Optical Gap Values Research Articles

Optical behaviour of swift heavy ions irradiated poly(vinyl alcohol) films

Polyvinyl alcohol films were irradiated to 90 MeV O 6+ and 150 MeV Si 14+ ions at fluence ranging from 1010 to 1012 ions/cm2. The observed changes in optical energy gap of this polymer have been investigated and results are tried to be explained in terms of energy transferred by the incident ions. It has been noticed that the value of optical energy gap decreases with increasing energy loss during the ion–polymer interaction process.

Structural, Morphological and Optical Properties of (Cu2S)100-x(SnS2)x Thin Films

The structural , optical and morphological properties of SnS2 , Cu2S thin films and their mixture prepared by spray pyrolysis technique , were studied. SnS2 , Cu2S thin films and their mixture were deposited on glass substrates at temperature of 334°C, 283°C and 300°C respectively. XRD studies showed that all the prepared films were polycrystalline in nature with a hexagonal structure and the preferential orientation for Cu2S thin film was along (002) plane , while the preferential orientation for SnS2 thin films was along (101) plane . The absorbance and transmittance spectra have been recorded in the wavelength (310-1100) nm in order to study the optical properties . It was found that the electronic transitions on fundamental absorption edge were direct allowed and the values of the optical energy gap for SnS2 andCu2S was equal to 2.2eV and 2.35eV respectively. Also it was found that the values of the optical energy gap for the mixture decreased with the increase in SnS2 in the mixture from (2.32-2.22) eV. The optical constants which include refractive index and extinction coefficient as a function of photon energy were also studied.

A new strontium antimonateIII Sr5Sb22O38: Synthesis, crystal structure and characterizations

A new strontium antimonate{sup III}, Sr{sub 5}Sb{sub 22}O{sub 38}, has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. It crystallizes in the P2{sub 1}/n space group of the monoclinic system with a=11.739(9) A, b=12.014(10) A, c=16.412(13) A, β=91.460(8)°, V=2314.0(3) A{sup 3}. The crystal structure is built of seven trigonal–pyramidal SbO{sub 3} and four sphenoid SbO{sub 4} polyhedra which are connected through sharing corner-oxygen atoms to form the complex three-dimensional {sub ∞}{sup 3}[Sb{sub 22}O{sub 38}]{sup 10−} anionic network with two different intersectant tunnels along the [111-bar ] and [11-bar 1-bar ] directions accommodating the electric charge balanced Sr{sup 2+} cations. First-principles electronic structure calculations based on the density functional theory (DFT) and the UV–vis diffuse reflectance spectroscopy measurements both indicate that the compound belongs to a direct band insulator with an optical gap value of 3.3 eV. - Graphical abstract: The 2D Sb–O slabs are stacked through sharing oxygen atoms to form the 3D network structure of the new strontium antimonate{sup III} Sr{sub 5}Sb{sub 22}O{sub 38}. - Highlights: • A new strontium antimonate{sup III}, Sr{sub 5}Sb{sub 22}O{sub 38}, has been hydrothermally synthesized. • The single crystal structure was determined by X-ray diffraction. • The powder XRD and UV–vismore » absorption spectroscopy were studied. • Theoretical studies interpret the relationships between optical absorption and crystal structure.« less

Optical Band Gaps and Electrical Conductance of Si Nanocrystals in SiO<sub>2</sub> Matrix for Optoelectronic Applications

In this study, silicon nanocrystal (Si-nc) films were synthesized by compositing of Si-nc powder embedded in silicon oxide phase. The Si-nc film produced by the spin-coating methode using Tetraethylorthosilicate, ethanol, phosphoric acid, and Si-nc powder as suspension precursors. The variation in structural and optical properties of Si-nc sol films with the amounts of Si-nc powder have been characterized. Atomic force microscopy (AFM) shows that low density level of Si-nc power can result in the amount of porosity in the Si-nc films. It is found that when the Si-nc films have the higher Si-nc density, the small pores in the SiO2 phase were removed. In addition, optical energy gap (Eg) of Si-nc samples was evaluated by the Tauc plot method. It is a crucial attribute for a promising photonic device. The obtained optical bang gap values were extended from 1.10 eV to 1.40 eV as compared with the typical Si bulk. In addition, density of Si-nc clusters has a considerable effect on the electrical conductance of the Si-nc films measured at room temperature.

