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Atomically thin molybdenum disulfide (MoS2) is a promising semiconductor material for integrated flexible electronics due to its excellent mechanical, optical and electronic properties. However, the fabrication of large-scale MoS2-based flexible integrated circuits with high device density and performance remains a challenge. Here, we report the fabrication of transparent MoS2-based transistors and logic circuits on flexible substrates using four-inch wafer-scale MoS2 monolayers. Our approach uses a modified chemical vapour deposition process to grow wafer-scale monolayers with large grain sizes and gold/titanium/gold electrodes to create a contact resistance as low as 2.9 kΩ μm−1. The field-effect transistors are fabricated with a high device density (1,518 transistors per cm2) and yield (97%), and exhibit high on/off ratios (1010), current densities (~35 μA μm−1), mobilities (~55 cm2 V−1 s−1) and flexibility. We also use the approach to create various flexible integrated logic circuits: inverters, NOR gates, NAND gates, AND gates, static random access memories and five-stage ring oscillators. Wafer-scale monolayers of MoS2 can be used to create flexible transistors and circuits that exhibit on/off ratios of 1010, current densities of ~35 μA μm−1 and mobilities of ~55 cm2 V−1 s−1.

Two-dimensional molybdenum disulfide (MoS2) is an emergent semiconductor with great potential in next-generation scaled-up electronics, but the production of high-quality monolayer MoS2 wafers still remains a challenge. Here, we report an epitaxy route toward 4 in. monolayer MoS2 wafers with highly oriented and large domains on sapphire. Benefiting from a multisource design for our chemical vapor deposition setup and the optimization of the growth process, we successfully realized material uniformity across the entire 4 in. wafer and greater than 100 μm domain size on average. These monolayers exhibit the best electronic quality ever reported, as evidenced from our spectroscopic and transport characterizations. Our work moves a step closer to practical applications of monolayer MoS2.

One of the main factors affecting the heat transfer efficiency of solar collector is that the ordinary fluid in it is in the state of natural convection. Supercritical fluid is expected to improve ...

Efficient control of the phase and polarization of light is of significant importance in modern optics and photonics. However, traditional methods are often accompanied with cascaded and bulky designs that cannot fulfill the ongoing demand for further integrations. Here, a single-layered metasurface composed of nonvolatile phase-change material Ge2Sb2Se4Te1 (GSST) is proposed with tunable spin-orbit interactions in subwavelength scale. According to the spin-dependent destructive or constructive interference, asymmetric transmission for circularly polarized incidence (extinction ratio > 8:1) can be achieved when GSST is in an amorphous state. Moreover, when GSST changes to crystalline state, reversed chiral transmission (extinction ratio > 12:1) can be observed due to the existence of intrinsic chirality. In addition, as the average cross-polarized transmitted amplitude is larger than 85%, arbitrary wavefront manipulations can be achieved in both states simultaneously based on the theory of Pancharatnam-Berry phase. As a proof of concept, several functional metasurface devices are designed and characterized to further demonstrate the validation of our design methodology. It is believed that these multifunctional devices with ultrahigh compactness are promising for various applications including chiroptical spectroscopy, EM communication, chiral imaging, and information encryption.

Compared with conventional mirrors that behave as isotropic electromagnetic (EM) reflectors, metamirrors composed of periodically aligned artificial meta-atoms exhibit increased degrees of freedom for EM manipulations. However, the functionality of most metamirrors is fixed by design, and how to achieve active EM control is still elusive. Here, we propose a multistate metamirror based on the nonvolatile phase change material Ge2Sb2Te5 (GST) with four distinct functionalities that can be realized in the infrared region by exploiting the temperature-activated phase transition. When varying the crystallinity of GST, the metamirror has the capability to perform as a right-handed circular polarization chiral mirror, a narrowband achiral mirror, a left-handed circular polarization chiral mirror, or a broadband achiral mirror, respectively. The inner physics is further explained by the construction or cancellation of extrinsic two-dimensional chirality. As a proof of concept, experimental verification is carried out and the measured results agree well with their simulated counterparts. Such a multifunctional tunable metamirror could address a wide range of applications from sensing and spectroscopy to analytical chemistry and imaging.

Supercritical CO2 is widely used in the HVAC facilities, such as gas coolers and solar collectors. The solar collector is a fluid-filled cavity, and the heat and mass transfer characteristi...

