Based on the modification of the simplified coherent potential approximation （SCPA）, a model is developed to calculate the composition dependence of the band gap energy of Ⅲ-V ternary alloys with the same anion. Th...Based on the modification of the simplified coherent potential approximation （SCPA）, a model is developed to calculate the composition dependence of the band gap energy of Ⅲ-V ternary alloys with the same anion. The derived equation is used to fit the experimental band gap energy of InxAl1-xN, InxGa1-xN and A1xGal xN with x from 0 to 1. It is found that the fitting results are better than those done by using SCPA. The fitting results are also better than those obtained by using the formula with a small bowing coefficient, especially for InxAl1-xN. In addition, our model can also be used to describe the composition de- pendence of band gap energy of other Ⅲ-V ternary alloys.展开更多
We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor;the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques.Th...We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor;the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques.The thin films were deposited at different substrate temperatures ranging between 200 and 500℃. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation（2）, so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.展开更多
The n-type semiconducting titanium oxide thin films are well-known as electron transporting interlayer in photovoltaic cells. The favorable characteristics of interlayers in photovoltaics are high optical transmittan...The n-type semiconducting titanium oxide thin films are well-known as electron transporting interlayer in photovoltaic cells. The favorable characteristics of interlayers in photovoltaics are high optical transmittance （T%）, wide band gap energy （Eg） and high electrical conductivity （σ）. Modifying titanium oxide films with metal nanoparticles would increase electrical conductivity but reduce optical band gap energy. We developed the sol-gel derived titanium suboxide （TiOx） films modified with silver （Ag） or gold （Au） or copper （Cu） nanoparticles （NPs）. This study explores a tradeoff between narrowing optical band gap and enhancing electrical conductivity of nanostructured TiOx films by controlling the Au- or Ag- or Cu-NPs loading concentrations （mol%） in titania. The Au- and Cu-NPs loading concentration of 4 mol% should meet a tradeoff which yields the higher T%, wider Eg and higher compared to those of pure TiOx films. In addition, since the pure Cu is not thermodynamically stable in ambience as compared to Au and Ag, the stability of as-obtained colloidal CuNPs is also examined. A careful examination of the time evolution of surface plasmon resonance （SPR） bands of CuNPs indicates that their stability is only up to 4 h.展开更多
With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recen...With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density(W_(rec)).Nevertheless,the dielectric loss also increases as the external electric field increases,which will generate much dissipated energy and raise the temperature of ceramic capacitors.Thus,an effective strategy is proposed to enhance the energy storage efficiency(η)via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na_(0.5)K_(0.5))-NbO_(3)-0.1Bi(Zn_(2/3)(Nb_(x)Ta_(1−x))1/3)O_(3) ceramics.On the one hand,the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short−range polar nanoregions(PNRs),resulting in the highη.On the other hand,the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the Eb.As a result,high Wrec of 3.29 J/cm^(3) and ultrahighηof 90.1%at the high external electric field of 310 kV/cm are achieved in x=0.5 sample.These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.展开更多
This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical...This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].展开更多
In this paper,we have reported the synthesis of FeS2 of higher band gap energy（2.75 eV） by using capping reagent and its successive application in organic-inorganic based hybrid solar cells.Hydrothermal route was ad...In this paper,we have reported the synthesis of FeS2 of higher band gap energy（2.75 eV） by using capping reagent and its successive application in organic-inorganic based hybrid solar cells.Hydrothermal route was adopted for preparing iron pyrite（FeS2） nanoparticles with capping reagent PEG-400.The quality of synthesized FeS2 material was confirmed by X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,Fourier transform infrared,thermogravimetric analyzer,and Raman study.The optical band gap energy and electro-chemical band gap energy of the synthesized FeS2 were investigated by UV-vis spectrophotometry and cyclic voltammetry.Finally band gap engineered FeS2 has been successfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy.The energy conversion efficiency was obtained as 0.064%with a fill-factor of 0.52.展开更多
