@article{wang_gupta_garguilo_liu_qin_nemanich_2005, title={Growth and field emission properties of small diameter carbon nanotube films}, volume={14}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2004.10.003}, abstractNote={Vertically aligned carbon nanotube films with diameters smaller than 5 nm, high densities up to 1012/cm2, and lengths of ∼ 5–8 μm were deposited by microwave plasma-assisted chemical vapor deposition. Experiments show that, by continuous reduction in the thickness of the iron film (i.e., ∼0.3–0.5 nm), small diameter carbon nanotubes can be achieved with diameters that ranged from 1–5 nm, and the films are comprised of both single- and double-wall nanotubes. The electron field emission properties of the films were investigated by variable distance field emission and temperature-dependent field electron emission microscopy (T-FEEM). The films showed an emission site density of ∼104/cm2 and a threshold field of 2.8 V/μm similar to multiwalled nanotubes (1.9 V/μm). In addition, they also exhibited a temperature dependence of the emission site intensity.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Wang, YY and Gupta, S and Garguilo, JM and Liu, ZJ and Qin, LC and Nemanich, RJ}, year={2005}, pages={714–718} }
 @article{wang_gupta_nemanich_liu_qin_2005, title={Hollow to bamboolike internal structure transition observed in carbon nanotube films}, volume={98}, ISSN={["1089-7550"]}, DOI={10.1063/1.1946198}, abstractNote={The transition of the internal structure in microwave chemical-vapor-deposited carbon nanotubes is investigated using scanning electron microscopy and high-resolution transmission electron microscopy. By controlling the thickness of the iron catalyst layer, a sequence of carbon nanotube films was obtained with diameters ranging from a few nanometers to over 100nm. Experiments have established that by continuous reduction of the Fe layer thickness to <1nm, single- and double-wall carbon nanotube films can be produced, whereas for an Fe film thickness >1nm, multiwall carbon nanotube films can be synthesized. It was also found that for an Fe thickness ⩾5nm, interlayers (i.e., bamboolike or periodically compartmentalized nanotubes) were formed, while for an iron thickness <2nm the tubes were primarily hollow. For an intermediate Fe thickness the internal structure of the carbon nanotubes was a mixture of hollow and bamboolike. A growth model which considers bulk and surface diffusions of carbon into and∕or onto the Fe catalyst surface is proposed to describe this transition and the internal periodic structure.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, YY and Gupta, S and Nemanich, RJ and Liu, ZJ and Qin, LC}, year={2005}, month={Jul} }
 @article{gupta_wang_garguilo_nemanich_2005, title={Imaging temperature-dependent field emission from carbon nanotube films: Single versus multiwalled}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1850616}, abstractNote={Field emission properties of vertically aligned single- and multiwalled carbon nanotube films at temperatures up to 1000°C are investigated by electron emission microscopy, enabling real-time imaging of electron emission to provide information on emission site density, the temporal variation of the emission intensity, and insight into the role of adsorbates. The nanotube films showed an emission site density of 104∼105∕cm2, which is compared to the areal density (from 1012–1013∕cm2to108–109∕cm2). At ambient temperature, the emission indicated temporal fluctuation (∼6%–8%) in emission current with minimal changes in the emission pattern. At elevated temperatures, the emission site exhibited an increase in emission site intensity. From the experimental observations, it is proposed that the chemisorbed molecules tend to desorb presumably at high applied electric fields (field-induced) in combination with thermal effects (thermal-induced) and provide a contrasting comparison between semiconducting (single-walled) and metallic (multiwalled) nanotubes.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Gupta, S and Wang, YY and Garguilo, JM and Nemanich, RJ}, year={2005}, month={Feb} }
 @article{wang_gupta_liang_nemanich_2005, title={Increased field-emission site density from regrown carbon nanotube films}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1897836}, abstractNote={Electron field-emission properties of as-grown, etched, and regrown carbon nanotube thin films were investigated. The aligned carbon nanotube films were deposited by the microwave plasma-assisted chemical vapor deposition technique. The surface of the as-grown film contained a carbon nanotube mat of amorphous carbon and entangled nanotubes with some tubes protruding from the surface. Hydrogen plasma etching resulted in the removal of the surface layer, and regrowth on the etched surface displayed the formation of a new carbon nanotube mat. The emission site density and the current–voltage dependence of the field emission from all of the samples were analyzed. The results showed that the as-grown sample had a few strong emission spots and a relatively high emission current density (∼20μA∕cm2 at 1V∕μm), while the regrown sample exhibited a significantly increased emission site density.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, YY and Gupta, S and Liang, M and Nemanich, RJ}, year={2005}, month={May} }
