Energy distribution of O− ions during reactive magnetron sputtering

This article is a critical review of the M n+1 AX n phases ("MAX phases", where n =1, 2, or 3) from a materials science perspective. MAX phases are a class of hexagonal-structure ternary carbides and nitrides ("X") of a transition metal ("M") and an A-group element. The most well known are Ti 2 AlC, Ti 3 SiC 2 , and Ti 4 AlN 3 . There are ~60 MAX phases with at least 9 discovered in the last five years alone. What makes the MAX phases fascinating and potentially useful is their remarkable combination of chemical, physical, electrical, and mechanical properties, which in many ways combine the characteristics of metals and ceramics. For example, MAX phases are typically resistant to oxidation and corrosion, elastically stiff, but at the same time they exhibit high thermal and electrical conductivities and are machinable. These properties stem from an inherently nanolaminated crystal structure, with M n+1 X n slabs intercalated with pure A-element layers. The research on MAX phases has been accelerated by the introduction of thin-film processing methods.Magnetron sputtering and arc deposition have been employed to synthesize single-crystal material by epitaxial growth, which enables studies of fundamental materials properties. However, the surface-initiated decomposition of M n+1 AX n thin films into MX compounds at temperatures of 1000-1100 °C is much lower than the decomposition temperatures typically reported for the corresponding bulk material. We also review the prospects for low-temperature synthesis, which is essential for deposition of MAX phases onto technologically important substrates. While deposition of MAX phases from the archetypical Ti-Si-C and Ti-Al-N systems typically require synthesis temperatures of ~800 °C, recent results have demonstrated that V 2 GeC and Cr 2 AlC can be deposited at ~450 °C. Also, thermal spray of Ti 2 AlC powder has been used to produce thick coatings. We further treat progress in the use of first-principles calculations for predicting hypothetical MAX phases and their properties. Together with advances in processing and materials 3 analysis, this progress has led to recent discoveries of numerous new MAX phases such as Ti 4 SiC 3 , Ta 4 AlC 3 , and Ti 3 SnC 2 . Finally, important future research directions are discussed. These include charting the unknown regions in phase diagrams to discover new equilibrium and metastable phases, as well as research challenges in understanding their physical properties, such as the effects of anisotropy, impurities, and vacancies on the electrical properties, and unexplored properties such as superconductivity, magnetism, and optics. 4

show abstract

“…For example, thin-film growth of oxides often yields energetic negative oxygen ions [134,135,136,137,138,139,140,141,142,143].…”

Section: 31)mentioning

confidence: 99%

The M+1AX phases: Materials science and thin-film processing

et al. 2010

View full text Add to dashboard Cite

show abstract

“…On the contrary, few works deal with negative ion surface-production in cesium-free plasmas 41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68 . Most of them are related to the industrial process of layer deposition by sputtering and concern mainly oxygen negative ions [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]. H-surface-production in Cs-free plasmas has been mainly studied in 59, 60, 61, 62 (carbon materials), 63 (stainless steel), and 64,65,66,67,68 (barium surfaces).…”

Section: A-introductionmentioning

confidence: 99%

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

et al. 2012

View full text Add to dashboard Cite

In previous works, surface-produced negative-ion distribution-functions have been measured in H 2 and D 2 plasmas using graphite surfaces (HOPG). In the present paper we use the SRIM software to interpret the measured negative-ion distribution-functions. For this purpose the distribution-functions of backscattered and sputtered atoms arising due to the impact of hydrogen ions on a-CH and a-CD surfaces are calculated. The SRIM calculations confirm the experimental deduction that backscattering and sputtering are the mechanisms of the origin of the creation of negative ions at the surface. It is shown that the SRIM calculations compare well with the experiments regarding the maximum energy of the negative ions and reproduce the experimentally observed isotopic effect. A discrepancy between calculations and measurements is found concerning the yields for backscattering and sputtering. An explanation is proposed based on a study of the emitted-particle angulardistributions as calculated by SRIM. A-IntroductionThe ITER project and its successor DEMO (first nuclear-fusion based power plant prototype) aim at demonstrating power production by magnetic confinement nuclear fusion. Plasma start-up and continuous operation in the case of a tokamak reactor require very efficient heating and non-inductive current drive systems. Neutral beam injection (NBI) which uses high power beams of fast neutral atoms of hydrogen isotopes to heat the plasma is a promising candidate. In most existing NBI systems on contemporary fusion experiments a beam of positive ions is extracted from a conventional ion source, accelerated to energies of the order of 100 keV and neutralized via charge exchange in a background of neutral hydrogen. Due to the much larger physical dimensions the NBI systems for both ITER and DEMO require neutral beam energies in the 1 to 2 MeV range where the neutralization of positive ions becomes very inefficient and only the negative ions can be neutralized with sufficient yield. Hence the development of high current negative ion sources (50A D-beam for ITER) is crucial to the development of the ITER and DEMO NBI systems. The highcurrent-density negative-ion source for ITER 1 is currently the subject of intense research

show abstract

“…Such ions, produced in the cathode fall region and arriving on the growth surface with a kinetic energy corresponding to the potential just in front of the cathode (maximal 250-300 V in our case [3]), appear to play a role in the formation of the structure of growing (oxide) films [23][24][25][26][27]. A hypothesis could be that with increasing O 2 partial pressure, and thus with increasing x-value, the flux of the energetic O À increases [27,5].…”

Section: Argonmentioning

confidence: 99%