Romaneh Jalilian

Electronic transport in chemical vapor deposited graphene synthesized on Cu: Quantum Hall effect and weak localization

We report on electronic properties of graphene synthesized by chemical vapor deposition (CVD) on copper then transferred to SiO2/Si. Wafer-scale (up to 4 in.) graphene films have been synthesized, consisting dominantly of monolayer graphene as indicated by spectroscopic Raman mapping. Low temperature transport measurements are performed on microdevices fabricated from such CVD graphene, displaying ambipolar field effect (with on/off ratio ∼5 and carrier mobilities up to ∼3000u2002cm2/Vu2009s) and “half-integer” quantum Hall effect, a hall-mark of intrinsic electronic properties of monolayer graphene. We also observe weak localization and extract information about phase coherence and scattering of carriers.

Effect of electron-beam irradiation on graphene field effect devices

Electron beam exposure is a commonly used tool for fabricating and imaging graphene-based devices. Here, we present a study of the effects of electron-beam irradiation on the electronic transport properties of graphene and the operation of graphene field-effect transistors (GFETs). Exposure to a 30 keV electron-beam caused negative shifts in the charge-neutral point (CNP) of the GFET, interpreted as due to n-doping in the graphene from the interaction of the energetic electron beam with the substrate. The shift in the CNP is substantially reduced for suspended graphene devices. The electron beam is seen to also decrease the carrier mobilities and minimum conductivity, indicating defects created in the graphene. The findings are valuable for understanding the effects of radiation damage on graphene and for the development of radiation-hard graphene-based electronics.

Scanning gate microscopy on graphene: charge inhomogeneity and extrinsic doping

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 response of graphene resistance to the tip voltage shows significant variation with tip position, and SGM imaging displays mesoscopic domains of electron-doped and hole-doped regions. Our measurements reveal substantial spatial fluctuation in the carrier density in graphene due to extrinsic local doping from sources such as metal contacts, graphene edges, structural defects and resist residues. Our scanning gate measurements also demonstrate graphenes excellent capability to sense the local electric field and charges.

Graphene Field-Effect Transistors on Undoped Semiconductor Substrates for Radiation Detection

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.

Detection of ionizing radiation using graphene field effect transistors

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.

Effect of Energetic Electron Irradiation on Graphene

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 SiO2/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.