Critical Point Drying of Graphene Field-Effect Transistors Improves Their Electric Transport Characteristics.

A critical point drying (CPD) technique is reported with supercritical CO2 as a cleaning step for graphene field-effect transistors (GFETs) microfabricated on oxidized Si wafers, which results in an increase of the field-effect mobility and a decrease of the impurity doping. It is shown that the polymeric residues remaining on graphene after the transfer process and device microfabrication are significantly reduced after the CPD treatment. Moreover, the CPD effectively removes ambient adsorbates such as water therewith reducing the undesirable p-type doping of the GFETs. It is proposed that CPD of electronic, optoelectronic, and photonic devices based on 2D materials as a promising technique to recover their intrinsic properties after the microfabrication in a cleanroom and after storage at ambient conditions.

An Improved Method for Fabrication of Ag-GO Nanocomposite with Controlled Anti-Cancer and Anti-bacterial Behavior; A Comparative Study.

In this study, two green procedures for Silver-Graphene Oxide (Ag-GO) nanocomposite synthesis were investigated. As a common method, AgNO3 was first loaded on the GO surface and then was reduced and stabilized by walnut green husk extract, producing Ag-GO-І. As an innovative approach, GO was first exposed to the extract and then the AgNO3 was added as the second step, producing Ag-GO-П. Physicochemical properties, antibacterial and cytotoxicity activity of both nanocomposites were subsequently studied comparing with free silver nanoparticles (AgNPs) and pure GO. Based on the results, exposure of GO to the extract, as a reducing agent, at the first/last step of the synthesis process resulted in the fundamental differences in the final products. So that, high amounts of agglomerated silver nanoparticles were formed between the GO sheets, when using the common method, whereas in Ag-GO-П, small AgNPs were formed on the GO sheets without aggregation, entirely covering the sheets. Antibacterial and cytotoxic behavior of these nanomaterials could be compared as AgNPs > Ag-GO-П > Ag-GO-І. It is assumed that these differences are due to control of unwanted nucleation in the synthesis process that Ag nanoparticles are smaller with less agglomeration when the GO surfaces are pre-treated with reducing agent.

Lithium ion-selective membrane with 2D subnanometer channels.

In the last two years, the rapidly rising demand for lithium has exceeded supply, resulting in a sharp increase in the price of the metal. Conventional electric driven membrane processes can separate Li+ from divalent cations, but there is virtually no commercial membrane that can efficiently and selectively extract Li+ from a solution containing chemically similar ions such as Na+ and K+. Here, we show that the different movement behavior of Li+ ion within the sub-nanometre channel leads to Li+ ion-selectivity and high transport rate. Using inexpensive negatively charged 2D subnanometer hydrous phyllosilicate channels with interlayer space of 0.43 nm in a membrane-like morphology, we observed that for an interlayer spacing of below 1 nm, Li+ ions move along the length of the channel by jumping between its two walls. However, for above 1 nm spacing, the ions used only one channel wall to jump and travel. Molecular dynamic (MD) simulation also revealed that ions within the nanochannel exhibit acceleration-deceleration behavior. Experimental results showed that the nanochannels could selectively transport monovalent ions of Li+> Na+> and K+ while excluding other ions such as Cl- and Ca2+, with the selectivity ratios of 1.26, 1.59 and 1.36 for Li+/Na+, Li+/K+, and Na+/K+ respectively, which far exceed the mobility ratios in traditional porous ion exchange membranes. The findings of this work provide researchers with not only a new understanding of ions movement behavior within subnanometer confined areas but also make a platform for the future design of ion-selective membranes.