Optical properties of nanostructure boron doped NiO thin films

Boron doped NiO films were prepared by sol–gel method. The effects of B content on the morphological and optical properties of NiO films were studied with atomic force microscopy, and optical characterization method. The average transmittance at the visible region is reached to 75 % for lower doped films (0.1 and 0.2 % B), whereas, the recorded average value of transmittance was about 62 % for doped film with 1 % B throughout the region. The optical energy gap value for pure NiO film was found to be 3.73 eV. These values were affected by B doping with non-monotonic variation and reached to 3.64 eV for 0.1 % B doped NiO. Also, the refractive index dispersion and dielectric constants of the NiO films were studied throughout the investigated range of wavelengths. The obtained results indicate that the optical parameters of the NiO film are controlled with boron doping.

Optical Properties of Gallium Oxide Clusters from First-Principles Calculations

The optical properties of the (Ga(2)O(3))(n) clusters, with n = 1-10, have been studied within the framework of time dependent density functional theory. The gallium oxide cluster geometries showed evolution from planar configuration (C(2v)) for Ga(2)O(3) to layered globular configuration (C(s)) for (Ga(2)O(3))(10) via corundum configuration (D(3d)) for (Ga(2)O(3))(4). For n ≤ 5, with the increase in coordination of Ga and O atoms, the polarizability decreases with the size of the cluster. For n ≥ 6, with the stabilization of average coordination number for gallium and oxygen atoms, the decrease in polarizability is very small. Further, the optical absorption spectra and the corresponding optical gap have been calculated. The overall shape of the calculated spectra strongly depend on cluster geometries. With the increase in size, the discrete spectra of small clusters evolves into quasicontinuous spectra. For n = 10, the spectra show a smooth absorption edge that is a characteristic of the bulk. It is observed that the optical gap oscillate with an increase in the cluster size. The calculated optical gap of these clusters are lower than the band gap of α- and β-Ga(2)O(3) phases. The underestimation of the calculated values of the cluster optical gap is due to the use of local density approximation.

Optical characterization of poly(methyl methacrylate) implanted with low energy ions

The samples of poly(methyl methacrylate) (PMMA) were subjected to 100keV N+ and Ar+ ion implantation up to a maximum fluence of 2×1016ions/cm2. The effect of ion implantation on the optical energy gap and the refractive index has been studied through UV–visible spectroscopy. The results clearly indicate a decrease in the values of optical energy gap and an increase in the values of refractive index as an effect of ion implantation corresponding to both of the ions. It has also been observed that the changes induced by the implanted ions are more pronounced for N+ ions in comparison to Ar+ ions. This variation has been correlated with the calculated ranges of these ions in PMMA polymer using Stopping and Range of Ions in Matter (SRIM) code. Finally, an attempt has been made to correlate all the observed changes with the induced structural changes as revealed through Raman spectroscopy.

A novel synthesis and optical properties of cuprous oxide nano octahedrons via microwave hydrothermal route

A novel and efficient synthesis of cuprous oxide (Cu2O) nano-octahedron was successfully prepared via a green chemie douce approach utilized a microwave hydrothermal route at low growth temperature without the presence of any surfactant. The crystalline structure of the Cu2O was characterized by several techniques like X-ray powder diffraction (XRD), Fourier transformation spec- troscopy, field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM). XRD results indicate that the size of Cu2O nano—octahedron is 71 nm which is calculated with the help of Scherer equation, as supported by FESEM and TEM. The formation mechanism of the Cu2O octahedral was discussed. Optical absorption spectra reveal that the optical band gap of the Cu2 Oi s controlled by quantum confinement effect. The obtained optical energy gap value Eg of Cu2O octahedron was about 2.43 eV. The photoluminescence emission spectra of the Cu2O nano-octahedrons exhibit two emission peaks located at 342 and 365 nm due to the quantum effect. It is evalu- ated that the green chemie douce approach is a cheap and fast to synthesize Cu2O nano-octahedrons and could be potentially extended to other inorganic systems for indus- trial production.

