Universal Transfer and Stacking of Chemical Vapor Deposition Grown Two-Dimensional Atomic Layers with Water-Soluble Polymer Mediator

Broadband Light Harvesting from Scalable Two-Dimensional Semiconductor Multi-Heterostructures

Broadband absorption in the visible spectrum is essential in optoelectronic applications that involve power conversion such as photovoltaics and photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic structures that maximize absorption using surface plasmons and/or Fabry-Perot cavities, which limits the weight efficiency of the device. Here, we show the theoretical and experimental realization of an unpatterned/planar semiconductor thin-film absorber based on monolayer transition-metal dichalcogenides. We experimentally demonstrate an average total absorption in the visible range (450-700 nm) of >70% using <4 nm of semiconductor absorbing materials scalable over large areas with vapor phase growth techniques. Our analysis suggests that a power conversion efficiency of 15.54% and a specific power >300 W g-1 may be achieved in a photovoltaic cell based on this metamaterial absorber.

Clean Transfer of Two-Dimensional Materials: A Comprehensive Review

The growth of two-dimensional (2D) materials through chemical vapor deposition (CVD) has sparked a growing interest among both the industrial and academic communities. The interest stems from several key advantages associated with CVD, including high yield, high quality, and high tunability. In order to harness the application potentials of 2D materials, it is often necessary to transfer them from their growth substrates to their desired target substrates. However, conventional transfer methods introduce contamination that can adversely affect the quality and properties of the transferred 2D materials, thus limiting their overall application performance. This review presents a comprehensive summary of the current clean transfer methods for 2D materials with a specific focus on the understanding of interaction between supporting layers and 2D materials. The review encompasses various aspects, including clean transfer methods, post-transfer cleaning techniques, and cleanliness assessment. Furthermore, it analyzes and compares the advances and limitations of these clean transfer techniques. Finally, the review highlights the primary challenges associated with current clean transfer methods and provides an outlook on future prospects.

Bipolar Resistive Switching in 2D MoSe2 Grown by Atmospheric Pressure Chemical Vapor Deposition

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are highly promising nanomaterials for various electronic devices such as field-effect transistors, junction diodes, tunneling devices, and, more recently, memristors. 2D MoSe2 stands out for having high electrical conductivity, charge carrier mobility, and melting point. While these features make it particularly appropriate as a switching layer in memristive devices, reliable and scalable production of large-area 2D MoSe2 still represents a challenge. In this study, we manufacture 2D MoSe2 films by atmospheric-pressure chemical vapor deposition and investigate them on the atomic scale. We selected and transferred MoSe2 bilayer to serve as a switching layer between asymmetric Au-Cu electrodes in miniaturized crossbar vertical memristors. The electrochemical metallization devices showed forming-free, bipolar resistive switching at low voltages, with clearly identifiable nonvolatile states. Other than low-power neuromorphic computing, low switching voltages approaching the range of biological action potentials could unlock hybrid biological interfaces.

Tuning the optical absorption performance of MoS2 monolayers with compressive strain

Strain engineering has been extensively applied as a promising strategy in the regulation of physical and chemical properties of two-dimensional (2D) materials, which remarkably broadens their application prospects in flexible electronics and chip manufacturing. However, the difficulty in fixing a flexible substrate under compression and the challenge in adjusting the focal distance have hindered the in-depth investigation of compressive strain. Here, we fabricated a home-made strain loading device and proposed a compressive strain measurement method, via which the strain-dependent optical absorption properties of MoS₂ monolayers under compression has been studied. According to the measured optical absorption spectra, the first blueshift and then redshift trend under compression was obviously observed. The reliability of the experimentally observed trend in peak position shift was theoretically verified by density functional theory calculation. Our work offers a feasible way to characterize optical properties of 2D materials under compressive strain and expands the space for the development of next-generation micro/nano-scale optoelectronic devices.

