Investigation of carrier density and mobility variations in graphene caused by surface adsorbates

Abstract

Conductivity, carrier concentration and carrier mobility in graphene were investigated as a function of time in response to ionized donor and acceptor adsorbates. While a reduction in conductivity and hole density in graphene was observed upon exposure to a weak electron donor NH3, the carrier mobility was found to increase monotonically. The opposite behavior is observed upon exposure to NO2, which is expected based on its typical electron withdrawing property. Upon exposure to C9H22N2, a strong donor, it resulted in the transformation of graphene from p-type to n-type, although the inverse variation of carrier concentration and mobility was still observed. The variational trends remained unaltered even after intentional introduction of defects in graphene through exposure to oxygen plasma. The responses to C9H22N2, NH3 and NO2 exposures underline a strong influence by ionized surface adsorbates, that we explained via a simple model considering charged impurity scattering of carriers in graphene.

Impact of oxygen plasma treatment on carrier transport and molecular adsorption in graphene

“…We find that graphene's carrier (hole) density drops with the NH3 exposure, which is expected since NH3 is a typical electron donor for graphene. [10,[14][15] Interestingly, mobility increases with NH3 adsorption on graphene, which is consistent with our earlier study. [10] When NH3 molecules interact with graphene, they lose electrons and become positively charged impurities.…”

“…[10,[14][15] Interestingly, mobility increases with NH3 adsorption on graphene, which is consistent with our earlier study. [10] When NH3 molecules interact with graphene, they lose electrons and become positively charged impurities. Typically, ionized impurities on graphene's surface affect its carrier transport properties by inducing carrier scattering which can cause a reduction in mobility.…”

“…Further details about setup can be found in an earlier report. [10] To study the effect of plasma treatment on the molecular interaction property of graphene, it was exposed to 475 ppm NH3 gas diluted in N2 sequentially after various durations of plasma treatment. The oxygen plasma was generated with a plasma etch system PE25-JW (Plasma Etch, Inc.) with a starting pressure of 200 mTorr before flowing oxygen gas.…”

Direct measurement of K+ ion efflux from neuronal cells using a graphene-based ion sensitive field effect transistor

“…Graphene was synthesized using a home-built semi-automated CVD system on a copper foil (Alfa Aesar, 99.999% purity) at 1035 C using CH 4 , H 2 , and Ar gases, following standard synthesis process developed in our lab. 6,7,10 Following synthesis, a 1.5 Â 3 mm graphene-on-copper foil was cut out of the large area sample to transfer the graphene onto a target SiO 2 /Si substrate. A solution based transfer process was followed using an initial PMMA coating on the graphene followed by treatment with ammonium persulfate to etch out the copper substrate.…”

“…6,17 Both the mobility and the carrier concentration are similar to those reported earlier. 8,10 GISFET characterization…”