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## The β to α phase transition of tantalum coatings deposited by modulated pulsed power magnetron sputtering

Myers, Sterling; Jianliang, Lin; Souza, Roberto Martins de; Sproul, Willian D; Moore, John J
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
76.25%
Tantalum coatings are of particular interest today as promising candidates to replace potentially hazardous electrodeposited chromium coatings for tribological and corrosion resistant applications, such as the internal lining on large-caliber gun barrels. Tantalum coatings have two crystalline phases, α-Ta (body-centered-cubic) and β-Ta (metastable tetragonal) that exhibit relatively different properties. Alpha-Ta is typically preferred for wear and corrosion resistant applications and unfortunately, is very difficult to deposit without the assistance of substrate heating or post-annealing treatments. Furthermore, there is no general consensus on the mechanism which causes α or β to form or if there is a phase transition or transformation from β → α during coating deposition. In this study, modulated pulsed power (MPP) magnetron sputtering was used to deposit tantalum coatings with thicknesses between 2 and 20 μm without external substrate heating. The MPP Ta coatings showed good adhesion and low residual stress. This study shows there is an abrupt β → α phase transition when the coating is 5–7 μm thick and not a total phase transformation. Thermocouple measurements reveal substrate temperature increases as a function of deposition time until reaching a saturation temperature of ~ 388 °C. The importance of substrate temperature evolution on the β → α phase transition is also explained.

## Projeto, desenvolvimento e construção de um modulador de pulso estado-solido para transmissores pulsados de alta potencia; Design, development and implementation of a solid-state pulse modulator for high-power pulse transmitters

Bruno Rondani
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
46.06%

## Characterization of the micro and nanostructure of biocide nanocomposites based in transparent titanium dioxide nanocoatings deposited on polymeric foils for food packaging applications; Caracterização da micro e nanoestrutura de nanocompósitos biocidas à base de nanorevestimentos transparentes de dióxido de titânio depositados em polímeros para aplicações em embalagens alimentares

Morais, Bruno Daniel Pinto
Relevância na Pesquisa
15.81%
Dissertação de mestrado em Biophysics and Bionanosystems; Packaging provides containment and protects food products during distribution and storage from external and internal unfavorable conditions, such as water vapor, microorganisms, gases and odors. Nowadays consumers’ demands require the development functional packaging systems with enhanced quality and self-life such as active food packaging which directly interacts with the food product through a mechanism triggered by intrinsic and/or extrinsic factors. Due to the rise in deaths and hospitalizations related with food poisoning and foodborne diseases, much effort has been made to design efficient antimicrobial active packaging systems. Many antimicrobial agents are available, including both organic and inorganic. One of these potential agents is titanium dioxide (TiO2). Since the discovery of the photocatalytic potential of TiO2, there has been an increase in research and products that take advantage of this process for depollution and disinfection applications and, more recently, antimicrobial food packaging. Its strong photocatalytic yield is the result of the high oxidizing power under UV-light. Other attractive properties include high chemical stability, non-toxic to both human and the environment...

## High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2films: the effect of repetition frequency

Šícha, J; Heřman, D; Musil, J; Strýhal, Z; Pavlík, J
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36%
The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO2thin films using dc dual magnetron (DM) sputtering in Ar + O2mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature Tsurfmeasured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency frwas investigated in detail. It was found that the increase of frfrom 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate aDof sputtered TiO2films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO2films can be sputtered on unheated glass substrates at aD = 80 nm/min, Tsurf < 180 °C when high value of fr = 350 kHz was used. Properties of a thin hydrophilic TiO2film deposited on a polycarbonate substrate are given.

## Low Friction CrNMPP/TiNDCMS Multilayer Coatings

Paulitsch, J.; Maringer, C.; Mayrhofer, P. H.
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36%
Transition metal nitrides like CrN and TiN are widely used in automotive applications due to their high hardness and wear resistance. Recently, we showed that a multilayer architecture of CrN and TiN, deposited using the hybrid—high power impulse magnetron sputtering (HIPIMS) and direct current magnetron sputtering (DCMS)—HIPIMS/DCMS deposition technique, results in coatings which indicate not only increased mechanical and tribological properties but also friction coefficients in the range of diamond-like-carbon coatings when tested at RT and ambient air conditions. The modulated pulsed power (MPP) deposition technique was used to replace the HIPIMS powered cathode within this study to allow for a higher deposition rate, which is based on the complex MPP pulse configuration. Our results on MPP/DCMS deposited CrN/TiN multilayer coatings indicate excellent mechanical and tribological properties, comparable to those obtained for HIPIMS/DCMS. Hardness values are around 25 GPa with wear rates in the range of 2 × 10−16 Nm/m3 and a coefficient of friction around 0.05 when preparing a superlattice structure. The low friction values can directly be correlated to the relative humidity in the ambient air during dry sliding testing. A minimum relative humidity of 13% is necessary to guarantee such low friction values...

