Transmission Spectra Of Thin Films Research Articles

Enhancement of mechanical, thermal and optical properties of TiO2 thin films using glancing angle deposition technique

RF Magnetron sputtering has been used to compare the mechanical, thermal, and electrical characteristics of titanium oxide (TiO2) thin films. The Glancing Angle Deposition methods (GLAD) have been implemented during the deposition of a thin film of TiO2. After annealing thin films on an ITO substrate, X-RD indicates the anatase phase, and SEM investigation confirms the deposition of TiO2 thin films and their surface morphology. The mechanical, thermal, and electrical properties of TiO2 thin films prepared by magnetron sputtering with RF supply have been investigated. Using GLAD deposition, a clear change in thermal conductivity and elastic properties has been observed. Experimental specific heat of thin film deposited at zero angles follows Debye and Einstein equation, while with GLAD deposition specific heat shows an increase in deviation as the angle of deposition increases. With a rise in inclination angle, a clear change in transmission spectra towards a higher wavelength has been observed. Following heat treatment, the optical transmission spectra of thin films with GLAD deposition confirm the formation of fringes and have been shifted towards the higher wavelength side to increase in inclination. Hence, using GLAD deposition on TiO2 plays an important role to change thermal conductivity, specific heat, elastic and electronic properties and which leads to many applications in thermal solar collectors, thermal sensors, thermo-optical switching, and sensing-based industries.

The multi-dimensional characterization of Al-doped CuO thin films by laser-induced breakdown spectroscopy (LIBS) with nanosecond and picosecond lasers

Glasses coated with various optical thin film materials are widely used in people's life and scientific research. In this study, a series of aluminum-doped (Al-doped) copper oxide (CuO) thin films with different sputtering pressures and powers were deposited on soda-lime glass substrates by RF-magnetron sputtering to explore the effect of doping element on the optical properties of the thin films. However, laser-induced breakdown spectroscopy (LIBS) with nanosecond and picosecond lasers was employed to achieve the multi-dimensional analysis of the Al element. With ns-LIBS, the rapid quantitative analysis was performed by drawing the calibration curves of LIBS intensity ratio of Al/Cu versus concentration ratio under different sputtering pressures and powers. Furthermore, the 2D chemical mappings were drawn to provide a more complete and detailed relative spatial distribution of the Al element according to the LIBS intensity ratio of Al/Cu. Meanwhile, the thin film thickness was determined by the picosecond laser pulse number since the depth ablated by a single laser pulse was assessed as nearly 46.75 ± 4.25 nm. Moreover, the variation trends of optical band gaps with sputtering parameters were similar to that of LIBS intensity ratios with sputtering parameters, as suggested by analyzing the transmission spectra of thin films. The results demonstrated that the multi-dimensional characterization (quantitative analysis, 2D chemical mapping, thin-film thickness estimation, and optical properties analysis) of Al-doped CuO thin films prepared by RF-magnetron sputtering can be effectively realized by LIBS.

Synthesis and Characterization of Polymeric (PMMA-PVA) Hybrid Thin Films Doped with TiO2 Nanoparticles Using Dip-Coating Technique

We report the synthesis of hybrid thin films based on Poly(MethylMethAcrylate) (PMMA) and Poly(VinylAlcohol) (PVA), doped with different concentrations of titanium dioxide nanoparticles (TiO2 NPs). As-prepared thin films of (PMMA-PVA) doped by TiO2 NPs (wt.% = 2%, 4%, 8%, and 16%) are deposited on glass substrate. Transmittance (T%), reflectance (R%), absorption coefficient (α), optical constants (n and k), and optical dielectric functions (ε1 and ε2) are deduced using the experimental transmittance and reflectance spectra. Furthermore, a combination of classical models such as Tauc, Urbach, Spitzer-Fan, and Drude models are applied to calculate the optical and optoelectronic parameters and the energy gaps of the prepared nanocomposite thin films. The optical bandgap energy of PMMA-PVA thin film is found to be 4.101 eV. Incorporation of TiO2 NPs into PMMA-PVA polymeric thin films leads to a decrease in the optical bandgap and thus bandgap engineering is possible. Fourier-transform infrared spectroscopy (FTIR) transmittance spectra of thin films are measured and interpreted to identify the vibrational modes. To elucidate the chemical stability, thermogravimetric (TGA) curves are measured. We found that (PMMA-PVA)/TiO2 NPs polymeric thin films are thermally stable below 110 °C enable them to be attractive for a wide range of optical and optoelectronic applications.

