Optical characterization of electron beam evaporated chloroindium phthalocyanine thin films

In present study, the optical properties of chloroindium phthalocyanine (ClInPc) thin films prepared by electron beam evaporation have been investigated. The optical characteristics of the prepared thin films have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incidence in the spectral range 300–1,100 nm. Surface morphology of thin films is studied using field emission scanning electron microscopy. The absorption spectra recorded in UV-Visible region for the deposited films show two well defined intense absorption bands of phthalocyanine molecule; namely the Q-band and the Soret (B-band). The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region have been performed to determine the optical band gap energy and type of the electronic transition, which reveals the probability of direct and indirect transitions. Moreover, by studying the absorption coefficient spectra just below the fundamental absorption edge, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been evaluated. The obtained results of this novel grown ClInPc thin films support the desirable feature for the optoelectronic devices.     

Influence of temperature and frequency on electrical properties of electron beam evaporated bromoaluminum phthalocyanine, BrAlPc, thin films

The AC electrical properties of electron beam evaporated Bromoaluminum phthalocyanine (BrAlPc) thin films have been studied in the frequency range 10²–10⁵ Hz and in the temperature range of 303–413 K. The BrAlPc thin films are characterized by field emission scanning electron microscopy (FESEM). The capacitance is found to be sensitive to the frequency and increases with increasing temperature and decreases with increasing frequency. A loss minimum has been observed in the frequency dependence of the dissipation factor. Such behavior is found to be in good qualitative agreement with the model of Goswami and Goswami. The AC conductivity $\sigma \left( \omega \right)$ σ ( ω ) is found to vary as $\omega^{s}$ ω s in the studied frequency range. At frequencies 10–10² Hz, s is less than unity and decreases with increase in temperature indicating a dominant hopping process. At frequency ranges 10²–10⁴ Hz, exponent s lies very close to the unity and is independent of temperature, which shows the quantum mechanical tunneling is dominated conduction mechanism. At higher frequencies 10⁴–10⁵ Hz, s is found to be temperature independent. The temperature dependence of AC conductivity shows a linear increase with the increase in temperature. Moreover, the activation energies of device are determined as a function of frequency.     

Morphology, surface topography and optical studies on electron beam evaporated MgO thin films

Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol-gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh like morphology. The bar regions are believed to be of magnesium hydroxide formed due to absorption of moisture. Their AFM images exhibit columnar/pyramidal/truncated cone structure, providing support to the 3D Stranski-Krastanov model for film growth. Further, they are shown to have high transmittance (∼90%) in the wavelength range 400–600 nm, but absorb radiation below 350 nm substantially giving signature of a band transition.     

Effects of post-deposition annealing on morphology and optical properties of electron beam evaporated Bromoaluminium phthalocyanine thin films

In this paper, effects of post-deposition annealing on morphology and optical properties of electron beam evaporated Bromoaluminium phthalocyanine thin films have been investigated. Surface morphology of the films have been characterized by field emission scanning electron microscopy (FESEM). The FESEM micrographs have shown densely packed nanoparticles and nanorod-like structures for the films annealed at different temperatures. Conditions leading to β-phase have been identified by monitoring post-deposition annealing using optical absorption spectroscopy (UV–Vis). The optical absorption measurements on the as-deposited and annealed films shows that the absorption mechanism is due to direct transition. Also, it is found that the optical band gap decreases with increase in annealing temperature.     

Structural and optical properties of electron beam evaporated CdSe thin films

Thin films of cadmium selenide (CdSe) as a semiconductor is well suited for opto-electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, a preliminary and thorough study of optical and structural properties of the host material is an important step. Based on the above view, the structural and optical properties of CdSe films have been studied thoroughly in the present work. The host material, CdSe film, has been prepared by the physical vapour deposition method of electron beam evaporation (PVD: EBE) technique under a pressure of 5 × 10⁻⁵ mbar. The structural properties have been studied by XRD technique. The hexagonal structure with a preferred orientation along the (0 0 2) direction of films has been confirmed by the X-ray diffraction analysis. The films have been analysed for optical band gap and absorbed a direct intrinsic band gap of 1·92 eV.     

