Structural and dielectrical studies on mechano-chemically synthesized indium doped CdS nanopowders

Incorporation of indium (dopant) into CdS crystals have been successfully achieved by a mechanical alloying process. Powders are prepared with various In/Cd ratio from 1 to 10 at% and milled at 300 revolution per minute (rpm) for 60 min. X-ray diffraction (XRD) analysis of milled In doped CdS compound showed that the major phase of the product was wurtzite with grain sizes varying from 37 to 42 nm corresponding to change in In/Cd compositions. High resolution transmission electron microscopy (HRTEM) images as well as Fourier transformation in reciprocal space provide a good pathway to identify the structure of individual CdS nanocrystals, whose dominant phase was determined to be wurtzite structure along with zinc blende structure. Field emission scanning electron microscopy (FESEM) images reveal that CdS crystal prefers to grow along the (001) direction rather than (110) due to its high surface energy. The Raman spectra of CdS:In particles present well-resolved lines at approximately 303 and 600 cm⁻¹, corresponding to the first and second-order scatterings, respectively, of the longitudinal optical (LO) phonon mode. Dielectrical studies showed that dielectrical constant (ε′) decreased with increase in frequency, whereas AC conductivity (σ_AC) in In doped CdS increases with increase in frequency and also both the values increased with increase in doping concentration.     

Structural,optical and magnetic properties of Ba and Ni doped CdS thin films prepared by spray pyrolysis method

Pure, Barium and Nickel doped cadmium sulphide (CdS) thin films have been coated on glass substrates at 400?°C by spray pyrolysis technique. The prepared CdS and doped CdS thin films were analysed by various measurements such as X-ray diffraction (XRD), SEM, optical and Vibrating Sample Magnetometer (VSM). X-ray diffraction measurements show that the coated pure, Ba and Ni-doped CdS thin films belong to the cubic crystal structure with orientation preferentially along (111) direction. The average crystallite size of pure, Ba and Ni doped CdS thin films were determined as 31, 33 and 45 nm, respectively. The average dislocation density (δ) and stacking fault (SF) of pure, Ba and Ni doped CdS thin films were also determined. The surface morphology and elemental analysis of the thin films were determined by scanning electron microscopy and energy dispersive X-ray spectrum (SEM with EDAX). It is observed that the optical energy bandgap has been decreased from 2.43 to 2.1 eV due to the doping Ba. The luminescence spectrum shows a strong emission peak at 517 nm in the case of pure CdS thin film and a meager red shift has been observed due to the doping. VSM studies were employed to study the magnetic behaviour of Ba and Ni doped CdS thin films.     

Influence of incorporation of Al3+ ions on the structural, optical and AC impedance characteristics of spin coated ZnO thin films

Aluminium doped zinc oxide thin films were deposited onto glass substrate using spin coating technique. The effects of Al doping on structural, optical and electrical properties of these films were investigated. X-ray diffraction analysis showed that all the thin films were of polycrystalline hexagonal wurtzite structure with (002) as preferential orientation except 2 at.% of Al doped ZnO films. The optical band gap was found to be 3.25 eV for pure ZnO film. It increases up to 1.5 at.% of Al doping (3.47 eV) and then decreased slightly for the doping level of 2 at.% (3.42 eV). The reason for this widening of the optical band gap up to 1.5 at.% is well described by Burstein–Moss effect. The photoluminescence spectra of the films showed that the blue shift and red shift of violet emission were due to the change in the radiative centre between zinc vacancy and zinc interstitial. Variation in ZnO grain boundary resistance against the doping concentration was observed through AC impedance study.     

Nitrogen doped n-type CdS nanoribbons with tunable electrical and photoelectrical properties

Single-crystal nitrogen doped CdS nanoribbons (NRs) with wurtzite structure were synthesized in ammonia atmosphere via a thermal evaporation deposition route. X-ray diffraction patterns reveal a significant contraction of the lattice constants due to the incorporation of nitrogen. Temperature-varied photoluminescence spectra of CdS:N NRs exhibit spectral features near the band edge, which can be ascribed to free excition and neutral acceptor-bound excition emissions. Electrical and photoelectrical properties of the CdS:N NRs were systemically studied by constructing the field-effect transistors based on individual NRs. The conductivity of the NRs can be tuned by two orders of magnitude by controlling the N doping concentration. Moreover, by post-annealing, the device performance is remarkably improved, in particular, the mobility of the CdS:N NRs is increased by nearly three orders of magnitude from approximately 10(-1) to hundreds of cm2/Vs. I(on)I(off) ratio of the annealed device reaches over 10(4). Photoconductive properties of the CdS:N NRs were also studied. The doped NRs show high sensitivity to the light with energy larger than band-gap and the response amplitude and speed depend on the doping concentration.     

