Electron paramagnetic resonance study of ion implantation induced defects in amorphous hydrogenated carbon (original) (raw)
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Effects of ion implantation on electron centers in hydrogenated amorphous carbon films
Journal of Applied Physics, 2003
Electron spin resonance (ESR) and Raman spectra measurements are carried out on a-C:H and a-C:H:N films both as grown and implanted with W and Ni ions with doses ranged from 0.5×1015 to 1.2×1016 cm-2. The as-grown films have small concentration of paramagnetic centers with a spin density Ns of 1017 cm-3. Upon implantation a significant increase in Ns of (0.5-22)×1019 cm-3 centers with g(Si)=2.0055 and g(C)=2.0025 was observed. These defects are ascribed to dangling bonds in the silicon substrate and in the carbon film, respectively. The correlation between variation of Ns value with implantation dose and behavior of D and G band position and their intensity ratio in the visible Raman spectra is observed. The effects are attributed to changes in the sp2-sp3 systems and hydrogen loss due to ion induced annealing of the carbon films at high ion doses. The temperature and concentration dependencies of the ESR line shape and linewidth are explained using the mechanism of motional narrowing over the temperature range 4.2-300 K. Low temperature anisotropy of the g value is found in the ESR spectra and is explained as arising from the dipole-dipole interaction in the infinitely thin films.
Characterisation of defects in thin films of hydrogenated amorphous carbon
Diamond and Related …, 2000
Electron paramagnetic resonance (EPR) measurements have been made at X-band (f9.5 GHz) and W-band (f95 GHz) of a-C:H films on (1 0 0) silicon substrates; the sample temperature was varied in the range 5-300 K. Two types of film were examined. The first type are amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapour deposition (PECVD) with negative self bias voltages in the approximate range 100-500 V. The second type were initially highly polymeric-like a-C:H films grown on Si placed on the earthed electrode of a PECVD system but were subsequently implanted with either 6=10 cm B or 2=10 cm B ions. At both X-and W-band and throughout the temperature range 5-300 K 15 y2 q 16 y2 q the EPR signal of the carbon unpaired electrons consists of a single symmetric line with gs2.0026"0.0002. As the temperature is lowered, several samples develop a dependence on sample orientation of the external field required for resonance. This anisotropy is explained in terms of the demagnetising fields more usually encountered in ferromagnetic resonance. ᮊ
An EPR study of defects in hydrogenated amorphous carbon thin films
Diamond and related …, 1998
The defect states, with unpaired spins, in hydrogenated amorphous carbon (a-C:H) films have been studied using electron paramagnetic resonance (EPR). These EPR measurements were made at room temperature at about 9.9 GHz. The a-C:H thin films were deposited using plasma enhanced chemical vapour deposition (PECVD), firstly for various negative self-bias voltages at constant pressure, and secondly with various nitrogen contents at constant bias. Changing the self bias from -50 to -540 volts leads to a reduction in linewidth from approx. !.4 to 0.3 mTesla although the g-value of the single Lorentzian line is unchanged at g= 2.0025 +0.0002. Increasing the atomic nitrogen content from zero to 15% causes the g-value of the single line to shift from 2.0025+0.0002 to 2.0(133 +0.1)003, while the linewidth and spin populations both decrease. The effect on these defects of postannealing the films is also reported. ~:,:3 1998 Elsevier Science S.A.
Ion-implantation into amorphous hydrogenated carbon films
Journal of non-crystalline solids, 2000
Amorphous hydrogenated carbon is being investigated as a possible semiconducting material. A required property of a semiconductor is electronic doping, and this may be achieved either by in situ addition of gaseous precursors during deposition or ex situ ion-implantation. This study shows that resulting ion beam damage produced by ion-implantation may be kept to a minimum as long as the ion dose is less than approximately 10 14 cm À2 . Polymer-like carbon ®lms grown using radio frequency plasma enhanced chemical vapour deposition have been implanted with carbon, nitrogen and boron ions, and the electronic and optical properties of the material analysed. An analysis of the electrical and optical data is carried out to distinguish between the physical and chemical changes that occur within the microstructure of the ®lms. Ó
Paramagnetic defects in hydrogenated amorphous carbon powders
2003
Hydrogenated amorphous carbon materials typically contain high concentrations of paramagnetic defects, the density of which can be quantified by electron paramagnetic resonance (EPR). In this work EPR measurements near 9.5, 94, and 189 GHz have been performed on polymeric and diamond-like hydrogenated amorphous carbon (a-C:H) powder samples. A similar single resonance line was observed at all frequencies for the two forms of a-C:H studied. No contributions to the spectrum from centres with resolved anisotropic g-values as reported earlier were detected. An increase in linewidth with microwave frequency was observed. Possible contributions to this frequency dependence are discussed.
Carbon, 1999
The properties of polymer-like amorphous hydrogenated carbon thin films with low defect density have been studied. These films were implanted with carbon ions with a dose range of 1012-1016 cm−2. The purpose of the study is to investigate the effects of ion beam damage on this type of film. Optical absorption measurements observe a narrowing of the optical band gap, suggesting the introduction of a large number of defect states subsequent to the implantation resulting in the broadening of the band tails, only after a threshold ion dose of 1015 cm−2. Nuclear reaction analysis suggests also a reduction in the hydrogen content of the film which coincides with film thinning.
EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon
Physical Review B, 2000
Electron paramagnetic resonance ͑EPR͒ measurements have been made of amorphous hydrogenated carbon ͑a-C:H͒ films grown by plasma enhanced chemical vapor deposition ͑PECVD͒ with negative self-bias voltages V b in the approximate range 10-540 V. For V b Ͻ100 V, as the film changes from polymerlike to diamondlike, the changes in linewidth and shape are interpreted in terms of changes to two contributions-one due to dipolar interactions between the unpaired spins and one due to unresolved lines arising from hyperfine interactions with H 1 . The former yields a Lorentzian line, the latter a Gaussian, and the resultant spectrum has the Voigt shape. The empirical relation ⌬B pp G ͑in Gauss͒ϭ͑0.18Ϯ0.05͒ϫ͑at. % H) between the peak-to-peak Gaussian contribution ͑in Gauss͒ ⌬B pp G and the hydrogen content in atomic percentage is obtained. For V b Ͼ100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as V b increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the -type radicals.
Photobleaching of paramagnetic defects in hydrogenated amorphous carbon films
Solid State Communications, 1993
ABSTRACT We report the light-induced annealing (photobleaching) of thermally induced paramagnetic defects in hydrogenated amorphous carbon films prepared by RF-plasma decomposition of methane at RF-power densities of 0.4 and 0.8 W cm−2. The decrease in the ESR signal due to illumination is maximum after annealing at 300°C; moreover, the relative decrease is larger for the sample prepared at 0.8 W cm−2. We used an exponential function to model the kinetics for photobleaching. Due to the reversibility of this process we propose the redistribution of optically excited charges as the mechanism responsible for photobleaching.