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Photoelectrocatalytic Carbon Dioxide Reduction to Value-Added Products
Published in Anirban Das, Gyandshwar Kumar Rao, Kasinath Ojha, Photoelectrochemical Generation of Fuels, 2023
Paras Kalra, Cini M. Suresh, Rashid, Pravin P. Ingole
The Fermi level is the energy level where the probability of finding an electron is 1/2 at 0 K. In the case of intrinsic semiconductors, the Fermi level is present at exactly the middle of the band gap whereas for extrinsic semiconductors, the Fermi level does not lie at the midpoint, i.e. in the case of p-type semiconductors, it lies slightly above the valence band and in the case of n-type semiconductors, it lies slightly below the conduction band. Fermi level is a very useful concept while studying the semiconductor-electrolyte interface (or here in PEC as electrode-electrolyte interface) as it is very much helpful in analyzing the electron transfer processes at the material interfaces [20].
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
The Fermi level is the energy at which there is a 50% probability of it being occupied by an electron. In an intrinsic semiconductor, the Fermi level is located approximately midway between the conduction and valence bands. When a semiconductor is doped with a donor impurity, this probability increases and therefore the Fermi level shifts upward. On doping with an acceptor impurity, the situation reverses and Fermi level shifts downward.
Thermal Distribution of Electrons, Holes, and Ions in Solids
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
In Chapter 2, we discussed a semiconductor with electrons in a rigid band of lowest energy level Ec. We introduced the notion of the electron Fermi level EFn, which is equivalent to the electrochemical potential of the electrons ηn. In the analysis of semiconductor devices, the Fermi level is most useful in two specific aspects: it determines the work and voltage that a collection of carriers in the semiconductor can deliver, and it provides a determination of the occupancy of the available electronic states, depending on the energy of the states.
Oxidation behavior with quantum dots formation from amorphous GaAs thin films
Published in Philosophical Magazine, 2018
Srikanta Palei, Bhaskar Parida, Keunjoo Kim
Figure 8 shows the UPS and IPS spectra of the amorphous GaAs layer on nanotextured Si substrate. After the thermal annealing at 100°C for 30 min to remove surface contamination, The measurement was carried out by spectrometry (MODEL: AXIS Ultra DLD, KRATOS Inc.) using UV source of He I (21.2 eV) in steps of 0.02 eV, and a base pressure of 4 × 10−8 Torr. UPS spectra were used to analyze energy levels of the occupied valence electrons below the Fermi level. From the range of binding energy, the low binding energy region of a red circle portion in Figure 8(a) is magnified to understand the valence band maximum (VBM) of the nanodot from the Fermi level. The magnified UPS spectrum showed the VBM value of 1.58 eV below the Fermi level as shown in Figure 8(b). The Fermi level is the minimum energy level occupied by electrons that are weakly bound to the nucleus of the atom. The He I UV source excites electrons to the vacuum level, to determine the work function of As2O3 (Φ = 21.22 eV (He I [1s-2p]) – 17.19 eV = 4.03 eV) above the Fermi level, thus defining the amount of energy required to remove an electron from the Fermi level, and placing it at a vacuum point at rest just outside the surface.
Experimental studies of electron affinity and work function from titanium on oxidised diamond (100) surfaces
Published in Functional Diamond, 2022
Fabian Fogarty, Neil A. Fox, Paul W. May
In order for an electron to be emitted from a metal surface, it must possess sufficient kinetic energy to overcome the work function (WF) situated at the surface–vacuum interface. The work function, ϕ, is defined as the energy difference between the Fermi level, EF, and that of the vacuum level. In semiconductors, electrons that reside in the valence band (VB) require additional energy equivalent to that of the band gap to first excite them into the conduction band (CB) before they can be emitted. ϕ typically has vales of a few eV for most metals and semiconductors. Therefore, high-energy ultraviolet photons or temperatures >1500 K are usually required to provide sufficient energy for electron emission. For some semiconductors and insulators, however, which include diamond [8], cubic boron nitride [9], and AlN and AlGaN [10], the work function is greatly reduced because, in these unusual cases, the CB minimum lies higher in energy than the vacuum level. This condition is known as NEA. Here, electrons located in the CB experience no emission barrier to escape the surface. Bulk electrons residing in the VB, or in mid-band-gap states because of doping, only require prior excitation (via photon absorption, thermalisation or electric fields) into the CB for emission to take place. Consequently, NEA materials are highly desirable for next-generation electron-emission applications. Because these are all wide band-gap materials, the advantages of NEA might be outweighed by the high energies needed to excite electrons from the VB into the CB. However, this problem can be reduced if the NEA is sufficiently large and negative, i.e. has a value approaching that of the band gap, and also by using suitable doping strategies, especially n-type, that raise the Fermi level and decrease the effective band gap [2].
Enhanced photocatalytic activity of Mg-doped ZnO thin films prepared by sol–gel method
Published in Surface Engineering, 2021
Muhammad R. Islam, Muhammad G. Azam
Such an increase in band gap could be attributed to the Burnstein‒Moss effect [32]. When semiconductor is heavily doped, the donor electrons occupy the states at the bottom of the conduction band, and the Fermi level moves towards the conduction band. As a consequence, the electron requires more energy to move to the unoccupied state of the conduction band resulting in an increase of band gap [32,33].