Porous ZnO films were prepared by electrodeposition method in zinc nitrate aqueous solution using ITO glass covered with polystyrene sphere （PS） colloidal crystal arrays as substrates. The preparation procedure incl...Porous ZnO films were prepared by electrodeposition method in zinc nitrate aqueous solution using ITO glass covered with polystyrene sphere （PS） colloidal crystal arrays as substrates. The preparation procedure includes two parts： deposition of ZnO in the interstices of the colloidal crystals and subsequent removal of the PS templates. The influences of deposition potential and temperature on the ZnO films were investigated. The ordered, uniform porous ZnO films with optical transmittance of approximately 63.6% at 600 nm could be obtained when the deposition potential and temperature were –1.1 V and 70 ℃, respectively. The optical band gap energy increased along with the absolute deposition potential and temperature, ranging from 3.33 to 3.43 eV and from 3.35 to 3.42 eV, respectively.展开更多
Zn-Cu-codoped SnO2 nanoparticles have been synthesized by chemical precipitation method. All nanoparticles are crystalline, with the average size increases from 2.55 nm to 4.13 nm as the calcination temperature increa...Zn-Cu-codoped SnO2 nanoparticles have been synthesized by chemical precipitation method. All nanoparticles are crystalline, with the average size increases from 2.55 nm to 4.13 nm as the calcination temperature increases from 400℃ to 600℃. The high calcination temperature can enhance the crystalline quality and grain growth. The oxygen content decreases with decreasing calcination temperature; at a low temperature of 400℃, Zn-Cu-codoped SnO2 nanoparticles are in a rather oxygen-poor state having many oxygen vacancies. The optical band gap energies of Zn-Cu-codoped SnO2 nanoparticles calcined at 400℃ and 600℃ are decreased from 3.93 eV to 3.62 eV due to quantum confinement effects. Both samples exhibit room-temperature ferromagnetism, with a larger saturation magnetization at 400℃ due to the presence of large density of defects such as oxygen vacancies. Zn-Cu-codoped SnO2 nanoparticles exhibit large optical band gap energies and room temperature ferromagnetism, which make them potential candidates for applications in optoelectronics and spintronics.展开更多
TiO2 nanotubes on Ti metal surface were prepared by the electrochemical anodization method. Then, nanosilver was deposited onto the nanotubes by the electroless dip coating and the anodization. The obtained TiO2 nanot...TiO2 nanotubes on Ti metal surface were prepared by the electrochemical anodization method. Then, nanosilver was deposited onto the nanotubes by the electroless dip coating and the anodization. The obtained TiO2 nanotubes were examined by using scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, cyclic voltammetry, and UV–Vis. The electrochemical band gap（Eg^CV） of the nanosilver-coated TiO2 nanotubes prepared by the anodization was found as 1.54 eV. Using the UV–Vis measurements, the optical band gap energy（Eg^op.） was calculated as 1.51 eV for the Ag/TiO2 nanotubes obtained by electroless dip coating. The electrical conductivity of the TiO2 nanotubes also increased from 3.0 × 10^-4 to 34.7 S/cm after nano Ag deposition by the anodization method.These Ag/TiO2 nanotubes with low band gap and high electrical conductivity are desirable for the applications in electronics, Li-ion batteries, and solar cells.展开更多
The title compounds have been respectively synthesized by solution process and solvothermal reaction, and their crystal structures were determined by X-ray diffraction method. For （CH3CH2CH2CH2NH3）6（BiI6）（I）2I3 ...The title compounds have been respectively synthesized by solution process and solvothermal reaction, and their crystal structures were determined by X-ray diffraction method. For （CH3CH2CH2CH2NH3）6（BiI6）（I）2I3 1, it crystallizes in tficlinic, space group P1^- with Mr = 2049.76, a = 8.5719（1）, b = 11.7461（3）, c = 15.700（1）A, V = 1451.4（1）A^3, Z = 1, Dc = 2.345 g/cm^3, F（000） = 924, μ（MoKα） = 8.907 mm^-1, T = 293（2） K, the final R = 0.0655 and wR = 0.0804 for 2399 observed reflections with I 〉 2σ（I）. For （NH3CH2CH2NH3）2Bi2I10 2, it crystallizes in monoclinic, space group P21/n with Mr= 1811.20, a = 8.434（4）, b = 13.862（6）, c = 13.362（6）A, V = 1499.9（12）A^3, Z = 2, Dc = 4.010 g/cm^3, F（000） = 1536,μ（MoKα） = 22.007 mm^-1, T = 293（2） K, the final R = 0.0584 and wR = 0.1451 for 1798 observed reflections with I 〉 2σ（I）. The structures of 1 and 2 contain halobismuthate monomer and dimers, respectively. It is noteworthy that the dimers and their organic counters in 2 connect each other by N…I hydrogen bonds to form a layered structure, and the electrostatic interactions and crystal packing forces between layers give rise to the packing of the crystal. The optical absorption spectra of 1 and 2 reveal the appearance of sharp optical gaps of 2.13 and 2.01 eV, respectively.展开更多
CdS thin films were prepared by chemical-bath-deposited method and the effect of temperature and time on the properties of CdS thin films was studied. Independent of the deposited temperature, the growth was mainly co...CdS thin films were prepared by chemical-bath-deposited method and the effect of temperature and time on the properties of CdS thin films was studied. Independent of the deposited temperature, the growth was mainly controlled by the ion-by-ion growth mechanism at the beginning of the film deposition, then the cluster-by-cluster mechanism came to be dominant. The growth rate increased faster with the increasing of temperature until the thickness reached the limitation, then thickness instead become thinner. The scanning electron micro- scope results revealed that the morphology of the CdS film changed from pinholes to rough, inhomogeneous surface with increasing deposition time and deposition temperature. The X- ray diffraction results showed the film structure was a mixture of two phases： hexagonal and cubic, and it was very important to controll deposition time to the film＇s crystal phase. All films in depth of approxilnate 100 nm existed above 65% transmittance, the absorption edge became ＂red-shift＂ with temperature rising. At 60 and 70℃, with 20 min deposited-time, the energy band gap was more than 2.42 eV and decreased with time, while at 80 and 90℃ the energy band gap was less than 2.42 eV and increased little when the time changed from 10min to 15 nfin at 80℃.展开更多