Optical and electrical properties of nonstoichiometric a-Ge1−xCx films prepared by magnetron co-sputtering

Amorphous non-hydrogenated germanium carbide (a-Ge1−xCx) films have been prepared by magnetron co-sputtering method in a discharge of Ar. The dependence of structural and chemical bonding properties on the Ge/C ratio (R) has been investigated by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The relationship between the chemical bonding and the optical and electrical properties of the a-Ge1−xCx films has also been explored. It has been shown that the refractive index of the films increases from 2.9 to 4.4 and the optical gap decreases from 1.55 to 1.05eV as R increases from 1.22 to 5.67. Moreover, the conductivity σ increases clearly and the activation energy Ea decreases with the increasing R owing to the reduction of sp3 CGe bonds. The a-Ge1−xCx films exhibit refractive index and optical gap values changing with x in a wide range, which may make a-Ge1−xCx films good candidates in the fields of protection coatings for IR windows and electronic devices.

The Effect of Helium Dilution on Optical and Photoelectric Properties of a-Si: H Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition Technique

The effect of Helium (He) dilution on optical and photoelectric properties of hydrogenated amorphous silicon (a-Si:H) thin film samples prepared at substrate temperature of 75°C with increased growth rate by plasma-enhanced chemical vapor deposition (PECVD) technique is studied using spectrophotometric (SP) and steady-state photocarrier grating techniques (SSPG). The values of refractive index, absorption coefficient, thickness and optical energy gap, which are found from the analysis of transmission spectra using Swanepoel method, are compared with those obtained by employing variable-angle spectroscopic ellipsometry technique. The samples exhibit a tendency towards an increase in energy gap and a decrease in refractive index with the increase in He dilution. The obtained optical absorption coefficients of a-Si:H samples are compared with those of hydrogenated microcrystalline silicon (μc-Si:H) and crystalline silicon (c-Si) samples. It is also found that the change in He dilution has an influence on the ambipolar diffusion length, minority and majority mobility-lifetime products.

Effect of annealing temperature on the optical properties of nanosilicon produced from silicon monoxide

Silicon nanoparticles (Si-NPs) capable of photoluminescence (PL) over the energy range from 790 nm to 900 nm were synthesized from silicon monoxide by increasing annealing temperatures from 25 °C to 950 °C. The PL of nanoparticles has remained stable for more than ten months from the date of the hydrosilylation of their surface by 1-octadecene. Solid samples of Si-NPs grafted with 1-octadecene are stable in the air up to 220 °C. The mean sizes of particles and their size distribution density function were derived from SAXS and XRD experiments and compared with TEM and HRTEM images and values calculated by the quantum limit model in accordance with the experimental optical absorption gap values. The absorption spectra of Si-NPs synthesized at 25 °C, 200 °C and 300 °C exhibited a blue shift of the fundamental absorption edge with respect to silicon single crystals; the absorption of Si600 and Si950 at the same incident photon shows energies increase. The PL peak of Si-NPs shifted toward longer waves as the synthesis temperature increased and exhibited a stronger red shift with respect to the photoexcitation wavelength. An analysis of the red shift led us to conclude that the surface states related to (Si–O) bonds influenced the effectiveness of PL. The Si-NPs PL quantum yield increased as the annealing temperature grew and reached a maximum of ∼12% for Si-NPs at 950 °C.

Comparative study of the properties of ZnO thin films deposited on poly propylene carbonate (PPC) and glass substrates

In this study, we report a comparative study of the structural, morphological, and optical properties of the deposited ZnO thin films on Poly Propylene Carbonate (PPC) and glass substrates by direct current (DC) sputtering technique. X-ray diffraction (XRD) spectra of the films on PPC and glass substrates show mainly the ZnO (002) diffraction peaks at 2θ = 34.1 and 34.3o with full width at half maximum (FWHM) of 0.31 and 0.34o, respectively. Scanning electron microscopy (SEM) images show that both ZnO thin films have smooth surface. Photoluminescence (PL) spectra show two peaks, the first intense peak was found in the UV region. The second weak peak was observed in the visible region. The transmission and absorption spectra of the ZnO thin films deposited on both substrates showed that the films have good transmission in the visible region and a good absorption in the UV region. The optical energy gap (Eg) values of the deposited ZnO thin films on PPC plastic and glass substrates were derived from absorption measurements and it found to be 3.38 and 3.40 eV, respectively.

