Full text loading...
Graphene device irradiation with electron beams. (a) SEM image of graphene devices with multiple metal contacts. The dark ribbons are graphene channels while the white regions are Ti/Au(10-nm/90-nm) electrodes. The scale bar is 2 μm. (b) Schematic of the irradiation process showing the area exposed to the electron beam. The whole area between the metal contacts is irradiated. (c) Raman spectrum of graphene before and after irradiation. The single-layer graphene signatures include G peak at ∼1584 cm−1 and symmetric 2D band at ∼2692 cm−1. The absence of the disorder D peak at ∼1350 cm−1 proves that graphene is high quality and defect-free before irradiation. Appearance of the disorder D and D′ peaks after irradiation indicates that electron bombardment introduced defects to graphene. (d) Intensity ratio I(D)/I(G) as a function of the irradiation dose. The inset shows the normalized 2D band at different irradiation doses shifted in energy to the same position for the ease of comparison. Note the asymmetric broadening and skewing toward the lower wave numbers. The full-width at half maximum of 2D band before irradiation was ∼28 cm−1 while after irradiation it increased to ∼36 cm−1 at the irradiation dose of 5 × 104 μC/cm2.
Irradiation effects on electrical characteristics of graphene. (a) Source-drain current as a function of the back-gate bias. The position of the Dirac point shifts to a smaller voltage as a result of irradiation. (b) Electron mobility dependence on the irradiation dose for two devices. The mobility values for the pristine devices were in the range from 2500 to 5000 cm2/Vs at room temperature. The inset shows a corresponding increase of the graphene channel resistance after irradiation for one of the devices. The initial areal irradiation dose of 300 μC/cm2 is comparable to the typical dose of 500 μC/cm2 in the lithographic process.
Noise suppression in graphene via electron beam irradiation. (a) Noise amplitude A as the function of the gate bias and channel resistance in pristine graphene. (b) Noise spectral density, SI/I 2, as a function of frequency for a graphene device shown after each irradiation step. The source-drain DC bias was varied between 10 mV and 30 mV during the noise measurements. Note that the 1/f noise decreases monotonically with the increasing irradiation dose. SI/I 2 is more than an order-of-magnitude smaller after 5 × 104 μC/cm2 radiation does than that in pristine graphene.
Mechanism of the noise suppression in graphene. (a) SI/I 2 as a function of the radiation dose at zero gate bias for three frequencies f = 20, 40, and 100 Hz. The arrows indicate the level of 1/f noise before irradiation. (b) SI/I 2 as the function of the gate bias, VG , referenced to the Dirac point, VD , for another graphene device before and after irradiation plotted for f = 20 Hz. The negative bias corresponds to the hole-transport regime. Note that the noise suppression in graphene via defect engineering works in the entire range of biasing conditions and frequencies pertinent to practical applications.
Article metrics loading...