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Two-dimensional transition metal dichalcogenides (TMDs), such as MoS 2 , hold great promise for next-generation electronics and optoelectronics due to their unique properties. However, the ultrathin nature of these materials renders them vulnerable to structural defects and environmental factors, which significantly impact their performance. Sulfur vacancies (V S ) are the most common intrinsic defects in MoS 2 , and their impact on device performance in oxidising environments remains understudied. This study investigates the impact of V S defects on the photoresponsivity of CVD-grown monolayer MoS 2 devices, when exposed to oxidising environments at high temperatures. Our findings reveal a dynamic process of defect generation and healing through oxygen passivation, leading to a significant difference in photocurrent between environments. Temperature-dependent analysis shows defect healing and a notable reduction in defect density upon cooling. This study provides crucial insights into the stability and performance of 2D materials-based devices under varying environmental conditions, essential for designing and controlling the performance of TMD-based devices. Our results pave the way for the development of robust and reliable 2D materials-based electronics and optoelectronics.

Photodetector technology has evolved significantly over the years with the emergence of new active materials. However, there remain trade-offs between spectral sensitivity, operating energy, and, more recently, an ability to harbor additional features such as persistent photoconductivity and bidirectional photocurrents for new emerging application areas such as switchable light imaging and filter-less color discrimination. Here, we demonstrate a self-powered bidirectional photodetector based on molybdenum disulfide/gallium nitride (MoS 2 /GaN) epitaxial heterostructure. This fabricated detector exhibits self-powered functionality and achieves detection in two discrete wavelength bands: ultraviolet and visible. Notably, it attains a peak responsivity of 631 mAW -1 at a bias of 0V. The device's response to illumination at these two wavelengths is governed by distinct mechanisms, activated under applied bias conditions, thereby inducing a reversal in the polarity of the photocurrent. This work underscores the feasibility of self-powered and bidirectional photocurrent detection but also opens new vistas for technological advancements for future optoelectronic, neuromorphic, and sensing applications.

Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/μm 2 . Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering.

Conventional absorbents for hemoperfusions suffer from low efficiency and slow absorption with numerous side effects. In this research, we developed cellulose acetate (CA) functionalized graphene oxide (GO) beads (∼1.5-2 mm) that can be used for direct hemoperfusion, aiming at the treatment of kidney dysfunction. The CA-functionalized GO bead facilitates adsorption of toxins with high biocompatibility and high-efficiency of hemoperfusion while maintaining high retention for red blood cell, white blood cells, and platelets. Our in vitro results show that the toxin concentration for creatinine reduced from 0.21 to 0.12 μM ( p < 0.005), uric acid from 0.31 to 0.15 mM ( p < 0.005), and bilirubin from 0.36 to 0.09 mM ( p < 0.005), restoring to normal levels within 2 h. Our in vivo study on rats (Sprague-Dawley, n = 30) showed that the concentration for creatinine reduced from 83.23 to 54.87 μmol L -1 ( p < 0.0001) and uric acid from 93.4 to 54.14 μmol L -1 ( p < 0.0001), restoring to normal levels within 30 min. Results from molecular dynamics (MD) simulations using free-energy calculations reveal that the presence of CA on GO increases the surface area for adsorption and enhances penetration of toxins in the binding cavities because of the increased electrostatic and van der Waals force (vdW) interactions. These results provide critical insight to fabricate graphene-based beads for hemoperfusion and to have the potential for the treatment of blood-related disease.

Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks 1 , recent experimental evidence favours the competing crystallite model in the case of amorphous silicon 2-4 . In two-dimensional materials, however,  the corresponding questions remain unanswered. Here we report the synthesis, by laser-assisted chemical vapour deposition 5 , of centimetre-scale, free-standing, continuous and stable monolayer amorphous carbon, topologically distinct from disordered graphene. Unlike in bulk materials, the structure of monolayer amorphous carbon can be determined by atomic-resolution imaging. Extensive characterization by Raman and X-ray spectroscopy and transmission electron microscopy reveals the complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and five-, six-, seven- and eight-member rings. The ring distribution is not a Zachariasen continuous random network, but resembles the competing (nano)crystallite model 6 . We construct a corresponding model that enables density-functional-theory calculations of the properties of monolayer amorphous carbon, in accordance with observations. Direct measurements confirm that it is insulating, with resistivity values similar to those of boron nitride grown by chemical vapour deposition. Free-standing monolayer amorphous carbon is surprisingly stable and deforms to a high breaking strength, without crack propagation from the point of fracture. The excellent physical properties of this stable, free-standing monolayer amorphous carbon could prove useful for permeation and diffusion barriers in applications such as magnetic recording devices and flexible electronics.

