Full Band Research Articles

Massively parallel FDTD-FBMC simulations of nonlinear hole dynamics in silicon at cryogenic temperatures driven by intense EM THz pulses

THz spectroscopy with intense electromagnetic (EM) pulses offers unique avenues to study the charge carrier dynamics in semiconductors. Quantitative analysis of the experiment requires a detailed microscopic model that is based on the wave propagation within the sample and on the strongly nonparabolic dispersion relation of the valence bands. With a finite difference time domain (FDTD) solver for the EM wave in conjunction with a full band Monte Carlo (FBMC) model for the holes the generation of higher harmonics by the nonlinear hole response in the p-doped silicon sample can be simulated. Due to impurity freeze-out at the cryogenic temperature the hole density is low and the FDTD solver can be decoupled from the FBMC model by a perturbation approach. This enables the independent processing of a very large number of holes on a computer cluster with nearly 100% computational efficiency resulting in a very low level of stochastic noise, which is necessary to achieve a reasonable signal to noise ratio for the faint higher harmonics. The simulations show that at THz frequencies and cryogenic temperatures strong generation of higher harmonics is only possible, if the band structure is nonparabolic.

Construction of highly ductile, UV-shielding polylactide/poly(butylene adipate-co-terephthalate) biocomposites with hyperbranched polysiloxane functionalized lignin as a biocompatibilizer

Biodegradable polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends have been widely utilized as packaging materials. However, it is urgent to develop a biocompatibilizer to improve the interfacial interaction of the biodegradable immiscible polymer blends in practice. In this paper, a novel type of hyperbranched polysiloxane (HBPSi) with terminal methoxy groups was synthesized and then utilized to functionalize lignin through a hydrosilation reaction. The HBPSi modified lignin (lignin@HBPSi) was incorporated into immiscible PLA/PBAT blends to serve as a biocompatibilizer. The lignin@HBPSi was uniformly dispersed in the PLA/PBAT matrix with improved interfacial compatibility. Dynamic rheological results revealed that the addition of lignin@HBPSi reduced the complex viscosity, improving the processing ability of the PLA/PBAT composite. The PLA/PBAT composite containing 5 wt% lignin@HBPSi had a superior toughness with an elongation at break of 300.2 % and a slight enhancement in tensile stress (34.47 MPa). In addition, the presence of lignin@HBPSi contributed to blocking ultraviolet rays in the full ultraviolet band. This work provides a feasible way to develop highly ductile PLA/PBAT/lignin composites with good UV-shielding properties for the packaging applications.

A p-Si/CoPc Hybrid Photodiode System for Looking at Frequency and Temperature Dependence on Dielectric Relaxation and AC Electrical Conductivity

In this work, a heterojunction of Al/p-Si/CoPc/Au was fabricated using the thermal evaporation technique by depositing CoPc on the p-Si. Complex impedance spectroscopy was employed to investigate the impedance characteristics and the full band profile measurements of the fabricated heterojunction. Arrhenius fitting of double relaxation operations was utilized to determine the activation energy of the tested device. The studied device gains a negative temperature resistance coefficient as interpreted from the electrical conductivity and Cole–Cole fitting. The lifetimes of the excess minority carriers, the coefficients of carrier diffusion, and the charge carrier mobilities at the interfaces were measured and estimated.

Study on excitation threshold of strong modulation response and vibration suppression performance of bistable nonlinear energy sink

The dynamics and vibration reduction performance of bistable nonlinear energy sink (BNES) are studied in this paper. First, the negative stiffness of BNES is realized by geometric nonlinearity, and the dynamics model of the system is established. The slow flow equation of the system under 1:1 main resonance is analyzed based on the complexification-averaging (CX-A) method, and the boundary conditions of saddle node bifurcation and Hopf bifurcation are analyzed. Second, the slow invariant manifold (SIM) of the BNES is studied based on multiscale analysis, and the excitation threshold of strongly modulated response (SMR) is analyzed; the analysis results are verified by the numerical method. The results show that the analytical solution is highly consistent with the numerical solution, and the error is less than 1%. Finally, the influence of structural parameters on the vibration reduction performance is analyzed and optimized. The vibration reduction performance of BNES and CNES is compared, and the results show that the BNES has better vibration reduction performance in the full frequency band.

