Change In Energy Band Structure Research Articles

Yellow rare earth sulfide powders with near‐infrared reflectance and spectral modulation for energy‐saving applications

AbstractRadiative cooling pigments offer new opportunities for sustainable carbon neutrality as zero‐energy and zero‐pollution functional materials. However, it is a challenge to prepare inorganic yellow pigments simultaneously with environmentally friendly, high color value, and weather resistance. In this study, a series of alkali metal‐doped γ‐Sm2S3 yellow pigments with near‐infrared reflectance were synthesized. The doping of alkali metal ions reduced synthesis temperature of Sm2S3 from 1300°C to 1000°C. The change in energy band structure induced by alkali metal doping allows the products to exhibit modifiable colors. Typical γ‐[Na]‐Sm2S3 pigment powders have a high near‐infrared reflectance and impressive colors (b* = 78.6, C* = 77.6). Furthermore, colored films made by prepared yellow powders with polyvinylidene fluoride in certain ratios had high near‐infrared reflectance and excellent environmental weathering, resulting in an effective cooling of 4–8°C in outdoor experiments. This work expands the range of options for energy‐efficient building and yellow colorant.

Multiple roles for LaFeO3 in enhancing the Photoelectrochemical performance of WO3

For photoelectrochemical (PEC) water splitting, constructing heterojunctions and loading co-catalysts are effective means to realizing sufficient light absorption, effective photogenerated carrier separation and fast charge transport. However, during implementation, the PEC performance of the catalyst is affected by both parasitic light absorption and reflection and the change in energy band structure due to the creation of new interfaces. Herein, in order to minimize the effect of recombination of photogenerated electron-hole pairs on the catalyst PEC performance due to the nascent interface arising from the co-catalyst compounding, WO3 and Ni/Co co-doped LaFeO3 (LFO) are constructed as heterojunctions, in which NiCo-LFO acts both as a part of the heterojunction to enhance photogenerated carrier separation and a co-catalyst to enhance the conductivity and modulate the surface state density at the catalyst-electrolyte interface. The current density of NiCo-LFO/WO3 reaches 3.92 mA cm−2, which is more than 7 times that of LFO/WO3. This work provides a reference for the efficient water splitting of B-site doped, especially the co-doped perovskite oxide as multifunctional roles integrated with conventional photoelectrodes.

Novel Gas-Sensitive Material for Monitoring the Status of SF6 Gas-Insulated Switches: Gese Monolayer

Detecting the decomposition components of SF6 insulating gas is recognized as an effective means to monitor the operating status of the SF6 insulating switch. In this paper, the adsorption characteristics of a new two-dimensional material GeSe for five SF6 decomposition gases (SO2, SOF2, SO2F2, H2S and HF) are reported by first-principles simulation. Through the analysis of the change of energy band structure, density of states distribution, and gas desorption time, it is found that GeSe has the potential as a gas-sensitive material for the selective detection of SO2F2, and the computational work in this paper provides theoretical guidance for the development of new gas-sensitive sensors applied in monitoring SF6 insulated switches.

Rectifying Characteristics of the Perovskite Oxide La1−xSrxMnO3/Nb‐0.7 wt%‐Doped SrTiO3 Heterojunction

The influence of Sr‐doping on the rectifying characteristics of the perovskite oxide La1−xSrxMnO3/Nb‐0.7 wt%‐doped SrTiO3(LSMO/NSTO) heterojunction is studied systematically. Clear rectification characteristics are observed in the Au/LSMO/NSTO heterojunction with Sr‐doping rate of 0.1–0.6 at 300 K. The threshold voltage and Schottky barrier height increase linearly with the increase in Sr‐doping. Combined with first‐principles calculations, it is found that the variation of Sr‐doping concentration directly leads to a change in the LSMO work function, then a change in barrier height, and finally a change in the threshold voltage and rectification characteristics. Ultimately, it is proved that the rectification characteristics of the perovskite metal oxide heterostructure are consistent with the potential barrier mechanism of semiconductors. The rectifying characteristics of the perovskite oxide p–n junction can be well modulated by the change in energy band structure caused by Sr‐doping. These results lay a foundation for further understanding of the rectification characteristics of the perovskite oxide heterostructure and improving its application value.