Structural and optical properties of thermally evaporated zinc phthalocyanine thin films

Thermally evaporated zinc phthalocyanine (ZnPc) films in the as deposited condition were identified to be as-amorphous. It undergoes structural transformation upon annealing up to 613 K. The optical properties and spectral behavior of as deposited and annealed thin films of ZnPc were studied using spectrophotometric measurements of the transmissivity and reflectivity at normal incidence of light in the wavelength range 200–2500 nm. The refractive index, n, and absorption index, k, were calculated and it was found that they are independent of film thickness in the thickness range 205–530 nm. Annealing at 613 K increases absorbance of films by 5–6 times in comparison with absorbance of as deposited ones and shifts peak positions of all bands towards low energy side of spectra except the peak position of N-band is shifted towards high energy side of spectra. The absorption spectra in the UV–VIS. region has been analyzed in terms of both molecular orbital and band theories. Indirect allowed transitions near the onset and fundamental absorption edges were observed. The energy at the onset was obtained and equals to 1.45 and 1.51 eV for as deposited and annealed films, respectively. The fundamental energy gap was obtained and equals to 2.94 and 2.88 eV for as deposited and annealed films, respectively. The absorption spectra shows four absorption bands. The oscillator strength, f, the electric dipole strength, q², the molar extinction coefficient, ζ_molar, were calculated for as deposited and annealed ZnPc thin films.     

Plasma oxidation of electron beam evaporated cadmium thin films

Thin films of pure cadmium have been deposited using electron beam evaporation technique. Effect of radio frequency (RF) plasma oxidation on structural, optical and electrical properties of cadmium thin films has been investigated. It was found that the RF plasma treatment affects on the physical properties of the oxidized cadmium films. Transmittance values of 87% in the visible region and 90% in the near infrared region have been obtained for cadmium oxide (CdO) film oxidized at a plasma-processing power of 600 W. The optical energy gap, E_g, was found to increase as the RF plasma-processing power increases. The resistivity values of 3 × 10^− 3 and 5 × 10^− 3 (Ω cm) have been obtained for CdO films oxidized at RF plasma-processing powers of 550 and 600 W respectively.     

Effect of annealing on the electrical and optical properties of electron beam evaporated ZnO thin films

Zinc oxide thin films have been grown on (100)-oriented silicon substrate at a temperature of 100 °C by reactive e-beam evaporation. Structural, electrical and optical characteristics have been compared before and after annealing in air by measurements of X-ray diffraction, real and imaginary parts of the dielectric coefficient, refractive index and electrical resistivity. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented with a full width at half maximum (FWMH) lower than 0.5°. The electrical resistivity increases from 10⁻² Ω cm to reach a value about 10⁹ Ω cm after annealing at 750 °C. The FWHM decreases after annealing treatment, which proves the crystal quality improvement. Ellipsometer measurements show the improvement of the refractive index and the real dielectric coefficient after annealing treatment at 750 °C of the ZnO films evaporated by electron beam. Atomic force microscopy shows that the surfaces of the electron beam evaporated ZnO are relatively smooth. Finally, a comparative study on structural and optical properties of the electron beam evaporated ZnO and the rf magnetron deposited one is discussed.     

Optical characterization of organic material bromoindium phthalocyanine thin films grown by electron beam evaporation

This paper presents the optical properties of organic material bromoindium phthalocyanine (BrInPc) thin films grown by electron beam evaporation technique. The paper describes the optical characteristics of BrInPc thin films, which have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incident of light in the spectral range 300–1,100 nm. The optical band gap energy and type of the electronic transition have been determined by analysis of spectral behavior of absorption coefficient, which reveals the probability of both direct and indirect transitions. Other optical constants, such as refractive index, extinction coefficient, complex dielectric constant and optical conductivity of thin films have been evaluated. Moreover, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been determined by studying the absorption coefficient spectra just below the fundamental absorption edge.     

Nano structure formation in vacuum evaporated zinc phthalocyanine (ZnPc) thin films

In this article we have reported the nano structure formation in ZincPhthalocyanine (ZnPc) thin films coated on glass substrates by thermal evaporation method. The structure of the films was analyzed by an X-ray diffractometer (using Cu K_α radiation with λ = 1.5418 Å). It reveals that the vacuum evaporated ZnPc thin films are having nano particles in its structure. It is confirmed by the scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical absorption studies. The results of the XRD, SEM and AFM studies have been discussed in this article. A metastable α to the stable β-phase transformation has been observed when the films are coated at higher substrate temperatures. The core structure of the ZnPc macrocycle is formed by four isoindole units endowing the molecule with a two-dimensional conjugated π electron system.     

Effect of substrate temperature on the electrical and optical properties of electron beam evaporated indium antimonide thin films

Thin films of non-stoichiometric indium antimonide (In_0.66Sb_0.34) have been deposited by electron beam evaporation technique on glass substrates at different substrate temperatures, (300?C473 K). The films have polycrystalline nature with zinc blende structure. The decrease in electrical resistivity with increasing temperature shows semiconducting behavior. Hall measurements indicate that the films are of n-type. Optical transmission spectra of as deposited thin films have been measured at different substrate temperatures. All the electrical parameters i.e. electron mobility (??), carrier concentration (n), resistivity (??), activation energy and band gap (E _g ) have been found to be temperature dependent. Suitable explanations are given in the paper.     

