Hyper power impulse magnetron – HyPIM – glow discharge

Glow discharges are known to be limited for running at high currents (< 0.1 A · cm−2). Magnetically enhanced plasmas could overcome this limitation, typically for the magnetron operated in pulsed mode during a few 100μs. Hence, the current density could be increased by two decades, but it still stays below 10 A · cm−2. Here we report on a long (∼1 ms) pulsed operation of magnetrons, while preserving the glow mode, for current densities exceeding at least 3 times the highest current density reported for high power pulsed magnetrons. Even if the density of energy surpasses 7 J ·  cm−2, no arc transition was observed. Three target materials have been successfully tested: carbon (C), molybdenum (Mo) and tungsten (W) in helium atmosphere, from 5 to 30 Pa. Two key parameters are required to reach the Hyper Power Impulse Magnetron (HyPIM) glow mode: i) the accurate control of the maximum voltage during the pulse and ii) the use of the pre-ionization. Operating conditions of HyPIM will be presented and compared to other discharges

XPS and NEXAFS characterisation of plasma deposited vertically aligned N-doped MWCNT

This paper is dedicated to carbon nanotubes grown by electron cyclotron resonance plasma-enhanced chemical vapour deposition. It has been shown that carbon nanotubes (CNTs) can be grown at temperature as low as 550 °C by this technique. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy were used to analyse nitrogen-doped CNTs. Independently of the synthesis temperature, about 4 at.% nitrogen are incorporated in the CNTs. A good correlation was found between XPS and NEXAFS results. Four components (397.3, 398.5, 400.8 and 402.5 eV) compose N 1s XPS spectra related to different chemical environments of nitrogen. This interpretation can be used as a simple check method of the presence of CNTs on as-deposited PECVD samples

Comparative study of the structure of a-CNx and a-CNx:H films using NEXAFS, XPS and FT-IR analysis

EMRS 2004, Symposium JAmorphous carbon nitride thin films have become a matter of great attention due to their remarkable electronic and mechanical properties. It has been shown that hydrogen and nitrogen incorporation deeply modifies the properties of carbon films. Therefore, the optimization of their properties requires a deep knowledge of various kind of chemical bonds composing in the film matrix. The topic of this presentation is to get more insight into the different local environment of the C and N atoms for hydrogenated and hydrogen-free amorphous carbon nitrides films. H-incorporation has been varied using different deposition technique from plasma-enhanced chemical vapor deposition (PECVD) leading to highly hydrogenated films up to 40 at.% to radio-frequency (RF) magnetron sputtering providing nearly hydrogen-free films. The study of the local structure is done using the combination of Fourier transform infrared (FT-IR), X-ray photo-emission spectroscopy (XPS) and high resolution near edge X-ray absorption fine structure (NEXAFS) analysis. FT-IR spectroscopy is widely used to probe the bonding configurations in the carbonaceous materials, especially the CN, CH and NH bonds in a-CNx:H. In addition, XPS and NEXAFS provide surface information on the environment around C and N atoms and on the chemical composition. NEXAFS gives a better description of the π* states inside the films, due to its remarkable energy resolution. The combination of both characterizations FT-IR and NEXAFS may leave the controversy about the interpretation of the XPS spectra, and allows a fine analysis of the evolution of the local structure as a function of nitrogen incorporation, according to the hydrogen concentration into the films. Fundamental differences can be revealed between hydrogenated and hydrogen-free carbon nitride: in the former, hydrogen promotes double bonds CNH, whereas in the latter nitrogen atoms prefer to substitute to carbon or interconnect aromatic rings through single bonds (>CN). A strong conjugation of imines (NCNH) for PECVD film and nitrile (NCN) groups for hydrogen-free films is evidenced

Angular and local spectroscopic analysis to probe the vertical alignment of N-doped well-separated carbon nanotubes

