Emission of cadmium excited ions upon α particle bombardment

Ion emission due to the sputtering of metallic cadmium by α particles from ²³⁸Pu is studied. Experiments are carried out in helium at different cadmium foil temperatures (from 20 to 280°C) and gas pressures (from 75 to 2200 torr). The sputtering of the metallic cadmium causes the emission of Cd(II) excited ions in the 4d ⁹5s ²² D _{3/2, 5/2} and 4d ¹⁰6s ² S _1/2 states. Above 160°C, the population of these stares grows exponentially. At a temperature of 240°C and a helium pressure in the chamber of 600 torr, the sputtering ratio of metallic cadmium is found to be 6.26×10⁻¹⁴ g per α particle; i.e., one α particle knocks out about 10⁸ cadmium atoms from the foil. From spectroscopy and microphotography examinations of the metallic sample surface, a two-step model of ion emission is suggested. The model involves (1) the formation of a high-temperature wedge, which ejects a cadmium droplet, and (2) self-diffusion of displaced cadmium atoms in the droplet toward the surface.     

High sputtering yields of organic compounds by large gas cluster ions

We measured the sputtering yield, surface roughness and surface damage of thin leucine films bombarded with Ar cluster ions and examined the usefulness of large gas cluster ions for the depth profiling of organic compounds. Ar cluster ion beams with a mean size of 2000 atoms/cluster and energies from 5 to 30 keV were used. Sputtering yields increased linearly with incident ion energy and were extremely high compared to inorganic materials. Surface damage was investigated by measuring positive secondary ions emitted from the leucine film before and after cluster ion irradiation. After irradiation the leucine surface became smoother. The yield ratio of protonated leucine ions to other fragment ions kept constant before and after Ar cluster ion irradiation. These results indicate that large gas cluster ions are useful for depth profiling of organic compounds.     

Preferential sputtering of TIC under keV Ar+ ion bombardment: Simultaneous sputtering-ISS measurement with He+ and Ar+ ions

The composition change of the outermost atom layer of TiC(110) under ion bombardment with 1.5–3 keV He⁺ and He⁺ + Ar⁺ ions has been measured by ion scattering spectroscopy with He⁺ ions at different sample temperatures. It has been found that the preferential sputtering of C atoms takes place for both the He⁺ and Ar⁺ ion bombardment, however the preferred sputtering is more pronounced for Ar⁺ ions than for He⁺ ions. The ion bombardment with He⁺ ions at elevated sample temperatures hardly results in any change in surface composition below ～800°C, while Ar⁺ ion bombardment results in C enrichment for elevated temperatures as reported so far.     

Friction model to describe cluster bombardment

Short time molecular dynamics simulations were performed to model C₆₀ and Au₃ bombardment of an amorphous water sample in the projectile energy range of 5-120 keV. A previously proposed friction model has been applied to describe the fundamental motion of a projectile during cluster bombardment of a solid. This simple analytical model uses a definition of friction on a single particle to describe the cluster movement through a medium. Although the mathematics of the friction model vary among systems, the projectile motion and energy deposition of a single particle into the sample as well as the reactive environment created is close to that of C₆₀ bombardment.     

Indium tin oxide nanowires growth by dc sputtering

Indium tin oxide nanowires have been grown by dc sputtering on different substrates without the use of catalysts or oblique deposition. The nanowire length was of the order of several μm, while their diameter was ∼50–100 nm. Small side branches on the nanowires were frequently observed. The nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The growth mechanism of the nanowires is discussed.     

Step edge sputtering yield at grazing incidence ion bombardment

The surface morphology of Pt(111) was investigated by scanning tunneling microscopy after 5 keV Ar+ ion bombardment at grazing incidence in dependence of the ion fluence and in the temperature range between 625 and 720 K. The average erosion rate was found to be strongly dependent on the ion fluence and the substrate temperature during bombardment. This dependence is traced back to the variation of step concentration with temperature and fluence. We develop a simple model allowing us to determine separately the constant sputtering yields for terraces and for impact area stripes in front of ascending steps. The experimentally determined yield of these stripes--the step-edge sputtering yield--is in excellent agreement with our molecular dynamics simulations performed for the experimental situation.     

