I. Bello

Modification of surface band bending of diamond by low energy argon and carbon ion bombardment

Argon and carbon ion bombardment of p‐diamond at 500–5000 eV in ultrahigh vacuum were studied by in situ x‐ray photoelectron spectroscopy (XPS) and low energy electron diffraction analysis. Both argon and carbon ion bombardment at room temperature in the present energy range created a defective surface layer. The radiation damage was manifested by the introduction of a distinct C 1s peak (referred to as the ‘‘defect’’ peak later) with a binding energy about 1 eV less than that of the bulklike diamond peak, and by the introduction of some additional filled states (referred to as the ‘‘filled states’’) near the valence band edge of diamond. It was found that in comparison to argon bombardment, carbon bombardment was more efficient in producing the filled states but less efficient in raising the C 1s defect peak. While the filled states disappeared by annealing at about 500 °C, the C 1s defect peak did not change much even with a 1000 °C anneal. These results suggest that the C 1s defect peak, which has also...

Direct ion beam deposition of carbon films on silicon in the ion energy range of 15-500 eV

Direct ion beam deposition of carbon films on silicon in the ion energy range of 15–500 eV and temperature range of 25–800 °C has been studied. The work was carried out using mass‐separated C+ and CH+3 ions under ultrahigh vacuum. The films were characterized with x‐ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and transmission electron diffraction analysis. In the initial stage of the deposition, carbon implanted into silicon induced the formation of silicon carbide, even at room temperature. Further carbon ion bombardment then led to the formation of a carbon film. The film properties were sensitive to the deposition temperature but not to the ion energy. Films deposited at room temperature consisted mainly of amorphous carbon. Deposition at a higher temperature, or post‐deposition annealing, led to the formation of microcrystalline graphite. A deposition temperature above 800 °C favored the formation of microcrystalline graphite with a preferred orientation in th...

Argon incorporation in Si(100) by ion bombardment at 15–100 eV

Argon incorporation in Si(100) by low energy ion bombardment has been studied by polar angle dependent x‐ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The bombardment was performed at 15, 20, and 100 eV in an ultrahigh vacuum chamber where a mass‐separated argon ion beam with an energy spread of less than 1 eV was directed to the target. Both the argon penetration depth and incorporation probability were found to increase with bombardment energy. With a fluence of 2×1017/cm2, most of the incorporated argon was located within 20 A of the target surface for the 100 eV bombardment and within 10 A for the 15 eV bombardment. In all cases, the argon depth distribution reached a maximum and then declined. At this fluence, the incorporation probabilities were 0.0015 and 0.0004 for the 100 and 15 eV bombardment, respectively. When the amount of incorporated argon was measured as a function of fluence, it increased with fluence at low fluences, reached a quasisaturation at about 1×1016/...

Mechanism of cleaning and etching Si surfaces with low energy chlorine ion bombardment

Effects of 35Cl+ bombardment of Si (100) surfaces were studied with a mass‐separated low energy ion beam system operated under ultrahigh vacuum and with in situ x‐ray photoelectron spectroscopy (XPS). Before ion bombardment, each silicon sample was etched with a hydrofluoric acid solution and rinsed in deionized water. XPS showed that the surface received no ion bombardment was effectively hydrogen passivated and had no silicon with an oxidation number higher than 2. However, oxygen was found which was probably present in the form of Si—OH or adsorbed water. Chlorine ion bombardment at room temperature initially drove the surface oxygen to the formation of silicon oxide which was subsequently etched off by further ion bombardment. The surface oxidation was initiated by the formation of Si—Cl bonds followed by the thermodynamically favorable replacement of Si—Cl with Si—O. The removal of the surface oxygen depended critically on the bombardment energy. At a bombardment energy of 1±0.6 eV, oxygen bonding wa...

Synchrotron radiation x‐ray absorption of ion bombardment induced defects on diamond (100)

The surface defect structures on diamond (100) surfaces induced by 500 eV neon ion bombardment and by subsequent annealing were studied in situ with x‐ray absorption near‐edge structure (XANES) spectroscopy using 250–800 eV synchrotron radiation and with low energy electron diffraction. Ex situ x‐ray photoemission spectroscopy (XPS) was also used to characterize the defective layer. Significant changes in the XANES spectra were identified for the defects induced by ion bombardment and subsequent annealing. The diamond discrete exciton absorption at 289.0 eV was clearly suppressed even at the lowest ion fluence used in this study, i.e., 3×1014/cm2, and no such exciton could be observed at 7×1014/cm2. However, the changes in the multi‐maxima shape‐resonance absorption structure in the range of 290–310 eV indicated that a loss of the diamond long range order required a fluence of 1×1015/cm2. The structural changes were also manifested by the transformation of gap state absorption typical of clean 2×1 surface...