Detailed infrared study of amorphous to crystalline propionitrile ices relevant to observed spectra of Titan's stratospheric ice clouds

We have conducted a comprehensive study of propionitrile (C2H5CN) ice from the amorphous to crystalline phase in order to provide detailed information on this specific cyanide, which may potentially contribute to the chemical composition of the Haystack ice cloud observed in Titan's stratosphere by the Cassini Composite InfraRed Spectrometer (CIRS). Infrared transmission spectra of thin films of pure propionitrile ices deposited at low temperature (30–160 K) were collected from 50 cm−1 to 11,700 cm−1 (200–0.85 μm). The far-infrared spectral region was specifically targeted to compare with CIRS far-infrared limb spectra. The temperature and time evolution of C2H5CN ice was thoroughly investigated to better understand discrepancies reported in previously published laboratory studies on the crystalline phase of C2H5CN. Specifically, we observe peculiar temperature and time-driven ice phase transitions, revealed by significant spectral variations in the ice, which stabilizes once a complete crystalline phase is achieved. From these results, the crystalline phase of propionitrile ice was identified at deposition temperatures greater than or equal to 135 K and <140 K. Our findings corroborate previous studies that ruled out pure propionitrile ice as the sole chemical identity of Titan's observed Haystack emission feature. In order to understand and identify the Haystack cloud, we have initiated co-deposition experiments that incorporate mixtures of Titan-relevant organics, many of which have corresponding vapors that are abundantly present in Titan's stratosphere. In this paper, we present the result of one example of a co-deposited ternary ice mixture containing 16% hydrogen cyanide (HCN), 23% C2H5CN, and 61% benzene (C6H6). Although this co-condensed ice mixture is the best fit thus far obtained to match the broad width of the Haystack, it is still not the appropriate chemical candidate. However, it reveals an intriguing result: the strong lattice mode of pure C2H5CN ice is drastically altered by the surrounding molecules as a result of mixing in a co-condensed phase. The laboratory results reported here on propionitrile ice may help to further constrain the chemical identification of Titan's stratospheric Haystack ice cloud, as well as improve on the current state of knowledge of Titan's stratospheric ice cloud chemistry.

Optical band gap and dispersion of optical constants of Cu-Ga-S thin films

Thermally deposited Cu-Ga-S thin films were optically characterized by means of experimental techniques of transmission measurements. The analyses of transmittance spectra were accomplished by derivative spectrophotometry analyses to get gap energies of thin films. The transmittance spectra of thin films annealed at different temperatures presented interference fringes which were analyzed by Swanepoel envelope method. The wavelength dependencies of optical parameters; refractive index (n), real part of complex dielectric function (εre) and extinction coefficient (k) were reported in the weak absorption region. The photon energy dependencies of n and εre were analyzed using single-oscillator and Spitzer-Fan models, respectively.

Optical characterization of nanostructured Ge1 − xSnxSe2.5 (x = 0, 0.3, 0.5) films

The paper reports the optical properties of thin films of nanostructured Ge1 − xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys. The glassy alloys of Ge1 − xSnxSe2.5 (x = 0, 0.3, 0.5) were prepared using melt quenching method. Thin films of nanostructured Ge1 − xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys were prepared using physical vapor deposition method. The films were characterized using XRD, EDX and TEM, which confirmed the amorphous nature, composition and formation of nanorods in the samples. Absorption and transmission spectra of thin films were recorded in the spectral range 400–2500 nm to obtain energy band gap, refractive index, extinction coefficient, dielectric constant etc. Results show that refractive index increases while band gap decreases on increase of Sn content in the Ge–Se system. This is due to the increase in density of defect states within band gap. The values of Urbach energy support the obtained results.

