RAMAN MICRO-IMAGING AND SOLID STATE PHYSICS

Raman Micro-imaging
Raman micro-imaging is a new technique and its potentials have not been fully explored. It allows for quick, non-destructive measurements that require very little sample preparation. Raman signal can be obtained from a specimen at a remote location, simply by having a microscope objective connected via an optical fiber with a spectrometer. Our laboratory has recently built a Raman microscopy system with the spatial resolution of 0.5 micron in the horizontal plane and 2 microns along the optical axis of the confocal microscope. By advancing a sample in small steps of 0.2 micron we can obtain three-dimensional distribution of components within the specimen. To reduce fluorescence, laser lines ranging from 488 nm to 785 nm can be selected. The system has been extensively tested and applied to study distribution of polymers and fillers in blends, phase transitions and interfaces in hydrogels, and distribution of strain in crystals.

Surface stress distribution in diamond crystals in diamond-silicon carbide composites, Diamond and Related Materials 17, 84 (2008); doi:10.1016/j.diamond.2007.10.035

Spatial distribution of residual stress in diamond-silicon carbide composites, J. Phys.: Conf. Ser. 121 062007 doi: 10.1088/1742-6596/121/6/062007

Solid State Physics
Carbon structures. The goal of this project is the understanding of the structure and properties of various carbon materials, including combustion engine deposits, carbon nanotubes, graphitic structures on diamond, nanodiamonds, and carbon blacks to be used in tires. In this research gas adsorption technique, atomic force microscopy, X-ray, neutron scattering, and Raman are employed.

Some interesting results include the discovery of nanosize cavities in engine deposits, onion-like structures formed during graphitization of nanosize diamonds, oriented growth of graphite on large diamond crystals, determination of fractal dimension of carbon blacks, modeling of spatial distribution of particles in carbon blacks aggregates, and characterization of sizes and strains in carbon nanocrystallites.

Size and shape of crystallites and internal stresses in carbon blacks, Composites A. Applied Science., 36, 431- 436 (2005); doi:10.1016/j.compositesa.2004.10.017

Graphitization of small diamond cluster – molecular dynamics simulation, Diamond Related Materials, 15, 1818-1821 (2006), doi:10.1016/j.diamond.2006.06.002

The Structural Influence of Erbium Centers on Silicon Nanocrystal Phase Transitions, Phys. Rev. Lett. 93, 175502 (2004); DOI: 10.1103/PhysRevLett.93.175502

Diamond-SiC Composites
We manufacture diamond SiC composites under high pressure and high temperature conditions. The composites are very hard and exhibit unusually high abrasive resistance, much higher than, for example, tungsten carbides. They find applications in drill bits used in gas/oil exploration. I am holding two drill bits in the photo on the left.

The mechanism of the reaction that results in diamond crystals being chemically bonded to SiC and the structure and properties of the final product are the main goal of our research. The reaction takes place at high temperature, T>1500 K, and is controlled by diffusion rate of carbon atoms through a layer of SiC formed on diamonds. At low hydrostatic pressures diamond spontaneously transforms into graphite and this process may affect properties of the composites. At high pressures graphitization process is suppressed and silicon may react only with diamonds.

Reaction kinetics of nanostructured silicon carbide, J. Phys. Condens. Mat. 20 325216 (2008); doi: 10.1088/0953-8984/20/32/325216

Structure of diamond-silicon carbide nanocomposites as a function of sintering temperature at 8 GPa, Materials Science Engineering A, 487, 180 (2008); doi:10.1016/j.msea.2007.10.006

Origin of macro- and microstrains in diamond-SiC nanocomposites based on the core-shell model, J. Appl. Phys, 102, 074303 (2007); DOI:10.1063/1.2785025