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Graphene absorbers have attracted lots of interest in recent years. They provide huge potential for applications such as photodetectors, modulators, and thermal emitters. In this letter, we design a high-quality (Q) factor resonant graphene absorber based on the phase change material Sb2S3. In the proposed structure, a refractive index grating is formed at the subwavelength scale due to the periodical distributions of amorphous and crystalline states, and the structure is intrinsically flat. The numerical simulation shows that nearly 100% absorption can be achieved at the wavelength of 1550 nm, and the Q factor is more than hundreds due to the loss-less value of Sb2S3 in the near-infrared region. The absorption spectra can be engineered by changing the crystallization fraction of the Sb2S3 as well as by varying the duty cycle of the grating, which can be employed not only to switch the resonant wavelength but also to achieve resonances with higher Q factors. This provides a promising method for realizing integrated graphene optoelectronic devices with the desired functionalities.

The white top-hat transformation has been widely used in small bright target extraction. It usually applies an erosion operation to remove the target and then a dilation operation to recover the intensity of the processed image. A bright target will be extracted by subtracting the opening operation (erosion followed by dilation) from the raw image. The drawback of this method is that its denoising ability is poor because the estimated background threshold by an opening operation is smaller than the raw image. This study puts forward the viewpoint that by use of a proposed one-dimensional (1D) symmetrical line-shaped structuring element a bright target can also be removed by the dilation operation. Consequently, the white top-hat transformation can be implemented by subtracting only the dilation operation from the raw image. To the best knowledge of the authors, it is the first time to use this method to achieve the top-hat transformation. The simulation experiment shows that the proposed 1D top-hat algorithm has excellent performance in denoising ability and detection ability. Moreover, real night experiments demonstrate that our proposed algorithm can work reliably under both complicated background conditions and good weather conditions. It is noticeable that the performance of computational efficiency and resource consumption have been considerably improved because a 1D structuring element is employed and the erosion operation is not included.

Stacking order plays a central role in governing a wide range of properties in layered two-dimensional materials. In the case of few-layer graphene, there are two common stacking configurations: ABA and ABC stacking, which have been proven to exhibit dramatically different electronic properties. However, the controllable characterization and manipulation between them remain a great challenge. Here, we report that ABA- and ABC-stacked domains can be directly visualized in phase imaging by tapping-mode atomic force microscopy with much higher spatial resolution than conventional optical spectroscopy. The contrasting phase is caused by the different energy dissipation by the tip-sample interaction. We further demonstrate controllable manipulation on the ABA/ABC domain walls by means of propagating stress transverse waves generated by the tapping of tip. Our results offer a reliable strategy for direct imaging and precise control of the atomic structures in few-layer graphene, which can be extended to other two-dimensional materials.

Atomically thin molybdenum disulfide (MoS2) has been treated as a promising optoelectronic material, due to its strong photoluminescence (PL) emission. Here, we demonstrate the tunability of the PL properties of bilayer MoS2 through interlayer twist. The PL emission peak position, full-width-at-half-maximum (FWHM) and intensity are found to be dependent on the twisted angle, which reach their extremum for the twisted angle around 40°. This PL modulation is attributed to the change of the interlayer coupling between the adjacent MoS2 layers. In addition, peak A splitting of PL spectra is found in twisted bilayer MoS2, due to the doping effect from substrate. These results enrich our understanding of the relationship between PL emission and interlayer coupling, which is significant for optical and electrical applications of twisted bilayer MoS2 (tBLM).

Controlling thermal radiation in nanoscale is critical for verifying the Planck’s law in subwavelength limit, and is the key for a range of innovative technologies including energy, display and sec...

Removal of expression of concern for ‘Controllable 2H-to-1T′ phase transition in few-layer MoTe2’ by Yuan Tan et al., Nanoscale, 2018, 10, 19964–19971.

A star tracker should be well calibrated before it is equipped in order to achieve high accuracy. There exists, however, the coupling problem between the internal and external parameters for most commonly used laboratory calibration methods, which affect the star tracker’s performance. We theoretically analyze the major aspects of the coupling mechanism based on the star tracker laboratory calibration model, which means the coupling between the principal point and the installation angle. The concept of equivalent principal point error, which illustrates the effectiveness of the calibration even with poor decoupling accuracy between the principal point and the installation angle, is introduced. Simulation and bench experiments are conducted to verify the laboratory calibration method and its coupling mechanism. The decoupling accuracy can be improved with more samples during calibration. In addition, the equivalent principal point error converges quickly and hardly affects the attitude of the star tracker, which is verified by both theory and experiment. The comprehensive calibration accuracy can still reach a high level even with poor decoupling accuracy.

