Optical characteristics of amorphous V2O5 thin films colored by an excimer laser

The V₂O₅ films were prepared by an RF sputtering method, and the amorphous films were colored by an UV excimer laser. The crystallinity of the as-grown V₂O₅ film was degenerated greatly by laser irradiation, as determined by X-ray diffraction (XRD) and Raman studies. The transmission and complex refractive index spectra of the V₂O₅ film were affected by variations in the microstructure, including the surface morphology, crystalline structure, and substoichiometry with an oxygen deficiency. Considerable emissions due to oxygen vacancies and band transition of photoluminescence (PL) peaks were observed, and the peaks were significantly changed after laser irradiation. The variations in the optical properties in both films may be attributed to oxygen deficiency induced by laser irradiation.     

Yttrium oxide thin films prepared under different oxygen-content atmospheres: microstructure and optical properties

Yttrium oxide films were prepared on silicon wafers by reactive magnetron sputtering at different oxygen flow rates to investigate the microstructure and optical properties for desirable planar optical waveguiding applications. Under the different conditions of target surface, the deposition rate, structure, and optical properties have great changes. The deposition rate increases to the maximum, and then monotonically decreases. Oxygen content in films increases and the composition of films transforms from stoichiometry to an oxygen-rich state. Y₂O₃ films grow with the (222) preferred growth orientation at low oxygen flow rate, and then turn into the (622) orientation; the microstructure evolves from crystal structure to amorphous state as oxygen flow rate increases from 2 to 12 sccm. Sufficient oxygen makes films low-order structure and oxygen-rich films have poor crystallinity. Very smooth film has been obtained at oxygen flow rate of 12 sccm. The refractive index can be greatly modulated by the oxygen-content factor. It is convincing that the controllable structure and optical properties of Y₂O₃ films can be achieved by adjustment the oxygen flow rate for desired optical design and applications.     

Analysis of codeposited Gd2O3/SiO2 composite thin films by phase modulated spectroscopic ellipsometric technique

Tailoring of the refractive index of optical thin films has been a very fascinating as well as challenging topic for developing new generation optical coatings. In the present work a novel Gd₂O₃/SiO₂ composite system has been experimented and probed for its superior optical properties through phase modulated spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The optical parameters of the composite films have been evaluated using Tauc-Lorentz (TL) formulations. In order to derive the growth dependent refractive index profiles, each sample film has been modeled as an appropriate multilayer structure where each sub-layer was treated with the above TL parameterizations. All codeposited films demonstrated superiority with respect to the band gap and morphological measurements. At lower silica mixing compositions such as in 10-20% level, the composite films depicted superior spectral refractive index profile, band gap as well as the morphology. This aspect highlighted the fact that microstructural densifications in composite films can override the chemical compositions while deciding the refractive index and optical properties in such thin films.     

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi<Subscript>1.5</Subscript>Zn<Subscript>1.0</Subscript>Nb<Subscript>1.5</Subscript>O<Subscript>7</Subscript> thin films

Bismuth Zinc niobate (Bi_1.5Zn_1.0Nb_1.5O₇) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.     

Effects of refractive index modifiers and UV light on an epoxy-functional inorganic-organic hybrid sol-gel derived thin film system

Thin film systems consisting of (3-glycidyloxypropyl)trimethoxysilane (GDPTMS), dimethyldimethoxysilane (DMDMOS) and, either zirconium(IV) n-propoxide (Zr(OPrⁿ)₄) or diphenyldimethoxysilane (DPDMS) were synthesised via the sol-gel method. GDPTMS and DMDMOS were employed as the main network formers, whereas Zr(OPrⁿ)₄ or DPDMS was both a network former and a refractive index modifier. The comparative effects of Zr and DPDMS content, and UV light on the optical and thermal properties of the system were evaluated. Refractive index measurements and cross-sectional scanning electron microscopy of the resultant thin films were performed. The thermal stability of each system, in terms of temperature at 10% mass loss, was characterised by dynamic thermogravimetry. It was demonstrated that the selection of refractive index modifier along with UV irradiation plays an important role in tuning the optical and thermal properties of an epoxy-functional inorganic-organic hybrid sol-gel derived thin film system.     

