Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation

Diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates using plasma deposition technique. The deposited films were irradiated using 2 MeV N⁺ ions at fluences of 1×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of 5×10¹⁵ ions/cm² show the lattice image with an average interplanar spacing of 0.34 nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.     

Study of the interaction of argon and nitrogen ions with the silicon dioxide surface

Angular dependences of the sputtering yield, surface layer composition, and changes in the mass spectra of residual atmosphere upon irradiation of silicon dioxide with argon and nitrogen ions are measured. It is found that the sputtering yield of SiO₂ bombarded by N ₂ ⁺ ions is almost two times higher than for Si. The sputtering yields of SiO₂ and Si irradiated with Ar ions are identical, although the binding energy of atoms in SiO₂ is almost two times higher than in Si. An analysis of the surface composition and residual atmosphere near the sample during its irradiation suggests that a chemical reaction is involved in SiO₂ sputtering. Molecules of SiO and NO gases form in the surface layer, whose subsequent desorption increases the SiO₂ sputtering rate.     

Low-density carbon material modified with pyrolytic carbon

Here we report a physicochemical investigation of low-density carbon materials modified with pyrolytic carbon (PC). Exfoliated graphite (EG) obtained by nitrate expandable graphite thermal destruction was pressed into low-density graphite materials (LDGMs) with densities of 0.045-0.50 g/cm³ and saturated with PC by impact CVI technique. LDGM infiltration with PC leads to sample weight and density growth. The amount of deposited PC strictly depends on synthesis conditions. The maximum surface and volume deposition of PC occurred for samples with density of 0.05 g/cm³. XRD, Raman spectroscopy and scanning electron microscopy revealed that the deposited PC is of smooth laminar (SL) type. Composite thermal conductivity is about 2-3.5 Wt/m K.     

On the dimerization of carbon dioxide in nitrogen and argon matrices

The ir spectrum of carbon dioxide in solid nitrogen and solid argon has been studied. In nitrogen, the NN stretching vibration becomes ir-active in the presence of carbon dioxide. Concentration dependency and diffusion studies allow the identification of a carbon dioxide dimer in solid argon. In solid nitrogen no clear evidence for a dimer was obtained.     

Modification and smoothing of patterned surface by gas cluster ion beam irradiation

Surface modification and smoothing of patterned surfaces with gas cluster ion beams were studied. In this work, line and space patterns having various intervals and depths were created on amorphous carbon films by focused Ga⁺ ion beams, and subsequently, Ar GCIB irradiations on the pattern were performed. When the acceleration voltage of Ar cluster ions was 20 kV, the grooves, whose interval was below 200 nm, were planarized. However, it required much higher ion dose for wider interval of patterns. It is estimated that the distance of lateral motions induced by one cluster ion impact defines the spatial wavelength dependence of smoothing.     

Optical transmittance spectroscopy of concentric-shell fullerenes layers produced by carbon ion implantation

Concentric-shell fullerenes, also called carbon onions, produced by carbon ion implantation into silver thin films, and subsequently deposited on a silica substrate, were studied by optical transmission spectroscopy in the wavelength range 0.2 - 1.2 μm. In this interval, the strongest absorption is due to the π-plasmon of sp²-like carbon. The position of the plasmon absorption band clearly evolved from 265 nm at low fluence to 230 nm at high implantation fluences. A simulation of the optical spectra based on dielectric models of the concentric-shell fullerenes layer allowed us to identify the first peak as due to disordered graphite and the latter to the carbon onions. The concentration of residual graphite and the filling fraction of the carbon onions produced at high fluences could be estimated by fitting the optical spectra with computed transmittance curves. Received 13 July 2000     

Erosion of solid surface under irradiation by high-power submicrosecond ion beams

The erosion of a solid surface under high-power pulsed ion beams is considered. The values of atom yield from an irradiated surface due to the evaporation are obtained by numerical simulation. The effect of beam parameters and target characteristics on atom emission intensity was investigated. The technological capabilities of high-power submicrosecond ion beams for solid surface etching are assessed.     