Star tracker is the most precise attitude measuring device, and its advantages include a high resolution and high update rate. Star centroid extraction, which is a very time-consuming process, has great influence on the attitude update rate. This paper proposes a real-time star centroid extraction algorithm based on a field programmable gate array. First, a 1D top-hat filter is used for star segmentation, which is suitable for both uniform and nonuniform background conditions. Second, multichannel image data is reorganized together into a complete frame through image stitching, which prevents the star spots on the channel boundary from being divided into different parts. Finally, star coordinates are extracted by the center-of-mass algorithm. For an image sensor with a resolution of 2048 × 2048 pixels, simulation results conducted by a ModelSim simulator show that the star centroid processing time of a single frame is roughly 5.2 ms. Real night experiments demonstrate that the standard deviation of a star centroid error is within 10 − 2 pixel and the standard deviation of attitude is (2.6 2.2 12.0) arcseconds, which proves that the proposed star centroid extraction algorithm can work continuously and stably.

Star trackers measures the attitude of spacecraft by matching the centroid coordinates extracted from star image with the star database. However, dim stars, fake stars, noise and irregularly shaped star spots interfere with star extraction. In order to solve these problems, a new star centroid extraction algorithm based on adjacent branch decision marker is proposed in this paper. The first step is to use labels to encode the pixel of star points which are processed by double threshold segmentation; the second step is to judge the validity of the labels by using the adjacent branch decision marker and output them. Compared with the traditional connected area segmentation method, the algorithm can solve the influence of irregular shape star points on Star Information segmentation, and two kinds of threshold segmentation method can effectively eliminate the influence of background on star point extraction. The experimental results show that the algorithm has high precision and speed of star centroid extraction, and the resource cost is low. Compared with other methods, this method has stronger anti background interference ability and better robustness.

Enhance light absorption in two-dimensional (2D) materials are of great importance for the development of many optoelectronic devices such as photodetectors, modulators and thermal emitters. In this paper, a resonant nanostructure based on subwavelength gratings of monolayer molybdenum disulphide (MoS

The stacking order plays a critical role in the electronic and optical properties of two-dimensional materials. It is however of great challenge to achieve large-size and homogeneous bilayer crystals with precisely controlled stacking orders. Here, we demonstrate an optimized chemical vapor deposition strategy to grow MoSe

The energy dissipation issue has become one of the greatest challenges of the modern electronic industry. Incorporating graphene into the electronic devices has been widely accepted as a promising approach to solve this issue, due to its superior carrier mobility and thermal conductivity. Here, using Raman spectroscopy and infrared thermal microscopy, we identify the energy dissipation behavior of graphene device with different thicknesses. Surprisingly, the monolayer graphene device is demonstrated to have a comparable energy dissipation efficiency per unit volume with that of a few-layer graphene device. This has overturned the traditional understanding that the energy dissipation efficiency will reduce with the decrease of functional materials dimensions. Additionally, the energy dissipation speed of the monolayer graphene device is very fast, promising for devices with high operating frequency. Our finding provides a new insight into the energy dissipation issue of two-dimensional materials devices, which will have a global effect on the development of the electronic industry.

The fused silica cylindrical resonator is a type of axisymmetric resonator that can be used for Coriolis vibratory gyroscopes. Although the resonant frequency, frequency mismatch, and Q factor are natural properties of the resonator, they can change with temperature. Therefore, the temperature drift severely limits the detection accuracy and bias stability of the gyroscope. In this paper, the influence of temperature variation on the vibrational characteristics of fused silica cylindrical resonators was investigated. Experiments were performed on a fused silica cylindrical resonator coated with Cr/Au films. It was shown that at the temperature range from 253.15 K to 353.15 K, the resonant frequency linearly increased with temperature, the frequency mismatch remained unchanged, and the Q factor gradually increased till about 333.15 K, when it began to decrease. Meanwhile, the change of thermoelastic damping with temperature may dominate the variation of Q factor at the temperature range from 253.15 K to 353.15 K. This phenomenon was theoretically analyzed and the variation trends of results were consistent with the theoretical analysis. This study indicates that, for the fused silica cylindrical resonator, to discover the influence of temperature variation on the resonant frequency, frequency mismatch, and Q factor, there are certain rules to follow and repeat. The relationship between temperature and frequency can be established, which provides the feasibility of using self-calibration based on temperature characteristics of the resonator for temperature drift compensations. Additionally, there is an optimum temperature that may improve the performance of the Coriolis vibratory gyroscope with the fused silica cylindrical resonator.