Two-dimensional molybdenum disulfide (MoS

We report on an all-fiber passively mode-locked ytterbium-doped (Yb-doped) fiber laser with monolayer molybdenum disulfide (ML-MoS 2 ) saturable absorber (SA) by three-temperature zone chemical vapor deposition (CVD) method. The modulation depth, saturation fluence, and non-saturable loss of this ML-MoS 2 are measured to be 3.6%, 204.8 μ J/cm 2 and 6.3%, respectively. Based on this ML-MoS 2 SA, a passively mode-locked Yb-doped fiber laser has been achieved at 979 nm with pulse duration of 13 ps and repetition rate of 16.51 MHz. A mode-locked fiber laser at 1037 nm is also realized with a pulse duration of 475 ps and repetition rate of 26.5 MHz. To the best of our knowledge, this is the first report that the ML-MoS 2 SA is used in an all-fiber Yb-doped mode-locked fiber laser at 980 nm. Our work further points the excellent saturable absorption ability of ML-MoS 2 in ultrafast photonic applications.

Connected vehicles continuously reveal their location information to the potential observers that then track vehicles over time and space. However, safety applications require disseminating such location information to the vicinity, which essentially urges to develop the awareness ability of the exposed location-privacy quantity. We propose an analytic framework to quantify location privacy from the perspective of temporal and spatial correlation, which permits connected vehicles to flexibly configure their preferential location-privacy sensitivity extent. We offer a novel approach so as to make the disclosure of location privacy more human-understandable and independent of the suffered attack pattern. This paradigm enables users to customize the location-privacy protection mechanisms for adapting to the frequently varying traffic context. Moreover, we put forward an adaptive lived-term pseudonym scheme for exampling how to utilize the presented quantitative framework. Finally, we move from theory to practice by applying the proposed theoretical framework to a simulation vehicular mobility data set TAPASCologne composed of more than two hundred and fifty thousand vehicles and a real trace set of more than ten million location sample points obtained from the Roman taxis. We investigate the accuracy and applicability of the presented quantification model and effects of combinations of various concerned parameters. The results show that the quantification model can identify the real-time exposure of location privacy efficiently and effectively as vehicles move and then provide quantitative control feedback to privacy protection mechanisms, which facilitates restrict the location privacy to a target value and tradeoff between the location privacy and service enjoyment.

Large scale epitaxial growth and transfer of monolayer MoS2 has attracted great attention in recent years. Here, we report the wafer-scale epitaxial growth of highly oriented continuous and uniform monolayer MoS2 films on single-crystalline sapphire wafers by chemical vapor deposition (CVD) method. The epitaxial film is of high quality and stitched by many 0°, 60° domains and 60°-domain boundaries. Moreover, such wafer-scale monolayer MoS2 films can be transferred and stacked by a simple stamp-transfer process, and the substrate is reusable for subsequent growth. Our progress would facilitate the scalable fabrication of various electronic, valleytronic, and optoelectronic devices for practical applications.

The complexity of the driving behavior restricts the realism of traffic simulation. This paper proposed that vehicle mobility models should be established according to diverse driving styles to further approximation of real driving behavior. With Krauss model represented, the conservative (driving style) of safe distance car-following model is analyzed. The analysis means that real vehicles can occasionally break the safe distance rule, and on average, real vehicle gap is slightly smaller than that in the Krauss model. An aggressive car-following model is proposed in the view of driving style. Simulation results show the new model can simulate aggressive driving style, which has significance to simulate traffic using diverse driving style models. Since it breaks the safe distance rule, the new model has the possibility of generating rear-end collisions when simulating. Drivers’ characteristics, prediction behavior, the cause of accidents, and the effects of time granularity on a simulation are studied. The concept of “road black hole” is put forward, which is believed to reduce velocity of traffic flow.

In this work, we report a facile, clean, controllable and scalable phase engineering technique for monolayer MoS2. We found that weak Ar-plasma bombardment can locally induce 2H→1T phase transition in monolayer MoS2 to form mosaic structures. These 2H→1T phase transitions are stabilized by point defects (single S-vacancies) and the sizes of induced 1T domains are typically a few nanometers, as revealed by scanning tunneling microscopy measurements. On the basis of a selected-area phase patterning process, we fabricated MoS2 FETs inducing 1T phase transition within the metal contact areas, which exhibit substantially improved device performances. Our results open up a new route for phase engineering in monolayer MoS2 and other transition metal dichalcogenide (TMD) materials.