Our calculations are based on the modeling technique and simulation Ab-Initio that appeals to the Density Functional Theory (DFT) relying on the Full-Potential Linearized Augmented Plane Waves (FP-LAPW) method that re...Our calculations are based on the modeling technique and simulation Ab-Initio that appeals to the Density Functional Theory (DFT) relying on the Full-Potential Linearized Augmented Plane Waves (FP-LAPW) method that requires a calculation process using approximations such as Local Density (LDA) and Generalized Gradient (GGA) developed in the modelling software of nanostructures WIEN2k. The optimal structure of the binary semiconductor ZnSe crystallizing in the complex phase of Zinc Blende (B3) was determined by studying the variation of energy depending on the volume of the elementary cell. Then the electronic properties of the optimized state were analyzed such as the gap energy, the total density of states (TDOS), the partial density of states (PDOS) and the repartition of the electronic charge density. The obtained results were successful compared with other theoretical and experimental values reported in literature.展开更多
Two sets of Organic dyes were developed using kassod and senna plant leaves. The first sets of dyes are the organic dye from the leaves of two plants while the second set is the dye produce after combining together th...Two sets of Organic dyes were developed using kassod and senna plant leaves. The first sets of dyes are the organic dye from the leaves of two plants while the second set is the dye produce after combining together the dyes from the kassod and senna plants leaves. The two sets of dyes were used to sensitize the grown films. The films were characterized and the current voltage values of the grown films were obtained. The solar simulation result of the grown film for Kassod dyed TiO<sub>2</sub> film was recorded for single dyes and for the <span "="">combination of the two dyes. The result also covers absorbance of the spectra lines, absorbance coefficient values of the dyed TiO<sub>2</sub>, as well as transmittance and energy band gap values of the developed films. The precursors of tin (IV) chloride (SnCl<sub>4</sub>) (60%) and hydrofluoric acid (40%) was deposited on the cleaned soda</span>-lime glass using the chemical vapour deposition method and <span "="">nitrogen gas was supplied as a carrier gas through the bubbler to form the FTO layer. Titanium dioxide paste (TiO<sub>2</sub>) was deposited using </span>a <span "="">screen printing method to form M-TiO<sub>2</sub>.展开更多
The optical properties of the pure polymer film and polymer films doped with Phenol Red dye at different concentrations were investigated. The films were prepared using the casting technique. Poly (methyl-methacrylate...The optical properties of the pure polymer film and polymer films doped with Phenol Red dye at different concentrations were investigated. The films were prepared using the casting technique. Poly (methyl-methacrylate) (PMMA) polymer was doped with the Phenol Red dye dissolved in a mixture of chloroform and little quantity of methanol, used as suitable solvent for both the dye and the polymer. The spectral absorption measurements of these films were carried out at different dye concentrations using UV-Vis double-beam spectrophotometer in the wavelength range 300 - 800 nm. The optical parameters of the prepared Phenol Red dye doped polymer films, absorption coefficient (α), extinction coefficient (κ), refractive index (n), optical and electrical conductivities (σ<sub>opt</sub> and σ<sub>elect</sub>), and optical energy band gap (E<sub>g</sub>), were determined. The results showed that the Phenol Red dye doped polymer film is a good candidate for photonic applications such as, solar cells, optical sensors, and other photonic devices.展开更多
The electronic properties and topological phases of ThXY （X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn） compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compoun...The electronic properties and topological phases of ThXY （X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn） compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases （insulator or metal） and normal phases within generalized gradient approximation （GGA） and Engel- Vosko generalized gradient approximation （GGA_EV） are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves.展开更多
