A Novel Study of the Growth and Resistivity of Nanocrystalline Pt Films Obtained from Pt(acac)2 in the Presence of Oxygen or Water Vapor

Abstract

d Mass production of millimeter long SWNTs with a very high production yield of SWNTs to catalyst.d Ease of up-scaling by introducing an antenna array (i.e., multiple antennae) for mass production of SWNTs on very large, flat substrates. Unlike other MPCVD, it is unnecessary to consider the geometric and electric boundary conditions. In conclusion, our point-arc MPCVD method is preferable for controlled growth of SWNTs at a low (600 C) temperature on Si substrates coated with a sandwich-like coating structure; Al 2 O 3 (0.5±0.7 nm, top)/Fe (0.5 nm)/ Al 2 O 3 (5±70 nm, bottom) by high frequency, magnetron sputtering. The as-grown SWNT films are extremely dense (66 kg m ±3) and vertically aligned. Despite the slight decrease in the average growth rate (from 340 lm h ±1 in 3 min to 210 lm h ±1 in 2 h), the thickness of SWNTs increases continuously with the growth time, indicating that there is almost no loss of catalyst activity during the long growth period. A film thickness of 420 lm and a very high production yield of 770 000 % were obtained within 2 h. Thus, a promising future for direct applications research using SWNTs prepared on large substrates by our point-arc MPCVD, without further purification, is expected. ExperimentalIn this study, we employed a high frequency, magnetron sputter for the preparation of substrates, and a novel point-arc MPCVD apparatus for the growth of SWNTs, as shown in Figures 5a and b, respectively. All the prepared substrates had a sandwich-like coating structure of 0.5±0.7 nm Al 2 O 3 /0.5 nm Fe/5±70 nm Al 2 O 3 (/Si), see Figure 5a. The Al 2 O 3 was oxidized from the Al coating at room temperature under atmospheric pressure. Reference to the thickness of Al 2 O 3 does not take account of the volume expansion after oxidizing the Al coating.The growth procedure of SWNTs is carried out in the following manner. First, a substrate placed 50 mm away from a tungsten antenna is heated to 600 C by an inductive heater under a chamber pressure of 20 torr, with constant gas flow rates of H 2 (45 sccm) and CH 4 (5 sccm) in a time of 5 min. A spot thermometer (TR-630) is employed to monitor the substrate temperature. Then, a microwave power of 60 W is switched on to start the deposition of SWNTs. The generated point-arc plasma ball (or plasma discharge sphere, about 10 mm in diameter) is concentrated and immobilized on the tip of the tungsten antenna, see Figure 5b. After a few minutes or hours, the microwave plasma and substrate heater are switched off to end the CVD process.All the as-grown samples were observed using FE-SEM (Hitachi S4800). Selected samples were characterized by Raman scattering (Renishaw invia Raman microscopes), and TEM (JEOL 2010). For the preparation of each TEM specimen, a small piece cut from an as-grown SWNT sample was subjected to an ultrasonic pulse for 30 min in a beaker filled with ethanol, then 1±3 drops of the suspension were dropped onto a Cu micro grid.

Overview of Coating Growth Mechanisms in MOCVD Processes as Observed in Pt Group Metals

“…A possible explanation could be the smaller particle size on initial stages, as observed in Ir depositions at lower deposition temperatures. Data obtained by Prof. Battiston and his colleagues [11] have confirmed our observations that decreasing deposition temperature results in Pt coatings with a more compact (111) structure. A third observation was the effect of precursor concentration.…”

“…The effects of decarburizing species like oxygen and water vapor were also confirmed in one of the last works of Prof. Battiston. [11] It was also observed that decreasing the deposition temperature leads to lower crystal sizes and more compact structures. A possible explanation could be the smaller particle size on initial stages, as observed in Ir depositions at lower deposition temperatures.…”

Titania‐Coated Platinum Thin Films by MOCVD: Electrochemical and Photoelectrochemical Properties

“…[39] In both cases, the surface reaction rates rose exponentially with temperature, suggesting a kinetic-controlled domain; the apparent activation energy was 110 and 91 kJ mol -1 in the presence of oxygen and water vapor, respectively. However, the films obtained with oxygen suffered from spatial non-homogeneity that caused a restriction in the useful temperature interval to 240-260°C, while at higher temperatures the films grew only in the first few centimeters of the reactor.…”

“…[ 39] On the basis of all the above observations, the platinum films utilized for further investigations were deposited at 380°C in the presence of water vapor. Moreover, in order to establish the minimum film thickness (and, in principle, low cost) that allowed good electrochemical properties to be achieved, Pt films with thicknesses over the range 10 to 200 nm were studied.…”

Chemical vapour deposition of platinum films on electrodes for pacemakers: Novel precursors and their thermal properties

“…Suitable MOCVD precursors are required to be volatile, thermally stable at vaporization, nontoxic, stable in air and easy to prepare in high yields . Pt forms volatile compounds with methyl, allyl, cyclopentadienyl (Cp) and β‐diketonato ligands . These types of Pt precursors were usually used for a definite purpose.…”