High-temperature surface diffusion of copper on the (112) face of tungsten under condition of film-layer growth of adsorbed film

The phase state of the epitaxial Cu film on W(112) face has been investigated by the method of the contact difference of potentials under condition of film-layer growth. We have determined desorption heat, critical temperature and critical coverage experimentally. The phase diagram has been plotted as well as the temperature dependence of heat of a two-dimensional phase transition “liquid – gas” has been obtained. An exponent of order parameter has been found. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2097

Surface Diffusion and Phase Transitions in Ultrathin Films with Quasi-One-Dimensional Long-Period Structures

The kinetics of surface diffusion in a submonolayer film with the structure p(1 × 4) on the (112) bcc crystal surface in the region of a second order phase transition is investigated by molecular dynamics method. It is shown that collective effects play an important role in the surface diffusion within films where long-period chain structures are present. This is due to the strong anisotropy of the surface atomic structure and lateral interaction of adatoms. Adatom chains which form a superstructure p(1 × N) block the path of easy diffusion of individual atoms along the substrate grooves. With increasing temperature, the diffusion coefficients increase rapidly because of the emergence of new vacancies in the chains. Domains of a chain-like structure incommensurate with the substrate are formed in the adsorbed film when passing through the critical temperature. The activation energy for diffusion decreases sharply at temperatures above the critical one. The commensurate islands gradually disappear in the presence of the incommensurate structure as the temperature increases. This increases the number of defects in the incommensurate chain structure. Collective effects in the adsorbed film play an important role even at high enough temperatures owing to fluctuations and destruction of interacting segments of the adatom chains. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3501

Adatom interaction effects in surface diffusion

Motivated by recent research of Nikitin et al. [J. Phys. D: Appl. Phys., 2009, 49, 055301], we examine the effects of interatomic interactions on adatom surface diffusion. By using a mean-field approach in the random walk problem, we derive a nonlinear diffusion equation and analyze its solutions. The results of our analysis are in good agreement with direct numerical simulations of the corresponding discrete model. It is shown that by analyzing a time dependence of adatom concentration profiles one can estimate the type and strength of interatomic interactions.Мотивованi недавнiми дослiдженнями Нiкiтiна та iн. [J. Phys. D: Appl. Phys., 2009, 49, 055301], ми вивчаємо вплив мiжатомних взаємодiй на адатомну поверхневу дифузiю. Використовуючи середньо-польовий пiдхiд у проблемi випадкових блукань, ми виводимо нелiнiйне рiвняння дифузiї i аналiзуємо його розв’язки. Результати нашого аналiзу добре узгоджуються з прямими числовими симуляцiями вiдповiдної дискретної моделi. Показано, що, аналiзуючи часову залежнiсть профiлiв адатомної концентрацiї, можна оцiнити тип i силу мiжатомної взаємодiї

Low-field electron emission and cathode luminescence of piezoelectric films of oxides and chalcogenides

Basic parameters of effective low-field emitters of electrons of piezoelectric films for bright flat cathode luminescent display and other activity are optimised. Specimens of electron emitters of cathode luminescent screens are based on compounds of SiO₂, ZnO, ZnS, solid solution of Zn1-xCdxS. High efficient "cold" emitters of electrons were prepared on the basis of mono- and polycrystalline films. The emission and cathode-luminescent properties of the films were investigated. It is shown that developed films are perspective like the flat displays with the brightness of 300 Cd/m²

