Determination of diffusion in polycrystalline platinum thin films (original) (raw)
Related papers
Applied Surface Science, 1998
Thin Pt/TiO,_,, sensing films are characterized with X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) to investigate the mechanism of resistance decreases measured in situ on exposure to hydrogen and propylene. The Pt/TiO,_, films are prepared by oxidizing 65 A Pt/65 A Ti films in IO-' mbar O2 at 800 to 900 K. The gas sensitivity of the films arises with activation that consists of a reduction step at 750 K followed by a final oxidation treatment at 900 K. Changes in the film stoichiometry during each of the pretreatment and activation steps can be clearly detected with XPS. The onset of gas sensitivity is attributed to oxidation of the titanium metal and the formation of a discontinuous film structure which is revealed in scanning electron microscopy @EM) images of activated Pt/TiO,_, sensing films. Resistance decreases in the I to 10% range are observed for these films following hydrogen or propylene exposure in the lO-6 to IO-' mbar range at T I 700 K. Larger resistance decreases are observed with increasing reducing gas pressure. The resistance decreases are caused by surface reduction at TI 700 K with increasing involvement of the sub-surface and bulk oxygen with increasing temperature. UPS measurements indicate that resistance decreases due to reducing gas exposure at film temperatures I 700 K can be correlated with decreases in the surface oxygen concentration too small to be observed by XPS. 0 1998 Elsevier Science B.V.
Study of platinum thin films deposited by MOCVD as electrodes for oxide applications
Microelectronic Engineering, 2002
Platinum thin films are suitable candidates as electrodes for high permittivity and ferroelectric oxides. Pt films were prepared by metal organic chemical vapor deposition (MOCVD) using a direct liquid delivery system. This method is based on the oxidative decomposition of (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe ), as a precursor, diluted in cyclohexane solvent. Different deposition conditions were used to grow 3 high purity platinum films on TiO / SiO / Si and SiO / Si substrates. Adhesion properties of the Pt CVD films 2 2 2 on TiO were found to be better than directly on SiO since TiO acts as a 'glue layer'. Platinum films 2 2 2 deposited exhibit a roughness ranged from 3.1 to 4.5 nm and a thickness between 60 and 100 nm.
Electroless deposition of Pt on Ti
Journal of Electroanalytical Chemistry, 2001
ABSTRACT The reduction of oxygen on electroless deposited platinum on a freshly polished titanium electrode was studied in aqueous 0.1 M HClO4 and 0.2 M NaOH solutions, utilising the rotating-disc electrode technique. TEM studies show that at short deposition times Pt is highly dispersed on titanium. At longer deposition times the degree of dispersion decreases due to coalescence and agglomeration processes and larger clusters are formed. The kinetics of oxygen reduction were affected substantially by the time of Pt deposition on Ti at the open-circuit potential. A kinetic analysis of the current–potential curves was made in the kinetically controlled region in the form of Tafel plots and in the mixed kinetic-diffusion control region in the form of Koutecky–Levich plots. The catalytic activity of the Pt crystals decreases with increasing deposition time. The results were interpreted in terms of the effect of the Pt crystal size. The larger the Pt particles the lower the catalytic activity. The role of titanium oxide formation and the electronic effects were also discussed.
International Journal of Hydrogen Energy, 2010
Platinum was deposited by pulsed laser deposition at different kinetic energy by varying the He background pressure in the deposition chamber. As a result, the porosity of the film varies from 5 to 86% as the He pressure is increased. This yields to an increase of the electrochemically active surface area and to an increased resistance to poisoning by CO, as evidenced by a 45 mV shift of the peak potential of the CO stripping peak towards less positive values. Similarly, the electrocatalytic activity of the films for the oxygen reduction reaction, as measured by the potential at half limiting diffusion current, is enhanced. However, a comparison between the intrinsic electrocatalytic activities of the films show that they have similar values (within a factor of 1.8) and do not significantly differ from that of a polycrystalline Pt disk, indicating that the increased activity for the ORR is mainly due to a geometric (electrochemically active surface area) effect.
