- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
ion bombardment effect on the band gap of anatase TiO2 ultrathin films
摘要： We report a study of the effect of nitrogen ion bombardment on the optical properties of anatase TiO2 ultrathin films, particularly the band gap energy. The TiO2 films were prepared by a sol-gel method and dip-coating process. The as-prepared TiO2 films were then exposed to a +N2 low-energy ion beam from a microwave electron cyclotron resonance (ESR) ion source. Raman and spectroscopic ellipsometry (SE) analysis were performed on TiO2 films prepared at different +N2 exposure times. The Raman measurements reveal the conservation of the anatase TiO2 crystalline structure after the ion beam exposure. From a detailed ellipsometric study, the thickness of layers, the dielectric function, the band gap and the Urbach energies were determined. The obtained results show an increase of the TiO2 band gap with the decrease of thickness of films during +N2 exposure time. The band gap energy was blue shifted from 20 meV to 140 meV as the exposure time was increased from 5 min to 20 min when the thickness was decreased from 30 nm to 21 nm. This increasing of band gap energy could be explained by the thickness effect. From the band tail, the Urbach energy was also affected by +N2 ion beam. These results are in good agreement with the observed broadending of the Raman band the OeTieO bending vibration mode, as the exposure time increases.
关键词： +N2 ion bombardment,TiO2,Urbach energy,Band gap energy,Raman,Ellipsometry
更新于2025-09-09 09:28:46
-
Modulation of the electronic properties of two-dimensional MoTe2/WSe2 heterostructure by electrical field
摘要： The structure and electronic properties of two-dimensional MoTe2/WSe2 van der Waals heterostructure under external electric field have been investigated by first-principles calculation. The interlayer distance between MoTe2 and WSe2 is 3.613? and the binding energy per unit is ?0.183eV, which indicated that MoTe2 is bound to WSe2 via van der Waals interaction. The interlayer distance can be modified by external electric field and the band gap of MoTe2/WSe2 heterostructure continuously decreases with increasing external electric field, eventually a transition from semiconductor to metal is observed, particularly, the band alignment of the MoTe2/WSe2 heterostructure can be effectively tuned from intrinsic type-II to type-I. Applying external electric field along +z direction and ?z direction has different effects on the band gap due to the intrinsic spontaneous polarization in MoTe2/WSe2 heterostructure. Our study indicates that the external electric field can significantly tune the band offsets and modify the band alignment between MoTe2 and WSe2. The present study would be helpful for application of such transition-metal dichalcogenides heterostructures in nano- and optoelectronics.
关键词： band gap,MoTe2/WSe2 heterostructure,external electric field,Density of States
更新于2025-09-09 09:28:46
-
Theoretical and Experimental Evidence of Modified Structure, Magnetism and Optical Properties in Ba and Mn Co-Substituted BiFeO <sub/>3</sub>
摘要： To improve the vacancy related defects associated with pure BiFeO3 (BFO) different Ba-Mn co-doped samples (Bi1-xBaxFeyMnyO3; x=0.1; y=0.0, 0.05, 0.1, 0.15) were prepared from sol-gel method. The influence of co-doping on structural, magnetic and optical properties of BiFeO3 has been studied in different experimental conditions. Particle size and magnetic properties were measured from SEM and VSM analysis respectively. Again band gap was calculated from UV analysis. The co-doped samples showed reduced particles size as well as better surface morphology. M-H loops suggest that the presence of Mn2+ increased ferromagnetic quantity at some levels. Still room temperature occurrence of ferromagnetism obtained from M-H loops of all samples showed weak ferromagnetic behaviour. In addition the incorporation of Ba2+ at Bi3+ site and Mn2+ at Fe3+ site decreased the band gap which was evidenced by increased optical property.
关键词： Surface morphology,Ferromagnetism,BFO,Multiferroics,Band gap
更新于2025-09-09 09:28:46
-
An over 20-W/mm S-band InAlGaN/GaN HEMT with SiC/Diamond-Bonded Heat Spreader
摘要： This letter reports on an InAlGaN/GaN high-electron-mobility transistor (HEMT) employing a SiC/diamond-bonded heat spreader with a record high output power density of 22.3 W/mm. A quaternary In-added InAlGaN barrier enabled both the large current of over 1 A/mm and high breakdown voltage of 257 V. The drain bias was increased as high as 100 V for the S-band load-pull measurement, leading to high power operation. Furthermore, the thermal resistance was reduced by 60%, from 18.8°C/W to 7.2°C/W, by employing the SiC/diamond heat spreader. This large heat dissipation effect was clearly observed in the output power density for the load-pull measurement. Our results demonstrate that the GaN HEMT with In-added barrier layer is promising not only for millimeter wave applications but also for high output power microwave amplifiers.
