Applications of 2D-Layered Palladium Diselenide and Its van der Waals Heterostructures in Electronics and Optoelectronics

The rapid development of two-dimensional(2D)transition-metal dichalcogenides has been possible owing to their special structures and remarkable properties.In particular,palladium diselenide(PdSe_(2))with a novel pentagonal structure and unique physical characteristics have recently attracted extensive research inter-est.Consequently,tremendous research progress has been achieved regarding the physics,chemistry,and electronics of PdSe_(2).Accordingly,in this review,we recapitulate and summarize the most recent research on PdSe_(2),including its structure,properties,synthesis,and appli-cations.First,a mechanical exfoliation method to obtain PdSe_(2) nanosheets is introduced,and large-area synthesis strate-gies are explained with respect to chemical vapor deposition and metal selenization.Next,the electronic and optoelectronic properties of PdSe_(2) and related hetero-structures,such as field-effect transistors,photodetectors,sensors,and thermoelec-tric devices,are discussed.Subsequently,the integration of systems into infrared image sensors on the basis of PdSe_(2) van der Waals heterostructures is explored.Finally,future opportunities are highlighted to serve as a general guide for physicists,chemists,materials scientists,and engineers.Therefore,this com-prehensive review may shed light on the research conducted by the 2D material community.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors.Indeed,the 5 G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices.In this perspective,we deliver the readers with the latest trends in carbon nanotube research,including high-frequency transistors,biomedical sensors and actuators,brain–machine interfaces,and flexible logic devices and energy storages.Future opportunities are given for calling on scientists and engineers into the emerging topics.

Design and Optimization of Steel Car Body Structures via Local Laser-Strengthening

Continuously rising demands of legislators require a significant reduction of CO2-emission and thus fuel consumption across all vehicle classes. In this context, lightweight construction materials and designs become a single most important factor. The main engineering challenge is to precisely adapt the material and component properties to the specific load situation. However, metallic car body structures using “Tailored blanks” or “Patchwork structures” meet these requirements only insufficiently, especially for complex load situations (like crash). An innovative approach has been developed to use laser beams to locally strengthen steel crash structures used in vehicle bodies. The method tailors the workpiece hardness and thus strength at selected locations to adjust the material properties for the expected load distribution. As a result, free designable 3D-strengthening-patterns surrounded by softer base metal zones can be realized by high power laser beams at high processing speed. The paper gives an overview of the realizable process window for different laser treatment modes using current high brilliant laser types. Furthermore, an efficient calculation model for determining the laser track properties (depth/width and flow curve) is shown. Based on that information, simultaneous FE modelling can be efficiently performed. Chassis components are both statically and cyclically loaded. Especially for these components, a modulation of the fatigue behavior by laser-treated structures has been investigated. Simulation and experimental results of optimized crash and deep drawing components with up to 55% improved level of performance are also illustrated.

Modulating p-type doping of two-dimensional material palladium diselenide

The van der Waals heterostructures have evolved as novel materials for complementing the Si-based semiconductor technologies.Group-10 noble metal dichalcogenides(e.g.,PtS_(2),PtSe_(2),PdS_(2),and PdSe_(2))have been listed into two-dimensional(2D)materials toolkit to assemble van der Waals heterostructures.Among them,PdSe_(2) demonstrates advantages of high stability in air,high mobility,and wide tunable bandgap.However,the regulation of p-type doping of PdSe_(2) remains unsolved problem prior to fabricating p–n junction as a fundamental platform of semiconductor physics.Besides,a quantitative method for the controllable doping of PdSe_(2) is yet to be reported.In this study,the doping level of PdSe_(2) was correlated with the concentration of Lewis acids,for example,SnCl_(4),used for soaking.Considering the transfer characteristics,the threshold voltage(the gate voltage corresponding to the minimum drain current)increased after SnCl_(4) soaking treatment.PdSe_(2) transistors were soaked in SnCl_(4) solutions with five different concentrations.The threshold voltages from the as-obtained transfer curves were extracted for linear fitting to the threshold voltage versus doping concentration correlation equation.This study provides in-depth insights into the controllable p-type doping of PdSe_(2).It may also push forward the research of the regulation of conductivity behaviors of 2D materials.

