Papers by Romaneh Jalilian
We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET), usi... more We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET), using a biased metallic nanowire coated with a dielectric layer as a contact mode tip and local top gate. Electrical transport through graphene at various back gate voltages is monitored as a function of tip voltage and tip position. Near the Dirac point, the dependence of graphene resistance on tip voltage shows a significant variation with tip position. SGM imaging reveals mesoscopic domains of electron-doped and hole-doped regions. Our measurements indicate a substantial spatial fluctuation (on the order of 10^12/cm^2) in the carrier density in graphene due to extrinsic local doping. Important sources for such doping found in our samples include metal contacts, edges of graphene, structural defects, and resist residues.
We report a study of the effects of electron-beam irradiation and oxygen plasma etching on graphe... more We report a study of the effects of electron-beam irradiation and oxygen plasma etching on graphene and graphene field-effect transistors (GFET). For both types of exposure, Raman spectra show a characteristic evolution with increasing irradiation-induced disorder. Electron-beam exposure causes a down-shifting in the charge-neutral point (CNP), interpreted as due to a hole-doping in the substrate. Oxygen plasma etching causes an
In this presentation we describe work on the formation of heterojunctions between single-wall car... more In this presentation we describe work on the formation of heterojunctions between single-wall carbon nanotubes (SWNTs) and one-dimensional (1D) gold nanorods (AuNRs) assembled directly on surfaces. The chemical procedure is a simple benchtop method using commercially available reagents. Au NRs are grown directly and selectively on surface-attached SWCNTs by depositing hexanethiolate-terminated Au monolayer protected clusters (MPCs) on the SWCNTs and
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
We propose schemes of using graphene field effect transistors (GFET) to detect ionizing radiation... more We propose schemes of using graphene field effect transistors (GFET) to detect ionizing radiation. The detection is based on the high sensitivity of graphene to local change of electrical field that can result from the interaction of radiation with a semiconductor substrate in a GFET. We present preliminary modeling and experimental work to develop a prototype sensor, and discuss potential advantages compared to conventional detectors.
We present measurements of the thermal conductivity of suspended graphene, using Raman spectrosco... more We present measurements of the thermal conductivity of suspended graphene, using Raman spectroscopy on graphene subject to electrical heating. Joule heating is generated by passing a current through the suspended graphene, while the Cr/Au contact leads act as heatsinks. Raman spectrum is used as a thermometer for graphene, because of the temperature dependence of the amplitude and frequency for the
Energetic charged particles are commonly used in the fabrication and characterization of graphene... more Energetic charged particles are commonly used in the fabrication and characterization of graphene devices. For example, oxygen ions are used in plasma etching processes and energetic electrons are used for electron beam lithography as well as electron microscopy. Using electronic transport measurements and Raman spectroscopy, we have studied the effect of exposure to electrons and oxygen ions on exfoliated graphene
Physical Review B, 2006
We explore the combined effects of phonon confinement and local heating caused by laser beam abso... more We explore the combined effects of phonon confinement and local heating caused by laser beam absorption on the Raman spectra of Germanium nanowires of different diameters ( 6nm , 7nm , and 12nm ). The asymmetric broadening and downshifting of the first order Raman band is studied as a function of the average wire diameter and the local temperature of
Electron beam exposure is a commonly used tool for fabrication and imaging of graphene-based devi... more Electron beam exposure is a commonly used tool for fabrication and imaging of graphene-based devices. Using Raman spectroscopy and electronic transport measurements, we have studied the effect of prolonged exposure of electron beams on exfoliated graphene on SiO 2 /Si substrates and the performance of electronic devices based on exfoliated graphene. Raman spectra indicate emergence of characteristic defects. Electronic transport measurements show an overall decrease in graphene's conductivity and a shift of the Dirac point. Our results are valuable for understanding the possible defects generated in graphene by electron beam exposure and in high-radiation environment in general.
Bulletin of the American …, 2011
... 4:30 PM–4:42 PM. Preview Abstract. Authors: Romaneh Jalilian (NaugaNeedles). Isaac Childres (... more ... 4:30 PM–4:42 PM. Preview Abstract. Authors: Romaneh Jalilian (NaugaNeedles). Isaac Childres (Purdue University). Luis A. Jauregui (Purdue University). Michael Foxe (Penn State). Jifa Tian (Purdue University). Igor Jovanovic (Penn State). Yong P. Chen (Purdue University). ...
Semiconductor multi-component alloys provide a natural means of tuning the band gap and other par... more Semiconductor multi-component alloys provide a natural means of tuning the band gap and other parameters to optimize and extend the application of semiconductor electronic/optoelectronic devices. In this study, multi-component nanowires have been synthesized in vapor phase by laser ablation of solid targets consisting of initial bulk materials. Growth of nano-crystals is believed to seed from low melting metallic droplets generated from laser bombardment and heating of the target. Curved tips have been observed at one end of the nanowires which contain same elemental components as the body of the nanowires. This technique is proven to be a successful approach to eliminate the need for external catalyst which can have detrimental consequences affecting the performance of an optoelectronic device. As-synthesized nanowires were characterized using TEM, SEM, XRD, EDS, photo luminescence, Vis-IR absorption and Raman spectroscopy. Results of transport properties of individual nanowires wi...
