Transmission Gap Research Articles

Effect of Triton X-100 surfactant on thiol-amine cosolvents assisted facile synthesized CdS thin films on glass substrate by spin coating method

In this article, the effect of Triton X-100 surfactant on the spin coated and vacuum annealed CdS thin films on glass substrates using thiol-amine cosolvents have been explored in details. The SEM study reveals that the surfactant assisted CdS films are uniform, homogeneous and smooth having less cracks, voids, pinholes compared to CdS films synthesized without surfactant. The X-ray diffraction spectra indicate the hexagonal structure of the surfactant-added films with (002) and (100) planes having relatively high intensity whereas a weak hexagonal (002) peak appears for the films deposited without surfactant. Two prominent Raman peaks of CdS thin films are observed at the wavenumber 207 and 212 cm−1 due to the multi-phonon vibration of hexagonal CdS. A relatively strong and broad FTIR peaks at 1647 and 670 cm−1 were observed due to the Cd-S bending and stretching vibration in the surfactant mediated films. Surfactant induced CdS films are nearly stoichiometric as manifested by the energy dispersive X-ray report. Finally, higher optical transmission and band gap have been achieved for the CdS thin films deposited with Triton X-100 surfactant. This study reveals that surfactant mediated CdS thin films with thiol-amine cosolvents can be exploited effectively in higher efficiency thin film solar cell technologies with low cost.

Impact of ZnO Atomic Ratio on Structural, Morphological and Some Optical Properties of (SnO2)1-x (ZnO)x Thin Films

In this work, SnO2 and (SnO2)1-x(ZnO)x composite thin films with different ZnO atomic ratios (x=0, 5, 10, 15 and 20%) were prepared by pulsed laser deposition technique on clean glass substrates at room temperature without any treatment. The deposited thin films were characterized by x-ray diffraction atomic force microscope and UV-visible spectrophotometer to study the effect of the ZnO atomic ratio on their structural, morphological and optical properties. It was found that the crystallinety and the crystalline size vary according to ZnO atomic ratio. The surface appeared as longitudinal structures which was convert to spherical shapes with increasing ZnO atomic ratio. The optical transmission and energy gap increased with increasing ZnO atomic ratio.

Utilization of Bi2WO6-encapsulated polyaniline-based redox reactions for the efficient detoxification of organic pollutants

Water contamination by toxic organic pollutants remains a serious public health problem for humans due to their long-lasting effects, so attention on specific methods and technologies to remove organic pollutants from waste water is desired. Numerous methods and photocatalysts are reported for the degradation of organic pollutants. In this work, BiVO4/Bi2WO6@polyaniline nanostructures were prepared successfully through facile wet chemical co-precipitation method and in sequence deposited over the BiVO4 surface for the first time. The surface morphology of synthesized photocatalysts was observed by scanning electron microscopy (SEM) and structural properties were investigated by X-ray diffraction (XRD). The addition of polyaniline and Bi2WO6 into BiVO4 shifted the characteristic peaks of BiVO4 towards lower 2θ angle which is clear evidence of doping of these elements into BiVO4 structure under these conditions. In addition, the crystallite size of BiVO4 was also decreased due to incorporation of doping elements. Compared with pure BiVO4, hybrid photocatalysts exhibit higher photocatalytic activity and stability for degradation of phenol and ciprofloxacin under visible-light irradiation. When the effect of PANI in BiVO4–Bi2WO6 was examined, 1% PANI/BiVO4–Bi2WO6 heterojunction exhibited the highest photocatalytic performance. The degradation efficiency for phenol was 98% and 99% for ciprofloxacin at 90 min and this value was about seven times and three times higher than as compared to pure BiVO4 and BiVO4–Bi2WO6, respectively. The obviously improved photocatalytic performance of BiVO4–Bi2WO6/PANI composite was mainly ascribed to unique hierarchical structures, harvesting extended region of visible light, higher surface area, higher crystallinity, electronic transmission and narrow band gap, which significantly enriched the adsorption capacity and accordingly facilitated the separation of photogenerated charge carriers. The current findings may provide new insights into the employment of hybrid photocatalysts and improving the photocatalytic activity to address energy and environmental issues.