Nanopores on 2D materials have great potential for DNA sequencing, which is attributed to their high sequencing speed and reduced cost. However, identifying DNA bases at such a high speed with nanometer precision has remained a big challenge. Here, we implemented theoretical calculations to show the translocation of single-stranded DNA (ssDNA) through solid-state nanopores on a 2D hexagonal boron nitride (h-BN) and graphene sheet. A base-specific ssDNA sequencing technique was devised, based on the individual differences in the ion current responses for the (polyA) 16 , (polyG) 16 , (polyC) 16 , and (polyT) 16 bases of ssDNA. Our sequential procedure for sequencing is built on a comparative approach between the current signals obtained from the nanopores to achieve base-specific detection. Our results indicate that at higher voltages (1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 V nm -1 ), DNA translocation is tracked though the 1.5 and 2.0 nm nanopores, and at the 1.5 nm pore size, folded ssDNA close to the nanopore accounts for 93% and 81% of events for graphene and h-BN. Our calculations indicate charge transfer from the graphene to ssDNA, while the reverse happens in the case of the h-BN membrane. These results provide critical insights into our understanding of single molecule sequencing through solid-state nanopore research.

To enhance interlayer lithium diffusion, we engineer electrodes consisting of epitaxially grown ReSe 2 nanosheets by chemical vapor deposition, supported on three-dimensional (3D) graphene foam, taking advantage of its weak van der Waals coupling and anisotropic crystal structure. We further demonstrate its excellent performance as the anode for lithium-ion battery and catalyst for hydrogen evolution reaction (HER). Density functional theory calculation reveals that ReSe 2 exhibits a low energy barrier for lithium (Li) interlayer diffusion because of negligible interlayer coupling and anisotropic structure with low symmetry that creates additional adsorption sites and leads to a reduced diffusion barrier. Benefitting from these properties, the 3D ReSe 2 /graphene foam electrode displays excellent cycling and rate performance with 99.6% capacity retention after 350 cycles and a capacity of 327 mA h g -1 at the current density of 1000 mA g -1 . Additionally, it has exhibited a high activity for HER, in which an exchange current density of 277.8 μA cm -2 is obtained and only an overpotential of 106 mV is required to achieve a current density of -10 mA cm -2 . Our work provides a fundamental understanding of the interlayer diffusion of Li in transition-metal dichalcogenide (TMD) materials and acts as a new tool for designing a TMD-based catalyst.

We developed a general platform for the fabrication of transition metal oxide nanoparticles supported by a graphene foam (GF) by first coating it with a methacrylated gelatin (GelMA) hydrogel, which served as a 3D matrix for nanoparticle dispersion. The engineered GelMA/GF matrix was hydrophilic with good mechanical strength and high conductivity, therefore providing a good platform for the dispersion of a variety of metal/oxide precursors. Due to this platform, well-dispersed Co3O4 nanoparticles with the smallest size of 3 nm assembled on the nitrogen-doped graphene foam (Co3O4/NGF). The crystalline transformation from a CoCl2[H2O]2 precursor to Co3O4 was revealed by in operando X-ray diffraction and absorption techniques. After applying Co3O4/NGF as a free-standing electrocatalyst for water splitting, the nanoparticles of size 3 nm exhibited optimal catalytic activity in alkaline media; the corresponding cell could promote water splitting at a current density of 10 mA cm-2 with only 1.63 V and exhibited excellent stability in a 25 h long-term operation. Our results demonstrate that the GelMA hydrogel-coated 3D graphene foam can be a promising platform for the design and fabrication of graphene-based multifunctional materials.

