How the thickness of a liquid helium film influences the spectrum of electrons localized above its surface

We consider the problem of finding the energy spectrum of electrons localized above the surface of a liquid helium film under the electrostatic attraction of induced charges. We show that the forces of attraction to the charges induced on the surface of a conductor located beneath the film begin to additionally influence the forces of attraction of the electrons to the free liquid surface as the film thickness decreases. When the film thickness becomes less than 10μm, this influence causes a significant increase in the energy difference between the lower levels and a decrease in their depth. We suggest a numerical method for solving the problem and present the results of our calculations of the energy spectrum of electrons localized above the surfaces of liquid ³He, ⁴He, and neon films. The influence of the pressing electric field on the energy spectrum is considered.     

Resonance fluctuation-electromagnetic energy losses during the glancing reflection of a neutral atomic beam from the smooth amorphous surface of a solid

The energy losses of a Cs⁺ion beam are theoretically studied during its glancing reflection from a smooth amorphous surface of a dielectric or a semiconductor and films made of these materials on a metallic substrate. The conditions of resonance fluctuation-electromagnetic interaction between neutralized Cs atoms and surface polaritons are considered for surfaces where the effects of interest seem to be the most significant. Calculations indicate that, at the optimized initial glancing angle and the Cs⁺ ion beam energy (ψ_in = 0.1–1.0 mrad, E ₀ ～ 50–100 keV), the fluctuation-electromagnetic forces substantially contribute to the total energy losses and this contribution has characteristic dependences on the temperature, particle velocity, and material parameters.     

Formation of an energy cascade in a system of vortices on the surface of water

The formation of an energy cascade in a system of vortices generated by perpendicular standing waves with a frequency of 6 Hz on the water surface has been experimentally studied. It has been found that peaks appear on the energy distribution over wave vectors E(k) after switching on pumping. These peaks are transformed with time because of the energy redistribution over scales. The stationary distribution E(k) established 300 s after switching on pumping can be described by a power-law function of the wave vector E(k) ～ k^1.75. It has been shown that waves with frequencies of about 18, 15, 12, 9, and 3 Hz appear on the surface of water owing to the nonlinear interaction at the excitation of a 6-Hz wave. It is assumed that the energy cascade of the turbulent motion in the wave vector range of 0.3–5 cm^?1 is formed by the nonlinear interaction between vortices generated by all waves propagating on the surface and direct energy fluxes toward high wave vectors dominate.     

Peculiarities of the capacitance-voltage characteristic of a photoelectric solar energy convertor based on a silicon p-n junction with a porous silicon antireflection coating

Experimental results on the high-frequency capacitance-voltage characteristic of a photoelectric solar energy converter based on the n ⁺-p junction with a thin porous silicon film on the frontal surface are considered. It is shown that the capacitance-voltage characteristic is determined by the surface metal-insulator-semiconductor (MIS) structure formed as a result of growing of a porous silicon layer by electrochemical anode etching. The effective thickness of the insulator layer of the MIS structure, the impurity concentration in its semiconductor region, and the density of surface states are determined.     

On the surface properties of a nanodiamond

The dependences of the specific surface energy, the surface tension, and the surface pressure on the size, the surface shape, and the temperature of a nanodiamond with a free surface have been investigated using the Mie-Lennard-Jones interatomic interaction potential. The nanocrystal has the form of a parallelepiped faceted by the (100) planes with a square base. The number of atoms N in the nanocrystal varies from 5 to ∞. The isothermal isomorphic dependences of the specific surface energy, its isochoric derivative with respect to the temperature, the surface tension, and the surface pressure on the nanodiamond size have been calculated at temperatures ranging from 20 to 4300 K. According to the results of the calculations, the surface energy under this conditions is positive, which indicates that the nanodiamond cannot be fragmented at temperatures up to 4300 K. The surface pressure for the nanodiamond P _sf (N) ∼ N ^−1/3 is considerably less than the Laplace pressure P _ls (N)^−1/3 ∼ N ^−1/3 for the same nanocrystal at the given values of the temperature, the density, and the number of atoms N. As the temperature increases from 20 to 4300 K, the lowering of the isotherm P _sf (N) is considerably more pronounced than that of the isotherm P _ls (N). At high temperatures, the isotherm P _sf (N) changes the shape of the size dependence and goes to the range of extension of small nanocrystals. It has been demonstrated that the lattice parameter of the nanodiamond can either decrease or increase with a decrease in the nanocrystal size. The most significant change in the lattice parameter of the nanodiamond is observed at temperatures below 1000 K.     