Quaternary glasses were successfully fabricated using melt quenching technique based on the chemical compound composition(x)Bi_(2)O_(3)–(0:5-x)ZnO-(0.2)B_(2)O_(3)–(0.3)SiO_(2),where(x=0.1,0.2,0.3,0.4,0.45)mole.The s...Quaternary glasses were successfully fabricated using melt quenching technique based on the chemical compound composition(x)Bi_(2)O_(3)–(0:5-x)ZnO-(0.2)B_(2)O_(3)–(0.3)SiO_(2),where(x=0.1,0.2,0.3,0.4,0.45)mole.The sources of SiO_(2)was produced from rice husk ash(RHA)at 99.36%of SiO_(2).The Urbach energy was increased from 0.16 eV to the 0.29 eV as the mole of Bi_(2)O_(3)increased in the glass structure.The indirect energy band gap is indicated in decrement pattern with 3.15 eV towards 2.51 eV.The results of Urbach energy and band gap energy that were obtained are due to the increment of Bi^(3+)ion in the glass network.The refractive indexes for the prepared glasses were evaluated at 2.36 to 2.54 based on the Lorentz–Lorentz formulation which correlated to the energy band gap.The calculated of molar polarizability,electronic polarizability and optical basicity exemplify fine complement to the Bi_(2)O_(3)addition in the glass network.The glass sample was indicated in amorphous state.展开更多
ZnO thin films were synthesised by a new method which uses polyvinyl alcohol （PVA） as the polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural paramet...ZnO thin films were synthesised by a new method which uses polyvinyl alcohol （PVA） as the polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and time. All the films possess tensile strain, which relaxes as the annealing temperature and time increase. The photoluminescence （PL） spectra contain only ultraviolet （UV） peaks at low temperature, but as the annealing temperature and time increase, we observe peaks at the blue and green regions with a variation in the intensities of these peaks with annealing temperature and time.展开更多
This paper reports the synthesis and characterization of ZnO thin films prepared by sol-gel spin coating technique. The sol-gel was prepared from zinc acetate dehydrate as a precursor, 2-me- thoxyethanol as a solvent ...This paper reports the synthesis and characterization of ZnO thin films prepared by sol-gel spin coating technique. The sol-gel was prepared from zinc acetate dehydrate as a precursor, 2-me- thoxyethanol as a solvent and di-ethanolamine as a stabilizer, and then deposited on glass substrate using spin coater at the coating speed of 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm and 6000 rpm. After pre-heated at 150℃, the samples were post-heated at 250oC and also annealed at 400℃. X-ray diffraction (XRD) of the films showed polycrystalline hexagonal structure, with (002) orientation as most intense peak having a grain size of 28.1 nm. The absorbance of the film decreases with increasing wavelength and the transmittance was generally high between visible regions from 280 nm - 1200 nm. The ZnO films deposited at a spinning speed of 2000 rpm had highest transmittance of 88% in the visible region from 280 nm - 1200 nm. The energy band gap was found to be in the range of 3.23 - 3.40 eV. The thicknesses of the films decreased with increase in coating speed. Based on these results, ZnO thin films obtained could have useful application in transparent conducting oxide electrode in solar cells.展开更多
Coral-like structures of the Y_(3-x)Pr_(x)Fe_(5-y)Yb_(y)O_(12),(0.00 ≤ x ≤ 0.04, 0.00 ≤ y ≤ 0.02) compound were synthesized using the sol-gel method. Structural investigation certified the YIG cubic crystal struct...Coral-like structures of the Y_(3-x)Pr_(x)Fe_(5-y)Yb_(y)O_(12),(0.00 ≤ x ≤ 0.04, 0.00 ≤ y ≤ 0.02) compound were synthesized using the sol-gel method. Structural investigation certified the YIG cubic crystal structure formation, without any secondary phase. It is shown that, the relatively large ionic radius of the dopant cations results in an expansion of the lattice parameter, variations in the Iona-O-Iondangle, Iona-O,Iond-O and Ionc-O bond distances and decrease in the average crystallite size. Fourier transform infrared(FTIR) and Raman measurements are essential to testify the single-phase formation of YIG crystal structure and are observed changes in the stretching and vibrational modes, respectively. The morphological study, energy dispersive spectroscopy(EDS) spectra and textural properties show corallike structures, peaks associated with Pr^(3+) and Yb^(3+) atoms and the effect of dopants on surface area,diameter, and pore volume, respectively. The optical analysis from diffuse reflectance spectra witnessed an increase in the optical gap band, a decrease in Urbach energy and blue shift in the charge transfer,correlated with the expansion of the unit cell due to the dopant's insertion in the YIG structure. A typical ferrimagnetic behavior is exhibited by the Y_(3-x)Pr_(x)Fe_(5-y)Yb_(y)O_(12)compound. The saturation magnetization(M_(s)), cubic anisotropy constant(K_(1)) and coercive field(H_(c)) increase with the Pr^(3+)cations content, as consequence of their magnetic nature and distribution around of Fe^(3+)ions due to the coexistence with the Yb^(3+). Finally, for the first time, antibacterial tests by mean of the direct contact method were performed for YIG co-doped with Pr^(3+)and Yb^(3+)and it is shown that, relatively high dosages of Pr^(3+) cations favored the activity against S. aureus, therefore, a new biological property for YIG doped with rare earths is presented.展开更多
Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different substrate temperatures of 300, 350 and 400 ℃. The obtained films had a hexagon...Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different substrate temperatures of 300, 350 and 400 ℃. The obtained films had a hexagonal wurtzite structure with a strong （002） preferred orientation. The maximum crystallite size value of the film deposited at 350 ℃ is 55.46 nm. Spectrophotometer （UV-vis） of a Co doped ZnO film deposited at 350 ℃ shows an average transmittance of about 90%. The band gap energy increased from 3.351 to 3.362 eV when the substrate temperature increased from 300 to 350 ℃. The electrical conductivity of the films deposited at 300, 350 and 400 ℃ were 7.424, 7.547 and 6.743 （Ω·cm）^-1 respectively. The maximum activation energy value of the films at 350 ℃ was 1.28 eV, indicating that the films exhibit a n-type semiconducting nature.展开更多
基金supported by the Special Funds for Major State Basic Research Project (Grant No. 2011CB301900)the National Natural Science Foundation of China (Grant No. 60990311)
文摘Based on the modification of the simplified coherent potential approximation （SCPA）, a model is developed to calculate the composition dependence of the band gap energy of Ⅲ-V ternary alloys with the same anion. The derived equation is used to fit the experimental band gap energy of InxAl1-xN, InxGa1-xN and A1xGal xN with x from 0 to 1. It is found that the fitting results are better than those done by using SCPA. The fitting results are also better than those obtained by using the formula with a small bowing coefficient, especially for InxAl1-xN. In addition, our model can also be used to describe the composition de- pendence of band gap energy of other Ⅲ-V ternary alloys.
文摘We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor;the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques.The thin films were deposited at different substrate temperatures ranging between 200 and 500℃. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation（2）, so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.
文摘The n-type semiconducting titanium oxide thin films are well-known as electron transporting interlayer in photovoltaic cells. The favorable characteristics of interlayers in photovoltaics are high optical transmittance （T%）, wide band gap energy （Eg） and high electrical conductivity （σ）. Modifying titanium oxide films with metal nanoparticles would increase electrical conductivity but reduce optical band gap energy. We developed the sol-gel derived titanium suboxide （TiOx） films modified with silver （Ag） or gold （Au） or copper （Cu） nanoparticles （NPs）. This study explores a tradeoff between narrowing optical band gap and enhancing electrical conductivity of nanostructured TiOx films by controlling the Au- or Ag- or Cu-NPs loading concentrations （mol%） in titania. The Au- and Cu-NPs loading concentration of 4 mol% should meet a tradeoff which yields the higher T%, wider Eg and higher compared to those of pure TiOx films. In addition, since the pure Cu is not thermodynamically stable in ambience as compared to Au and Ag, the stability of as-obtained colloidal CuNPs is also examined. A careful examination of the time evolution of surface plasmon resonance （SPR） bands of CuNPs indicates that their stability is only up to 4 h.
基金supported by the National Natural Science Foundation of China(Grant No.52072150)the Young Elite Scientists Sponsorship Program of the Chinese Academy of Space Technology(CAST)and Open Foundation of Guangdong Provincial Key Laboratory of Electronic Functional Materials and Devices(EFMD2021002Z).
文摘With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density(W_(rec)).Nevertheless,the dielectric loss also increases as the external electric field increases,which will generate much dissipated energy and raise the temperature of ceramic capacitors.Thus,an effective strategy is proposed to enhance the energy storage efficiency(η)via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na_(0.5)K_(0.5))-NbO_(3)-0.1Bi(Zn_(2/3)(Nb_(x)Ta_(1−x))1/3)O_(3) ceramics.On the one hand,the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short−range polar nanoregions(PNRs),resulting in the highη.On the other hand,the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the Eb.As a result,high Wrec of 3.29 J/cm^(3) and ultrahighηof 90.1%at the high external electric field of 310 kV/cm are achieved in x=0.5 sample.These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.
文摘This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].
基金supported by University Grants Commission (UGC),Govt.of India under project 39-508/2010(SR)
文摘In this paper,we have reported the synthesis of FeS2 of higher band gap energy（2.75 eV） by using capping reagent and its successive application in organic-inorganic based hybrid solar cells.Hydrothermal route was adopted for preparing iron pyrite（FeS2） nanoparticles with capping reagent PEG-400.The quality of synthesized FeS2 material was confirmed by X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,Fourier transform infrared,thermogravimetric analyzer,and Raman study.The optical band gap energy and electro-chemical band gap energy of the synthesized FeS2 were investigated by UV-vis spectrophotometry and cyclic voltammetry.Finally band gap engineered FeS2 has been successfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy.The energy conversion efficiency was obtained as 0.064%with a fill-factor of 0.52.
