Due to the rise of 5G, IoT, AI, and high-performance computing applications, datacenter traffic has grown at a compound annual growth rate of nearly 30%. Furthermore, nearly three-fourths of the datacenter traffic resides within datacenters. The conventional pluggable optics increases at a much slower rate than that of datacenter traffic. The gap between application requirements and the capability of conventional pluggable optics keeps increasing, a trend that is unsustainable. Copackaged optics (CPO) is a disruptive approach to increasing the interconnecting bandwidth density and energy efficiency by dramatically shortening the electrical link length through advanced packaging and co-optimization of electronics and photonics. CPO is widely regarded as a promising solution for future datacenter interconnections, and silicon platform is the most promising platform for large-scale integration. Leading international companies (e.g., Intel, Broadcom and IBM) have heavily investigated in CPO technology, an inter-disciplinary research field that involves photonic devices, integrated circuits design, packaging, photonic device modeling, electronic-photonic co-simulation, applications, and standardization. This review aims to provide the readers a comprehensive overview of the state-of-the-art progress of CPO in silicon platform, identify the key challenges, and point out the potential solutions, hoping to encourage collaboration between different research fields to accelerate the development of CPO technology.
In this work, a high-energy and high peak power chirped pulse amplification system with near diffraction-limited beam quality based on tapered confined-doped fiber (TCF) is experimentally demonstrated. The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250 μm at the thin end and 56/400 μm at the thick end. With a backward-pumping configuration, a maximum single pulse energy of 177.9 μJ at a repetition rate of 504 kHz is realized, corresponding to an average power of 89.7 W. Through partially compensating for the accumulated nonlinear phase during the amplification process via adjusting the high order dispersion of the stretching chirped fiber Bragg grating, the duration of the amplified pulse is compressed to 401 fs with a pulse energy of 126.3 μJ and a peak power of 207 MW, which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fiber laser. At the highest energy, the polarization extinction ratio and the M2 factor were respectively measured to be ∼ 19 dB and 1.20. In addition, the corresponding intensity noise properties as well as the short- and long-term stability were also examined, verifying a stable operation of the system. It is believed that the demonstrated laser source could find important applications in, for example, advanced manufacturing and photomedicine.
Thermally activated delayed fluorescence (TADF) small molecule bis-[3-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone (m-ACSO2) was used as a universal host to sensitize three conventional fluorescent polymers for maximizing the electroluminescent performance. The excitons were utilized via inter-molecular energy transfer and the non-radiative decays were successfully refrained in the condensed states. Therefore, the significant enhancement of the electroluminescent efficiencies was demonstrated. For instance, after doping poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) into m-ACSO2, the external quantum efficiency (EQE) was improved by a factor of 17.0 in the solution-processed organic light-emitting device (OLED), as compared with the device with neat F8BT. In terms of the other well-known fluorescent polymers, i.e., poly (para-phenylene vinylene) copolymer (Super Yellow, SY) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), their EQEs in the devices were respectively enhanced by 70% and 270%, compared with the reference devices based on the conventional host 1,3-di(9H-carbazol-9-yl) benzene (mCP). Besides the improved charge balance in the bipolar TADF host, these were partially ascribed to reduced fluorescence quenching in the mixed films.
Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems.
Flexible and wearable electronics represent paramount technologies offering revolutionized solutions for medical diagnosis and therapy, nerve and organ interfaces, fabric computation, robot-in-medicine and metaverse. Being ubiquitous in everyday life, piezoelectric materials and devices play a vital role in flexible and wearable electronics with their intriguing functionalities, including energy harvesting, sensing and actuation, personal health care and communications. As a new emerging flexible and wearable technology, fiber-shaped piezoelectric devices offer unique advantages over conventional thin-film counterparts. In this review, we survey the recent scientific and technological breakthroughs in thermally drawn piezoelectric fibers and fiber-enabled intelligent fabrics. We highlight the fiber materials, fiber architecture, fabrication, device integration as well as functions that deliver higher forms of unique applications across smart sensing, health care, space security, actuation and energy domains. We conclude with a critical analysis of existing challenges and opportunities that will be important for the continued progress of this field.