Improvement of Cu2ZnSnS4 thin film morphology using Cu–Zn–Sn–O precursor fabricated by sputtering

The new precursor of Cu–Zn–Sn–O (CZTO) was proposed for Cu₂ZnSnS₄ (CZTS) thin film fabrication to improve film morphology. The CZTS thin film grown from Cu–Zn–Sn (CZT) precursors has many bumps. We deposited CZTO precursors on Mo/soda-lime glass (SLG) substrates by RF sputtering using a CZT (Cu:Zn:Sn = 2:1:1) target in Ar and O₂ atmosphere at various O₂ partial pressures (0%, 5%, 17% and 20%). Subsequently, the CZTO precursors were sulfurized in Ar and S atmosphere to fabricate CZTS thin films. The CZTO precursors were amorphous. The morphology of the CZTS thin films was improved by the CZTO precursors. All of the CZTS films fabricated in this study had the same crystal structure. Composition analysis revealed that 50% of O were detected in the CZTO precursor, but O was not detected after sulfurizing process, indicating that O was substituted by S. The CZTS thin film from the CZTO precursor fabricated at O₂ partial pressure of 20% had similar composition for solar cell absorber.     

Spectroscopic ellipsometry modeling of ZnO thin films with various O2 partial pressures

ZnO films were deposited on thermally oxidized SiO₂/p-type Si (100) substrates and glass substrates by DC magnetron sputtering using a metal Zn target. Three types of samples were prepared with various O₂/(Ar + O₂) ratios (O₂ partial pressure) of 20%, 50%, and 80%. The properties of these ZnO thin films were investigated using X-ray diffraction (XRD), optical transmittance, atomic force microscopy (AFM), and spectroscopic ellipsometry in the spectral region of 1.7–3.1 eV. The structural and optical properties of ZnO thin films were affected by O₂ partial pressure. Relationships between crystallinity, the ZnO surface roughness layer, and the refractive index (n) were investigated with varying O₂ partial pressure. It was shown that the spectroscopic ellipsometry extracted parameters well represented the ZnO thin film characteristics for different O₂ partial pressures.     

Gamma irradiation effects on structural and optical properties of amorphous and crystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films

The structural and optical properties of RF sputtered Nb₂O₅ thin films are studied before and after gamma irradiation. The films are subjected to structural and surface morphological analyses by using X-ray (XRD) and field emission scanning electron microscope techniques. In the wavelength range of 300–2000 nm, the optical parameters for amorphous and crystalline Nb₂O₅ thin films are estimated at differently exposed γ-irradiation doses (0, 50, 100 and 200 kGy). The optical constants, such as optical energy band gap, absorption coefficient, refractive index and oscillators parameters of amorphous and crystalline Nb₂O₅ thin films are calculated. The optical band gaps of γ-irradiated amorphous and crystalline Nb₂O₅ thin films are determined. In the non-absorbing region, the real part of the refractive index of amorphous and crystalline Nb₂O₅ thin films slightly increases with the increase in the exposed γ-irradiation dose.     

Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

Thin films of SnO₂ were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O₂. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap (E_g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.     

Study of well adherent DLC film deposited on piezoelectric LiTaO3 substrate

A well adherent diamond-like carbon (DLC) film was deposited on piezoelectric LiTaO₃ substrate using PECVD by inserting SiO₂ interlayer. DLC film was characterized using Raman spectroscopy and AFM. Physical and mechanical properties were measured using XRR, ellipsometry, scratch test and nano-indentation. The DLC film exhibits the characteristics of hydrogenated amorphous carbon and a very smooth surface with a 0.25 nm RMS. Scratch test shows that critical load (L_c) is 18 N, which is good enough for applying DLC film to SAW device. The measured mass density, refractive index, hardness and Young’s modulus of DLC film deposited on LiTaO₃ are comparable to the reported values for hydrogenated amorphous carbon film, irrespective of substrates on which the films were deposited.     

