Interlayer Charge Transfer Induced Electrical Behavior Transition in 1D AgI@sSWCNT van der Waals Heterostructures.

The emergence of one-dimensional van der Waals heterostructures (1D vdWHs) opens up potential fields with unique properties, but precise synthesis remains a challenge. The utilization of mixed conductive types of carbon nanotubes as templates has imposed restrictions on the investigation of the electrical behavior and interlayer interaction of 1D vdWHs. In this study, we efficiently encapsulated silver iodide in high-purity semiconducting single-walled carbon nanotubes (sSWCNTs), forming 1D AgI@sSWCNT vdWHs. We characterized the semiconductor-metal transition and increased the carrier concentration of individual AgI@sSWCNTs via sensitive dielectric force microscopy and confirmed the results through electrical device tests. The electrical behavior transition was attributed to an interlayer charge transfer, as demonstrated by Kelvin probe force microscopy. Furthermore, we showed that this method of synthesizing 1D heterostructures can be extended to other metal halides. This work opens the door for the further exploration of the electrical properties of 1D vdWHs.

Molecular Doping Modulation and Applications of Structure-Sorted Single-Walled Carbon Nanotubes: A Review.

Single-walled carbon nanotubes (SWCNTs) that have a reproducible distribution of chiralities or single chirality are among the most competitive materials for realizing post-silicon electronics. Molecular doping, with its non-destructive and fine-tunable characteristics, is emerging as the primary doping approach for the structure-controlled SWCNTs, enabling their eventual use in various functional devices. This review provides an overview of important advances in the area of molecular doping of structure-controlled SWCNTs and their applications. The first part introduces the underlying physical process of molecular doping, followed by a comprehensive survey of the commonly used dopants for SWCNTs to date. Then, it highlights how the convergence of molecular doping and structure-sorting strategies leads to significantly improved functionality of SWCNT-based field-effect transistor arrays, transparent electrodes in optoelectronics, thermoelectrics, and many emerging devices. At last, several challenges and opportunities in this field are discussed, with the hope of shedding light on promoting the practical application of SWCNTs in future electronics.

Detection of a spinning object using a superimposed optical vortex array.

The optical vortex (OV) carries unique orbital angular momentum (OAM) and experiences a Doppler frequency shift when backscattered from a spinning object. This rotational Doppler effect (RDE) has provided a solution for the non-contact detection of rotating motion. The reported RDE researches mainly use a single OV that generates frequency shifts proportional to its topological charge and has low robustness to light incidence. Here, we show the distinctive RDE of superimposed optical vortex array (SOVA). We analyze the holistic OAM of SOVA which is represented in terms of a superposition of azimuthal harmonics and displays a unique modal gathering effect. In the experiment of RDE, the frequency shift signals of SOVA show a precise mapping to the OAM modes and the modal gathering effect contributes to enhance the amplitude of signals, which has the potential to enhance robustness against non-coaxial incidence. This finding provides a new aspect of RDE and a pioneered example for introducing various SOVAs into rotation detection.

Analysis of rotational Doppler shift with multi-ring vortex beams.

Vortex beams (VBs) with orbital angular momentum have shown great potential in the detection of transverse rotational motion of spatial targets which is undetectable in the classical radar scheme. However, most of the reported rotational Doppler measurements based on VBs can only be realized under ideal experimental conditions. The long-range detection is still a challenge. The detection distance based on rotational Doppler effect (RDE) is mainly limited by the scattered signal's signal-to-noise ratio (SNR). In this work, we investigated the influence of multi-ring vortex beams (MVBs) on the rotational Doppler frequency spectrum of scattered light from an object based on RDE and proposed a method of SNR enhancement of RDE signal. Firstly, different types of MVBs composed of a set of single-ring VBs with the same topological charge and different radii are designed, including multi-ring Laguerre Gaussian beam (MLGB), multi-ring perfect vortex beams (MPVB), and high-order Laguerre Gaussian beam (HLGB). Then, the influence of the number of rings and radial radius interval on the intensity profiles of MVBs and rotational Doppler frequency spectra under aligned and misaligned conditions is studied in detail. And the reasons why different types of MVBs lead to different SNR enhancement effectiveness with the increase of rings are also analyzed theoretically. Finally, proof-of-concept experiments were conducted to verify the effectiveness of the SNR enhancement method for RDE signals. The results showed that the amplitudes of the Doppler spectra generated by the MLGB and MPVB are improved substantially with the increase of rings, but the enhancement effect caused by the former is superior to the latter. The gain of HLGB on the RDE signal is the lowest. This study provides a useful reference for the optimization of rotational Doppler detection systems and may be of great application value in telemetry, long-range communication and optical imaging.

Simultaneous measurement of spin and precession based on light's orbital angular momentum.