Dissociative scattering of molecular BF+ and BF+2 ions from Au surfaces

Abstract Dissociative scattering of molecular BF + and BF + 2 ions from a polycrystalline Au surface has been investigated in the incident energy range of 10 to 200 eV with a polar incident angle of 45° and a scattering angle of 90°. The energy distributions of dissociative ion fragments and survival molecular ions were measured by means of a quadrupole mass spectrometer equipped with a cylindrical mirror energy analyzer. The measured distributions show an onset beam energy of 35 eV for BF + dissociation and 20 eV for BF + 2 dissociation. The experimental results, when compared with the theoretical data from a classical collisional approach, suggest a high probability of dissociation via vibrational excitation during collision. The lack of any strong antibonding states in BF + and BF + 2 which can receive electrons from the valence band of gold further indicates the unlikeliness of dissociation via an electronic process such as dissociative attachment.

X‐ray photoelectron spectroscopy study of low energy CF+ ion interactions with silicon

Surface modifications of silicon by exposure to a mass‐separated, reactive ion beam of CF+ were studied by x‐ray photoelectron spectroscopy. The effects of ion kinetic energy were characterized in terms of the various surface chemical states induced by the bombardment. The results showed that with an ion kinetic energy of 2 eV, which was much lower than the C–F bond energy of about 5 eV, molecular adsorption took place. At a bombardment energy of 10 eV, dissociative chemisorption was observed but the reaction was confined to the top surface with disproportionation of CF as the main route and little fluorination of silicon. With an ion energy of 100 eV, the atomic fragments generated by the CF dissociation possessed enough energy to penetrate below the silicon surface. It was found that silicon carbide and fluorosilyl species comprised the modified surface region and that fluorine atoms were situated closer to the surface than the carbon atoms of the carbide. Fluorocarbon species were minor surface reactio...

Cleaving C–H bonds with hyperthermal H2: facile chemistry to cross-link organic molecules under low chemical- and energy-loads

A facile method for cross-linking organic molecules has been developed by computational modeling, instrumentation design, and experimental research. Briefly, organic molecules are hit by H2 with controllable kinetic energy in our novel apparatus where a high flux of hyperthermal H2 is generated. When a C–H bond of the organic molecule is hit by H2 at about 20 eV, efficient kinematic energy-transfer in the H2→H collision facilitates the C–H dissociation with nearly 100% reaction probability. When H2 hits other atoms which are by nature much heavier than H2, mass disparity bars effective energy transfer and this both blocks undesirable bond dissociation and reduces unnecessary energy wastage. The recombination of the carbon radicals generated by the C–H cleavage efficiently completes the production of C–C cross-links at room temperature with no additional energy/chemicals requirements. In addition to these green chemistry merits, this new method is better than other cross-linking techniques which rely on prerequisite reactions to add cross-linkers to the organic molecules or additional reactants and additives. These promising features are validated by several cross-linking trials which demonstrate desirable mechanical, electrical, chemical, and biochemical changes while inducing no undesirable damage of chemical functionalities in the original molecules.

Interfacial characterization of ion‐beam‐deposited a‐C films on Ge

Diamondlike carbon films were deposited on germanium crystals with a mass‐separated C+ ion beam in ultrahigh vacuum over the energy range 20–275 eV, and the interfaces were characterized with x‐ray photoelectron spectroscopy. It was found that ion bombardment induced a carbide phase on the germanium surface. Further carbon accumulation then led to the growth of an amorphous carbon overlayer. The carbide phase was identified by a rather low C 1s binding energy (at about 283.8 eV) and small positive shift of the Ge 3p peak (about 0.4 eV). The valence‐band spectra of these samples also suggested that germanium carbide formed with a pure carbon beam for the bombardment energy range considered has a band gap between germanium and diamondlike carbon.

Thin film growth by aggregation of carbon implanted into copper crystals

Abstract Carbon films have been prepared on copper crystals by implantation of carbon at 50–390 keV and at implantation temperatures of 25–100 °C. In order to determine the orientation dependence, Cu (100), (110), (111) and (210) crystals were used. Film characterization was carried out with X-ray diffraction, transmission electron diffraction, Raman microprobe analysis, and X-ray photoelectron spectroscopy. Samples implanted at or below 400°C were subjected to either rapid thermal annealing or pulsed laser annealing. Carbon overlayers on copper were found in all cases. However, (0001) graphite was identified to be the main product and no diamond formation was observed.