CdS/CdSSe quantum dots in glass matrix

The compositions containing 55 and 60% of silica have been formulated for preparation of glass filters having sharp cut-off at 475 and 575 nm. To achieve cut-off at these wavelengths, the glasses have been doped with CdS/CdSSe and melted at 1200–1300°C. The glass samples were transparent and pale yellow in colour due to presence of CdS/CdSSe tiny nano crystal (Q-dots). In situ growth of CdS/CdSSe nano crystals imparts the yellow/orange/red colour to these glasses. Optical study shows that as prepared glasses have optical cut-off in the range 350–370 nm. The linear crystal growth of CdS/CdSSe in glasses exhibits red shift in optical cut-off. The optical filter having cut-off at 475 nm can be prepared by doping CdS and cut-off filter of wavelength 575 nm by CdSSe. The TEM results show that the CdS/CdSSe nano crystals (Q-dots) ranging from 2–5 nm are uniformly distributed into the glass matrix.     

Na to tailor the band gap and morphology of ZnO nanograins

Sodium doped and undoped zinc oxide compounds are synthesized using sol–gel auto combustion method. The doping has five different concentrations of sodium in zinc oxide. They are characterized for phase and crystal structure using X-ray diffractrometer. It is confirmed that the doping of the impurity atoms show lattice changes. The average particle size of samples are found to be in the range between 32 and 62 nm. Williamson–Hall plots show strain induced in crystallites. Scanning electron microscope micrographs show the morphology of the Na doped samples as nano pebbles, nano platelets and nano rods having considerable width and length; while small thickness. Fourier transform infra-red spectrophotometer and FT Raman studies show the persistent peaks corresponding to characteristic Zn–O bonds. Ultraviolet–visible–near infra-red spectrophotometer studies reveal the decrease in absorbance and red shift in band gap with increasing Na content. The fluorescence spectral analysis of the samples demystifies the existence of oxygen deficient sites. The varying of oxygen vacancy helps band gap tailoring while enhancing Na doping in ZnO.     

Structural,morphological, optical and electrical properties of CdS thin films simultaneously doped with magnesium and chlorine

CdS thin films simultaneously doped with Mg and Cl at different doping concentrations (0, 2, 4, 6 and 8 at%) were prepared on glass substrates by spray pyrolysis technique using perfume atomizer at 400 °C. The effect of Mg and Cl doping concentration on the structural, morphological, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy, UV–Vis spectroscopy and dc electrical measurements, respectively. XRD analysis showed that the undoped and doped CdS films exhibit hexagonal structure with a preferential orientation along the (0 0 2) plane. The 2θ angle position of the (0 0 2) peak of the doped films was shifted towards a higher angle with increasing Mg and Cl concentration. The UV–Vis–NIR absorption spectra of Mg and Cl doped thin films are measured and classical Tauc approach was employed to estimate their band gap energies. The increase in band gap energy from 2.46 to 2.73 eV with the reduction in crystallite size supports quantum size effect. Raman spectra implied that more defects existed in the doped samples. Electrical studies showed that all the films have resistivity in the order of 10¹ Ω-cm and the CdS film with 6 at% Mg and Cl concentration has a minimum resistivity of 1.332 × 10¹ Ω-cm.     

Ni掺杂浓度对CdS:Ni体系电子和光学性质的影响

采用基于密度泛函理论框架下的第一性原理计算方法,对纤锌矿结构CdS:Ni的几何结构、能带结构、电子态密度和光学性质随Ni掺杂浓度的变化进行了系统地研究。计算结果显示,无论是在富镉,还是富硫条件下,计算得到不同Ni掺杂浓度的形成能都较小,说明CdS:Ni系统在实验上是可以实现的;Ni掺杂的CdS在价带顶附近出现杂质带,大大提高了材料的导电率。光学性质的计算结果显示,Ni掺杂后体系的光学性质有很大的改变,在吸收光谱上产生了新的吸收峰,并且随着掺杂浓度的增加,吸收范围增大。所有结果表明,CdS:Ni体系是极具潜力的透明导电材料。     

Influence of Al doping on the structural,morphological and opto-electrical properties of spray deposited lead sulfide thin films

This paper reports the synthesis of Al-doped PbS (PbS:Al) thin films by spray pyrolysis technique on glass substrates. Al doping concentration is varied as 0, 2, 4, 6 and 8 at.% in undoped PbS. Undoped and doped films exhibit cubic crystal structure with a (2 0 0) preferential orientation. The 2θ value of the doped films shifts towards higher Bragg angles confirming a contraction in their unit cell volume. The crystallite size values determined using the Scherrer formula decreased from 27.88 to 25.79 nm with increase in Al doping concentration. EDX spectra confirmed the presence of Al in the doped films. Increased transparency and blue shift in the optical band gap is observed with Al doping. The resistivity range of all the films were found to be in the order of 10² Ω-cm. Increased transparency, widened band gap and decreased resistivity observed make PbS:Al films suitable for tandem solar cells which uses multilayered pn junctions.     

