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MoS2 is widely used in many fields including spin-valleytronics, logic transistors, light emitting devices, clean energy and biology. However, controllable synthesis of two-dimensional MoS2 sheets remains a great challenge. We report the formation of round-shaped monolayer MoS2 domains with a tunable size and the shape transformation from triangle...
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... The demand for image sensors is increasing rapidly due to technological advancement in devices including visual recognition, medical imaging, surveillance systems, robotic technologies, quality assurance, and defense applications, emphasizing the need for high-performance device technologies [1][2][3][4][5]. The technology advancements are achieved by extensive research on the structural modification and miniaturization of the device as well as the application of two-dimensional (2D) materials like graphene, BP, hBN, and transition metal dichalcogenides (TMDs), such as MoS 2 , MoSe 2 , MoTe 2 , WSe 2 , PdSe 2 , and PtSe 2 [6][7][8][9][10][11][12]. These materials have also innovated flexible and wearable electronics. ...
The demand for photodetectors and image sensors has grown exponentially in the past decade in biomedical, security surveillance, robotics, automotive, quality control, image recognition, and military applications, due to their superior quality, broadband detection, lower noise, and economic viability. Here, we report a MoS2 channel-based phototransistor over an HfO2/n-Si substrate isolated by an hBN layer. The high photoresponse is achieved through the integration of the photoconduction, photogating, and mobility enhancement process by utilizing excellent features of MoS2, HfO2/Si, and hBN. The capacitive coupling of the photogenerated carriers by high-k dielectric HfO2 leads to modulation of MoS2 Fermi level due to electrostatic doping. Furthermore, the MoS2 also contributes to the photogeneration of carriers due to its semiconducting nature, leading to additional photocurrent. Ultimately, the combination of photogating, photoconduction, and swift carrier extraction with remarkable mobility of 11.65 cm2 · V−1 · s−1 results in high responsivity, external quantum efficiency, and detectivity of 4.5 × 108 A · W−1, 0.72 × 106, and 6.20 × 1016 Jones at 266 nm illumination, respectively. The device also demonstrates broadband photoresponse from 266–1000 nm wavelengths. The high responsivity distinguishes the potential of our device for the future of optoelectronics and broadband image sensing applications.
... 6 Similarly, a MoS 2 domain shapes of mainly round, nearly round and hexagonal, truncated triangles, and triangles are observed at the temperatures of the MoO 3 precursor of 760 • C, 750 • C, 730 • C, and 710 • C, respectively. 7 The density and size of the domain have also been shown to decrease with temperature, 7,8 with a random orientation of the MoS 2 domain associated with the growth temperature below 850 • C 9 or at a much higher temperature. 10 In the former, the authors linked the phenomenon to the inability to achieve a thermodynamically stable state at the lower temperature, and in the latter, the inferred culprit is the step edges and step edge meanderings of sapphire substrate surface. ...
... 6 Similarly, a MoS 2 domain shapes of mainly round, nearly round and hexagonal, truncated triangles, and triangles are observed at the temperatures of the MoO 3 precursor of 760 • C, 750 • C, 730 • C, and 710 • C, respectively. 7 The density and size of the domain have also been shown to decrease with temperature, 7,8 with a random orientation of the MoS 2 domain associated with the growth temperature below 850 • C 9 or at a much higher temperature. 10 In the former, the authors linked the phenomenon to the inability to achieve a thermodynamically stable state at the lower temperature, and in the latter, the inferred culprit is the step edges and step edge meanderings of sapphire substrate surface. ...
... The grain size and crystal coverage of the the MoS 2 have also been shown to be tunable with the growth time. 7 The authors showed that the grain size increased when the growth time was increased from 20 minutes to 30 minutes. With the materials grown for 45 minutes, the grains merged to form a continuous MoS 2 . ...
... 2D materials and Si Nanocomposites: Since the first realization of graphene in 2004 [367], various graphene like 2D materials such as transition metal dichalcogenides, black phosphorus, metallic sulfide compounds and etc have been explored for several applications including antibacterial [79,368] 2D material systems exhibit interesting energy band structure, photo-electronics, electrical and magnetic properties which may provide new opportunities for advanced medical applications. [369][370][371] Notably, some 2D materials also found to be lethal to microorganism and fungi. [79] These materials possess several advantages such as ultra large specific area for drug loading, chemically and physically neutralizing bacteria, high density of active site and outstanding photothermal/photocatalyst properties compared to other materials and their topology [372,373]. ...