Chemical Vapor Deposition, 2003
A potentially manufacturable liquid-source MOCVD process was applied to deposit platinum (Pt) films (12±140 nm) on thermally oxidized Si substrates. The deposition of Pt films was carried out at a substrate temperature of 350 C by oxygen-assisted pyrolysis of complex precursors in a low-pressure, hot-wall reactor. The effects of two different metal±organic precursors, a) trimethyl methyl cyclopentadienyl platinum [(CH 3) 3 CH 3 CpPt], and b) platinum acetylacetonate [Pt(acac) 2 ], on the properties of Pt films were studied. Although the polycrystalline Pt films deposited from Pt(acac) 2 exhibited a preferred (111) orientation with a X-ray intensity ratio of I (111) /I (200) = 40, the films deposited from (CH 3) 3 CH 3 CpPt were highly (111) oriented with I (111) /I (200) = 270. The following properties were typical of Pt films from Pt(acac) 2 as compared to Pt films from (CH 3) 3 CH 3 CpPt: finer grain size (25 nm vs. 50 nm), smaller root mean square (rms) surface roughness (5 nm vs. 15 nm), and better step coverage (95 % vs. 35 %). These experimental findings indicated that growth of Pt films from Pt(acac) 2 occurred under the kinetically-limited regime, whereas the deposition of Pt from (CH 3) 3 CH 3 CpPt was limited by the mass transport rate. Additionally, the temperature (4.2±293 K) dependence of the electrical resistivities (r) of Pt films was measured and the electron mean free paths were estimated. It was observed that r(T) deviated from Matthiessen's rule.
Low temperature diffusion of Pt and Au atoms through thin TiO2 films on a Ti substrate
Surface Science, 1987
We have characterized with XPS and UPS thin films of titanium oxide grown by oxidizing a Ti(0001) surface. The oxide films are easily reduced by thermal treatments. Typically, annealing to 500 K causes-20% of anionic vacancies. We present evidences for the existence of anionic overlayers on the surface of TiO 2 films that are stable at or below room temperatures. Deposition of Pt or Au atoms on thin (few atomic layers) TiO2 films at 80 K results in diffusion of the deposited metals through the oxide to the metal-oxide interface. This result may be interpreted on the basis of the Cabrera-Mott theory for oxidation of metals at low temperatures.
Pt-Cr thin-film interdiffusion processes and the role of a Ti interlayer on Fe (99.998%) substrates
Applied Surface Science, 1994
Auger electron spectroscopy with composition depth profiling was used to study the HV thermal interdiffusion processes of consecutive thin films of Pt, Cr and Ti vapour deposited on Fe substrates. The Ti interlayer serves as a "getter" for possible contaminants (C, N, etc.) diffusing mostly from the bulk of the metallic substrates. The unbound 0 which was trapped during the vapour deposition of the Cr layer also diffuses into the Ti layer upon annealing. Although the diffusion of the N, C and 0 was limited by the influence of the Ti interlayer the phases formed at the respective temperatures were similar to those formed in samples without Ti interlayers. At an annealing temperature of 400°C in high vacuum no phases were observed while for an annealing temperature of 500°C the phase Pt,Cr was detected by XRD. Annealing at 600°C in HV yielded two phases namely PtCr and PtCr,. The latter is not indicated on the bulk Pt-Cr phase diagram.
Thin Solid Films, 2010
Platinum thin films were grown onto (001) oriented SrTiO 3 substrates by means of the pulsed laser deposition technique. Structural and morphological characterizations were performed using XRD and AFM. The influence of substrate temperature and deposition rate was analyzed on the crystallographic properties of the film. As a result, an increment in the crystallinity of the film due to the change on the temperature was observed. On the other hand, Pt films showed a granular morphology and its roughness was related to the fluence and low deposition temperature. Finally their electrical properties were analyzed and discussed as a function of the previous morphological results.
Electrodeposition and Sputter Deposition of Platinum Nanoparticles on Gas Diffusion Electrodes
The polymer electrolyte fuel cells (PEFCs) have high potentiality for their use in electrical vehicles, electric power production and power for consumer electronic. The PEFC's gas diffusion electrodes are catalyzed by deposition of Pt nanoparticles on carbon powder. Such particles must be localized on the electrode surface to achieve high electrocatalyst utilization. The traditional techniques for the electrocatalyst deposition (impregnation followed chemical reduction of metal precursors) do not allow a surface localization and therefore it is necessary to deposit high quantity of Pt. By means of electrodeposition (EDP) and sputter deposition (PVD) it is possible to localize the Pt on the electrode surface. In fact, both techniques ensure catalyst will be located only in regions that have access to electrons and protons, and the catalyst loading will be highly reduced. In this work we describe the preparation methods based on the electrochemical and sputter deposition of low-lo...