Influence of Cu doping on the microstructure,optical properties and photoluminescence features of Cd0.9Zn0.1S nanoparticles

Cd_0.9−xZn_0.1Cu_xS (0≤x≤0.06) nanoparticles were successfully synthesized by a conventional chemical co-precipitation method at room temperature. Crystalline phases and optical absorption of the nanoparticles have been studied by X-ray diffraction (XRD) and UV–visible spectrophotometer. XRD confirms the phase singularity of the synthesized material, which also confirmed the formation of Cd–Zn–Cu–S alloy nanocrystals rather than separate nucleation or phase formation. Elemental composition was examined by the energy dispersive X-ray analysis and the microstructure was examined by scanning electron microscope. The blue shift of absorption edge below Cu=2% is responsible for dominance of Cu⁺ while at higher Cu concentration dominated Cu²⁺, d–d transition may exist. It is suggested that the addition of third metal ion (Cu²⁺/Cu⁺) is an effective way to improve the optical property and stability of the Cd_0.9Zn_0.1S solid solutions. When Cu is introduced, stretching of Cd–Zn–Cu–S bond is shifted lower wave number side from 678 cm⁻¹ (Cu=0%) to 671 cm⁻¹ (Cu=6%) due to the presence of Cu in Cd–Zn–S lattice and also the size effect. The variation in blue band emission peak from 456 nm (∼2.72 eV) to 482 nm (∼2.58 eV) by Cu-doping is corresponding to the inter-band radiation combination of photo-generated electrons and holes. Intensity of red band emission centered at 656 nm significantly increased up to Cu=4%; beyond 4% it is decreased due to the quenching of Cu concentration.     

Effect of substrate temperature and oxygen partial pressure on microstructure and optical properties of pulsed laser deposited yttrium oxide thin films

Yttrium oxide thin films were deposited on Si (1 1 1) and quartz substrates by pulsed laser deposition technique at different substrate temperature and oxygen partial pressure. XRD analysis shows that crystallite size of the yttrium oxide thin films increases as the substrate temperature increases from 300 to 873 K. However the films deposited at constant substrate temperature with variable oxygen partial pressure show opposite effect on the crystallite size. Band gap energies determined from UV-visible spectroscopy indicated higher values than that of the reported bulk value.     

Radiative properties of optical board embedded with optical black holes

Unique radiative properties, such as wavelength-selective transmission or absorption, have been intensively studied. Historically, geometries for wavelength-selective of light absorption were developed based on metallic periodical structures, which were only applied in the case of TM wave incidence due to the excitation of surface plasmons. In this paper, we develop an alternative approach to selective wavelength of light absorption (both TE and TM waves), based on an optical board periodical embedded with optical black holes. Numerical work was carried out to study such structure’s radiative properties within the wavelength range of 1-100 μm. The electromagnetic wave transmission through such a structure is predicted by solving Maxwell’s equations using the finite-difference time-domain (FDTD) method. Spectral absorptance varies with the period of optical black holes. When the incidence wavelength is much larger than the inner core radius, most of the light energy will be transmitted through the inner core. Otherwise, the energy will be mainly absorbed. Numerical results of the radiative properties of the optical board with different incidence wavelengths are also obtained. The effect of the oblique incidence wave is investigated. This study helps us gain a better understanding of the radiative properties of an optical board embedded with optical black holes and develop an alternative approach to selective light absorption.     

Electronic and optical properties of black phosphorus doped with Au,Sn and I atoms

In this study, the electronic and the optical properties of monolayer black phosphorus (BP) doped with Gold (Au), Tin (Sn) and Iodine (I) atoms have been investigated by the density-functional theory (DFT) method. In the calculations, the electronic and the optical properties of monolayer BP have been substantially changed with doping. Monolayer BP has a narrow bandgap as 0.85 eV, BP doped with these atoms, results in a metallic behaviour and nearly spin gapless band gap behaviour. The dielectric constant of BP which shows anisotropic optical properties due to different edge states as zigzag and armchair has been changed with doping especially with Au.     