Single perylene diimide (PDI) used as a non-fullerene acceptor (NFA) in organic solar cells (OSCs) is enticing because of its low cost and excellent stability. To improve the photovoltaic performance, it is vital to narrow the bandgap and regulate the stacking behavior. To address this challenge, we synthesize soluble perylenetetracarboxylic bisbenzimidazole (PTCBI) molecules with a bulky side chain at the bay region, by replacing the widely used “swallow tail” type alkyl chains at the imide position of PDI molecules with a planar benzimidazole structure. Compared with PDI molecules, PTCBI molecules exhibit red-shifted UV–vis absorption spectra with larger extinction coefficient, and one magnitude higher electron mobility. Finally, OSCs based on one soluble PTCBI-type NFA, namely MAS-7, exhibit a champion power conversion efficiency (PCE) of 4.34%, which is significantly higher than that of the corresponding PDI-based OSCs and is the highest PCE of PTCBI-based OSCs reported. These results highlight the potential of soluble PTCBI derivatives as NFAs in OSCs.
This paper proposes a mode-locked fiber laser based on graphene-coated microfiber. The total length of the fiber laser resonant cavity is 31.34 m. Under the condition of stable output of bright-dark soliton pairs from the fiber laser, dual-wavelength tuning is realized by adjusting the polarization controller (PC), and the wavelength tuning range is 11 nm. Furthermore, the effects of polarization states on bright-dark solitons are studied. It is demonstrated that the mode-locking state can be switched between conventional solitons and bright-dark solitons in the graphene mode-locked fiber laser. Bright-dark soliton pairs with different shapes and nanosecond pulse width can be obtained by adjusting the PC and pump power.
Most learning-based methods previously used in image dehazing employ a supervised learning strategy, which is time-consuming and requires a large-scale dataset. However, large-scale datasets are difficult to obtain. Here, we propose a self-supervised zero-shot dehazing network (SZDNet) based on dark channel prior, which uses a hazy image generated from the output dehazed image as a pseudo-label to supervise the optimization process of the network. Additionally, we use a novel multichannel quad-tree algorithm to estimate atmospheric light values, which is more accurate than previous methods. Furthermore, the sum of the cosine distance and the mean squared error between the pseudo-label and the input image is applied as a loss function to enhance the quality of the dehazed image. The most significant advantage of the SZDNet is that it does not require a large dataset for training before performing the dehazing task. Extensive testing shows promising performances of the proposed method in both qualitative and quantitative evaluations when compared with state-of-the-art methods.
We report self-organized periodic nanostructures on amorphous silicon thin films by femtosecond laser-induced oxidation. The dependence of structural periodicity on the thickness of silicon films and the substrate materials is investigated. The results reveal that when silicon film is 200 nm, the period of self-organized nanostructures is close to the laser wavelength and is insensitive to the substrates. In contrast, when the silicon film is 50 nm, the period of nanostructures is much shorter than the laser wavelength, and is dependent on the substrates. Furthermore, we demonstrate that, for the thick silicon films, quasi-cylindrical waves dominate the formation of periodic nanostructures, while for the thin silicon films, the formation originates from slab waveguide modes. Finite-difference time-domain method-based numerical simulations support the experimental discoveries.
Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications. As a versatile approach, ultrafast laser ablation has been widely studied for surface micro/nano structuring. Increasing research efforts in this field have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures. In this paper, we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation. From an overview perspective, we firstly summarize the different roles that plasma plumes, from pulsed laser ablation of solids, play in different laser processing approaches. Then, the distinctive in-situ deposition process within surface micro/nano structuring is highlighted. Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures, through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase. The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches, adding a new dimension and more flexibility in controlling the fabrication of functional surface micro/nano structures.
The mechanisms of interaction between pulsed laser and materials are complex and indistinct, severely influencing the stability and quality of laser processing. This paper proposes an intelligent method based on the acoustic emission (AE) technique to monitor laser processing and explore the interaction mechanisms. The validation experiment is designed to perform nanosecond laser dotting on float glass. Processing parameters are set differently to generate various outcomes: ablated pits and irregular-shaped cracks. In the signal processing stage, we divide the AE signals into two bands, main and tail bands, according to the laser processing duration, to study the laser ablation and crack behavior, respectively. Characteristic parameters extracted by a method that combines framework and frame energy calculation of AE signals can effectively reveal the mechanisms of pulsed laser processing. The main band features evaluate the degree of laser ablation from the time and intensity scales, and the tail band characteristics demonstrate that the cracks occur after laser dotting. In addition, from the analysis of the parameters of the tail band very large cracks can be efficiently distinguished. The intelligent AE monitoring method was successfully applied in exploring the interaction mechanism of nanosecond laser dotting float glass and can be used in other pulsed laser processing fields.