基金Funded by the Key Project of Chinese Ministry of Education (No. 208008)China Postdoctoral Science Foundation Funded Project (No. 20080440674)
文摘Porous ZnO films were prepared by electrodeposition method in zinc nitrate aqueous solution using ITO glass covered with polystyrene sphere （PS） colloidal crystal arrays as substrates. The preparation procedure includes two parts： deposition of ZnO in the interstices of the colloidal crystals and subsequent removal of the PS templates. The influences of deposition potential and temperature on the ZnO films were investigated. The ordered, uniform porous ZnO films with optical transmittance of approximately 63.6% at 600 nm could be obtained when the deposition potential and temperature were –1.1 V and 70 ℃, respectively. The optical band gap energy increased along with the absolute deposition potential and temperature, ranging from 3.33 to 3.43 eV and from 3.35 to 3.42 eV, respectively.
基金Project supported by the Natural Science Foundation of Zhejiang Province,China(Grant No.LR16F040001)
文摘Zn-Cu-codoped SnO2 nanoparticles have been synthesized by chemical precipitation method. All nanoparticles are crystalline, with the average size increases from 2.55 nm to 4.13 nm as the calcination temperature increases from 400℃ to 600℃. The high calcination temperature can enhance the crystalline quality and grain growth. The oxygen content decreases with decreasing calcination temperature; at a low temperature of 400℃, Zn-Cu-codoped SnO2 nanoparticles are in a rather oxygen-poor state having many oxygen vacancies. The optical band gap energies of Zn-Cu-codoped SnO2 nanoparticles calcined at 400℃ and 600℃ are decreased from 3.93 eV to 3.62 eV due to quantum confinement effects. Both samples exhibit room-temperature ferromagnetism, with a larger saturation magnetization at 400℃ due to the presence of large density of defects such as oxygen vacancies. Zn-Cu-codoped SnO2 nanoparticles exhibit large optical band gap energies and room temperature ferromagnetism, which make them potential candidates for applications in optoelectronics and spintronics.
基金supported by Sakarya University with Project No. BAPK-2012-50-01-018
文摘TiO2 nanotubes on Ti metal surface were prepared by the electrochemical anodization method. Then, nanosilver was deposited onto the nanotubes by the electroless dip coating and the anodization. The obtained TiO2 nanotubes were examined by using scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, cyclic voltammetry, and UV–Vis. The electrochemical band gap（Eg^CV） of the nanosilver-coated TiO2 nanotubes prepared by the anodization was found as 1.54 eV. Using the UV–Vis measurements, the optical band gap energy（Eg^op.） was calculated as 1.51 eV for the Ag/TiO2 nanotubes obtained by electroless dip coating. The electrical conductivity of the TiO2 nanotubes also increased from 3.0 × 10^-4 to 34.7 S/cm after nano Ag deposition by the anodization method.These Ag/TiO2 nanotubes with low band gap and high electrical conductivity are desirable for the applications in electronics, Li-ion batteries, and solar cells.
基金the NSF of Fujian Province (2005I017)NSF for Young Scientist of CAS.Electronic supplementary information (ESI) available:additional plots of the structures
文摘The title compounds have been respectively synthesized by solution process and solvothermal reaction, and their crystal structures were determined by X-ray diffraction method. For （CH3CH2CH2CH2NH3）6（BiI6）（I）2I3 1, it crystallizes in tficlinic, space group P1^- with Mr = 2049.76, a = 8.5719（1）, b = 11.7461（3）, c = 15.700（1）A, V = 1451.4（1）A^3, Z = 1, Dc = 2.345 g/cm^3, F（000） = 924, μ（MoKα） = 8.907 mm^-1, T = 293（2） K, the final R = 0.0655 and wR = 0.0804 for 2399 observed reflections with I 〉 2σ（I）. For （NH3CH2CH2NH3）2Bi2I10 2, it crystallizes in monoclinic, space group P21/n with Mr= 1811.20, a = 8.434（4）, b = 13.862（6）, c = 13.362（6）A, V = 1499.9（12）A^3, Z = 2, Dc = 4.010 g/cm^3, F（000） = 1536,μ（MoKα） = 22.007 mm^-1, T = 293（2） K, the final R = 0.0584 and wR = 0.1451 for 1798 observed reflections with I 〉 2σ（I）. The structures of 1 and 2 contain halobismuthate monomer and dimers, respectively. It is noteworthy that the dimers and their organic counters in 2 connect each other by N…I hydrogen bonds to form a layered structure, and the electrostatic interactions and crystal packing forces between layers give rise to the packing of the crystal. The optical absorption spectra of 1 and 2 reveal the appearance of sharp optical gaps of 2.13 and 2.01 eV, respectively.