The SPECTRAL Ice Chamber: Application to Titan’s Stratospheric Ice Clouds

Abstract An ice chamber for obtaining thin-film transmission spectra of Titan-relevant organic ices between 50 and 11,700 cm−1 (200–0.85 μm) is described in detail in this work. The ice chamber, called the SPECtroscopy of Titan-Related ice AnaLogs chamber, is located in the Spectroscopy for Planetary ICes Environments laboratory at NASA Goddard Space Flight Center. Organic vapors are typically deposited between 30 and 150 K via a variable leak valve onto a chemical vapor deposition diamond substrate, where condensation directly into the solid state occurs. Quantitative thin-film infrared transmission spectra of the given ice or ice mixture are then measured, from which optical constants (complex indices of refraction) are computed. These optical constants in turn provide the necessary input for interpreting radiative transfer analyses of Cassini’s Composite InfraRed Spectrometer observations of Titan’s organic stratospheric ice clouds to determine their chemical compositions, abundances, and vertical distributions as functions of Titan latitude and season.

Effect of Bi addition on the physical and optical properties of Ge20Te74-xSb6Bix (x = 2, 4, 6, 8, 10) thin films deposited via thermal evaporation

Chalcogenide materials in different forms (bulk, thin film, nanocrystals etc.) are finding applications in various sectors e.g. in infrared optics for communication, imaging, limiting, remote sensing and laser power delivery etc. Here we report the synthesis of Ge20Te74-xSb6Bix (x = 2, 4, 6, 8, 10) chalcogenide alloys and estimation of some physical properties i.e. average coordination number, lone pair electron, number of constraints, heat of atomization, compactness, glass transition temperature etc. The transmission spectra of thin films have been acquired using UV–Visible–NIR spectrophotometer in the wavelength range of 400 nm–2600 nm. Various optical properties like refractive index, extinction coefficient, optical band gap, real and imaginary parts of dielectric constants have been evaluated using the transmission spectrum. The optical band gap of the synthesized samples has shown similar trend with the band gap determined theoretically. The average coordination number has been found to increase whereas the number of lone pair electron is found to decrease. This shows that the system under investigation is moving towards more rigid region as per constraint theory. The heat of atomization energy and theoretical band gap has also shown variation with the addition of Bi content. The tailoring of band gap along with an increase in rigidity may lead to an increase in the domain of technological applications for these alloys.

Optical properties of dip coated titanium-di-oxide (TiO2) thin films annealed at different temperatures

Titanium dioxide (TiO2) thin films were synthesized by hydrothermal assisted sol-gel dip coating method on quartz substrate. The sol was prepared by hydrothermal method at 90 °C. Dip coating method was used to deposit the thin films. Later films were annealed at four different temperatures −600 °C, 800 °C, 1000 °C and 1200 °C. XRD study showed samples annealed at 600 °C are almost amorphous. At 800 °C, film turns into anatase phase and with further increment of annealing temperature they turn into rutile phase. Transmission spectra of thin films show sharp rise in the violet-ultraviolet transition region and a maximum transmittance of ∼60% was observed in the visible region for the sample annealed at the lowest temperature. Band gap of the prepared films varies from 2.9 eV to 3.5 eV.

Annealing Temperature Dependence of Optical Properties of Sol-Gel ZnO Thin Films with Different Sol Aging Time

ZnO thin films on glass substrates have been successfully fabricated by sol-gel method for various aging time and annealing temperature. X-ray diffraction (XRD) patterns showed the crystallites at (100), (002) and (101) plane of hexagonal wurtzite structure. Atomic force microscope (AFM) images were used to investigate the surface morphology. The transmittance, energy gap, Urbach energy and photoluminescence (PL) of samples were investigated to explore the effects of annealing temperature on optical properties of ZnO thin films under different sol aging time. The transmittance spectra of thin films aged for 24 hours and 48 hours revealed the enhanced transmittance in visible region as rising annealing temperature, also, the optical band gap of the samples increased and Urbach energy decreased. The photoluminescence (PL) spectra of samples aged for 24 hours and 48 hours were studied and found the increased ultraviolet emission at ~387 nm, and various decreased visible emissions with rising annealing temperature. Nevertheless, the excessive sol aging time for 72 hours deteriorated the optical characteristics of thin films, resulting in that transmittance, energy gap and ultraviolet emission declined, and visible emissions increased with rising annealing temperature. The optical performances of the ZnO films aged for different time have no the same dependence of annealing temperature.