Flexible 2D Materials beyond Graphene: Synthesis, Properties, and Applications

2D materials are now at the forefront of state-of-the-art nanotechnologies due to their fascinating properties and unique structures. As expected, low-cost, high-volume, and high-quality 2D materials play an important role in the applications of flexible devices. Although considerable progress has been achieved in the integration of a series of novel 2D materials beyond graphene into flexible devices, a lot remains to be known. At this stage of their development, the key issues concern how to make further improvements to high-performance and scalable-production. Herein, recent progress in the quest to improve the current state of the art for 2D materials beyond graphene is reviewed. Namely, the properties and synthesis techniques of 2D materials are first introduced. Then, both the advantages and challenges of these 2D materials for flexible devices are also highlighted. Finally, important directions for future advancements toward efficient, low-cost, and stable flexible devices are outlined.

Review and comparison of layer transfer methods for two-dimensional materials for emerging applications

Two-dimensional (2D) materials offer immense potential for scientific breakthroughs and technological innovations. While early demonstrations of 2D material-based electronics, optoelectronics, flextronics, straintronics, twistronics, and biomimetic devices exploited micromechanically-exfoliated single crystal flakes, recent years have witnessed steady progress in large-area growth techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and metal-organic CVD (MOCVD). However, use of high growth temperatures, chemically-active growth precursors and promoters, and the need for epitaxy often limit direct growth of 2D materials on the substrates of interest for commercial applications. This has led to the development of a large number of methods for the layer transfer of 2D materials from the growth substrate to the target application substrate with varying degrees of cleanliness, uniformity, and transfer-related damage. This review aims to catalog and discuss these layer transfer methods. In particular, the processes, advantages, and drawbacks of various transfer methods are discussed, as is their applicability to different technological platforms of interest for 2D material implementation.

Steric Hindrance- and Work Function-Promoted High Performance for Electrochemical CO Methanation on Antisite Defects of MoS2 and WS2

CO methanation from electrochemical CO reduction reaction (CORR) is significant for sustainable environment and energy, but electrocatalysts with excellent selectivity and activity are still lacking. Selectivity is sensitive to the structure of active sites, and activity can be tailored by work function. Moreover, intrinsic active sites usually possess relatively high concentration compared to artificial ones. Here, antisite defects Mo_S2 and W_S2 , intrinsic atomic defects of MoS₂ and WS₂ with a transition metal atom substituting a S₂ column, were investigated for CORR by density functional theory calculations. The steric hindrance from the special bowl structure of Mo_S2 and W_S2 ensured good selectivity towards CO methanation. Coordination environment variation of the active sites, the under-coordinated Mo or W atoms, effectively lowered the work function, making Mo_S2 and W_S2 highly active for CO methanation with the required potential of -0.47 and -0.49 V vs. reversible hydrogen electrode, respectively. Moreover, high concentration of active sites and minimal structural deformation during the catalytic process of Mo_S2 and W_S2 enhanced their attraction for future commercial application.

Phosphorescent MoS2 quantum dots as a temperature sensor and security ink

Currently, few phosphorescent materials (PMs) possess a long phosphorescence lasting time and have potential for application in chemical sensors. Herein, we disclose that the incorporation of few-layer molybdenum disulfide quantum dots (FL-MoS2 QDs) into poly(vinyl alcohol) (PVA) matrices leads to the emission of bright green phosphorescence with a long lasting time of 3.0 s and a phosphorescence quantum yield of 20%. This enhanced phosphorescence originates from the formation of O-H⋯S hydrogen bonding networks between the rich sulfur sites of the FL-MoS2 QDs and the hydroxyl groups of the PVA molecules, which not only rigidifies the vibration modes of the FL-MoS2 QDs but also provides an oxygen barrier. Further investigations reveal that the FL-MoS2 QD/PVA composites exhibit a longer phosphorescence lasting time than N,S-doped carbon dots, few layer tungsten disulfide quantum dots, Rhodamine 6G, and Rhodamine B in PVA matrices. Since heat efficiently induced the removal of water moisture from PVA matrices, the FL-MoS2 QD/PVA composites could be implemented for phosphorescence turn-on and naked-eye detection of temperature variations ranging from 30 to 70 °C. By contrast, the carbon dot/PVA composites were incapable of sensing environmental temperature due to their weak hydrogen bonding with the hydroxyl groups of PVA matrices. Additionally, this study reveals the potential of the FL-MoS2 QD/PVA composites as an advanced security ink for anti-counterfeiting and encryption applications. The given results could open a new direction for potential application of two-dimensional quantum dots in phosphorescence-based sensors and security inks.