The rotational Doppler effect of the vortex beam is a recently emerged promising application of the optical vortex with orbital angular momentum. In this paper, we combine the method of the micro-Doppler effect of the traditional radar and the rotational Doppler effect of the vortex beam and propose an approach of rotational micro-Doppler effect, realizing the simultaneous measurement of spin and precession. We firstly analyze the rotational micro-Doppler characteristic introduced by precession under the illuminating of vortex beam and calculate the rotational micro-Doppler parameters related to the spin and precession. Then we conduct an experiment of using the vortex beam to detect a spinning object with precession and the rotational micro-Doppler frequency is successfully observed. By extracting the rotational micro-Doppler parameters, the simultaneous and independent measurement of spin and precession is realized. Both the theoretical analysis and experimental results indicate that the rotational micro-Doppler effect is an effective extension of the rotational Doppler effect and is also a feasible application of the vortex beam detection.

Graphene-like wrapped Ni@C catalyst with magnetic recyclability for selective hydrogenation of nitro-aromatics.

The graphene-like wrapped Ni@C catalysts were facilely synthesized by a modified sol-gel method. Nickel nitrate and citric acid (CA) were adopted as the raw materials to form sol-gel mixture. Under the circumstances, the additive CA were employed not only as a complexing agent but also as a carbon source. It is found that the calcination temperature and the mole ratios between Ni and CA are the key factors affecting the physical property and the catalytic performance of catalysts in the conversion of nitroarenes into corresponding anilines. The results show that the Ni@C-500(1:1) catalyst exhibited the best performance in the hydrogenation ofo-chloronitrobenzenes (o-CNB) too-chloroanilines (o-CAN). The yield ofo-CAN was achieved at 100% wheno-CNB was completely converted at 40.0 °C under 2.0 MPa H2for 2.0 h. Furthermore, the Ni@C-500(1:1) catalyst could be separated and recovered easily after reaction by an external magnetic field. The investigated results indicate that the Ni@C-500(1:1) catalyst remained higher activity after using twelve times. More importantly, this kind of catalyst is also active for the selective hydrogenation of other nitroarenes into the corresponding anilines. This new synthetic method may pave a way for producing low-cost Ni@C catalysts on a large scale, which is attractive for industrial anilines applications.

Rotational object detection at noncoaxial light incidence based on the rotational Doppler effect.

The rotational Doppler effect (RDE) of optical vortex which can be used to detect the rotation speed, has become a well-known phenomenon and a hot topic of research in recent years. However, because the beam axis must be coaxial with the rotational axis of the object, it can only be used to detect cooperative targets in practical application. Here, we provide a novel approach for measuring rotational speed under light non-coaxial incidence relative to the rotating axis that uses the adjacent frequency difference of rotational Doppler shift signals. Theoretically, the rotational Doppler shift is proportional to the OAM mode of the incident beam, and the nature of the OAM carried by each photon is a discrete or quantized quantity under off-axis conditions leading to the discrete distribution of the Doppler shift signals. Experimentally, by extracting the difference between two adjacent Doppler shift signals, the rotating speed of the object can be determined. Based on our method, the rotational speed of the object can be measured precisely without the pre-known information about the position of the rotating axis. Our work supplies a significant complement to the conventional RDE theory and we believe it may promote the realistic application of the optical RDE-based metrology.

Fragmental optical vortex for the detection of rotating object based on the rotational Doppler effect.

Rotational Doppler effect (RDE), as a counterpart of the conventional linear Doppler effect in the rotating frame, has attracted increasing attention in recent years on rotational object detection. Many previous works have investigated the RDE based on the whole optical vortex field. In this work, we report on the RDE of the partially obstructed optical vortex and the corresponding rotational speed extraction method. Based on the orbital angular momentum (OAM) mode analysis theory, we establish the relationship between the OAM spectrum and the RDE frequency shift of fragmental optical vortex (FOV). The mechanism of the rotational speed extraction is analysed and validated by the numerical simulation and experiments. Further, a dual Fourier transformation method is proposed to accurately obtain the rotational speed which successfully overcomes the problem of the discrete distribution of the RDE signals. Our work may be useful for practical remote sensing based on the optical RDE metrology.

Detection of a spinning object with circular procession using an optical vortex beam.

The rotational Doppler effect (RDE) provides an efficient way to measure rotational frequency using an optical vortex beam. Crucially, most research based on the RDE just involves a spinning object or a spinning object coupled with a longitudinal velocity along the beam propagation. We analyze the interaction mechanism between optical orbital angular momentum and a spinning object with circular procession and experimentally demonstrate simultaneous measurements of two rotational frequencies. This technique broadens application of the RDE in optical metrology and remote detection of targets with micro-motions.