Graphene, as well as other two-dimensional materials, is a promising candidate for use in bioimaging, therapeutic drug delivery, and bio-sensing applications. Here, we developed a protocol to functionalize graphene with recombinant proteins using genetically encoded SpyTag-SpyCatcher chemistry. SpyTag forms a covalent isopeptide bond with its genetically encoded partner SpyCatcher through spontaneous amidation under physiological conditions. The functionalization protocol developed is based on the use of short proteins as a linker, where two graphene-binding-peptides (GBPs) are attached to both ends of SpyTag (referred to as GStG), followed by the covalent conjugation with SpyCatcher-fusion proteins. The proposed method enables the decoration of crystalline graphene with various proteins, such as fluorescent proteins and affibody molecules that bind to cancerous cells. This scheme, which takes advantage of the cleanness of single-crystal graphene and the robustness of SpyTag-SpyCatcher chemistry, provides a versatile platform on which to study the biomolecule-surface and cell-substrate interactions and, indeed, may lead to a new way of designing biomedical devices. The interaction between peptides and graphene was clearly shown using molecular dynamics simulation and proven using specially designed experiments.

Ferroelectric thin film has attracted great interest for nonvolatile memory applications and can be used in either ferroelectric Schottky diodes or ferroelectric tunneling junctions due to its promise of fast switching speed, high on-to-off ratio, and nondestructive readout. Two-dimensional α-phase indium selenide (In 2 Se 3 ), which has a modest band gap and robust ferroelectric properties stabilized by dipole locking, is an excellent candidate for multidirectional piezoelectric and switchable photodiode applications. However, the large-scale synthesis of this material is still elusive, and its performance as a ferroresistive memory junction is rarely reported. Here, we report the low-temperature molecular-beam epitaxy (MBE) of large-area monolayer α-In 2 Se 3 on graphene and demonstrate the use of α-In 2 Se 3 on graphene in ferroelectric Schottky diode junctions by employing high-work-function gold as the top electrode. The polarization-modulated Schottky barrier formed at the interface exhibits a giant electroresistance ratio of 3.9 × 10 6 with a readout current density of >12 A/cm 2 , which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of In 2 Se 3 to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.

Trilayer graphene (TLG) synthesized by chemical vapor deposition (CVD), in particular the twisted TLG, exhibits sophisticated electronic structures that depend on their stacking modes. Here, we computationally and experimentally demonstrate the chemical reactivity differences of CVD-TLG induced by the stacking modes and corroborated by a photoexcited phenyl-grafting reaction. The experimental results show that the ABA stacking TLGs have the most inert chemical property, yet 30°-30° stacking twisted TLGs are the most active. Further, density functional theory calculations have shown that the chemical reactivity difference can be quantitatively explained by the differences in the number of hot electrons generated in their valence band during irradiation. The activity difference is further verified by the calculated adsorption energy of phenyl on the TLGs. Our work provides insight into the chemistry of TLG and addresses the challenges associated with selective functionalization of TLG with phenyl groups. The understandings developed in this project can also guide the future development of TLG-based functional devices.

We developed a high-yield synthesis of highly crystalline bilayer graphene (BLG) with two preferential stacking modes using a Ni-Cu gradient alloy growth substrate. Previously reported approaches for BLG growth include flat growth substrates of Cu or Ni-Cu uniform alloys and "copper pocket" structures. Use of flat substrates has the advantage of being scalable, but the growth mechanism is either "surface limited" (for Cu) or carbon precipitation (for uniform Ni-Cu), which results in multicrystalline BLG grains. For copper pockets, growth proceeds through a carbon back-diffusion mechanism, which leads to the formation of highly crystalline BLG, but scaling of the copper pocket structure is expected to be difficult. Here we demonstrate a Ni-Cu gradient alloy that combines the advantages of these earlier methods: the substrate is flat, so easy to scale, while growth proceeds by a carbon back-diffusion mechanism leading to high-yield growth of BLG with high crystallinity. The BLG layer stacking was almost exclusively Bernal or twisted with an angle of 30°, consistent with first-principles calculations we conducted. Furthermore, we demonstrated scalable production of transistor arrays based crystalline Bernal-stacked BLG with a band gap that was tunable at room temperature.