CNT cluster arrays grown on carbon fiber for excellent green EMI shielding and microwave absorbing

Carbon fiber (CF) is a flexible shielding material with excellent electrical conductivity, thermal stability and mechanical properties, which is crucial to solve electromagnetic pollution problems. However, its application in green electromagnetic interference (EMI) shielding is hampered due to high secondary reflection. Herein, we proposed a method to selectively grow CNT cluster arrays on the CF surface for tunable green EMI shielding and microwave absorbing. The density of CNT cluster arrays can be manipulated by controlling of CF surface functional groups in the preparation route of metal-organic framework derived Co-doped CNTs. The CF/CNTs cluster array composites exhibit excellent electromagnetic wave absorbing performance, with an effective absorption bandwidth of 4.4 GHz with a matching thickness of 1.38 mm, which can be extended to full frequency band from 2 to 18 GHz through metastructure design. The green EM shielding index is greater than 12 in the whole frequency range from 2 to 18 GHz, with the maximum value up to 351. The strategy developed here provides a valuable guide for the preparation of electromagnetic functional materials with multilevel hierarchical structure.

Broad bandgap active metamaterials with optimal time-delayed control

In this paper, a metamaterial with time-delayed feedback control for broadband vibration suppression is investigated. Genetic algorithm is used to optimize the time-delayed feedback controller to achieve low broadband vibration suppression and even full frequency vibration suppression. Time-delayed feedback controller is introduced between the visible and internal masses of the metamaterial. Time-delayed control tunes the bandgap of the metamaterial and achieves broadband tunable vibration suppression. To further broaden the bandgap, a supercell model with time-delayed control is established, and the time-delayed controller is optimized using the genetic algorithm to determine the optimal control gain and time delay. Two optimization schemes with different objectives are designed. Optimization I: Achieve the widest bandgap at the target attenuation rate. Optimization II: Achieve the maximum attenuation rate in the target frequency range. The results show that multiple bandgaps can be coupled to achieve the widest bandgap at the target attenuation rate. The controller is optimized over the full frequency band to achieve the maximum attenuation rate. Numerical results verify that the metamaterial with optimal controller can achieve vibration suppression over the full frequency range.

Spatial-Temporal EEG Fusion Based on Neural Network for Major Depressive Disorder Detection.

In view of the major depressive disorder characteristics such as high mortality as well as high recurrence, it is important to explore an objective and effective detection method for major depressive disorder. Considering the advantages complementary of different machine learning algorithms in information mining process, as well as the fusion complementary of different information, in this study, the spatial-temporal electroencephalography fusion framework using neural network is proposed for major depressive disorder detection. Since electroencephalography is a typical time series signal, we introduce recurrent neural network embedded in long short-term memory unit for extract temporal domain features to solve the problem of long-distance information dependence. To reduce the volume conductor effect, the temporal electroencephalography data are mapping into a spatial brain functional network using phase lag index, then the spatial domain features were extracted from brain functional network using 2D convolutional neural networks. Considering the complementarity between different types of features, the spatial-temporal electroencephalography features are fused to achieve data diversity. The experimental results show that spatial-temporal features fusion can improve the detection accuracy of major depressive disorder with a highest of 96.33%. In addition, our research also found that theta, alpha, and full frequency band in brain regions of left frontal, left central, right temporal are closely related to MDD detection, especially theta frequency band in left frontal region. Only using single-dimension EEG data as decision basis, it is difficult to fully explore the valuable information hidden in the data, which affects the overall detection performance of MDD.Meanwhile, different algorithms have their own advantages for different application scenarios. Ideally, different algorithms should use their respective advantages to jointly address complex problems in engineering fields.To this end, we propose a computer-aided MDD detection framework based on spatial-temporal EEG fusion using neural network, as shown in Fig.1. The simplified process is as follows: (1) Raw EEG data acquisition and preprocessing. (2) The time series EEG data of each channel are input as recurrent neural network (RNN), and RNN is used to process and extract temporal domain (TD) features. (3) The BFN among different EEG channels is constructed, and CNN is used to process and extract the spatial domain (SD) features of the BFN. (4) Based on the theory of information complementarity, the spatial-temporal information is fused to realize efficient MDD detection. Fig. 1 MDD detection framework based on spatial-temporal EEG fusion.

