Tradeoffbetween Narrowing Optical Band Gap and Enhancing Electrical Conductivity of the Metal Nanoparticles-Modified Titanium Oxide Films

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.

Superior energy storage efficiency through tailoring relaxor behavior and band energy gap in KNN-based ferroelectric ceramic capacitors

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.

Determination of Band Structure of Gallium-Arsenide and Aluminium-Arsenide Using Density Functional Theory

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].

Synthesis of Nanocrystalline FeS_2 with Increased Band Gap for Solar Energy Harvesting

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.

A modified simplified coherent potential approximation model of band gap energy of III-V ternary alloys

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.

The calculation of band gap energy in zinc oxide films

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.

CdS Thin Films Deposited by CBD Method on Glass

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℃.

Power Voltage Characteristics of Fabricated DSSC Incorporating Multiple Organic Dyes as Photosensitizer

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 TiO2 film was recorded for single dyes and for the combination of the two dyes. The result also covers absorbance of the spectra lines, absorbance coefficient values of the dyed TiO2, as well as transmittance and energy band gap values of the developed films. The precursors of tin (IV) chloride (SnCl4) (60%) and hydrofluoric acid (40%) was deposited on the cleaned soda-lime glass using the chemical vapour deposition method and nitrogen gas was supplied as a carrier gas through the bubbler to form the FTO layer. Titanium dioxide paste (TiO2) was deposited using a screen printing method to form M-TiO2.

Synthesis and Investigation of Phenol Red Dye Doped Polymer Films

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 (σopt and σelect), and optical energy band gap (Eg), 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.

Electronic properties and topological phases of ThXY(X= Pb, Au, Pt and Y= Sb, Bi, Sn) compounds

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.

Comprehensive study of electronic polarizability and band gap of B_(2)O_(3)-Bi_(2)O_(3)-ZnO-SiO_(2)glass network

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.

Effect of Spin Coating Speed on Some Optical Properties of ZnO Thin Films

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.

Effects of Potential and Temperature on the Electrodeposited Porous Zinc Oxide Films

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.

Zn-Cu-codoped SnO_2 nanoparticles: Structural, optical, and ferromagnetic behaviors

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.

Syntheses and Characterizations of(CH_3CH_2CH_2CH_2NH_3)_6(BiI_6)(I)_2I_3 and (NH_3CH_2CH_2NH_3)_2Bi_2I_(10)

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.

Electro-Optics and Band Gap Energies of Nanosilver-Coated TiO2 Nanotubes on Titanium Metal

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.

Effect of post-thermal annealing on the structural and optical properties of ZnO thin films prepared from a polymer precursor

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.

A Study by Ab-Initio Calculation of Structural and Electronic Properties of Semiconductor Nanostructures Based on ZnSe

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.

Synthesis of coral-like structures of Pr-Yb co-doped YIG: Structural,optical, magnetic and antimicrobial properties

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.

Impact of surface coating on morphological, optical and photoluminescence properties of YF3：Tb^3＋ nanoparticles

A simple polyol and sol–gel Stober process were employed for synthesis of YF_3：Tb~＋（core）, YF_3：Tb~＋@LaF_3（core/shell） and YF_3：Tb~＋@LaF_3@SiO_2（core/shell/SiO_2） nanoparticles（NPs）. The phase purity, crystalinity,morphology, optical and photoluminescence properties were investigated and discussed with the help of various analytical techniques including X-ray diffraction pattern,FE-transmission electron microscopy（TEM）,FTIR, UV/vis absorption, energy band gap and emission spectra. XRD andFE-TEM studies indicate the formation of core/shell nanostructure and ~10 nm thick amorphous silica surface coating surrounding the core-NPs, which is also confirmed byFTIR spectral results. The surface modifications of core-NPs significantly affect the optical features in the form of energy band gap, which were correlated with particle size of the nanomaterials. The comparative emission spectral results show that after inert layer coating the luminescent core-NPs display stronger emission intensity in respect to core and silica coated core/shell/SiO_2-NPs. The solubility character along with colloidal stability was improved after silica surface modification, whereas luminescent intensity was suppressed causing the surface functionalized with high energy silanol（Si-OH） molecules. These novel luminescent nanomaterials with enhanced emission intensity and excellent solubility in aqueous solvents would be potentially useful for fluorescence bioimaging/optical bio-probe etc.