Low-Temperature Synthesis of Wafer-Scale MoS2-WS2 Vertical Heterostructures by Single-Step Penetrative Plasma Sulfurization

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD-TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD-TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS₂-WS₂ vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS₂ and WS₂. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO₂/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD-TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD-TMD vertical heterostructures.

Interfaces determine the nucleation and growth of large NbS2 single crystals

The synthesis of large NbS₂ single crystals benefits from Na–Nb–O droplet interfaces, which reduces nucleation density and increases growth rate.

1D/2D Heterostructures as Ultrathin Catalysts for Hydrogen Evolution Reaction

2D MoS₂ has emerged as a promising alternative to Pt-based catalysts for hydrogen evolution reaction (HER) due to its low cost and earth abundance. However, insufficient active sites of basal plane and poor conductivity become the foremost factors restricting the catalytic performance of MoS₂ . Here, a facile strategy is presented to enhance the HER performance of MoS₂ by converting its 2D structure into 1D/2D heterostructures of Mo₆ Te₆ /MoS_{2(1- x )} Te_{2 x} by the in situ tellurization. As-prepared 1D/2D heterostructures exhibit excellent HER performance with the Tafel slope of ≈56 mV dec^-1 (only one-third of that for pristine MoS₂ ). The enhanced HER catalytic activity is attributed to more Te/S vacancies introduced by tellurization, which serve as the active sites as suggested by theoretical calculations. Besides, the formation of highly conductive well-aligned quasi-1D Mo₆ Te₆ nanobelts facilitate charge transport in HER. Previous work provides a facile approach to construct mixed dimensional materials, and opens up a new avenue to the properties modulation of 2D transition metal chalcogenides.

Ultrathin high-κ antimony oxide single crystals

Ultrathin oxides have been reported to possess excellent properties in electronic, magnetic, optical, and catalytic fields. However, the current and primary approaches toward the preparation of ultrathin oxides are only applicable to amorphous or polycrystalline oxide nanosheets or films. Here, we successfully synthesize high-quality ultrathin antimony oxide single crystals via a substrate-buffer-controlled chemical vapor deposition strategy. The as-obtained ultrathin antimony oxide single crystals exhibit high dielectric constant (~100) and large breakdown voltage (~5.7 GV m^-1). Such a strategy can also be utilized to fabricate other ultrathin oxides, opening up an avenue in broadening the applicaitons of ultrathin oxides in many emerging fields.

Shape-dependent close-edge 2D-MoS2 nanobelts

Atomic-thin MoS₂ materials have attracted increasing attention due to their potentials in numerous fields. However, in 2D-MoS₂ sheets, the edge region usually has unique features differing from the interior region, which has potential application in enhancing catalysts and shape-dependent 2D-nanodevices. However, fabricating it cost-effectively is still very difficult. Here, we present one universal method to obtain various shape-dependent closed-edge 2D-MoS₂ nanobelts only using one simple step, and width of the MoS₂ nanobelts (minimum of 270 nm) were adjustable. Our strategy opens a new fabrication route for closed-edge 2D-MoS₂ nanobelts, and in principle, this method is also suitable for other CVD-grown 2D materials.

A very simple mechanical peeling method to obtain various closed and shape-dependent MoS₂ edge nanobelt.

Optical Imaging of Charges with Atomically Thin Molybdenum Disulfide

Mapping local surface charge distribution is critical to the understanding of various surface processes and also allows the detection of molecules binding to the surface. We show here that the optical absorption of monolayer MoS₂ is highly sensitive to charge and demonstrate optical imaging of local surface charge distribution with this atomically thin material. We validate the imaging principle and perform charge sensitivity calibration with an electrochemical gate. We further show that binding of charged molecules to the atomically thin material leads to a large change in the image contrast, allowing determination of the charge of the adsorbed molecules. This capability opens possibilities for characterizing impurities and defects in two-dimensional materials and for label-free optical detection and charge analysis of molecules.

Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS2/WS2/Graphene Devices

Atomically thin vertical heterostructures are promising candidates for optoelectronic applications, especially for flexible and transparent technologies. Here, we show how ultrathin all two-dimensional vertical-stacked type-II heterostructure devices can be assembled using only materials grown by chemical vapor deposition, with graphene (Gr) as top and bottom electrodes and MoS₂/WS₂ as the active semiconductor layers in the middle. Furthermore, we show that the stack symmetry, which dictates the type-II directionality, is the dominant factor in controlling the photocurrent direction upon light irradiation, whereas in homobilayers, photocurrent direction cannot be easily controlled because the tunnel barrier is determined by the doping levels of the graphene, which appears fixed for top and bottom graphene layers due to their dielectric environments. Therefore, the ability to direct photovoltaic current flow is demonstrated to be only possible using heterobilayers (HBs) and not homobilayers. We study the photovoltaic effects in more than 40 devices, which allows for statistical verification of performance and comparative behavior. The photovoltage in the graphene/transition-metal dichalcogenide-heterobilayer/graphene (Gr/TMD-HB (MoS₂/WS₂)/Gr) increases up to 10 times that generated in the monolayer TMD devices under the same optical illumination power, due to efficient charge transfer between WS₂ and MoS₂ and extraction to graphene electrodes. By applying external gate voltages ( V_g), the band alignment can be tuned, which in turn controls the photovoltaic effect in the vertical heterostructures. The tunneling-assisted interlayer charge recombination also plays a significant role in modulating the photovoltaic effect in the Gr/TMD-HB/Gr. These results provide important insights into how layer symmetry in vertical-stacked graphene/TMD/graphene ultrathin optoelectronics can be used to control electron flow directions during photoexcitation and open up opportunities for tandem cell assembly.

Near-Field Coupled Integrable Two-Dimensional InSe Photosensor on Optical Fiber

Two-dimensional (2D) van der Waals layered materials possess innate advantages as integrable sensors, due to their thinness, flexibility, and sensitivity. They can be seamlessly integrated onto surfaces with different geometries where detection for near-field signal is desired. In this study, we develop a device transfer technique to integrate device assemblies based on 2D materials onto an arbitrary smooth surface. Such technique utilizes a sacrificial polymer underlayer and achieves clean and nondestructive full device transfer. For demonstration, we transferred a complete 2D multilayer InSe photodetector device onto a stripped optical fiber. Due to the extreme vicinity of the 2D photodetector with the fiber core, the device can effectively couple with the evanescent field and accurately detect information transmitted inside the optical fiber. In addition, these super thin flexible device assemblies can be integrated onto the fibers themselves to non-invasively monitor the optical fiber performance. The demonstration of optically coupled, conformal 2D devices on substrates of different form factors can enable a variety of near-field optical and sensing applications.

Unidirectional Enhanced Emission from 2D Monolayer Suspended by Dielectric Pillar Array

Monolayers of transition metal dichalcogenides show great promise for optoelectronic devices as atomically thin semiconductors. Although dielectric or metal nanostructures have been extensively studied for tailoring and enhancing emission from monolayers, their applications are limited because of the mode concentrating inside the dielectric or the high optical losses in metals, together with the low quantum yield in monolayers. Here, we demonstrate that a metal-backed dielectric pillar array can suspend monolayers to increase the radiative recombination, and simultaneously, create strongly confined band-edge modes on surface directly accessible to monolayers. We observe unidirectional enhanced emission from WSe₂ monolayers on polymer pillar array.

