Imaging DNA on a graphite surface using a Scanning Tunneling Microscope
John A. Cowan Jr. (Final Project: Junior Lab)
Davidson College, May 7, 1996
The scanning tunneling microscope provides an effective and efficient means for analyzing the surface structure of a solid. Besides analyzing one surface the STM is capable of producing images of molecules adsorbed to the surface of another. In this experiment, linear DNA is placed on a highly ordered pyrolytic graphite (HOPG) substrate and imaged using the STM. The image is taken in the open laboratory using both a mechanically constructed and etched tip. Surface features were then analyzed revealing measurements of molecular width, and major/minor groove lengths.
Band gap energy measurements for silicon and germanium diodes
John A. Cowan Jr. and Andrew O'Dell
Davidson College, February 2, 1996
Semiconductors are very useful electronic devices which have charge carrier densities between conductors and insulators. An important element for determining the electronic properties of a semiconductor is the band gap energy. The band gap energy (Eg) represents the energy difference between the conducting band and the valence band. This report describes simple laboratory techniques for measuring the band gap energy in silicon and germanium diodes.
John A. Cowan Sr. and John A. Cowan Jr.
The Operations Manager was developed using Microsoft's Visual Basic 3.0. My father and I began development at the beginning of the summer of 1995. By the end of the summer a suitable beta version and manual had been created. Currently, the Operations Manager is undergoing beta-testing at several different sites in Georgia and North Carolina. Hopefully, by the beginning of the summer 1996 a new version will be ready for distribution.
Bragg Diffraction Using Microwaves
John A. Cowan Jr., Martin Young, and Andy Borleske
Davidson College, March 22, 1996
The stucture of a solid material may be obtained by shining a particular wavelength of radiation incident at some angle onto a solid and analyzing the reflected pattern. Such analysis is called Bragg Diffraction named after Sir Lawrence Bragg who discovered the technique. On the microscopic level Bragg Diffraction uses x-rays to map out the structure of solids with a lattice whose separation is on the order of 1 angstrom. For our experiment, we are attempting to comfirm Bragg Diffraction on the macroscopic level using microwave ( 3.0 cm) to map the structure of a lattice of aluminum ball-bearings encased in Styrofoam.
John A. Cowan Jr. and Doug Neumann
Davidson College, April 12, 1996
The scanning tunneling microscope (STM) is one type of scanning probe microscopy. In STM, a needle-like probe scans approximately 10 angstroms from the surface the substance being examined. By measuring the rate at which electrons travel from the surface to the needle, the distance to the surface of the sample can be determined using quantum mechanics. The goal of this project is to become familiar with operating the apparatus, constructing a suitable tip, and obtaining images of graphite and molybdenum disulfide surfaces.
