I. Gouzman

Possibility of carbon nitride formation by low‐energy nitrogen implantation into graphite: In situ electron spectroscopy studies

The possibility of carbon nitride formation by low‐energy nitrogen ion irradiation of graphite was investigated by in situ x‐ray photoelectron spectroscopy. Room‐temperature and hot 500‐eV N+2 implantations were performed with saturation doses for which a constant nitrogen concentration was obtained. Analysis of the N(1s) core level line indicates the existence of three different carbon–nitrogen bonding states in the room‐temperature implanted layer. Annealing experiments up to 500 °C revealed a slight, gradual decrease of nitrogen concentration in the implanted layer accompanied by a partial redistribution of the nitrogen bonding states. Hot nitrogen implantations at 300 and 500 °C resulted in a predominant population of the more covalent, with higher N(1s) binding energy, nitrogen bonding state. Such a distribution of carbon–nitrogen chemical bonds could not have been obtained by annealing of the room‐temperature implanted layer. These results may be of importance in finding a way to produce the elusive...

Evolution and properties of nanodiamond films deposited by direct current glow discharge

Nanocrystalline carbon films possessing a prevailing diamond character are deposited by a direct current glow discharge chemical vapor deposition method using a 9:91 vol % methane to hydrogen gas mixture. In the present work the evolution and properties of nanodiamond films deposited by this method onto silicon substrates as a function of time were studied by various complementary techniques. Our analysis showed that prior to formation and growth of continuous films of a predominantly nanodiamond character, a graphitic phase is formed. After the nanodiamond phase is stabilized, near edge x-ray adsorption fine structure measurements proved the predominant diamond character of the film to be about 80%. By electron energy loss spectroscopy analysis the sp2-like character of the nanodiamond grain boundaries has been determined. The nanodiamond films were found to be thermally stable up to temperatures of ∼950 °C as established by vacuum heating. By scanning electron microscopy and atomic force microscopy the ...

Sensitivity of near-edge x-ray absorption fine structure spectroscopy to ion beam damage in diamond films

In the present work, we study the sensitivity of the near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to ion induced defects in polycrystalline diamond films. The ion bombardment of hydrogenated films is performed using 30 keV Xe+ ions at room temperature for doses ranging from 2×1013 ions/cm2, producing local point defects, to 2×1015 ions/cm2, which results in almost complete amorphization of the diamond surface. Auger electron spectroscopy measurements are not sensitive to the modifications induced by the lowest implantation dose. Whereas partial electron yield (PEY) NEXAFS measurements, applied in surface and bulk-sensitive modes, using 35, 15, and 8 eV secondary electrons, respectively, reveals the formation of a defective structure and gradual deterioration of diamond in the near-surface region. From PEY NEXAFS spectra measured using 15 eV secondary electrons, the position of C(1s) binding energy is measured. The x-ray photoelectron spectra of the samples were measured using an inciden...

POSS-Polyimide Nanocomposite Films: Simulated Hypervelocity Space Debris and Atomic Oxygen Effects

The combined effect of hypervelocity space debris impact and atomic oxygen (AO) attack on the degradation of reinforced polyhedral oligomeric silsesquioxanes (POSS)-polyimide films was studied. A laser-driven flyer (LDF) system was used to accelerate aluminum flyers to impact velocities of up to 3 km s -1. The impacted films were exposed to an RF-plasma source, which was used to simulate the effect of AO in the low Earth orbit. Scanning electron microscopy (SEM) was used to characterize the fracture morphology. The extent of damage in POSS-polyimide impacted films was found to be much smaller compared to POSS-free films, insinuating on a toughening mechanism developed due to POSS incorporation. When exposed to air RF-plasma, the impacted POSS-free film revealed a synergistic effect associated with a large increase in the erosion rate while impacted POSS-containing samples showed improved erosion resistance. The increased erosion rate of the impacted POSS-free film is explained by formation of residual stresses that affect the oxidation mainly by increasing the diffusivity of oxygen.