Hydrogel templated CdS quantum dots synthesis and their characterization

This work reports a facile method for preparation of CdS quantum dots (Q-dots), using a crosslinked hydrophilic p(AMPS) hydrogel network by absorption of Cd(II) ions and sequential precipitation with aqueous Na 2S within the network at room temperature. The TEM images revealed that prepared CdS Q-dots were distributed throughout the p(AMPS) hydrogel network and their sizes were about 5 nm. The amount of inorganic material inside p(AMPS) hydrogel was determined by TGA measurements to be 16.9% by weight. Additionally, the Cd and S amounts inside the p(AMPS) network were determined by dissolution of particles with HCl (three treatments with 3 M HCl) and by using ICP-AES (for Cd) and an elemental analyzer (for S). From UV–visible absorbance measurements, optical energy gap values of 5.1 ± 0.1 eV for p(AMPS) and 2.4 ± 0.05 eV for p(AMPS)–CdS were determined. From the fluorescence spectrum of the p(AMPS)–CdS hydrogel, the peak energy was observed at 2.30 eV. The in situ prepared Q-dots were recovered from hydrogel matrices by placing the p(AMPS)–CdS composite in purified water.

Some physical properties of (Bi 2O 3) x(BaO) 0.5− x(B 2O 3) 0.5 glasses

A series of (Bi 2O 3) x (BaO) 0.5− x (B 2O 3) 0.5 glasses were prepared from pure oxides. The glass transition temperature little decreased from 450 to 419 °C with the increase in x from 0.2 to 0.4. The coefficient of thermal expansion was found at around 10 ± 1 ppm °C −1, practically independent on x. The structural make-up of the glasses was suggested to be formed by structural groups of BaBi 2B 4O 10 and BiBO 3 for 0.25 < x ≤ 0.5, BaBi 2B 4O 10 and BaB 2O 4 for x < 0.25 and by BaBi 2B 4O 10 for x = 0.25. The optical band gap was determined in the region 3.35–3.54 eV and the coefficient of the temperature dependence of the optical gap for the temperatures between 30 and 250 °C was found nearly constant at around (5.5 ± 0.5) × 10 −4 eV K −1. The non-linear refractive index of the studied glasses was estimated from the optical gap values at around 0.9 × 10 −11 esu.

Influence of bias voltage on the structure and deposition mechanism of diamond‐like carbon films produced by RF (13.56 MHz) CH4 plasma

AbstractPlasma enhanced chemical vapour deposition technique (PECVD) was used to grow diamond‐like carbon films using pure methane gas plasma. Structural, optical and mechanical properties of the obtained a‐C:H films were investigated as a function of bias voltage in the range 120–270 V, using different techniques. Elastic recoil detection analysis (ERDA) was employed to determine the hydrogen content and Fourier transform infrared spectroscopy (FTIR) was used to analyse the absorption of optically active hydrogen in the deposited films. The relative concentrations of sp2 and sp3 groups were determined from fitting of both X‐ray photoelectron spectroscopy (XPS) and FTIR spectra. Mechanical hardness and optical transmission were determined using nanoindentation and spectrophotometry, respectively. The results showed that the structure and properties of the films formed strongly depended on the applied bias voltage. In the range of energy considered the growth of the films was governed by a competition between both chemical and physical processes, with a dominance of physical process (subplantation) above 240 V, the energy at which more than 90% sp3 hybridization was obtained. Nanoindentation tests revealed hardness and Young's modulus of the films ranging from 12–15 and 116–155 GPa, respectively. The optical gap values deduced from the optical transmission spectra varied between 1.13 and 1.60 eV.

Photocatalytic reduction of CO2 using H2 as reductant over ATaO3 photocatalysts (A = Li, Na, K)

ATaO3 (A=Li, Na, K) compound oxides exhibit photocatalytic activity for the reduction of CO2 in the presence of H2. Only CO gas was generated over all samples under photoirradiation. The photocatalytic activity was higher in the order corresponding to KTaO3, NaTaO3 and LiTaO3 (LiTaO3>NaTaO3>KTaO3). The order of the photocatalytic activities was consistent with that of the Eg (optical gap) values. After 24h of photoirradiation, the amount of evolved CO reached 0.42μmolg−1 over LiTaO3. TPD experiments indicated that the broad peak which is assigned to chemisorbed CO2 gas was observed at 573K in the case of LiTaO3. On the contrary, there was no peak in the spectra of NaTaO3 and KTaO3. The amount of evolved CO gas almost strongly depends on the amount of chemisorbed CO2 in the case of ATaO3 (A=Li, Na, K). In addition, the photocatalytic activity increased with increasing the calcination temperature of LiTaO3. This means that a smooth charge separation in a LiTaO3 photocatalyst and chemisorption of CO2 on the surface contribute to effective reduction of CO2 in the presence of H2.