International audienceVertically aligned well-separated N-doped multiwalled carbon nanotubes (CNTs) were grown on a silicon substrate by plasma enhanced chemical vapor deposition (PECVD). Angular near-edge X-ray absorption fine structure (NEXAFS) was used to investigate the vertical alignment of as-grown CNTs. In addition, both individual tubes and tube bundles were characterized by high-resolution electron energy loss spectroscopy (HREELS). Simultaneous analysis of both spectroscopic techniques provides information on chemical environment, orbital orientation between carbon and heteroatoms, and local curvature effects. We demonstrate the utility of NEXAFS as an in situ probe of CNTs

Nanostructured tantalum nitride films as buffer-layer for carbon nanotube growth

International audienceTantalum nitride (TaN(x)) films are usually used as barriers to the diffusion of copper in the substrate for electronic devices. In the present work, the TaN(x) coating plays an extra role in the iron catalyzed chemical vapor deposition production of carbon nanotubes (CNT). The CNTs were grown at 850 degrees C on TaN(x) films prepared by radio frequency magnetron sputtering. The correlation between the CNT morphology and growth rate, and the pristine TaN(x) film nature, is investigated by comparing the evolution of the nano-composition, roughness and nano-crystallinity of the TaN(x) films both after annealing and CVD at 850 degrees C

On the work function and the charging of small (r &lt;= 5 nm) nanoparticles in plasmas

The growth of nanoparticles (NPs) in plasmas is an attractive technique where improved theoretical understanding is needed for quantitative modeling. The variation of the work function W with size for small NPs, r(NP) amp;lt;= 5 nm, is a key quantity for modeling of three NP charging processes that become increasingly important at a smaller size: electron field emission, thermionic electron emission, and electron impact detachment. Here we report the theoretical values of the work function in this size range. Density functional theory is used to calculate the work functions for a set of NP charge numbers, sizes, and shapes, using copper for a case study. An analytical approximation is shown to give quite accurate work functions provided that r(NP) amp;gt; 0.4 nm, i.e., consisting of about amp;gt; 20 atoms, and provided also that the NPs have relaxed close to spherical shape. For smaller sizes, W deviates from the approximation, and also depends on the charge number. Some consequences of these results for nanoparticle charging are outlined. In particular, a decrease in W for NP radius below about 1 nm has fundamental consequences for their charge in a plasma environment, and thereby on the important processes of NP nucleation, early growth, and agglomeration. Published by AIP Publishing.Funding Agencies|Knut and Alice Wallenberg foundation (KAW) [2014.0276]; Swedish Research Council via the Linkoping Linneaus Environment LiLi-NFM [2008-6572]</p

An ionization region model of the reactive Ar/O 2 high power impulse magnetron sputtering discharge

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Interface study between nanostructured tantalum nitride films and carbon nanotubes grown by chemical vapour deposition

International audienceWe present the role of nitrogen content in tantalum nitride ultra-thin buffers, on the carbon nanotubes (CNTs) growth by chemical vapour deposition at 850 °C, assisted by ferrocene as catalyst source. Tantalum nitride (TaNx) films with a very large range of concentration x = [0, 1.8] and various nanostructures, from amorphous Ta(N) to Ta3N5, were deposited by Highly Pulsed Plasma Magnetron Sputtering. The buffer films are characterized after heat treatment at 850 °C, and after the CNT growth, by wide angle X-ray scattering in grazing incidence and scanning electron microscopy. The CNT diameter explored by transition electron microscopy shows an all-out value for under stoichiometric thin films (Ta1-N1−δ, Ta3-N5−δ) and a minimum value just above the stoichiometric phases (Ta1-N1+δ, Ta3-N5+δ). Firstly one shows that the buffer films under the heat treatment present surface modification highly dependent on their initial state, which influences the catalyst particles diffusion. Secondly at the stoichiometric TaN phase we show that a specific ternary phase FeTa2O6 is formed at the interface CNT/buffer, not present in the other cases, leading to a special CNT growth condition

Microwave air plasmas in capillaries at low pressure II. Experimental investigation

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