Papers by Keyword: Work Function

Abstract: Magnesium Oxide (MgO) thin films were deposited on SiO₂/Si substrate by electron beam evaporation. The properties of MgO thin film with and without oxygen partial pressure have been investigated by X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS), and Ultra-Violet Photoemission Spectroscopy (UPS). The XPS was used to investigate the chemical state of the film. REELS spectra revealed that MgO thin films deposited under oxygen partial pressure had band gaps of 6.07 eV. Meanwhile, the band gap for MgO thin films grown without oxygen partial pressure was 7.17 eV. The UPS results showed that the work functions of MgO thin film with and without oxygen partial pressure are 4.75 and 4.84 eV, respectively. In the MgO thin film with oxygen partial pressure, the intensity for the valence band peak at 12.16 eV decreased, but the work function remained relatively the same. Our results demonstrated that the oxygen partial pressure played a crucial role in improving the electronic properties of MgO thin films.

Abstract: Heterojunction semiconductor photocatalysis is an auspicious technique for clear up organic pollutants from water, and have been of valuable strategy in the area of photocatalysis. Herein, electrophoretic deposition procedure was used to prepare α-Bi₂O₃/CdS type-Ⅱ heterojunction photocatalysts. The results of PL, Raman, and EIS show that there is a heterojunction effect in α-Bi₂O₃/CdS, which is propitious to improve the separation efficiency of photogenerated electron-hole pairs. The DFT calculation reveals that the work function of CdS (4.57 eV) is higher than that of α-Bi₂O₃ (3.37 eV), which facilitates the migrating of e^- from the CB of α-Bi₂O₃ to the CB of CdS, and the migrating of h⁺ from the VB of CdS to the VB of α-Bi₂O₃, thus the e^--h⁺ pairs with high redox ability are retained. The performances were assessed by degrading methyl orange (MO), acid magenta under simulated visible light irradiation. Under simulated visible light irradiation, BC45 composite exhibited the highest degradation efficiency of 87% (MO) and 81% (acid fuchsin) for 4 h, which was about 2 times higher than that of CdS (MO) and (acid fuchsin). It is believed that the dual characteristics of H₂O wettability and dye adsorption performance in α-Bi₂O₃/CdS composites promote photocatalytic process compared with single CdS and α-Bi₂O₃. The study could provide new insights to develop efficiently capable photocatalysts of the α-Bi₂O₃/CdS composites.

Abstract: In this paper, we have investigated the effect of the work function of transparent conducting oxides (TCO) on the performance of a-Si:H p-i-n solar cells, including open circuit voltage (V_OC), short circuit current (J_SC), fill factor (FF) and conversion efficiency, using AFORS-HET software. The simulation has focused on two layers: front contact work function (Φ_TCO-front) and back contact work function (Φ_TCO-back) with various band from 4.7 eV to 5.3 eV and 4.2 eV to 4.9 eV respectively. From the simulation results, we know that the work function of TCO greatly affects the performance of solar cells such as Voc, Jsc, FF and conversion efficiency. By optimization, we arrive at results for V_oc, J_sc, FF and conversion efficiencies of 0.88 V, 8.95 mA / cm², 65% and 5.1% respectively. This result is obtained on Φ_TCO-front 5.2 eV. When Φ_TCO-front 5.2 eV, the value of V_OC, FF and conversion efficiency has been saturated, while the value of the J _sc actually begins to decrease. Furthermore, when the Φ_TCO - back is 4.3 eV, we get the best results for V_OC, J_sc, FF and conversion Efficiency of 0.9 V, 8.96 mA / cm², 73 % and 5.9 % respectively. When Φ_TCO-back 4.3 eV, the value of V_OC, FF and conversion efficiency begins to decrease, while the value of the J_sc does’t change significantly. These optimizations may help in producing low cost high efficiency p-i-n solar cells experimentally.

Abstract: In this study, Al and N implantation effect on surface properties of 4H-SiC epitaxial layers were investigated before annealing process. AFM results indicated that all implanted samples indicated relatively low RMS roughness values. From UPS and XPS analysis, work function and Si-C binding energy of implanted samples were increased compared to the reference 4H-SiC sample. Those variations may be caused by lattice disorder and amorphization. In addition, TEM image showed damaged area in 4H-SiC epitaxial layer.

Abstract: The method of manufacturing BaO thin layers on carbon nanotubes (CNT) from Ba(NO₃)₂ aqueous solutions was demonstrated. Ordered carbon nanotubes arrays were synthesized by catalytic plasma-stimulated chemical deposition from the gas phase. The influence of the BaO content on the work function and, accordingly, carbon nanotubes emission properties were investigated. Significant field emission threshold voltage of CNT arrays treated by solutions with the lowest Ba(NO₃)₂ concentrations was demonstrated.

Abstract: The material properties of electroplated NiW alloys with potential for use as emitters in thermionic energy converters were investigated. NiW alloy films with W content ranging from 11 to 25 at% were electroplated and the material properties of the alloy films including their surface morphologies, and crystallinities, were determined. The work functions of the NiW films were also evaluated using photoemission yield spectroscopy and were found to be independent of the W content. In addition, heat treatment up to 700°C in a vacuum chamber of a NiW film with 21.4 at% W content decreased the electron yield with increasing its work function.

Abstract: The growth and the atomic structure of alumina films of submonolayer to multilayer thickness evaporated onto the surface of Mo (110) crystal have been studied by Auger electron spectroscopy, high resolution electron energy loss spectroscopy and scanning tunneling microscopy. It is shown that the stoichiometry of the submonolayer film corresponds to that of the bulk oxide, and after achieving two monolayers the properties of the film largely resemble the properties of massive alumina. Deposition of the oxide at a substrate temperature of 1100 K results in the film structure corresponding to α-Al₂O₃. Such ultrathin oxide film is of considerable potential application in sensor physics and technology.

Abstract: It is very important to effectively evaluate the adhesion strength of coating. A nondestructive method to evaluate the adhesion strength of laser induction hybrid rapid cladding Cu-Fe-based coatings was investigated. The electron work function of coatings was measured by scanning Kelvin probe. It was demonstrated that the Fe-rich particles and solid solution of Fe can increase the EWF and the tensile strength. A logarithmic relationship between the ratio of EWF to dilution and the adhesion strength was established.

Abstract: The PCE has a great relationship with the work function of conductors in organic and printed electronics devices. And organic photovoltaics require an electrode with a work function (WF) that is low enough to either facilitate the transport of electrons in and out of various optoelectronic devices or collect electrons from the lowest unoccupied molecular orbital (LUMO) of a given organic semiconductor. In inverted organic photovoltaics, the ITO is normally used as cathode to collect electrons .By using PDDA deposition, the surface work function of ITO can be decreased by 0.3 eV, which is able to improve the electrons transport and the PCE in OPV, as it has been proved that the surface electronic potential of ITO is very sensitive to the presence of self-assembled molecular layers.

Abstract: Cu-BTC, also known as H-KUST 1, belongs to Metal Organic Frameworks (MOFs). Nanoporosity, relatively good thermal stability and unsaturated metal sites are some of its properties that make this MOF promising for application as a gas sensing material. In this work we chose different experimental approaches to examine trace gas sensing (5 to 50 ppm) of ethanol with Cu-BTC. Measurements with mass sensitive, as well as work function based readout, were successfully performed in dry synthetic air at room temperature. Strong, fast and concentration dependent response to ethanol was observed. In-situ measurements with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were additionally applied to visualize the adsorption of ethanol molecules on the Cu-BTC sensing layer.