@article{fahmy_shen_tucker_spontak_koch_1999, title={Possible evidence for the stabilization of beta-carbon nitride by high-energy ball milling}, volume={14}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.1999.0334}, abstractNote={The possibility of stabilizing the theoretically predicted β–C3N4phase by high-energy ball milling is investigated. Charges of graphitic carbon were milled with and without minor alloying additions under different atmospheric media, namely gas and/or liquid phases of nitrogen, air, or ammonia. Milling was performed at either of two energy levels for periods of up to 48 h. The β–C3N4phase was found to exist as small crystallites in a matrix of primarily amorphous carbon at volume fractions estimated between 5 and 10 at.%. High-resolution electron diffraction and x-ray diffraction indicate that the crystalline nature of the C3N4phase corresponds with a hexagonal lattice witha= 6.46 Å andc/a= 0.374, which are within 2% of the theoretically calculated lattice parameter values. Analysis of electron energy-loss spectroscopy (EELS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectra verify the presence of chemically bonded carbon and nitrogen with chemical states reflecting combinedsp2andsp3hybridization. Chemical analysis confirms nitrogen enrichment at levels consistent with the C3N4stoichiometry and the estimated degree of stabilization. The possible mechanism(s) responsible for the stabilization of the β–C3N4phase are briefly discussed.}, number={6}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Fahmy, Y and Shen, TD and Tucker, DA and Spontak, RL and Koch, CC}, year={1999}, month={Jun}, pages={2488–2499} }
 @article{shen_shmagin_koch_kolbas_fahmy_bergman_nemanich_mcclure_sitar_quan_1997, title={Photoluminescence from mechanically milled Si and SiO2 powders}, volume={55}, ISSN={["0163-1829"]}, DOI={10.1103/physrevb.55.7615}, abstractNote={The photoluminescence (PL) in as-received and milled Si and SiO2 powder is reported. The Si and SiO2 powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous SiO2 component is formed by milling crystalline SiO2. The PL spectra for as-received Si, milled Si, and SiO2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO2 powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled SiO2 can be related to both the increased volume fraction of the amorphous SiO2 component and the increased density of defects introduced in the amorphous SiO2 upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled SiO2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or SiO2 components existing in these powder samples. The PL measurement for milled SiO2 is dependent on air pressure whereas that for as-received SiO2 is not, suggesting that new emitting centers are formed by milling.}, number={12}, journal={PHYSICAL REVIEW B}, author={Shen, TD and Shmagin, I and Koch, CC and Kolbas, RM and Fahmy, Y and Bergman, L and Nemanich, RJ and McClure, MT and Sitar, Z and Quan, MX}, year={1997}, month={Mar}, pages={7615–7623} }
 @article{shen_koch_wang_quan_wang_1997, title={Solid-state reaction in nanocrystalline Fe/SiC composites prepared by mechanical alloying}, volume={32}, ISSN={["0022-2461"]}, DOI={10.1023/A:1018688009913}, number={14}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Shen, TD and Koch, CC and Wang, KY and Quan, MX and Wang, JT}, year={1997}, month={Jul}, pages={3835–3839} }