Recently, monolayer molybdenum disulphide (MoS2) has emerged as a promising and non–precious electrocatalyst for hydrogen evolution reaction. However, its performance is largely limited by the low density and poor reactivity of active sites within its basal plane. Here, we report that domain boundaries in the basal plane of monolayer MoS2 can greatly enhance its hydrogen evolution reaction performance by serving as active sites. Two types of effective domain boundaries, the 2H-2H domain boundaries and the 2H-1T phase boundaries, were investigated. Superior hydrogen evolution reaction catalytic activity, long-term stability and universality in both acidic and alkaline conditions were achieved based on a multi-hierarchy design of these two types of domain boundaries. We further demonstrate that such superior catalysts are feasible at a large scale by applying this multi-hierarchy design of domain boundaries to wafer-scale monolayer MoS2 films., While water-splitting electrocatalysts enable energy storage in carbon-neutral fuels, a recent challenge has been the discovery and understanding of catalyst active sites. Here, authors find domain boundaries in MoS2 materials to present high-activity, stable, and scalable sites for H2 evolution.

MoS2 nanoscrolls are formed by argon plasma treatment on monolayer MoS2 sheet. The nanoscale scroll formation is attributed to the partial removal of top sulfur layer in MoS2 during the argon plasma treatment process. This convenient, solvent-free, and high-yielding nanoscroll formation technique is also feasible for other 2D transition metal dichalcogenides.

Magnetic Resonance Imaging(MRI) has been proven to be important for in vivo quantitative characterization of iron deposition, either endogenous or exogenous(Iron Nanoparticles, IONPs). Iron has endogenous paramagnetic characteristics, and causes shortened T1, T2, and T2* relaxation times as well as phase and susceptibility changes by affecting the magnetic environment of water protons [1–2]. Among all the quantitative MRI methods, quantitative susceptibility mapping (QSM) has gained increased interest as iron is paramagnetic, leading to a linear increase in susceptibility with iron concentration. 2017, it has been shown that the iron could be quantified by both QSM and R2* to a range as high as 22 mM by using ultra-short TE(UTE) technics [3]. However, for in vivo study environment, as fat is an essential contents exists everywhere in human body, the chemical shift effects caused by fat will cause severe streaking artifacts in the QSM results and make the quantification failure [4].The H protons of fat, are nestled within long-chain triglycerides and covered by electron clouds. These clouds partially shield the fat protons from the full effects of an externally applied magnetic field. It is still unknown how much the fat will effects the MRI phase signals with UTE acquisitions, as at a very short TE, the chemical shift effects caused phase shift could not be very obvious. In this study, simulation study was performed to evaluate the chemical shift effect on the quantification of the magnetic susceptibility with UTE sequences based on a fat combined susceptibility-phase change model.

The investigation and control of quantum degrees of freedom (DoFs) of carriers lie at the heart of condensed-matter physics and next-generation electronics/optoelectronics. van der Waals heterostructures stacked from distinct two-dimensional (2D) crystals offer an unprecedented platform for combining the superior properties of individual 2D materials and manipulating spin, layer, and valley DoFs. $\mathrm{Mo}{\mathrm{S}}_{2}$/graphene heterostructures, harboring prominent spin-transport properties of graphene, giant spin-orbit coupling, and spin-valley polarization of $\mathrm{Mo}{\mathrm{S}}_{2}$, are predicted as a perfect venue for optospintronics. Here, we report the epitaxial growth of commensurate $\mathrm{Mo}{\mathrm{S}}_{2}$ on graphene with high quality by chemical vapor deposition, and demonstrate robust temperature-independent spin-valley polarization at off-resonant excitation. We further show that the helicity of B exciton is larger than that of A exciton, allowing the manipulation of spin bits in the commensurate heterostructures by both optical helicity and wavelength. Our results open a window for controlling spin DoF by light and pave a way for taking spin qubits as information carriers in the next-generation valley-controlled optospintronics.

Large scale epitaxial growth and transfer of monolayer MoS

In order to solve the problem of low intrusion detection rate and weak generalization ability of Intrusion Detection System (IDS), it proposes a new hybrid method based on the relationship of feature and spatial correlation for IDS. The proposed IDS reduces the dimension of network data flow by spatial correlation-based dimension reduction method (SCDR). It improves the effectiveness of intrusion detection, and the negative feedback learning method can also improve the generalization ability of IDS. Experiments show that the method in this paper can improve the detection rate notably and also enhance the detection ability of unknown attacks.