Toward High Carrier Mobility and Low Contact Resistance:Laser Cleaning of PMMA Residues on Graphene Surfaces

Poly(methyl methacrylate)(PMMA) is widely used for graphene transfer and device fabrication.However,it inevitably leaves a thin layer of polymer residues after acetone rinsing and leads to dramatic degradation of device performance.How to eliminate contamination and restore clean surfaces of graphene is still highly demanded.In this paper,we present a reliable and position-controllable method to remove the polymer residues on graphene films by laser exposure.Under proper laser conditions,PMMA residues can be substantially reduced without introducing defects to the underlying graphene.Furthermore,by applying this laser cleaning technique to the channel and contacts of graphene fieldeffect transistors(GFETs),higher carrier mobility as well as lower contact resistance can be realized.This work opens a way for probing intrinsic properties of contaminant-free graphene and fabricating high-performance GFETs with both clean channel and intimate graphene/metal contact.

Pollination Methods and Embryo Rescue Techniques of Hybridization between Lilium Oriental Hybrids

The pollination methods and embryo rescue techniques of hybridization between I.ilium Oriental hybrids were studied in this paper. The results showed that ： （ 1 ） in the combination of ＇ Justina＇ x ＇ Shala＇, pollen tubes were observed to grow downward in styles and target to ovules in ovaries when normal sti^na 13o1- lination method was used; pollen tubes were found to grow directionless to a different degree at stylar cuts and in ovaries when cut-style pollination method was used; the longer the styles were left, the more pollen tubes toward to ovules were observed and more plump seeds were produced; the maximum plump seeds were obtained via normal stigma pollination. （2） Hybridization experiments were performed for the 56 combinations of Lilium Oriental hybrids with normal stigma pollina- tion, and one combination generated no plump ovule and three combinations generated fewer than 10 plump ovules while the other 52 combinations generated plenty of plump ovules, which preliminarily indicated that normal stigma pollination method could be used as an universal pollination technique for hybridization between Lilium Oriental hybrids. The experiment results of different embryo rescue techniques showed that using cut-ovule inoculation about 70 d after pollination had a fas- ter germination speed and a higher germination rate of hybrid embryo than normal ovule inoculation, and embryo rescue efficiency of the former method was obviously higher than ＂embryo isolated inoculation＂ on 40 d after pollination. The research suggested that ＂cut-ovule inoculation＂ about 70 d after pollination could be regarded as an universal embryo rescue technique for hybridization between Lilium Oriental hybrids.