Surface modification effects of fluorine-doped tin dioxide by oxygen plasma ion implantation

SnO2:F (FTO), as a kind of transparent conductive oxide (TCO), exhibits excellent transmittance and conductivity and is widely used as transparency electrodes in solar cells. It’s very important to modifying the surface of FTO for it plays a critical role in CdTe solar cells. In this study, modifying effects of oxygen plasma on FTO was investigated systematically. Oxygen plasma treatment on FTO surface with ion accelerating voltage ranged from 0.4 kV to 1.6 kV has been processed. The O proportion of surface was increased after ion implantation. The Fermi level of surface measurement by XPS valance band spectra was lowered as the ion accelerating voltage increased to 1.2 kV and then raised as accelerating voltage was elevated to 1.6 kV. The work function measured by Kelvin probe force microscopy increased after ion implanting, and it was consistent with the variation of Fermi level. The change of energy band structure of FTO surface mainly originated from the surface composition variation. As FTO conduction was primarily due to oxyanion hole, the carrier was electron and its concentration was reduced while O proportion was elevated at the surface of FTO, as a result, the Fermi level lowered and the work function was enlarged. It was proved that oxygen plasma treatment is an effective method to modulate the energy band structure of the surface as well as other properties of FTO, which provides much more space for interface and surface modification and then photoelectric device performance promotion.

The influence of strain on the energy band structures of phosphorene nanoribbons

The electric properties of the strained phosphorene and phosphorene nanoribbons are investigated using the tight-binding model. The influence of the strain on the phosphorene nanoribbons with different edges subjected to different type and magnitude of strains are examined. The results show that the bandgap could be narrowed by compressive in-plane strain or by tensile vertical strain. The influence on the edge states in the zigzag–zigzag phosphorene nanoribbons are also highlighted. It is found that the increasing energy difference of its two edge states always accompanies with the decreasing bandgap induced by the strain. The reasons causing the change of energy band structure are studied based on the numerical calculations.

In Ukrainian

Unique physical properties of multi-walled nanosystems have been the subject of keen interest lately. Their specific energy-band structures with a zero band gap and linear dependence of electron and hole energy spectrum on the wave-vector cause the electric charges to behave like relativist particles with zero effective mass. Anomalous transportation and field effects open a wide prospect of their applying in nanoelectronics. Such nanostructures are assumed to be promising spintronics materials due to the long electron free path, weak spin-orbital interaction and the long spin scattering. What is more, the chemical or physical modification of multi-walled nanosystems enables to reveal their new extraordinary features. Thus, intercalation with molecules allows to change the Fermi level position, relative electron and hole concentration without considerable changes in energy-band structure of source nanomaterials. On the other hand, unique optical, electrical and magnetic, and also biological behaviour of cyclopentadienyl complexes stimulates creation on their base of intercalates with multi-walled CNT, since the capability of these complexes to coordinate with MWCNT allows to obtain new materials as effective elements for photo- and magnetosensitive devices, drug delivery, imaging and therapy, as well to use these materials as an antidetonant in motor and aviation fuels. By employing the methods of MM+, РМ3 and Monte-Carlo, there has been studied the positioning of molecules of bis(cyclopentadienyl)nickel in a double-walled (5,5)@(10,10) carbon nanotube depending on intercalate concentration and intercalation temperature. The temperature increase (over ~455 K) causes gradual bond ruining followed by extrusion of interwall intercalate. Further temperature increase up to 620 K is characterised with intercalate external surface desorption, stabilising the whole system and keeping the interwall intercalate only. There have been calculated the UV-spectra for (5,5)@(10,10) DWCNT depending on the intercalate concentration as well as an association constant of the system which makes 36,2 l·mol -1 .