文摘CdS thin films were prepared by chemical-bath-deposited method and the effect of temperature and time on the properties of CdS thin films was studied. Independent of the deposited temperature, the growth was mainly controlled by the ion-by-ion growth mechanism at the beginning of the film deposition, then the cluster-by-cluster mechanism came to be dominant. The growth rate increased faster with the increasing of temperature until the thickness reached the limitation, then thickness instead become thinner. The scanning electron micro- scope results revealed that the morphology of the CdS film changed from pinholes to rough, inhomogeneous surface with increasing deposition time and deposition temperature. The X- ray diffraction results showed the film structure was a mixture of two phases： hexagonal and cubic, and it was very important to controll deposition time to the film＇s crystal phase. All films in depth of approxilnate 100 nm existed above 65% transmittance, the absorption edge became ＂red-shift＂ with temperature rising. At 60 and 70℃, with 20 min deposited-time, the energy band gap was more than 2.42 eV and decreased with time, while at 80 and 90℃ the energy band gap was less than 2.42 eV and increased little when the time changed from 10min to 15 nfin at 80℃.
文摘Our calculations are based on the modeling technique and simulation Ab-Initio that appeals to the Density Functional Theory (DFT) relying on the Full-Potential Linearized Augmented Plane Waves (FP-LAPW) method that requires a calculation process using approximations such as Local Density (LDA) and Generalized Gradient (GGA) developed in the modelling software of nanostructures WIEN2k. The optimal structure of the binary semiconductor ZnSe crystallizing in the complex phase of Zinc Blende (B3) was determined by studying the variation of energy depending on the volume of the elementary cell. Then the electronic properties of the optimized state were analyzed such as the gap energy, the total density of states (TDOS), the partial density of states (PDOS) and the repartition of the electronic charge density. The obtained results were successful compared with other theoretical and experimental values reported in literature.
文摘Two sets of Organic dyes were developed using kassod and senna plant leaves. The first sets of dyes are the organic dye from the leaves of two plants while the second set is the dye produce after combining together the dyes from the kassod and senna plants leaves. The two sets of dyes were used to sensitize the grown films. The films were characterized and the current voltage values of the grown films were obtained. The solar simulation result of the grown film for Kassod dyed TiO<sub>2</sub> film was recorded for single dyes and for the <span "="">combination of the two dyes. The result also covers absorbance of the spectra lines, absorbance coefficient values of the dyed TiO<sub>2</sub>, as well as transmittance and energy band gap values of the developed films. The precursors of tin (IV) chloride (SnCl<sub>4</sub>) (60%) and hydrofluoric acid (40%) was deposited on the cleaned soda</span>-lime glass using the chemical vapour deposition method and <span "="">nitrogen gas was supplied as a carrier gas through the bubbler to form the FTO layer. Titanium dioxide paste (TiO<sub>2</sub>) was deposited using </span>a <span "="">screen printing method to form M-TiO<sub>2</sub>.
文摘The optical properties of the pure polymer film and polymer films doped with Phenol Red dye at different concentrations were investigated. The films were prepared using the casting technique. Poly (methyl-methacrylate) (PMMA) polymer was doped with the Phenol Red dye dissolved in a mixture of chloroform and little quantity of methanol, used as suitable solvent for both the dye and the polymer. The spectral absorption measurements of these films were carried out at different dye concentrations using UV-Vis double-beam spectrophotometer in the wavelength range 300 - 800 nm. The optical parameters of the prepared Phenol Red dye doped polymer films, absorption coefficient (α), extinction coefficient (κ), refractive index (n), optical and electrical conductivities (σ<sub>opt</sub> and σ<sub>elect</sub>), and optical energy band gap (E<sub>g</sub>), were determined. The results showed that the Phenol Red dye doped polymer film is a good candidate for photonic applications such as, solar cells, optical sensors, and other photonic devices.
文摘The electronic properties and topological phases of ThXY （X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn） compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases （insulator or metal） and normal phases within generalized gradient approximation （GGA） and Engel- Vosko generalized gradient approximation （GGA_EV） are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves.
基金the University Science Malaysia for the financial support for this research under two USM(Short Term Grant)which are 304/PFIZIK/6313152 and 304/PFIZIK/6313249.
文摘Quaternary glasses were successfully fabricated using melt quenching technique based on the chemical compound composition(x)Bi_(2)O_(3)–(0:5-x)ZnO-(0.2)B_(2)O_(3)–(0.3)SiO_(2),where(x=0.1,0.2,0.3,0.4,0.45)mole.The sources of SiO_(2)was produced from rice husk ash(RHA)at 99.36%of SiO_(2).The Urbach energy was increased from 0.16 eV to the 0.29 eV as the mole of Bi_(2)O_(3)increased in the glass structure.The indirect energy band gap is indicated in decrement pattern with 3.15 eV towards 2.51 eV.The results of Urbach energy and band gap energy that were obtained are due to the increment of Bi^(3+)ion in the glass network.The refractive indexes for the prepared glasses were evaluated at 2.36 to 2.54 based on the Lorentz–Lorentz formulation which correlated to the energy band gap.The calculated of molar polarizability,electronic polarizability and optical basicity exemplify fine complement to the Bi_(2)O_(3)addition in the glass network.The glass sample was indicated in amorphous state.
