Jiuxiang Dai

Author(s): Shenyang Huang, Yang Lu, Fanjie Wang, Yuchen Lei, Chaoyu Song, Jiasheng Zhang, Qiaoxia Xing, Chong Wang, Yuangang Xie, Lei Mu, Guowei Zhang, Hao Yan, Bin Chen, and Hugen Yan

Through infrared spectroscopy, we systematically study the pressure effect on electronic structures of few-layer black phosphorus (BP) with layer number ranging from 2 to 13. We reveal that the pressure-induced shift of optical transitions exhibits strong layer dependence. In sharp contrast to the b...

[Phys. Rev. Lett. 127, 186401] Published Tue Oct 26, 2021

Nature Materials, Published online: 25 October 2021; doi:10.1038/s41563-021-01125-w

Nature Electronics, Published online: 22 October 2021; doi:10.1038/s41928-021-00666-x

Nature Electronics, Published online: 22 October 2021; doi:10.1038/s41928-021-00668-9

Nature Electronics, Published online: 22 October 2021; doi:10.1038/s41928-021-00657-y

Heat transfer with homogeneous structures of Si3N4 system and the effects of oxygen defects in the Si3N4 grains are reported by Jung Woo Lee and co-workers in article number 2100566. The oxygen defects in the grains are moving to the surface of the grains and effectively captured by oxygen getter. The inhibition of the Si3N4 grain oxidization improves a spontaneous dissipation of thermal energy.

Atomically thin graphene covered silicon textured surface is pivotal for nanoscale robotics and nanogear operations. The conformation of graphene over serrated grooves provides mechanical strength and controlled frictional energy dissipation. It can channelize the mobility of nanoscale objects in a specific direction. Also, the asymmetrical straining in graphene over different grooves separation begins an era of straintronics.

Abstract

Friction-induced energy dissipation impedes the performance of nanomechanical devices. Nevertheless, the application of graphene is known to modulate frictional dissipation by inducing local strain. This work reports on the nanomechanics of graphene conformed on different textured silicon surfaces that mimic the cogs of a nanoscale gear. The variation in the pitch lengths regulates the strain induced in capped graphene revealed by scanning probe techniques, Raman spectroscopy, and molecular dynamics simulation. The atomistic visualization elucidates asymmetric straining of CC bonds over the corrugated architecture resulting in distinct friction dissipation with respect to the groove axis. Experimental results are reported for strain-dependent solid lubrication which can be regulated by the corrugation and leads to ultralow frictional forces. The results are applicable for graphene covered corrugated structures with movable components such as nanoelectromechanical systems, nanoscale gears, and robotics.

2D PdSe₂ has emerged as a new 2D material exhibiting prominent layer-dependent electronic structures. Herein, layer-tunable optical bandgap, nonlinear absorption, and photocarrier dynamics of 2D PdSe₂ films in broadband visible-to-near-infrared wavelengths are systematically demonstrated. This work enriches the understanding of the correlations between layer/electronic structure and nonlinear optical properties in PdSe₂ for further exploring their versatile applications.

Abstract

Layered 2D transition metal dichalcogenides (TMDCs) exhibited fascinating nonlinear optical (NLO) properties for constructing varied promising optoelectronics. However, exploring the desired 2D materials with both superior nonlinear absorption and ultrafast response in broadband spectra remain the key challenges to harvest their greatest potential. Here, based on synthesizing 2D PdSe₂ films with the controlled layer number, the authors systematically demonstrated the broadband giant NLO performance and ultrafast excited carrier dynamics of this emerging material under femtosecond visible-to-near-infrared laser-pulse excitation (400–1550 nm). Layer-dependent and wavelength-dependent evolution of optical bandgap, nonlinear absorption, and photocarrier dynamics in the obtained 2D PdSe₂ are clearly revealed. Specially, the transition from semiconducting to semimetallic PdSe₂ induced dramatic changes of their interband absorption–relaxation process. This work makes 2D PdSe₂ more competitive for future ultrafast photonics and also opens up a new avenue for the optical performance optimization of various 2D materials by rational design of these materials.

The thermoelectric properties of GeTe-based materials usually suffer from reduced carrier mobility. In this study, alloying CuBiSe₂ into GeTe allows high intrinsic carrier mobility and a high zT of ≈2.2 at 723 K and an average zT of 1.4 from 300 to 723 K in (GeTe)_0.94(CuBiSe₂)_0.06.

Abstract

According to the Mott's relation, the figure-of-merit of a thermoelectric material depends on the charge carrier concentration and carrier mobility. This explains the observation that low thermoelectric properties of GeTe-based materials suffer from the degraded carrier mobility, on account of the fluctuation of electronegativity and ionicity of various elements. Here, high-performance CuBiSe₂ alloyed GeTe with high carrier mobility due to the small electronegativity difference between Cu and Ge atoms and the weak ionicity of CuTe and BiTe bonds, is developed. Density functional theory calculations indicate that CuBiSe₂ alloying increases the formation energy of Ge vacancies and correspondingly reduces the amount of Ge vacancies, leading to an optimized carrier concentration and a high power factor of ≈37.4 µW cm⁻¹ K⁻² at 723 K. Moreover, CuBiSe₂ alloying induces dense point defects and triggers ubiquitous lattice distortions, leading to a reduced lattice thermal conductivity of 0.39 W m⁻¹ K⁻¹ at 723 K. These synergistic effects result in an optimization of the carrier mobility, the carrier concentration, and the lattice thermal conductivity, which favors an enhanced peak figure-of-merit of ≈2.2 at 723 K in (GeTe)_0.94(CuBiSe₂)_0.06. This study provides guidance for the screening of GeTe-based thermoelectric materials with high carrier mobility.

