Research Area: Surface Functionalization
This work focuses on the functionalization of semiconductor surfaces through the controlled attachment of organic materials. The goal is to covalently bond to semiconductor surfaces organic layers with custom-tailored properties that could be used in applications such as lithography, low k dielectric materials, sensors, and molecular electronics. We have investigated a number of chemical strategies for vacuum-based attachment, including several with direct analogs in organic reaction chemistry. These systems are studied under vacuum using a variety of spectroscopic and theoretical techniques, including in-situ multiple internal reflection infrared spectroscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy, temperature programmed desorption, scanning tunneling microscopy, and ab initio quantum chemistry calculations.
Left: Period trends are observed in adsorption of organic molecules at Group 14 semiconductor surfaces. Right: Many analogies are seen between reactions of organic molecules at Si and Ge(100)-2x1 surfaces and solution organic chemistry.
One direct application of this research is the deposition of ultra-thin organic layers, using an ermerging technique known as Molecular layer deposition (MLD). Similar to atomic layer deposition (ALD), MLD reactants that undergo self-saturating reactions are introduced in sequential schemes to grow films in a layer-by-layer manner. In these reaction schemes, MLD utilizes multifunctional organic molecules to build oligomer films, rather than the inorganic films deposited by ALD. Use of MLD for growth of organic films has many advantages over traditional chemical vapor deposition methods: precise control over film thickness, conformal coating of surfaces, and an unprecedented control over the film composition. In MLD, the organic backbone of each monomer can be changed to meet the needs of the desired applications. Our group investigates both coupling and backbone chemistries, and we are currently studying the morphology and nucleation behavior of MLD. We are also currently working on several applications of MLD films: organic copper diffusion barrier layers, photoresists for extreme ultra-violet lithography, and area selective MLD.
Left: Illustration of MLD of nanoscale organic thin films. Right: TEM image of 50 MLD cycle polythiourea film on a silica nanoparticle.