The Coriolis Vibratory Gyroscopes are a type of sensors that measure angular velocities through the Coriolis effect. The resonator is the critical component of the CVGs, the vibrational characteristics of which, including the resonant frequency, frequency mismatch, Q factor, and Q factor asymmetry, have a great influence on the performance of CVG. The frequency mismatch and Q factor of the resonator, in particular, directly determine the precision and drift characteristics of the gyroscope. Although the frequency mismatch and Q factor are natural properties of the resonator, they can change with external conditions, such as temperature, pressure, and external forces. In this paper, the influence of electrostatic forces on the vibrational characteristics of the fused silica cylindrical resonator is investigated. Experiments were performed on a fused silica cylindrical resonator coated with Cr/Au films. It was shown that the resonant frequency, frequency mismatch, and the decay time slightly decreased with electrostatic forces, while the decay time split increased. Lower capacitive gaps and larger applied voltages resulted in lower frequency mismatch and lower decay time. This phenomenon was theoretically analyzed, and the variation trends of results were consistent with the theoretical analysis. This study indicates that, for fused silica cylindrical resonator with electrostatic transduction, the electrostatic influence on the Q factor and frequency, although small, should be considered when designing the capacitive gap and choosing bias voltages.

We show that the performance of single-walled carbon nanotubes (SWCNTs) based infrared photodetector can be greatly enhanced through the combination with colloidal PbS quantum dots (QDs). To improve the photo-induced charge transport efficiency and the carrier mobility, the colloidal PbS QDs are modified by short-chain inorganic. Under illumination, the light-induced electron-hole pairs can be effectively separated by the internal electric field formed at the interfaces between SWCNTS and PbS QDs, which will lead to the increase of both conductivities in them. Photocurrent is formed under the driving of source-drain voltage ( V ds) applied by the interdigital finger electrodes. Our hybrid phototransistor achieves a responsivity of 7.2 A/W, a specific detectivity (defined below) of 7.1×1010 Jones, and a response time of 1.58 ms at the same time under 1550-nm illumination with low intensity. Through gate voltage tuning, the responsivity can be increased to 353.4 A/W. In addition, our hybrid phototransistor is stable, low-cost, and compatible with complementary metal oxide semiconductor, which benefits a lot in real applications.

This paper proposes a hybrid metal-graphene plasmonic sensor which can simultaneously perform multi-spectral sensing in near- and mid-IR ranges. The proposed sensor consists of an array of asymmetric gold nano-antennas integrated with an unpatterned graphene sheet. The gold antennas support sharp Fano-resonances for near-IR sensing while the excitation of graphene plasmonic resonances extend the sensing spectra to the mid-IR range. Such a broadband spectral range goes far beyond previously demonstrated multi-spectral plasmonic sensors. The sensitivity and figure of merit (FOM) as well as their dependence on the thickness of the sensing layer and Fermi energy of graphene are studied systematically. This new type of sensor combines the advantages of conventional metallic plasmonic sensors and graphene plasmonic sensors and may open a new door for high-performance, multi-functional plasmonic sensing.

The near-infrared (NIR) photoelectric properties of multilayer Bi2O2Se nanofilms were systematically studied in this paper. Multilayer Bi2O2Se nanofilms demonstrate a sensitive photo response to NIR, including a high photoresponsivity (~ 101 A/W), a quick response time (~ 30 ms), a high external quantum efficiency (~ 20,300%), and a high detection rate (1.9 × 1010 Jones). These results show that the device based on multilayer Bi2O2Se nanofilms might have great potentials for future applications in ultrafast, highly sensitive NIR optoelectronic devices.

We propose a broadband terahertz absorber consisting of nonstructured graphene loaded with arrays of elliptic dielectric cylinders. The relative bandwidth for the absorption above 90% reaches about 65%. The working mechanism of broad bandwidth mainly comes from two aspects. One is that the nonstructured graphene loaded with elliptic dielectric cylinders provides multiple discrete graphene plasmon resonances with large relative frequency interval. The other is that, for each discrete resonance, there exists a set of continuous plasmon resonances because the width of the dielectric structure varies continuously and gradiently. The broadband terahertz absorber we demonstrate here, based on geometrically gradient dielectric structures and nonstructured graphene, avoids the graphene processing, which shows great potential applications in related devices.