The properties of the Y2O3 films exposed at elevated temperature

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (1 1 1) substrates by RF magnetron sputtering. The influences of thermal exposure at high temperature in air on the structure, the surface morphology, roughness, and the refractive index of the Y₂O₃ thin film were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). The results indicate that chemical composition of the as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio, and it has a cubic polycrystalline structure but the crystallinity is poor. The monoclinic and cubic phases can coexist in the Y₂O₃ film after thermal exposure to 900 °C, and the monoclinic phase disappears completely after 300 s exposure to 950 °C. The changes of the surface morphology, roughness, and the refractive index of the Y₂O₃ film are closely related to the crystal structure, the internal stress, and various defects influenced by thermal exposure temperature and time.     

Optical and structural properties of thin films deposited from laser fused Zirconia,Hafnia, and Yttria

The optical and structural properties of films deposited from laser sintered Zirconia (ZrO₂), Hafnia (HfO₂), and Yttria (Y₂O₃) and from the commercially available (unprocessed material) Zirconia, Hafnia and Yttria, were studied and compared. All the films had low absorption. Films deposited from the laser sintered material had very low optical inhomogeneity. ZrO₂ films showed negative inhomogeneity for films deposited from the unprocessed material. The refractive index increased for ZrO₂ films deposited from the laser sintered material. HfO₂ and Y₂O₃ films showed positive inhomogeneity when deposited from the unprocessed material. The refractive index of the films of these materials decreased when deposited from the laser sintered material. The thin films of ZrO₂ and Y₂O₃ prepared from laser sintered material had stable monoclinic and cubic structures respectively while HfO₂ films were found to be amorphous.     

The comparison of Ag–As33S67 films prepared by thermal evaporation (TE), spin-coating (SC) and a pulsed laser deposition (PLD)

Chalcogenide thin films could be prepared by many experimental methods resulting in some differences in structure and physicochemical properties of prepared films. In this work, the As₃₃S₆₇ amorphous films were prepared by three different preparation techniques: vacuum thermal evaporation (TE), pulsed laser deposition (PLD) and spin-coating (SC). A silver film was deposited on the top of the As₃₃S₆₇ films and photodoped.The X-ray diffraction analysis showed significant differences in arrangement between bulk glass and thin films and also among films themselves. The Raman spectroscopy showed that the Raman spectra of PLD film and bulk glass are almost similar. On the other hand, TE films contain higher amount of homopolar bonds As–As and S–S. The value of refractive index of As₃₃S₆₇ bulk glass was 2.31. All prepared films have lower index of refraction contrary to bulk glass, i.e. TE∼2.27, PLD∼2.20 and SC∼1.90. The increase of refractive index with silver concentration is shown either. The optical bandgap of undoped As–S prepared films was different: TE∼2.42 eV, PLD∼2.45 eV and SC∼2.54 eV.     

Structural and optical properties of Ba(Zn1/3Ta2/3)O3 thin films deposited by pulsed laser deposition

Ba(Zn_1/3Ta_2/3)O₃, (BZT), is a high-k and low loss dielectric resonator material which finds applications in the area of microwave communication and related areas. While there are reports on its bulk properties, there is hardly any report on its thin films. We report here preparation of thin films of BZT deposited on to borosilicate and quartz substrates using the pulsed laser deposition (PLD) technique under different oxygen mixing percentage (OMP) and preliminary studies on their structural and optical properties. The EDAX spectra show that the deposited films exhibit the composition of the target. As-deposited films, whether on a glass or quartz substrate, were found to be amorphous. The refractive index and energy bandgap of the films were found to be around 1.5 in the dispersion free region (500–1500 nm) and 5.2–5.5 eV, respectively. The Dynamic Force Microscopy (DFM) study of the BZT films exhibited columnar growth and films deposited at higher OMPs showed the smaller grain size.     

