Basic mechanisms in laser etching and deposition

Optically-Monitored Nanopore Fabrication Using a Focused Laser Beam

Solid-state nanopores (ssNPs) are extremely versatile single-molecule sensors and their potential have been established in numerous biomedical applications. However, the fabrication of ssNPs remains the main bottleneck to their widespread use. Herein, we introduce a rapid and localizable ssNPs fabrication method based on feedback-controlled optical etching. We show that a focused blue laser beam irreversibly etches silicon nitride (SiN_x) membranes in solution. Furthermore, photoluminescence (PL) emitted from the SiN_x is used to monitor the etching process in real-time, hence permitting rate adjustment. Transmission electron microscopy (TEM) images of the etched area reveal an inverted Gaussian thickness profile, corresponding to the intensity point spread function of the laser beam. Continued laser exposure leads to the opening of a nanopore, which can be controlled to reproducibly fabricate nanopores of different sizes. The optically-formed ssNPs exhibit electrical noise on par with TEM-drilled pores, and translocate DNA and proteins readily. Notably, due to the localized thinning, the laser-drilled ssNPs exhibit highly suppressed background PL and improved spatial resolution. Given the total control over the nanopore position, this easily implemented method is ideally suited for electro-optical sensing and opens up the possibility of fabricating large nanopore arrays in situ.

Chemical Vapor Deposition Route to the Fabrication of thin Films of High Temperature Oxide Superconductors

High quality Y‐Ba‐Cu‐O thin films were produced by metal‐organic chemical vapor deposition (MOCVD) using metal chelates of P‐diketonate ligands. The films were grown in a cold‐wall CVD reactor at a reactor pressure of 10 torr and substrate temperature in the range 450‐550°C. Characterization studies were performed using Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDXS). These studies showed that the films were uniform, continuous, adherent and highly pure—carbon and fluorine contents were below the detection limits of the techniques used. Four point resistivity measurements showed that the films had a sharp superconducting transition at 9OK and exhibited current densities of ‐3x105 A/cm2 (B=0, T=65K) . The Y‐Ba‐Cu‐0 films thus grown were subsequently compared to radio‐frequency (rf) sputtered Y‐Ba‐Cu‐O films. It was found that the MOCVD‐produced films were superior in terms of uniformity, adherence, and electrical properties.

Analysis of laser-assisted chemical etching processes of a pinhole by monitoring diffraction patterns of reflected beams

The detailed processes of laser-assisted chemical etching are studied by using an optical in situ monitoring method. Various Al thin-film specimens are processed in aqueous H(3)PO(4) solutions by shining focused Ar(+) laser beams. As etching progresses, it is observed in the backreflected laser beam that a concentric circular fringe pattern appears and shrinks. The development of the etching process is explained by analyzing the diffraction patterns with an etched shape function of a Gaussian nature.