Tunable photoluminescence in a van der Waals heterojunction built from a MoS2 monolayer and a PTCDA organic semiconductor

We report the photoluminescence (PL) characteristics of a van der Waals (vdW) heterojunction constructed by simply depositing an organic semiconductor of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) onto a two-dimensional MoS2 monolayer. The crystallinity of PTCDA on MoS2 is significantly improved due to the vdW epitaxial growth. We observe an enhanced PL intensity and PL peak shift of the MoS2/PTCDA heterojunction compared with the solo MoS2 and PTCDA layer. The synergistic PL characteristics are believed to originate from the hybridization interaction between the MoS2 and the PTCDA as evidenced by density functional theory calculations and Raman measurements. The hybridization interfacial interaction is found to be greatly influenced by the crystalline ordering of the PTCDA film on the 2D MoS2. Our study opens up a new avenue to tune the PL of vdW heterojunctions consisting of TMDs and organic semiconductors for optoelectronic applications.

Synthesis of Easily Transferred 2D Layered BiI3 Nanoplates for Flexible Visible-Light Photodetectors

Bismuth triiodide, BiI₃, is one of the promising 2D layered materials from the family of metal halides. The unique electronic structure and properties make it an attractive material for the room-temperature gamma/X-ray detectors, high-efficiency photovoltaic absorbers, and Bi-based organic-inorganic hybrid perovskites. Other possibilities including optoelectronic devices and optical circuits are envisioned but rarely experimentally confirmed yet. Here, we report the synthesis of vertical 2D BiI₃ nanoplates using the physical vapor deposition mechanism. The obtained products were found easy to be separated and transferred to other substrates. Photodetectors employing such 2D nanoplates on polyethylene terephthalate substrate are demonstrated to be quite sensitive to red light (635 nm) with good responsivity (2.8 A W^-1), fast stable photoresponse (3/9 ms for raise/decay times), and remarkable specific detectivity (1.2 × 10¹² jones), which attest to high comparability of the assembled components with many latest 2D nanostructured light sensors. In addition, such photodetectors exhibit outstanding mechanical stability and durability under different bending strains within the theoretically affordable levels, suggesting a variety of potential applications of 2D BiI₃ for flexible devices.

2D library beyond graphene and transition metal dichalcogenides: a focus on photodetection

Two-dimensional materials beyond graphene and TMDs can be promising candidates for wide-spectra photodetection.

Damage-free and rapid transfer of CVD-grown two-dimensional transition metal dichalcogenides by dissolving sacrificial water-soluble layers

As one of the most important family members of two-dimensional (2D) materials, the growth and damage-free transfer of transition metal dichalcogenides (TMDs) play crucial roles in their future applications. Here, we report a damage-free and highly efficient approach to transfer single and few-layer 2D TMDs to arbitrary substrates by dissolving a sacrificial water-soluble layer, which is formed underneath 2D TMD flakes simultaneously during the growth process. It is demonstrated, for monolayer MoS₂, that no quality degradation is found after the transfer by performing transmission electron microscopy, Raman spectroscopy, photoluminescence and electrical transport studies. The field effect mobility of the post-transfer MoS₂ flakes was found to be improved by 2-3 orders compared with that of the as-grown ones. This approach was also demonstrated to be applicable to other TMDs, other halide salts as precursors, or other growth substrates, indicating its universality for other 2D materials. Our work may pave the way for material synthesis of future integrated electronic and optoelectronic devices based on 2D TMD materials.

Centimeter-Scale 2D van der Waals Vertical Heterostructures Integrated on Deformable Substrates Enabled by Gold Sacrificial Layer-Assisted Growth

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as molybdenum or tungsten disulfides (MoS₂ or WS₂) exhibit extremely large in-plane strain limits and unusual optical/electrical properties, offering unprecedented opportunities for flexible electronics/optoelectronics in new form factors. In order for them to be technologically viable building-blocks for such emerging technologies, it is critically demanded to grow/integrate them onto flexible or arbitrary-shaped substrates on a large wafer-scale compatible with the prevailing microelectronics processes. However, conventional approaches to assemble them on such unconventional substrates via mechanical exfoliations or coevaporation chemical growths have been limited to small-area transfers of 2D TMD layers with uncontrolled spatial homogeneity. Moreover, additional processes involving a prolonged exposure to strong chemical etchants have been required for the separation of as-grown 2D layers, which is detrimental to their material properties. Herein, we report a viable strategy to universally combine the centimeter-scale growth of various 2D TMD layers and their direct assemblies on mechanically deformable substrates. By exploring the water-assisted debonding of gold (Au) interfaced with silicon dioxide (SiO₂), we demonstrate the direct growth, transfer, and integration of 2D TMD layers and heterostructures such as 2D MoS₂ and 2D MoS₂/WS₂ vertical stacks on centimeter-scale plastic and metal foil substrates. We identify the dual function of the Au layer as a growth substrate as well as a sacrificial layer which facilitates 2D layer transfer. Furthermore, we demonstrate the versatility of this integration approach by fabricating centimeter-scale 2D MoS₂/single walled carbon nanotube (SWNT) vertical heterojunctions which exhibit current rectification and photoresponse. This study opens a pathway to explore large-scale 2D TMD van der Waals layers as device building blocks for emerging mechanically deformable electronics/optoelectronics.

