Energy Gap Of Thin Films Research Articles

The effect of rGO and chemical reduction under hydrazine on the structural, electrical and optical properties of nanostructured SnO2:F/rGO thin films

In this study, SnO2:F-rGO thin films were prepared by spray pyrolysis method on glass substrates. The effect of rGO and chemical reduction with Hydrazine on the structural, electrical, and optical properties of FTO:rGO thin films has been investigated. To deposition FTO: rGO thin films, different atomic ratios of fluorine to tin were changed as [F/Sn] = 0, 0.25, 0.5, 0.7 and 1 with a constant value of reduced graphene oxide (rGO). The X-ray diffraction study showed that all FTO: rGO thin films have a polycrystalline structure with tetragonal crystal structure and were preferably oriented in (200) direction. FE-SEM images showed that hydrazine as a reduction agent increased grain size and decreased porosity of FTO: rGO samples. The results of electrical measurements of thin films showed that the minimum sheet resistance equal to 118 Ω/□ was obtained for FTO: rGO with [F/Sn] = 0.5 thin films. The Hall Effect test showed the conductivity of all samples to be n-type and the carrier concentration was obtained from the order of 1021 cm−3. Also, the values of dislocation density and, micro-strain of FTO: rGO thin films were calculated. Finally, the results of UV–Vis spectroscopy showed that the energy gap of thin films varies in the range of 3.10–3.64 eV.

GROWTH AND OPTOELECTRONIC PROPERTIES OF p-CuO:Al/n-Si HETEROJUNCTION

A thin films of CuO and CuO:Al as well as p-CuO:Al/n-Si heterojunction with different Al ratios (0,1,2,3)%wt has been successfully fabricated by thermal oxidation with exist oxygen. The energy gap for thin films was calculated from optical properties. The capacitance was calculated as a function of voltage at reverse bias, and it demonstrate that these heterojunctions are abrupt. The capacitance values decreases with increasing the reverse bias while it increases with increasing Al ratio. The results indicated that the width of depletion layers and highest built in potential values decreases as Al concentration increases. The difference between reverse and forward current with applied voltage confirm for p -Cu O /n-Si and p -CuO:Al/n-Si that the heterojunction have a high rectification characteristic.

Investigation of structural, optical and thermoelectric properties of 2H–MoTe2 and MoO3–TeO2 thin films

Easy synthesis of two-dimensional chalcogenide materials sach as MoTe2 and WTe2 is an important challenge for researchers. In this paper, we are showed that using Mo and Te oxides percursors as inexpensive initial materials and spray pyrolysis method, the MoO3–TeO2 thin film binary compounds, and the important two-dimensional structure of 2H–MoTe2 are prepared. . In this method, through the preparation of thin films of the MoO3–TeO2 binary composition by changing the molar concentration of Mo and Te in a solid-state reaction process, with molar ratios (a) MoO3 (0.05 M) -TeO2 (0.15 M), (b) MoO3 (0.1 M) -TeO2 (0.1 M) and (c) MoO3 (0.15 M) -TeO2 (0.05 M), we can obtain the 2H–MoTe2 phase. After synthesis of MoO3–TeO2 and 2H–MoTe2 compounds, structural and optical characterization of thin films, as well as thermoelectric properties of the prepared thin films were studied before and after annealing at T = 500 °C. X-ray diffraction results showed that the structure of thin films before annealing is amorphous structure, and after annealing at T = 500 °C for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M), the two-dimensional structure of 2H–MoTe2 was formed. The images of the field emittion scanning electron microscope (FE-SEM) showed that the morphology of the nanoparticles is the pseudo-spherical shape, rod and polygon, indicating the presence of particles in different phases at before annealing and flat – like form after annealing. The results of UV–Vis spectrometry showed that the energy gap of thin films varied in the range of 2.3–2.87 eV. The nanoparticle bonding structure was also studied by FT-IR spectroscopy. Studies on the thermoelectric properties of thin films before and after annealing showed that for synthsis (c): MoO3 (0.15 M) -TeO2 (0.05 M) with formation of the 2-H-MoTe2 phase, the seebeck coefficient was larger than other samples, and the majority carrier are holes. Also, ZT increases with decreasing molar concentration of TeO2 and reached to 1.32 at room temperature for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M).