In-fiber whispering gallery mode (WGM) microsphere resonators have received remarkable attention due to the superiorities of compact structure, high stability and self-alignment. As an in-fiber structure, WGM microsphere resonators have been demonstrated in various applications, such as sensors, filters and lasers, which have significant impacts on modern optics. Herein, we review recent progress of in-fiber WGM microsphere resonators, which involve fibers of diverse structures and microspheres of different materials. First, a brief introduction is given to in-fiber WGM microsphere resonators, from structures to applications. Then, we focus on recent progresses in this field, including in-fiber couplers based on conventional fibers, capillaries and micro-structure hollow fibers, and passive/active microspheres. Finally, future developments of the in-fiber WGM microsphere resonators are envisioned.
An integrated microwave photonic mixer based on silicon photonic platforms is proposed, which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector. The modulated optical signals from microwave photonic links can be directly demodulated and down-converted to intermediate frequency (IF) signals by the photonic mixer. The converted signal is obtained by conducting off-chip subtraction of the outputs from the balanced photodetector, and subsequent filtering of the high frequency items by an electrical low-pass filter. Benefiting from balanced detection, the conversion gain of the IF signal is improved by 6 dB, and radio frequency leakage and common-mode noise are suppressed significantly. System-level simulations show that the frequency mixing system has a spurious-free dynamic range of 89 dB·Hz2/3, even with deteriorated linearity caused by the two cascaded modulators. The spur suppression ratio of the photonic mixer remains higher than 40 dB when the IF varies from 0.5 to 4 GHz. The electrical-electrical 3 dB bandwidth of frequency conversion is 11 GHz. The integrated frequency mixing approach is quite simple, requiring no extra optical filters or electrical 90° hybrid coupler, which makes the system more stable and with broader bandwidth so that it can meet the potential demand in practical applications.
Black phosphorus quantum dots (BPQDs) are synthesized and combined with graphene sheet. The fabricated BPQDs/graphene devices are capable of detecting visible and near infrared radiation. The adsorption effect of BPQDs in graphene is clarified by the relationship of the photocurrent and the shift of the Dirac point with different substrate. The Dirac point moves toward a neutral point under illumination with both SiO2/Si and Si3N4/Si substrates, indicating an anti-doped feature of photo-excitation. To our knowledge, this provides the first observation of photoresist induced photocurrent in such systems. Without the influence of the photoresist the device can respond to infrared light up to 980 nm wavelength in vacuum in a cryostat, in which the photocurrent is positive and photoconduction effect is believed to dominate the photocurrent. Finally, the adsorption effect is modeled using a first-principle method to give a picture of charge transfer and orbital contribution in the interaction of phosphorus atoms and single-layer graphene.
As a member of Xenes family, germanene has excellent nonlinear saturable absorption characteristics. In this work, we prepared germanene nanosheets by liquid phase exfoliation and measured their saturation intensity as 0.6 GW/cm2 with a modulation depth of 8%. Then, conventional solitons with a pulse width of 946 fs and high-energy noise-like pulses with a pulse width of 784 fs were obtained by using germanene nanosheet as a saturable absorber for a mode-locked Erbium-doped fiber laser. The characteristics of the two types of pulses were investigated experimentally. The results reveal that germanene has great potential for modulation devices in ultrafast lasers and can be used as a material for creation of excellent nonlinear optical devices to explore richer applications in ultrafast photonics.
Microwave photonic sensors are promising for improving sensing resolution and speed of optical sensors. In this paper, a high-sensitivity, high-resolution temperature sensor based on microwave photonic filter (MPF) is proposed and demonstrated. A micro-ring resonator (MRR) based on silicon-on-insulator is used as the sensing probe to convert the wavelength shift caused by temperature change to microwave frequency variation via the MPF system. By analyzing the frequency shift with high-speed and high-resolution monitors, the temperature change can be detected. The MRR is designed with multi-mode ridge waveguides to reduce propagation loss and achieves an ultra-high Q factor of 1.01 × 106. The proposed MPF has a single passband with a narrow bandwidth of 192 MHz. With clear peak-frequency shift, the sensitivity of the MPF-based temperature sensor is measured to be 10.22 GHz/℃. Due to higher sensitivity and ultra-narrow bandwidth of the MPF, the sensing resolution of the proposed temperature sensor is as high as 0.019 ℃.