Raman studies and some physical properties of selected (PbO) x(Nb 2O 5) y(TeO 2) 1−x−y glasses

Selected Nb 2O 5–TeO 2, PbO–Nb 2O 5–TeO 2 and PbO–TeO 2 glasses were prepared from very pure oxides. The glass-transition temperature increased from 281 to 411 °C with an increase in Nb 2O 5 content and, simultaneously, the coefficient of thermal expansion decreased from 21 to 11 ppm/°C. Raman scattering measurements indicated that TeO 4 trigonal bipyramids, TeO 3+1, TeO 3 trigonal unit and NbO 6 octahedra were the basic structural units of Nb 2O 5–TeO 2 and PbO–Nb 2O 5–TeO 2 glasses. The optical band gap was determined in the region 3.39–3.60 eV and the coefficient of the temperature dependence of the optical gap for the temperatures between 30 and 250 °C in the region 4.1 × 10 −4–6.8 × 10 −4 eV/K was found. Non-linear refractive index of the studied glasses was estimated from the optical gap values at around 0.85 × 10 −11 esu.

Morphology Evolution of One-Dimensional-Based ZnO Nanostructures Synthesized via Electrochemical Corrosion

Various morphologies of ZnO nanostructures can be obtained through a novel method, incorporating electrochemical corrosion with three modes: liquid membrane and above and below the water line in partial immersion. X-ray diffraction (XRD) patterns, high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) are employed to characterize their structure. The mechanism of the growth of NRs is proposed as electrochemical corrosion and oriented attachment, which occur in a liquid membrane or partial immersion in a vapor membrane. The evolution of ZnO nanostructures such as nanorods, nanowires, nanopins, and nanodentrites is observed, and the influence of concentration, reaction time, additives, state of substrate, membrane thickness, and solvent on the morphology of ZnO is investigated. Optical properties of ZnO nanostructures are studied by using UV−visible absorption spectra and photoluminescence (PL). Their optical gaps vary from different morphologies. Among the studied samples, short nanorods show the largest optical gap, while big nanorods present the smallest value of optical gap. PL properties demonstrate that peaks of near-band emission and defect-related luminescence are basically in the same position. However, intensities for different morphologies are of different values, and short nanorods exhibit the best near-band emissions.

Optical band gap and Raman spectra in some (Bi 2O 3) x(WO 3) y(TeO 2) 100−x−y and (PbO) x(WO 3) y(TeO 2) 100−x−y glasses

The glasses representing (Bi 2O 3) x (WO 3) y (TeO 2) 100− x − y and (PbO) x (WO 3) y (TeO 2) 100− x − y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30 2 to 6.80 8 g/cm 3. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10 −4 to 5.24 × 10 −4 eV/K. It is suggested that Raman feature observed at around 350 cm −1 can be assigned to an overlap of Raman bands attributed to WO 6 corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.

STUDYING THE EFFECT OF DOPING BY SILVER ON THE OPTICAL PROPERTIES OF ZNIN2S4 THIN FILM

In this research the optical properties of ternary ZnIn2S4 compound thin film of thickness (0.17 0.05)μm , which deposited on glass slides by chemical spray pyrolysis at 360oC were studied, Also studied the effect of doping by Ag element on the optical properties of the prepared thin films . From the absorption and transmission spectrum of the prepared thin films in the range (300 – 1000) nm, the optical constants were calculated. The absorption coefficient (α) was found to be greater than( 104)cm-1 for all films , this means that the electronic transitions of allowed direct type and the absorption edge is (442.85)nm for thin film ZnIn2S4 but when this thin film was doped by Ag element with amount of (1, 2, 3, 4 and 5)wt% the absorption edge was shifted toward the greater wavelength and arrive to (506.12)nm at 5%wt(Ag) without change in the electronic transitions type. The value of optical energy gap (Eg) for thin film ZnIn2S4 was (2.80)eV decreased non linearly with increases Ag element and arrive (2.45)eV at 5%wt(Ag).The higher value of extinction coefficient (K) were shifted toward the larger wavelength when the thin film ZnIn2S4 was doped by Ag .Also the higher values of refractive index (n) were shifted toward the larger wavelength with increases in doping ratio. The behavior of real dielectric constant (€1)and imaginary dielectric constant (€2) is similar to refractive index, and higher values shifted toward greater wavelength with increases in doping ratio . The tail width of the local states in the energy gap were calculated which was increased by adding the silver to the deposited film.