Investigation of forming-gas annealed CeO<Subscript>2</Subscript> thin film on GaN

The effects of post-deposition annealing temperatures (400, 600, 800, and 1,000°C) in forming gas (95% N₂ + 5% H₂) ambient on metal–organic decomposed cerium oxide (CeO₂) thin films deposited on n-type GaN substrate had been investigated. The occurrence of CeO₂ phase transformation was reported and presence of CeO₂, α-Ce₂O₃, and β-Ga₂O₃ had been detected, depending on the annealing temperature. As the annealing temperature increased, grain size and microstrains of CeO₂ films were, respectively, increased and reduced. Metal–oxide–semiconductor characteristics of the annealed samples were systematically investigated. The highest dielectric breakdown field was perceived by sample annealed at 400°C due to the reduction of semiconductor–oxide interface trap density and effective oxide charge.     

Influence of annealing times on morphological characteristics of ceramic thin films by RF-magnetron sputtering using Zn-enriched (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramic target

The BaO–SrO–ZnO–Nb₂O₅ ceramic thin films have been deposited by radio frequency (RF) magnetron sputtering, using a Zn-enriched (Ba_0.3Sr_0.7) (Zn_1/3Nb_2/3)O₃ target, followed by annealing in O₂ atmosphere at 1,200 °C for 15, 30, 45, and 60 min. The results show that the surface morphologies of samples are crack-free and compact with well-crystallized structures. Grain sizes of thin films annealed at different times increase with the increasing annealing times, and when the annealing time is of 45 and 60 min, the grains change from spherical shape to columnar shape. RMS values of the thin films decrease with the increase in the annealing times from 15 to 30 min, while the RMS values increase with the increase in the annealing times from 30 to 60 min.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Structural and optical properties of nanocrystalline WO<Subscript>3</Subscript> thin films

The nanocrystalline WO₃ thin films were deposited by r.f. magnetron sputtering on quartz and p- type Si (100) substrates at a constant power of 25 W and at three different sputtering pressures (0.05, 0.01 and 0.5 mbar) and post annealed at different temperatures. The deposited films were characterized by XRD, UV–VIS spectrophotometry, ellipsometry and atomic force microscopy (AFM). The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and post annealed at 573 and 673 K have the predominant orthorhombic phase, whereas at 0.1 mbar and 573, 673 K triclinic phase is predominant. When sputtering pressure is at 0.5 mbar the predominant phase is monoclinic when annealed at 473 K and triclinic at 673 K. The optical energy gap is influenced significantly by sputtering pressure and post annealing temperatures. The optical energy gap of the films deposited at higher sputtering pressures and post annealed at lower temperatures is high due to smaller crystallite sizes. The thickness of all deposited films at different conditions is around 200 nm.     

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.     

Effect of oxygen to argon ratio on the properties of thin SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films deposited by r.f. sputtering

Energy Dispersive X-ray and X-ray Photoelectron (XPS) spectroscopies show that SiO _x films deposited by reactive r.f. magnetron sputtering at partial pressure ratios R between oxygen and argon in a wide range (1–0.005) have compositions close to the stoichiometric one. For these films high temperature annealing at 1,000 °C shifts the band in the Fourier Transform-Infrared spectrum due to the Si–O–Si stretching vibration to values typical of stoichiometric SiO₂. Further decrease of R leads to splitting of the Si 2p XPS line indicating increase of the Si content and formation of a second phase in a SiO₂ matrix. The electrical properties of test MOS structures with SiO _x gate dielectric, regarding defect density in the oxide and at the SiO _x /c-Si interface, degrade with the decrease of R. High temperature annealing at 1,000 °C strongly improves the properties of all films regarding leakage current and properties of the interface.     

The effect of growth conditions and N<Subscript>2</Subscript>/O<Subscript>2</Subscript> ambient on LO-phonon replicas during epitaxial growth of ZnO on c-sapphire

High quality heteroepitaxial thin films of ZnO:N were grown by pulsed laser deposition using a two-step growth method and annealed in situ at different temperatures and ambient conditions. Films were analyzed by X-ray diffraction (XRD), electrical measurements, and photoluminescence experiments at low temperatures to investigate the effect of nitrogen doping. The XRD results demonstrate epitaxial growth on the c-sapphire substrates, with average grain size of 57 nm. Photoluminescence spectra reveals a peak at 3.061 eV (405.1 nm) which is part of the longitudinal-optical-phonon replicas of excitons bound to neutral acceptors \textA₁⁰  \textX_\textA {\text{A}}_{1}^{0} \,{\text{X}}_{\text{A}} at 3.348 eV (370.4 nm), attributed in recent investigations to a newly reported donor–acceptor pair. Electrical resistivity and Hall effect measurements were performed using standard four point van der Pauw geometry at room temperature. Fresh films exhibited a resistivity of 3.1 × 10⁻³ Ω cm, a carrier density of 1.3 × 10¹⁹ cm⁻³, and a mobility of 53 cm²/V s. During approximately 2 weeks the as-deposited films presented a p-type behavior, as shown by the positive sign of the Hall constant measured. Thereafter, films reverted to n-type. From electrical measurements and photoluminescence spectra, the acceptor energy was determined to be 150 meV, in close agreement with reported values. These results are consistent with those presented in the literature for high purity crystals or homoepitaxial thin films, even though samples for the present study were processed at lower annealing temperature.     

