Computer simulation of thin nickel films on single-layer graphene

The energy, mechanical, and transport properties of nickel films on a single-layer graphene sheet in the temperature range 300 K ≤ T ≤ 3300 K have been investigated using the molecular dynamics method. The stresses generated in the plane of the metallic film are significantly enhanced upon deposition of another nickel film on the reverse side of the graphene sheet. In this case, the self-diffusion coefficient in the film plane above 1800 K, in contrast, decreases. An appreciable temperature elongation per unit length of the film also occurs above 1800 K and dominates in the “zigzag” direction of the graphene sheet. The vibrational spectra of the nickel films on single-layer graphene for horizontal and vertical displacements of the Ni atoms have very different shapes.     

Computer simulation of the xenon-cluster bombardment of mercury on graphene

The bombardment of a target with Xe₁₃ clusters with kinetic energies ranging from 5 to 30 eV and an incident angle of θ = 0° is studied using the molecular dynamics method. The target consists of mercury on partially hydrogenated imperfect graphene. The complete cleaning of a graphene sheet from mercury is not reached after 125 cluster impacts. The radial distribution functions and vertical density profiles indicate the formation of Hg monomer vapor around the bombarded target. The Hg film has a tendency to curl into a droplet. For all cluster energies, the Hg atom mobility and stresses in the Hg film in the horizontal directions are higher than in the vertical direction. The roughness of the graphene sheet increases continuously under bombardment.     

Computer stability test for aluminum films heated on a graphene sheet

The behavior of single- and double-sided monatomic aluminum films on graphene heated from 300 to 3300 K is studied by the molecular dynamics method. Atoms of single-sided coating are preserved on graphene up to 3300 K, while atoms of double-sided coating leave graphene even at 1800 K; upon a further increase in temperature, this leads to an increase in the horizontal and vertical components of the self-diffusion coefficient. The stresses produced by vertical forces are found to be most significant in metallic films; these stresses almost disappear when temperature reaches 2300 K. The stresses in graphene, the highest of which are concentrated in the zone of formation of the metal film, substantially decrease upon heating.     

Computer simulation of nanoindentation into polymer films

We present computer simulations of nanoindentation into amorphous polymer films. The bulk polymer is treated through a united atom model in connection with molecular dynamics methods. The dynamics of the indenter is modeled as overdamped, such that the indentation velocity is proportional to the difference between the external force acting onto the tool and the resistance force built up in the polymer film. We concentrate on the initial, kinetic stage of the indentation process and give results for the motion of the indenter, the deformation field of the polymer film, the stress field, and the field of total monomer energy. We propose an effective coefficient as a new measure for the resistivity of a surface against indentation. Its value can be determined in an experiment with constant indentation velocity. In addition, we investigate the free drift behavior when the external driving force has been set to zero and the tool is expelled from the polymer film. For different polymer chain lengths, the tool’s motion is exponential in time and we determine the relaxation scale.     

Computer simulation and study of radiation defects in graphene

Computer simulation has been used to study the properties of radiation defects in a graphene sheet. Several possible stable configurations of 3D radiation defects in graphene have been simulated. Several types of absorbed species were calculated involving a single carbon atom and a dumbbell absorbed at graphene sheet surface and a dumbbell configuration at a vacancy created by radiation knocking out a carbon atom. The calculations also included the effect of structural relaxation. The defect caused by the atom being displaced from the structure converted the sheet from metallic to semiconducting.     

Computer simulation of the bombardment of a copper film on graphene with argon clusters

The process of graphene cleaning of a copper film by bombarding it with Ar_(13) clusters is investigated by the molecular dynamics method.The kinetic energies of the clusters are 5,10,20,and 30 eV and the incident angles are θ= 90°,75°,60°,45°,and 0°.It is obtained that the cluster energy should be in the interval 20 eV-30 eV for effective graphene cleaning.There is no cleaning effect at vertical incidence(θ =0°) of Ar_(13) clusters.The bombardments at 45° and 90° incident angles are the most effective on a moderate and large amount of deposited copper,respectively.     

Spin-wave dispersion in two-layer magnetic films

The change in spin-wave resonance spectra in multilayer magnetic films occurring under the gradual transformation of a spin-pinned layer from the reactive medium into a dispersive state or vice versa is studied. Spatial spin-wave dispersion associated with the spin-pinned layer is established to occur. This dispersion is most markedly pronounced in films with a mixed mechanism of spin pinning. The dispersion observed allows the so-called effect of “repulsion” of spin-wave modes to be accounted for.     

数值模拟飞秒激光加热金属的热电子发射

研究了超短超强激光脉冲与薄膜靶相互作用中产生的电子热发射.当超短激光脉冲与薄膜靶相互作用时,首先入射超短脉冲激光对吸收深度内的自由电子进行热激发,接下来热激发电子将能量传递到附近的晶格,再通过电子和晶格二体系的热传导,以及电子晶格间的热耦合,将能量传递到材料的内部.因此,电子在皮秒级甚至更短的时间内不能与晶格进行能量耦合,使电子温度超出晶格温度很多,电子热发射就变得非常明显了.用双温方程联合Richardson-Dushman方程的方法对飞秒脉冲激光照射金属靶的电子热发射进行了研究,结果发现电子热发射对飞     

Modeling of femtosecond laser damage threshold on the two-layer metal films

The heating processes of the single-layer gold thin film and the two-layer film assembly of gold padded with other metal (silver, copper and nickel) irradiated by femtosecond laser pulse are studied by the two-temperature model. It is found that the substrate metal can change energy transport, which is corresponding to the temperature changing process, and the thermal equilibrium time. Compared with the single-layer gold film at the same laser fluence, the two-layer film structure can change the damage threshold of the gold surface. Our results indicate that we can maximize the damage threshold of the gold film surface by altering the thickness ratio of the gold layer and the substrate layer in the two-layer film assembly.     