Optimization with a Genetic Algorithm for Multilayer Electromagnetic Wave Absorption Cement Mortar Filled with Expended Perlite

Abstract: Due to the complexity of the design of multilayer electromagnetic (EM) wave absorbing materials, it is difficult to establish the relationship between material parameters (type and filling ratios) and EM properties using traditional trial and error methods. Based on the measured EM parameters within a few materials and Boltzmann mixing theory, a database of EM parameters was thereafter built up. In this study, the genetic algorithm (GA) was used to design the multilayer wave-absorbing cement mortar. In order to verify this method, a multilayer mortar was fabricated and measured. The simulated and measured results are well consistent, which convincingly verifies computer-aided design. In addition, the optimized result expresses that the first layer as a matching layer guides EM waves into the interior of the material, while the other layers as absorption layers attenuate EM waves. The multilayer material may not meet the impedance gradient principle but still exhibits better EM wave absorption performance. The reflection loss (RL) of all optimized three layer sample is below –6.89 dB in the full frequency band and the minimum RL is –26.21 dB. This composite absorbing material and the GA method provide more design ideas for the design of future cement-based wave-absorbing materials and save a lot of time and material cost.

W-Band Switch-Less Reconfigurable-Push Dual-Band VCO Using Clover-Shaped Inductor and Robust Triple Cores for 6G Communications

This study proposes a switchless reconfigurable triple-push/push–push dual-band voltage-controlled oscillator (VCO) topology to design a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band metal–oxide–semiconductor (CMOS) for 6G communications. The proposed clover-shaped inductor consists of three branch inductors, where each node had a symmetrical layout, connecting to each another and to the output pad. This topology was demonstrated in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band VCO using three cross-coupled cores with an ON/OFF-state control to achieve triple-push and push–push operations. An oscillating core based on a robust cross-coupled structure avoids the oscillation startup issue, while achieving a 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> phase offset through a vector-sum-based method. The measured center frequencies of the bands were 91.04 and 102.33 GHz, with the tuning ranges of 10.4% and 14.1%, respectively. The proposed VCO with an independent core ON/OFF-state control enables a low parasitic switchless frequency band shift, resulting in a superior tuning range compared with those of conventional dual-/single-band VCOs. The effectiveness of this approach was demonstrated through fabrication in a 28-nm CMOS process, with a best FOM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_T$</tex-math> </inline-formula> value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 178.6 dBc/Hz for the full band.

The MeerKAT Absorption Line Survey: Homogeneous continuum catalogues towards a measurement of the cosmic radio dipole

The number counts of homogeneous samples of radio sources are a tried and true method of probing the large-scale structure of the Universe, as most radio sources outside the Galactic plane are at cosmological distances. As such, they are expected to trace the cosmic radio dipole, an anisotropy analogous to the dipole seen in the cosmic microwave background (CMB). Results have shown that although the cosmic radio dipole matches the direction of the CMB dipole, it has a significantly larger amplitude. This unexplained result challenges our assumption of the Universe being isotropic, which can have large repercussions for the current cosmological paradigm. Though significant measurements have been made, sensitivity to the radio dipole is generally hampered by systematic effects that can cause large biases in the measurement. Here we assess these systematics with data from the MeerKAT Absorption Line Survey (MALS), a blind search for absorption lines with pointings centred on bright radio sources. With the sensitivity and field of view of MeerKAT, thousands of sources are observed in each pointing, allowing for the possibility of measuring the cosmic radio dipole given enough pointings. We present the analysis of ten MALS pointings, focusing on systematic effects that could lead to an inhomogeneous catalogue. We describe the calibration and creation of full band continuum images and catalogues, producing a combined catalogue containing 16 307 sources and covering 37.5 square degrees of sky down to a sensitivity of 10 μJy beam−1. We measure the completeness, purity, and flux recovery statistics for these catalogues using simulated data. We investigate different source populations in the catalogues by looking at flux densities and spectral indices and how they might influence source counts. Using the noise characteristics of the pointings, we find global measures that can be used to correct for the incompleteness of the catalogue, producing corrected number counts down to 100–200 μJy. We show that we can homogenise the catalogues and properly account for systematic effects. We determine that we can measure the dipole to 3σ significance with 100 MALS pointings.

