Nanolithography by tip-enhanced laser irradiation

Abstract

Recently, scanning probe lithography by applying an electric field between the tip and the sample has been shown to be a promising technique for nanofabrication. In this paper, we present a novel method of nanofabrication, namely, nanolithography by tip-enhanced laser irradiation. Based on the operation of the laser-assisted scanning tunneling microscope (STM), we established a nanolithography system using tip-enhanced laser irradiation, which was developed from a commercial scanning probe microscope (SPM). In our investigation, the SPM was operated as an STM. During imaging and lithography, the STM is in a constant current mode. The tip is fixed and the sample moves via a tube scanner. Nanolithography software controls the scanner movement in the x and y direction. The SPM has an open architecture, allowing an external laser beam incident on the tip at an incident angle between 0 to 45°. A vertical polarized Nd:YAG pulsed laser with a pulse duration of 7 ns was focused on the surfaces of the tip and the sample. An electrical shutter was introduced to switch the laser irradiation during lithography. Alignment of the laser to the tip-sample gap was performed under a high power charge coupled device (CCD) microscope. Nanolithography was performed on hydrogen (H)-passivated Si (100) surfaces and H-passivated Ge (100) surfaces. The Si samples and the Ge samples were passivated in HF solution. STM tips were homemade electrochemically from a 0.5-mm tungsten wire. Oxide features were created by tip-enhanced laser irradiation. The experimental results will be discussed.