 @article{monteiro-riviere_nemanich_inman_wang_riviere_2005, title={Multi-walled carbon nanotube interactions with human epidermal keratinocytes}, volume={155}, ISSN={["1879-3169"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000226645800005&KeyUID=WOS:000226645800005}, DOI={10.1016/j.toxlet.2004.11.004}, abstractNote={Carbon nanotubes have widespread applications in multiple engineering disciplines. However, little is known about the toxicity or interaction of these particles with cells. Carbon nanotube films were grown using a microwave plasma enhanced chemical vapor deposition system. Human epidermal keratinocytes (HEK) were exposed to 0.1, 0.2, and 0.4 mg/ml of multi-walled carbon nanotubes (MWCNT) for 1, 2, 4, 8, 12, 24 and 48 h. HEK were examined by transmission electron microscopy for the presence of MWCNT. Here we report that chemically unmodified MWCNT were present within cytoplasmic vacuoles of the HEK at all time points. The MWCNT also induced the release of the proinflammatory cytokine interleukin 8 from HEKs in a time dependent manner. These data clearly show that MWCNT, not derivatized nor optimized for biological applications, are capable of both localizing within and initiating an irritation response in a target epithelial cell that composes a primary route of occupational exposure for manufactured nanotubes.}, number={3}, journal={TOXICOLOGY LETTERS}, author={Monteiro-Riviere, NA and Nemanich, RJ and Inman, AO and Wang, YYY and Riviere, JE}, year={2005}, month={Mar}, pages={377–384} }
 @article{wang_tang_koeck_brown_garguilo_nemanich_2004, title={Experimental studies of the formation process and morphologies of carbon nanotubes with bamboo mode structures}, volume={13}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2004.01.009}, abstractNote={Carbon nanotubes (CNT) were synthesized by microwave plasma chemical vapor deposition, and the formation process and morphologies of bamboo mode structures were systematically analyzed. Thin films of Fe on Si substrates were used as the catalyst, and the CNT films were characterized with electron microscopy, Raman spectroscopy, and Auger electron spectroscopy. For growth up to 15 min, the films grow with vertically aligned CNT with evidence of amorphous carbon at the top surface. For longer growth times the films exhibit a layer of amorphous carbon and a CNT mat on top of the aligned carbon nanotube ‘forest.’ Transmission electron microscopy measurements displayed multiwalled CNT with bamboo structure and encapsulated tips some of which contained catalyst particles. Two kinds of bamboo mode structures were observed: cone shaped, and cylindrical. The results indicate that the CNT growth is predominantly of the base growth mode, and the formation of the compartments was attributed to the difference in the bulk and surface diffusion of carbon species at the catalyst.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Wang, YY and Tang, GY and Koeck, FM and Brown, B and Garguilo, JM and Nemanich, RJ}, year={2004}, pages={1287–1291} }
 @article{wang_gupta_nemanich_2004, title={Role of thin Fe catalyst in the synthesis of double- and single-wall carbon nanotubes via microwave chemical vapor deposition}, volume={85}, ISSN={["0003-6951"]}, DOI={10.1063/1.1796529}, abstractNote={Synthesis of vertically aligned small diameter (single- and double-wall) carbon nanotube films on thermally oxidized n+-Si(001) wafers, with acetylene diluted with ammonia gas mixture using a microwave plasma-assisted chemical vapor deposition technique, is reported. Experiments show that by continuous reduction in the thickness of the iron catalyst film to ∼0.3–0.5nm, or alternately, smaller catalyst particles produces hollow concentric tubes with a fewer number of walls. Double- and single-wall carbon nanotubes with diameters ranging from 1 to 5nm were identified using transmission electron microscopy and Raman spectroscopy. A relatively higher deposition temperature (∼850°C) in conjunction with a controlled catalyst and rapid growth (<40s) allowed for the growth of well-graphitized, high areal density (∼1012-1013∕cm2) nanotubes with reduced amorphous carbon and iron. Our results also indicate that the base growth is the most appropriate model to describe the growth mechanism for the nanotube films.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Wang, YY and Gupta, S and Nemanich, RJ}, year={2004}, month={Sep}, pages={2601–2603} }