Electrodeposition of epitaxial nickel films on GaAs

The structural and magnetic properties of Ni films grown by electrodeposition from simple sulfate solutions directly onto the (0 0 1) and (0 1 1) surfaces of n-GaAs have been studied. In-plane X-ray diffraction has been used to show that Ni grows on (0 0 1) GaAs with two different preferred epitaxial relationships: (1) perpendicular to plane (0 0 1)_Ni(0 0 1)_GaAs and preferred orientation in-plane [1 0 0]_Ni[1 1 0]_GaAs and (2) perpendicular to plane (0 1 1)_Ni(0 0 1)_GaAs and preferred orientation in-plane [1 1 1]_Ni[1 1 0]_GaAs. Nickel films grown on (0 1 1) n-GaAs show only a single preferred growth relationship: perpendicular to plane (1 1 1)_Ni(0 1 1)_GaAs and in-plane [1 1 0]_Ni[1 1 0]_GaAs. The magnetic properties were strongly dependent on the substrate orientation. The films grown on GaAs (0 0 1) showed a small but definite four-fold magnetic anisotropy in plane with the highest remanence being found along the GaAs [1 0 0] direction. In contrast, the Ni films grown on the (0 1 1) GaAs showed a pronounced uniaxial anisotropy with an anisotropy field of approximately 500 Oe.     

Influence of layer thickness on Neel coupling energy of two-layer magnetic films

The torsional-vibration method is used to investigate the relationship between Neel-type magnetostatic coupling and the thickness of the dielectric interlayer in two-layer Co¦SiO¦FeNiCo magnetic films. A comparison is made with the Neel theory, and qualitative agreement is obtained for a layer 200 Å thick. The observed discrepancy between experimental and theoretical values for thin layers is explained by exchange interaction between magnetic layers.     

Temperature of phase transitions in thin two-layer metal films

It is experimentally established that the melting temperatures of Pb/Bi, Pb/Sn, Mg/Sn, Sn/Zn, and In/Zn two-layer films decrease with a decrease in their thickness.     

Measurement of magnetostatic coupling in two-layer ferromagnetic films on a transverse-field magnetometer

A procedure is described for measuring the magnetic properties of two-layer ferromagnetic films on a magnetometer with a transverse field. Measurements of positive and negative coupling between ferromagnetic layers separated by a nonmagnetic layer are reported.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 93–96, September, 1969.     

Ferromagnetism of fcc iron films grown on nickel

Polycrystalline multilayers of Fe-Ni produced by thermal evaporation are studied; some results obtained by a vibrating sample magnetometer, Mössbauer spectrometer and X-ray diffractometer are reported and discussed. Fe seems to grown on Ni with fcc structure. Fe atoms at the Ni/Fe interface seem to have localizated magnetic moments depending on the crystallographic orientations of the grains of the substrate; the remaining Fe atoms between the two interfaces appear as highly susceptible metal.     

Adsorption of carbon monoxide on polycrystalline nickel films

The adsorption states of carbon monoxide on polycrystalline nickel films have been investigated by measuring the thermal desorption, the heat of adsorption, the change in resistivity, and the change in work function in dependence on coverage and temperature. It can be shown that there are two chemisorbed (β₂, β₂) and one weakly bound (γ) species. Desorption peaks appear at 170K, 310–360 K, and 460–490 K. The differential heat of adsorption is $\text{30}\text{kcal}\text{mole}$ at low coverages and approximately $\text{25}\text{kcal}\text{mole}$ between 0.3 and 0.6 monolayers. The resistivity of the nickel film is characteristically changed with increasing coverage, and there is a maximum of resistivity at half a monolayer. At low coverages the increase in the work function is proportional to the amount adsorbed; at a monolayer the total increase is 1.26 eV at 77 K and 1.46 eV at 273 K. The two chemisorbed species differ only in the structures they form in the adsorption phase, β₂ being the species that is stable at low coverages, β₁ being the species that is stable at high coverages. These results are in good agreement with those recently found for CO adsorption on single crystal surfaces.     

Properties of oxide films on nickel contact surfaces

The possibilities of changing the conductivity of surface films during electrolysis are studied. The results of experimental research into films on nickel contacts are presented. From a comparison of ellipsometric, X-ray diffraction, and Auger-spectrum measurements of nickel coating surfaces obtained from electrolytes with organic components, it is revealed that the structure and composition of the surface films undergo changes which result in a decrease in the contact resistance. This makes it possible to employ such films in low-current contacts instead of silver or silver-alloy coatings.     

Influence of the heating temperature on the properties of nickel doped TiO2 films prepared by sol-gel method

Formation and properties of nickel doped TiO₂ films prepared by sol-gel method were studied using X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and energy dispersive X-ray analysis. The results demonstrate that sizes of TiO₂ crystallites increase with increasing heating temperature. Also, at temperatures above 800 ° C diffusion of nickel onto the surfaces results in increased concentrations of nickel compounds on the surfaces. Similar to pure TiO₂ films the light-induced modification of hydrophilicity is observed also in the case of nickel doped TiO₂ films.