Nanostructure fabrication with a point contact formation between a gold tip and a Si(111)-(7×7) surface with an ultrahigh vacuum scanning tunneling microscope

Abstract

Ultra-small gold dots of ∼5 nm in diameter have been fabricated reproducibly on a Si(111)-(7 × 7) surface in ultrahigh vacuum at room temperature and at 50 K by applying pulses to a piezo z-axis of a scanning tunneling microscope (z-pulse method). Nanodot formation by the z-pulse method can be attributed to the spontaneous formation of a nanometer-scale point contact of a gold-tip apex on the surface. Atomically resolved images of the reconstructed structure are still observable even after many cycles of point contact formation. Owing to its high deposition probability, fabrication of a continuous gold nanoline of 5 nm wide and 50 nm long can be realized.Fabrication of nanometer-scale structures has become very important during the last decade, not only for scientific interests [1, 2], but also for the potential technological applications in nanoelectronics [3]. The advent of a scanning tunneling microscope (STM) and related scanning probe microscopes (SPM) has spurred this trend significantly. The STM-based techniques have already proved themselves to be extremely powerful tools for nanotechnology [4]. Various nanofabrication techniques using SPM have been proposed and realized: for example, atom manipulation [5], local deposition from organometallic gases [6], nanoscale selective oxidation [7], nanoscale lithography [8], field induced transfer of tip material [9][10][11][12], and so on. The final goal of our research project is to create nanodevices such as single electron tunneling (SET) circuits on a clean surface by using STM nanofabrication techniques. Matsumoto et al. have already fabricated SET transistors by the STM nano-oxidation process in air [13].

Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

“…Consequently, local electrical resistivity increases near the surface with respect to its bulk value. Similar space-charge regions under gold nanodots on n-Si(111) were also demonstrated by artificial point contact [31].…”

“…An image of a typical gold nanodot formed after applying a single z-pulse ( z = −0.3 nm, T pulse = 1 ms) at 50 K [31] is shown in figure 6(b). The image clearly shows a gold nanodot protruding from the Si(111)-(7×7) surface, whose dimensions are about 6 nm in diameter across the base and 0.9 nm in height.…”

“…If tip-material transfer is mainly caused by the spontaneous formation of a point contact, then it will be possible to deposit the tip material by artificial point-contact formation. On the basis of this idea, the so-called 'z-pulse method' was developed [31]. This technique uses the controlled approach of the tip to the surface to form an atomic point contact by applying a voltage pulse to a z-direction piezo-actuator.…”