R. Brener

Damage threshold for ion‐beam induced graphitization of diamond

The critical dose for graphitization of diamond as a result of ion implantation induced damage (boron and arsenic) and subsequent thermal annealing is determined by combining secondary ion mass spectroscopy measurements, chemical etching of the graphitized layer, and TRIM simulations. Li ions are implanted as a deep marker to accurately determine the position of the graphite/diamond interface. The damage density threshold, beyond which graphitization occurs upon annealing, is found to be 1022 vacancies/cm3. This value is checked against published data and is shown to be of general nature, independent of ion species or implantation energy.

ENHANCEMENT OF DIAMOND NUCLEATION BY ULTRASONIC SUBSTRATE ABRASION WITH A MIXTURE OF METAL AND DIAMOND PARTICLES

A method of surface treatment was found to enhance diamond chemical vapor deposition nucleation on nondiamond substrates such as Si, SiO2, and Al2O3. The nucleation density obtained by ultrasonic abrasion with diamond powder alone was found to be enhanced by a few orders of magnitude using a mixed slurry consisting of diamond and metal powders. No strong nucleation enhancement was observed using a metal slurry only for surface treatment. The metal powders used were W, Ta, Mo, Nb, Ti, Al, Fe, Ni, Cu, and Si. It is concluded that the enhanced nucleation is associated with a physico‐chemical modification of the substrate surface, attained through a cooperative effect of both the metal and diamond particles during the ultrasonic abrasion process.

Characteristics of metal-insulator-semiconductor capacitors based on high-k HfAlO dielectric films obtained by low-temperature electron-beam gun evaporation

We describe the characteristics of thin HfAlO films deposited at low temperature by electron beam gun evaporation. As-deposited films thinner than 6 nm exhibit an effective dielectric constant (keff) of 9–11.5. The minimum quantum mechanical corrected effective oxide thickness is ∼1.45nm and the leakage currents are very low. Rapid thermal annealing in a N2 environment improves the leakage further and up to 750 °C does not affect keff. Higher annealing temperatures reduce keff, but even at 950 °C, it has a value of 6.5. These HfAlO films have the potential to serve as a substitute for SiO2 in small-scale metal-insulator-semiconductor structures.

Hydrogen diffusion in B-ion-implanted and B-doped homo-epitaxial diamond: passivation of defects vs. passivation of B acceptors

Drastic differences in diffusion of H (deuterium) in diamond, B-doped by ion implantation and during homo-epitaxial film growth, and its influence on electrical properties are found by SIMS depth profiling, and by electrical (Hall effect) measurements. Type IIa natural diamond, B-doped by ion implantation and high quality homo-epitaxial B-doped diamond films were subjected to D plasma treatment under similar conditions. The results of SIMS measurements clearly show a huge difference in D diffusion profile for these two samples. While the sample doped during growth was totally deuterated, the implanted one showed only minor D penetration. Electrical measurements indicated that while the homo-epitaxial samples became insulating or showed strong decrease in their free hole concentration following deuteration, the identical treatment to the B-ion implanted sample caused only slight changes in electrical properties. The electrical properties and their dependence on annealing are correlated with the deuterium diffusion into diamond. A possible mechanism of (B, H) and (defect, H) pair formation is suggested as a possible explanation of the observed differences.

Nitridation of diamond and graphite surfaces by low energy N+2 ion irradiation

Low energy 500 eV N 2 + ion irradiation of diamond and graphite surfaces has been investigated by AES and XPS in order to model the possibility of carbon nitride formation by ion implantation methods. In this work we present experimental data demonstrating the crucial influence of sample temperature during irradiation on the carbon-nitrogen chemical bonds formation. The distribution of bonding states of the implanted nitrogen is shown to be different for diamond and graphite substrates. The effect of post-implantation annealing and implantation temperature on the distribution of nitrogen bonding states is investigated. Structural effects were assessed by changes in the C(KVV) Auger lineshape fine structure.

Nitrogen implantation into glassy carbon as an attempt to grow a carbon nitride thin film

Abstract The current interest in carbon nitride comes from the recent theoretical prediction that this material could have superior structural, thermal and electronic properties to those of diamond. Over the last few years considerable efforts have been made in an attempt to grow thin films of the β-C 3 N 4 phase by employing various deposition techniques. In the present work, the possibility of carbon nitride formation by ion implantation of nitrogen into glassy carbon was investigated with particular attention to the effect of the implantation parameters and post-annealing processes. The distribution and bonding states of the implanted nitrogen as well as the composition and the structure of the modified layer have been studied by AES, XPS and Raman techniques. Highenergy, up to 50 keV, and high-dose, up to 1 × 10 18 cm −2 , nitrogen ion implantations into glassy carbon were performed as an attempt to form a continuous carbon nitride layer. Low-energy (0.5 keV) nitrogen implantation was performed as a model study of possible chemical bond formation between nitrogen and carbon atoms. In this work we present experimental data demonstrating the predominant formation of an almost unpolarized carbon-nitrogen bond during hot nitrogen implantation. Such bonds are expected to be present in the elusive carbon nitride β-phase.