Most two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit more than one structural phase, leading to a number of remarkable physics and potential device applications beyond graphene. Here, we demonstrated a feasible route to trigger 2H-to-1T′ phase transition in few-layer molybdenum ditelluride (MoTe2) by laser irradiation. The effects of laser power and irradiation duration were systematically studied in this study, revealing the accumulated heating effect as the main driving force for such a phase transition. By carefully adjusting laser power and irradiation time, we could control the structural phases of MoTe2 as 2H, 2H + 1T′, and 1T′. After thermal annealing at a rather low temperature, the laser-irradiated MoTe2 showed a completely suppressed 2H component and a more stabilized 1T′ phase, demonstrating that the microscopic origin of the irreversible 2H-to-1T′ phase transition is the formation of Te vacancies in MoTe2 due to laser local instantaneous heating. Our findings together with the unique properties of MoTe2 pave the way for high-performance nanoelectronics and optoelectronics based on 2D TMDs and their heterostructures.

Controllable synthesizing of one-dimensional–two-dimensional (1D–2D) heterostructures and tuning their atomic and electronic structures is nowadays of particular interest due to the extraordinary properties and potential applications. Here, we demonstrate the temperature-induced phase-controlled growth of 1D Mo6Te6–2D MoTe2 heterostructures via molecular beam epitaxy. In situ scanning tunneling microscopy study shows 2D ultrathin films are synthesized at low temperature range, while 1D nanowires gradually arise and dominate as temperature increasing. X-ray photoelectron spectroscopy confirms the good stoichiometry and scanning tunneling spectroscopy reveals the semimetallic property of grown Mo6Te6 nanowires. Through in situ annealing, a phase transition from 2D MoTe2 to 1D Mo6Te6 is induced, thus forming a semimetal–semiconductor junction in atomic level. An upward band bending of 2H-MoTe2 is caused by lateral hole injection from Mo6Te6. The work suggests a new route to synthesize 1D semimetallic transit...

The coupling strength between two-dimensional (2D) materials and substrate plays a vital role on thermal transport properties of 2D materials. Here we systematically investigate the influence of vacuum thermal annealing on the temperature-dependence of in-plane Raman phonon modes in monolayer graphene supported on silicon dioxide substrate via Raman spectroscopy. Intriguingly, raising the thermal annealing temperature can significantly enlarge the temperature coefficient of supported monolayer graphene. The derived temperature coefficient of G band remains mostly unchanged with thermal annealing temperature below 473 K, while it increases from −0.030 cm−1/K to −0.0602 cm−1/K with thermal annealing temperature ranging from 473 K to 773 K, suggesting the great impact of thermal annealing on thermal transport in supported monolayer graphene. Such an impact might reveal the vital role of coupling strength on phonon scattering and on the thermal transport property of supported monolayer graphene. To further interpret the thermal annealing mechanism, the compressive stress in supported monolayer graphene, which is closely related to coupling strength and is studied through the temperature-dependent Raman spectra. It is found that the variation tendency for compressive stress induced by thermal annealing is the same as that for temperature coefficient, implying the intense connection between compressive stress and thermal transport. Actually, 773 K thermal annealing can result in 2.02 GPa compressive stress on supported monolayer graphene due to the lattice mismatch of graphene and substrate. This study proposes thermal annealing as a feasible path to modulate the thermal transport in supported graphene and to design future graphene-based devices.

Perfect absorbers are of great importance in various applications such as photodetectors, optical sensors and optical modulators. Recently, perfect absorption metasurface based on monolayer graphene has attracted lots of research interest. In this paper, a graphene-lithium niobate (LN) perfect absorption metasurface is constructed, where graphene works as a thin absorptive layer as well as a conductive electrode. The proposed device achieves 99.99% absorption at 798.42 nm and 1.14 nm redshift of the absorption peak is realized at 300 V(from -150 V to 150 V) external bias voltage through the electro-optical effect of LN, which enables the proposed device work as a electrically tunable absorber in the visible and near infrared range. The switching ratio of reflected light R/R0 could reach -44.08 dB with an applied voltage tuning from -150 V to 0 V at 798.42 nm. Our work demonstrates the potential of LN integrated high-Q resonant metasurface in realizing electro-optic tunable nanophotonic devices in the visible and near infrared band. It will promote the research of graphene integrated optoelectronic devices as well as LN based tunable nanophotonic devices which have widespread applications such as modulators and optical phase arrays.