Synergetic approach to studying material sputtering under ion bombardment

The use of the synergetic approach to studying the sputtering of materials under ion bombardment is considered. The applicability of this approach is based on complete correspondence between the main concepts of ion sputtering and synergetics, i.e., the disequilibrium and nonlinearity of multiparticle processes. The systematic application of synergetic methods within a uniform approach allow us to analyze such characteristics as the formation of mass and energy distributions (mass and energy spectra), and to develop a universal approach to studying the processes of elastic displacements and thermal spike based on the principles of nonlinear dynamics. A conclusion is drawn regarding the usefulness of the synergetic approach to the whole spectrum of problems of radiation physics.     

Multiple processes during the sputtering of materials by ion bombardment

A new method of statistical analysis dedicated to filling the gap between dynamic and thermodynamic theories of secondary-particle emission under ion bombardment is proposed. Expressions for the average number of emitted atomic particles and electrons are obtained, and the relationships between their yields are established.     

Indium oxide thin-film holographic recorders grown by excimer laser reactive sputtering

2 O₃) thin films on glass substrates is performed by pulsed laser ablation of a metallic indium target in an oxygen atmosphere. X-ray diffraction analysis verifies that a transition, from amorphous to polycrystalline film growth, occurs at a temperature of 150 °C. Films grown under optimized conditions exhibit optical transmission higher than 80% in the visible light. Ultraviolet radiation (λ= 325 nm) induced dynamic holographic recording in films deposited at specific temperature and oxygen pressure settings is also demonstrated. Received: 25 April 1997/Accepted: 27 May 1997     

Indium zinc oxide thin films deposited by sputtering at room temperature

The deposition of amorphous indium zinc oxide (IZO) thin films on glass substrates with n-type carrier concentrations between 10¹⁴ and 3 × 10²⁰ cm⁻³ by sputtering from single targets near room temperature was investigated as a function of power and process pressure. The resistivity of the films with In/Zn of ∼0.7 could be controlled between 5 × 10⁻³ and 10⁴ Ω cm by varying the power during deposition. The corresponding electron mobilities were 4-18 cm² V⁻¹ s⁻¹.The surface root-mean-square roughness was <1 nm under all conditions for film thicknesses of 200 nm. Thin film transistors with 1 μm gate length were fabricated on these IZO layers, showing enhancement mode operation with good pitch-off characteristics, threshold voltage 2.5 V and a maximum transconductance of 6 mS/mm. These films look promising for transparent thin film transistor applications.     

Analysis of cardiac tissue by gold cluster ion bombardment

Specific molecules in cardiac tissue of spontaneously hypertensive rats are studied by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The investigation determines phospholipids, cholesterol, fatty acids and their fragments in the cardiac tissue, with special focus on cardiolipin. Cardiolipin is a unique phospholipid typical for cardiomyocyte mitochondrial membrane and its decrease is involved in pathologic conditions. In the positive polarity, the fragments of phosphatydilcholine are observed in the mass region of 700-850 u. Peaks over mass 1400 u correspond to intact and cationized molecules of cardiolipin. In animal tissue, cardiolipin contains of almost exclusively 18 carbon fatty acids, mostly linoleic acid. Linoleic acid at 279 u, other fatty acids, and phosphatidylglycerol fragments, as precursors of cardiolipin synthesis, are identified in the negative polarity. These data demonstrate that SIMS technique along with Au₃⁺ cluster primary ion beam is a good tool for detection of higher mass biomolecules providing approximately 10 times higher yield in comparison with Au⁺.     