The effect of carbon on strain relaxation and phase formation in the Ti/Si1-x-yGexCy/Si contact system

We report the first study of interfacial reactions of a metal with Si1−x−yGexCy epitaxially grown on Si. The Ti/Si1−x−yGexCy/Si (0<y<1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1−xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C‐containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations.

Carbon nitride formation by low-energy nitrogen implantation into graphite

Abstract Recently, some attempts to produce the new β-C 3 N 4 phase withhardnes higher than diamond have been reported. In this paper, a model study of carbon nitride formation by low-energy nitrogen implantation into graphite is presented. Room temperature (RT) and hot (500°C) nitrogen implantations were performed at saturation and low doses. The formation of chemical bonds between implanted nitrogen and carbon atoms was assessed by in situ X-ray photoelectron spectroscopy. It was found that two dominant nitrogen bonding states are formed in the implanted layer. The relative distribution of these states depends on the implantation temperature, dose and post-annealing process. Hot nitrogen implantation results in a predominant population of the more covalent (higher binding energy) nitrogen bonding state which has been suggested to be characteristic of the β-C 3 N 4 phase. Post-annealing of a low-dose nitrogen-implanted graphite results in a distribution of the nitrogen bonding states similar to the hot implantation case. RT implantation at saturation doses followed by annealing leads to a different distribution of the nitrogen bonding states. The implantation-induced damage was investigated by means of electron-excited C(KVV) Auger line shape measurements. Hot implantation results in point defect formation, although the graphite structure is not completely amorphized. The experimental results suggest that hot nitrogen ion beam-assisted deposition can lead to the formation of the new β-C 3 N 4 phase.

Mechanism of diamond formation on substrates abraded with a mixture of diamond and metal powders

In this work we report a study of CVD diamond formation on silicon substrates abraded with diamond, metal, and a mixture of diamond and metal powders. It was found that the deposited diamond particles density (DPD) obtained after abrasion with diamond powder can be enhanced by a few orders of magnitude by abrasion with a mixed metal/diamond slurry, whereas no enhancement was observed by use for surface abrasion a metal slurry alone. The residual diamond slurry density (RDSD) left on the substrates by abrasion with diamond slurry was measured from AFM images. It was observed that DPD followed by abrasion with pure diamond slurry does not exceed 10% of RDSD, whereas the presence of some metal residues alongside with diamond debris, may increase this value almost to 100%. The enhancement in DPD was in the order: virgin ≈(Cu, Fe or Ti) < Di < (Cu + Di) < (Fe + Di) < (Ti + Di). These effects are explained qualitatively as follows. It is suggested that metal residues influence the rates of CVD diamond growth through facilitation of conversion of non-sp3-bonded carbon species to the sp3-one above the growing surface. This enhancement in sp3-bonded carbon surface concentration at the initial stages of deposition (before a stable substrate is formed) prevents the smallest diamond residues from being completely etched by atomic hydrogen.

Spontaneous interlayer formation in OPVs by additive migration due to additive–metal interactions

The presence of interlayers between the active layer and the electrode are known to modify the metal work-function and enhance carrier extraction, consequently improving OPV device performance. Spontaneous formation of interlayers by surface-enrichment of suitable additives eliminates separate processing steps and hence is technically advantageous and cost effective. However, surface enrichment is limited to additives with low surface energy. Here we show that additive migration to the organic/electrode interface could be induced by additive–metal interactions, modulated by the interactions between the additive and the underlying substrate. In this study, additive migration induced by metal evaporation is studied by blending P3HT with PEG, an established interlayer material with a surface energy higher than that of P3HT. XPS analysis reveals that, as expected, PEG is not present on the surface of the organic spun film. However, Ca or Al evaporation induces a significant migration of PEG to the organic/metal interface. In contrast, Au evaporation does not induce such migration. The comparison between Al, Ca and Au, metals with significantly different reduction potentials, revealed that the driving force for PEG migration is its chemical interaction with the deposited metal atoms. The extent of PEG migration was also found to depend on the type of underlying substrate, ITO/PEDOT:PSS or ITO. Finally, the PEG interlayer is shown to reduce the Al work function confirming that spontaneous additive migration induced by metal–additive interactions could be harnessed for charge extraction in organic electronic devices.