a majority charge carrier density of ND = 2.6 × 1017 cm−3 and possess a highly textured surface which is assumed to be mainly responsible for the high photovoltaic efficiency. The highly textured CdTe samples obtained by this process, however, show a photovoltaic conversion efficiency of only 0.2%, and this is seen to be mainly due to their high majority charge carrier density of ND = 7.8 × 1019 cm−3.

Declustering and melting threshold study in laser irradiated Si(As)

The sheet resistivity of 40-keV, 1016 As/cm2-implanted Si decreases by a factor of 3 after irradiation with a suitable energy density of Nd:YAG laser at 1.06 or 0.53 μm. The changes in conductivity occur with the melting and quenching of the surface layer as indicated by profile broadening, and they are associated with the declustering process during solidification. The threshold energy density for melting is studied. At 0.53 μm, the threshold is the same (∼0.4 J/cm2) for both as-implanted and thermally preannealed Si. At 1.06 μm, the threshold for the as-implanted sample is ∼5 J/cm2, while the threshold for the preannealed sample is ∼10 J/cm2. These results are in agreement with the absorption changes due to crystalline structure alterations and dopant.