Ni掺杂ZnO晶体结构和红外光谱特性的研究

采用水热法制备了不同比例的Ni掺杂ZnO晶体.XRD和SEM结果表明,Ni掺杂浓度较低时,生成置换型氧化锌镍固溶体;当Ni掺杂浓度增加到5%时,Ni2+过饱和,析出部分斜方NiO.FT-IR发现样品在9001400cm-1之间出现了一个较宽的吸收带,且随Ni掺杂量的增加而加强,表现出良好的红外吸收特性.     

Effect of cobalt (Co<Superscript>2+</Superscript>) concentration on structural,optical, thermal and mechanical properties of potassium acid phthalate (KAP) crystals

Single crystals of pure and Co²⁺ (0.2, 0.4 and 0.6 mol%) doped KAP crystals were grown by low temperature slow evaporation method. The grown crystals were subjected to various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV–visible spectroscopy and Second Harmonic Generation studies. The XRD profile confirms that Co²⁺ ions incorporated into the KAP crystal lattice. The existence of functional groups in the grown crystals have been studied by FTIR analysis. Optical transmission is decreased when doping Co²⁺ concentration increase. After melting point, no decomposition is found in the pure crystal. Vickers micro hardness studies revealed that the doped crystals possess very high hardness values. The dielectric constant, dielectric loss and thermal stability values have been measured as a function of frequency and temperature respectively for the doped crystals.     

The threshold effect of incident exposure energy flux for photorefractive light-induced scattering in doped lithium niobate crystals

The threshold effect of incident exposure energy flux is proposed to measure the light-induced scattering in doped LiNbO₃ crystals. The dependences of the exposure energy flux threshold on the concentration of damage-resistant dopants as well as oxidation–reduction treatment are investigated experimentally in doped LiNbO₃ crystals. The results show that doping with damage-resistant dopants and oxidation–reduction treatment are simple and effective methods to control and optimize the photorefractive properties of doped LiNbO₃ crystals. The high signal-to-noise ratio reconstructions are also demonstrated experimentally according to the incident exposure energy flux threshold in triply-doped LiNbO₃ crystals. Comparing with the known incident intensity threshold method, the exposure energy flux threshold method is more effective for estimating the light-induced scattering of photorefractive recording materials.     

Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl₂ and CuCl₂ were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above CdS valence band, resulting in lower bandgap energy values for the doped CdS films.     

Effect of doping concentration on UV accelerated chemically deposited ZnS:Mn thin films

Pure and Mn alloyed ZnS thin films have been prepared by UV accelerated chemical deposition technique which is simple, economic and easy to monitor. Influence of doping concentration on ZnS thin films was investigated through the structural, compositional, morphological, optical and luminescent studies. The XRD studies confirmed the formation of crystalline films with hexagonal structure. In doped samples the intensities of the prominent peaks increased up to 0.5 wt% Mn and then decreased. The optimum concentration means the amount required to get most suitable characteristics for photovoltaic application. The thickness of the films and the sizes of the crystallites varied in consistent with the structural results. Crystallites became larger in size on doping and appeared to be denser than undoped film. Various structural parameters like stress and micro strain were calculated. The observed strain is compressive in nature which rapidly increased with doping and then remained almost same with doping concentration. The SEM studies revealed the formation of films with almost similar morphology of spherical architectures. All the films exhibited uniform transmission in the high visible region, with a maximum of 80 % for the sample with optimum Mn concentration. Both direct and indirect band gap decreased due to the incorporation of Mn, but showed a blue shift in the fundamental absorption edge with doping concentration up to the optimum dopant content. Undoped and doped films exhibit five distinct luminescence peaks located around 391, 451, 458, 482 and 492 nm. The observed variation in the intensity of the luminescence in doped films clearly indicated the influence of thickness of the films which varied on doping.     

