Tuning of Optical Properties via Annealing of Bismuth Ferrite (BiFeO3) Thin Films

In this study we are reporting annealing induced optical properties of bismuth ferrite (BiFeO3) thin films deposited on glass substrate via spin coating at 5000 rpm. The structural, optical and surface morphology of BiFeO3 (BFO) thin films have been studied via X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Optical absorption (UV-Vis) and Photoluminescence (PL) spectroscopy. XRD spectra confirm annealing induced phase formation of BiFeO3 possessing a rhombohedral R3c structure. The films are dense and without cracks, although the presence of porosity in BFO/glass was observed. Moreover, optical absorption spectra indicate annealing induced effect on the energy band structure in comparison to pristine BiFeO3. It is observed that annealing effect shows an intense shift in the UV-Vis spectra as diffuse absorption together with the variation in the optical band gap. The evaluated optical band gap values are approximately equal to the bulk band gap value of BiFeO3.

Optical and electrical properties of BaSnO_(3) and In_2O_(3) mixed transparent conductive films deposited by filtered cathodic vacuum arc technique at room temperature

For the crystalline temperature of BaSnO_(3)(BTO)was above 650℃,the transparent conductive BTO-based films were always deposited above this temperature on epitaxy substrates by pulsed laser deposition or molecular beam epitaxy till now which limited there application in low temperature device process.In the article,the microstructure,optical and electrical of BTO and In_(2)O_(3) mixed transparent conductive BaInSnO_(x)(BITO)film deposited by filtered cathodic vacuum arc technique(FCVA)on glass substrate at room temperature were firstly reported.The BITO film with thickness of 300 nm had mainly In_(2)O_(3) polycrystalline phase,and minor polycrystalline BTO phase with(001),(011),(111),(002),(222)crystal faces which were first deposited at room temperature on amorphous glass.The transmittance was 70%–80%in the visible light region with linear refractive index of 1.94 and extinction coefficient of 0.004 at 550-nm wavelength.The basic optical properties included the real and imaginary parts,high frequency dielectric constants,the absorption coefficient,the Urbach energy,the indirect and direct band gaps,the oscillator and dispersion energies,the static refractive index and dielectric constant,the average oscillator wavelength,oscillator length strength,the linear and the third-order nonlinear optical susceptibilities,and the nonlinear refractive index were all calculated.The film was the n-type conductor with sheet resistance of 704.7Ω/□,resistivity of 0.02Ω⋅cm,mobility of 18.9 cm2/V⋅s,and carrier electron concentration of 1.6×10^(19) cm^(−3) at room temperature.The results suggested that the BITO film deposited by FCVA had potential application in transparent conductive films-based low temperature device process.

Dual-phase coexistence enables to alleviate resistance drift in phase-change films

The amorphous phase-change materials with spontaneous structural relaxation leads to the resistance drift with the time for phase-change neuron synaptic devices. Here, we modify the phase change properties of the conventional Ge_2Sb_2Te_5(GST) material by introducing an SnS phase. It is found that the resistance drift coefficient of SnS-doped GST was decreased from 0.06 to 0.01. It can be proposed that the origin originates from the precipitation of GST nanocrystals accompanied by the precipitation of SnS crystals compared to single-phase GST compound systems. We also found that the decrease in resistance drift can be attributed to the narrowed bandgap from 0.65 to 0.43 eV after SnS-doping. Thus, this study reveals the quantitative relationship between the resistance drift and the band gap and proposes a new idea for alleviating the resistance drift by composition optimization, which is of great significance for finding a promising phase change material.

DDI METHOD FOR MEASURING OPTICAL CONSTANTS OF THIN FILMS

双光束双波长激光干涉（ＤＤＩ）法采用自行设计的可测双波长氦氖激光器作光源，可在同一光路中通过二次测量获得薄膜样品两个波长（０．６３３μｍ，３．３９μｍ）下的光学常数，即折射率、消光系数和厚度，文中论述了调量原理、测量装置和测量结果．

Effect of annealing treatment on the structural, optical, and electrical properties of Al-doped ZnO thin films

Highly conductive and transparent Al-doped ZnO （AZO） thin films were prepared from a zinc target containing Al （1.5 wt.%） by direct current （DC） and radio frequency （RF） reactive magnetron sputtering. The structural, optical, and electrical properties of AZO films as-deposited and submitted to annealing treatment （at 300 and 400℃, respectively） were characterized using various techniques. The experimental results show that the properties of AZO thin films can be further improved by annealing treatment. The crystallinity of ZnO films improves after annealing treatment. The transmittances of the AZO thin films prepared by DC and RF reactive magnetron sputtering are up to 80% and 85% in the visible region, respectively. The electrical resistivity of AZO thin films prepared by DC reactive magnetron sputtering can be as low as 8.06 x 10-4 Ωcm after annealing treatment. It was also found that AZO thin films prepared by RF reactive magnetron sputtering have better structural and optical properties than that prepared by DC reactive magnetron sputtering.