Optical and Structural investigations of LiNbO3 thin films by PLD

Lithium niobate (LiNbO3) nanostructure thin film was prepared and deposited on the substrates made of quartz by utilizing pulse laser deposition (PLD) technique. The effect of substrate temperature changing on the optical and structural properties of LiNbO3 films was investigated and studied. The chemical mixture was prepared by mixing the raw material (Li2CO3, Nb2O5) with Ethanol liquid without any further purification, at the stirrer time 3hrs without heating, then the formed material was overexposed to annealing process at 1000°C for 4hrs. LiNbO3 nanostructure thin film was characterized and analyzed by utilizing the Ultra-Violet visible (UV-vis) and X-Ray Diffraction (XRD). The UV-vis results showed that the increase in the substrate temperature to 300°C leads to decrease in the values of transmission (T%), absorption (A) and optical energy gap (Eg) and increase in the values of reflection (R%) and refractive index (n). While, the XRD results explained that the LiNbO3 structure became more pure and crystalline with increase the substrate temperature, because the intensity of the phase 2θ at the value of 34.8°, 40.06° and 48.48° correspond to (110), (113) and (024) planes disappeared at the substrate temperature 300°C. So, all presented results give a good indication to use LiNbO3 nanostructure thin film prepared at the substrate temperature 300°C for manufacturing the optical waveguide to give the best results.

Optical Investigations of Nanophotonic LiNbO<sub>3</sub> Films Deposited by Pulsed Laser Deposition Method

The nanocrystalline structure of Lithium niobate (LiNbO3) was prepared and deposited onto substrate made of quartz by utilize pulse laser deposition technique. The effect of substrate temperature on the structural, optical and morphological properties of lithium niobate photonic film grown was studied. The chemical mixture was prepared by mixing the raw material (Li2CO3, Nb2O5) with Ethanol liquid without any further purification, at time of stirrer 3hrs but without heating, then annealing process the formed material at 1000C° for 4hrs. We characterized and analyzed the LiNbO3 nanostructure thin films by utilize Ultra-Violet Visible (UV-vis). The UV-vis measurements show that, when the substrate temperature increases, the values of transmission, absorption and energy band gap will decreased, but the values of reflection and refractive index will increased. That means the LiNbO3 thin film prepared at substrate temperatures 300C° give the best result for manufacture the optical waveguide.

Synthesis, crystal structure, optical, thermal, mechanical, dielectric and DFT studies of 3, 5-dimethylprazole:1,3,5-benzene tricarboxylic acid molecular adduct crystal

An organic molecular adduct, 3, 5-Dimethylpyrazole:1,3,5-benzene tricarboxylic acid was synthesized and single crystals grown in methanol-acetone (1:1) solvent mixture by slow solvent evaporation solution growth technique at room temperature. The formation of the molecular adduct and crystal structure have been confirmed by single crystal X-ray diffraction studies and NMR spectroscopic techniques. Further, the title crystal belongs to monoclinic crystal system with space group, P21/c and the supramolecular architecture of adduct involves extensive intermolecular O-H…N, N-H…O, O-H…O and C-H…O hydrogen bonding interactions. UV–Vis-NIR spectrum was recorded to find out the lower cut-off wavelength, percentage transmission and optical band gap energy. The fluorescence properties of the title crystal were identified by Photoluminescence spectral studies. Fourier transform infrared (FT-IR) spectral analysis was carried out to confirm the presence of various functional groups in the grown crystal. The quantum chemical analyses were performed by density functional theory (DFT) using B3LYP/6-311G (d,p) basis set. The thermal and mechanical properties of the grown crystal have been investigated by TG/DTA analyses and Vickers micro hardness measurement, respectively. The dielectric behaviours of title single crystal have also been investigated as a function of frequency at different temperatures.