Van der Waals epitaxy growth of two-dimensional materials promise controllable fabrication of novel artificial heterostructures. Here, we report molecular beam epitaxy growth of continuous molybdenum ditelluride (MoTe2) films on graphene substrates with good stoichiometry in both 2H and 1T′ phases. Post-growth annealing reveal phase transition suppressed in Te-rich atmosphere, through in-situ scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy. Our results suggest a new route to fabricate atomically ultrathin MoTe2 lateral heterophase homojunctions, showing potential applications in future lateral thin-film transistors.

Hull structure monitoring is needed to provide healthy suggestions for a ship. Inertial Measurement Units (IMUs) are available for this application. By installing IMUs on different points of the ship hull, the angular velocity and acceleration of each point can be measured. Once the hull flexure changes, the movement parameters of those points will be different, and the hull flexure can be estimated through matching these parameters by a Kalman filter. We deduced proper measurement equations of the Kalman filter, which is essential for the flexure estimation, and designed real data and simulation data experiments to verify the equation. Results showed that the hull structure can be effectively monitored by the proposed method.

Coulomb blockade mediated field-emission current was observed in single-electron tunneling devices based on self-assembled gold nanoparticles at 300 K. According to Raichev's theoretical model, by fixing a proper geometric distribution of source, island and drain, the transfer characteristics can be well explained through a combination of Coulomb blockade and field emission. Coulomb blockade and field emission alternately happen in our self-assembled devices. The Coulomb island size derived from the experimental data is in good agreement with the average size of the gold nanoparticles used in the device. The integrated tunneling can be adjusted via a gate electrode.

We report an electron-beam lithography process to directly fabricate graphene@copper composite patterns without involving metal deposition, lift-off and etching processes using copper naphthenate as a high-resolution negative-tone resist. As a commonly used industrial painting product, copper naphthenate is extremely cheap with a long shelf time but demonstrates an unexpected patterning resolution better than 10 nm. With appropriate annealing under a hydrogen atmosphere, the produced graphene@copper composite patterns show high conductivity of ∼400 S cm−1. X-ray diffraction, conformal Raman spectroscopy and X-ray photoelectron spectroscopy were used to analyze the chemical composition of the final patterns. With the properties of high resolution and high conductivity, the patterned graphene@copper composites could be used as conductive pads and interconnects for graphene electronic devices with ohmic contacts. Compared to common fabrication processes involving metal evaporation and lift-off steps, this pattern-transfer-free fabrication process using copper naphthenate resist is direct and simple but allows comparable device performance in practical device applications.

Removal of expression of concern for 'Controllable 2H-to-1T' phase transition in few-layer MoTe

Planar optical resonant structures with high quality (Q) factors play a crucial role in modern photonic technologies. In this paper, a type of remarkably high-Q resonant nanostructure based on atomically thin two-dimensional (2D) materials is proposed. It is shown theoretically and numerically that with the excitation of leaky modes in the proposed structures, guided mode resonant (GMR) gratings, can achieve resonances with extremely narrow linewidths down to 0.0005 nm and high Q-factors up to millions in the telecom range. The thickness of 2D materials and thus the high-Q resonances can be precisely controlled by changing the layer number of 2D materials, providing a versatile platform for strong light–matter interactions. As an example, dramatic nonlinear reflectance can be realized around the resonance at a power level of a few kW cm−2 with the Kerr effect. This new type of 2D material resonant nanostructure can be employed for a variety of applications ranging from lasers, filters and polarizers to nonlinear optical devices.

Bi

Monolayer graphene has high symmetrical crystal structure and exhibits in-plane isotropic physical properties. However, twisted bilayer graphene (tBLG) is expected to differ physically, due to the broken symmetry introduced by the interlayer coupling between adjacent graphene layers. This symmetry breaking is usually accompanied by in-plane anisotropy in their electrical, optical and thermal properties. However, the existence of in-plane anisotropy in tBLG has remained evasive until now. Here, an unambiguous identification of the in-plane anisotropy in tBLG is established by angle-resolved polarized Raman spectroscopy. It was found that the double-resonant two-dimensional band is anisotropic. The degree of in-plane anisotropy is found to be dependent on the misorientation angles, which is two- and four-fold for tBLG with misorientation angles of 15° and 20°, respectively. This finding adds a new dimension to the properties of graphene, which opens a possibility to the development of graphene-based angle-resolved photonics and electronics.