AC electrical conductivity of electron beam evaporated Cu-GeO2 thin cermet films

AC electrical properties of 410 nm think 30 at.wt% Cu-70 at.wt% GeO₂ thin films are reported for the frequency range 10⁴ to 10⁶ Hz and temperature range 150 to 425 K. The loss tangent (tan ) and the dielectric loss (/₀) are found to show striking minima around a cut-off frequency 10⁵ Hz. In the lower frequency range (10⁵ Hz), ₁() ^s T ⁿ is obeyed with s (0 to 0.51) increasing as a function of temperature and n (0.10 to 0.14) showing a very weak temperature dependence. In the higher frequency region (10⁵ Hz), ₁() and /₀ increase sharply leading to the quadratic behavior of ₁() with s equal to 2. These processes are discussed by analyzing an equivalent circuit which shows that at lower frequencies, the effects of series resistance in leads and contacts can be neglected, while at higher frequencies such effect give rise to spurious ² dependance for the conductance. A weakly activated AC conductivity and a frequency exponent s that increases with increasing temperature suggest that the low frequency behavior originates from carrier migration by tunneling process.     

Annealing effects on the structural and optical characteristics of electron beam deposited Ge-Se-Bi thin films

Measurements of absorbance and transmittance in Ge₂₀Se_80-xBi_x (0 x 10 at %) chalcogenide thin films in the visible range at room temperature were carried out. The dependence of the optical absorption on the photon energy is described by the relation hv=B(hv-E₀)². It was found that the optical energy gap E₀ decreases gradually from 1.93 to 1.205 eV with increasing Bi content up to 10 at %. The rate of the change decreases with increasing Bi content. The composition dependence of the optical energy gap is discussed on the basis of the concentration of covalent bonds formed in the chalcogenide film. The decrease of optical energy gap with increasing Bi content is related to the increase of Bi–Se bonds and the decrease of Se-Se bonds. The effect of thermal annealing for different periods of time on the behavior of optical absorption of the as-deposited films was investigated. The optical gap increases with increasing annealing time. The rate of change decreases with increasing annealing time, then E₀ reaches a steady state. The increase in the values of the optical gap of the amorphous films with heat treatment is interpreted in terms of the density of states model. The structure of the as-prepared and thermally annealed films were investigated using transmission electron microscopy, energy dispersive analysis and X-ray diffraction. It was confirmed that the as-prepared films were in the amorphous state. Phase separation was observed after thermal annealing. The separated crystalline phases were identified.     

Characterization of ITO/CdO/glass thin films evaporated by electron beam technique

Abstract

A thin buffer layer of cadmium oxide (CdO) was used to enhance the optical and electrical properties of indium tin oxide (ITO) films prepared by an electron-beam evaporation technique. The effects of the thickness and heat treatment of the CdO layer on the structural, optical and electrical properties of ITO films were carried out. It was found that the CdO layer with a thickness of 25 nm results in an optimum transmittance of 70% in the visible region and an optimum resistivity of 5.1×10^?3 Ω cm at room temperature. The effect of heat treatment on the CdO buffer layer with a thickness of 25 nm was considered to improve the optoelectronic properties of the formed ITO films. With increasing annealing temperature, the crystallinity of ITO films seemed to improve, enhancing some physical properties, such as film transmittance and conductivity. ITO films deposited onto a CdO buffer layer heated at 450 °C showed a maximum transmittance of 91% in the visible and near-infrared regions of the spectrum associated with the highest optical energy gap of 3.61 eV and electrical resistivity of 4.45×10^?4 Ω cm at room temperature. Other optical parameters, such as refractive index, extinction coefficient, dielectric constant, dispersion energy, single effective oscillator energy, packing density and free carrier concentration, were also studied.     

Characterization of ITO/CdO/glass thin films evaporated by electron beam technique

A thin buffer layer of cadmium oxide (CdO) was used to enhance the optical and electrical properties of indium tin oxide (ITO) films prepared by an electron-beam evaporation technique. The effects of the thickness and heat treatment of the CdO layer on the structural, optical and electrical properties of ITO films were carried out. It was found that the CdO layer with a thickness of 25 nm results in an optimum transmittance of 70% in the visible region and an optimum resistivity of 5.1×10⁻³ Ω cm at room temperature. The effect of heat treatment on the CdO buffer layer with a thickness of 25 nm was considered to improve the optoelectronic properties of the formed ITO films. With increasing annealing temperature, the crystallinity of ITO films seemed to improve, enhancing some physical properties, such as film transmittance and conductivity. ITO films deposited onto a CdO buffer layer heated at 450 °C showed a maximum transmittance of 91% in the visible and near-infrared regions of the spectrum associated with the highest optical energy gap of 3.61 eV and electrical resistivity of 4.45×10⁻⁴ Ω cm at room temperature. Other optical parameters, such as refractive index, extinction coefficient, dielectric constant, dispersion energy, single effective oscillator energy, packing density and free carrier concentration, were also studied.     