Optical fiber communication networks play an important role in the global telecommunication network. However, nonlinear effects in the optical fiber and transceiver noise greatly limit the performance of fiber communication systems. In this paper, the product of mutual information (MI) and communication bandwidth is used as the metric of the achievable information rate (AIR). The MI loss caused by the transceiver is also considered in this work, and the bit-wise MI, generalized mutual information (GMI), is used to calculate the AIR. This loss is more significant in the use of higher-order modulation formats. The AIR analysis is carried out in the QPSK, 16QAM, 64QAM and 256QAM modulation formats for the communication systems with different communication bandwidths and transmission distances based on the enhanced Gaussian noise (EGN) model. The paper provides suggestions for the selection of the optimal modulation format in different transmission scenarios.
Due to the advantages of low propagation loss, wide operation bandwidth, continuous delay tuning, fast tuning speed, and compact footprints, chirped Bragg grating waveguide has great application potential in wideband phased array beamforming systems. However, the disadvantage of large group delay error hinders their practical applications. The nonlinear group delay spectrum is one of the main factors causing large group delay errors. To solve this problem, waveguides with nonlinear gradient widths are adopted in this study to compensate for the nonlinear effect of the grating apodization on the mode effective index. As a result, a linear group delay spectrum is obtained in the experiment, and the group delay error is halved.
Thin film p-side up vertical-cavity surface-emitting lasers (VCSELs) with 940 nm wavelength on a composite metal (Copper/Invar/Copper; CIC) substrate has been demonstrated by twice-bonding transfer and substrate removing techniques. The CIC substrate is a sandwich structure with a 10 µm thick Copper (Cu) layer/30 µm thick Invar layer/10 µm thick Cu layer. The Invar layer was composed of Iron (Fe) and Nickel (Ni) with a proportion of 70:30. The thermal expansion coefficient of the composite CIC metal can match that of the GaAs substrate. It results that the VCSEL layers can be successfully transferred to CIC metal substrate without cracking. At 1 mA current, the top-emitting VCSEL/GaAs and thin-film VCSEL/CIC had a voltage of 1.39 and 1.37 V, respectively. The optical output powers of VCSEL/GaAs and VCSEL/CIC were 21.91 and 24.40 mW, respectively. The 50 µm thick CIC substrate can play a good heat dissipation function, which results in improving the electrical and optical characteristics of thin film VCSELs/CIC. The VCSEL/CIC exhibited a superior thermal management capability as compared with VCSEL/GaAs. The obtained data suggested that VCSELs on a composite metal substrate not only affected significantly the characteristics of thin film VCSEL, but also improved considerably the device thermal performance.
Infrared photovoltaic cells (IRPCs) have attracted considerable attention for potential applications in wireless optical power transfer (WOPT) systems. As an efficient fiber-integrated WOPT system typically uses a 1550 nm laser beam, it is essential to tune the peak conversion efficiency of IRPCs to this wavelength. However, IRPCs based on lead sulfide (PbS) colloidal quantum dots (CQDs) with an excitonic peak of 1550 nm exhibit low short circuit current (Jsc) due to insufficient absorption under monochromatic light illumination. Here, we propose comprehensive optical engineering to optimize the device structure of IRPCs based on PbS CQDs, for 1550 nm WOPT systems. The absorption by the device is enhanced by improving the transmittance of tin-doped indium oxide (ITO) in the infrared region and by utilizing the optical resonance effect in the device. Therefore, the optimized device exhibited a high short circuit current density of 37.65 mA/cm2 under 1 sun (AM 1.5G) solar illumination and 11.91 mA/cm2 under 1550 nm illumination 17.3 mW/cm2. Furthermore, the champion device achieved a record high power conversion efficiency (PCE) of 7.17% under 1 sun illumination and 10.29% under 1550 nm illumination. The PbS CQDs IRPCs under 1550 nm illumination can even light up a liquid crystal display (LCD), demonstrating application prospects in the future.