Nanotechnology, 2011
We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET), usi... more We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET), using a biased metallic nanowire coated with a dielectric layer as a contact mode tip and local top gate. Electrical transport through graphene at various back gate voltages is monitored as a function of tip voltage and tip position. Near the Dirac point, the dependence of graphene resistance on tip voltage shows a significant variation with tip position. SGM imaging reveals mesoscopic domains of electron-doped and hole-doped regions. Our measurements indicate a substantial spatial fluctuation (on the order of 10 12 /cm 2 ) in the carrier density in graphene due to extrinsic local doping. Important sources for such doping found in our samples include metal contacts, edges of graphene, structural defects, and resist residues.
Nanotechnology, 2011
Individual metal alloy nanowires of constant diameter and high aspect ratio have previously been ... more Individual metal alloy nanowires of constant diameter and high aspect ratio have previously been self-assembled at selected locations on atomic force microscope (AFM) probes by the method reported in Yazdanpanah et al (2005 J. Appl. Phys. 98 073510). This process relies on the room temperature crystallization of an ordered phase of silver-gallium. A parallel version of this method has been implemented in which a substrate, either an array of micromachined tips (similar to tips on AFM probes) or a lithographically patterned planar substrate, is brought into contact with a continuous, nearly planar film of melted gallium. In several runs, freestanding wires are fabricated with diameters of 40-400 nm, lengths of 4-80 µm, growth rates of 80-170 nm s −1 and, most significantly, with yields of up to 97% in an array of 422 growth sites. These results demonstrate the feasibility of developing a batch manufacturing process for the decoration of wafers of AFM tips and other structures with selectively patterned freestanding nanowires.
Nanotechnology, 2007
Loose graphene sheets, one to a few atomic layers thick, are often observed on freshly cleaved HO... more Loose graphene sheets, one to a few atomic layers thick, are often observed on freshly cleaved HOPG surfaces. A straightforward technique using electrostatic attraction is demonstrated to transfer these graphene sheets to a selected substrate. Sheets from one to 22 layers thick have been transferred by this method. One sheet after initial deposition is measured by atomic force microscopy to be only an atomic layer thick (∼0.35 nm). A few weeks later, this height is seen to increase to ∼0.8 nm. Raman spectroscopy of a single layer sheet shows the emergence of an intense D band which dramatically decreases as the number of layers in the sheet increase. The intense D band in monolayer graphene is attributed to the graphene conforming to the roughness of the substrate. The disruption of the C-C bonds within the single graphene layer could also contribute to this intense D band as evidenced by the emergence of a new band at 1620 cm −1 .
Journal of the American Chemical Society, 2005
In this communication we describe the formation of heterojunctions between metallic one-dimension... more In this communication we describe the formation of heterojunctions between metallic one-dimensional (1D) gold nanorods (Au NRs) and single-wall carbon nanotubes (SWCNTs) assembled directly on surfaces. The synthesis of multicomponent structures with junctions of different 1D materials is important for many electronic, 1 optoelectronic, 2 and sensing applications. 3 Carbonsemiconductor (SC), 1a SC-metal, 1b,c carbon-metal, 1c,d carboncarbide, 1e and SC-SC 2 1D heterojunctions have been fabricated and shown to exhibit Schottky diode behavior, 1a Ohmic contact, 1d,e thermoelectric properties, 2a photoluminescence, 2c and electroluminescence. 2c Striped nanorods composed of different metalmetal junctions have served as biobarcode sensors. 3 Previous methods have led mostly to end-to-end junctions by electrochemical deposition in porous templates, 1b-d,3 a solid-solid reaction, 1e or vapor-phase growth onto catalysts. 1a,2
Journal of Applied Physics, 2008
In this work, we have performed a systematic study of the electrical transport properties ͑both t... more In this work, we have performed a systematic study of the electrical transport properties ͑both the resistivity and the thermoelectric power͒ on bundles of single-walled carbon nanotubes ͑SWCNTs͒, double-walled carbon nanotubes ͑DWCNTs͒, and peapods ͑derived from the same batch of initial SWNTs͒ during in situ doping with potassium ͑donor͒. The charge transfer effects in K-doping are similar in SWNTs and DWNTs, but drastically different in C 60 at SWNTs. An impurity level associated with the chain of C 60 in the band gap of the tube with the Fermi level pinned near the top of the valence band, leading to the p-type behavior for the peapod. Significant charge transfer is found to occur only in the case of very low coverage of these nanostructures.
IEEE Transactions on Nanotechnology, 2000
The use of a graphene field-effect transistors (GFETs) to detect radiation is proposed and analyz... more The use of a graphene field-effect transistors (GFETs) to detect radiation is proposed and analyzed. The detection mechanism used in the proposed detector architecture is based on the high sensitivity of graphene to the local change of electric field that can result from the interaction of radiation with a gated undoped semiconductor absorber (substrate) in a GFET. We have modeled a GFET-based radiation detector, and discussed its anticipated performance and potential advantages compared to conventional detector architectures.
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Papers by Romaneh Jalilian