Structural and surface morphological properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>S<Subscript>2</Subscript> thin film

Preparation of layered type semiconductor Mo_0.5W_0.5S₂ ⁻ thin films has been successfully done by using chemical bath deposition method. Objective of the studies are related to structural, optical, morphological and electrical properties of the thin films. The preparation method is based on the reaction between tartarate complex of Mo and W with thiourea in an aqueous alkaline medium at 363 K. X-Ray diffraction reveals a polycrystalline film composed of both MoS₂ and WS₂ phases. The optical study shows that the band gap of the film is 1.6 eV. Electrical conductivity is high which is in the order of 10⁻³–10⁻² (Ώ cm)⁻¹.     

Structural,optical and microscopic properties of chemically deposited In<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films

Solar cell technologically important binary indium selenide thin film has been developed by relatively simple chemical method. The reaction between indium chloride, tartaric acid, hydrazine hydrate and sodium selenosulphate in an aqueous alkaline medium at room temperature gives deposits In₂Se₃ thin film. Various preparative parameters are discussed. The as grown films were found to be transparent, uniform, well adherent, red in color. The prepared films were studied using X-ray diffraction, scanning electron microscopy, atomic absorption spectroscopy, Energy dispersive atomic X-ray diffraction, optical absorption and electrical conductivity properties. The direct optical band gap value E_g for the films was found to be as the order of 2.35 eV at room temperature and having specific electrical conductivity of the order of 10⁻² (Ω cm)⁻¹ showing n-type conduction mechanism. The utility of the adapted technique is discussed from the point of view of applications considering the optoelectric and structural data obtained.     

Electrical and crystallographic properties of nanocrystalline CdSe<Subscript>0.5</Subscript>S<Subscript>0.5</Subscript> composite thin films deposited by dip method

A dip method is employed for the deposition of CdSe_0.5S_0.5 composite thin film at room temperature. Cadmium sulphate, thiourea and sodium selenosulphate were used as the basic source material. Solid solution with cubic phase was observed from X-ray diffraction studies. The specific conductivity of the film was found to be in order of 10⁻⁷ (Ωcm)⁻¹. The temperature dependence of an electrical conductivity, thermoelectrical power, carrier density and carrier mobility for CdSe_0.5S_0.5 thin films have been examined. The low temperature conductivity is governed by a variable range of conduction while grain boundary limited conduction mechanism is predominant at higher temperature.     

Optical,structural and electrical investigations on PbTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The fabrication of devices with lead salts and their alloys with detecting and lasing capabilities has been an important technological development. The high quality polycrystalline thin films of PbTe_1−x S _x with variable composition (0 ≤ x ≤ 1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. Optical, structural and electrical properties of PbTe_1−x S _x thin films have been examined. Absorption coefficient and band gap of the films were determined by absorbance measurements in wavelength range 2,500–5,000 nm using FTIR spectrophotometer. Sample nature, crystal structure and lattice parameter of the films were determined from X-ray diffraction patterns. DC conductivity and activation energy of the films were measured in temperature range 300–380 K through I–V measurements.     

Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Optical band gap of Sn<Subscript>0.2</Subscript>Bi<Subscript>1.8</Subscript>Te<Subscript>3</Subscript> thin films

Sn_0.2Bi_1.8Te₃ thin films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500–4000 cm⁻¹. From the optical absorption data the band gap was evaluated and studied as a function of film thickness and deposition temperature. The data indicate absorption through direct interband transition with a band gap of around 0.216 eV. The detailed results are reported here.     

Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Deposition of AgGaS<Subscript>2</Subscript> thin films by double source thermal evaporation technique

In this study, polycrystalline AgGaS₂ thin films were deposited by the sequential evaporation of AgGaS₂ and Ag sources with thermal evaporation technique. Thermal treatment in nitrogen atmosphere for 5 min up to 700 °C was applied to the deposited thin films and that resulted in the mono phase AgGaS₂ thin films without the participation of any other minor phase. Structural and compositional analyses showed the structure of the films completely changes with annealing process. The measurements of transmittance and reflectance allowed us to calculate the band gap of films lying in 2.65 and 2.79 eV depending on annealing temperature. The changes in the structure with annealing process also modify the electrical properties of the films. The resistivity of the samples varied in between 2 × 10³ and 9 × 10⁶ (Ω-cm). The room temperature mobility depending on the increasing annealing temperature was in the range of 6.7–37 (cm² V⁻¹ s⁻¹) with the changes in carrier concentrations lying in 5.7 × 10¹³–2.5 × 10¹⁰ cm⁻³. Mobility-temperature dependence was also analyzed to determine the scattering mechanisms in the studied temperature range with annealing. The variations in the electrical parameters of the films were discussed in terms of their structural changes.     