Generation of a fast-ion beam upon the interaction of a multiterawatt picosecond laser pulse with a solid target

The parameters of fast particles generated upon the interaction of 10¹⁹ W/cm² laser pulses with solid targets are studied. The spatial and energy parameters of fast ions are investigated. It is found that approximately 1–3% of the laser energy is transformed to the energy of mega-and submegaelectronvolt ions at laser pulse intensities ≥10¹⁸ W/cm². It is shown experimentally that an ion beam is directed perpendicular to the target surface. The analytic and numerical simulations agree with experimental results and predict the propagation of fast electrons in the mirror direction with respect to the incident laser beam and of ions perpendicular to the target. The theoretical calculations are compared with the experimental output and spectra of fast electrons and ions.     

Formation of relief on a metallic target surface under the action of compression-plasma flows

The results of experimental and theoretical investigations of relief formation on the surface of a steel target (grade St 3 steel, GOST (State Standard) 380) during treatment by compression-plasma flows are represented. The density of energy absorbed by the target varied in the range from 15 to 25 J/cm², the pulse duration was 100 μs, and the pulse number was N = 1, 3, 5, 7. The experiment revealed the expansion of boundaries of the central area (the area on which the plasma flow is incident normally to the surface) with increasing pulse number. This is explained by the more uniform surface treatment at a greater pulse number. It is shown that to describe relief formation in the central area there is a need to take into account the pressure of the plasma flow on the target surface, apart from surface tension forces and energy dissipation due to viscosity.     

The scattering of hydrogen from a cesiated tungsten surface

The reflection of protons from a partially cesiated tungsten surface is studied in the energy domain between 100 and 2000 eV and in the angular domain between 75° and 85° with respect to the surface normal. The study is performed by measuring the angular and energy distribution of the scattered negative ions. The reflection can take place along two paths. One path is reflection from the cesium surface layer, the other one is reflection from the tungsten substrate. A dependence of the final charge state on the path is observed. It is inferred that this phenomenon is due to incomplete neutralization of the protons scattered from the cesium layer. The energy loss of the reflected ions cannot be accounted for by using only the binary collision model. Also the electronic stopping of the atoms by the metal electrons is shown to be an important energy loss mechanism. Total conversion measurements of H⁺ to H^- combined with the measurements of the negatively charged fraction of the scattered particles, as reported in the proceeding paper, yield the particle reflection coefficient as a function of the angle of incidence. These reflection coefficients show that for angles of incidence less than 75° already more than 50% of the particles do not reflect from the surface. Total conversion efficiency measurements with H^- ions as primary ions show that the influence of the initial charge state on the total conversion is very small.     

Sputtering yields for light ions as a function of angle of incidence

The sputtering yield of Ni, Mo, and Au have been measured at oblique angles of incidence for H⁺-, D⁺-, and⁴He⁺-ion irradiation in the energy region from 1 to 8 keV. The yields were determined from the weight loss of the targets. For Ni and Mo the dependence of the sputtering yield on the angle of incidence was found to be much stronger for H⁺- and D⁺-ion than for⁴He⁺-ion irradiation. In all cases the maximum in the yield was found at angles of incidence ϑ≧80°, where ϑ is the angle measured from the surface normal. Furthermore the ratio of the maximum yield to the yeild at normal incidence increases with increasing surface binding energy of the target material as well as with increasing ion energy in the energy region inveestigated. The results are discussed qualitatively in view of a model for the sputtering mechanism for light ions.     

The effect of bombardment with neutralized neon ions on the roughness of a fused silica and beryllium surface

The effect of Ne ion beam etching on the roughness of materials for optical substrates—fused silica and beryllium—is studied. It is shown that the treatment of a fused silica surface by neutralized Ne ions with an energy of 400–800 eV makes it possible to smooth roughnessed in the range of higher spatial frequencies of 3–63 μm^–1 at an incidence angle of 0°–30°. For beryllium, the possibility of smoothing the surface roughness at an ion energy of 400 eV is found.     