Smartphone-Based Data Collection System for Repetitive Concrete Temperature Monitoring in High-Rise Building Construction

The systematic collection and management of on-site information in high-rise building construction are important factors in construction management. Recently, wireless sensor network (WSN) technology has been utilized to manage the various tasks involved in high-rise construction efficiently and in a timely manner. However, because of the repeated installation of sensors and repeaters along with the construction progress, the existing WSN technology is ineffective when applied to the temperature management of concrete in structural work. Here, we propose a new data collection method in which a worker uses a smartphone to repeatedly monitor concrete temperature. In field implementation, the proposed system enables concrete temperature management without a transmission gap for monitoring in 60-min intervals with smartphones provided to 20% of the structural workers. Next, a case study was performed on a high-rise building construction site to analyze the effectiveness of the proposed system in terms of cost savings by avoiding schedule delay. The results of the case study show that the proposed system can reduce the additional work costs resulting from delays in concrete curing and save up to $18,907 in labor costs. In addition, this system can reduce the temperature management time of the quality manager and enable more efficient management. It is also expected that this system will contribute to on-site waste management by reducing the number of embedded sensors.

Ethnoveterinary remedies used in the Algerian steppe: Exploring the relationship with traditional human herbal medicine

Ethnopharmacological relevanceEthnoveterinary medicine is vastly under-documented, especially in North Africa, where livestock care is increasingly medicalised. Despite evidence of the interdependence of ethnoveterinary practices and ethnomedicine for human care, the overlap between these two systems and the possible drivers of similarity are rarely addressed in ethnopharmacological literature. Here, we present the first quantitative comparison of remedies used to treat human and animal health among a pastoral society. AimsThis study aims to document the plants and other materials used in ethnoveterinary medicine among nomadic herders in the Algerian steppe. We calculate the overlap with remedies used for human health and evaluate some of the possible drivers of similarities between the two interlinked medical systems. MethodsThe field study was conducted in spring 2018 with 201 local knowledge holders in five provinces in the central part of the Algerian steppe. Forty-six camps and ten weekly animal markets were visited. After obtaining prior informed consent, data was collected through structured interviews. Anonymous sociodemographic information was collected along with veterinary use data. Plant specimens were acquired, identified and deposited in the Botanical Laboratory Herbarium of the University of Tiaret. Ethnobotanical information was structured in use reports and therapeutic applications organised into 13 simple categories. Plants used in ethnoveterinary medicine were compared to those used in human health care using a Chi square test, and ethnoveterinary use was predicted using a generalised linear model with use for human care and plant family as predictive variables. Logistic regressions were also used to test if any specific medicinal application predicts shared use in human and veterinary medicine. ResultsSixty-six plant species from 32 botanical families and ten non-vegetable remedies were documented. Plants from the Lamiaceae, Asteraceae, Fabaceae and Apiaceae families were most commonly used. The plants most often cited by interviewees are all harvested from the wild (Echinops spinosissimus Turra, Atriplex halimus L., Artemisia campestris L., Juniperus phoenicea L. and Peganum harmala L.). Leaves are the most commonly used plant part and decoction is the most common preparation method. There are important similarities between remedies used to treat humans and other animals: two thirds of the remedies used in ethnoveterinary medicine are also used in human health care, and these represent half of the human health treatments. Use for human health and plant family both predict the use of a medicinal plant in veterinary medicine, but no correlation is found regarding specific therapeutic applications. ConclusionsTraditional veterinary knowledge is still key to sheep and goat herders in the Algerian steppe, but a knowledge transmission gap seems to exist between older and younger generations, and ethnoveterinary practices may disappear in the near future. Treatments for human and animal care overlap to a large extent, and a causal relationship possibly exists for, at least, some of them. However, overall a smaller number of remedies are used to treat animals than humans and for less therapeutic applications. This difference in the diversity of therapeutic applications and remedies should be the object of future research.