Orientation controlling of Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin films prepared on silicon substrates with the thickness of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> electrodes

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Phase transition and electrical properties in the Li-modified Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Phase transition and electrical properties were demonstrated for a Li-modified Bi_0.5Na_0.5TiO₃-based solid solution. (0.935 − x)Bi_0.5Na_0.5TiO₃ − xBi_0.5Li_0.5TiO₃ − 0.065BaTiO₃ with 0.5 mol% Mn doping was prepared by a conventional solid state reaction method. Close inspection of X-ray diffraction patterns indicated that no characteristic peaks splitting happened, indicating the pseudocubic structure for all the compositions. At a critical composition x of 0.06, optimized performance was obtained with piezoelectric constant d ₃₃ of 176 pC/N, electromechanical coupling factors k _P of 0.33, and k _t of 0.52, respectively. In addition, it was found that the Li substitution could lead to a disruption of long-range ferroelectric order and obtain enhanced frequency dispersion behavior accompanied with the decreasing of the depolarization temperature T _d, which was responsible for the observed weaker ferroelectric polarization and electromechanical response. The composition induced structure evolution was also discussed combined with the Raman spectroscopy.     

Synthesis and optical properties of CeO<Subscript>2</Subscript> nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO₂) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO₂ thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO₂ was observed at 465 cm⁻¹. The optical properties of the CeO₂ films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (E _g) of CeO₂ nanocrystalline films was calculated as 2.58 eV.     

Deposition and optoelectronic properties of ITO (In<Subscript>2</Subscript>O<Subscript>3</Subscript>:Sn) thin films by Jet nebulizer spray (JNS) pyrolysis technique

Nanocrystalline ITO thin films were deposited on glass substrates by a new spray pyrolysis route, Jet nebulizer spray (JNS) pyrolysis technique, for the first time at different substrate temperatures varying from 350 to 450 °C using a precursor containing indium and tin solution with 90:10 at% concentration. The structural, optical and electrical properties have been investigated as a function of temperature. X-ray diffraction analysis showed that the deposited films were well crystallized and polycrystalline with cubic structure having (222) preferred orientation. The optical band gap values calculated from the transmittance spectra of all the ITO films showed a blue shift of the absorbance edge from 3.60 to 3.76 eV revealing the presence of nanocrystalline particles. AFM analysis showed uniform surface morphology with very low surface roughness values. XPS results showed the formation of ITO films with In³⁺ and Sn⁴⁺ states. TEM results showed the nanocrystalline nature with grain size about 12-15 nm and SAED pattern confirmed cubic structure of the ITO films. The electrical parameters like the resistivity, mobility and carrier concentration are found as 1.82 × 10⁻³ Ω cm, 8.94 cm²/Vs and 4.72 × 10²⁰ cm⁻³, respectively for ITO film deposited at 400 °C. These results show that the ITO films, prepared using the new JNS pyrolysis technique, have the device quality optoelectronic properties when deposited under the proposed conditions at 400 °C.     

The effect of post-annealing under CdCl<Subscript>2</Subscript> atmosphere on the properties of ITO thin films deposited by DC magnetron sputtering

Indium tin oxide (ITO) films deposited by DC magnetron sputtering were annealed under CdCl₂ atmosphere at different temperatures. The effects of CdCl₂ heat-treatment on the structural, electrical and optical properties of the films were investigated. The X-ray diffraction measurement proves the annealing results in a change of preferred orientation from (400) to (222). It is found the resistivity increases from 1.49 × 10⁻⁴ Ω cm of the as-deposited film to 6.82 × 10⁻⁴ Ω cm of the film annealed at 420 °C. The optical energy gap for the film varies from 3.97 to 3.89 eV. It is also found that the CdCl₂ heat-treatment results in narrowing the energy gap of ITO film.     

Effect of Cr doping on the structure,optical and magnetic properties of multiferroic BiFeO<Subscript>3</Subscript> thin films

Multiferroic BiCr _x Fe_1−x O₃ (BCFO) (0 ≤ x ≤ 0.12) thin films were fabricated on silicon substrates by sol–gel technique. The microstructure and properties of the films are characterized using X-ray diffraction, spectroscopic ellipsometry, micro-Raman spectrometry and a Modular Control system. The BCFO films are the rhombohedral structure with the Cr content up to 7%. Raman scattering spectra of the BCFO films demonstrate the transformation of structure with the Cr content exceeding 10%. The band gap of the BCFO films is from 2.53 to 2.82 eV with the Cr content being from 0 to 12%. The magnetization of the BCFO films is significantly enhanced with the increasing of the Cr content.     

