Conference Report: Nano Tech + Future 2003 Chiba, Japan, February ’03

0 M.B. Cortie 1st April 2003 Director Institute for Nanoscale Technology UTS Sydney Australia 1. Introduction 2. Nanotechnology + Future 2003 2.1 Exhibition With over 200 stands, the exhibition hall was large and busy. It was very well attended and the organisers reported that by the end of the week over 25,000 persons had passed through. My observation was that it was a more significant drawcard than the conference itself. My colleagues and I spent at least ten hours, spread over the three days of the event, trawling the exhibition for technical information. A minor problem encountered was that the larger proportion of the posters and written information was in Japanese. However, in most (but not all) cases an individual manning the booth was able to elucidate the content. A close examination of the materials on display was frequently able to reveal some aspect, even if minor, that involved the use of gold. Use of gold bonding wire, contacts and substrates was not uncommon, however in the present report I will concentrate rather on the specifically nanotechnological uses of gold. The large NEDO stand1 contained posters describing the use of gold electrodes for determining the concentration of organic species in aqueous solution (evidently by electrooxidation but some language difficulties intruded in this respect so I am not absolutely sure) and the well-known use of gold-coated substrates as platforms on which to perform self-assembly of organic molecules. A collaborative poster by Mitsubishi Materials and Dai Nippon Toryo described the manufacture of gold nano-rods, of 70 nm length by about 8 nm diameter. These were described as having potential applications in optical filters and for manipulating infra-red radiation. These particular gold rods have excellent aspect ratios compared to those reported by others. The SET Tsukuba Research Centre had a poster describing gold deposited onto Ni alloy bumps for packaging chips using ultrasonic flip chip technology. The nickel was deposited by the electroless method, and the gold layer is required to protect the nickel from oxidation. The individual gold-coated bumps were 12 x 12 m square and 7.5 m deep. Flip-chip technology has the potential to displace gold bonding wire from much or some (opinions differ!) of its previous market niche. The use of gold coatings in flip chip technology is therefore a partial compensation for this change. A poster of the MIRAI project (a multi-institute initiative which seeks to develop the next generation of electronics, and which lies within Japans AIST science organization), described the use of gold as the gate electrode in new experimental transistors using high- dielectrics such as HfO2. The gold is evidently used for reasons of chemical compatibility with the production process. Japans AIST had a stand showcasing the best of local research, and there information was presented on a correlated electron spin tunnelling device which, once again, used gold electrodes. Unfortunately the main text was in Japanese and a reference provided on the poster to an English-language scientific paper proved, when followed up, to relate to something completely different. AIST and Fujitsu Limited also displayed a magnetoresistive switching device made from GaAs and gold nanoclusters. It was said to have the highest magneto-resistance ratio (10,000%) ever achieved. The application would ostensibly be as an ultra-sensitive magneto-resistance sensor or as a spin-electronics device. Tanaka Kikinzoku Kogyo K.K. had samples of gold nanoparticles in colloidal suspension on display, and advertised these materials as being for sale in the 20 and 40 nm sizes. They also offered HAuCl4, and a variety of PGM colloids. At the Indian stand, posters described how gold nanoparticles could be printed at very high resolution onto a flexible plastic substrate, using a hydrosol and the dip pen method. Another poster described how lysine-modified gold particles could be attached to DNA molecules, however, no particular application for these technologies was cited. More immediate perhaps, was the use of gold nano-particles for a colorimetric test for the pesticide endosulfan, which was claimed to be sensitive down to levels of 0.1 ppm. Endosulfan is an orgonochlorine pesticide linked to serious public health problems in India on account of poorly controlled use (3). Finally, a stand of Germanys Fraunhofer Institute showcased the stacked patch antennae of Porches (experimental?) new adaptive cruise control. Evidently, the device operates like an on-road radar, and would bring the vehicle out of cruise control and de-accelerate if it detected an obstacle ahead. The device used nanoscale layers of gold. On being questioned regarding the choice of gold, as opposed to some other conductor, Dr Michael Popall explained that at the high frequencies involved (from 28 to 77 GHz!) the current is carried only on the extreme surface layers of the conductor, necessitating an oxide-free surface. Hence gold. If generally true, this implies that other new applications for gold in analogue circuits should open up as the region of spectrum from 1 GHz to 1 THz is increasingly exploited. 2.2 Conference According to the conference organisers, over 3,500 people registered for the conference. However, there were many parallel sessions, and as usual, attendance tailed off in the 1NEDO is the umbrella Japanese government science agency, and was one of the main sponsoring organizations for the exhibition afternoon. Nevertheless, the quality of the presentations was in general very good. The use of gold as a mask in new generation lithography techniques was mentioned by a Japanese team (4). Most research is focused in ultra-violet lithography, which might use chromium metal in the mask. However these workers used a flux of high energy bromine ions for their lithography, and chose to use a mask of gold, as apparently do many individuals working with X-ray lithography. When immersed in dielectric matrices, gold nanoparticles can have non-linear optical properties, and this topic has been the focus of a modest amount of research around the world. This theme saw expression at the conference in a paper submitted (5) from Singapores A*STAR Institute of Microelectronics. The author was supposed to be showing how hybrid core-shell nano-particles comprised of gold and cadmium selenide could be used to obtain very high, third-order, non-linear behaviour. Unfortunately he or she did not pitch. This topic is of interest in the context of optical telecommunication circuitry, for use in optical switches and polymer waveguides, although it must be pointed out that conventional bulk non-linear materials are still completely dominant in current devices. My own talk (1) was not directly concerned with gold, however, I did mention its occasional use in nano-scale coatings on window glass to selectively block infra-red radiation. Currently, other coating (...truncated)