Smart Glove for Hearing-Impaired

Individuals communicate with one another to pass on their thoughts to the general population around them. There are 2.78% of the total populations of India who can’t speak. Gesture based communication is really a mode of correspondence for the general population who are either deaf or deaf-mute. Ordinary individuals don't become familiar with the gesture based communication. It causes conveyance gap between deafdumb and normal people. The past system of this project involved using image processing concept. But the downside of these past frameworks are projects were non portable and excessively costly. The aim behind this work is to build up a framework for perceiving the gesture based communication, which provides interaction between people who are deaf-dumb and normal people, thereby diminishing the interaction gap between them. Generally hearing-impaired people use linguistic communication based on hand gestures with specific movements to represent the ideas to others. The proposed glove is an robotic gadget that interprets American Sign Language Standard into text or speech in order to evacuate the information transmission gap between the mute and the ordinary public. This glove has been actualized with the assistance of flex sensors, accelerometer, microcontroller (Arduino Nano) and the Bluetooth chip.

Shock wave-induced defect engineering for investigation on optical properties of triglycine sulfate crystal

A systematic investigation of shock wave-induced defect engineering on optical transport properties of triglycine sulfate (TGS) crystalline material is carried out under shock waves of Mach number 1.7 with a different number of shock pulses. Surface morphological changes and defect concentration are evaluated by the optical microscopic technique. Optical transmission of pre- and postshock wave-treated TGS crystal is analyzed using UV–visible spectrometer over the range between 200 and 800 nm. Unexpectedly, during the shock wave impact conditions, the test crystal exhibits vulnerability due to defects on its surface and it is confirmed by optical micrographs. Optical transmission is continually reduced while the number of shock pulses is increased due to the formation of defects on the surface of the test sample. Followed by the observation of optical transmission, optical constants and band gap energies are also calculated. The obtained results clearly show that surface morphology and optical transport properties of TGS crystal are greatly affected by the impact of shock waves.

Thickness-dependent structural, spectral, linear, nonlinear and z-scan optical studies of V2O5 thin films prepared by a low-cost sol-gel spin coating technique

Vanadium Pentoxide (V2O5) films were synthesized on a glass substrate by a spin coating method. The coated films were analyzed by XRD, UV–vis-NIR, SEM, EDX, and Raman Spectroscopy. SEM and EDX studies confirmed the surface and the elemental analysis of the prepared films. XRD studies confirmed the monoclinic crystalline structure of present films. The spectral studies were recorded by Raman spectroscopy. Optical properties such as transmission, absorption, and band gap analysis were done in the range of 190–2500 nm by UV–vis-NIR spectroscopy technique for different thickness of V2O5 thin films. The linear and nonlinear optical properties were analyzed systematically and reported. Further, Z-scan studies Viz., nonlinear refraction absorption index and third-order susceptibilities were studied in terms of thickness variation and their results were discussed. The results suggest that the prepared thin films have huge applications in linear and nonlinear optical devices and some other optoelectronic applications.

The influence of the thermal annealing treatments on the microstructure and optical properties of a-C:H films prepared by PECVD method

In this work, hydrogenated amorphous carbon (a-C:H) films were prepared by using a radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) method at 220 °C. The influence of the annealing treatments on the microstructure and optical properties of the a-C:H films has been investigated. Raman and X-ray photo electron spectroscopy (XPS) results showed that the sp2 carbon fraction and sp2/sp3 ratio increase and sp3 carbon fraction decrease with increasing the annealing temperature. However, with increasing annealing temperature, the D and G peak positions and the G peak FWHM have no obvious changes. The spectroscopic ellipsometry suggested that the density, refractive index n and the extinction coefficient k of the as-deposited film and the films annealed at 300 and 400 °C are not affected obviously by thermal annealing treatments. However, when the annealing temperature is higher than 400 °C, the films become high-density and opaque, meanwhile, the film thickness decrease significantly. The UV-VIS spectroscopy measurement indicated that the increase of sp2 fraction and graphitization features of the a-C: H films result in the decrease of the films transmission and optical band gap.