Effect of the oxygen pressure on the microstructure and optical properties of ZnO films prepared by laser molecular beam epitaxy

A series of ZnO films were prepared on the Si (1 0 0) or glass substrate at 773 K under various oxygen pressures by using a laser molecular beam epitaxy system. The microstructure and optical properties were investigated through the X-ray diffraction, Raman spectrometer, scanning electron microscope, ultraviolet–visible spectrophotometer and spectrofluorophotometer. The results showed that ZnO thin film prepared at 1 Pa oxygen pressure displayed the best crystalinity and all ZnO films formed a columnar structure. Meanwhile, all ZnO films exhibited an abrupt absorption edge near the wavelength of 380 nm in transmission spectra. With increasing the oxygen pressure, the transmission intensity changed non-monotonically and reached a maximum of above 80% at 1 Pa oxygen pressure, based on which the band gaps of all ZnO films were calculated to be about 3.259–3.315 eV. Photoluminescence spectra indicated that there occurred no emission peak at a low oxygen pressure of 10⁻⁵ Pa. With the increment of the oxygen pressure, there occurred a UV emission peak of 378 nm, a weak violet emission peak of 405 nm and a wide green emission band centered at 520 nm. As the oxygen pressure increased further, the position of UV emission peak remained and its intensity changed non-monotonically and reached a maximum at 1 Pa. Meanwhile the intensity of green emission band increased monotonically with increasing the oxygen pressure. In addition, it was also found that the intensity of UV emission peak decreased as the measuring temperature shifted from 80 to 300 K. The analyses indicated that the UV emission peak originated from the combination of free excitons and the green emission band originated from the energy level jump from conduction band to O_Zn defect.     

Influence of sputter-etching of substrate on the microstructural and optical properties of ZnO films deposited by RF magnetron sputtering

ZnO films were prepared using radio frequency magnetron sputtering on Si(1 1 1) substrates that were sputter-etched for different times ranging from 10 to 30 min. As the sputter-etching time of the substrate increases, both the size of ZnO grains and the root-mean-square (RMS) roughness decrease while the thickness of the ZnO films shows no obvious change. Meanwhile, the crystallinity and c-axis orientation are improved by increasing the sputter-etching time of the substrate. The major peaks at 99 and 438 cm⁻¹ are observed in Raman spectra of all prepared films and are identified as E₂(low) and E₂(high) modes, respectively. The Raman peak at 583 cm⁻¹ appears only in the films whose substrates were sputter-etched for 20 min and is assigned to E₁(LO) mode. Typical ZnO infrared vibration peak located at 410 cm⁻¹ is found in all FTIR spectra and is attributed to E₁(TO) phonon mode. The shoulder at about 382 cm⁻¹ appearing in the films whose substrates were sputter-etched for shorter time (10-20 min) originates from A₁(TO) phonon mode. The results of photoluminescence (PL) spectra reveal that the optical band gap (Eg) of the ZnO films increases from 3.10 eV to 3.23 eV with the increase of the sputter-etching time of the substrate.     

Interrelation between microstructure and optical properties of erbium-doped nanocrystalline thin films

Nanocrystalline silicon thin films codoped with erbium, oxygen and hydrogen have been deposited by co-sputtering of Er and Si. Films with different crystallinity, crystallite size and oxygen content have been obtained in order to investigate the effect of the microstructure on the photoluminescence properties. The correlation between the optical properties and microstructural parameters of the films is investigated by spectroscopic ellipsometry. PL response of the discussed structures covers both the visible wavelength range (a crystallite size-dependent photoluminescence detected for 5–6 nm sized nanocrystals embedded in a SiO matrix) and near IR range at 1.54 μm (Er-related PL dominating in the films with 1–3 nm sized Si nanocrystals embedded in a-Si:H). It is demonstrated that the different PL properties can be also discriminated on the basis of ellipsometric spectra.     

Correlation of sp and sp fraction of carbon with electrical, optical and nano-mechanical properties of argon-diluted diamond-like carbon films

In the present work the correlation of electrical, optical and nano-mechanical properties of argon-diluted diamond-like carbon (Ar-DLC) thin films with sp³ and sp² fractions of carbon have been explored. These Ar-DLC thin films have been deposited, under varying C₂H₂ gas pressures from 25 to 75 mTorr, by radio frequency-plasma enhanced chemical vapor deposition technique. X-ray photoelectron spectroscopy studies are performed to estimate the sp³ and sp² fractions of carbon by deconvoluting C 1s core level spectra. Various electrical, optical and nano-mechanical parameters such as conductivity, I-V characteristics, optical band gap, stress, hardness, elastic modulus, plastic resistance parameter, elastic recovery and plastic deformation energy have been estimated and then correlated with calculated sp³ and sp² fractions of carbon and sp³/sp² ratios. Observed tremendous electrical, optical and nano-mechanical properties in Ar-DLC films deposited under high base pressure conditions made it a cost effective material for not only hard and protective coating applications but also for electronic and optoelectronic applications.     