Silicon (Si) nanomaterials are extensively explored to address the multidrug resistance bacteria/diseases and to enable developments of novel and innovative approaches for next-generation highly efficient, cost-effective, and reliable multifunctional biomedical tools. This article reviews the contemporary developments in the utilization of Si nanostructures (Si-NSs) and nanocomposites for antibacterial surfaces and theranostic agents as powerful instruments to tackle pathogenic bacteria and diseases related to them. Realization of nature-inspired antibacterial surfaces, photoresponsive smart antibacterial surfaces, and selective functionality of Si-NSs has been discussed by biomedical imaging and drug delivery applications of Si-NSs. Photoresponsive Si nanocomposite systems enable in-situ non-invasive process monitoring utilizing surface-enhanced Raman spectroscopy (SERS) or photothermal imaging phenomenon is also addressed. Finally, crucial challenges and several research trends of implementing Si-NSs and their hybrid systems as multifunctional platforms for advanced biomedical tools and their clinical translation are highlighted.
... Exposure to many active sites by exfoliation in multiple layers or a single layer using ultrasonic Liquidphase exfoliation (LPE) can easily be done [34] . For example, bulk MoSx obtained by thermal decomposition of (NH4)2MoS4 can be exfoliated in a suitable polar micromolecular solvent into monolayers or individual nanoflakes using ultrasonic radiation [62,63] . This process creates a force greater than the Van der Waals attraction between the layers, causing the bulk structure to crumble and be sliced into single-layer nanotubes that can easily be dispersed in polar micromolecular solvents. ...
... Rounded MoS 2 was synthesized before and control over its shape occurred by changing the growth temperature, leading to round, nearly round, hexagonal or truncated triangular structures, therefore serving as a proof-of-concept that the concentration of precursor on the surface can heavily affect the shape of the 2D crystals [61]. ...
... In figure 4(b), the PL spectra of the samples grown at lower temperatures are blue shifted with respect to the one from the sample grown with the pristine powder at a higher temperature. It was shown before that charge density heavily influences the PL spectra and that the two factors that can strongly affect charge density and, consequently, the PL spectra are doping and strain [61,64]. Grain boundaries and edges of the flakes are the regions with a high number of defects and cell reconstructions, in turn, produce local changes in doping and strain [64]. ...
Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been proposed for a wide variety of applications, such as neuromorphic computing, flexible field effect transistors, photonics, and solar cells, among others. However, for most of these applications to be feasible, it is necessary to integrate these materials with the current existing silicon technology. Although chemical vapor deposition (CVD) is a promising method for the growth of high-quality and large-area TMD crystals, the high temperatures necessary for the growth make this technique incompatible with the processes used in the semiconductor industry. Herein, we demonstrate the possibility of low-temperature growth of TMDs, using tungsten selenide (WSe2) as a model, by simply using moisture-assisted defective tungsten oxide (WO3) precursor powders during the growth of these materials. DFT calculations reveal the mechanism by which moisture promotes the defect formation on the precursor crystal structure and how it dictates the reduction of the temperature of the growth. The results were compared with the standard growth at high temperatures and with a precursor mixture with alkali salts to show the high quality of the WSe2 grown at temperatures as low as 550 °C. To conclude, the work improves the understanding of nucleation and growth mechanisms of WSe2 at low temperatures and provides a useful strategy for the growth of TMDs at temperatures required for the back-end-of-line (BEOL) compatibility with current silicon technology.
... Thus, it is crucial to investigate materials with neuromorphic behaviors and potential compatibility with Si technology, as well as to elucidate their underlying mechanism for further SNN applications. Recently, two-dimensional (2D) materials have come to the fore in materials science research, which demonstrate their superior fine-tuning electronic properties enabling the feasible device structure design [21][22][23][24][25][26][27][28][29] . Silicon nanosheets (SiNSs) are 2D thin films of Si which have different crystalline structures than bulk Si, while are potentially compatible with well-developed Si technology. ...
Silicon is vital for its high abundance, vast production, and perfect compatibility with the well-established CMOS processing industry. Recently, artificially stacked layered 2D structures have gained tremendous attention via fine-tuning properties for electronic devices. This article presents neuromorphic devices based on silicon nanosheets that are chemically exfoliated and surface-modified, enabling self-assembly into hierarchical stacking structures. The device functionality can be switched between a unipolar memristor and a feasibly reset-able synaptic device. The memory function of the device is based on the charge storage in the partially oxidized SiNS stacks followed by the discharge activated by the electric field at the Au-Si Schottky interface, as verified in both experimental and theoretical means. This work further inspired elegant neuromorphic computation models for digit recognition and noise filtration. Ultimately, it brings silicon - the most established semiconductor - back to the forefront for next-generation computations.
... Next, growth occurs during the temperature ramp down process on the surface of Cu in contact with sapphire, and a mix of triangular and round crystal edges can be observed as shown in the optical image in figure 1(a). Although the triangular geometry is thermodynamically favorable, the abundance of precursor Cu and high reaction temperature may push to a kinetically controlled rapid growth, leading to some round crystal edges [26,27]. Random, non-uniform distribution of crystals throughout the copper surface suggests saturation via the molten catalyst. ...