Chemical synthesis and characterization of hydrous tin oxide (SnO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>:H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>O) thin films

In the present investigation, we report chemical synthesis of hydrous tin oxide (SnO ₂ :H ₂ O) thin films by successive ionic layer adsorption and reaction (SILAR) method at room temperature ( \thicksim \thicksim 300 K). The films are characterized for their structural and surface morphological properties. The formation of nanocrystalline SnO ₂ with porous and agglomerated particle morphology is revealed from X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, respectively. The Fourier transform infrared spectroscopy (FTIR) study confirmed the formation of Sn–O phase and hydrous nature of the deposited film. Static water contact angle studies showed the hydrophilic nature of SnO ₂ :H ₂ O thin film. Electrical resistivity showed the semiconducting behaviour with room temperature electrical resistivity of 10 ⁵  W\boldsymbol\Omega cm. The electrochemical properties studied in 0·5 M Na ₂ SO ₄ electrolyte showed a specific capacitance of 25 F g ^− 1 at 5 mVs ^− 1 scan rate.     

Physicochemical properties of La<Subscript>3</Subscript>Ga<Subscript>5.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>14</Subscript>

We report the optical and dielectric properties and microhardness of La₃Ga_5.5Ta_0.5O₁₄ lanthanum gallium tantalate (langatate) crystals. Analysis of the optical transmission spectra of the crystals in relation to their refined compositions indicates that the bands at 34000–35000 and 27000–28000 cm⁻¹ are due to lanthanum and oxygen vacancies, respectively, and that the band at 20000–21000 cm⁻¹ is responsible for the yellow (orange) coloration of the crystals. Their resistivity and microhardness decrease with increasing oxygen vacancy concentration.     

Linear and nonlinear optical properties of RF sputtered (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ferroelectric thin films

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O₃ (PLZT) ferroelectric thin films were presented in this paper. The PLZT ferroelectric thin films have been in situ grown on quartz substrates by radio-frequency (RF) magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by X-ray diffraction and atomic force microscopy, respectively. It can be found that the PLZT thin films exhibit well-crystallized perovskite structure and good surface morphology. The fundamental optical constants (the band gap energy, linear refractive index, and linear absorption coefficient) were obtained through the optical transmittance measurements. A Z-scan technique was used to investigate the optical nonlinearity of the PLZT thin films on quartz substrates. The films display the strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n ₂ is determined to be 1.21 × 10⁻⁶ esu for the PLZT thin films. All results show that the PLZT ferroelectric thin films have potential applications in optical limiting, switching, and modulated-type optical devices.     

Microstructure and H<Subscript>2</Subscript>S gas sensing properties of nanocrystalline perovskite-type La<Subscript>0.6</Subscript>Co<Subscript>0.4</Subscript>Mn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Nanocrystalline La_1−x Co _x Mn_1−y Ni _y O₃ (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H₂S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H₂S gas response of pure LaMnO₃ was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and B-site, respectively. The La_0.6Co_0.4Mn_0.5Ni_0.5O₃ shows high response towards H₂S gas at an operating temperature 250 °C. The Pd-doped La_0.6Co_0.4Mn_0.5Ni_0.5O₃ sensor was found to be highly sensitive to H₂S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed.     

Fabrication,dielectric and ferroelectric properties of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> film with preferred orientation

Ba_0.6Sr_0.4TiO₃ films were fabricated by RF magnetron sputtering method. The X-ray diffraction (XRD) showed that the preferred orientation of films growing on platinum Si substrates can be tailored by sputtering pressure. The processing parameters such as sputtering pressure and substrate temperature were optimized to obtain a developed perovskite film with (110) preferred orientation. The polarization hysteresis loops and permittivity–voltage curves of the (110)-oriented film have been investigated,which demonstrated that the film is in ferroelectric phase at room temperature. Besides, it had excellent fatigue properties without polarization reduction after about 10¹⁰ switch cycles, and showed low leakage current (10⁻⁹–10⁻⁷ A/cm²) within an applied voltage of 5 V. Finally, the leakage current mechanism was studied.