Applying Artificial Neural Networks to Monitor Deposition Rate of Roll-to-roll Sputtering System in Real Time

A back propagation neural network (BPNN) is applied to determine the deposition rate of a roll-to-roll magnetron sputtering system in real time. Because the transmittance spectra of thin films are highly related to their thicknesses, the spectrum is a function of the thickness. Thus, determining deposited thickness through the functions is possible. However, these functions are not simple one-to-one functions; solving the inverse function to find thicknesses from spectra is difficult. Therefore, BPNNs are introduced to build approximate functions of spectra and output thicknesses. They are trained with various spectra which correspond to different film thicknesses, and will have abilities to estimate thicknesses of thin films. In this study, the estimation error of BPNNs was less than 0.6%. The results of low error and real-time response make BPNNs a promising method for monitoring a deposition process.

Preparation, characterization and ab-initio study of CdSnTe2 thin films by closed space sublimation technique

The cadmium tin telluride (CdSnTe) alloy was prepared by direct reaction of high purity elemental constituents using rotating furnace. Thin films of CdSnTe different thickness were prepared on glass substrates by vacuum closed space sublimation method. The films were subjected to XRD, SEM, EDAX and UV–vis–NIR studies. The crystalline structure of CdSnTe alloy was found to be face-centered cubic with lattice parameter 6.30 Å. EDAX studies confirmed the composition of the alloy as CdSnTe2 compound. The UV–vis–NIR optical transmission spectra of thin films of different substrate temperatures were obtained. The energy band gap found to be in the order of 1.5 eV. The band gap is suitable for LEDs, optoelectronics and photovoltaic applications. First principle density functional theory calculations of CdSnTe2 structure were performed by using Vienna ab-initio simulation package software. The results of theoretical calculations are in good agreement with experimental data.

Effect of substrate temperature on structural, morphology and optical properties of RF magnetron sputtered CZT thin films

Cadmium zinc telluride (CdZnTe) or CZT, a direct band gap semiconductor is used in a variety of applications such as radiation detectors, photo refractive gratings, solar cells and electro-optic modulators. In the present investigation, we have studied the influence of substrate temperature on the structure, morphology and optical properties of radio frequency magnetron sputtered cadmium zinc telluride (Cd0·4Zn0·1Te0·5) thin films deposited onto well cleaned glass substrates. CZT thin films of different thicknesses in the range from 128 to 549 nm with stoichiometric composition were prepared by optimising the process parameters. Transmittance spectra of thin films were recorded using UV-vis spectrophotometer in the wavelength range of 200 to 1500 nm and the optical band gap was determined. Surface topography of CZT thin films was analysed using atomic force microscopy and the root mean square roughness was determined. X-ray diffraction and transmission electron microscopy analysis revealed the presence of zinc blende structure exhibiting the predominant (111) and other planes along (220) and (311) directions. The d-spacing and crystallite size were also calculated. The results are discussed.

Optical and Dielectric Characteristics of Photoactive Layer Thin Films for Organic Photovoltaic Cells

The thin films of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH- PPV) used as photoactive layer in organic photovoltaic cells were prepared on glass substrates by the spin-coating technique. The transmittance spectra of thin films were measured by a double beam spectrophotometer. The optical constants such as refractive index and extinction coefficient of the thin films were determined from the measured transmittance spectra using the method of whole optical spectrum fitting. The complex dielectric constant and the complex optical conductivity of the thin films were obtained. In addition, the optical bandgap of the thin film were calculated according to the Tauc's law. The results show that the thin films exhibit direct allowed transitions and the optical bandgap is about 2.18 eV. These results provide some useful references for the design and optimization of device structure in organic photovoltaic cells.

Validation of a correction procedure for removing the optical effects from transmission spectra of thin films on substrates

Transmission spectra of thin films on double side polished substrates feature a quasi sinusoidal baseline superimposed onto the true absorption spectra of the thin film. The quasi sinusoidal baseline is due to strong interference from multiple reflections within the film and can directly affect the relative degree of the measured absorption in the film. In a previous article [S. W. King and M. Milosevic, J. Appl. Phys. 111, 073109 (2012)], we described a method for the removal of these optical effects from infrared transmission spectra. This method renormalizes the spectrum and removes modulations imprinted onto the absorption by interference fringes. Here, we use simulated spectra for a model material to explicitly validate that the proposed correction procedure accurately extracts the pure absorption coefficient of the thin film and is not an ad hoc baseline correction procedure.