Effects of the substrate and oxygen partial pressure on the microstructures and optical properties of Ti-doped ZnO thin films

Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Si substrates using radio frequency reactive magnetron sputtering. The effects of substrate on the microstructures and optical properties of ZnO:Ti thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer. The structural analyses of the films indicated that they were polycrystalline and had a hexagonal wurtzite structure on different substrates. When ZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferred orientation, while preferred orientation of ZnO:Ti thin film deposited on glass substrate changed towards (1 0 0). Finally, we discussed the influence of the oxygen partial pressures on the structural and optical properties of glass-substrate ZnO:Ti thin films. At a high ratio of O₂:Ar of 18:10 sccm, the intensity of (0 0 2) diffraction peak was stronger than that of (1 0 0) diffraction peak, which indicated that preferred orientation changed with the increase of O₂:Ar ratios. The average optical transmittance with over 93% in the visible range was obtained independent of the O₂:Ar ratio. The photoluminescence (PL) spectra measured at room temperature revealed four main emission peaks located at 428, 444, 476 and 527 nm. Intense blue-green luminescence was obtained from the sample deposited at a ratio of O₂:Ar of 14:10 sccm. The results showed that the oxygen partial pressures had an important influence for PL spectra and the origin of these emissions was discussed.     

Temperature-dependent optical properties of wurtzite InN

Optical properties and carrier recombination dynamics of a series of InN epilayers, with varying free electron concentrations, grown by molecular beam epitaxy were studied by steady-state photoluminescence (PL) and time-resolved differential transmission spectroscopy. At room temperature strong PL around 0.7 eV was observed. Temperature-dependent PL measurements show a redshift of the peak energy and a linear increase of the emission linewidth with temperature. Furthermore, our results demonstrate that room temperature carrier lifetimes are inversely proportional to the free electron concentrations for theses samples. Carrier lifetime as long as 1.3 ns was observed in the best quality sample, indicating a highly improved crystalline quality.     

Comparative study on structural and optical properties of CdS films fabricated by three different low-cost techniques

Highly crystalline and transparent cadmium sulphide films were fabricated at relatively low temperature by employing an inexpensive, simplified spray technique using perfume atomizer (generally used for cosmetics). The structural, surface morphological and optical properties of the films were studied and compared with that prepared by conventional spray pyrolysis using air as carrier gas and chemical bath deposition. The films deposited by the simplified spray have preferred orientation along (1 0 1) plane. The lattice parameters were calculated as a = 4.138 Å and c = 6.718 Å which are well agreed with that obtained from the other two techniques and also with the standard data. The optical transmittance in the visible range and the optical band gap were found as 85% and 2.43 eV, respectively. The structural and optical properties of the films fabricated by the simplified spray are found to be desirable for opto-electronic applications.     

Effect of K-doping on structural and optical properties of ZnO thin films

In this work, K-doped ZnO thin films were prepared by a sol–gel method on Si(111) and glass substrates. The effect of different K-doping concentrations on structural and optical properties of the ZnO thin films was studied. The results showed that the 1 at.% K-doped ZnO thin film had the best crystallization quality and the strongest ultraviolet emission ability. When the concentration of K was above 1 at.%, the crystallization quality and ultraviolet emission ability dropped. For the K-doped ZnO thin films, there was not only ultraviolet emission, but also a blue emission signal in their photoluminescent spectra. The blue emission might be connected with K impurity or/and the intrinsic defects (Zn interstitial and Zn vacancy) of the ZnO thin films.     

Study on the electrical and optical properties of Ag/Al-doped ZnO coatings deposited by electron beam evaporation

A layer of silver was deposited onto the surface of glass substrates, coated with AZO (Al-doped ZnO), to form Ag/AZO film structures, using e-beam evaporation techniques. The electrical and optical properties of AZO, Ag and Ag/AZO film structures were studied. The deposition of Ag layer on the surface of AZO films resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. Ag (11 nm)/AZO (25 nm) film structure, with an accuracy of ±0.5 nm for the thickness shows a sheet resistance as low as 5.6 ± 0.5 Ω/sq and a transmittance of about 66 ± 2%. A coating consisting of AZO (25 nm)/Ag (11 nm)/AZO (25 nm) trilayer structure, exhibits a resistance of 7.7 ± 0.5 Ω/sq and a high transmittance of 85 ± 2%. The coatings have satisfactory properties of low resistance, high transmittance and highest figure of merit for application in optoelectronics devices including flat displays, thin films transistors and solar cells as transparent conductive electrodes.     