Closing the gap between atomic-scale lattice deformations and continuum elasticity

Crystal lattice deformations can be described microscopically by explicitly accounting for the position of atoms or macroscopically by continuum elasticity.In this work,we report on the description of continuous elastic fields derived from an atomistic representation of crystalline structures that also include features typical of the microscopic scale.Analytic expressions for strain components are obtained from the complex amplitudes of the Fourier modes representing periodic lattice positions,which can be generally provided by atomistic modeling or experiments.The magnitude and phase of these amplitudes,together with the continuous description of strains,are able to characterize crystal rotations,lattice deformations,and dislocations.Moreover,combined with the so-called amplitude expansion of the phase-field crystal model,they provide a suitable tool for bridging microscopic to macroscopic scales.This study enables the in-depth analysis of elasticity effects for macroscale and mesoscale systems taking microscopic details into account.

High-performance electronics and optoelectronics of monolayer tungsten diselenide full film from pre-seeding strategy

Tungsten diselenide (WSe2) possesses extraordinary electronic properties forapplications in electronics, optoelectronics, and emerging exciton physics. Thesynthesis of monolayer WSe2 film is of topmost for device arrays and integratedcircuits. The monolayer WSe2 film has yet been reported by thermal chemicalvapor deposition (CVD) approach, and the nucleation mechanism remainsunclear. Here, we report a pre-seeding strategy for finely regulating the nucleidensity at an early stage and achieving a fully covered film after chemicalvapor deposition growth. The underlying mechanism is heterogeneous nucle-ation from the pre-seeding tungsten oxide nanoparticles. At first, we optimized the precursor concentration for pre-seeding. Besides, we confirmed the superi-ority of the pre-seeding method, compared with three types of substrate pre-treatments, including nontreatment, sonication in an organic solvent, andoxygen plasma. Eventually, the high-quality synthetic WSe2 monolayer filmexhibits excellent device performance in field-effect transistors and photodetec-tors. We extracted thermodynamic activation energy from the nucleation andgrowth data. Our results may shed light on the wafer-scale production ofhomogeneous monolayer films of WSe2, other 2D materials, and their van derWaals heterostructures.

Applications of nanogenerators for biomedical engineering and healthcare systems

The dream of human beings for long living has stimulated the rapid development of biomedical and healthcare equipment.However,conventional biomedical and healthcare devices have shortcomings such as short service life,large equipment size,and high potential safety hazards.Indeed,the power supply for conventional implantable device remains predominantly batteries.The emerging nanogenerators,which harvest micro/nanomechanical energy and thermal energy from human beings and convert into electrical energy,provide an ideal solution for self-powering of biomedical devices.The combination of nanogenerators and biomedicine has been accelerating the development of self-powered biomedical equipment.This article first introduces the operating principle of nanogenerators and then reviews the progress of nanogenerators in biomedical applications,including power supply,smart sensing,and effective treatment.Besides,the microbial disinfection and biodegradation performances of nanogenerators have been updated.Next,the protection devices have been discussed such as face mask with air filtering function together with real-time monitoring of human health from the respiration and heat emission.Besides,the nanogenerator devices have been categorized by the types of mechanical energy from human beings,such as the body movement,tissue and organ activities,energy from chemical reactions,and gravitational potential energy.Eventually,the challenges and future opportunities in the applications of nanogenerators are delivered in the conclusive remarks.

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight,hearing,smell,taste,touch,space,and balance.The first five senses are prerequisites for people to live.The sensing organs upload information to the nervous systems,including the brain,for interpreting the surrounding environment.Then,the brain sends commands to muscles reflexively to react to stimuli,including light,gas,chemicals,sound,and pressure.MXene,as an emerging two-dimensional material,has been intensively adopted in the applications of various sensors and actuators.In this review,we update the sensors to mimic five primary senses and actuators for stimulating muscles,which employ MXene-based film,membrane,and composite with other functional materials.First,a brief introduction is delivered for the structure,properties,and synthesis methods of MXenes.Then,we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas,gas sensors,chemical biosensors,acoustic devices,and tactile sensors for electronic skin.Besides,the actuators of MXene-based composite are introduced.Eventually,future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot,which may induce prospects in accompanying healthcare and biomedical engineering applications.

A unified field theory of topological defects and non-linear local excitations

Topological defects and smooth excitations determine the properties of systems showing collective order.We introduce a generic non-singular field theory that comprehensively describes defects and excitations in systems with O(n)broken rotational symmetry.Within this formalism,we explore fast events,such as defect nucleation/annihilation and dynamical phase transitions where the interplay between topological defects and non-linear excitations is particularly important.To highlight its versatility,we apply this formalism in the context of Bose-Einstein condensates,active nematics,and crystal lattices.