关键词： InAlGaN,HEMTs,Wide band gap semiconductors,GaN,Microwave transistors
更新于2025-09-09 09:28:46
-
Group 10 metal–thiocatecholate capped magnesium phthalocyanines – coupling chromophore and electron donor/acceptor entities and its impact on sulfur induced red-shifts
摘要： A new and facile method of generating thiolate groups at the phthalocyanine (Pc) β-position is presented as well the unique properties that these groups confer on the Pc ligand upon coordination of group 10 metals Ni, Pd and Pt(dppe) or SnMe3. In particular, the Q-band is shifted to almost 800 nm for all group 10 metals used, and the complexes show panchromatic absorption owing to new absorbance bands that appear between 400 and 650 nm. Enhanced intersystem-crossing for all transition metal co-ordinated Mg(Pc) complexes was demonstrated by the moderate to very high singlet oxygen quantum yields of 0.36, 0.76 and 0.91 for the Ni, Pd and Pt coordinating complexes, respectively, which show that the heavy metals have direct influence on the Pc π-system and inter-system-crossing (ISC). This was further confirmed by MO calculations, which show mixing of metal and ligand orbitals, as well as suggest that the Q-band transition has both π → π* and ligand-to-metal charge transfer characteristics. Furthermore, the origin of the Q-band red-shift was shown to be due to greater destabilization of the HOMO compared to LUMO/LUMO+1, thus decreasing the HOMO–LUMO band gap.
关键词： thiolate groups,intersystem-crossing,phthalocyanine,MO calculations,HOMO–LUMO band gap,panchromatic absorption,singlet oxygen quantum yields,group 10 metals,Q-band
更新于2025-09-04 15:30:14
-
Heat-Resistant Microporous Ag Die-Attach Structure for Wide Band-Gap Power Semiconductors
摘要： In this work, efforts were made to prepare a thermostable die-attach structure which includes stable sintered microporous Ag and multi-layer surface metallization. Silicon carbide particles (SiCp) were added into the Ag sinter joining paste to improve the high-temperature reliability of the sintered Ag joints. The use of SiCp in the bonding structures prevented the morphological evolution of the microporous structure and maintained a stable structure after high temperature storage (HTS) tests, which reduces the risk of void formation and metallization dewetting. In addition to the Ag paste, on the side of direct bonded copper (DBC) substrates, the thermal reliability of various surface metallizations such as Ni, Ti, and Pt were also evaluated by cross-section morphology and on-resistance tests. The results indicated that Ti and Pt diffusion barrier layers played a key role in preventing interfacial degradations between sintered Ag and Cu at high temperatures. At the same time, a Ni barrier layer showed a relatively weak barrier effect due to the generation of a thin Ni oxide layer at the interface with a Ag plating layer. The changes of on-resistance indicated that Pt metallization has relatively better electrical properties compared to that of Ti and Ni. Ag metallization, which lacks barrier capability, showed severe growth in an oxide layer between Ag and Cu, however, the on-resistance showed fewer changes.
关键词： wide band-gap semiconductor,die attachment,sinter joining
更新于2025-09-04 15:30:14
-
Electronic and electrical properties of siligraphene (g-SiC3) in the presence of several strains
摘要： Based on the first principles density functional theory (DFT), we have investigated the electronic and electrical properties of siligraphene (g-SiC3) under various percentages of strain. Our results show that the electronic and electrical properties can be controlled using (0% to -10%) strain. The behavior of g-SiC3 is altered from a semi metallic to semiconductor. The electronic band gap is opened under -9% and -10% strain. Also, the geometry of g-SiC3 is altered under with these two percentages of strain due to the bond length between C-Si atoms is increasing. The electrical conductivity of siligraphene g-SiC3 as a function temperature without and with strain has been given. We detected very exciting results. It is affected and changed when at the same percentage of strain, which applied to alter the behavior of g-SiC3 to semiconductor. Then, these properties can be led to generate new 2-D nanomaterials and devices with huge control over their physical properties for a wide range of applications ranging from photovoltaic to photo-catalysis. We show that siligraphene is a very promising 2D material with great impact that can lead to exceptional results in the field of solar energy and other application. Consequently, we push the experimental researches to discover this new 2D nanomaterial (siligraphene) for using in solar cell application.