Dye-sensitized solar cells using TiO<Subscript>2</Subscript> nanoparticles transformed from nanotube arrays

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ mesoporous layers obtained by very simple method—transformation of TiO₂ nanotube (NT) films grown by electrochemical oxidation to nanoparticle (NP) films. This transformation is based on thermal annealing of TiO₂ NT arrays formed by anodization of titanium foil in fluorine ambient. Performance of DSSCs fabricated with different size NPs was studied in the range from 35 to 350 nm. Highest nominal efficiency (9.05%) was achieved for DSSC with NP size 65 nm while the lowest nominal efficiency (1.48%) was observed for DSSCs with NP size 350 nm. The dependence of the solar cell parameters with NP size is discussed.     

Electrical properties of pulsed laser deposited Bi<Subscript>2</Subscript>Zn<Subscript>2/3</Subscript>Nb<Subscript>4/3</Subscript>O<Subscript>7</Subscript> thin films for high K gate dielectric application

Metal Insulator Semiconductor (MIS) capacitors with monoclinic bismuth zinc niobate pyrocholre having the composition Bi2Zn2_/3Nb_4/3O₇ (m-BZN) dielectric layer were fabricated and characterized. Capacitance voltage (C–V) and current voltage measurements were utilized to obtain the dielectric properties, leakage current density and interface quality. The results shows that the obtained m-BZN thin films presents a high dielectric constant in between 30 and 70, a good interface quality with silicon and a leakage current density of 10 μA/cm² for a field strength of 100 kV/cm which is acceptable for high performance logic circuits. The equilent oxide thickness for the films annealed at 200 °C was 10 nm. These results suggest that m-BZN thin films can be potentially integrated as gate dielectric materials in CMOS technology.     

Study of surface morphology and optical properties of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films with annealing

Nb₂O₅ films have been deposited on variety of substrates using the sol-gel dip coating technique. As-deposited films on all substrates are amorphous. Films were annealed under controlled ambience at 300, 400 and 600°C for 5 h. As-deposited films on glass substrate show uniform surface structure. The crystal structure and surface topography are found to depend strongly on the annealing temperature and nature of the substrates. The average grain size of 40 nm is observed in films annealed at 300°C. On annealing at 400°C increasing grain size and resulting fusing of them, enhanced surface roughness. Films deposited on NaCl substrates crystallized into a stable monoclinic phase and those deposited on single crystal Si substrates crystallized into hexagonal phase after annealing at 600°C. The as-deposited films show very high transmittance (>90%) in the visible region. The optical band gap is observed to increase from 4.35 eV when the films are in amorphous state to 4.87 eV on crystallization.     

Structural,optical and electrical studies on nanocrystalline tin oxide (SnO<Subscript>2</Subscript>) thin films by electron beam evaporation technique

Nanocrystalline tin oxide (SnO₂) thin films were coated using electron beam evaporation technique on glass substrates. To study the gleaming out look of the structure and surface morphological changes, the films were annealed in the temperature 350–550 °C for 1 h. The annealed films were subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) studies. The XRD patterns of SnO₂ thin films as-deposited and annealed at 350 °C illustrate that the films were amorphous, and beyond 350 °C and thereafter they became polycrystalline with tetragonal structure. The crystallite size of the annealed films, obtained through the XRD analysis, increased with the increasing annealing temperature, and it was found to be from 3.6 to 12 nm. The photoluminescence (PL) studies on these films were also carried out. The origin of luminescence was assigned to the defects of the nanocrystalline SnO₂ films. The Optical studies (UV-VIS) were performed and the optical band gab energy (Eg) calculations, the dependence of absorption coefficient on the photon energy at short wavelengths, were found to be increasing from 3.65 to 3.91 eV is also investigated.     

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.     

Facile fabrication of NiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> films and their unique electrochromic properties

The electrochromic (EC) NiO _x H _y films were fabricated through a facile sol–gel method. The formation of high quality NiO _x H _y films came from adding the xerogel back into the sol and prolonging the annealing time at gradually increasing temperature up to 250 °C. Scanning electron microscopy and atomic force microscopy characterizations indicated films were compact, homogenous, and smooth. Glance angle X-ray diffraction investigation testified NiO _x H _y films were of poor crystallization. The Fourier transform infrared, and thermogravimetry and differential thermal analysis showed that films contained the mixture of NiO, Ni(OH)₂, NiOOH, water, and organic substance. With the increasing of the xerogel ratio, the optical absorbance and reflectance of films had larger differences between the colored and bleached state, respectively. The film with the xerogel ratio of 1:5 showed excellent EC properties with a transmittance contrast as high as 60.88% at λ = 560 nm, which was higher than other sol–gel nickel oxide films reported.     

