593 research outputs found
Influence of inert gases on the reactive high power pulsed magnetron sputtering process of carbon-nitride thin films
The influence of inert gases (Ne, Ar, Kr) on the sputter process of carbon and carbon-nitride (CNx)
thin films was studied using reactive high power pulsed magnetron sputtering (HiPIMS). Thin solid
films were synthesized in an industrial deposition chamber from a graphite target. The peak target
current during HiPIMS processing was found to decrease with increasing inert gas mass. Time
averaged and time resolved ion mass spectroscopy showed that the addition of nitrogen, as reactive
gas, resulted in less energetic ion species for processes employing Ne, whereas the opposite was
noticed when Ar or Kr were employed as inert gas. Processes in nonreactive ambient showed
generally lower total ion fluxes for the three different inert gases. As soon as N2 was introduced
into the process, the deposition rates for Ne and Ar-containing processes increased significantly.
The reactive Kr-process, in contrast, showed slightly lower deposition rates than the nonreactive.
The resulting thin films were characterized regarding their bonding and microstructure by x-ray
photoelectron spectroscopy and transmission electron microscopy. Reactively deposited CNx thin
films in Ar and Kr ambient exhibited an ordering toward a fullerene-like structure, whereas carbon
and CNx films deposited in Ne atmosphere were found to be amorphous. This is attributed to an
elevated amount of highly energetic particles observed during ion mass spectrometry and indicated
by high peak target currents in Ne-containing processes. These results are discussed with respect to
the current understanding of the structural evolution of a-C and CNx thin films. VC 2013 American
Vacuum Society. [http://dx.doi.org/10.1116/1.4769725
Electronic excitation of transition metal nitrides by light ions with keV energies
We investigated the specific electronic energy deposition by protons and He
ions with keV energies in different transition metal nitrides of technological
interest. Data were obtained from two different time-of-flight ion scattering
setups and show excellent agreement. For protons interacting with light
nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom
were found, which coincide with literature data of N2 gas for primary energies
<= 25 keV. In case of the chemically rather similar nitrides with metal
constituents from the 5th and 6th period, i.e. ZrN and HfN, the electronic
stopping cross sections were measured to exceed what has been observed for
molecular N2 gas. For He ions, electronic energy loss in all nitrides was found
to be significantly higher compared to the equivalent data of N2 gas.
Additionally, deviations from velocity proportionality of the observed specific
electronic energy loss are observed. A comparison with predictions from density
functional theory for protons and He ions yields a high apparent efficiency of
electronic excitations of the target for the latter projectile. These findings
are considered to indicate the contributions of additional mechanisms besides
electron hole pair excitations, such as electron capture and loss processes of
the projectile or promotion of target electrons in atomic collisions
Effect of impurities on morphology and growth mode of (111) and (001) epitaxial-like ScN films
ScN material is an emerging semiconductor with an indirect bandgap. It has
attracted attention for its thermoelectric properties, use as seed layers, and
for alloys for piezoelectric application. ScN or other transition metal nitride
semiconductors used for their interesting electrical properties are sensitive
to contaminants, such as oxygen or fluorine. In this present article, the
influence of depositions conditions on the amount of oxygen contaminants
incorporated in ScN films were investigated and their effects on the electrical
properties (electrical resistivity and Seebeck coefficient) were studied. The
epitaxial-like films of thickness 125 +-5 nm to 155 +-5 nm were deposited by
D.C.-magnetron sputtering on c-plane Al2O3, MgO(111) and r-plane Al2O3 at a
substrate temperature ranging from 700 to 950 degree C. The amount of oxygen
contaminants presents in the film, dissolved into ScN or as an oxide, was
related to the adatom mobility during growth, which is affected by the
deposition temperature and the presence of twin domain growth. The lowest
values of electrical resistivity of 50 micro-ohm cm were obtained on
ScN(111)/MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degree C with no
twin domains and the lowest amount of oxygen contaminant. At the best, the
films exhibited an electrical resistivity of 50 micro-ohm cm with Seebeck
coefficient values maintained at -40 microV K-1, thus a power factor estimated
at 3.2 10-3 W m-1 K-2 (at room temperature)
CrNx Films Prepared by DC Magnetron Sputtering and High-Power Pulsed Magnetron Sputtering: A Comparative Study