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 E_g (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 E_g 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.     

Optical characteristics of transparent samarium oxide thin films deposited by the radio-frequency sputtering technique

Transparent metal oxide thin films of samarium oxide (Sm₂O₃) were prepared on pre-cleaned fused optically flat quartz substrates by radio-frequency (RF) sputtering technique. The as-deposited thin films were annealed at different temperatures (873, 973 and 1073 K) for 4 h in air under normal atmospheric pressure. The topological morphology of the film surface was characterized by using atomic force microscopy (AFM). The optical properties of the as-prepared and annealed thin films were studied using their reflectance and transmittance spectra at nearly normal incident light. The estimated direct optical band gap energy (\(E_{\mathrm {g}}^{\mathrm {d}}\)) values were found to increase by increasing the annealing temperatures. The dispersion curves of the refractive index of Sm₂O₃ thin films were found to obey the single oscillator model.     

Annealing temperature dependent on structural,optical and electrical properties of indium oxide thin films deposited by electron beam evaporation method

In the present work the influence of annealing temperature on the structural and optical properties of the In₂O₃ films deposited by electron beam evaporation technique in the presence of oxygen was studied. The deposited films were annealed from 350 to 550 °C in air. The chemical compositions of In₂O₃ films were carried out by X-ray photoelectron spectroscopy (XPS). The film structure and surface morphologies were investigated as a function of annealing temperature by X-ray diffraction (XRD) and atomic force microscopy (AFM). The structural studies by XRD reveal that films exhibit preferential orientation along (2 2 2) plane. The refractive index (n), packing density and porosity (%) of films were arrived from transmittance spectral data obtained in the range 250–1000 nm by UV–vis-spectrometer. The optical band gap of In₂O₃ film was observed and found to be varying from 3.67 to 3.85 eV with the annealing temperature.     

氟化铒薄膜晶体结构与红外光学性能的关系

使用热蒸发技术在锗(111)衬底上制备了氟化铒(ErF₃)薄膜. XRD衍射结果表明，随着衬底温度的增加，氟化铒薄膜发生了从非晶状态到结晶状态的转变，薄膜的表面形貌和红外光学性能也发生了显著的变化，部分结晶的氟化铒薄膜的远红外透射谱和完全非晶的薄膜基本一致，但是与结晶薄膜则没有相似之处. 晶格常数计算表明薄膜中存在压应力. 使用洛伦兹谐振子模型对薄膜的透射率曲线进行拟合计算，得到ErF₃薄膜的折射率和消光系数. 在10μm处非晶薄膜的折射率和消光系数最小值分别为1.38和0.01，结晶薄膜的折射率和消光系数最小值分别为1.32和0.006. 关键词： 氟化铒 红外光学性质 光学常数 洛伦兹谐振子模型     

Effect of Cd and Pb impurities on the optical properties of?fresh?evaporated amorphous (As2Se3)90Ge10 thin films

Transmission spectra (400–1500 nm) of thermally evaporated amorphous [(As₂Se₃)₉₀Ge₁₀]₉₅M₅ thin films have been analyzed to study the effect of impurities (M = Cd and Pb) on their optical properties. The refractive index increases with addition of metal impurities. The dispersion of refractive index has been studied using Wemple–DiDomenico single oscillator model. The optical gap has been estimated using Tauc’s extrapolation and was found to decrease with the addition of metal impurities from 1.46 to 1.36 eV (Cd) and 1.41 eV (Pb) with an uncertainty of ±0.01 eV. The change in optical properties with metal impurities has been explained on the basis of density, polarizability and bond energy of the system.