Photoresponse properties and energy gap of CsPbBr3–CsPb2Br5 compound thin film prepared by one-step thermal evaporation method

We proposed the preparation of the compound thin film of CsPb2Br5 and CsPbBr3 perovskites via thermal evaporation method with post-annealing. The optical absorption, energy gap, and photoresponse properties of the compound thin films were investigated. Over 90% transmittance in visible region of 550–700 nm was obtained, and the energy gap of thin film was found to be in the range of 2.28–2.35 eV. Using 405 nm laser, the compound thin film showed obvious response dependence on light power. Even if the large conductive channel of 1 mm × 100 μm was used, thin film possessed still good cycle characteristics, available responsivity, and a rapid response at applying 5 V.

The effect of annealing temperature variation on the optical properties test of LiTaO3 thin films based on Tauc Plot method for satellite technology

The purpose of the present research is to observe the energy gap of thin films made from LiTaO3 in 1 M-solubility deposited on n-type Si (111) substrates with annealing temperature variation. The manufacture of thin films has been formed by Chemical Solution Deposition (CSD) method using spin coater on 3000 rpm speed for 30 seconds and performed annealing process using furnace (Nabertherm type B180) at a temperature of 750°C, 800°C and 850°C for 15 hours. The absorbance of thin films is measured by using an Ocean Optics USB2000 device and processed into the energy gap curve using Tauc Plot method. The result shows that the energy gap of thin films associated with indirect transitions are increased from 2.78 eV to 2.93 eV with the rise of annealing temperature. The research shows that the thin films on n-type Si (111) substrates made of LiTaO3 produces sensitivity to violet light spectrum and have the potential to be developed as a sensor on satellite technology.

INFLUENCE OF ANNEALING ON THE STRUCTURAL AND OPTICAL CHARACTERISTICS OF INDIUM OXIDE THIN FILMS PREPARED USING THERMAL EVAPORATION IN A VACUUM METHOD

In the work, the structures and the optical parameters were studied for In2O3 thin films Before and after annealing at different temperatures (400 and 500 ) thin films were prepared on glass substrate by by vacuum thermal evaporation. The X-Ray diffraction showed that In2O3, In2O3 Plasticizedthin films which were prepared to have a polycrystalline cubic structure. The most preferential orientation is along the (321) direction for all deposited In2O3 films. Some parameters of the films were calculated as the average grain size and the dislocation density. Optical properties measurement transmittance (T) of the film shows that they have high transmittance (82.7%) is obtained for at annealing 500 . The optical properties such as absorption coefficient (α) using the transmittance measurement from an UV-vis spectrophotometer, with a range of wavelength (300-1100) nm. And also calculated energy gap for thin films. and also calculated energy gap for thin films, the result has been shown that the optical energy gap increasing with increasing annealing.

The semi-empirical tight-binding model for carbon allotropes “between diamond and graphite”

The new carbon allotropes “between diamond and graphite” have come under intensive examination during the last decade due to their numerous technical applications. The modification of energy gap in thin films of these allotropes was studied experimentally using optical methods. The proposed simple model of carbon clusters with variable lengths of chemical bonds allows us to imitate the transfer from diamond and diamond-like to graphite-like structures, as well as the corresponding modification of hybridization sp3/sp2 for diamond-like and spz for graphite-like phases. This enables us to estimate various allotropes parameters, like the gap Eg, energies of valence Ev, and conduction Ec band edges, and the value of electronic affinity, i.e., optical work function X, which are all of practical importance. The obtained estimations correspond to the experimental data.

Optical properties of thermally evaporated 4-(4-nitrobenzalideneamino) antipyrine Schiff base thin films

4-(4-nitrobenzalideneamino) antipyrine (NBAA) have been synthesized by refluxed ethanolic solution of 4-aminoantipyrine and p-nitrobenzaldehyde for 4 h and characterized with various physico-chemical techniques. Thin films of NBAA have been prepared by the thermal deposition technique in a vacuum of 1.5 × 10−5 mbar onto optical flat glass substrates. X-ray diffraction patterns show amorphous nature for all NBAA thin films except UV irradiated thin film which shows amorphous nature with some crystallinity but with small amount. The optical constants of thermally deposited NBAA thin film were investigated in the wavelength range 200–2500 nm. The type of optical transition near the edge of the band gap is found to be indirect allowed transition. The effect of UV irradiation as well as the effect of annealing on the optical properties of NBAA thin films was investigated. The value of the energy gap for thin films under investigation is calculated and found to be 1.56 eV for as-deposited, 1.45 eV for annealed and 1.82 eV for UV irradiation.