"Shuttle effect" of lithium polysulfides (LiPS) leads to a poor performance and a short cycle life of the Li-S battery, thus limiting their practical application. We demonstrate here that after coating polypropylene (PP) separator with a continuous monolayer graphene, the shuttle effect can be significantly suppressed by limiting the passage of long-chain LiPS. The graphene/PP separator can be further modified by sealing the big holes or pores on graphene with in situ polymerized nylon-66 via an interfacial polymerization reaction between diamine and adipoyl chloride supplied by the aqueous and oil phase, respectively, from each side of the membrane. With this engineered membrane, an initial specific capacity of 1128.4 mAh g -1 at 0.05C is achieved after test in a coin cell, higher than that of 983.2 mAh g -1 with pristine PP, along with increased Coulombic efficiency from 96.0 to 99.9% and enhanced cycling durability. Molecular dynamics simulations attest that the nanopores with appropriate size and structure are effective in acting as a "sieve" to selectively allow only Li + ions to pass through but prevent LiPS from migrating to the anode, consequently alleviating the shuttle effect. Our method provides a facile solution toward the mitigated shuttle effect and eventually contributes to the high performance of Li-S battery.

The 2D geometry nature and low dielectric constant in transition-metal dichalcogenides lead to easily formed strongly bound excitons and trions. Here, we studied the photoluminescence of van der Waals heterostructures of monolayer MoS 2 and graphene at room temperature and observed two photoluminescence peaks that are associated with trion emission. Further study of different heterostructure configurations confirms that these two peaks are intrinsic to MoS 2 and originate from a bound state and Fermi level, respectively, of which both accept recoiled electrons from trion recombination. We demonstrate that the recoil effect allows us to electrically control the photon energy of trion emission by adjusting the gate voltage. In addition, significant thermal smearing at room temperature results in capture of recoil electrons by bound states, creating photoemission peak at low doping level whose photon energy is less sensitive to gate voltage tuning. This discovery reveals an unexpected role of bound states for photoemission, where binding of recoil electrons becomes important.

Graphene and graphene oxides (GO), or their reduced forms, have been introduced in a variety of biosensing platforms and have exhibited enhanced performance levels in these forms. We herein report a DNA sensing platform consisting of aggregation-induced emission (AIE) molecules and complementary DNA (comDNA) adsorbed on GO. We experimentally turned the AIE molecule on and off by adjusting its distance, which correlates with DNA structures as shown in our computational results, from the GO sheet, which quenches depending on its distance from the graphene plane. The changes in florescence are reproducible, which demonstrates the probe's ability to identify the binding state of the DNA. Our molecular dynamics simulation results reveal strong π-π interactions between single-strand DNA (ssDNA) and GO, which enable the ssDNA molecule to move closer to the graphene oxide. This reduces the center of mass and binding free energies in the simulation. When hybridized with comDNA, the increased distance, evidenced by the reduced interaction, eliminates the quenching effect and turns on the AIE molecule. Our protocol use of the AIE molecule as a probe thus avoids the complicated steps involved in covalent functionalization and allows the rapid and label-free detection of DNA molecules., Statement of Significance: A simple, rapid method of fluorescent measurement of DNA hybridization in the presence of graphene (oxide) is presented. Conventional fluorescent dyes offer high performance in biosensors. However, labeling procedures are synthetically demanding in time and resources making it less cost-effective. Molecules with aggregation-induced-emission (AIE) property have advantages over traditional fluorescent molecules because of their intrinsic preference for detection as a turn-on probe and their single-molecule detection ability. Previous work has shown AIE dyes act as excellent "label-free" bioprobes with high sensitivity but with limited selectivity. Graphene oxide (GO) with its unique optical properties and affinity to different kinds of biomolecules can be used as an auxiliary to enhance selectivity of AIE dyes. In this work, we report a label-free strategy to detect DNA of particular sequence by water-soluble AIE probes with the aid of GO, supported by the computational explanations for this phenomenon., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

We demonstrate the fabrication of a graphene-based field effect transistor (GFET) incorporated in a two-dimensional paper network format (2DPNs). Paper serves as both a gate dielectric and an easy-to-fabricate vessel for holding the solution with the target molecules in question. The choice of paper enables a simpler alternative approach to the construction of a GFET device. The fabricated device is shown to behave similarly to a solution-gated GFET device with electron and hole mobilities of ∼1256 cm(2) V(-1) s(-1) and ∼2298 cm(2) V(-1) s(-1) respectively and a Dirac point around ∼1 V. When using solutions of ssDNA and glucose it was found that the added molecules induce negative electrolytic gating effects shifting the conductance minimum to the right, concurrent with increasing carrier concentrations which results to an observed increase in current response correlated to the concentration of the solution used., (Copyright © 2016 Elsevier B.V. All rights reserved.)