Flexible Device Applications of 2D Semiconductors

Graphene-like single- or few-layer semiconductors, such as dichalcogenides and buckled nanocrystals, possess direct and tunable bandgaps, and excellent electrical, optical, mechanical and thermal properties. This unique set of desirable properties of 2D semiconductors has triggered great interest in developing ultra-thin 2D flexible electronic devices, which ranges from realizing better material quality and simplified fabrication processes, to improving device performance and expanding the application horizon. The most explored 2D flexible devices based on transition metal dichalcogenides and black phosphorous include field-effect transistors, optoelectronics, electronic sensors and supercapacitors. By taking advantage of a large portfolio of materials and properties of 2D crystals, a new generation of low-cost, high-performance, transparent, flexible and wearable devices looks attractive and promising in advancing flexible electronic technologies.

Probing the crystallographic orientation of two-dimensional atomic crystals with supramolecular self-assembly

Probing the crystallographic orientation of two-dimensional (2D) materials is essential to understand and engineer their properties. However, the nondestructive identification of the lattice orientations of various 2D materials remains a challenge due to their very thin nature. Here, we identify the crystallographic structures of various 2D atomic crystals using molecules as probes by utilizing orientation-dependent molecule–substrate interactions. We discover that the periodic atomic packing of 2D materials guides oleamide molecules to assemble into quasi-one-dimensional nanoribbons with specific alignments which precisely indicate the lattice orientations of the underlying materials. Using oleamide molecules as probes, we successfully identify the crystallographic orientations of ~12 different 2D materials without degrading their intrinsic properties. Our findings allow for the nondestructive identification of the lattice structure of various 2D atomic crystals and shed light on the functionalization of these 2D materials with supramolecular assembly.

Identifying the crystallographic orientations of 2D materials is important, but methods to do so are typically destructive. Here, the authors show that the orientational dependency of self-assembled nanoribbons of oleamide molecules can be used to non-invasively probe the lattice orientations of various 2D substrates.

In-Plane Anisotropies of Polarized Raman Response and Electrical Conductivity in Layered Tin Selenide

The group IV-VI compound tin selenide (SnSe) has recently attracted particular interest due to its unexpectedly low thermal conductivity and high power factor and shows great promise for thermoelectric applications. With an orthorhombic lattice structure, SnSe displays intriguing anisotropic properties due to the low symmetry of the puckered in-plane lattice structure. When thermoelectric materials, such as SnSe, have decreased dimensionality, their thermoelectric conversion efficiency may be improved due to increased power factor and decreased thermal conductivity. Therefore, it is necessary to elucidate the complete optical and electrical anisotropies of SnSe nanostructures in realizing the material's advantages in high-performance devices. Here, we synthesize single-crystal SnSe nanoplates (NPs) using the chemical vapor deposition method. The SnSe NPs' polarized Raman spectra exhibit an angular dependence that reveals the crystal's anomalous anisotropic light-matter interaction. The Raman's anisotropic response has a dependence upon the incident light polarization, photon, and phonon energy, arising from the anisotropic electron-photon and electron-phonon interactions in the SnSe NPs. Finally, angle-resolved charge-transport measurements indicate strong anisotropic conductivity of the SnSe NPs, fully elucidating the anisotropic properties necessary for ultrathin SnSe in electronic, thermoelectric, and optoelectronic devices.