Physical and mathematical model of the surface segregation in binary alloys of transition metals

The surface segregation in binary alloys of transition metals based on platinum and palladium with different surface-face orientations are simulated via the electron-density functional method. The concentrations of the surface-active components of the binary alloys and displacements of the surface ion planes thereof are calculated self-consistently. The influence of surface segregation and lattice relaxation on the surface energy and electron work function on the surface of alloys of transition metals with various concentrations is investigated. The simulation results are compared with experimental data.     

Charge transfer and stability of NFE random alloys

The stability of random alloys is determined primarily by a balance between the energy of the volume change upon alloy formation (elastic energy), and the charge transfer between atomic cells. The charge transfer in homovalent, nearly free electron alloys was determined by taking the wave function to be that of the free atoms inside the ion cores, and to be plane waves in the interstitial regions. For a given valence, it was possible to establish an electronegativity series based on charge transfer, to determine charge transfer as a function of composition, and to compute the energy of alloy formation. The theory properly accounts for the formation of alloys of the alkali and alkaline earth metals, and shows why so few such alloys form.     

Calculation of energy characteristics of adsorption of metals

Within the framework of the electron density functional, a technique is developed for calculation of the adsorption energy and variation in the electron work function for metal substrates due to metal atom adsorption. The corrections to the local density approximation, which are associated with non-uniformity of the electron density in the subsurface region and discontinuous ion charge distribution over the crystal lattice sites, are included into consideration. It is shown that adsorption of alkali metal atoms results in lower electron work function, while that of transition metals (cobalt, iron, and chromium) might both decrease and increase the electron work function. Formation of a variety of adsorption structures from metal atoms depending on the temperature is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 14–19, July, 2007.     

Thermodynamische Untersuchung der Systeme Kalzium-Strontium,Kalzium-Barium und Strontium-Barium

Regarding the thermodynamic properties of the liquid alloys of the earth alkali metals (Calcium, Strontium, Barium), due to considerable experimental difficulties up to now scarcely any investigations have been undertaken. These systems, however, similar to the alloys of the alkali metals, are peculiarly suitable for theoretical considerations about the energetics of alloy formation, as their electronic properties are easily to comprehend. Therefore it was necessary to perform experiments on liquid alloys of the earth alkali metals in order to get reliable data for the enthalpies of mixing as a basis for some theoretical calculations.     

Alkali-metal-affected adsorption of molecules on metal surfaces

The study of coadsorption of alkali metals and simple molecules on transition metal surfaces has been a favored topic of research ever since the pioneering work by Langmuir in 1923. The main reasons for this continued interest are both of fundamental and applied nature. There are a number of interesting physical effects, such as work function changes, charge transfer, two-dimensional ordering, bond energy and molecule orientational changes, and altered surface reactive properties, which have been investigated by a large number of different surface analytical techniques. From an applied point of view, alkali metal covered surfaces are important in the areas of electron and ion emission and heterogenous catalysis, for example.In this paper we will give a short review of the adsorption of alkali metals on well-defined transition metal surfaces. The interaction of these adsorbed alkali metals with subsequently adsorbed atomic or molecular species will be treated more extensively. The emphasis will be on recent experiments dealing with well-characterized surfaces. In particular we will consider questions of adsorption energetics and kinetics, but also review in detail the vibrational, electronic, structural and reactive properties of the coadsorbed complex. Based on a wealth of experimental data, several models of the coadsorbed alkali metal-molecule complex will be introduced and discussed.     

Electron Dispersion in Liquid Alkali and Their Alloys

Ashcroft's local empty core (EMC) model pseudopotential in the second-orderperturbation theory is used to study the electron dispersion relation, theFermi energy, and deviation in the Fermi energy from free electron value forthe liquid alkali metals and their equiatomic binary alloys for the firsttime. In the present computation, the use of pseudo-alloy-atom model (PAA)is proposed and found successful. The influence of the six different formsof the local field correction functions proposed by Hartree (H), Vashishta-Singwi (VS), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F), andSarkar et al. (S) on the aforesaid electronic properties is examined explicitly,which reflects the varying effects of screening. The depth of the negativehump in the electron dispersion of liquid alkalis decreases in the orderLi →K, except for Rb and Cs, it increases. The results of alloys are in predictive nature.     