Influence of oxygen gas content on the structural and optical properties of ZnO thin films deposited by RF magnetron sputtering at room temperature

Zinc oxide （ZnO） thin films were deposited on sapphire （0001） substrates at room temperature by radiofrequency （RF） magnetron sputtering at oxygen gas contents of 0%, 25%, 50% and 75%, respectively. The influence of oxygen gas content on the structural and optical properties of ZnO thin films was studied by a surface profile measuring system, X-ray diffraction analysis, atomic force microscopy, and UV spectro- photometry. It is found that the size of ZnO crystalline grains increases first and then decreases with the increase of oxygen gas content, and the maximum grain size locates at the 25% oxygen gas content. The crystalline quality and average optical transmittance （〉90%） in the visi- ble-light region of the ZnO film prepared at an oxygen gas content of 25% are better than those of ZnO films at the other contents. The obtained results can be attributed to the resputtefing by energetic oxygen anions in the growing process.

Optical and magnetic properties of porous anodic alumina films embedded with Co nanowires

A simple method to tune the optical properties of porous anodic alumina （PAA） films embedded with Co nanowires （PAA@Co nanocomposite films） is reported in this paper. The films exhibit vivid structural colors and magnetic properties. The optical properties of the films can be effectively tuned by adjusting the thickness of the PAA template. The deposition of Co nanowires greatly increases the color saturation of the PAA films. The theoretical results of the changes in structural color according to the Bragg-Snell formula are consistent with the experimental results. PAA@Co films can be used in many areas, including decoration, display, and multifunctional anti-counterfeiting applications.

Optical and Electrical Properties of ZnO/CdO Composite Thin Films Prepared by Pulse Laser Deposition

ZnO/CdO composite films with different CdO contents are obtained by pulse laser deposition technique. The structural, optical and electrical properties of the composite [liras are investigated by x-ray diffraction, photolu- minescence and electrical resistivity measurements, respectively. The results show that the UV emission is at a constant peak position in the photoluminescence spectra. Meanwhile, their electrical resistivity decreases to very low level approaching to the value of the CdO film, which can be explained by the Matthiessen composite rule for resistivity. The peculiarity of low resistivity and high transnlittance in the visible region enables these Rims suitable for optoelectronic device fabrication.

Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm-1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e., refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film. Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.

Preparation and optical characteristics of ZnO films by chelating sol-gel method

The effect of different annealing temperatures on the structure, morphology,and optical properties of ZnO thin films prepared by the chelating sol-gel method was investigated.Zinc-oxide thin films were coated on quartz glass substrates by dip coating. Zinc nitrate, absoluteethanol, and citric acid were used as precursor, solvent, and chelating agent, respectively. Theresults show that ZnO films derived from zinc-citrate have lower crystallization temperature (below400℃), and that the crystal structure is wurtzite. The films, treated over 500℃, consist ofnano-particles and show to be porous at 600℃. The particle size of the film increases with theincrease of the annealing temperature. The largest particle size is 60 nm at 600℃. The opticaltransmittances related to the annealing temperatures become 90% higher in the visible range. Thefilm shows a starting absorption at 380 nm, and the optical band-gap of the thin film (fired at500℃) is 3.25 eV and close to the intrinsic band-gap of ZnO (3.2 eV).

Microstructure and optical properties of sprayed γ-CuI thin films for CuInS_2 solar cells

γ-CuI thin films were prepared by a spraying method using acetonitrile as a solvent,CuI and iodine as reagents.The influences of substrate temperature on the structure,topography,and optical properties of CuI films were investigated.Scanning electron microscope（SEM） photos revealed that the shape and grain size of CuI grains were related to substrate temperature.X-ray diffraction results showed that substrate temperature affected the crystalline quality of CuI films.When the substrate temperature was 110°C,CuI thin films showed γ-phase zinkblende structure with（111） preferred orientation.The dimension of the globular CuI crystallite was approximately 35 nm,the energy band gap was 2.97 eV,the maximum transmittance was 87.3% in the part of the visible region,and the open circuit voltage was close to 380 mV.This opened a route for a cadmium-free buffer layer for CuInS2 solar cells.