Some properties of electron beam evaporated amorphous Mo-N films

A series of amorphous Mo-N films was prepared by electron beam evaporation of molybdenum in varying partial pressures of nitrogen and deposited onto substrates cooled to about 80 K. The alloy films were characterized by X-ray diffraction, the superconducting transition temperature,T _c, and the crystallization temperature,T _x. The maximumT _c (8.3 K) and sharpest transition occurred with the minimum nitrogen pressure necessary to form the amorphous structure, as revealed by X-ray diffraction. After annealing the as-deposited films, both bcc and fcc phases were found with the bcc/fcc ratio decreasing with increasing nitrogen partial pressure. Differential scanning calorimetry (DSC) measurements showed significant differences in the shape of peaks associated with either bcc, bcc+fcc, or fcc phases. The temperature,T _x, associated with the fcc crystallization increased with nitrogen content. Heats of crystallization had an average value of about 63 J g^?1. Changes in position of the first amorphous X-ray diffraction peak showed that the amorphous structure was expanded by increasing nitrogen content.     

Gamma-ray irradiation induced structural and optical constants changes of thermally evaporated neutral red thin films

Neutral red (NR) is polycrystalline in powder form, it transforms to nanocrystallite phase upon thermal deposition. Gamma-ray irradiation with doses 1.25–6 KGy induced partial transformation of nanocrystallite phase to amorphous structure. The changes of optical constants with γ-ray doses were calculated using spectrophotometer measurements of transmittance and reflectance at normal incidence of light over spectral range 200–2500 nm. The complex refractive index of NR film is highly influenced by exposure to γ-ray irradiation, the onset and optical energy gaps decrease with increasing γ-ray doses, and Urbach tail increases linearly with increasing irradiation dose. The type of electronic transition, oscillator, and electric dipole strengths and dispersion parameters were determined before and after irradiation. The spectral behavior of dielectric constant with γ-ray doses was also estimated.     

Structural characterization of vacuum evaporated ZnSe thin films

Thermally evaporated ZnSe thin films deposited on glass substrates within substrate temperatures (T _s)at 303 K-623 K are of polycrystalline nature having f.c.c. zincblende structure. The most preferential orientation is along [111] direction for all deposited films together with other abundant planes [220] and [311]. The lattice parameter, grain size, average internal stress, microstrain, dislocation density and degree of preferred orientation in the film are calculated and correlated with T _s.     

Comparison study of microstructure, chemical composition and optical properties between resistive heating and electron beam evaporated LaF3 thin films

LaF₃ thin films were deposited by electron beam (EB) and resistive heating (RH) evaporation, respectively. Properties such as microstructure, chemical composition, surface morphology and optical constants of the LaF₃ thin films were characterized by measurements of X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and spectrophotometer, then comparison was made between this two deposition methods. It's found that the microstructure properties of the LaF₃ films deposited by these two methods were different, and slight content of oxyfluoride films was formed during deposition according to the result of chemical composition analysis. The microstructure of LaF₃ bulk materials after interaction with electron beam and resistive heating was also characterized to analyze how the two deposition processes affect the formation of LaF₃ thin films and their microstructure properties. When it was for the laser resistance of the films, although the EB evaporated LaF₃ thin films occupied lower absorption and optical loss than those of the RH films, they showed slightly smaller laser induced damage thresholds at 355 nm, which was thought to be related to their much more rougher surface and higher tensile stress.     

Optical and structural properties of flash evaporated HgTe thin films

Thin films of HgTe were thermally flash evaporated onto glass and quartz substrates at room temperature. The structural investigations showed that stoichiometric and amorphous films were produced. The transmittance, T, and reflectance, R, of thin films of HgTe have been measured over the wavelength ranges 300–2500 nm. From analysis of the transmittance and reflectance results, the refractive index, n, and the extinction coefficient, k, has been studied. Analysis of the refractive index yields a high frequency dielectric constant, ɛ_∞, and the energy of the effective oscillator, E_o, the dispersion energy, E_d, the covalent value β and the M₋₁ and M₋₃ moments of the imaginary dielectric function of optical spectrum. Also, the dependence of the real part dielectric constant ɛ₁(hν) on its imaginary part ɛ₂(hν) of HgTe films can be used to determine the molecular relaxation time τ, the distribution parameter α^\ and the macroscopic (electronic) relaxation time τ_o. The graphical representations of surface and volume energy loss functions, dielectric constant, the optical conductivity as well as the relaxation time as a function of photon energy revealed three transitions at 0.63, 2.21 and 2.76 eV.