Changes in work function due to charge transfer in chemisorbed layers

In a simple tight-binding model well suited to transition and noble metals, we calculate the work function change due to adsorption of alkali metals. A decrease is found to be caused by ionic bonds formed on the surface through charge transfer between the two metals. The local density of states and the number of electrons in the substrate and the chcmisorbed layer are evaluated for various alkali metals and coverages. The method is applicable in both the high and low coverage limits in contrast to existing theories.     

Basic Relationships of the Autowave Model of a Plastic Flow

Russian Physics Journal - Macroscopic laws of the development of plastic flow localization autowaves in metals, alloys, alkali halide crystals, and rocks are investigated. It is shown that the...     

Electrical resistivity of alkali metals: Inflation–deflation effect of Fermi surface

The electrical resistivity of liquid alkali metals was calculated using the extended Ziman formula. The possible role of Fermi surface (FS) inflation–deflation (ID) was examined. The calculations reveal that replacing the sharp free electron FS by the expanded (respectively, contracted) one substantially improves the results. This was achieved directly by considering a FS correction factor of the Fermi radius and indirectly by a shift in the muffin-tin zero (MTZ) of the potential from its initial values. Consequently, a correlation between the shift of the MTZ of the potential and the FS factor parameter is revealed. The role of this correlation might contribute to a better understanding of the electron transport properties of other liquid metals and their alloys.     

Neutron investigation of collective excitations in liquid K-Cs alloys: the role of the electron density

The investigation of the ion dynamics in the liquid alloy K52Cs48, which has the same electron density as Rb, was carried out by neutron inelastic scattering. Well defined collective excitations were observed up to the maximum value of momentum transfer of the experiment. A scaling of the dispersion relation data was found to hold between K-Cs alloys, Rb and Cs. The suggested scaling points out the key role of the conduction electron density in the collective dynamics of alkali metals.     

Electron work function in alloys from the tin-lead system

The temperature and concentration dependences of the electron work function in Sn-Pb alloys are determined by the Fowler photoelectric method. It is shown that alloying of Sn with Pb decreases the electron work function rather than increasing it, as was reported in the literature. From the published data and experimental data obtained by the authors for the electron work function in the tin-lead system, it follows that the rate of decrease of the electron work function with increasing Pb concentration depends on the vacuum quality in the measuring cell and features in the electron work function isotherms are the more distinct the higher the vacuum.     

Secondary ion emission processes of sputtered alkali ions from alkali/Si(100) and Si(111)

The secondary alkali ion yield vs. the work function change (Δφ) of Na, K and Cs/Si(100) and Si(111) was measured to discuss the details of secondary ion emission processes. In the case of alkali/metal systems, the secondary ion emission is explained by the electron tunneling model. In this model, the ionization of the ejected atom occurs as a result of electron resonant tunneling through the potential barrier separating an atom and a metal, and the secondary ion yield depends on exponentially the work function change of metal surface. For alkali/Si(100) systems, the secondary ion emission processes are explained in terms of the electron tunneling model since the secondary alkali ion yield vs. the work function change (Δφ) follows the exponential manner. However, it is not easy to apply the simple electron tunneling model to our experimental results for alkali/Si(111) systems. There is the essential difference in surface structures between Si(100) and Si(111). Therefore, it is suggested that the local electronic environment around the adsorbates might be taken into consideration for alkali/Si(111) systems.     

The limiting electron activity of cesium in potassium-based alloys

Temperature and concentration dependences of the electron work function in cesium-potassium alloys were studied by the Fowler photoelectric method for the first time. Our results indicate that the limiting electron activity of cesium in potassium-cesium alloys is six times larger than that obtained by extrapolating the work function isotherm to pure potassium.     