Doping effect by SiO2 on optical properties of ZnO Thin Films Prepared by pulsed laser depositions (PLD) technique

In this paper,Zinc oxide was dopped by various concentrations (5,10,15,20,25) % wt, silicon oxide The mixture was deposited on glass substrate by laser pulse deposition at room temperature to obtain (Zn2SiO4) thin films .The optical properties of thin films prepared on spectral absorption and transmission recording were studied at the wavelength range (200- 1100) nm. Some of the optical constants, including absorptance, transmission, absorption coefficient, and energy gap are calculated before and after annealing at (400 ̊C) for (1 hr). Absorptance values and absorption coefficient increase after doping and transmission and energy gap decreases after the doping. Absorbance values and absorption coefficient decreases after annealing and transmission and energy gap increase after the annealing .

A metal-semiconductor transition triggered by atomically flat zigzag edge in monolayer transition-metal dichalcogenides

Due to the structure of three stacked layers, monolayer transition-metal dichalcogenides (TMDs) is different from graphene. Creating atomically flat graphene-like edges in them has long been expected, which is crucial to the modulation of electronic structures in two-dimensional systems. Recently, by thermal annealing, Chen et al. [21] successfully synthesized atomically flat Mo-terminated edge in monolayer MoS2. Inspired by this, through first-principles calculations, we studied the electronic and transport properties of typical TMD monolayers with transition atom-terminated flat zigzag edges, i.e., ScS2, VS2, CrS2, FeS2, NiS2, MoS2 and WS2. It is found that the nanoribbons with and without flat edges are both metallic. Interestingly, the vacancy in the flat edge could open a transmission gap at the Fermi level in the ScS2 ribbon, and trigger a metal-semiconductor transition. Further analysis shows that, the opening of bandgap around the Fermi level induced by the specific pattern of vacancies is the mechanism behind, which could be used as an modulating method for electronic structures. We believe our results are quite beneficial for the development of many other monolayer transition-metal dichalcogenides configurations, showing great application potential.

Analysis of magnesium zinc oxide layers for high efficiency CdTe devices

CdTe thin film solar cells are the most successful thin film photovoltaic devices in terms of production yield, as attested by the remarkable market performance. Typically the junction is made with n-type CdS that, however, absorbs some of the light spectrum due to its band-gap of 2.4 eV. Therefore, in order to exceed 20% efficiency it is crucial to increase the wavelength range convertible by the absorber. One possible alternative buffer that, at the same time, allows a larger transparency and a proper band alignment with CdTe is Magnesium Zinc Oxide (MZO).In this paper, we present low temperature CdTe solar cells in superstrate configuration without CdS, by the introduction of MZO as buffer layer. Efficiencies above 12% have been obtained, with remarkable open circuit voltage and superior values of current density.The transmission and band gap of the different MZO layers have been analysed and presented. Moreover, the optimum type of MZO layer, made with higher oxygen content and with a band gap of 3.72 eV, has been characterized by X-ray diffraction, and its morphology has been studied by atomic force microscopy, whereas the finished cells have been characterized by current-voltage and by external quantum efficiency measurements.

Validation and IMRT/VMAT delivery quality of a preconfigured fast-rotating O-ring linac system.