Study of surface morphology of ferrofluid deposited etched ion tracks in dielectric layers

An AFM study is reported on swift heavy irradiated Si/SiO₂ substrates which have been etched by aqueous hydrofluoric acid solution leading to ion tracks in which ferrofluids have been deposited leading to tunable electronic materials with pores in oxide on silicon (TEMPOS) structure. Two ferrofluids with different carrier fluids (aqueous and non-aqueous) have been deposited in the tracks. Atomic force microscopy has been used to study the empty as well as filled tracks. Since the ferrofluids contain iron oxide particles, there is a possibility of agglomeration of these particles inside and outside the tracks. Surface area and pore volume of the tracks have been measured by Brunauer-Emmett-Teller (BET) method. The track properties (empty and filled) as observed by AFM have been correlated with BET measurements.     

Study of near surface layer of graphite produced by nitrogen ion bombardment at high doses

To study the modified surface layers of graphites and deposited films of sputtered material, the dependences of sputtering yield Y , and ion-electron emission coefficient γ on ion incidence angle and target temperature under high dose 30 keV N⁺ ₂ ion irradiation have been measured. In the angular range θ=0-80° Y and γ increase approximately as inverse cosθ, Y of POCO-AXF-5Q are 1.5 times larger than of MPG-LT. The dependences of γ (T) manifests a step-like behaviour typical for the radiation induced phase transitions. EPR analysis shows that at near room temperatures the point electron defects are typical of carbon and the defects due to carbon atoms interacting with 14 N nuclei. At elevated temperatures (≥ 300°C) there are the defects typical of graphite-like structures. The films deposited on glass collectors shows for cold targets only the defects typical of carbon, for the heated graphites - also the defects associated with C-¹⁴N nuclei interaction.     

Two waveguide layers in lithium niobate crystal formed by swift heavy Kr ion irradiation

We report the formation of two waveguide layers in a lithium niobate crystal by irradiation with swift heavy Kr ions with high(Ge V) energies and ultralow fluences. The micro-Raman spectra are measured at different depths in the irradiated layer and show that the high electronic energy loss can cause lattice damage along the ion trajectory, while the nuclear energy loss causes damage at the end of the ion track. Two waveguide layers are formed by confinement with two barriers associated with decreases in the refractive index that are caused by electronic and nuclear energy losses, respectively.     

Formation of carbon nanostructures containing single-crystalline cobalt carbides by ion irradiation method

Carbon nanofibers (CNFs) with a diameter of 17 nm, and carbon nanoneedles (CNNs) with sharp tips have been synthesized on graphite substrates by ion irradiation of argon ions with the Co supplies rate of 1 and 3.4 nm/min, respectively. Energy dispersive X-ray spectrometry, combined with selected area electron diffraction patterns has been used to identify the chemical composition and crystallinity of these carbon nanostructures. The CNFs were found to be amorphous in nature, while the structures of the CNNs consisted of cubic CoC_x, orthorhombic Co₂C and Co₃C depending on the cobalt content in the CNNs. The diameter of the carbide crystals was almost as large as the diameter of the CNN. Compared to the ion-induced nickel carbides and iron carbides, the formation of single-crystalline cobalt carbides might be due to the high temperature produced by the irradiation.     

Topological and chemical investigation on super-hydrophobicity of PTFE surface caused by ion irradiation

Super-hydrophobic PTFE surfaces were obtained by irradiation of 200 keV Xe⁺ ion with the fluence of 6.2×10¹³ ions/cm². The contact angle of water on such surface is as large as 161±3°. SEM and XPS were used to investigate how the topological and chemical changes affect the wettability of the irradiated surface. Needle like structures at nanometer scale caused by irradiation are considered to be the reason of the super-hydrophobicity. The formation of oxygen containing group and defluorination effect on the treated surface are inferred to have negative contribution to the hydrophobic optimization of PTFE surface.     

Study of nitrogen ion implantation and diffusion phenomena on thin chromium layers followed by the atomic force microscopy and secondary ion mass spectroscopy techniques characterization

This research investigates the effect of ion implantation dosage level and further thermal treatment on the physical characteristics of chromium coatings on Si(1 1 1) substrates. Chromium films had been exposed to nitrogen ion fluencies of 1 × 10¹⁷, 3 × 10¹⁷, 6 × 10¹⁷ and 10 × 10¹⁷ N⁺ cm⁻² with a 15 keV energy level. Obtained samples had been heat treated at 450 °C at a pressure of 2 × 10⁻² Torr in an argon atmosphere for 30 h. Atomic force microscopy (AFM) images showed significant increase in surface roughness as a result of nitrogen ion fluence increase. Secondary ion mass spectroscopy (SIMS) studies revealed a clear increased accumulation of Cr₂N phase near the surface as a result of higher N⁺ fluence. XRD patterns showed preferred growth of [0 0 2] and [1 1 1] planes of Cr₂N phase as a result of higher ion implantation fluence. These results had been explained based on the nucleation-growth of Cr₂N phase and nitrogen atoms diffusion history during the thermal treatment process.     