Quantum effects in multilayer Si-Ge nanoheterostructures

The lateral photoconductivity spectra and photofield electron emission were used to investigate multilayer Ge/Si heterostructures with Ge quantum dots. Earlier we have revealed a close connection between elastic strain in Ge quantum dots originating due to the lattice mismatch during the epitaxial growth and additional energy level forming in the strained Si-Ge heterojunction region. Thus, it appeared to be possible observing intraband transitions in Ge quantum dots that are absent in two-dimensional Si-Ge heterostructures using such simple and informative methods. While an influence of the number of Ge quantum dot layers on lateral photoconductivity spectra is not essential, the photofield electron emission characteristics showed considerable shift to middle infrared area, as the number of Ge quantum dot layers increased. It was revealed that size and composition parameters of Ge quantum dots correspond to energy levels in the valence band of the latter with the energy distance between them about 0.32 and 0.34 eV with a high accuracy. The results of our investigation make it possible to expect their possible application in new nano- and optoelectronic devices.Методами фотопольової емісії та повздовжньої фотопровідності було досліджено багатошарові наногетероструктури з квантовими точками германію. Попередні дослідження показали тісний зв'язок пружних напружень, що виникають при епітаксійному рості матеріалів з різними постійними граток, з виникненням додаткових рівнів в зоні такого гетеропереходу. Таким чином, відносно простими але інформативними методами спостерігалися міжзонні переходи, які відсутні в двовимірних гетероструктурах Si-Ge. Якщо вплив кількості шарів на фотопольову емісію несуттєвий, то при дослідженні фотопровідності виявлено прямий зв'язок зсуву чутливості повздовжньої фотопровідності в середній інфрачервоний діапазон від кількості шарів з квантовими точками германію. Показано, що розмірні характеристики та мольний склад квантових точок відповідають енергетичним рівням з енергетичною відстанню між ними приблизно 0,32 та 0,34 еВ з дуже високою точністю. Результати досліджень дозволяють сподіватися на їх використання в перспективних приладах нано- та оптоелектроніки

Ground states of a one-dimensional lattice-gas model with an infinite range nonconvex interaction. A numerical study

We consider a lattice-gas model with an infinite range pairwise noncovex interaction. It might be relevant, for example, for adsorption of alkaline elements on W(112) and Mo(112). We study a competition between the effective dipole-dipole and indirect interactions. The resulting ground state phase diagrams are analysed (numerically) in detail. We have found that for some model parameters the phase diagrams contain a region dominated by several phases only with periods up to nine lattice constants. The remaining phase diagrams reveal a complex structure of usually long periodic phases. We also discuss a possible role of surace states in phase transitions.Comment: 16 pages, 5 Postscript figures; Physical Review B15 (15 August 1996), in pres

Adsorption of oxygen on Mo (112) surface precovered with beryllium: formation of overlayer and electronic properties

Adsorption of oxygen on the Mo (112) surface precovered with a pseudomorphic monolayer of beryllium has been investigated at room temperature by AES, LEED and contact potential difference methods. Such a Be/Mo (112) substrate is actually a bimetallic surface where closely-packed atomic Mo ridges alternate with rows of Be atoms. It has been found that at small oxygen exposures (Q < 0.3 Langmuir), the initial sticking coefficient for oxygen SO on Be/Mo (112) is lower by a factor of ~1/15 than on the clean Mo (112) surface where SO is close to unity. However, with increasing the oxygen coverage above θO ≈ 0.1, the sticking coefficient showed a nonlinear growth, and oxygen saturation of the surface was achieved at Q = 1.6–1.7 L. Oxygen adsorption decreases the work function of the Be/Mo (112) surface and gives rise to appearance of some Auger peaks specific to beryllium oxide, which indicates a change in the chemical nature of the surface. The formation of a polar-covalent BeO compound may be responsible for a self-activation of the surface with respect to oxygen which is reflected in the increase of the sticking coefficient observed under growth of oxygen coverage (a kind of autocatalytic reaction). Annealing of the O/Be/Mo (112) system to Tan = 1100 K resulted in an additional decrease of the work function and a growth of the ratio between the Auger signals of Be in the oxide and metallic Be adsorbed phases. The presence of BeO molecules was detected up to Tan = 1600 K, above which they dissociated with desorption of Be

Oxygen submonolayers on Mo(112): structure and work function

Correlation between the work function change and the structure of oxygen submonolayers on the Mo(112) surface are studied using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and contact potential difference (CPD) methods. Oxygen was adsorbed at temperatures T = 78−300 K and thereafter the adlayers were annealed in a wide temperature range up to oxygen desorption. Temperature induced irreversible and reversible phase transitions are investigated. With coverage growth, formation of the monolayer proceeds through three first-order phase transitions, one of which is featured by a specific change in the course of the work function dependence on coverage. It is suggested that during this transition the oxygen adatoms may change their sites on the substrate from those of a short-bridge type to quasi-threefold ones, thus increasing their coordination number from two to three