Effect of the dose and energy of Ar+ ions on the surface properties of vanadium and its alloys

The features of processes occurring on the surface of vanadium and its alloys irradiated using the ILU ion-beam accelerator with Ar⁺ ions at an energy of 20 and 40 keV up to doses of 5.0 × 10²¹ m^?2 and 1.0 × 10²² m^?2 at T _irr ≈ 700 K are studied. The effect of the dose and energy of implanted ions on the surface hardness is obtained. The thickness of the hardened layer is more than two orders of magnitude higher than the theoretical and experimental projected range of Ar⁺ ions at an energy of 20 and 40 keV in vanadium. Structural changes in the surface layers, which are expressed in a change in the intensity of reflections from a number of planes and an increase in the crystal-lattice parameter of the irradiated materials, are also observed.     

Initiation of ecton processes by interaction of a plasma with a microprotrusion on a metal surface

Evolution of rapid (～10 ns) Ohmic overheating of a microprotrusion on a surface in contact with a plasma by emission current is studied taking into account the energy carried by plasma ions and electrons, as well as Ohmic heating, emissive source of energy release (Nottingham effect), and heat removal due to heat conduction. Plasma parameters were considered in the range of n = 10¹⁴?10²⁰ cm^?3 and T _e = 0.1 eV?10 keV. The threshold value of energy transferred to the surface from the plasma is found to be 200 MW/cm²; above this value, heating becomes explosive (namely, an increase in the temperature growth rate (δ² T/δt ² > 0) and in passing current (δJ/δt > 0) is observed in the final stage at T ～ 10⁴ K and j ～ 10⁸ A/cm²). In spite of the fact that Ohmic heating does not play any significant role for plasmas with a density lower than 10 18 cm^?3 because the current is limited by the space charge of electrons, rapid overheating of top of microprotrusion is observed much sooner (over a time period of ～1 ns) when the threshold is exceeded. In this case, intense ionization of vapor of the wall material leads to an increase in the plasma density at the surface, and the heating becomes of the Ohmic explosion type. Such conditions for the formation of a micr?xplosion on the surface and of an ecton accompanying it can be created during the interaction of a plasma with the cathode, anode, or an insulated wall and may lead to the formation of cathode and anode spots, as well as unipolar arcs.     

The structure of a stepped copper (410) surface determined by ion scattering spectroscopy

Ion Scattering Spectroscopy applied in the multiple scattering mode is used to determine the structure of a stepped Cu(410) surface. The energy of singly scattered ions is influenced by the presence of neighbour surface atoms. This effect can be used to determine interatomic distances up to about 10Å, as is shown by the results of 8 keV Ar⁺ and 11 keV Ne⁺ scattered through θ = 50°. The edge-edge distance of the stepped copper surface appears to be in accordance with the results of LEED experiments obtained by other investigators. The experiments show a good agreement with the results of the analytical 3-atom model of Poelsema. The energy of the so-called “plateau collision” appears to depend on the effective plateau length l as measured in the plane of incidence. Lengths l between 15 and 60 Å can be determined with an accuracy of 5 Å. Results are shown for 8 and 12 keV Ar⁺, θ = 40° and 60°, and 8 keV Kr⁺ θ = 40°. The experimental dependence of the energy on lis described correctly by a phenomenological model.     

Properties and structural state of the surface layer in a zirconium alloy modified by a pulsed electron beam and saturated by hydrogen

A pulsed action of an electron beam on a Zr-1% Nb zirconium alloy is studied. Alloy samples are irradiated by three 50-μs pulses at an energy density of 15–25 J/cm², a power of (3–6) × 10⁴ W/cm², a current density of 10–50 A/cm², and an electron energy of 18 keV. This method of processing is found to modify the surface layer of the alloy without changing the structure-phase state of its volume. This surface modification increases the hydrogen saturation resistance of the alloy.     

Microwave discharge on a dielectric surface in vacuum

The paper describes the results of investigation of a discharge arising in vacuum on the surface of solid dielectric materials when irradiated by intense (up to 25 MW/cm²) electromagnetic centimeter wave radiation. When the density of the microwave energy flux exceeds some threshold value depending on the target material, a discharge emerges in the vicinity of the surface. Its emergence is associated with the evaporation of the target material and the breakdown of evaporated matter. The thus forming plasma initially has the form of a thin (on the wavelength scale) layer with the electron density of the order of 10¹⁶ cm^?3. It is demonstrated experimentally that effective generation of multiply charged ions occurs in the plasma. The measured energy distribution of ions in expanding plasma agrees with the predicted distribution obtained in solving the problem on quasineutral expansion into vacuum of a localized bunch of collisionless plasma with cold ions.     

