Monitoring and engineering interface coupling between monolayer WS_(2)and substrate through controllably introducing interfacial strain

The interface properties in two-dimensional(2D)layered materials and their van der Waals(vdW)homo-/heterostructures are of importance in both uncovering novel physical phenomena and optimizing device performance.Despite considerable research interest and enthusiasm direct toward the interlayer coupling in 2D homo-and heterostructures,there is limited research on the coupling at the 2D layered material-substrate interface.This limitation is due to the challenges in achieving direct detection.Currently,the coupling mechanisms at the 2D layered material-substrate interface is ambiguous,which needs greater attention.In this study,we have systematically investigated the interface coupling between monolayer WS_(2)and its supported substrates using high-temperature and high-vacuum in-situ Raman spectroscopy through monitoring the low-frequency Raman mode of monolayer WS_(2).Our findings reveal that both interfacial spacing and strain can significantly affect the coupling strength between the monolayer WS_(2)and the supported substrate.More notably,we found that the strategic introduction of appropriate interfacial strain can effectively enhance the interface coupling.Consequently,we have succeeded in achieving effective regulation of the sample-substrate coupling via a convenient way of controlling the cooling process during annealing.Our findings contribute to a deeper understanding of the coupling correlation between 2D layered materials and substrates,which is of great significance for the design and optimization of high-performance devices based on 2D layered semiconductors.

Influence of seeding promoters on the properties of CVD grown monolayer molybdenum disulfide

Chemical vapor deposition (CVD) is the most efficient method to grow large-area two dimensional (2D) transition metal dichiacogenides (TMDCs) in high quality.Monolayer molybdenum disulfide (MoS2) and seed-assistant are the mostly selected 2D TMDC and growth strategy for such CVD processes,respectively.Though the advantages of seed catalysts in facilitating the nucleation,achieving higher yield and better repeatability,as well as their effects on the morphologies of as-grown MoS2 have been studied,the influence of seeding promoters on both optical and electrical properties of as-grown monolayer MoS2 is not known comprehensively,which is indeed critical for understanding fundamental physics and developing practical application of such emerging 2D semiconductors.In this report,we systematically investigated the effect of different seeding promoters on the properties of CVD-grown monolayer MoS2.It is found that different seed molecules lead to different impacts on the optical and electrical properties of as-grown monolayer MoS2.Among three different seed catalysts (perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS),copper phthalocyanine (CuPc),and crystal violet (CV)),PTAS performs better in obtaining large area monolayer MoS2 with good optical quality and high electrical mobility than the other two.Our work gives a guide for modifying the properties of as-grown monolayer MoS2 and other 2D transition metal dichalcogenides in seeding promoters-assisted synthesis process.

Molecular ferroelectric/semiconductor interfacial memristors for artificial synapses

With the burgeoning developments in artificial intelligence,hardware implementation of artificial neural network is also gaining pace.In this pursuit,ferroelectric devices(i.e.,tunneling junctions and transistors)with voltage thresholds were recently proposed as suitable candidates.However,their development is hindered by the inherent integration issues of inorganic ferroelectrics,as well as poor properties of conventional organic ferroelectrics.In contrast to the conventional ferroelectric synapses,here we demonstrated a two-terminal ferroelectric synaptic device using a molecular ferroelectric(MF)/semiconductor interface.The interfacial resistance can be tuned via the polarization-controlled blocking effect of the semiconductor,owing to the high ferroelectricity and field amplification effect of the MF.Typical synaptic features including spike timing-dependent plasticity are substantiated.The introduction of the semiconductor also enables the attributes of optoelectronic synapse and in-sensor computing with high image recognition accuracies.Such interfaces may pave the way for the hardware implementation of multifunctional neuromorphic devices.

Molecular interactions induced collapse of charge density wave quantum states in 2H tantalum disulfide nanosheets

2H-tantalum disulfide(2H-TaS_(2))is a layered metallic transition metal dichalcogenide(TMD)that has recently been studied from the perspective of new physics phenomena,including simultaneous lattice distortion and charge density modulation known as the charge density wave(CDW)phase.Here we explored the collapse of CDW states in few-layer 2H-TaS_(2)induced by molecular interactions using Raman spectroscopy.Our results indicate that the CDW states disappear in few-layer 2H-TaS_(2)with rhodamine 6G(R6G)adsorbed due to the charge transfer,which is reflected by the change of behaviors of lattice vibrational modes in 2HTaS_(2).We observed the 2-phonon mode that signifies the CDW formation in 2H-TaS_(2),becomes a phonon-hardened mode when R6G molecules are absorbed on its surface.R6G adsorption further induces the breakdown of the Raman polarization selection rule in 2H-TaS_(2),which results in the alteration of the A_(1g)phonon mode polarization state of 2H-TaS_(2).This study can shed light not only on the underlying mechanisms of CDW states but also on controlling the CDW states under a variety of environmental conditions.

In-situ artificial retina with all-in-one reconfigurable photomemristor networks

Despite that in-sensor processing has been proposed to remove the latency and energy consumption during the inevitable data transfer between spatial-separated sensors,memories and processors in traditional computer vision,its hardware implementation for artificial neural networks(ANNs)with all-in-one device arrays remains a challenge,especially for organic-based ANNs.With the advantages of biocompatibility,low cost,easy fabrication and flexibility,here we implement a self-powered in-sensor ANN using molecular ferroelectric(MF)-based photomemristor arrays.Tunable ferroelectric depolarization was intentionally introduced into the ANN,which enables reconfigurable conductance and photoresponse.Treating photoresponsivity as synaptic weight,the MFbased in-sensor ANN can operate analog convolutional computation,and successfully conduct perception and recognition of white-light letter images in experiments,with low processing energy consumption.Handwritten Chinese digits are also recognized and regressed by a large-scale array,demonstrating its scalability and potential for low-power processing and the applications in MF-based in-situ artificial retina.