关键词： g-SiC3,DFT,Strain,siligraphene,electronic band gap
更新于2025-09-04 15:30:14
-
Highly UV sensitive polycrystalline zinc selenide thin film grown by chemical bath deposition technique
摘要： In this communication, we report a significantly high UV sensitivity of polycrystalline zinc selenide thin films prepared by chemical bath deposition technique. A three order of magnitude of photo current to dark current ratio is obtained for the as-deposited film under UV exposure. However, the photosensivity is found to decrease sharply upon open air isochronal annealing of the sample. The variation of the photocurrent to dark current ratio with annealing temperature is attributed to shrinking diameter of nano-wire like structures exhibited by the films, variation of the band gap energy and a decrease in the grain boundary charge density of the material which collectively enhance the free carrier concentration in the band leading to a substantial loss in the photosensitivity of annealed films compared to the as-deposited film.
关键词： ZnSe thin film,UV sensitivity,SEM,Band gap energy,Optical absorption co-efficient,Grain boundary charge density
更新于2025-09-04 15:30:14
-
Crystallographic, optical, and electronic properties of (Cu, Li)GaS2
摘要： We synthesized chalcopyrite-type (Cu1-xLix)GaS2 solid solution samples with a composition of 0.00 ≤ x ≤ 0.20 by mechanochemical process and sequential heating at 550oC in 5% H2S/N2 gas atmosphere. The X-ray powder diffraction (XRD) peaks of (Cu1-xLix)GaS2 shifted by substitution of Li atoms for Cu atoms in CuGaS2. Their crystallographic parameters were refined by Rietveld analysis using XRD data. The lattice constant a of the (Cu1-xLix)GaS2 solid solution increased with increasing Li content, x, while the lattice constant c decreased with increasing Li content, x. We determined band-gap energies of (Cu1-xLix)GaS2 solid solution by diffuse reflectance spectra. The band-gap energy of the (Cu1-xLix)GaS2 solid solution increased from 2.44 eV of CuGaS2 (x = 0.0) to 2.54 eV of (Cu0.8Li0.2)GaS2 (x = 0.2). To understand the band diagram of (Cu1-xLix)GaS2 solid solution, the energy level of the valence band maximum (VBM) was estimated from the ionization energy, which was measured by photoemission yield spectroscopy. The energy level of the conduction band minimum (CBM) was also determined by adding the band-gap energy to the VBM level. The VBM level of the (Cu1-xLix)GaS2 solid solution decreased with increasing Li content, x. On the other hand, the CBM level was approximately constant. Li-doping in CuGaS2 is effective for decreasing the VBM level without increasing the CBM level.
关键词： Mechanochemical process,Band-gap energy,(Cu1-xLix)GaS2,Chalcopyrite-type,Photoemission yield spectroscopy
更新于2025-09-04 15:30:14
-
Charge Carrier Polarity Modulation in Diketopyrrolopyrrole–Based Low Band Gap Semiconductors by Terminal Functionalization
摘要： Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP) based D–A molecules having three different terminal groups (amide, ester and dicyano) and studied their electronic properties. Increase in electron acceptor strength from amide to dicyano, leads to a bathochromic shift in absorption. Photoconductivity and field–effect transistor (FET) measurements confirmed that a small increase in acceptor strength can results in a large change in the charge transport properties from p–type to n–type. The molecule with amide group, DPP–Amide, exhibited a moderate p–type mobility (1.3 × 10–2 cm2V?1s?1), whereas good n–type mobilities were observed for molecules with an ester moiety, DPP–Ester (1.5 × 10–2 cm2V?1s?1) and with a dicyano group, DPP–DCV (1 × 10–2 cm2V?1s?1). The terminal functional group modification approach presented here is a simple and efficient method to alter the charge carrier polarity of organic semiconductors.
关键词： FP-TRMC,self-assembly,p-n switch,low band gap,Diketopyrrolopyrrole
更新于2025-09-04 15:30:14