This work reports the interlayer difference of exciton and phonon performance between the top and bottom layer of a bilayer-stacked two-dimensional materials structure (BSS). Through photoluminescence (PL) and Raman spectroscopy, we find that, compared to that of the bottom layer, the top layer of BSS demonstrates PL redshift, Raman E 2 g 1 mode redshift, and lower PL intensity. Spatial inhomogeneity of PL and Raman are also observed in the BSS. Based on theoretical analysis, these exotic effects can be attributed to substrate-coupling-induced strain and doping. Our findings provide pertinent insight into film&ndash, substrate interaction, and are of great significance to researches on bilayer-stacked structures including twisted bilayer structure, Van der Waals hetero- and homo-structure.

The phenomenon of optical activity has fundamental importance and widespread applications in polarization optics, analytical chemistry, and molecular biology. In the past two decades, there has been much research on designing metamaterials with strong optical activity, which generally employs chiral plasmonic or dielectric nanostructures with resonant responses. In this Letter, we show theoretically and numerically that strong optical activity can be obtained in unpatterned monolayer black phosphorus (BP) without using resonant structures. The optical activity can be attributed to the extrinsic chirality from the mutual orientation of the BP film with in-plane anisotropy and the incident light. The obtained circular dichroism in this atomically thick material is comparable to that in previously reported chiral metamaterials, and the optical activity is inherently tunable by controlling the Fermi level of monolayer BP.

Due to the lack of true ship angular flexure data, it is difficult to evaluate its measurement error of the angular velocity matching method in practice. In this paper, the cause of the measurement error of the ship flexure angle is analyzed in theory, and an evaluation method for the ship angular flexure measurement error based on the principle of relevance is proposed. The proposed method provides a prediction formula to describe the estimation error of the static flexure angle based on the off-diagonal elements of the error covariance matrix P in Kalman filtering. In addition, the optimized coefficient F is introduced to make the prediction error range better describe the real error variation. The optimized coefficient F ensures that the proposed formula has good prediction effects in all three directions. Simulations based on the actual measured ship flexure data are carried out, and the simulation results verify the capability of the prediction formula. The proposed method can be used in the evaluation of the ship flexure measurement error.

High quality p-n junctions based on 2D layered materials (2DLMs) are urgent to exploit, because of their unique properties such as flexibility, high absorption, and high tunability which may be utilized in next-generation photovoltaic devices. Based on transfer technology, large amounts of vertical heterojunctions based on 2DLMs are investigated. However, the complicated fabrication process and the inevitable defects at the interfaces greatly limit their application prospects. Here, an in-plane intramolecular WSe

The stellar/inertial integrated navigation system, which combines the inertial navigation system (INS) and the star tracker, can restrain the accumulated INS errors. In the traditional loosely coupled stellar/inertial integration method, the star tracker needs to observe more than two navigation stars on an image for attitude determination and to use the attitude information as the observation to estimate the systematic errors of the INS. However, under strong background radiation conditions, the star number in the field of view (FOV) usually drops below 3; thus, the loosely coupled method fails to work. To overcome this difficulty, an improved tightly coupled stellar/inertial integration method based on the observation of the star centroid prediction error (SCPE) is proposed in this paper. It calculates the difference between the extracted star centroid and the predicted star centroid, namely, the SCPE, as the observation and then estimates the INS errors with a Kalman filter. Numerical simulations and ground experiments are conducted to validate the feasibility of the tightly coupled method. It is proved that the proposed method, which makes full use of all star observation information, can improve the navigation accuracy compared with the loosely coupled method and is more robust when there are not enough stars in the FOV.

When a graphene sheet is placed near a metal surface, it supports a special type of highly confined and low‐loss electromagnetic mode called acoustic graphene plasmons (AGPs). AGPs squeeze infrared photons into extremely confined areas down to a subnanometric scale and provides a unique platform for strong light–matter interactions. However, the efficient excitation of AGPs is a challenge due to the large momentum mismatch between free‐space light and AGPs. With theoretical analysis and numerical simulations, it is shown that the far‐field excitation of AGPs is realized by integrating graphene in a metal–insulator–metal (MIM) metamaterial with magnetic resonance (MR). More than ten graphene plasmonic modes are excited in the midinfrared range, resulting in a multiresonant spectra with Fano‐like characteristics at each resonant wavelength. The proposal opens a new door to explore the strong plasmonic coupling between graphene and metallic metamaterials down to atomic scale for extreme nanophotonics. The potential applications range from ultracompact tunable metamaterials and ultrasensitive infrared spectroscopy to single‐molecule optics, quantum plasmonics, and others.

