More Like this

1. Roll‐to‐Roll Dry Transfer of Large‐Scale Graphene

   https://doi.org/10.1002/adma.202106615  

   Hong, Nan ; Kireev, Dmitry ; Zhao, Qishen ; Chen, Dongmei ; Akinwande, Deji ; Li, Wei ( November 2021 , Advanced Materials)

   A major challenge for graphene applications is the lack of mass production technology for large‐scale and high‐quality graphene growth and transfer. Here, a roll‐to‐roll (R2R) dry transfer process for large‐scale graphene grown by chemical vapor deposition is reported. The process is fast, controllable, and environmentally benign. It avoids chemical contamination and allows the reuse of graphene growth substrates. By controlling tension and speed of the R2R dry transfer process, the electrical sheet resistance is achieved as 9.5 kΩ sq⁻¹, the lowest ever reported among R2R dry transferred graphene samples. The R2R dry transferred samples are used to fabricate graphene‐based field‐effect transistors (GFETs) on polymer. It is demonstrated that these flexible GFETs feature a near‐zero doping level and a gate leakage current one to two orders of magnitude lower than those fabricated using wet‐chemical etched graphene samples. The scalability and uniformity of the R2R dry transferred graphene is further demonstrated by successfully transferring a 3 × 3 in²sample and measuring its field‐effect mobility with 36 millimeter‐scaled GFETs evenly spaced on the sample. The field‐effect mobility of the R2R dry transferred graphene is determined to be 205 ± 36 cm² V⁻¹.

    

   more » « less
2. Mechanically tunable elastic modulus of freestanding Ba1− x Sr x TiO3 membranes via phase-field simulation

   https://doi.org/10.1063/5.0099772  

   Zhang, Kena ; Ren, Yao ; Cao, Ye ( October 2022 , Applied Physics Letters)

   The freestanding ferroelectric membranes with super-elasticity show promising applications in flexible electronic devices such as transducers, memories, etc. While there have been recent studies on the effect of mechanical bending on the domain structure evolutions and phase transitions in ferroelectric membranes, its influence on Young's modulus of these freestanding membranes is less explored, which is crucial for the design and application of flexible electronics. Here, a phase-field model is developed to simulate the tunability of Young's modulus of freestanding Ba1−xSrxTiO3 membranes under mechanical bending. It is demonstrated that the bended membrane shows a uniform Young's modulus compared with unbended membrane. By increasing the bending angle, Young's modulus tunability is enhanced, which can be attributed to the vortex-like domain structures induced by the mechanical bending. These vortex-like domains with large domain wall energy inhibit the subsequent domain switching under externally applied tensile strain and reduce the eigenstrain variation, which leads to a large Young's modulus. In addition, the formation of vortex domain structure is suppressed with increasing Sr2+ content in Ba1−xSrxTiO3 membranes at the same bending degree, resulting in a decrease in Young's modulus tunability. Our work reveals that the tunability of Young's modulus of freestanding ferroelectric membranes can be achieved by mechanical bending, which provides guidance for designing flexible electronic devices. 

   more » « less
3. Lateral Graphene p–n Junctions Realized by Nanoscale Bipolar Doping Using Surface Electric Dipoles and Self‐Organized Molecular Anions

   https://doi.org/10.1002/admi.201801380  

   Zhang, Yong ; Hu, Guangliang ; Gong, Maogang ; Alamri, Mohammed ; Ma, Chunrui ; Liu, Ming ; Wu, Judy Z. ( November 2018 , Advanced Materials Interfaces)

   Lateral p–n junctions take the unique advantages of 2D materials, such as graphene, to enable single‐atomic layer microelectronics. A major challenge in fabrication of the lateral p–n junctions is in the control of electronic properties on a 2D atomic sheet with nanometer precision. Herein, a facile approach that employs decoration of molecular anions of bis‐(trifluoromethylsulfonyl)‐imide (TFSI) to generate p‐doping on the otherwise n‐doped graphene by positively polarized surface electric dipoles (pointing toward the surface) formed on the surface oxygen‐deficient layer “intrinsic” to an oxide ferroelectric back gate is reported. The characteristic double conductance minimaV_Dirac−andV_Dirac+illustrated in the obtained lateral graphene p–n junctions can be tuned in the range of −1 to 0 V and 0 to +1 V, respectively, by controlling the TFSI anions and surface dipoles quantitatively. The unique advantage of this approach is in adoption of polarity‐controlled molecular ion attachment on graphene, which could be further developed for various lateral electronics on 2D materials.

    

   more » « less
4. Graphene quantum dots, graphene non-circular n{p{n-junctions: Quasi-relativistic pseudopotential approach

   H. V. Grushevskaya, G. G. ( January 2018 , NATO science for peace and security series. A, Chemistry and biology)

   We have constructed a continuous model of graphene quantum dot (GQD) as the hydrodynamic limit of the discrete model of n{p{n graphene junction in the form of a rhombic supercell on the graphene plane. The topological type of the proposed GQD-model corresponds bijectively to the GQD-edge topology and can be similar to a sphere or torus. The Hamiltonian of the discrete model of n{p{n graphene junction is chosen to be the Dirac{Weyl type with one Dirac point and 6 pairs of Weyl nodes{antinodes in the folding-zone approximation. The bending-band structure of the proposed GQD-model is ensured by a GQD pseudopotential barrier, which is given by a set of well pseudopotentials for individual carbon atoms of the GQD. The main specic feature of the structure of electron levels of both spherical and toroidal GQDs is the self-similar energy bands located subsequently one behind another on the energy scale. The atom-like distribution of the electron density is realized from the geometric viewpoint only for toroidal GQDs due to the absence of the curvature for a torus. Though the quasi-zero-energy band exists for spherical and toroidal GQDs, no electron density is present on this band for toroidal GQDs. This causes the formation of a pseudogap between the hole and electron bands, because of the absence of the electron density at the quantum dot center like the case of an ordinary atom. However, the confinement of the electron density is observed for both spherical and toroidal GQDs. 

   more » « less
5. Mechanically controllable nonlinear dielectrics

   https://doi.org/10.1126/sciadv.aaz3180  

   Ko, D. L. ; Tsai, M. F. ; Chen, J. W. ; Shao, P. W. ; Tan, Y. Z. ; Wang, J. J. ; Ho, S. Z. ; Lai, Y. H. ; Chueh, Y. L. ; Chen, Y. C. ; et al ( March 2020 , Science Advances)

   Strain-sensitive Ba x Sr 1− x TiO 3 perovskite systems are widely used because of their superior nonlinear dielectric behaviors. In this research, new heterostructures including paraelectric Ba 0.5 Sr 0.5 TiO 3 (BSTO) and ferroelectric BaTiO 3 (BTO) materials were epitaxially fabricated on flexible muscovite substrate. Through simple bending, the application of mechanical force can regulate the dielectric constant of BSTO from −77 to 36% and the channel current of BTO-based ferroelectric field effect transistor by two orders. The detailed mechanism was studied through the exploration of phase transition and determination of band structure. In addition, the phase-field simulations were implemented to provide theoretical support. This research opens a new avenue for mechanically controllable components based on high-quality oxide heteroepitaxy. 

   more » « less