The electron microscopy of thin metal foils

In this article, the nature of the defects in crystal structures and the way in which they can be studied by electron microscopy of thin metal foils are discussed in detail. Examples of phenomena observed in metals with the electron microscope are briefly presented. These include the dislocation structures introduced by work hardening, fatigue, quenching and irradiation; examples of microstructures found in alloys; and magnetic domain walls.     

Advanced metal alloy systems for massive high-current photocathodes

The physical principles of precise alloying are formulated with the aim of increasing the low quantum efficiency (QE) of suitable simple metals (Mg, Al, Cu) as well as of decreasing their electron work function (e φ) in the UV spectral range. The new approach provides valuable information for elucidating the origin of photoemission enhancement in bulk metal-based alloy systems. Bulk in-situ nanoclustering promises to be the most effective way of producing a much higher QE and a lower e φ in simple metals. In this article we show that the quantum efficiency of the metal-based alloys Mg–Ba, Al–Li, and Cu–BaO is considerably higher than the simple metals Mg, Al, and Cu, respectively.     

Inelastic processes in the scattering of metastable rare gas atoms at metal surfaces

Electron spectra of various metastable rare gas atoms systematically measured on a Pt(111) surface with Rb coverages ranging from submonolayers (3%) to multilayers are presented. The different decay channels of the excited particles are discussed in terms of resonant electron exchange processes between the substrate and the projectile in relation to the work function. It is shown that below a certain value of the work function a highly excited negative rare gas atom is formed which can undergo different de-excitation processes. A careful discussion of the branching ratios into the decay channels offers a natural explanation of the variations in the electron spectra induced by alkali metal adsorption. Additionally, an attempt is made to extract information about the alkali metal chemisorption state from the observed electron spectra.     

Pressure effect on the melting point of alkali metals

The mean-square displacement of alkali metals is studied theoretically using our local Heine-Abarenkov-type model potential in the perturbational scheme. The temperature-dependent mean-square displacement of alkali metals decreases as function of the compressed volume. Lindemann's criterion for melting x_m, which is defined as the ratio of two times the root-mean-square displacement to the nearest-neighbour distance, is found to be nearly constant for five alkali metals. The volume effect on the melting temperature of alkali metals is studied by keeping x_m constant. The obtained melting curve increases as function of the compressed volume and are qualitatively in good agreement with the observed tendency for alkali metals.     

CdTe(111)表面碱金属吸附的电子结构特性研究

从理论和实验两个方面对ＣｄＴｅ（１１１）表面碱金属吸附的电子结构特性进行了研究．实验结果表明碱金属Ｋ在ＣｄＴｅ（１１１）表面吸附是Ｃｄ替位吸附，它影响了ＣｄＴｅ（１１１）表面的表面态分布，产生了费密钉扎现象．在理论方面，首先采用线性糕模轨函数（ＬＭＴＯ）方法对ＣｄＴｅ（１１１）表面的Ｋ吸附电子结构特性作了研究，得出了与实验符合的结果．对碱金属在ＣｄＴｅ（１１１）表面的吸附电子结构特性系统对比研究表明ＣｄＴｅ（１１１）表面的碱金属吸附特性不仅受碱金属原子序数的影响，而且与碱金属原子的内层电子组态有关 关键词：     

Electron work function of Rb-Cs alloys

The temperature and concentration dependences of the electron work function (EWF) of rubidium, cesium, and nine Rb-Cs alloys are studied by the Fowler photoelectric method under the conditions of an ultra-high vacuum. It is shown that the polytherms of the electron work function for the pure components and alloys decrease by a linear law with increasing temperature. Based on the experimental data obtained, it is concluded that the concentration dependence of the EWF for the binary Rb-Cs system has a linear (additive) character within the limits of experimental error (about 1%). The presence of the azeotropic point on the state diagram of the system is not visualized in the concentration dependence of the work function.