Effects of irradiation parameters on metal surface erosion by pulsed ion beams

Potential application of high-power ion beams of submicrosecond and microsecond durations with the initial particle energy from 50 to 1000 keV and power density 10⁷–10⁹ W/cm² to ensure metal surface erosion are investigated. Evaporation is treated as a major erosion mechanism and the erosion coefficient is taken as an efficiency indicator. Dependences of the erosion coefficients of several metals on beam parameters obtained via calculations using a technique based on the solution of thermal conductivity equation with phase transitions are presented. The ion species, their initial energy, current pulse duration and power density are used as the beam parameters controlling the result of irradiation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 49–54, August, 2007.     

Model of metal surface erosion under irradiation by high-power pulsed ion beams

The mechanisms of erosion of metal surfaces under the action of submicrosecond (10⁻⁹−10⁻⁶ s) ion beams in the power density range of P = 10⁶−10⁹ W/cm² with a particle energy of 1–2000 keV are considered. It is shown that the collective processes associated with the radiation heating of the surface are of great importance. A model for the erosion is proposed. In accordance with this model, the flow of atoms of the target leaving the surface being irradiated consists of two independent components caused by collisional sputtering and evaporation, respectively. The influence of the irradiation parameters on the erosion coefficient and the ratio between the sputtering and evaporation factors is analyzed.     

The formation of developed morphology on the indium phosphide surface by ion argon beam sputtering

Self-organizing structures on the InP surface that are formed by ion-beam sputtering in the energy range 0.1–15 keV are investigated. It is shown that the processing of the InP surface by monochromatic argon beams can give rise to the formation of two, “grass” and “cone-in-pit,” morphologies. The formation of the relief is treated in terms of a qualitative model including the processes of sputtering, cascade mixing, and surface transport. The model adequately predicts the fluence dependence of the density and size of morphological features. In addition, it enables one to clarify conditions under which the morphologies form, as well as to explain the effect of target temperature on the demarcation line between the morphologies. It is demonstrated that the morphology may become anisotropic in the case of mask etching. In particular, the application of regularly spaced strips as masks makes it possible to produce a texture-like surface structure.     

Ionization by low energy heavy ions in nitrogen,carbon dioxide,argon and hydrocarbon gases

Experimental data on the variation of W, the mean energy expended by a charge particle in producing an ion pair in a gas, with the mass, charge and energy of the particle is examined with a view to discovering how far these variations may be explained in terms of elastic nuclear scattering. In nitrogen and carbon dioxide W appears to depend not only on the elastic nuclear scattering but also on the parameter E/MZ^4/3 for ions other than piotons. In argon any relationship is obscured by apparent discrepancies in the data, although it is possible that the variation may be similar to that in nitrogen and carbon dioxide. The data for the hydrocarbon gases is not so extensive as for the other gases and it may be that the variation of W with the mass and charge of the ion is different from that in nitrogen and carbon dioxide. It is speculated that this difference, if real, is due to super-excited states in the hydrocarbon gases.

Some empirical relationships are suggested as a practical guide for use in dosimetry.     

Self-organized nanostructure formation on the graphite surface induced by helium ion irradiation

The effects of helium ion irradiation on the graphite surface are studied by employing a plasma focus device. The device emits helium ion pulse having energies in the range of a few keV to a few MeV and flux on the order of 10²⁵ m^?2?s^?1 at 60 mm axial position from the anode tip. The field emission scanning electron microscopy confirms the formation of multi-modal spherical and elongated agglomerated structures on irradiated samples surface with increase in agglomerate size with increasing number of irradiation shots. The transient annealing in each irradiation was not enough to cause the Oswald ripening or sintering of particles into bigger particle or crystal size but only resulted in clustering. The atomic force micrographs reveal an increase in average surface roughness with increasing ion irradiation. The Raman study demonstrates increase in disordered D peak along with reduced crystallite size ($L_a$) with increasing number of irradiation shots.