Photoluminescence of Si<Subscript>0.9</Subscript>Ge<Subscript>0.1</Subscript>O<Subscript>2</Subscript> and GeO<Subscript>2</Subscript> films irradiated with silicon ions

We have studied the photoluminescence (PL) of GeO₂ and 90 mol % SiO₂-10 mol % GeO₂ films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO₂ films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO₂-10 mol % GeO₂ films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.     

Structural study of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> by electron microscopy

Detailed crystallographic data on high-quality Li₂MnO₃ material has been obtained using a combination of X-ray diffraction (XRD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), and 0.1 nm probe high-angle annular dark-field imaging (HAADF) in a scanning transmission electron microscope. A high-purity Li₂MnO₃ powder was annealed at 950 °C for 3 days to obtain predominantly defect-free grains which average size was 3.0 ± 1.5 μm. Rietveld refinement indicated that the C2/m spacegroup provided the best fit for the XRD data. Electron diffraction patterns obtained along various zone axes, on defect-free oxide particles, could be uniquely indexed to the monoclinic structure. HREM and HAADF images of defect-free grains were consistent with a Li–Mn–Mn– arrangement, i.e., lithium ordering in the transition metal planes. Low-magnification TEM images occasionally revealed stacking defects within oxide particles. HREM images of sample areas containing defects revealed a low density of stacking faults within the monoclinic sequence, resulting in a trigonal P3 ₁ 12 local arrangement.     

Luminescence properties and electronic structure of Sm<Superscript>3+</Superscript>-doped YAl<Subscript>3</Subscript>B<Subscript>4</Subscript>O<Subscript>12</Subscript>

The luminescence properties of Sm³⁺ ions in YAl₃B₄O₁₂ were studied upon synchrotron excitation in the 3.8–11 eV region. In addition to the 4f → 4f excitation bands, the excitation spectra of the Sm³⁺ emission contain broad bands at 6.1 and ~7.0 eV. These bands are attributed to charge transfer transition in Sm³⁺–O²⁻ complexes and 4f → 5d transition of Sm³⁺ ions, respectively. The optical absorption edge of YAl₃B₄O₁₂ was determined at 7.3 eV. A comparison with the results of electronic structure calculations on YAl₃B₄O₁₂ is also made.     

Influence of Sm substitution on the phase,microstructure and microwave dielectric properties of SrLa<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript>

New dielectric ceramics in the SrLa_4−xSm_xTi₅O₁₇ (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route to investigate the effect of Sm⁺³ substitution for La⁺³ on the phase, microstructure and microwave dielectric properties. At x = 0–3, all the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1500–1580 °C. At x = 4, a mixture of Sm₂Ti₂O₇ and SrTiO₃ formed. The maximum Sm⁺³-containing single phase ceramics, SrLaSm₃Ti₅O₁₇, exhibited relative permittivity (ε_r) = 42.6, temperature coefficient of resonant frequency (τ _f ) = −96 ppm/^oC and quality factor (Q _u f _o ) = 7332 GHz. An analysis of results presented here indicates that SrLa_4−xSm_xTi₅O₁₇ ceramics, exhibiting τ _f  ~ 0 and ε_r ~ 53 could be achieved at x ~ 1.4 but at the cost of decrease in Q _u f _o .     

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.     

Tunable optical and nano-scale electrical properties of WO<Subscript>3</Subscript> and Ag-WO<Subscript>3</Subscript> nanocomposite thin films

WO₃ and Ag-WO₃ nanocomposite thin films have been synthesized from pure WO₃ and Ag-WO₃ composite pressed powder targets submitted to pulses generated by a frequency quadrupled Nd:yttrium aluminium garnet (YAG; λ = 266 nm, τ ~ 5 ns, ν = 10 Hz) laser source. The irradiations were performed in low pressure oxygen atmosphere. The obtained results proved the possibility to tailor the synthesized thin films optical properties in the UV–Visible spectral region and their nano-scale electrical characteristics through the process parameters, as ambient oxygen pressure value during the thin films deposition and Ag concentration of the Ag-WO₃ composite targets. The tunable optical and electrical features allow for the creation of new materials for future applications as photocatalysts, transparent conducting electrodes, electrochromic or chemical and biological sensor devices.     

Memory characteristics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/LaAlO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> multilayer structures with tunnel oxide thickness variation

Charge trap flash (CTF) memory devices are candidates to replace NAND flash devices. In this study, Pt/Al₂O₃/LaAlO₃/SiO₂/Si multilayer structures with lanthanum aluminate charge traps were fabricated for nonvolatile memory device applications. An aluminum oxide film was used as a blocking oxide for low power consumption in the program/erase operation and to minimize charge transport through the blocking oxide layer. The thickness of SiO₂ as tunnel oxide layer was varied from 30 to 50 Å. Thicknesses of oxide layers were confirmed by high resolution transmission electron microscopy (HRTEM) and all the samples showed amorphous structure. From the C–V measurement, a maximum memory window of 3.4 V was observed when tunnel oxide thickness was 40 Å. In the cycling test for reliability, the 30 Å tunnel oxide sample showed a relatively large memory window reduction by repeated program/erase operations due to the high electric field of ~10 MV/cm through tunnel oxide. The other samples showed less than 10% loss of memory window during 10⁴ cycles.