Two-dimensional layered heterostructures show great potential to develop optoelectronic systems. Here, we have investigated the photoresponse properties of two contact interfaces in few-layer graphene–WSe2 heterostructures. The photoresponsivity of graphene–WSe2 contact interface is about 2.67 mA/W, and the photoresponsivity of WSe2–metal contact interface is about 0.2 mA/W. Photocurrent images show that the two contact interfaces behave differently under drain voltage from − 0.5 V to 0.5 V. The photoresponsivity of one contact interface increases with the drain voltage, and that of the other decreases with the drain voltage. Experimental results and band diagram studies prove that the photoresponse properties of contact interfaces are tuned by small drain voltage. This study will be beneficial for understanding the effect of drain voltage on the heterostructures.

Van der Waals junctions of two-dimensional materials with an atomically sharp interface open up unprecedented opportunities to design and study functional heterostructures. Semiconducting transition metal dichalcogenides have shown tremendous potential for future applications due to their unique electronic properties and strong light-matter interaction. However, many important optoelectronic applications, such as broadband photodetection, are severely hindered by their limited spectral range and reduced light absorption. Here, we present a p-g-n heterostructure formed by sandwiching graphene with a gapless bandstructure and wide absorption spectrum in an atomically thin p-n junction to overcome these major limitations. We have successfully demonstrated a MoS2-graphene-WSe2 heterostructure for broadband photodetection in the visible to short-wavelength infrared range at room temperature that exhibits competitive device performance, including a specific detectivity of up to 1011 Jones in the near-infrared region. Our results pave the way toward the implementation of atomically thin heterostructures for broadband and sensitive optoelectronic applications., Submitted to Nano Letters; 25 pages, 4 figures, 7 supplementary figures

Due to the lack of surface dangling bonds in graphene, the direct growth of high-κ films via atomic layer deposition (ALD) technique often produces the dielectrics with a poor quality, which hinders its integration in modern semiconductor industry. Previous pretreatment approaches, such as chemical functionalization with ozone and plasma treatments, would inevitably degrade the quality of the underlying graphene. Here, we tackled this problem by utilizing an effective and convenient physical method. In detail, the graphene surface was pretreated with the deposition of thermally evaporated ultrathin Al metal layer prior to the Al2O3 growth by ALD. Then the device was placed in a drying oven for 30 min to be naturally oxidized as a seed layer. With the assistance of an Al oxide seed layer, pinhole-free Al2O3 dielectrics growth on graphene was achieved. No detective defects or disorders were introduced into graphene by Raman characterization. Moreover, our fabricated graphene top-gated field effect transistor exhibited high mobility (∼6200 cm2V−1s−1) and high transconductance (∼117 μS). Thin dielectrics demonstrated a relative permittivity of 6.5 over a large area and a leakage current less than 1.6 pA/μm2. These results indicate that Al oxide functionalization is a promising pathway to achieve scaled gate dielectrics on graphene with high performance.

Semiconducting molybdenum disulfide (MoS2) has drawn a lot of attention for its exceptional electronic and optoelectronic properties. Despite the potential advantages, the large contact resistance at the metal–MoS2 interfaces has been one of the biggest obstacles for the realization of ideal MoS2 transistors. One solution to improve the metal–MoS2 interfaces is to use the graphene electrodes. Here, we provide a selective etching method for fabricating graphene-contacted MoS2 transistors. It has been proved that the graphene could be totally etched with Ar+ plasma treatment, and the multilayer MoS2 flake can also be reduced layer by layer with Ar+ plasma treatment. By etching graphene selectively in graphene–MoS2 heterostructures, one can obtain graphene-contacted MoS2 transistors successfully. The transistor reported in this paper shows an on–off ratio about 106 and a carrier mobility about 42 cm2 V−1 s−1. This selective etching method would be beneficial for some other graphene-contacted electronic devices.

Carried on the deck of the satellite maritime tracking and control ship, Yuan Wang 6, we have conducted a long-term on-ship dynamic experiment for a star sensor in the South Pacific. Motion-blurred star images of the star sensor obtained under different dynamic conditions are processed by our previously proposed region confined restoration method method, after which the SNR of the motion-blurred star images and the identification rate of the star sensor have been improved remarkably. With the attitude-correlated frames approach, the random noise aroused by the motion of the ship is reduced further. As a result, considering the accuracy and star observation length of the ship-borne star sensor, we believe reported for the first time, a three-axis attitude accuracy of better than 5 arcseconds is obtained in our on-ship experiment.