Abstract-CrN x (0 ≤ x ≤ 0.91) films synthesized using highpower pulsed magnetron sputtering, also known as high-power impulse magnetron sputtering (HiPIMS), have been compared with those made by conventional direct-current (dc) magnetron sputtering (DCMS) operated at the same average power. The HiPIMS deposition rate relative to the DCMS rate was found to decrease linearly with increasing emission strength from the Cr ions relative to Cr neutrals, in agreement with the predictions of the target-pathway model. The low deposition rate in HiPIMS is thus a direct consequence of the high ionization level (∼56%) of the target material and effective capturing of Cr ions by the cathode potential. Although the HiPIMS deposition rate did not exceed 40% of the DCMS rate, the drop in the relative deposition rate upon increasing the N 2 -to-Ar flow ratio, f N 2 /Ar , was found to be similar for both sputtering techniques. Films prepared by HiPIMS contained similar amounts of atomic nitrogen as the dc-sputtered samples grown at the same f N 2 /Ar , indicating that the nitride formation at the substrate takes place mostly during the time period of the high-power pulses, and the N 2 uptake between the pulses is negligible. The microstructure evolution in the two types of CrN x films, however, differed clearly from each other. A combination of a high substrate bias and a high flux of doubly charged Cr ions present during the HiPIMS discharge led to a disruption of the grain growth and renucleation, which resulted in column-free films with nanosized grains not observed in the conventional DCMS-based process. The comparison of nanoindentation hardness as a function of f N 2 /Ar revealed superior properties of HiPIMS-sputtered films in the entire range of gas compositions. Index Terms-CrN, high-power impulse magnetron sputtering (HiPIMS), high-power pulsed magnetron sputtering, magnetron sputtering
Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy
The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge
(1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption
fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target
from which the film was synthesized as well as a bulk {\alpha}-Zr reference.
Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at
the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound
target and ~22% O in the bulk {\alpha}-Zr reference after completed sputter
cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but
visible -111, 111, and 220 peaks from monoclinic ZrO2 together with peaks from
ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly
oriented target material. For the bulk {\alpha}-Zr reference no peaks from any
crystalline oxide were visible in the diffractogram recorded from the
0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples
demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in
the bulk ZrB2 attributed to the high atomic ordering within the columns of the
film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2,
but with a chemical shift towards higher energy of 4 eV in the film and 6 eV
for the bulk compared to {\alpha}-Zr (17.993 keV) from the charge-transfer from
Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen
content than in the epitaxial film, which is supported by XPS. In EXAFS, the
modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 {\AA},
c=3.520 {\AA}) in comparison to the bulk target material (a=3.175 {\AA},
c=3.540 {\AA}) while in hexagonal closest-packed metal ({\alpha}-phase, a=3.254
{\AA}, c=5.147 {\AA}).Comment: 15 pages, 5 Figures, 4 table
Compositional and structural studies of ion-beam modified AlN/TiN multilayers
This work was supported the Serbian Ministry of Education, Science and Technological Development (project ON 171023), ERC Advanced Investigator grant (226470 SILAMPS), and the International Atomic Energy Agency, Vienna (CRP 12024). We thank Petro Parisse and Loredana Casalis of the NanoInnovation Laboratory of Elettra – Sincrotrone Trieste SCpA for the AFM measurements
Thermoelectric properties and electronic structure of Cr(Mo,V)Nx thin films studied by synchrotron and lab-based X-ray spectroscopy
Chromium-based nitrides are used in hard, resilient coatings, and show
promise for thermoelectric applications due to their combination of structural,
thermal, and electronic properties. Here, we investigated the electronic
structures and chemical bonding correlated to the thermoelectric properties of
epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films.
Due to minuscule N vacancies, finite population of Cr 3d and N 2p states appear
at the Fermi level and diminishes the band opening for Cr0.51N0.49.
Incorporating holes by alloying V in N deficient CrN matrix results in enhanced
thermoelectric power factor with marginal change in the charge transfer of Cr
to N compared to Cr0.51N0.49. Further alloying Mo isoelectronic to Cr increases
the density of states across the Fermi level due to hybridization of the (Cr,
V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. The hybridization effect with
reduced N 2p states off from stoichiometry drives the system towards metal like
electrical resistivity and reduction in Seebeck coefficient compensating the
overall power factor still comparable to Cr0.51N0.49. The N deficiency also
depicts a critical role in reduction of the charge transfer from metal to N
site. The present work envisages ways for enhancing thermoelectric properties
through electronic band engineering by alloying and competing effects of N
vacancies.Comment: 27 pages, 11 figures, 2 table
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