We report a new nBn photodetector (nBn-PD) design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for mid-wavelength infrared (MWIR) applications. In this structure, delta-doped compositionally graded barrier (δ-DCGB) layers are suggested, the advantage of which is creation of a near zero valence band offset in nBn photodetectors. The design of the δ-DCGB nBn-PD device includes a 3 μm absorber layer (n-InAs0.81Sb0.19), a unipolar barrier layer (AlSb), and 0.2 μm contact layer (n-InAs0.81Sb0.19) as well as a 0.116 μm linear grading region (InAlSb) from the contact to the barrier layer and also from the barrier to the absorber layer. The analysis includes various dark current contributions, such as the Shockley–Read–Hall (SRH), trap-assisted tunneling (TAT), Auger, and Radiative recombination mechanisms, to acquire more precise results. Consequently, we show that the method used in the nBn device design leads to diffusion-limited dark current so that the dark current density is 2.596 × 10-8 A/cm2 at 150 K and a bias voltage of - 0.2 V. The proposed nBn detector exhibits a 50% cutoff wavelength of more than 5 μm, the peak current responsivity is 1.6 A/W at a wavelength of 4.5 μm and a - 0.2 V bias with 0.05 W/cm2 backside illumination without anti-reflective coating. The maximum quantum efficiency at 4.5 μm is about 48.6%, and peak specific detectivity (D*) is of 3.37 × 1010 cm·Hz1/2/W. Next, to solve the reflection concern in this nBn devices, we use a BaF2 anti-reflection coating layer due to its high transmittance in the MWIR window. It leads to an increase of almost 100% in the optical response metrics, such as the current responsivity, quantum efficiency, and detectivity, compared to the optical response without an anti-reflection coating layer.
Second-order (χ(2)) optical nonlinearity is one of the most common mechanisms for modulating and generating coherent light in photonic devices. Due to strong photon confinement and long photon lifetime, integrated microresonators have emerged as an ideal platform for investigation of nonlinear optical effects. However, existing silicon-based materials lack a χ(2) response due to their centrosymmetric structures. A variety of novel material platforms possessing χ(2) nonlinearity have been developed over the past two decades. This review comprehensively summarizes the progress of second-order nonlinear optical effects in integrated microresonators. First, the basic principles of χ(2) nonlinear effects are introduced. Afterward, we highlight the commonly used χ(2) nonlinear optical materials, including their material properties and respective functional devices. We also discuss the prospects and challenges of utilizing χ(2) nonlinearity in the field of integrated microcavity photonics.
Although perovskite light-emitting diodes (PeLEDs) have seen unprecedented development in device efficiency over the past decade, they suffer significantly from poor operational stability. This is especially true for blue PeLEDs, whose operational lifetime remains orders of magnitude behind their green and red counterparts. Here, we systematically investigate this efficiency-stability discrepancy in a series of green- to blue-emitting PeLEDs based on mixed Br/Cl-perovskites. We find that chloride incorporation, while having only a limited impact on efficiency, detrimentally affects device stability even in small amounts. Device lifetime drops exponentially with increasing Cl-content, accompanied by an increased rate of change in electrical properties during operation. We ascribe this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice due to an increased chemically and structurally disordered landscape with reduced migration barriers. Our results indicate that the stability enhancement for PeLEDs might require different strategies from those used for improving efficiency.
Lead selenide (PbSe) colloidal quantum dots (CQDs) are suitable for the development of the next-generation of photovoltaics (PVs) because of efficient multiple-exciton generation and strong charge coupling ability. To date, the reported high-efficient PbSe CQD PVs use spin-coated zinc oxide (ZnO) as the electron transport layer (ETL). However, it is found that the surface defects of ZnO present a difficulty in completion of passivation, and this impedes the continuous progress of devices. To address this disadvantage, fluoride (F) anions are employed for the surface passivation of ZnO through a chemical bath deposition method (CBD). The F-passivated ZnO ETL possesses decreased densities of oxygen vacancy and a favorable band alignment. Benefiting from these improvements, PbSe CQD PVs report an efficiency of 10.04%, comparatively 9.4% higher than that of devices using sol-gel (SG) ZnO as ETL. We are optimistic that this interface passivation strategy has great potential in the development of solution-processed CQD optoelectronic devices.
976 nm + 1976 nm dual-wavelength pumped Er-doped ZBLAN fiber lasers are generally accepted as the preferred solution for achieving 3.5 µm lasing. However, the 2 µm band excited state absorption from the upper lasing level (4F9/2 → 4F7/2) depletes the Er ions population inversion, reducing the pump quantum efficiency and limiting the power scaling. In this work, we demonstrate that the pump quantum efficiency can be effectively improved by using a long-wavelength pump with lower excited state absorption rate. A 3.5 µm Er-doped ZBLAN fiber laser was built and its performances at different pump wavelengths were experimentally investigated in detail. A maximum output power at 3.46 µm of ∼ 7.2 W with slope efficiency (with respect to absorbed 1990 nm pump power) of 41.2% was obtained with an optimized pump wavelength of 1990 nm, and the pump quantum efficiency was increased to 0.957 compared with the 0.819 for the conventional 1976 nm pumping scheme. Further power scaling was only limited by the available 1990 nm pump power. A numerical simulation was implemented to evaluate the cross section of excited state absorption via a theoretical fitting of experimental results. The potential of further power scaling was also discussed, based on the developed model.