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.

Er^(3+) Doped BaTiO_3 Optical-Waveguide Thin Films Elaborated by Sol-Gel Method

Erbium doped BaTiO 3 optical-waveguide films on Pyrex substrate was elaborated successfully through sol-gel method. BaTiO 3 is well crystallized when the film is annealed at 650 ℃ in air circumstance. The so-prepared films with 13 layers have comparatively lower refractive index than bulk BaTiO 3, and it can support two TM and TE modes. Photoluminescence and up-conversion luminescence spectra proved the successful doping of rare earth ions.

Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO_3 bulk:Effects of annealing temperatures

Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400 ℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400 ℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400 ℃. After annealing at 400 ℃, the film becomes almost transparent. Increasing annealing time at 400 ℃ can lead to a small blue shift of the optical gap of the film.

Enhanced Optical Absorption of Amorphous Silicon Films by Ag Nanostructures

The optical absorption of amorphous silicon （α-Si） films is enhanced by silver （Ag） nanostructures deposited on the films. The reflection at the long wavelength side of localized plasmon polaritons （LPPs） resonance originated from Ag nanostructures is significantly decreased, i.e. the optical absorption is enhanced. The results show that the average reflection value of the amorphous silicon films in the wavelength range of 900-1200 nm could be decreased by 11.4%. Moreover, the reduction of the reflection is found to be mainly dependent on the size of the Ag nanostructures, which is related to the island sizes, i.e. the LPP＇s resonance peak position.

Optical properties of hexagonal boron nitride thin films deposited by radio frequency bias magnetron sputtering

The optical properties of hexagonal boron nitride （h-BN） thin films were studied in this paper. The films were characterized by Fourier transform infrared spectroscopy, UV-visible transmittance and reflection spectra, h-BN thin films with a wide optical band gap Eg （5.86 eV for the as-deposited film and 5.97 eV for the annealed film） approaching h-BN single crystal were successfully prepared by radio frequency （RF） bias magnetron sputtering and post-deposition annealing at 970 K. The optical absorption behaviour of h-BN films accords with the typical optical absorption characteristics of amorphous materials when fitting is made by the Urbach tail model. The annealed film shows satisfactory structure stability. However, high temperature still has a significant effect on the optical absorption properties, refractive index n, and optical conductivity σ of h-BN thin films. The blue-shift of the optical absorption edge and the increase of Eg probably result from stress relaxation in the film under high temperatures. In addition, it is found that the refractive index clearly exhibits different trends in the visible and ultraviolet regions. Previous calculational results of optical conductivity of h-BN films are confirmed in our experimental results.

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temperature. The as-deposited films are annealed at different temperatures from 400℃ to 800 ℃ in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400℃ to 800℃. The band gap of the as-deposited ZnO：In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400℃. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400℃ to 800℃.

Influence of Bath Temperature, Deposition Time and S/Cd Ratio on the Structure, Surface Morphology, Chemical Composition and Optical Properties of CdS Thin Films Elaborated by Chemical Bath Deposition

Cadmium sulphide (CdS) thin films were deposited on glass substrates by the chemical bath deposition (CBD) method, using anhydrous cadmium chloride (CdCl2) and thiourea (CS(NH2)2) as sources of cadmium and sulphur ions respectively. The influence of bath temperature (Tb), deposition time (td) aSnd [S]/[Cd] ratio in the solution on the structural, morphological, chemical composition and optical properties of these films were investigated. XRD studies revealed that all the deposited films were polycrystalline with hexagonal structure and exhibited (002) preferential orientation. The films deposited under optimum conditions (Tb = 75?C, td = 60 min and [S]/[Cd] ratio = 2.5) were relatively well crystallized. These films showed large final thickness and their surface morphologies were composed of small grains with an approximate size of 20 to 30 nm and grains grouped together to form large clusters. EDAX analysis revealed that these films were nonstoichiometric with a slight sulphur deficiency. These films exhibited also a transmittance value about 80% in the visible and infra red range.