Locating the center of rotation of a planar object using an optical vortex.

The rotational Doppler effect (RDE) of optical vortex beams provides an efficient way to measure the rotational frequency of objects based on rotational Doppler frequency shifts, while the frequency shift signals display a distinct broadening effect when the vortex beam is laterally misaligned with the center of rotation of a planar object. We use a modal decomposition method to reveal the broadening effect and obtain a linear fitting equation between the quantity of signals and lateral misalignments. In an experiment of RDE, the lateral misalignment is extracted from the quantity of signal peaks. The fitting equation is proved to be precise within the uncertainty of ±0.17mm (±2.8% of the vortex beam radius), and the center of rotation is located with an error less than 3.33% of the beam radius. Our work provides a new approach to locate the center of rotation of noncooperative objects, which may be valuable in mechanical manufacturing and optical noncontact metrology.

Direction-sensitive rotational speed measurement based on the rotational Doppler effect of cylindrical vector beams.

The Doppler effect has inspired numerous applications since its discovery, initially enabling measurement of the relative velocity between a moving object and a wave source. In recent years, it has been found that scalar vortex beams with orbital angular momenta can produce the rotational Doppler effect, which can be used to measure the rotational speeds of rotating objects. However, in practice, only the absolute value of the rotational Doppler frequency shift can be obtained, and it is difficult to distinguish the direction of the object directly by a single measurement. This difficulty can be solved by using cylindrical vector beams with spatially varying polarization states. The cylindrical vector beam is formed by coaxial superposition of two vortex beams with opposite orbital angular momenta and orthogonal polarization states. By using two different polarization channels, the rotation direction can be directly recognized according to the relative phase difference between the two channels. In this paper, the scattering point model is employed to analyze the rotational Doppler effect of cylindrical vector beams, and a variety of cylindrical vector beams are generated by using vortex half-wave plates. The scheme can realize measurement of the rotational speed and direction simultaneously, and the system has simple construction, high accuracy of angular velocity measurement, and accurate direction identification.

A Learning-Based Vehicle-Cloud Collaboration Approach for Joint Estimation of State-of-Energy and State-of-Health.

The state-of-energy (SOE) and state-of-health (SOH) are two crucial quotas in the battery management systems, whose accurate estimation is facing challenges by electric vehicles' (EVs) complexity and changeable external environment. Although the machine learning algorithm can significantly improve the accuracy of battery estimation, it cannot be performed on the vehicle control unit as it requires a large amount of data and computing power. This paper proposes a joint SOE and SOH prediction algorithm, which combines long short-term memory (LSTM), Bi-directional LSTM (Bi-LSTM), and convolutional neural networks (CNNs) for EVs based on vehicle-cloud collaboration. Firstly, the indicator of battery performance degradation is extracted for SOH prediction according to the historical data; the Bayesian optimization approach is applied to the SOH prediction combined with Bi-LSTM. Then, the CNN-LSTM is implemented to provide direct and nonlinear mapping models for SOE. These direct mapping models avoid parameter identification and updating, which are applicable in cases with complex operating conditions. Finally, the SOH correction in SOE estimation achieves the joint estimation with different time scales. With the validation of the National Aeronautics and Space Administration battery data set, as well as the established battery platform, the error of the proposed method is kept within 3%. The proposed vehicle-cloud approach performs high-precision joint estimation of battery SOE and SOH. It can not only use the battery historical data of the cloud platform to predict the SOH but also correct the SOE according to the predicted value of the SOH. The feasibility of vehicle-cloud collaboration is promising in future battery management systems.

Direction-sensitive detection of a spinning object using dual-frequency vortex light.

Rotational Doppler effect (RDE) has attracted much attention in recent years which opens new avenues to angular velocity measurement. However, most previous studies used single-frequency vortex light as the detection beam so that the rotational Doppler signal is in the low frequency domain where most of noise signals exist. In this article, we use the dual-frequency 2-fold multiplexed vortex light as the probe beam and transform the Doppler signals from the low frequency domain to the high frequency domain successfully. The results show hardly any noise compared with the measurement in the low frequency domain. More importantly, the direction of rotation can be obtained directly by comparing the modulated signal and the reference signal. Our work demonstrates a new detection method for the RDE and provides a reference for its practical application.

Rotational Doppler effect detection by LG beams with a nonzero radial index.