Quasimolecular K X-ray excitation by bombardment of Ge atoms with Ge ions

By bombardment of Ge targets with ⁷⁴₃₂Ge⁵⁺ of 81 MeV, a continuous X-ray intensity distribution has been obtained, which ranges up to the K X-ray energies of ₆₄Gd. The shape of the spectra, corrected for the detector efficiency, confirms the assumption that this continuum is caused by K X-rays of Z = 64 quasimolecules, which are transiently formed during the adiabatic heavy-ion collision. The yield of quasimolecular radiation was determined to be about 4 x 10⁻⁵ X-rays per beam K-vacancy.     

The sputtering mechanism for low-energy light ions

The computer simulation program MARLOWE which follows the trajectories of energetic ions and recoiling target atoms in solids has been used to calculate sputtering yields for low energy (0.1–10keV) light ions (H, D, T,⁴He). Recoil energy densities were calculated for comparison with analytical theories. The sputtering yields obtained for amorphous Fe agree within a factor of two with experimentally measured values for polycrystalline stainless steel, while the calculated yields for protons on amorphous molybdenum are more than twice the experimental values on polycrystalline material. The calculations show that in the parameter range investigated, ions backscattered in the solid contribute a major part to sputtering. This result confirms earlier calculations of the threshold energy for sputtering which are in agreement with recent measurements. Operated for the United States Department of Energy by the Union Carbide Corporation.     

On the mechanism of cluster emission in sputtering

The intensity and the energy distribution of Si⁺_n cluster ions emitted from clean silicon have been measured for different target orientations as a function of the primary ion energy (3–30 keV) and the projectile mass (noble gas ion bombardment). The results favour the idea that clusters are emitted as such rather than being produced by vacuum recombination of individually emitted atoms and ions.     

Relative sputtering yields from close-packed directions in nickel under low-energy Ar bombardment

A new approach to low-energy sputtering was developed wherein a monoenergetic Ar⁺ ion beam of the order of 10⁻⁹ A impinged onto a crystalline nickel target. Target preparation consisted of plating about 100 monolayers of high specific activity Ni-63 onto a coldrolled nickel substrate and then heating the target above its recrystallization temperature under ultra-high vacuum. The result was a highly ordered polycrystalline structure which, when sputtered, behaved like the (100) surface of a nickel single crystal. Approximately 25 percent of the surface atoms were Ni-63. Sputtered material was collected on a molybdenum foil which was subsequently analyzed by radiotracer techniques.

Experimental results concerning sputtering from [110] and [100] close-packed directions in nickel under bombardment by Ar⁺ ions of energy 25 eV to 600 eV are reported. The relative sputtering yields from [110] directions are presented as a function of incident ion energy for 75° and 15° ion incidence measured with respect to the [110] directions, and the extrapolated thresholds are compared with theoretical predictions.

In addition to the expected deposits on the foil due to sputtering from individual closepacked directions, secondary deposits occurred which are attributed to specular reflection of sputtered nickel atoms from the molybdenum foil.     

Energy deposition,reflection and sputtering in hyperthermal rare-gas→Cu bombardment

Using molecular-dynamics simulation, we study the scattering and penetration of normally incident hyperthermal (5–400 eV) Ne, Ar, and Xe atoms off a Cu crystal. We find that between 80% and 98% of the incident energy is deposited in the solid; the fraction depends primarily on the projectile mass, and — for not too low energies — only slightly on the bombarding energy. At low energy, the major part of the non-deposited energy is carried away by the reflected projectile. At energies above the sputter threshold, an increasingly important contribution of between 2% and 6% of the incident energy is carried away by sputtered particles. These results compare well with experiment. Electronic inelastic losses show only little influence on this behaviour. We demonstrate that the inclusion of a realistic attractive interaction between the projectile and the target atoms influences the energy deposition considerably at energies below around 100 eV.     

Study of the physical sputtering of a carbon-ceramic composite by ion bombardment

The results of experimental study and computer simulation of SG-P-0.1 carbon-ceramic composite sputtering under 30 keV Ar⁺ ion irradiation at normal incidence are presented. A comparison with the simulation data shows that taking into account the nanometric wave-like relief well describes an approximately threefold increase in the sputtering yield observed in the experiment in comparison to the smooth surface calculation.