Tunneling Effect Of Photon-assisted AZO/SiOx/n-Si Heterojunction Device At Reverse Bias

Physical asymmetrical Metal / AZO / SiOx / n-Si / Metal devices in semiconductor-insulator-semiconductor (A-SIS) framework were investigated for their anormaly current-voltage characteristics under light irradiation. The devices showed a normal rectifying character in dark but manifested a peculiar current-voltage feature at reverse bias under illumination. Considering the change of energy band structure at the reverse electric field, it was found that the transport of electrons was mainly dominated by the thermionic emission and quantum tunneling at low voltage. With the increase of the reverse bias, the electrons were able to tunnel through the reduced barrier of ultra-thin SiOx layer (<1nm) and an effective triangle-like barrier of silicon. An appropriate simulation of the J-V relationship demonstrated that the photons acting as the assisted part magnified the reverse current density, and the thickness of SiOx layer managed the amount of the reverse saturation current.

Enzymatic Ring Opening Polymerization Of É›-caprolactone By Using A Novel Immobilized Biocatalyst

Physical asymmetrical Metal / AZO / SiOx / n-Si / Metal devices in semiconductor-insulator-semiconductor (A-SIS) framework were investigated for their anormaly current-voltage characteristics under light irradiation. The devices showed a normal rectifying character in dark but manifested a peculiar current-voltage feature at reverse bias under illumination. Considering the change of energy band structure at the reverse electric field, it was found that the transport of electrons was mainly dominated by the thermionic emission and quantum tunneling at low voltage. With the increase of the reverse bias, the electrons were able to tunnel through the reduced barrier of ultra-thin SiOx layer (<1nm) and an effective triangle-like barrier of silicon. An appropriate simulation of the J-V relationship demonstrated that the photons acting as the assisted part magnified the reverse current density, and the thickness of SiOx layer managed the amount of the reverse saturation current. Copyright © 2016 VBRI Press. amplification of the reverse current with the increase of the negative bias from -1.0 to - 4.0 V, especially, the reverse current is maintained at a saturation value in the range of about - 3.5 to - 4.0 V. The unusual optoelectronic property has been observed with the reduced thickness of SiOx buffer layer in the scope of 0.5-1.0 nm within AZO/SiOx/Si heterojunction structure, rather than PV characteristics for the metal/AZO/SiOx/Si/metal device. What is the mechanism by which results in the change of physical

Luminescent properties of Ce:Gd3(Al,Ga,Mg,M)5O12 crystal (M = Zr, Hf)

To obtain a new scintillator with a higher gamma-ray stopping power than conventional Ce:Gd3Al2Ga3O12 (Ce:GAGG), which has excellent light output and energy resolution, new scintillators based on Ce:GAGG, Ce:Gd3Al2Mg0.5Hf0.5Ga2O12, and Ce:Gd3Al2Mg0.5Zr0.5Ga2O12 were grown by the micro-pulling down method as the first step. We found that the emission wavelengths of these crystals became slightly longer than that of Ce:GAGG by approximately 10–20 nm owing to the change in energy band structure.

First-Principles Study of Li Doping in a Double-Wall Carbon Nanotube

By performing first-principles calculations, we study Li doping in a double-wall carbon nanotube where a (5,0) tube is confined inside a (14,0) tube. There are three possible sites for Li doping and two of them are energetically favorable. The change of energy band structure is closely related to the doping sites and the charge transfer is investigated. Bader charge analysis indicates that Li prefers to donate its electron to the inner (5,0) tube. Moreover, the Li capacity of the system can reach LiC4.75 which makes it a promising candidate for Li-ion battery materials.

Luminescence and photoconductivity properties of porous polycrystalline silicon

In recent years, the photoluminescence and the photoconductivity of porous silicon were comprehensively studied. But the photoluminescence and the photoconductivity of porous polycrystalline silicon have not been wholely studied. In this paper, the results showed that luminescent property of the samples prepared by poly-crystal silicon wafers may be related to the defects on Si complexes surface, which can be proved by microwave-detected photoconductivity decay measurements. Furthermore, the luminescence of samples was disappeared under the external illumination, which may be related to the elimination of luminescent-centers. In addition, the conductivities of the samples were dependent on etched time and current density, and the large porosity of samples led to isotropic photoconductivity, which may be related to the change of energy band structure of the devices.