Spectroscopic ellipsometry study of Cd1−xMnxTe∕CdTe superlattices

We studied, by means of spectroscopic ellipsometry, dilute magnetic Cd1−xMnxTe∕CdTe semiconductor superlattices and Cd1−xMnxTe thin films grown by molecular beam epitaxy. In superlattices, the pseudodielectric function measured by ellipsometry shows specific features related to the excitonic transition between quantized minibands. In thin films, ellipsometry allows the clear identification of the energy gap. Additionally, critical point transitions are observable both in the spectra of the superlattices and films. Photoluminescence experiments have also been measured in order to evidence the fundamental interminiband excitonic transitions in superlattices and the energy gap in thin films, respectively. The electronic structure of the superlattices has been calculated in the framework of the envelope function approximation and compared with the experimental spectra. Ellipsometry appears to be a suitable technique to monitor the molecular beam epitaxy growth, ultimately also in situ, of dilute magnetic low-dimensional semiconductor systems.

Investigations on chemically deposited Cd1−xZnxS thin films with low Zn content

Thin films of Cd1−xZnxS (0≤x≤0.8) were deposited on glass substrates by the chemical bath deposition technique. The as-deposited films were exposed to a stream of slowly flowing nitrogen at annealing temperature ranging 100–500 °C. XRD patterns of as-deposited Cd1−xZnxS over all mixture ratio values showed the cubic zincblende structure of which reflection peaks associated to (111), (220) and (311) planes were clearly identified. However, XRD characteristics of hexagonal wurtzite structure appeared at annealing temperature beyond 400 °C. From scanning electron microscope, the as-deposited films were formed by different sizes of clusters of grains of which average grain size smaller than 50 nm was observed. The increase in mixture ratio value in the starting solution was found to produce a decrease in the grain size. Energy gap value of annealed films, which is obtained from optical transmission measurements, seems to shift to lower energy as the annealing temperature increases. Electrical sheet resistance of the films, performed in the darkness and under illumination conditions by using a halogen lamp, as a function of annealing temperature was also investigated. The variation of energy gap of thin films with annealing temperature was discussed by employing quantum size effect phenomena.

Conjugated Aromatic Polyimines. 2. Synthesis, Structure, and Properties of New Aromatic Polyazomethines

Abstract : A series of 20 conjugated aromatic Polyimines, containing p-phenylene, p-biphenylene, p-terphenylene, 4,4'- stilbene, and 1,5-naphthalene linkages in the backbone and various electron-donating and electron-withdrawing side-group substitutions, have been synthesized, characterized, and used to investigate the effects of molecular structure on the electronic structure and properties of conjugated polymers. Soluble gallium trichloride or diarylphosphate complexes of the aromatic polyimines in organic solvents facilitated their solution spectroscopic characterization and their processing into thin film and coatings. Electrochemical reduction of the aromatic polyimines was reversible with formal potential of -1.93 to -1.52 V (SCE) and 0.22 to 0.86 charge transferred whereas oxidation was irreversible. The electron affinity and ionization potentials of the series of polymers varied from 2.46 to 2.94 eV and from 4.80 to 5.38 eV, respectively. The associated LUMO and HOMO energy levels are thus tunable by up to 0.48 eV and 0.58 eV, respectively. The electrochemically and optically determined LUMO-HOMO energy gaps of thin films were very close and in the range of 2.08-2.77 eV. The results of this study show that aromatic polyimines are an interesting class of pi-conjugated polymers whose structure and properties can be regulated over a wide range by variation in backbone structure, side group substitution, and through intramolecular hydrogen bonding or complexation, backbone planarity. jg

Studies of superconductors using a low-temperature, high-field scanning tunneling microscope

We have developed a scanning tunneling microscope (STM) capable of operating at temperatures as low as 0.4 K and fields as high as 8 T. We have used this STM to study the energy gap of the high-Tc superconductors La–Sr–Cu–O and Y–Ba–Cu–O. We find that the reduced gap for these oxide superconductors falls in the range 3<2Δ/kBTc<7, for polycrystalline, single-crystal, and thin-film samples. We have also simultaneously imaged the surface topography and superconducting energy gap for thin films of the granular superconductor NbN. We occasionally see regions with smaller best-fit gaps that correlate with surface topographical features, but have been unable so far to image flux vortices.