A fast-rotating O-ring dedicated intensity modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) delivery system, the Halcyon, is delivered by default with a fully preconfigured photon beam model in the treatment planning system (TPS). This work reports on the validation and achieved IMRT/VMAT delivery quality on the system. Acceptance testing followed the vendor's installation product acceptance and was supplemented with mechanical QA. The dosimetric calibration was performed according to the IAEA TRS-398 code-of-practice, delivering 600 cGy/min at 10 cm depth, a 90 cm source-surface distance, and a 10 × 10 cm² field size. The output factors, multileaf collimator (MLC) transmission and dosimetric leaf gap (DLG) were validated by comparing measurements with the modeled values in the TPS. Validation of IMRT/VMAT was conducted following AAPM reports (MPPG 5.a, TG-119). Next, dose measurements were performed for end-to-end (E2E) checks in heterogeneous anthropomorphic phantoms using radiochromic film in multiple planes and using ionization chambers (IC) point measurements. E2E checks were performed for VMAT (cranial, rectum, spine, and head and neck) and IMRT (lung). Additionally, IROC Houston mailed dosimetry audits were performed for the beam calibration and E2E measurements using a thorax phantom (IMRT) and a head and neck phantom (VMAT). Lastly, extensive patient-specific QA was performed for the first patients of each new indication, 26 in total (nrectum = 2, nspine = 5, nlung = 5, nesophagus = 2, nhead and neck = 7, ncranial = 5), treated on the fast-rotating O-ring linac. The patient-specific QA followed the AAPM TG-218 guidelines and comprised of portal dosimetry, ArcCHECK diode array, radiochromic film dosimetry in a MultiCube phantom, and IC point measurements. The measured output factors showed an agreement <1% for fields ≥3 × 3 cm². Field sizes ≤2 × 2 cm² had a difference of <2%. The measured single-layer MLC transmission was 0.42 ± 0.01% and the measured DLG was 0.27 ± 0.22 mm. The AAPM MPPG 5.a measurements were fully compliant with the guideline criteria. Dose differences larger than 2% were found for the PDD at large depths (>25 cm). TG-119's confidence limits were achieved for the VMAT point dose measurements and for both the IMRT and VMAT radiochromic film measurements. The TG-119 confidence limits were not achieved for IMRT point dose measurements in both the target (5.9%) and the avoidance structure (6.4%). All E2E tests had point differences below 2.3% and gamma agreement scores above 90.6%. The IROC beam calibration audit showed agreement of <1%. The IROC lung IMRT audit and head and neck VMAT audit had results compliant with the IROC Houston's credentialing criteria. All IMRT and VMAT plans selected for patient-specific QA were within the action limits suggested by TG-218. The fast-rotating O-ring linac and its preconfigured TPS are compliant with the international commissioning criteria of AAPM MPPG 5.a and AAPM TG-119. E2E measurements on heterogeneous anthropomorphic phantoms were within clinically acceptable tolerances. IROC Houston's audits satisfied the credentialing criteria. This work comprises the first extensive dataset reporting on the preconfigured fast-rotating O-ring linac.

Realizing fully spin polarized transport in graphene nanoribbons with design of van der Waals vertical heterostructure leads

Zigzag-edged graphene and h-BN nanoribbons with passivated edges in the ground state are either spin-degenerate or spin-unpolarized systems, which are not directly applicable for spin-polarized transport. In this work, based on density functional calculations, we demonstrate that the combination of them to form van der Waals (vdW) heterostructures can be adopted to realize fully spin polarized transport. As an example, the ballistic transport properties of a zigzag-edged graphene nanoribbon (ZGNR) with six zigzag carbon chains is studied first with each lead as a vdW heterostructure formed by attaching a h-BN monolayer to each side of the ZGNR with AA-stacking. A greatly decreased transmission gap (0.28 eV) in one spin and a greatly increased transmission gap (0.82 eV) in the other spin is achieved in the transmission function, resulting in fully spin polarized transport at low bias. This arises from the stagger potential imposed by the h-BN layers, which not only exists in the leads, but also extends to the channel region. It changes the energy of the edge states of different spins localized at different sublattices in an opposite way in the whole device. The transmission gap and the threshold voltage can be further modulated by applying a vertical pressure to the vdW leads to tune the strength of the stagger potential or simply by changing the ribbon width. Finally, the increase of the channel length will greatly reduce the magnitude of the transmission around the Fermi level and the transmission gap will eventually recover the value of the band gap of the pristine ZGNR. These findings not only provide a novel way for achieving fully spin polarized transport in graphene, but also demonstrate the great importance of vdW heterostructures in the design of spintronic devices.