Strain Control of Stripe Patterned Si/Si1-xGex/Si(100) Heterostructures

In Si/Si1-xGex/Si(100) heterostructure patterned into stripe shape with <110> direction, strain control of capping Si and Si1-xGex layers is investigated. The Raman scattering analysis of the stripe patterned Si/Si1-xGex/Si(100) heterostructure indicates strain relaxation in Si1-xGex layer and introduction of tensile strain into capping Si layer by submicron stripe patterning. It is found that the effect of heat-treatment (750ºC, 3 h) on the strain relaxation in Si0.6Ge0.4 layer of stripe has a negligibly small. The metal-oxide-semiconductor capacitor and photoluminescence measurements for strain controlled stripe patterned Si/Si1-xGex/Si(100) heterostructure shows the change of energy band structure.

Dramatic reduction of gate leakage current of ultrathin oxides through oxide structure modification

We study in detail a new effect, phonon-energy-coupling enhancement (PECE) effect, produced by rapid thermal processing (RTP). It includes two aspects: (1) strengthening Si–D bonds and Si–O bonds and (2) change of energy band structure and effective mass. It is shown that not only Si–D bonds but also Si–O bonds have been strengthened dramatically, leading to enhancement of robustness of the oxide structure and the oxide/Si interface. For thick oxides (>3 nm), the gate leakage current has been reduced by two-orders of magnitude and the breakdown voltage has been improved by ∼30% due to phonon energy coupling. For ultrathin oxides (2.2 nm), the direct tunnelling current has been reduced by five orders of magnitude, equivalent to that of HfO 2, probably due to increased effective mass and barrier height.

Enhanced Phonon-Energy Coupling: Dramatic Reduction of Leakage Current of Silicon Oxide

AbstractWe study in detail a newly discovered effect, phonon-energy-coupling enhancement (PECE) effect, produced by rapid thermal processing (RTP). It includes two aspects: (1) Strengthening Si-D bonds and Si-O bonds and (2) Change of energy band structure and effective mass due to thermal shock. It is shown that not only Si-D bonds but also Si-O bonds have been strengthened dramatically, leading to enhancement of robustness of the oxide structure and the oxide/Si interface. For thick oxides (&gt;3 nm), the gate leakage current has been reduced by two orders of magnitude and the breakdown voltage has been improved by ~30% due to phonon-energy coupling. For ultrathin oxides (2.2 nm), the direct tunneling current has been reduced by five-orders of magnitude, equivalent to that of HfO2, probably due to the increased effective mass and barrier height.

Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals

The magnetic field dependence of the transverse magnetoresistance Δρ/ ρ0 and the Hall coefficient RH was measured for the graphite films of various thickness ranging from around 20 to 110 nm at temperatures between 4.2 K and 300 K. High quality of the crystallinity of these graphite films prepared by cleaving could be confirmed from the observation of Shubnikov-de Haas oscillation in RH. The saturation tendency revealed in the resistivity ρ versus magnetic field B characteristics for graphite films thinner than about 50 nm in the strong magnetic field region at low temperature, while as for all graphite films in this study, ρ varied in proportion to Bn (n>1) in the strong magnetic field region at high temperature. According to the transport theory for the simple two carriermodel in the strong magnetic field region, this saturation tendency should be due to the differencebetween electron and hole densities. It may be caused by some change of energy band structure in thin films. Furthermore, at high temperature, ρ versus B characteristics, common to all these graphite films, may be explained by the equal number density ofelectrons and holes due to thermal excitation.

On the Dispersion Relation of Holes in Bismuth

AbstractFrom the known change of energy band structure of bismuth and bismuth‐antimony alloys Bi1−xSbx under hydrostatic pressure the dependence of carrier concentration on the Fermi energy of holes is calculated. This dependece points to a non‐parabolic dispersion relation of holes.