Stable picosecond dissipative soliton pulses were observed in an ytterbium-doped fiber laser employing a high-quality mixture of BP/SnSe2-PVA saturable absorber (SA). The modulation depth, saturation intensity, and non-saturable loss of the mixture of BP/SnSe2-PVA SA were measured with values of 5.98%, 18.37 MW/cm2, and 33%, respectively. Within the pump power range of 150–270 mW, stable dissipative soliton pulses were obtained with an output power of 1.68–4 mW. When the minimum pulse duration is 1.28 ps, a repetition rate of 0.903 MHz, center wavelength of 1064.38 nm and 3 dB bandwidth of 2 nm were obtained. The maximum pulse energy of 4.43 nJ and the signal-to-noise ratio up to 72 dB were achieved at pump power of 270 mW. The results suggest that the BP/SnSe2-PVA mixture SA has outstanding nonlinear saturable absorption characteristics and broad ultrafast laser applications.
Multi-dimensional heterojunction materials have attracted much attention due to their intriguing properties, such as high efficiency, wide band gap regulation, low dimensional limitation, versatility and scalability. To further improve the performance of materials, researchers have combined materials with various dimensions using a wide variety of techniques. However, research on growth mechanism of such composite materials is still lacking. In this paper, the growth mechanism of multidimensional heterojunction composite material is studied using quasi-two-dimensional (quasi-2D) antimonene and quasione-dimensional (quasi-1D) antimony sulfide as examples. These are synthesized by a simple thermal injection method. It is observed that the consequent nanorods are oriented along six-fold symmetric directions on the nanoplate, forming ordered quasi-1D/quasi-2D heterostructures. Comprehensive transmission electron microscopy (TEM) characterizations confirm the chemical information and reveal orientational relationship between Sb2S3 nanorods and the Sb nanoplate as substrate. Further density functional theory calculations indicate that interfacial binding energy is the primary deciding factor for the self-assembly of ordered structures. These details may fill the gaps in the research on multi-dimensional composite materials with ordered structures, and promote their future versatile applications.
Dynamically engineering the optical and electrical properties in two-dimensional (2D) materials is of great significance for designing the related functions and applications. The introduction of foreign-atoms has previously been proven to be a feasible way to tune the band structure and related properties of 3D materials; however, this approach still remains to be explored in 2D materials. Here, we systematically demonstrate the growth of vanadium-doped molybdenum disulfide (V-doped MoS2) monolayers via an alkali metal-assisted chemical vapor deposition method. Scanning transmission electron microscopy demonstrated that V atoms substituted the Mo atoms and became uniformly distributed in the MoS2 monolayers. This was also confirmed by Raman and X-ray photoelectron spectroscopy. Power-dependent photoluminescence spectra clearly revealed the enhanced B-exciton emission characteristics in the V-doped MoS2 monolayers (with low doping concentration). Most importantly, through temperature-dependent study, we observed efficient valley scattering of the B-exciton, greatly enhancing its emission intensity. Carrier transport experiments indicated that typical p-type conduction gradually arisen and was enhanced with increasing V composition in the V-doped MoS2, where a clear n-type behavior transited first to ambipolar and then to lightly p-type charge carrier transport. In addition, visible to infrared wide-band photodetectors based on V-doped MoS2 monolayers (with low doping concentration) were demonstrated. The V-doped MoS2 monolayers with distinct B-exciton emission, enhanced p-type conduction and broad spectral response can provide new platforms for probing new physics and offer novel materials for optoelectronic applications.
Optical beating is the usual approach to generation of microwave signals. However, the highest frequency achievable for microwave signals is limited by the bandwidths of optoelectronic devices. To maximize the microwave frequency with a limited bandwidth of a photodetector (PD) and relieve the bandwidth bottleneck, we propose to generate microwave signals with the single sideband (SSB) format by beating a continuous wave (CW) light with an optical SSB signal. By simply adjusting the frequency difference between the CW light and the carrier of the optical SSB signal, the frequency of the generated microwave SSB signal is changed correspondingly. In the experiment, amplitude shift keying (ASK) microwave signals with the SSB format are successfully generated with different carrier frequencies and coding bit rates, and the recovered coding information agrees well with the original pseudo random binary sequence (PRBS) of 27–1 bits. The proposed approach can significantly relieve the bandwidth restriction set by optoelectronic devices in high-speed microwave communication systems.