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.

DC-glow discharge as a key step for the bias-enhanced nucleation of diamond by the HF CVD method

Abstract A novel method for in situ substrate surface pretreatment for the enhancement of CVD diamond nucleation density on mirror polished Si(100) is reported. During the pretreatment, a dc-glow discharge between a grounded substrate and a positively biased electrode is generated using a CH 4 /H 2 gas mixture. No additional gas phase activation by a hot filament (HF) is carried out during this stage. For subsequent diamond deposition, the dc-glow discharge is switched off, and the standard HF CVD growth conditions are applied. This method is compared with a thermal-assisted (TA) dc-glow discharge pretreatment, i.e. a generation of the dc-glow discharge concurrently with thermal activation of CH 4 /H 2 gas mixture by HF. It is observed that both pretreatment methods result in the formation of carbon-containing film which serves as a precursor for subsequent diamond growth. The development of the film as a function of the deposition time is found to be similar after dc-glow discharge with and without additional gas phase activation by HF. From our results, it is suggested that the key step in the bias-enhanced nucleation (BEN) is generation of a stable dc-glow discharge. The deposited films are characterized by Raman spectroscopy, and High Resolution Scanning Electron Microscopy (HR SEM).

Formation of the precursor for diamond growth by in situ direct current glow discharge pretreatment

A direct current (dc) glow discharge—surface interaction process for in situ substrate surface pretreatment, for the promotion of diamond growth on mirror polished Si(100) is reported. A key step of the pretreatment is a generation of a stable dc-glow discharge between a grounded substrate and a positively biased electrode using a CH4/H2 gas mixture. During this stage, no additional gas phase activation by a hot filament is carried out. For subsequent diamond deposition, the dc-glow discharge is switched off and the standard hot filament CVD growth conditions are applied. The nature of the deposits formed by the dc-glow discharge process and after standard diamond deposition conditions, are investigated by Raman spectroscopy and high resolution scanning electron microscopy. It is found that the properties of the films, deposited following the dc-glow discharge pretreatment, strongly depend on the pretreatment conditions: methane concentration, substrate temperature, and pretreatment time. It is suggested ...

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.

Atomic-Oxygen-Durable and Electrically-Conductive CNT-POSS-Polyimide Flexible Films for Space Applications

In low Earth orbit (LEO), hazards such as atomic oxygen (AO) or electrostatic discharge (ESD) degrade polymeric materials, specifically, the extensively used polyimide (PI) Kapton. We prepared PI-based nanocomposite films that show both AO durability and ESD protection by incorporating polyhedral oligomeric silsesquioxane (POSS) and carbon nanotube (CNT) additives. The unique methods that are reported prevent CNT agglomeration and degradation of the CNT properties that are common in dispersion-based processes. The influence of the POSS content on the electrical, mechanical, and thermo-optical properties of the CNT-POSS-PI films was investigated and compared to those of control PI and CNT-PI films. CNT-POSS-PI films with 5 and 15 wt % POSS content exhibited sheet resistivities as low as 200 Ω/□, and these resistivities remained essentially unchanged after exposure to AO with a fluence of ∼2.3 × 10(20) O atoms cm(-2). CNT-POSS-PI films with 15 wt % POSS content exhibited an erosion yield of 4.8 × 10(-25) cm(3) O atom(-1) under 2.3 × 10(20) O atoms cm(-2) AO fluence, roughly one order of magnitude lower than that of pure PI films. The durability of the conductivity of the composite films was demonstrated by rolling film samples with a tight radius up to 300 times. The stability of the films to thermal cycling and ionizing radiation was also demonstrated. These properties make the prepared CNT-POSS-PI films with 15 wt % POSS content excellent candidates for applications where AO durability and electrical conductivity are required for flexible and thermally stable materials. Hence, they are suggested here for LEO applications such as the outer layers of spacecraft thermal blankets.