文摘ZnO thin films were synthesised by a new method which uses polyvinyl alcohol （PVA） as the polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and time. All the films possess tensile strain, which relaxes as the annealing temperature and time increase. The photoluminescence （PL） spectra contain only ultraviolet （UV） peaks at low temperature, but as the annealing temperature and time increase, we observe peaks at the blue and green regions with a variation in the intensities of these peaks with annealing temperature and time.
文摘This paper reports the synthesis and characterization of ZnO thin films prepared by sol-gel spin coating technique. The sol-gel was prepared from zinc acetate dehydrate as a precursor, 2-me- thoxyethanol as a solvent and di-ethanolamine as a stabilizer, and then deposited on glass substrate using spin coater at the coating speed of 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm and 6000 rpm. After pre-heated at 150℃, the samples were post-heated at 250oC and also annealed at 400℃. X-ray diffraction (XRD) of the films showed polycrystalline hexagonal structure, with (002) orientation as most intense peak having a grain size of 28.1 nm. The absorbance of the film decreases with increasing wavelength and the transmittance was generally high between visible regions from 280 nm - 1200 nm. The ZnO films deposited at a spinning speed of 2000 rpm had highest transmittance of 88% in the visible region from 280 nm - 1200 nm. The energy band gap was found to be in the range of 3.23 - 3.40 eV. The thicknesses of the films decreased with increase in coating speed. Based on these results, ZnO thin films obtained could have useful application in transparent conducting oxide electrode in solar cells.
基金The authors are grateful to the Brazilian Agencies:Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior(CAPES),Conselho Nacional de Desenvolvimento Cientifico e Tecnologico(CNPq),(CNPq N 4/2021-Bolsa de Produtividade em Pesquisa-PQ 307659/2021-6),(Chamada CNPq/MCTI/FNDCT N°18/2021-Faixa A,407796/2021-5)Financiadora de Estudos e Projetos(FINEP)and Fundacao de Amparo a Ciencia e Tecnologia de Pernambuco(FACEPE)(APQ-0635-3.03/21-Jovens Pesquisadores).
文摘Coral-like structures of the Y_(3-x)Pr_(x)Fe_(5-y)Yb_(y)O_(12),(0.00 ≤ x ≤ 0.04, 0.00 ≤ y ≤ 0.02) compound were synthesized using the sol-gel method. Structural investigation certified the YIG cubic crystal structure formation, without any secondary phase. It is shown that, the relatively large ionic radius of the dopant cations results in an expansion of the lattice parameter, variations in the Iona-O-Iondangle, Iona-O,Iond-O and Ionc-O bond distances and decrease in the average crystallite size. Fourier transform infrared(FTIR) and Raman measurements are essential to testify the single-phase formation of YIG crystal structure and are observed changes in the stretching and vibrational modes, respectively. The morphological study, energy dispersive spectroscopy(EDS) spectra and textural properties show corallike structures, peaks associated with Pr^(3+) and Yb^(3+) atoms and the effect of dopants on surface area,diameter, and pore volume, respectively. The optical analysis from diffuse reflectance spectra witnessed an increase in the optical gap band, a decrease in Urbach energy and blue shift in the charge transfer,correlated with the expansion of the unit cell due to the dopant's insertion in the YIG structure. A typical ferrimagnetic behavior is exhibited by the Y_(3-x)Pr_(x)Fe_(5-y)Yb_(y)O_(12)compound. The saturation magnetization(M_(s)), cubic anisotropy constant(K_(1)) and coercive field(H_(c)) increase with the Pr^(3+)cations content, as consequence of their magnetic nature and distribution around of Fe^(3+)ions due to the coexistence with the Yb^(3+). Finally, for the first time, antibacterial tests by mean of the direct contact method were performed for YIG co-doped with Pr^(3+)and Yb^(3+)and it is shown that, relatively high dosages of Pr^(3+) cations favored the activity against S. aureus, therefore, a new biological property for YIG doped with rare earths is presented.
文摘Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different substrate temperatures of 300, 350 and 400 ℃. The obtained films had a hexagonal wurtzite structure with a strong （002） preferred orientation. The maximum crystallite size value of the film deposited at 350 ℃ is 55.46 nm. Spectrophotometer （UV-vis） of a Co doped ZnO film deposited at 350 ℃ shows an average transmittance of about 90%. The band gap energy increased from 3.351 to 3.362 eV when the substrate temperature increased from 300 to 350 ℃. The electrical conductivity of the films deposited at 300, 350 and 400 ℃ were 7.424, 7.547 and 6.743 （Ω·cm）^-1 respectively. The maximum activation energy value of the films at 350 ℃ was 1.28 eV, indicating that the films exhibit a n-type semiconducting nature.
