This study investigates the strong photoluminescence (PL) and X-ray excited optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes (GNFs:N), which arise from the significantly enhanced density of states in the region of π states and the gap between π and π* states. The increase in the number of the sp 2 clusters in the form of pyridine-like N−C, graphite-N-like, and the CO bonding and the resonant energy transfer from the N and O atoms to the sp 2 clusters were found to be responsible for the blue shift and the enhancement of the main PL emission feature. The enhanced PL is strongly related to the induced changes of the electronic structures and bonding properties, which were revealed by the X-ray absorption near-edge structure, X-ray emission spectroscopy, and resonance inelastic X-ray scattering. The study demonstrates that PL emission can be tailored through appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way for new optoelectronic devices.

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Monolayer transition metal dichalcogenides (TMDCs) with high crystalline quality are important channel materials for next‐generation electronics. Researches on TMDCs have been accelerated by the development of chemical vapor deposition (CVD). However, antiparallel domains and twin grain boundaries (GBs) usually form in CVD synthesis due to the special threefold symmetry of TMDCs lattices. The existence of GBs severely reduces the electrical and photoelectrical properties of TMDCs, thus restricting their practical applications. Herein, the epitaxial growth of single crystal MoS2 (SC‐MoS2) monolayer is reported on Au (111) film across a two‐inch c‐plane sapphire wafer by CVD. The MoS2 domains obtained on Au (111) film exhibit unidirectional alignment with zigzag edges parallel to the <110> direction of Au (111). Experimental results indicated that the unidirectional growth of MoS2 domains on Au (111) is a temperature‐guided epitaxial growth mode. The high growth temperature provides enough energy for the rotation of the MoS2 seeds to find the most favorable orientation on Au (111) to achieve a unidirectional ratio of over 99%. Moreover, the unidirectional MoS2 domains seamlessly stitched into single crystal monolayer without GBs formation. The progress achieved in this work will promote the practical applications of TMDCs in microelectronics.

The metal-graphene contact resistance has been identified to be a key bottleneck for achieving high performance of graphene transistors. It is crucial to understand the electrical properties of graphene and the carrier transport mechanism under the contact metal. Here, we have developed a new method of characterizing the electrical properties of graphene under the metal contact. It was found that the electrical properties of graphene under the metal can be tuned via the back-gate voltage and display ambipolar behavior. A quantum tunneling model for graphene-metal physical contact has been proposed. The probability of electric field-tunable tunneling has been derived from the results of measurements for the first time. The model predicts that even for physical contact the contact resistance can be much lower than 100 Ω μm when graphene is more heavily doped and the interfacial layer is eliminated. This study paves the way to achieving ultralow graphene-metal contact resistance in graphene devices for terahertz applications.

A top-gated graphene FET with an ultralow 1/f noise level of 1.8 × 10 μmHz (f = 10 Hz) has been fabricated. The noise has the least value at Dirac point, it then increases fast when the current deviates from that at Dirac point, the noise slightly decreases at large current. The phenomenon can be understood by the carrier-number-fluctuation induced low frequency noise, which caused by the trapping-detrapping processes of the carriers. Further analysis suggests that the effect trap density depends on the location of Fermi level in graphene channel. The study has provided guidance for suppressing the 1/f noise in graphene-based applications.

Reconfigurable artificial synapse with synaptic responses modulated between excitatory and inhibitory modes is critical for building artificial intelligence systems. However, it is still a challenge to realize such reconfigurability with a simple single‐gated transistor. Here, hydrogen‐rich silicon nitride film is employed as the gate dielectric to construct a single‐gate controlled graphene‐based artificial synapse to realize the reconfigurable synaptic responses. In this dielectric, both traps and movable hydrogen ions are introduced to induce the carrier trapping effect and the capacitive gating effect, respectively. Comparatively, the capacitive gating effect needs stronger electrical fields excitation and can significantly modulate the graphene channel in a longer time. Utilizing the carrier trapping effect and the ambipolar property of graphene, the fundamental potentiation and depression behaviors can be emulated in each response mode. Then, utilizing the capacitive gating effect, the reconfiguration between excitatory and inhibitory response modes can be achieved. All synaptic responses only depend on the signals inputted through the back‐gate electrode, which is distinctively different from previous dynamic devices with additional modulating terminals. Such reconfiguration feature provides the artificial synapse the ability to emulate some complicated biological behaviors in future artificial intelligence systems, such as the adjustable perception of different external stimuli under different conditions.

Wrinkling is a universal phenomenon in graphene transfer process and significantly degrades the electronic transport properties of graphene. Taking advantage of the special surface morphology of the growth substrate of copper foil, graphene is prepared with oriented wrinkles. Furthermore, the electronic transport properties are studied parallel and perpendicular to the wrinkles using cross‐shaped FET devices and it is found that the carrier mobility of graphene is anisotropic along these two directions. This discovery will help to prepare electronic devices with higher performance.

electronics. [1][2][3][4][5] The cause of the amazing electronic properties of graphene is its unique line-up band structure, in which the valence and conduction bands meet in a single point at the Fermi level. This peculiar point is the so-called Dirac points and cones. [1] In graphene field-effect transistor (GFET), the channel conductance is modulated by the electric field from a back-or top-gate. The transfer characteristics, I DS -V GS curves typically display a V shape, with a hole-dominated conductance (p-branch) at lower V GS and electron type transport at more positive gate voltages (n-branch). The valley of the curves is the charge neutrality where the concentration of electron is equal to that of hole. This valley corresponds to the Dirac point in graphene band structure and quite important for electronic applications of graphene. For example, both the graphene frequency doubler and ambipolar mixer are biased at the Dirac point for their best performance. [6][7][8][9] In most case, only one unique Dirac point was found in the transfer characteristic of GFET. [10][11][12][13] Recently, several research groups found that the transfer characteristics in GFET show an additional minimum other than the major Dirac point, in other words, a doubledips curves. Nouchi and Tanigaki have found an anomalous distortion in GFET with ferromagnetic metal electrodes. [14] The transfer characteristics in these GFETs show two local minimal current points at hole branch. They attribute this phenomenon to the oxide layer induced weaker pinning of charge density at the metal contacts. Brenner and Murali have utilized hydrogen silsesquoxane film to partially cover the graphene channel, which leads to the different doping levels in channel region and a formation of p-n junction. An additional minimum conductance other than the Dirac point can also be observed in this GFET. [15] Chiu et al. found that an additional dip will appear on the left-hand side of the original Dirac point in I DS -V BG curve in the high field regime. They claim that this double dip structure can be attributed to the formation of a p-n junction in drain region, which is induced by the trapped charge doping under high bias conditions. [16] Bartolomeo et al. show that a double Dirac point can also been achieved while keeping the drain bias very low (20 mV). They have clarified that the double Dirac point is related to charge transfer between graphene and metal contact and that it is enhanced by the charge storage at The Dirac point(s) in graphene field-effect transistors (GFETs) are of great importance for electronic application. However, the lack of the effective means to distinguish the electrical properties of graphene at the contact and channel regions limits a clear understanding of their contributions to the Dirac point(s). A method, which can characterize the electrical properties of graphene under metal contact and in the channel, is developed, respectively. It is found that the Fermi levels of graphene at the contact and channel regions are quite ...