Change in the relief of a target surface treated by compression plasma flows

The change in the surface relief of a steel-3 target (GOST 380) treated by compression plasma flows is experimentally studied. The energy density absorbed by the target varies in the range of 10–35 J/cm² and the pulse duration is 100 μs. It is shown experimentally and numerically that the development of KelvinHelmholtz instability strongly affects the formation of the target surface treated with compression plasma flows: a large-scale wave-like relief with characteristic sizes of 200 × 1000 μm is formed on the target surface and, as a result, the roughness of the surface increases. However, the microrelief at the scale of individual elements is smoothed to a maximum roughness of about 0.5 μm.     

Decay of capillary turbulence on the surface of a viscous liquid

Decay of the turbulence of capillary waves on the surface of a real liquid is studied in the presence of the viscous damping of the waves at all frequencies after stepwise removal of external pumping. The investigation is performed using two different models: the weak turbulence approximation and the local turbulence model in which the energy redistribution over frequencies is described by the polynomial expression in the wave-occupation number. It is shown that the decay of turbulence in the viscous liquid proceeds self-similarly and begins at high frequencies. In the decay process, the frequency distribution of the energy of waves is close to the stationary form E _ω ～ ω^?3/2 in a wide frequency range below the boundary frequency of the inertial range during a relatively long time after removal of the external force. The calculation results agree qualitatively with the results of the experiments on capillary turbulence on the charged surface of liquid hydrogen.     

State vector evolution localized over the edges of a square tight-binding lattice

We study the time evolution of a state vector in a square tight-binding lattice, focusing on its evolution localized over the system surfaces. In this tight-binding lattice, the energy of atomic orbital centred at surface site is different from that at the interior (bulky) site by an energy shift U. It is shown that for the state vector initially localized on a surface, there exists an exponential law (y=a\e^x/b+y₀) determined by the absolute value of the energy shift, |U|, which describes the transition of the state evolving on the square tight-binding lattice, from delocalized over the whole lattice to localized over the surfaces.     

Hyperthermal scattering of Cs from Pt(1 1 1): the effect of image charge on the ion-surface energy transfer

We have studied the energy exchange between hyperthermal (5-100 eV) Cs⁺ projectiles and a Pt(1 1 1) surface by measuring the kinetic energy of the scattered ions. The scattering geometry was chosen to be in-plane with specular scattering angles, and the energy of the scattered ions was analyzed as functions of incidence energy and angle. For low incidence energy (<40 eV), the energy transfer to the Pt surface is substantially enhanced due to the attractive image charge force between Cs⁺ and the surface. The image charge effects are highlighted by the different energy transfer on Pt(1 1 1) and Si(1 1 1) surfaces. Analysis of the experimental results using two- and three-dimensional theoretical models revealed a well depth of 1 eV for the image charge potential. Hyperthermal Cs⁺ ions scatter from Pt(1 1 1) predominantly via double collisions with Pt atoms, though the scattering phenomena are insensitive to the impact site at the surface.     

Mechanism of the direct three-body recombination of atomic ions in a central collision

The detailed dynamics of direct three-body recombination of the Cs⁺ and Br⁻ heavy ions in the presence of the Xe atom as a third body is studied by the quasiclassical trajectory method. A potential energy surface that quantitatively correctly describes the dynamics of the reverse process of ion formation induced by collisions of CsBr with Xe is used. Depending on the impact parameter of the third body, the stabilization of the product molecule proceeds by several different mechanisms. At impact parameters of b _R ≤ 7 au, the stabilization of the nascent molecule is largely controlled the repulsion potential between one of the ions or both the ions and the third body. The energy transferred to the third body does not depend directly on the repulsive potential energy between the ion and the third body. The phase of collision of the ions at the instant of closest approach plays a key role in the process of energy transfer. For collinear collision configurations of the three particles, the ion-Xe shallow potential wells are demonstrated to produce a noticeable effect.