Work functions of elements

Michaelson HB. 1977. Work function of elements and its periodicity. J Appl Phys 48 4729-4733. 

Trigonal selenium is a -type semiconductor with an energy gap of 1.85 eV (104) and a work function of about 6 eV (105), which is the largest value reported for all the elements. Accordingly, a Schottky barrier should be created at the contact of selenium with any metal. This is consistent with the... 

Electron-tunneling Model. Several models based on quantum mechanics have been introduced. One describes how an electron of the conducting band tunnels to the leaving atom, or vice versa. The probability of tunneling depends on the ionization potential of the sputtered element, the velocity of the atom (time available for the tunneling process) and on the work function of the metal (adiabatic surface ionization, Schroeer model [3.46]). 

Starting with this definition the semiconductor diemical sensors can be arbitrary classified with respect to following features the type of electrophysical characteristics diosen for monitoring, such as electric conductivity, thermal-electromotive force, work function of electron, etc. type and nature of semiconductor adsorbent used as an operational element of the sensor and, finally, the detection method used for monitoring the adsorption response of electrophysical characteristics of die sensor. 

The TID design proposed Patterson consists of an alkali metal doped cerwlc cylinder, containing an embedded heater surrounded by a cylindrical collector electrode [100]. The ceramic thermionic emitter is biased at a negative potential with respect to the collector electrode, and it is heated to a surface temperature of 400-800 C, depending on the mode of detection. The response of the detector to different elements depends on the electronic work function of the thermionic surface (i.e., the... 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

WF Work Function is an electron work function of the elements a quantity (eV) that determines the extent to which emission will occur. The experimental method thermoionic, field emission, photoelectric, and contact potential difference at the experimental conditions (e.g., vacuum of 10 8 Pa, clean surfaces, and identifi-cation of crystal-face distribution). 

This is the famous Saha-Langmuir equation. In it, g+/g0 is the ratio of the statistical weights of the ionic and atomic states, is the work function of the surface, / is the first ionization potential of the element in question, k is the Boltzmann constant, and T is the absolute temperature. Note that gjg0 is close to 1 for electronically complex elements for simpler elements it can take on a variety of values depending on how many electronic states can be populated in the two species for alkali atoms, for example, it is often Vi. Attainment of thermodynamic equilibrium was assumed in the derivation of this equation, and it is applicable only to well-defined surfaces. 

The Saha-Langmuir equation has been used to obtain both ionization potentials [25] and work functions [26]. Measuring ion beam intensities at several different temperatures and plotting their logarithms vs. 1/7" yield a straight line whose slope is ( - f)/k. If either or / is known, the other is readily calculated. Hertel introduced a method of measuring ionization potentials that was independent of the work function of the surface, using instead as reference an element of known ionization potential he applied it in the determination of the first ionization potentials of the lanthanide elements [27]. 

The work function of the metal electrode does not influence the bias. Imagine two electrodes in contact with each other and with the electrolyte. As all three elements are conducting, they will have a common Fermi level. At both sides, we let the equilibrium of the reversible hydrogen electrode evolve ... 

Finally, the most likely value of x in the CPs of interest here is about 2.5 eV or less. Therefore, an ohmic contact for electrons should have a work function of at most 3 eV. This is the case for the alkali metals from Li (2.9 eV) to Cs (2.15 eV) these elements are also, for the same reason, good n-dopants of the CPs slight diffusion into the polymer may then generate an n+ contact favorable for electron injection. The most widely used low-work-function cathode in CP EL is, however, Ca (2.9 eV) [269]. One could try to increase x by a proper choice of the monomer chemical structure, but unless one succeeds in avoiding having Eg reduced simultaneously, the emission will be shifted to the red part of the spectrum. 

In a similar fashion, adsorption of atoms or molecules onto a surface can raise or lower the value of the work function. Figures 16 and 17 illustrate the affect of CO and Na adsorption on the work function of Rh(l 11). For the case of carbon monoxide, the presence of the double layer at the surface leads to the polarization of CO with the negative end of the induced dipole oriented away from the surface. The presence of this dipole reinforces the dipole potential and conseqnently increases the work function. For the case of sodinm, charge transfer occurs upon adsorption leaving an electropositive element at the surface. This in turn decreases the effective magnitude of the dipole potential and lowers the work fhnction. The data of Figure 17 also illustrate the role of adsorbate-adsorbate interactions as depolarization of the sodinm occurs at near-monolayer coverage and reduces the effect. The adsorption of gas molecules on insulator... 

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