The capability to detect the rotational speed of non-cooperative targets in a long distance is a difficult problem to be solved. In recent years, vortex light provides a feasible solution for the measurement of rotational speed for its spiral phase and the orbital angular momentum. Laguerre-Gaussian (LG) mode, as the typical vortex beam, has been widely employed in rotational Doppler effect (RDE) experiments. Here, we show that the nonzero radial index LG beam not only has a specific physical meaning but also can enhance the light intensity and the amplitude of RDE frequency signal relative to a zero radial index LG beam. To this end, we theoretically analyze the reason of intensity enhancement of a nonzero radial index beam and verify the conclusion in a variable control experiment. Our study provides a new aspect of LG beams that can be considered in rotational speed detection based on RDE. It may produce an improvement of the detection range of rotating targets in practical applications.

Generating a new type of polygonal perfect optical vortex.

We generate a new type of perfect optical vortex called the polygonal perfect optical vortex (PPOV) by combining the Bessel-Gauss beam with the high-order cross-phase (HOCP) at the plane of a spatial light modulator (SLM). This is the first time that the HOCP is applied to the Fourier plane of an optical field (POV) instead of directly acting on an optical field itself. Experimentally, the symmetrical PPOV is generated, and the capability of asymmetric distribution is demonstrated. Furthermore, we discuss the influence of parameters on a PPOV. On this basis, we show a novel function of the PPOV that can adjust the energy distribution at the vertices while maintaining the orbital angular momentum as much as possible, which facilitates applications in optical micro-manipulation.

Analysis of misaligned optical rotational Doppler effect by modal decomposition.

The optical rotational Doppler effect (RDE) is closely related to the unique orbital angular momentum (OAM) carried by optical vortex, whose topological charge means the mode of OAM. Compared with the coaxial incidence, the rotational Doppler frequency shift spectrum of a misaligned optical vortex (misaligned RDE) widens according to a certain law. In this paper, an OAM modal decomposition method of the misaligned optical RDE is proposed and the relative intensity of different OAM modes, namely the OAM spectrum, is derived based on an inner product computation. Analyses show that lateral displacements and angular deflections change the distribution of OAM modes relative to the rotation axis of the object. A misaligned Laguerre-Gaussian (LG) vortex can be represented as a specific combination of coaxial LG modes, and the difference between the topological charge of two adjacent modes is 1 or 2 with lateral displacements or angular deflections respectively. An experiment of misaligned optical RDE using a superimposed LG vortex is executed, and the obtained frequency shift spectrum with misaligned incidence expands into a set of discrete signals, which agrees well with the theoretical results. Moreover, we can get the rotation frequency of the object from an expanded frequency spectrum more quickly and accurately based on the difference between two adjacent signal peaks. The proposed method contributes to analyze the misaligned optical RDE comprehensively, which is significant in remote sensing and optical metrology.

Directly observing the skew angle of a Poynting vector in an OAM carrying beam via angular diffraction.

A new, to the best of our knowledge, method for directly measuring the skew angle of a Poynting vector of optical vortices is reported in this Letter. We design an incomplete optical vortex phase to mimic the occlusion of actual objects on the light path. By capturing the intensity cross section of the incomplete vortex field, the energy flow can be observed directly; thus, the skew angle of the Poynting vector can be directly measured. In this Letter, we measure the skew angle of the Poynting vector with an error less than 3%. Further, the work in this Letter may provide a new way to sense the translational distance and measure the topological charge of the optical vortex.

Doppler effect of polarization grating.

The Doppler effect of motional polarization grating is studied for the first time to the best of our knowledge. Based on the optical properties of polarization grating, the Doppler effect principle of polarization grating is elucidated theoretically. A method to obtain the Doppler frequency shift based on beat frequency signal that is produced by superposition of order ±1 diffraction beams of polarization grating is proposed, and a proof-of-concept experiment is conducted to measure the frequency signal of the motional polarization grating. The movement characteristics of polarization grating varying with time can be obtained after a short-time Fourier transformation of the light signal. The experimental results are in good agreement with the theoretical predication, which verifies the correctness of the theoretical analysis and achieves the measurement of linear motion velocity and acceleration of motional polarization grating with high accuracy. This study proposes a new idea for laser frequency shift and has potential significance for further development of optical heterodyne detection.

Mode analyzer for known optical vortices from a spatial light modulator with collinear holography.

The optical vortex has already found lots of applications in various domains. Among such applications, the precise and quantitative mode analysis of optical vortices is of great significance. In this work, we experimentally validate a simple method to analyze the mode of an already known optical field with collinear holography based on the phase-shifting technology. Further, we propose a ring interference strategy to improve the accuracy of mode analysis. In the proof-of-concept experiment, the complex amplitude is characterized, and the mode purity is well analyzed. This method has excellent accuracy and rapidity, which can be implemented in micro-manipulation, optical communication, and rotation speed measurement based on the rotating Doppler effect.

Detection of spinning objects at oblique light incidence using the optical rotational Doppler effect: erratum.

An erratum is presented to correct funding section of [Opt. Express 27(17), 24781-24792 (2019)].