Study of the microstructure and mechanical properties of white clam shell

The microstructure and mechanical properties of white clam shell were investigated, respectively. It can be divided into horny layer, prismatic layer and nacreous layer. Crossed-lamellar structure was the microstructural characteristic. The extension direction of lamellae in prismatic layer was different from that in nacreous layer, which formed an angle on the interface between prismatic layer and nacreous layer. The phase component of three layers was CaCO₃ with crystallization morphology of aragonite, which confirmed the crossed-lamellar structural characteristic. White calm shell exhibited perfect mechanical properties. The microhardness values of three layers were 273 HV, 240 HV and 300 HV, respectively. The average values of flexure and compression strength were 110.2 MPa and 80.1 MPa, respectively. The macroscopical cracks crossed the lamellae and finally terminated within the length range of about 80 μm. It was the microstructure characteristics, the angle on the interface between prismatic and nacreous layer and the hardness diversity among the different layers that enhanced mechanical properties of white calm shell.     

Microstructure and optical characterizations of mechanosynthesized nanocrystalline semiconducting ZrTiO4 compound

A ZrO₂–TiO₂ solid solution is obtained by high energy ball milling of equimolar mixture of monoclinic (m) ZrO₂ and anatase (a) TiO₂. Nanocrystalline orthorhombic ZrTiO₄ compound is initiated from the nucleation of TiO₂–ZrO₂ solid solution with isostructural s-TiO₂ (srilankite) base after 30 min of milling. After 12 h of milling, 95 mol% non-stoichiometric ZrTiO₄ phase is formed. Post-annealing of 12 h ball-milled powder mixture at 1073 K for 1 h in open air results in complete formation of stoichiometric ZrTiO₄ compound. Microstructures of all powder mixtures milled for different durations have been characterized by Rietveld's structure and microstructure refinement method using X-ray powder diffraction data. HRTEM images of 12 h milled and annealed samples provide direct evidence of the results obtained from the Rietveld analysis. Optical bandgaps of ball milled and annealed ZrTiO₄ compounds lie within the semiconducting region (~2.0 eV) and increases with increase in milling time.     

Polarization phenomena in the optical properties of porous silicon

We examine the polarization memory effect for porous Si excited by linearly polarized light. The various observations for the red-luminescing, slow band are discussed in the general framework of particle shape asymmetry. We show that because of the intrinsically nonlinear luminescence response, measurement parameters influence the polarization response. The preparation of porous Si with photoassisted etching is found to control the polarization retention parameter ρ. Using linearly polarized light during etching produces in-plane asymmetries. We find a substantial ρ-anisotropy linked to crystal symmetry planes and axes as a consequence of anisotropic etching. The effects are discussed with reference to current models of the light emission mechanism.     

Sputtering pressure effects on the structural and mechanical properties of TiVCr alloy coatings

In this study, TiVCr alloy coatings were deposited on Si substrates by magnetron sputtering system at different working pressures (0.33-1 Pa). The TiVCr coatings have a composite structure with amorphous and body-centered cubic (bcc) crystal phases comprised of bundles of fine fibrous structures and V-shaped columnar structures, respectively. Compared with the amorphous zone, the crystalline zone has a denser and more compact structure. The coating microstructure became more porous as working pressure increased. Consequently, the crystal zones of the deposited coatings at 0.33 Pa obtained higher hardness (11.6 GPa) while the deposited coatings at 1 Pa achieved lower hardness (4.5 GPa).     

Size- and shape-dependent optical properties of assembled semiconductor spheres

The radiative corrections of nanostructures are investigated by applying a nonlocal theory to a model of semiconductor spheres which are assembled one-, two- and three-dimensionally. An approximate sum rule for radiative corrections and the relation between finite and infinite lattices are given. It is shown that radiative correction strongly depends on the shape as well as the size. For a linear chain, the radiative correction gets saturated when the system length becomes comparable to the wavelength of resonant light. For cubic systems, the radiative width deviates from the size linearity for a surprisingly small size. The two-dimensional case is marginal. This peculiar shape dependence originates from the dipole-dipole interaction.     

Porosity and effective mechanical properties of plasma-sprayed Ni-based alloy coatings

The aim of this paper was to address the relationship between the porosity and micro-mechanical properties of the Ni-based alloy coatings which were prepared by a novel plasma-spraying system. The porosity and the mechanical properties of the coatings varied through changing the spraying parameters. Experimental results showed that the measured data of porosity, Young’s modulus and micro-hardness of the coating exhibited high scattering and followed the Weibull distribution. From statistic trend, the micro-hardness and Young’s modulus of the coating decreased with increasing the porosity of the coating. Moreover, generally, with increasing the micro-hardness of the coating, Young’s modulus of the coating increased.