Chemical doping in graphene due to polymer molecules adsorption has attracted much recent interest because of the modification of electrical, magnetic, and optical properties of graphene. We show a reversible charge-transfer doping effect in graphene due to the reaction with poly(methyl methacrylate) (PMMA) residues. By helium ion irradiation and vacuum annealing without introducing an external dopant, reversible shifts in Raman G and 2D bands are observed as well as the change in the relative 2D band intensity to the G band. Chemical bonds between functional groups from PMMA residues and graphene could be formed due to He + ion irradiation, and the desorption of functional groups from graphene is dominant during the vacuum annealing process. Meanwhile, PMMA residue on the graphene surface is mostly removed and the surface morphology becomes smooth after irradiation and annealing. Both electrical conductance and Raman band shifts show nonmonotonic dependence on the dose density, which remains after annealing, indicating that the doping also involves an irreversible effect. Our study helps better the understanding of the doping effects in graphene due to polymer adsorption, which is efficient to tune the properties of graphene.

Conducting atomic force microscopy (C-AFM) is used to observe the formation and removal of conducting filaments of Mg0.6Zn0.4O thin film at a nanoscale in order to study the mechanisms of resistive switching. C-AFM probe with Pt coating is used as a movable top electrode for measuring local I-V and for C-AFM imaging. Writing and reading of micro-bits on the resistive switching thin film are demonstrated. The local I-V behavior is similar to the macroscopic behavior of the resistive switching thin film. However, the probability for successful in situ detection of resistive switching of formation in the current experiment is only one quarter, much less than that with a macroscopic top electrode. Experimental results are explained using the filament model which illustrates the switching mechanism of the thin film. The current work would be useful for the improvement of resistive switching thin films and their applications.

The as‐grown morphologies and background carrier concentrations of undoped normalInP epilayers grown at 650°C were determined as a function of phosphorus source [tertiarybutylphosphine (TBP) or phosphine false(PH3false) ] and V:III ratio in an inverted‐vertical (IV) metallorganic chemical vapor deposition (MOCVD) reactor. Specular surface morphology was obtained over the entire growth surface (16.6 cm2) at a minimum PH3 to trimethylindium (TMIn) ratio of 10, and at a minimum TBP to TMIn ratio of 33. Below these V:III ratios, the area of the normalInP epilayer surfaces exhibiting specular morphology decreased as the V:III ratio was reduced; however, the layer thicknesses remained uniform. All undoped normalInP epilayers were n‐type. The carrier concentration false(ND−NAfalse) obtained with PH3 in the specular area of the normalInP epilayers was on the order of 1.5×1014 cm−3 at V:III ratios up to ca. 20; at a V:III ratio of 40, ND−NA decreased to 1012 cm−3. The carrier concentration obtained with TBP in the specular area of the normalInP epilayers was about 3.6×1015 cm−3 at V:III ratios up to 33. The relation of V:III ratio to morphology and the distribution of visible phosphorus deposition on the reactor tube walls during growth indicated that the decomposition characteristics of PH3 and TBP are considerably different in the inverted vertical reactor than in other system configurations. The decomposition characteristics observed here are empirically correlated with decomposition mechanism unique to the IV geometry.