Thermal bridging of graphene nanosheets via covalent molecular junctions: A non-equilibrium Green's functions-density functional tightbinding study

Despite the uniquely high thermal conductivity of graphene is well known,the exploitation of graphene into thermally conductive nanomaterials and devices is limited by the inefficiency of thermal contacts between the individual nanosheets.A fascinating yet experimentally challenging route to enhance thermal conductance at contacts between graphene nanosheets is through molecular junctions,allowing covalently connecting nanosheets,otherwise interacting only via weak Van der Waals forces.Beside the bare existence of covalent connections,the choice of molecular structures to be used as thermal junctions should be guided by their vibrational properties,in terms of phonon transfer through the molecular junction.In this paper,density functional tight-binding combined with Green's functions formalism was applied for the calculation of thermal conductance and phonon spectra of several different aliphatic and aromatic molecular junctions between graphene nanosheets.Effects of molecular junction length,conformation,and aromaticity were studied in detail and correlated with phonon tunnelling spectra.The theoretical insight provided by this work can guide future experimental studies to select suitable molecular junctions,in order to enhance the thermal transport by suppressing the interfacial thermal resistances.This is attractive for various systems,including graphene nanopapers and graphene polymer nanocomposites,as well as related devices.In a broader view,the possibility to design molecular junctions to control phonon transport currently appears as an efficient way to produce phononic devices and controlling heat management in nanostructures.

Optoelectronic switching of nanowire-based hybrid organic/oxide/semiconductor field-effect transistors

A novel photosensitive hybrid field-effect transistor （FET） which consists of a multiple-shell of organic porphyrin film/oxide/silicon nanowires is presented. Due to the oxide shell around the nanowires, photoswitching of the current in the hybrid nanodevices is guided by the electric field effect, induced by charge redistribution within the organic film. This principle is an alternative to a photoinduced electron injection, valid for devices relying on direct junctions between organic molecules and metals or semiconductors. The switching dynamics of the hybrid nanodevices upon violet light illumination is investigated and a strong dependence on the thickness of the porphyrin film wrapping the nanowires is found. Furthermore, the thickness of the organic films is found to be a crucial parameter also for the switching efficiency of the nanowire FET, represented by the ratio of currents under light illumination （ON） and in dark conditions （OFF）. We suggest a simple model of porphyrin film charging to explain the optoelectronic behavior of nanowire FETs mediated by organic film/oxide/semiconductor junctions.

Emerging Internet of Things driven carbon nanotubes-based devices

Carbon nanotubes(CNTs)have attracted great attentions in the field of electronics,sensors,healthcare,and energy conversion.Such emerging applications have driven the carbon nanotube research in a rapid fashion.Indeed,the structure control over CNTs has inspired an intensive research vortex due to the high promises in electronic and optical device applications.Here,this in-depth review is anticipated to provide insights into the controllable synthesis and applications of high-quality CNTs.First,the general synthesis and post-purification of CNTs are briefly discussed.Then,the state-of-the-art electronic device applications are discussed,including field-effect transistors,gas sensors,DNA biosensors,and pressure gauges.Besides,the optical sensors are delivered based on the photoluminescence.In addition,energy applications of CNTs are discussed such as thermoelectric energy generators.Eventually,future opportunities are proposed for the Internet of Things(IoT)oriented sensors,data processing,and artificial intelligence.

Ionic effects on the transport characteristics of nanowire-based FETs in a liquid environment

For the development of ultra-sensitive electrical bio/chemical sensors based on nanowire field effect transistors （FETs）, the influence of the ions in the solution on the electron transport has to be understood. For this purpose we establish a simulation platform for nanowire FETs in the liquid environment by implementing the modified Poisson-Boltzmann model into Landauer transport theory. We investigate the changes of the electric potential and the transport characteristics due to the ions. The reduction of sensitivity of the sensors due to the screening effect from the electrolyte could be successfully reproduced. We also fabricated silicon nanowire Schottky-barrier FETs and our model could capture the observed reduction of the current with increasing ionic concentration. This shows that our simulation platform can be used to interpret ongoing experiments, to design nanowire FETs, and it also gives insight into controversial issues such as whether ions in the buffer solution affect the transport characteristics or not.