We report the results of an experimental study of polymer bulk material Polyamide-6 luminescence properties. A new effect of persistent time-delayed luminescence was revealed at room temperature. Detailed inspection of the effect has shown strong dependence on the microscopic crystalline structure of the polymer. Two morphological forms were recognized with the aid of X-ray Bragg reflection treating. The afterglow with the decay time exceeding 10 seconds was found to appear at about 150 K for the γ-form and is observed at room temperature for the α- form. The temporal dependence of time-delayed luminescence was found to satisfy hyperbolic Becquerel law, thus indicating the recombination origin of the effect. Also, emission realized with the excitation by third optical harmonics of a femtosecond Ti:Sapphire laser (267 nm) at room temperature was examined. The registered luminescence spectra were found quite different for these forms. While γ-form samples exhibit spectrum at the visible region, the α-form emits a pronounced luminescence output in the near UV (340 nm).

We report on the observation of time-delayed luminescence of bulk Polyamide-6 polymer material under the room temperature and liquid nitrogen temperature conditions. The excitation was taken from low power diode laser operating at the wavelength 407 nm. The afterglow duration amounts up to several seconds and the decay function was found to coincide with the Becquerel hyperbolic law. The conclusion that we have made with account of the results obtained is the charge-recombination origin of this effect.

Interaction of oxygen with the Mo(1 1 2) surface precovered by submonolayer beryllium films with various coverage degrees (θBe < 1) has been investigated by Auger electron spectroscopy, LEED and contact potential difference techniques. We have studied the effect of Be coverage degree on the oxygen adsorption kinetics, atomic structure and electronic properties of the O/Be/Mo(1 1 2) system. Contrary to the case of full-monolayer Be precoverage (θBe = 1), beryllium submonolayers can speed up the initial adsorption kinetics of oxygen by a factor of 10. The high sticking coefficient of oxygen on the Be/Mo(1 1 2) surface at θBe < 1 can be explained by the existence of areas on Mo(1 1 2) that are free of Be and provide fast oxygen adsorption, with O adatoms migrating further to the areas covered with Be (the spillover effect). The creation of beryllium oxide even on limited surface areas substantially decreases the oxygen sticking coefficient. This effect may originate from the surface deformation due to a structural misfit between the Be/O layer and the substrate. The coadsorbed Be/O layers with θBe < 1 modify the work function to values between those specific of the O/Be/Mo(1 1 2) systems with θBe = 0 and 1, which complies with the heterogeneous adlayer model.

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 S O on Be/Mo (112) is lower by a factor of ~1/15 than on the clean Mo (112) surface where S O is close to unity. However, with increasing the oxygen coverage above θ O ≈ 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 T an  = 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 T an  = 1600 K, above which they dissociated with desorption of Be.

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

Low-energy electron diffraction, Auger electron spectroscopy and contact potential difference methods have been used to study formation of Be overlayers on the Mo(1 1 2) and (0 1 1) surfaces in the temperature range from T = 78 K up to the beginning of Be desorption. At a coverage θ = 1, where θ is defined as the ratio between concentrations of adatoms and surface substrate atoms, overlayers were found to be pseudomorphic on both the substrates. Various types of close-packed Be structures were observed at θ > 1. Annealing of the Mo samples covered with Be caused not only overlayer ordering, but also a partial solution of Be in the near-surface layer of Mo and creation of a surface alloy. It is inferred that the work function changes, positive on Mo(1 1 2) up to 0.4 eV and negative on Mo(0 1 1) down to − 0.6 eV, are caused mainly by changes in surface roughness while the contribution of polarization of the BeMo adsorption bond seems to be only minor.