Terpolymer: Y6 system promotes significant breakthroughs in photovoltaic performance for both traditional opaque organic solar cells and semitransparent organic solar cells (ST-OSCs) based on all narrow bandgap (all-NBG) semiconductors. The terpolymer PCE10-BDT2F-0.8:Y6-based ST-OSCs achieve power conversion efficiencies (PCEs) of 12.00% and 10.85% with average visible transmittance (AVT) of 30.98% and 41.08%, respectively.

Abstract

Semitransparent organic solar cells (ST-OSCs) based on all narrow bandgap (all-NBG) semiconductors are attractive for building integration. Unfortunately, advanced NBG Y-series acceptors cannot well match with the NBG donors, resulting from their mismatched energy levels and poor compatibility. Herein, a facile terpolymer design strategy is adopted to improve the matching of Y6 with efficient NBG polymer donor PCE10. F or Cl atom functionalized benzodithiophene (BDT) are introduced into the PCE10 matrix to afford two series of terpolymers, namely PCE10-BDT2F and PCE10-BDT2Cl. Compared with PCE10, all terpolymers show deeper energy levels, higher extinction coefficients, enhanced face-on orientation, and better compatibility with Y6. Consequently, significant breakthroughs are achieved for both opaque and semitransparent devices. Particularly, a record power conversion efficiency (PCE) of 13.80% is achieved by PCE10-BDT2F:Y6-based device, nearly 40% higher than PCE10:Y6-based device. ST-OSCs also achieve impressive PCEs of 12.00% and 10.85% with average visible transmittance (AVT) of 30.98% and 41.08%, respectively, and both PCEs are the highest values with AVT over 30% and 40%. An outstanding light utilization efficiency (LUE) of 4.46% further demonstrates the successful balance of PCE and AVT. These results demonstrate that the design of NBG terpolymers is a facile and highly encouraging strategy for promoting breakthroughs in ST-OSCs.

A new architecture of photoelectrochemical devices composed of semiconductor nanowires demonstrates photocurrent polarity-switchable characteristics based on the photovoltage-competing dynamics across two photoelectrodes, aiming for spectrally distinctive photodetection. Importantly, a remarkable boost of photocurrent and responsivity can be achieved after rational surface modification of the nanowire structures, offering an unprecedented opportunity to construct multifunctional photosensing systems of the future.

Abstract

Multiple-band and spectrally distinctive photodetection play critical roles in building next-generation colorful imaging, spectroscopy, artificial vision, and optically controlled logic circuits of the future. Unfortunately, it remains challenging for conventional semiconductor photodetectors to distinguish different spectrum bands with photon energy above the bandgap of the material. Herein, for the first time, a photocurrent polarity-switchable photoelectrochemical device composed of group III-nitride semiconductors, demonstrating a positive photocurrent density of 10.54 µA cm⁻² upon 254 nm illumination and a negative photocurrent density of −0.08 µA cm⁻² under 365 nm illumination without external power supply, is constructed. Such bidirectional photocurrent behavior arises from the photovoltage-competing dynamics across two photoelectrodes. Importantly, a significant boost of the photocurrent and corresponding responsivity under 365 nm illumination can be achieved after decorating the counter electrode of n-type AlGaN nanowires with platinum (Pt) nanoparticles, which promote a more efficient redox reaction in the device. It is envisioned that the photocurrent polarity-switch behavior offers new routes to build multiple-band photodetection devices for complex light-induced sensing systems, covering a wide spectrum band from deep ultraviolet to infrared, by simply engineering the bandgaps of semiconductors.

To emulate the entire human visual system at the single device level, a multifunctional optoelectronic synapse based on ferroelectric α-In₂Se₃/GaSe vdW heterostructure is elaborately designed. Visual perception, logic functions, and memory are integrated into the device. The study shed light on creating a sophisticated artificial visual system analogous to that of humans and break the bottleneck of current image recognition technology.

Abstract

The development of optoelectronic synapses can provide an important breakthrough toward creating a sophisticated and adaptable artificial visual system analogous to that of humans. However, it remains a great challenge to implement the various functions of the biological visual neuromorphic system at the single device level. Intriguingly, 2D van der Waals (vdW) heterostructure may offer a platform to address the issue. Here, a novel multifunctional synaptic device based on ferroelectric α-In₂Se₃/GaSe vdW heterojunction is proposed to emulate the entire biological visual system. Essential synaptic behaviors are observed in response to light and electrical stimuli; additionally, the retina-like selectivity for light wavelengths and the achievement of Pavlov's dog experiment demonstrate the device's capacity for processing complex electrical and optical inputs. Beyond the optoelectronic synaptic behaviors, the device incorporates memory and logic functions analogous to those in the brain's visual cortex. The results of artificial neural network simulations show that the vdW heterojunction-based device is completely capable of performing logic operations and recognizing images with a high degree of accuracy. The study indicates that versatile devices with a rationally designed construction have great potential for efficiently processing complex visual information and may simplify the design of artificial visual systems.

Publication date: 15 February 2022

Source: Journal of Hazardous Materials, Volume 424, Part B

Author(s): Zhijie Guo, Kaituo Jiang, Huihui Jiang, Hang Zhang, Qian Liu, Tianyan You