Optimization study on the influence of rearview mirror and side window glass on interior noise

Based on the LES model, the compressible transient CFD simulation combined with the acoustic finite element method optimizes the effect of the rearview mirror and side window glass on in-vehicle noise from the perspective of sound source and transmission. The primary and secondary orders of the influence of different mirror shape and side window glass geometric parameters on the noise in the car were obtained through the design and analysis of orthogonal experiments, and the results of the flow and sound fields were compared. The following results are presented: acoustic source noise reduction from the rearview mirror is mainly affected by acoustic pressure excitation. The proportion of the mirror body of the rearview mirror, the angle of the lower edge, and the length of the mirror column affect the noise in the car in turn. The noise reduction control with PVB laminated glass as the transmission path is mainly limited by the low frequency turbulent pressure excitation. The inner and outer thicknesses of PVB laminated glass have different influences on the noise in the car under different frequency bands, and the results in the full frequency band are mainly affected by the low frequency band.

An Equal Precision Programmed Cymometer Design Using Low-Power Technique

Based on equal precision frequency measurement and pulse counting technique, a multi-period synchronous frequency measurement method is proposed in this paper. A programmed cymometer is designed with a full frequency band with equal precision measurement and improved measurement accuracy. In addition to adopting a low-power gate-control clock technique, the strong stability of our design is also carried out through the filtering of interference signals. Finally, the designed circuit is implemented with FPGA. The experimental results show that the static power consumption of the programmable frequency meter testing platform designed after continuous operation for 100 h is only 0.56 W, and the input impedance is 1 M Ω/40 pF. At the same time, the errors of frequency, cycle measurement, duty cycle measurement, and time interval are within a reasonable range. In addition, the measurement accuracy requirements for various indicators can also be met at a maximum frequency of 100 MHz. Therefore, this work can provide a feasible design method for low-power consumption electrical systems that are easy to replicate.

Pedestrians’ perceptions of automated vehicle movements and light-based eHMIs in real world conditions: A test track study

The development of increasingly automated vehicles (AVs) is likely to lead to new challenges around how they will interact with other road users. In the future, it is envisaged that AVs, manually driven vehicles, and vulnerable road users such as cyclists and pedestrians will need to share the road environment and interact with one another. This paper presents a test track study, funded by the H2020 interACT project, investigating pedestrians’ reactions towards an AV’s movement patterns and external Human Machine Interfaces (eHMIs). Twenty participants, standing on the side of a test-track road and facing an approaching AV, were asked to raise their arm to indicate: (1) when they could perceive the AV’s eHMI, which consisted of either a Full Light Band (FLB) or a Partial Light Band (PLB); (2) when they perceived the deceleration of the AV (with eHMI vs. no eHMI); and (3) when they felt safe to cross the road in front of the approaching AV (with eHMI vs. no eHMI). Statistical analyses revealed no effects of the presence of an eHMI on the pedestrians’ crossing decision or deceleration perception, but significant differences were found regarding the visibility of the FLB and PLB designs. The PLB design could be perceived at further distances than the FLB design. Both eHMI solutions were generally well-received, and participants provided high ratings of perceived safety, and confidence around the AV.

Traceable S-parameter measurements up to 90 GHz in 1.35 mm coaxial

As part of a joint program three National Measurement Institutes around Europe—the National Physical Laboratory in the UK, the Physikalisch-Technische Bundesanstalt in Germany and the Laboratoire National de métrologie et d’essais in France—have each established new capabilities for the traceable measurement of S-parameters up to 90 GHz in the new 1.35 mm (E band) coaxial connector. Each institution has established their own measurement systems to access the full frequency band for the connector, utilising a variety of commercially available equipment and measurement setups. Each have also developed their own calibration techniques and verification methods using different vector network analyser calibration routines. These include optimised multi-line Through Reflect Line, multiple Offset Shorts Through and Short Open Load Reciprocal (SOLR) schemes. Uncertainties for each of these setups and calibration schemes were determined utilising theoretical models of the systems and calibration standards, or through verification methods, with different effects being derived from the dimensional characteristics for each of the different standards or verification artifacts. The different dimensional systems used to make these measurements were also developed and established previously as part of the same program. The last part of this exercise was a three-way intercomparison between the laboratories. The comparison involved the measurement of a set of four traveling standards, including both 1-port and 2-port as well as plug (male) and jack (female) devices, each with different reflection and transmission characteristics to better test and demonstrate the equivalence of the capabilities.

