Mark A. Petrich

PREPARATION AND CHARACTERIZATION OF ACTIVATED CARBONS FROM SCRAP TIRES, ALMOND SHELLS, AND ILLINOIS COAL

Abstract Scrap tires, almond shells, and high sulfur coal are examples of materials that are currently an environmental liability, but which have potential as raw materials for the production of value-added solid products. In this study, activated carbons were prepared by first pyrolyzing these materials, and then partially gasifying the pyrolysis chars with steam. The pyrolysis chars were characterized by solid-state l3C nuclear magnetic resonance. Nitrogen adsorption experiments were performed on the chars before and after steam activation. Activation increased the surface areas of chars from all three raw materials. Surface areas greater than 400m2/g were obtained when burnoff was above 40%. A 670 m2/g carbon was prepared from Illinois No. 5 coal at 52% burnoff. The results of this study indicate that the conversion of these environmentally problematic materials to activated carbon is a viable strategy for resource recovery and improving pyrolysis economics.

29Si magnetic resonance study of amorphous hydrogenated silicon plasma deposited at 50 °C

We deposit compact amorphous hydrogenated silicon (a‐Si:H) films at 50 °C, using low silane partial pressures in silane/hydrogen reaction mixtures. The 29Si chemical shift and infrared signature of our films are strongly affected by the silane feed partial pressure, but are insensi‐ tive to the hydrogen feed partial pressure, indicating that hydrogen ‘‘etching’’ does not play a significant role in the film growth process. Interestingly, the 29Si chemical shift and infrared signature of our compact 50 °C films are similar to those of a‐Si:H films deposited at standard ‘‘optimum’’ conditions, but the electronic properties are very different. Upon thermal annealing at 150 °C for 3 h, the spin defect density may be reduced by as much as 2 orders of magnitude, while the hydrogen content, 29Si chemical shift and infrared signature remain unchanged. Therefore, it seems possible to first grow a compact silicon network structure in a‐Si:H at 50 °C, and then equilibrate the electronic structure at 150 °C, without s...

Control of microstructure in a‐SiC:H

We demonstrate a means of controlling the microstructure and carbon content in amorphous hydrogenated silicon carbide (a‐SiC:H) thin films prepared in a plasma‐enhanced chemical vapor deposition system. The capacitively coupled, parallel‐plate deposition apparatus includes provision for adjusting the potential of the powered electrode by application of an additional, independent dc voltage. This voltage affects the deposition chemistry. Films prepared when various positive and negative dc voltages are applied are studied with infrared absorption, nuclear magnetic resonance, and electron spin resonance. Their optical band gaps, electrical conductivities, and dark conductivity activation energies are also measured. The films have carbon contents ranging from 1 to 4 at. %. We find that we can alter the microstructure of a‐SiC:H by adjusting the powered‐electrode potential during deposition, and that these microstructural changes are reflected in the film properties. A small increase in the self‐biased voltag...

Effects of temperature and bias on the microstructure of plasma‐deposited amorphous silicon carbide

We report a new method of depositing amorphous hydrogenated silicon carbide (a‐SiC:H) at low substrate temperature in a plasma‐enhanced chemical vapor deposition reactor. By applying an external dc voltage to the rf‐excited powered electrode, we can shift the optimal deposition temperature from 250 °C to as low as 100 °C. We find that a‐SiC:H films deposited at positive powered‐electrode potential and low substrate temperature exhibit less microstructure, wider optical band gaps, and faster deposition rates than films deposited at conventional conditions.

A New Method of Depositing Amorphous Hydrogenated Silicon Carbide with Low Ir-Detected Microstructure

We report a new method of depositing amorphous hydrogenated silicon carbide thin films with low IR-detected microstructure in a plasma-enhanced chemical vapor deposition reactor. Films prepared at various conditions are studied with Fourier-transform infrared absorption. Their optical band gaps and photoconductivities are also measured. The amount of microstructure can be controlled by adjusting the powered-electrode potential during deposition, and the microstructural changes are reflected in the film properties. By applying an external dc voltage to the rf-excited powered electrode, we can shift the optimal deposition temperature from 250 °C to as low as 100 °C. We find that films deposited at positive powered-electrode potential and low substrate temperature exhibit less microstructure, wider optical band gaps, and faster deposition rates than films deposited at conventional conditions.

Preparation Of Moisture Resistant Polylmide Films By Plasma Treatment

Polyimides are an important class of polymeric materials used in microelectronics fabrication. These polymers could be used even more extensively if it were possible to improve their moisture resistance. We are using plasma processing techniques to modify the moisture resistance of polyimide films. Films are exposed to nitrogen trifluoride plasmas to introduce fluorine into the surface of the polyimide. Fluorination is monitored with x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. Water contact angle measurements are used to assess the hydrophobicity of the treated surfaces. Thus far, we have demonstrated that this plasma treatment is a good way of introducing fluorine into the polyimide surface, and that these treatments do enhance the hydrophobic nature of polyimide.