## Fast time resolved techniques as key to the understanding of energy and particle transport in HPPMS-plasmas

Maszl, Christian; Breilmann, Wolfgang; Berscheid, Lars; Benedikt, Jan; von Keudell, Achim
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.91%
High power pulsed magnetron sputtering (HPPMS) plasmas are pulsed discharges where the plasma composition as well as the fluxes and energies of ions are changing during the pulse. The time resolved energy distribution for Ar$^{1+}$ ions was measured and Phase Resolved Optical Emission Spectroscopy (PROES) for the Ar I line at 760 nm was done to get more insight in the transport properties of the plasma forming noble gas. These measurements were performed during HPPMS of titanium with argon at 0.5 Pa. The peak power density during the 50 $\mu$s pulses was 1.8 kW/cm$^2$. In this contribution we demonstrate how time resolved mass spectrometry and ICCD cameras can be used to shed more light on energy and particle transport in HPPMS-plasmas.; Comment: The manuscript was submitted to the 7th Triennial Special Issue of the IEEE Transactions on Plasma Science "Images in Plasma Science," scheduled for publication in September 2014. The manuscript length is limited to 2 pages!

## Time resolved measurement of film growth during reactive high power pulsed magnetron sputtering (HIPIMS) of titanium nitride

Mitschker, Felix; Prenzel, Marina; Benedikt, Jan; Maszl, Christian; von Keudell, Achim
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
86.06%
The growth rate during reactive high power pulsed magnetron sputtering (HIPIMS) of titanium nitride is measured with a temporal resolution of up to 25 us using a rotating shutter concept. According to that concept a 200 um slit is rotated in front of the substrate synchronous with the HIPIMS pulses. Thereby, the growth flux is laterally distributed over the substrate. By measuring the resulting deposition profile with profilometry and with x-ray photoelectron spectroscopy, the temporal variation of the titanium and nitrogen growth flux per pulse is deduced. The analysis reveals that film growth occurs mainly during a HIPIMS pulse, with the growth rate following the HIPIMS phases ignition, current rise, gas rarefaction, plateau and afterglow. The growth fluxes of titanium and nitrogen follow slightly different behaviors with titanium dominating at the beginning of the HIPIMS pulse and nitrogen at the end of the pulse. This is explained by the gas rarefaction effect resulting in a dense initial metal plasma and metal films which are subsequently being nitrified.

## Origin of the energetic ions at the substrate generated during high power pulsed magnetron sputtering of titanium

Maszl, Christian; Breilmann, Wolfgang; Benedikt, Jan; von Keudell, Achim
HiPIMS plasmas generate energetic metal ions at the substrate as a major difference to conventional direct current magnetron sputtering. The origin of these ions is still an open issue, which is unraveled by using two fast diagnostics: time resolved mass spectrometry with a temporal resolution of 2 $\mu$s and phase resolved optical emission spectroscopy with a temporal resolution of 1 $\mu$s. A power scan from dcMS-like to HiPIMS plasmas was performed, with a 2-inch magnetron and a titanium target as sputter source and argon as working gas. Clear differences in the transport as well in the energetic properties of Ar$^{+}$, Ar$^{2+}$, Ti$^+$ and Ti$^{2+}$ were observed. For discharges with highest peak power densities a high energetic group of Ti$^+$ and Ti$^{2+}$ could be identified. A cold group of ions is always present. It is found that hot ions are observed only, when the plasma enters the spokes regime, which can be monitored by oscillations in the IV-characteristics in the MHz range that are picked up by the used VI-probes. These oscillations are correlated with the spokes phenomenon and are explained as an amplification of the Hall current inside the spokes as hot ionization zones. To explain the presence of energetic ions, we propose a double layer (DL) confining the hot plasma inside a spoke: if an atom becomes ionized inside the spokes region it is accelerated because of the DL to higher energies whereas its energy remains unchanged if it is ionized outside. In applying this DL model to our measurements the observed phenomena as well as several measurements from other groups can be explained. Only if spokes and a double layer are present the confined particles can gain enough energy to leave the magnetic trap. We conclude from our findings that the spoke phenomenon represents the essence of HiPIMS plasmas...