Design and construct full invisible band metamaterial-based coating with layer-by-layer structure in the microwave range from 8 to 10 GHz

This paper presents the design and construction of a carpet-based anti-radar coating for frequencies from 8 to 10 GHz. The basic idea of the proposed method is to use a coating to guide microwaves around an object so that what is inside the coating becomes invisible. The proposed method uses metamaterial structures with heterogeneous properties to create coatings that provide complete bounding and prevent loss. Using the theory of light transformation and Zhukovsky mapping for the physical dimensions of the bulge to be invisible, the profile of the refractive index distribution with respect to the radiation of waves is determined. The simulation results of the refractive index profile have shown that it is possible to create an ideal invisible coating for each bulge by using the proposed unit cells and a layer-by-layer structure. Finally, after photolithography of the design on the 5880 fibers using a network analyzer and a pair of corrugated wave antennas, the accuracy of the proposed coating performance is confirmed.

Synthesis of nitrogen-doped carbon dots with 3-aminoquinoline and citric acid as an absorbent in full ultraviolet bands and application of transparent sunscreen umbrella

In recent years, as the global climate continues to deteriorate, the harm of ultraviolet(UV) radiation to the human body is increasing, but the development of commercial UV-blocking products has not followed the corresponding update. Carbon dots (CDs) are excellent candidates for UV absorbers because of their multi-functional groups, high stability, and low toxicity. In this study, full UV bond absorbing CDs (3A-CDs) were synthesized by a one-step hydrothermal method using anhydrous Citric acid(CA) and 3-aminoquinoline as raw materials. The 3A-CDs have super high UV absorption efficiency, light-aging resistance, and acid and alkaline resistance. Subsequently, different concentrations of 3A-CDs were doped into PVA to prepare 3A-CDs@PVA films with excellent full UV bond absorption and good mechanical properties. Finally, 3A-CDs@PVA films were sandwiched between two pieces of transparent umbrella cloth. The 0.3 wt% 3A-CDs@PVA film with transparent umbrella cloth can achieve a blocking efficiency of more than 97.2% in the full UV bands. Also, SPF is greater than 50, PFA is PA++++, and the visible light transmittance is as high as 93.8%. This study provides a new application and prospect for the development of CDs and their composite products into new, efficient, and durable UV-blocking products.

Exploring and machine learning structural instabilities in 2D materials

We address the problem of predicting the zero-temperature dynamical stability (DS) of a periodic crystal without computing its full phonon band structure. Here we report the evidence that DS can be inferred with good reliability from the phonon frequencies at the center and boundary of the Brillouin zone (BZ). This analysis represents a validation of the DS test employed by the Computational 2D Materials Database (C2DB). For 137 dynamically unstable 2D crystals, we displace the atoms along an unstable mode and relax the structure. This procedure yields a dynamically stable crystal in 49 cases. The elementary properties of these new structures are characterized using the C2DB workflow, and it is found that their properties can differ significantly from those of the original unstable crystals, e.g., band gaps are opened by 0.3 eV on average. All the crystal structures and properties are available in the C2DB. Finally, we train a classification model on the DS data for 3295 2D materials in the C2DB using a representation encoding the electronic structure of the crystal. We obtain an excellent receiver operating characteristic (ROC) curve with an area under the curve (AUC) of 0.90, showing that the classification model can drastically reduce computational efforts in high-throughput studies.