Structural, optical, dielectric, second and third-order nonlinear properties of new semiorganic crystal: Sodium (bis) boro succinate

A new semiorganic nonlinear optical crystal Sodium (bis) boro succinate (SBBS) [Na2 (C4H4O4) (H3BO3)(H2O)4]·H3BO3 was grown from aqueous solution by slow evaporation growth technique. Single crystal X-ray diffraction analysis revealed that the crystal belongs to monoclinic crystal system with space group of P21/n. The crystalline nature of SBBS crystal was analyzed by Powder X-ray diffraction. The morphology and growth axis of grown crystal were investigated. The functional groups present in the compound were confirmed by FTIR and FT-Raman spectroscopy techniques. The cut-off wavelength, optical transmission and band gap energy of the grown crystal were analysed by UV–Visible spectral studies. Electrical behaviour of SBBS crystal was analysed by dielectric studies. Laser induced damage threshold study was carried out for SBBS crystal using Nd:YAG laser. Second harmonic generation and relation between particle sizes with respect to generated output were investigated by Kurtz-Perry powder technique. Third order nonlinear properties of SBBS crystal were analyzed by Z-scan method and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility were calculated.

Investigation of the effects of acidic pH and annealing on the properties of nanostructured TiO2 thin films for waveguiding applications

In this work, titanium dioxide (TiO2) thin films are synthesized by the simple sol-gel process using the dip-coating technique at various pH values (pH 6, 4 and 2). The influence of acidic pH and annealing at 500 °C in air for one hour on the microstructure, morphology, optical and waveguide properties of the prepared thin films are investigated carefully using various characterization techniques. X-ray diffraction (XRD) and Raman spectroscopy (RS) analysis show that all the annealed films are polycrystalline and possess only anatase crystal structure with a preferential orientation along the (101) plane. The intensity of the diffraction and Raman peaks as well as crystallite size were found to increase with increasing sol acidity which indicates an improvement in the crystallinity of the films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images revealed that morphology, grain size and surface roughness of the films are influenced by heat treatment and pH of the sol. According to UV–Visible measurements, all the TiO2 thin films are highly transparent with an average transmittance of more than 74% in the visible region. It is also observed that the optical transmission and energy band gap decrease with sol acidity and annealing. M-lines spectroscopy (MLS) measurements at a 632.8 nm wavelength put into evidence that TiO2 planar waveguides support single confined guided modes for both transverse electric (TE) and transverse magnetic (TM) polarizations. Moreover, both TE and TM refractive indexes and the birefringence of the anatase films are found to increase with acidity of the sol.

Spin caloritronics in spin semiconducting armchair graphene nanoribbons

We designed a spin-caloritronics device based on armchair graphene nanoribbons (AGNRs). We theoretically show that a trapezoidal-shaped graphene flake consisting of four zigzag edges bridged between two AGNRs becomes a spin semiconductor with a tunable spin-dependent transmission gap. The results indicate that the appearance of spin semiconducting properties with spin-dependent localized transmission peaks around the Fermi level could produce the spin-caloritronics effects of AGNRs. Interestingly, the values of the spin Seebeck coefficient ${S}_{S}$ are comparable to values obtained for zigzag graphene nanoribbons, and also ${S}_{S}$ sensitively increases as the transmission gap increases. Furthermore, by engineering the position and orientation of a triangular antidot only in the scattering region, both ${S}_{S}$ and the spin figure of merit could be separately enhanced at room temperature.