The optical properties of alkali nitrate single crystals

Absorption of non-polarized light by a uniaxial crystal has been studied. The degree of absorption polarization has been calculated as a function of the ratio of optical densities in the region of low and high absorbances. This function is proposed for analysis of the qualitative and quantitative characteristics of uniaxial crystal absorption spectra. Non-polarized light spectra of alkali nitrate single crystals, both pure and doped with thallium, have been studied. It is shown that the absorption band at 300 nm is due to two transitions, whose intensities depend on temperature in various ways. There is a weak band in a short wavelength range of the absorption spectrum of potassium nitrate crystal, whose intensity increases with thallium doping. The band parameters of alkali nitrate single crystals have been calculated. Low-energy transitions in the nitrate ion have been located.     

Structural,morphological, optical and electrical properties of spray deposited zinc doped copper oxide thin films

Nanostructured spray deposited zinc (Zn) doped copper oxide (CuO) thin films were characterized by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy. XRD patterns of CuO and Zn doped CuO thin films indicated monoclinic structure with the preferred orientation along \(\left( {\bar 111} \right)\) plane. Maximum value of crystallite size is found about 28.24 nm for 5 at% Zn doped CuO thin film. In FESEM images, nanoparticles were observed around the nucleation center. EDX analysis confirms the presence of all component elements in CuO and Zn doped CuO thin films. Analysis by AFM of CuO and Zn doped CuO thin films figured out decrease of surface roughness due to Zn doping. UV–Vis–NIR spectroscopy showed that CuO and Zn doped CuO thin films are highly transparent in the NIR region. Optical band gap of CuO thin films decreased with substrate temperature and that of Zn doped CuO thin films increased with Zn concentration. Refractive index of CuO and Zn doped CuO thin films raised with photon wavelength and became constant in the NIR region. 5 at% Zn doped CuO thin film showed the highest optical conductivity and the lowest electrical resistivity at room temperature.     

Influence of Au Photodeposition and Doping in CdS Nanorods: Optical and Photocatalytic Study

Au-modified CdS nanorods (100–200 nm × 5–10 nm) are synthesized via two different techniques, namely photodeposition and doping. The prepared samples are characterized by x-ray powder diffraction, transmission electron microscopy (TEM), and UV–vis and fluorescence spectroscopy. X-ray diffraction study confirmed the hexagonal phase of bare and Au-CdS samples, whereas, 5 wt% Au³⁺ doping into CdS resulted in a slight distortion in the crystal structure toward higher degree side. TEM images revealed the fine distribution of Au nanodeposits of size in the range of 2.5–4.5 nm on to the CdS surface in the photodeposited sample. The optical spectrum shows a significant red-shift in absorption onset (485 nm → 515 nm) and band-edge emission (505 nm → 512 nm) of CdS nanorods with the replacement of certain Cd²⁺ ions with Au³⁺. The influence of Au photodeposition and doping in CdS nanorods was comparatively tested by photooxidation of RhB (50 ppm) dye aqueous solution under direct sunlight irradiation (35–40 mWcm^?2). Our results point out that 5 wt% Au³⁺ doping into CdS nanorods remarkably improved its activity and stability due to homogeneous dispersion of charge throughout the crystal, quick Fermi level equilibration, and an improvement in ionic bond formation.     

Synthesis of heavily doped nanocrystalline ZnO:Al powders using a simple soft chemical method

Aluminum doped nanocrystalline zinc oxide powders were synthesized using a simple soft chemical method from precursor solutions having different Al doping levels (0–20?at.% in steps of 5?at.%). X-ray diffraction studies showed that the product has pure hexagonal wurtzite structure without any secondary phases such as Al₂O₃ and ZnAl₂O₄ etc. The preferential orientation plane was found to be (101) for all the samples irrespective of the Al doping level. But the degree of crystallinity of the powder gradually decreased as the doping level increased. The SEM images revealed that the crystals have hexagonal prism like structure when the Al doping level was 5?at.% and the shape changes gradually and attains a thread like structure for heavy doping. The EDAX and FTIR studies confirmed the proper incorporation of Al³⁺ ions in the Zn²⁺ sites of the ZnO lattice even in the heavily doped powders. The optical band gap increased remarkably (from 3.12 to 3.48?eV) with the increase in the Al doping level.     

Hall Effect in Bulk‐Doped Organic Single Crystals

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N , cm^?3) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk‐doped organic single crystals. Here, the Hall effect in bulk‐doped single‐crystal organic semiconductors is measured. A key feature of this work is the ultraslow co‐deposition technique, which reaches as low as 10^?9 nm s^?1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N , cm^?3) and the Hall mobility (μ_H) of bulk‐doped rubrene single crystals, which have a band‐like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.