Biodiversity assessment using passive acoustic recordings from off-reef location—Unsupervised learning to classify fish vocalization

We present the quantitative characterization of Grande Island's off-reef acoustic environment within the Zuari estuary during the pre-monsoon period. Passive acoustic recordings reveal prominent fish choruses. Detailed characteristics of the call employing oscillograms and individual fish call parameters of the segmented data include vocal groups such as Sciaenidae, Terapon theraps, and planktivorous as well as invertebrate sounds, e.g., snapping shrimp. We calculated biodiversity parameters (i) Acoustic Evenness Index (AEI), (ii) Acoustic Complexity Index (ACI), and mean sound pressure level (SPLrms) for three frequency bands such as full band (50-22 050 Hz), the low-frequency fish band (100-2000 Hz), and the high-frequency shrimp band (2000-20 000 Hz). Here, ACI and AEI metrics characterize the location's soundscape data effectively indicating increased biodiversity of fish species for both the low-frequency and high-frequency bands. Whereas variations for SPLrms are prominent for three frequency bands. Moreover, we employ unsupervised classification through a hybrid technique comprising principal component analysis (PCA) and K-means clustering for data features of four fish sound types. Employed PCA for dimensionality reduction and related K-means clustering successfully provides 96.20%, 76.81%, 100.00%, and 86.36% classification during the dominant fish chorus. Overall, classification performance (89.84%) is helpful in the real-time monitoring of the fish stocks in the ecosystem.

Testing synchrotron models and frequency resolution in BINGO 21 cm simulated maps using GNILC

Context. The 21 cm hydrogen line is arguably one of the most powerful probes with which to explore the Universe, from recombination to the present times. To recover it, it is essential to separate the cosmological signal from the much stronger foreground contributions at radio frequencies. The Baryon Acoustic Oscillations from Integrated Neutral Gas Observations (BINGO) radio telescope is designed to measure the 21 cm line and detect baryon acoustic oscillations (BAOs) using the intensity mapping (IM) technique. Aims. This work analyses the performance of the Generalized Needlet Internal Linear Combination (GNILC) method when combined with a power spectrum debiasing procedure. This method was applied to a simulated BINGO mission, building upon previous work from the collaboration. It compares two different synchrotron emission models and different instrumental configurations and takes into account ancillary data in order to optimize both the removal of foreground emission and the recovery of the 21 cm signal across the full BINGO frequency band and to determine an optimal number of frequency (redshift) bands for the signal recovery. Methods. We produced foreground emission maps using the Planck Sky Model (PSM) and generated cosmological HI emission maps using the Full-Sky Log-normal Astro-Fields simulation Kit (FLASK) package. We also created thermal noise maps according to the instrumental setup. We apply the GNILC method to the simulated sky maps to separate the HI plus thermal noise contribution and, through a debiasing procedure, recover an estimate of the noiseless 21 cm power spectrum. Results. We find a near-optimal reconstruction of the HI signal using an 80-bin configuration, which resulted in a power-spectrum reconstruction average error over all frequencies of 3%. Furthermore, our tests show that GNILC is robust against different synchrotron emission models. Finally, adding an extra channel with C-Band All-Sky Survey (CBASS) foregrounds information, we reduced the estimation error of the 21 cm signal. Conclusions. The optimization of our previous work, producing a configuration with an optimal number of channels for binning the data, significantly impacts decisions regarding BINGO hardware configuration before commissioning. We were able to recover the HI signal with good efficiency in the harmonic space, but have yet to investigate the effect of 1/f noise in the data, which will possibly impact the recovery of the HI signal. This issue will be addressed in forthcoming work.

Pure spin current injection of single-layer monochalcogenides

We compute the spectrum of pure spin current injection in ferroelectric single-layer SnS, SnSe, GeS, and GeSe. The formalism takes into account the coherent spin dynamics of optically excited conduction states split in energy by spin–orbit coupling. The velocity of the electron’s spins is calculated as a function of incoming photon energy and angle of linearly polarized light within a full electronic band structure scheme using density functional theory. We find peak speeds of 520, 360, 270 and 370 Km s−1 for SnS, SnSe, GeS and GeSe, respectively which are an order of magnitude larger than those found in bulk semiconductors, e.g., GaAs and CdSe. Interestingly, the spin velocity is almost independent of the direction of polarization of light in a range of photon energies. Our results demonstrate that single-layer SnS, SnSe, GeS and GeSe are candidates to produce on demand spin-current in spintronics applications.