Low-energy electron diffraction, scanning tunneling microscopy, contact potential difference, and Auger electron spectroscopy methods are used to observe the formation of surface alloys during annealing of Dy, Gd, Sr, and Be monolayers adsorbed on Mo(112) surfaces. Surface alloys develop as a nanodispersed system of oligomeric clusters in the Dy and Sr films and as a continuous covering in the Be and Gd films. It is shown that Dy films, which form a Dy-Mo surface alloy on annealing, will enter a two-dimensional glassy state after cooling (quenching) to low temperatures, while the surface alloys of Be and Gd are formed in a crystalline state.

Low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and contact potential difference (CPD) methods have been used to investigate the structure of Gd monolayers deposited on Mo(112) at T = 78 K and the changes upon annealing in a wide temperature range, up to the beginning of desorption. In the submonolayer coverage range (θ < 0.67), the film structures p(1.3×1) and p(2×1) already formed at T = 78 K, testifying that Gd adatoms possess some mobility at rather low temperatures. The p(1.3×1) structure was found to appear at 0.07 < θ < 0.25, but it irreversibly turned into the p(2×1) structure when the annealing temperature, Tan, exceeded 500 K. Above θ = 0.25, the p(2×1) structure emerged immediately at 78 K. Formation of step arrays was observed in the range of Tan = 500–1200 K and is attributed to surface alloying. The suggestion of surface alloying is corroborated by data on annealing induced variations of the work function and Auger peak of Gd. In the coverage range 0.5 < θ < 0.67, the phase p(2×1) was found to coexist with the phase c(1.5×2), which corresponds to a physical monolayer. No evidence of surface alloy in the complete monolayer was revealed. Distinction between ordering scenarios for the systems Gd/Mo(1 1 2) and Dy/Mo(112) is discussed.

Using the experimental results obtained for the Dy–Mo(112) system, we discuss the possibilities and mechanisms of formation of two-dimensional (2D) glasses on metal surfaces. It has been found that in the coverage range 0.07<θ<0.58, ordered Dy superstructures formed and observed at T<400K are irreversibly destroyed by annealing to higher temperatures and turn into an amorphous (glass) structure on cooling. It is supposed that this conversion is caused by the formation, at T>400K, of a Dy–Mo surface alloy in which the rate of Dy surface diffusion is strongly reduced in comparison with its value in the absence of alloying. As a result, the mobility of Dy adatoms becomes too low at the temperatures corresponding to the ordered equilibrium state of the surface, and this state cannot be achieved in reasonable relaxation time. This interpretation is corroborated by the experimental data on substantial suppression of surface diffusion in some coadsorbed layers. Since surface glasses contact with ordered (crystalline) substrates, their structure may have a peculiar character different from that of “conventional” metal glasses. Surface glasses can find a number of applications as rather stable systems that combine low dimensionality, specific electronic structure of their constituents and extremely high density of defects.

The methods of the static skin effect and transverse electron focusing were used to study the reflection of electrons from an atomically clean surface of a tungsten crystal and from a surface containing adsorbed atoms and molecules. It was found that the specular reflectivity p for the atomically clean (110) face is 0.55–0.6 and p = 0.2−0.3 for the (100) face of tungsten; both methods give the same result when estimating the value of p. It was also shown that conduction electrons are diffusely reflected from (110) and (100) faces coated with a monolayer of adsorbed atoms.

The resistivity rho of thin tungsten and molybdenum single-crystal plates has been studied at low temperatures (4.2--60 /sup 0/K). It is found that the interaction of conduction electrons with the metal boundaries is important in determining rho/sub d/(T) when the size effect is significant. The experimental data are used to evaluate the probability of specular reflection of electrons at the surface as a function of angle of incidence.

The surface impedance Z = R +jX (over the 5−10 MHz frequency range) and the static resistivity ρ of thin single-crystal tungsten wafers were studied in relation to the intensity of an external magnetic field and to the surface state of a specimen. The experiments were performed at liquid-helium temperature with wafers which had been cleaned and stored under high vacuum. The changes in Z and ρ which occur with increasing surface purity are interpreted here as a result of an increase in the specularity for conduction electrons interacting with the crystal boundary.