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Graphene Transistors
Published in Changjian Zhou, Min Zhang, Cary Y. Yang, Nanocarbon Electronics, 2020
Min Zhang, Shuo Zhang, Qiuyue Huang, Chao Xie, Ni Li
Similar to GNR, graphene nanomesh (GNM) is another approach to open a gap. The GNM with perfect square lattices of hexagonal nano-holes and different size, as well as neck widths, has great advantages over the pristine graphene. The Ion/Ioff increases from 7 for pristine graphene FET to more than 7400 for GNM-FETs with a bandgap over 500 meV [95]. The highest on/off ratio up to now is achieved with the nanoperforated graphene as channel. The FET with nanopatterned graphene channel with 125 nm average hole diameter and 75 nm neck size exhibits an on/off ratio up to 108 at room temperature [96]. Apart from quantum confinement (GNRs and GNMs), many other techniques have been developed to improve Ion/Ioff. A bandgap up to a few hundred meV can be created by the perpendicular electronic field in bilayer graphene. Current on/off ratio of around 2 × 103 at room temperature was achieved in dual-gate bilayer graphene FETs with an electrical bandgap of more than 130 meV [97]. This method is highly advantageous for large-scale integration compared to GNR-FETs. Surface doping on opposite sides of bilayer graphene can generate a gap (∼350 meV) with only a gate instead of dual-gate structure. Experiments exhibit that current on/off ratio of this structure is up to 76.1, with a high mobility of ∼3100 cm2 V−1s−1 [54].
Hetero-Interfaces in 2D-Based Semiconductor Devices
Published in Mohammad Karbalaei Akbari, Serge Zhuiykov, Ultrathin Two-Dimensional Semiconductors for Novel Electronic Applications, 2020
Mohammad Karbalaei Akbari, Serge Zhuiykov
Another strategy to modulate the 2D nano-materials bandgap is a creation of periodic nano holes on the single monolayer materials, which also helps to create heterojunctions in the 2D films. In this regard the novel graphene nanostructure is synthesized by using block polymer lithography method, which is called graphene nanomesh (GNM) [56]. This approach can open up the bandgap characteristics in graphene monolayer contributing to the semiconducting characteristics of graphene (Figure 4.5d) [54]. The GNM p–n junctions have also observed with the negative differential conductance (NDC) properties. This is a progressing stage in fabrication of electronic 2D based units without using electrostatic tuning. It was also found that the shape of holes (circular, square, and triangular holes) inside of 2D graphene is another structural factor, which can modulate the properties of 2D graphene films. However, the mechanical strength and ductility of 2D monolayer films are destructively affected by the presence of nano holes in 2D monolayer films. Thus, the heterojunctions based on GNM may have limitation in the practical applications.
Bioelectronics on Graphene
Published in Li Jun, Wu Nianqiang, Biosensors Based on Nanomaterials and Nanodevices, 2017
While the chemical modification improved specificity, structural modification of graphene can improve its sensitivity. For example, the opening-up of a bandgap with electrical gating in bilayer graphene11 makes it a more sensitive system than single-layer graphene for bio-electronic sensors. It is expected that cellular interfaces with bilayer graphene will be able to detect lower-order signals more effectively via bioelectrical gating. This is expected to improve the signal-to-noise ratio in the detection of electrogenic activity of cardiomyocytes. Further, thin films of graphene nanoribbons (GNRs) will also provide an important opportunity for bio-interfacing. Here, the bandgap due to quantum confinement will produce a barrier for the carriers, which will further increase the sensitivity of the device. Similarly, graphene with punched holes (or graphene nanomesh62) can also be used as a sensitive graphenic substrate with a bandgap for biocellular interfacing and detection. Graphene nanomesh can be fabricated via transferring the film morphology of block copolymers on graphene via lithography.
Atomic-scale visualization of oxide thin-film surfaces
Published in Science and Technology of Advanced Materials, 2018
Katsuya Iwaya, Takeo Ohsawa, Ryota Shimizu, Yoshinori Okada, Taro Hitosugi
The single-atom-thick TiO2 nanomesh is analogous to graphene, and we expect unique properties to arise from such oxide nanostructures. We recently discovered that such an atomically controlled LAO/STO interface significantly affects transport properties compared with the conventional LAO/STO interface such as reduced critical thickness for the metallic interface and enhanced magnetoresistance [33]. We note that the TiO2 nanomesh cannot be fabricated by the deposition of TiO2 on LAO, as it is widely known that anatase TiO2 is formed on LAO surfaces [34,35]. Therefore, atomic-scale understanding of growth processes is of great importance.
Stretchable electronics: functional materials, fabrication strategies and applications
Published in Science and Technology of Advanced Materials, 2019
Conductive carbon nanomaterials are conventional materials used to fabricate the STEs, including the popular CNTs and graphene. For example, STEs are prepared by spray-depositing the SWCNTs, which could provide stretchabilities via applying strains along each axis, and then releasing these strains. This method yields spring-like structures in the CNTs, accommodating strain of as high as 150% and a high conductivity up to 2200 S cm−1 in the stretched state [275]. Figure 21(a) shows a template-driven self-assembly method used to integrate the SWCNTs with 2D rhombic nanomesh films (RNFs), in which the deformations of the rhombic shapes accommodate the strains, greatly enhancing the stretchabilities. The RNFs displayed excellent lower sheet resistance (∼10 times) at a similar optical transmittance (78%), greater stretchability (∼8 times less resistance increase at 30% strain), and good mechanical durability (∼42 times less resistance increase after 500 cyclic stretching tests at a strain of 30%) than those of random-CNT-networks films [276]. Additionally, because of its outstanding optical, electrical and mechanical properties on the microscale, graphene becomes a promising candidate as the basis carbon nanomaterial in the fabrication of SEs and STEs. However, large-area CVD growth graphene possess a real problem of low stretching ability, which is much lower than that of mechanically exfoliated pristine graphene owning to the yielded intrinsic and extrinsic defects during its preparation, etching-out of the catalytic metals, and the transferring process. This low stretchability becomes a major obstacle to commercially applying the CVD graphene in the field of STEs [277]. The large-scale production of high-quality SWCNTs and monolayer graphene is still a major challenge in the fabrication of carbon nanomaterial-based STEs, two major pathways toward obtaining these carbon nanomaterials separated by electronic structure: selective synthesis and post-synthesis separation.