With the development of military industry and intelligence, accelerometer with high-performance will be demanded imminently. The resonant graphene accelerometer combines excellent mechanics and mechanism properties of graphene with the technique of MEMS accelerometer, with the advantages of high-performance, low-energy consumption, lowcost and mass production. An optically driven resonant graphene accelerometer is resonated by a laser beam with periodically varying intensity. A single-layer graphene fixed on its substrate is heated by the laser beam to make the graphene film resonate. When there is external acceleration, a proof mass fixed on the single-layer graphene film can change the resonant frequency by adding a force on the film. The acceleration can be calculated through the variation of the resonant frequency. However, the deadly drawback of the optically driven resonant graphene accelerometer is its low quality factor, which is large dissipation. In this paper, the mechanism of the squeeze-film air damping of a resonant graphene accelerometer is theoretically modeled. The influential parameters are optimized to decrease the damping. The results show that the effect of squeezefilm damping on quality factor can be significant, while that on resonant frequency can be negligible. Meanwhile, the squeeze-film damping will increase as the pressure, free and fixed edges of the single-layer graphene grow. The influence on the quality factor by changing the size of the free edges is more remarkable, compared to that of fixed edges. Therefore, decreasing the pressure and geometrical size of the single-layer graphene, especially the free edges, is an effectively method to reduce the damping of the resonant graphene accelerometer.

Broadband optical absorption structures in the near infrared by coupling monolayer-graphene with periodical metal structures are proposed and demonstrated numerically. Optical absorption of graphene with over-50%-absorption bandwidth up to hundreds of nanometer caused by magnetic dipole resonances and magnetic coupling effect are investigated in detail, and the demonstrated bandwidths are one order higher than those caused by dielectric guiding mode resonances. In addition, the influences of geometrical parameters of structures are fully analyzed and these demonstrated structures show angular-insensitive absorption for oblique incidence in a large angular range. The demonstrated absorption structures in this work provide new design ideas in the realization of advanced graphene-based optoelectronic devices.

Growing uniform oxides with various thickness on TMDs is one of the biggest challenges to integrate TMDs into complementary metal oxide semiconductor (CMOS) logic circuits. Here, we report a layer-by-layer oxidation of atomically thin MoTe2 flakes via ozone (O3) exposure. The thickness of MoOx oxide film could be tuning with atomic-level accuracy simply by varying O3 exposure time. Additionally, MoOx-covered MoTe2 shows a hole-dominated transport behavior. Our findings point to a simple and effective strategy for growing homogeneous surface oxide film on MoTe2, which is promising for several purposes in metal-oxide-semiconductor transistor, ranging from surface passivation to dielectric layers.

In the stellar/inertial system, the accumulated error of inertial navigation system (INS) can be restrained by the star tracker, which is capable of providing 3-axis attitude information by using at least 2 stars in the field of view (FOV). Unfortunately, there are usually not enough bright stars in the FOV for attitude determination in the daytime. To overcome this limitation, a new tightly-coupled stellar-inertial integration method based on the observation of predicted star centroid error is developed in this paper. The mathematical model of the proposed method is derived in detail, and its feasibility is investigated by numerical simulations. The simulation results show that the tightly-coupled method can get better navigation performance than the loosely-coupled method, and is particularly suitable for the stellar/inertial system with small FOV star tracker for daytime applications.

The purpose of this work was to study bias error in acceleration-based transfer alignment, which is probably caused by cross-correlation between the dynamic lever-arm and the linear motion of a ship. A new prediction model for the cross-correlation-caused error is proposed in this paper. We adopt the Bernoulli-Euler Beam as a simplified ship hull-girder model to verify the existence of the cross-correlation. Then, the mathematical mechanism and the prediction model of the bias error are deduced via the ordinary least squares theory. Three factors influence the bias error in the prediction model: the amplitude of the dynamic lever arm acceleration, the amplitude of the ship motion acceleration, and the cross-correlation between them. Simulation experiments are then conducted to test the influence of the factors. The results show that the mechanism analysis is reasonable, and the bias error prediction model is in agreement with the experimental results. Thus, the proposed prediction model has the potential to deduce the bias error in high-accuracy transfer alignment.