Investigation of Optical Transmission in Thin Metal Films

Thin metal films have recently attracted large interest due to their practical application in photo-detectors, solar cells and quantum electronics. It is known that thin films of noble metals such as Au, Ag, and Cu have a maximum optical transmittance in the shorter part of spectrum. In our work, optical properties of thin metals films deposited by thermal evaporation and low pressure (1.33·10 -5 - 1.33·10 -4 Pa) DC plasma sputtering were investigated. Such low pressure is provided by triode sputtering method which supports a ballistic type of mass transfer between the sputtering target and the substrate. This method enables fine control of the film thickness and its density. Comparison of the films deposited by mentioned above two methods on glass substrates shows significant differences in their optical and electrical properties. Thin films of following metals: Sn, Al, V, Ti, Ni, Mo, Ta, W, Au, Ag, and Cu were deposited on glass and their optical and electrical properties were studied. The transmission spectra of thin films of various metals have significant differences. In our paper we discuss the causes of these differences.

Influence of ion implantation on optical parameters of Cu&lt;sub&gt;6&lt;/sub&gt;PS&lt;sub&gt;5&lt;/sub&gt;I thin films

The ion implantation of Cu 6 PS 5 I thin films by sulphur and phosphorous is carried out as well as the structural studies by methods of scanning electron microscopy and energy-dispersive X-ray spectroscopy are performed. Transmission spectra of thin films and influence of ion implantation on spectra and parameters of exponential absorption edge are investigated. Refractive indeces dispersion of implanted thin films is studied as well as its description by optical-refractometric relation is carried out. Dependences of the optical pseudogap, Urbach energy and refractive indeces in implanted films on fluence values are investigated and analyzed.

DETERMINATION OF OPTICAL CONSTANTS AND OPTICAL BAND GAP IN GE40TE60-XSBX THIN FILMS

The optical transmission spectra of thin films of Ge40Te60-xSbx (x = 0, 2, 4, 6 and 10), prepared by vacuum evaporation technique from their corresponding bulk samples, are recorded over the spectral region of 500–2700 nm. A simple straight forward method proposed by Swanepoel has been applied to determine various optical parameters like refractive index (n), extinction coefficient (k), absorption coefficient (α), real and imaginary dielectric constants (e' & e) in the measured range of wavelength. The optical band gap (Eg) has also been calculated by Tauc’s relation. It has been found that the Eg and n decreases with Sb concentration in Ge40Te60-xSbx system.

Preparation and photo-induced superhydrophilicity of composite TiO 2–SiO 2–In 2O 3 thin film

In this work, TiO 2–SiO 2–In 2O 3 composite thin films on glass substrates were prepared by the sol–gel dip coating process. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. UV–vis spectrophotometer was used to measure the transmittance spectra of thin films. The water contact angle (WCA) of thin films during UV/vis irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicated that fabrication of composite film has a significant effect on transmittance and superhydrophilicity of TiO 2 films.

Structural and Optical Studies of Hot Wall Vacuum Evaporated CdTeSn Thin Films

Bulk compounds of CdTe, Cd0.25Sn0.75Te and Cd0.25Te0.75Sn have been prepared by direct reaction of their high purity (99.9999%) elemental constituents employing rotating furnace. The hot wall system is optimized for the deposition of prepared alloys by using molecular flow studies with Monte Carlo simulation technique. Thin films have been deposited on well cleaned glass substrates using the prepared alloys by the optimized hot wall vacuum evaporation system. The compositions of the prepared bulk and thin films have been identified using energy dispersive X-ray analysis. The compositions are found to be same for both the bulk and thin films as the prepared alloys. The structural properties of the deposited films have been studied using X-ray diffraction technique. The results show that all the films are crystalline in nature and the peaks in the XRD graph of CdTe correspond to cubic zinc blende structure and that of Cd0.25Sn0.75Te and Cd0.25Te0.75Sn compounds to rock salt structure. The lattice parameters and grain sizes of all the films have been evaluated. The surface morphology of the thin films is studied using Scanning Electron Microscope (SEM). The SEM analysis shows that surface of the films are smooth and crystalline in nature. The optical transmittance spectra of thin films were recorded using spectrophotometer in the range of wavelength from 190 nm to 2500 nm. All the films exhibit direct optical band gap and their values are 1.45eV (CdTe), 0.9eV (Cd0.25Sn0.75Te) and 1.1eV (Cd0.25Te0.75Sn). Thicknesses of the thin films have been determined by multiple beam interferometric technique.