Daisuke Hobara

Production of a 100-m-long high-quality graphene transparent conductive film by roll-to-roll chemical vapor deposition and transfer process

A high-quality graphene transparent conductive film was fabricated by roll-to-roll chemical vapor deposition (CVD) synthesis on a suspended copper foil and subsequent transfer. While the high temperature required for the CVD synthesis of high-quality graphene has prevented efficient roll-to-roll production thus far, we used selective Joule heating of the copper foil to achieve this. Low pressure thermal CVD synthesis and a direct roll-to-roll transfer process using photocurable epoxy resin allowed us to fabricate a 100-m-long graphene transparent conductive film with a sheet resistance as low as 150 Ω/sq, which is comparable to that of state-of-the-art CVD-grown graphene films.

Channel‐Length‐Dependent Field‐Effect Mobility and Carrier Concentration of Reduced Graphene Oxide Thin‐Film Transistors

Nanosheetsareatomically thin two-dimensionalnanomaterials with high aspect ratios of more than 1000. Graphene oxide (GO) is one of the most widely studied nanosheets that is derived from graphene, an sp-bonded carbon monolayer, and is dispersible in water and organic solvents due to functionalization by several oxygen-containing groups. The lateral dimensions of GO nanosheets and their partially reduced version, reduced graphene oxide (RGO) nanosheets, range from less than 1mm to 100mm depending on the sample-preparation procedure. RGO nanosheets exhibit a gate-voltage-dependent conductance, taking over the zero-gap semiconductor nature of graphene. While it is difficult to mass produce large-area thin films of conventional graphene at low temperature, thin films that consist of water-dispersible GO and RGO can be produced by a costeffective, high-throughput solution process. Consequently, RGOthinfilmshavebeenattracting considerable attentionas a novel material for a variety of electronic devices, including field-effect transistors (FETs), transparent electrodes, capacitors, and chemical sensors. To improve the performances of the RGO electronic devices, it is vital to model and gain a better understanding of the electronic conduction processes in RGO thin films. Electronic conduction in thin films consisting of nanoparticles andnanowires hasbeenwidely studiedand ithas been found that the conduction is limited by hopping between individual components. Similarly, the weak coupling between adjacent nanosheets (i.e., the high internanosheet resistance, Rinter) may cause the device performance (e.g., the field-effect mobility, mFE) to be less than that of single nanosheets. [17]

Organic Single‐Crystal Arrays from Solution‐Phase Growth Using Micropattern with Nucleation Control Region

A method for forming organic single-crystal arrays from solution is demonstrated using an organic semiconductor, 3,9-bis(4-ethylphenyl)-peri-xanthenoxanthene (C(2) Ph-PXX). Supersaturation of C(2) Ph-PXX/tetralin solution is spatially changed by making a large difference in solvent evaporation to generate nuclei at the designated location. The method is simple to implement since it employs only a micropattern and control of the solvent vapor pressure during growth.

Solution-phase growth of organic single-crystal arrays

We have successfully developed a method for directly forming organic single-crystal thin films at designated locations on a substrate by solution-phase growth. An original micropattern, in which small rectangular regions were connected to a large rectangular region, was designed. The small regions and the large region were used as nucleation control regions (NCRs) and a growth control region (GCR), respectively. The key to success was to vary local supersaturation of a solution droplet by making a large difference in solvent evaporation between a NCR and a GCR. We found that the NCR played a very important role in forming a single nucleus and in investigating the possibility of control of the crystal orientation. By using the developed micropattern and controlling the solvent vapor pressure during growth, we fabricated single-crystal arrays of a stable organic semiconductor, 3,9-bis(4-ethylphenyl)-peri-xanthenoxanthene (C2Ph-PXX).