Junpeng Zeng, Daowei He, Jingsi Qiao, Yating Li, Li Sun, Weisheng Li, Jiacheng Xie, Si Gao, Lijia Pan, Peng Wang, Yong Xu, Yun Li, Hao Qiu, Yi Shi, Jian-Bin Xu, Wei Ji & Xinran Wang
Abstract:
Organic field-effect transistors (OFETs) are of interest in unconventional form of electronics. However, high-performance OFETs are currently contact-limited, which represent a major challenge toward operation in the gigahertz regime. Here, we realize ultralow total contact resistance (Rc) down to 14.0 Ω ∙ cm in C10-DNTT OFETs by using transferred platinum (Pt) as contact. We observe evidence of Pt-catalyzed dehydrogenation of side alkyl chains which effectively reduces the metal-semiconductor van der Waals gap and promotes orbital hybridization. We report the ultrahigh performance OFETs, including hole mobility of 18 cm2 V−1 s−1, saturation current of 28.8 μA/μm, subthreshold swing of 60 mV/dec, and intrinsic cutoff frequency of 0.36 GHz. We further develop resist-free transfer and patterning strategies to fabricate large-area OFET arrays, showing 100% yield and excellent variability in the transistor metrics. As alkyl chains widely exist in conjugated molecules and polymers, our strategy can potentially enhance the performance of a broad range of organic optoelectronic devices.
The aim of atom electronics, i.e. the final scale of electronics, is to make use of specific individual atoms as active electronic components. Here, we review recent researches on atom electronics in single-molecule transistors (SMTs) through single-atom access and manipulation. We begin by describing the basic concepts and characteristics of atom electronics in SMTs, before discussing some of the most recent examples, including atomic transistors and atomic storage. In our concluding remarks, we discuss some perspectives on fabrication, integration, and other potential atomic devices in which high precision access to, and manipulation of single atoms could be of great significance. This will affect integrated circuits, quantum computing, and other devices that will drive the electronics of the future.
Shiyuan Wang#, Yao Wang#, Shaohua Yan#, Cong Wang#, Bingke Xiang,Keyi Liang,Qiushi He,Kenji Watanabe,Takashi Taniguchi, Shangjie Tian, Hechang Lei, Wei Ji, Yang Qi, Yihua Wang*
Abstract
In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing anisotropies are present, the phase transition becomes nontrivial. Here, utilizing highly sensitive susceptometry of scanning superconducting quantum interference device microscopy, we probe the spin correlations of ABC-stacked CrBr3 under zero magnetic field. We identify a plateau feature in susceptibility above the critical temperature (�C) in thick samples. It signifies a crossover regime induced by the competition between easy-plane intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The evolution of the critical behavior from the bulk to 2D shows that the competition between the anisotropies is magnified in the reduced dimension. It leads to a strongly frustrated ferromagnetic transition in the bilayer with fluctuation on the order of �C, which is distinct from both the monolayer and the bulk. Our observation demonstrates unconventional 2D critical behavior on a honeycomb lattice.
A superatom is any cluster of atoms that collectively exhibits some properties of single atoms. When arranged into crystals through the noncovalent bonds, they can be readily assembled into nanostructures, because the reduced cohesive energy of the noncovalent bonds makes it easier to cleave the material. It is not yet clear whether such weakened energetic interaction is accompanied by a suppressed electronic interaction among the superatoms. To that end, we explore exotic electronic structures on the surface of one superatomic crystal and find strong electron-electron interactions do occur. We also find that two exotic charge orders emerge.
Recently, researchers synthesized a cubic superatom, Au6Te12Se8 (ATS), and assembled it into a 3D crystal with metallicity and superconductivity. In our experiments, we observe two charge orders on the ATS surface. One is a charge density wave that forms across repeating columns of ATS cubes. The other is a polar metallic state that arises between the columns. The polar metallic states are of particular interest, suggesting the ATS surface is an antipolar metal—a type of exotic metal where metallicity and orderly, antiparallel-oriented electric dipoles coexist. The discovery of this antipoloar metal goes one step further toward the realization of multifunctional devices, which could, in principle, perform simultaneous electrical, magnetic, and optical functions. However, we have not yet examined ATS’s ferroelectricity, which is needed for electrical control of its electrical polarization.