Transition metal dichalcogenides (TMDs) are known for their layered structure and tunable functional properties. However, a unified understanding on other transition metal chalcogenides (i.e., M2X) is still lacking. Here, the relatively new class of copper-based chalcogenides Cu2X (X=Te, Se, S) is thoroughly reported. Cu2X are synthesized by an unusual vapor-liquid assisted growth on a Al2O3/Cu/W stack. Liquid copper plays a significant role in synthesizing these layered systems, and sapphire assists with lateral growth and exfoliation. Similar to traditional TMDs, thickness dependent phonon signatures are observed, and high-resolution atomic images reveal the single phase Cu2Te that prefers to grow in lattice-matched layers. Charge transport measurements indicate a metallic nature at room temperature with a transition to a semiconducting nature at low temperatures accompanied by a phase transition, in agreement with band structure calculations. These findings establish a fundamental understanding and thrust Cu2Te as a flexible candidate for wide applications from photovoltaics and sensors to nanoelectronics.
... The stabilization energies of these three edges increase successively because of the increase in kink density [62][63][64]. Because the interfacial interaction between graphene and the Ru(0001) surface is significantly weakened by near-surface Ar nanobubbles, graphene overlayers are quasi-freestanding and display intrinsic properties [20,65]. Ru(0001) surfaces adopt a high catalytic activity for the decomposition of O 2 into O atoms, which provides sufficient etching agents [54]. ...
The synthesis of high-quality ultrathin overlayers is critically dependent on the surface structure of substrates, especially involving the overlayer-substrate interaction. By using in situ surface measurements, we demonstrate that the overlayer-substrate interaction can be tuned by doping near-surface Ar nanobubbles. The interfacial coupling strength significantly decreases with near-surface Ar nanobubbles, accompanying by an “anisotropic to isotropic” growth transformation. On the substrate containing near-surface Ar, the growth front crosses entire surface atomic steps in both uphill and downhill directions with no difference, and thus, the morphology of the two-dimensional (2D) overlayer exhibits a round-shape. Especially, the round-shaped 2D overlayers coalesce seamlessly with a growth acceleration in the approaching direction, which is barely observed in the synthesis of 2D materials. This can be attributed to the immigration lifetime and diffusion rate of growth species, which depends on the overlayer-substrate interaction and the surface catalysis. Furthermore, the “round to hexagon” morphological transition is achieved by etching-regrowth, revealing the inherent growth kinetics under quasi-freestanding conditions. These findings provide a novel promising way to modulate the growth, coalescence, and etching dynamics of 2D materials on solid surfaces by adjusting the strength of overlayer-substrate interaction, which contributes to optimization of large-scale production of 2D material crystals.
... This process creates a force greater than the Van der Waals attraction between the layers, causing the bulk structure to crumble and be sliced into single-layer nanotubes that can easily be dispersed in polar micromolecular solvents. The criteria for selecting a surfactant or solvent are based on the similarity between the liquid's surface tension and the absorbent surface's free energy [54]. LPE results in high exfoliation success on materials with low surface energy and can prevent agglomeration of MS NSs [55] in contrast to mechanical exfoliation, where much of the resulting MSs are multilayer structures, which still blocked the efficient active sites in comparison with that in the well-dispersed single-layer structure [3]. ...
... Precursors (usually molybdenum trioxide (MoO 3 ) or Mo metal and organic sulfides, respectively) containing Mo and S decompose, and the Mo and S atoms then combine via chemical reactions to form a MoS 2 layer on the substrate, usually at temperatures between 700 and 1000 • C, in the Chemical Vapor Deposition (CVD) process [12,54]. However, the temperature range is reduced to 150-300 • C with a modified version of CVD, called the Plasma Enhanced CVD (PECVD) technique, which allows the deposition of NMs on plastic and flexible substrates [75]. ...
Heavy metals pollution of aqueous solutions generates considerable concerns as they adversely impact the environment and health of humans. Among the remediation technologies, adsorption with metal sulfide nanomaterials has proven to be a promising strategy due to their cost-effective, environmentally friendly, surface modulational, and amenable properties. Their excellent adsorption characteristics are attributed to the inherently exposed sulfur atoms that interact with heavy metals through various processes. This work presents a comprehensive overview of the sequestration of heavy metals from water using metal sulfide nanomaterials. The common methods of synthesis, the structures, and the supports for metal sulfide nano-adsorbents are accentuated. The adsorption mechanisms and governing conditions and parameters are stressed. Practical heavy metal remediation application in aqueous media using metal sulfide nanomaterials is highlighted, and the existing research gaps are underscored.
... Such a growth process belongs to the thermodynamic control. 59,60 To further probe this growth process, we conducted a series of atomic force microscopy (AFM) observations. Figure S3a shows an AFM image of the γ-Fe 2 O 3 nanoflakes at the initial stage, where three branches grow in different directions by tiny triangular sheets. ...
... Such transformation reveals that the growth undergoes a transition from thermodynamically to kinetically dominated control, which successfully realizes morphology-tunable synthesis. 59,70 Moreover, the γ-Fe 2 O 3 nanoflakes are found to be air-stable, which can be stored in air for 3 months ( Figure S6). ...