This ATS crystal is, to the best of our knowledge, the first antipolar metal ever found and possesses the first polar metallic state hosted in superatomic units bound by noncovalent interactions. Thus, the strong electron-electron interactions, found in the 2D superatomic layers, open a category of quantum materials that contains versatile layered nanostructures exhibiting precisely tailorable electronic structures.
Abstract
Electronic properties of superatomic crystals have not been sufficiently explored due to the versatility of their building units; moreover, their interunit couplings are even poorly understood. Here, we present a joint experiment-theory investigation of a rationally designed layered superatomic crystal of Au6Te12Se8 (ATS) cubes stacked by noncovalent intercube quasibonds. We find a sequential-emerged anisotropic triple-cube charge density wave (TCCDW) and polarized metallic states below 120 K, as revealed via scanning tunneling microscopy and spectroscopy, angle-resolved photoemission spectroscopy, transport measurement, Raman spectra, and density-functional theory. The polarized states are locked in an antiparallel configuration, which is required for maintaining the inversion symmetry of the center cube in the TCCDW. The antipolar metallic states are thus interweaved by the CDW and the polarized metallic states, and primarily ascribed to electronic effects via theoretical calculations. This work not only demonstrates a microscopic picture of the interweaved CDW and polarized charge orders in the superatomic crystal of ATS, but also sheds light on expanding the existing category of quantum materials to noncovalent solids.
Jialei Miao#, Linlu Wu#, Zheng Bian, Qinghai Zhu, Tianjiao Zhang, Xin Pan, Jiayang Hu, Wei Xu, Yeliang Wang, Yang Xu, Bin Yu, Wei Ji, Xiaowei Zhang*, Jingsi Qiao*, Paolo Samorì*, and Yuda Zhao*
Abstract
Two-dimensional (2D) materials with the atomically thin thickness have attracted great interest in the post-Moore’s Law era because of their tremendous potential to continue transistor downscaling and offered advances in device performance at the atomic limit. However, the metal–semiconductor contact is the bottleneck in field-effect transistors (FETs) integrating 2D semiconductors as channel materials. A robust and tunable doping method at the source and drain region of 2D transistors to minimize the contact resistance is highly sought after. Here we report a stable carrier doping method via the mild covalent grafting of maleimides on the surface of 2D transition metal dichalcogenides. The chemisorbed interaction contributes to the efficient carrier doping without degrading the high-performance carrier transport. Density functional theory results further illustrate that the molecular functionalization leads to the mild hybridization and the negligible impact on the conduction bands of monolayer MoS2, avoiding the random scattering from the dopants. Differently from reported molecular treatments, our strategy displays high thermal stability (above 300 °C) and it is compatible with micro/nano processing technology. The contact resistance of MoS2 FETs can be greatly reduced by ∼12 times after molecular functionalization. The Schottky barrier of 44 meV is achieved on monolayer MoS2 FETs, demonstrating efficient charge injection between metal and 2D semiconductor. The mild covalent functionalization of molecules on 2D semiconductors represents a powerful strategy to perform the carrier doping and the device optimization.
Abstract: High-capacity electrochemical energy storage systems are more urgently needed than ever before with the rapid development of electric vehicles and the smart grid. The most efficient way to increase capacity is to develop electrode materials with low molecular weights. The low-cost metal halides are theoretically ideal cathode materials due to their advantages of high capacity and redox potential. However, their cubic structure and large energy barrier for deionization impede their rechargeability. Here, the reversibility of potassium halides, lithium halides, sodium halides, and zinc halides is achieved through decreasing their dimensionality by the strong π–cation interactions between metal cations and reduced graphene oxide (rGO). Especially, the energy densities of KI-, KBr-, and KCl-based materials are 722.2, 635.0, and 739.4 Wh kg−1, respectively, which are higher than those of other cathode materials for potassium-ion batteries. In addition, the full-cell with 2D KI/rGO as cathode and graphite as anode demonstrates a lifespan of over 150 cycles with a considerable capacity retention of 57.5%. The metal halides-based electrode materials possess promising application prospects and are worthy of more in-depth researches.
