Vertical Nanosheets Research Articles

Layer and orientation dependent optical anisotropic response of CVD grown MoS2 films under resonance/non-resonance excitation

The MoS2hasgained worldwide research interest owing to their strong light-matter interaction and their rich physics that offers unprecedented potential for next-generation nanotechnology applications. Theirelectrical and thermal properties are mainly governed by interaction mechanism of electrons with phonons and thus, studying the polarization-dependent anisotropic phonon response ofMoS2are of great interest. Here, we discuss the evolution of phonon modes with increasing layer number and their respective phonon DOS. Further, the optical anisotropic responseis experimentally investigated using ARPRSstudy for CVD-grown triangular MoS2with different layer numbers and different excitations, and has been discussedbased ontheory that includes deformation potential and Fröhlich interaction.Further, the ARPRS study of horizontally and vertically oriented MoS2films are studied. Thedifferent anisotropic response of vertically oriented film is observed due to symmetry breaking of the vertical nanosheets, thus providing wide-field applications in MoS2-based photonic and optoelectronic devices.

Simulation of different structured gate-all-around FETs for 2 nm node

This paper compares different types of Gate All Around (GAA) FET structures using TCAD simulation, including Lateral Nanosheet, Lateral Nanowire, Vertical Nanosheet, and Vertical Nanowire. The increase in electrostatic control and reduced short channel effects are key benefits to adopting GAAFET structures to meet scaling requirements for next generation process nodes. To understand channel geometry impacts on performance, the channel effective width (Weff) is swept around the projected dimensions, including ratio of height and width parameters. The performance is evaluated using the key device metrics such as on-state current (Ion), off-state current (Ioff), and threshold voltage (Vt) for transfer characteristics, and drain-induced barrier lowering (DIBL), subthreshold slope (SS), and gate induced drain leakage (GIDL) for short-channel effects. It is observed that thinner channel geometries, as often seen implemented in Nanosheet structures, have major benefits across SCE and Ioff metrics compared to more symmetrically square shaped channels. Additionally, stacking channels as a means to increase Weff appears to be an attractive option for increasing performance without significant increase in SCEs observed. For bulk technology the ratio between height and width of a Nanosheet structure can be optimized to reduce parasitic channel influence, so that optimal Ion/Ioff ratio is achieved.

In situ synthesis of vertical graphene on porous Si microparticle composite for high-performance anode material

Silicon is capable of delivering a high theoretical specific capacity (4200 mAh g-1) in lithium-ion batteries. However, silicon has poor electrical conductivity, huge volume expansion (∼300%), and unstable solid electrolyte interface (SEI) film, especially for micron-sized silicon particles. We proposed and prepared a novel vertical carbon (VG) coating on a porous silicon (p-Si) microparticle structure, which effectively alleviated the volume expansion and inhibited the interface reaction. The synthesized porous silicon p-Si@VG composite exhibited significant enhanced cycling stability and an excellent reversible capacity of 1563 mAh g-1 (capacity retention of 48.6%) after 200 cycles. The vertical carbon nanosheet structure constructed a three-dimensional conductive network. Therefore, the p-Si@VG composite showed better rate capability and higher lithium-ion diffusion rates. This work is expected to promote the application of micron Si-based composites in lithium-ion batteries.

Optimization of Al-doped NiCo2O4 hybrid nanostructures and their electrochemical activation feature in supercapacitors

The performance of supercapacitors majorly depends on electrode materials, while optimizing the composition and microstructure of materials is the key for boosting electrochemical activity. Herein, Al-doping and electrochemical activation strategy are combined to boost the electrochemical activity of NiCo2O4. The influence of Al dopant dosage on the performance is discussed firstly. With an increasing Al3+ dosage, Al-doped samples show a morphology transition from nanoneedles to hybrid structures of nanowire/nanosheet. Optimized Al1.0-NiCo2O4 sample with hybrid nanostructures delivers the highest areal capacitance of 8.22 F cm−2 at 1 mA cm−2, much higher than that of pristine NiCo2O4 and other Al-doped samples. Serving as a working electrode, the activation of Al1.0-NiCo2O4 is conducted to induce the reconstruction of microstructure and composition. When activated for 200 cycles, expansive rod structures consisted of vertical nanosheets are generated, which presents a high areal capacitance of 9.93 F cm−2. Under the same operating conditions, the activation is also proceeded on the Al0.5-NiCo2O4 sample with only nanowires. The maximum capacitance reaches 6.49 F cm−2, much lower than that of activated Al1.0-NiCo2O4, due to the absence of nanosheets in Al0.5-NiCo2O4. The activation process is confirmed as the structure transition from nanoparticles to thin nanosheets, with the composition transition from initial Al-doped NiCo2O4 to NiCoAl-OH/OOH. When applied in an asymmetric supercapacitor, the NF/Al1.0-NiCo2O4 electrode presents a superior electrochemical performance and a charge/discharge activation feature.

Terahertz-polarizing effect based on geometric anisotropy of Ti3C2Tx MXene nanosheets

Two-dimensional (2D) nanomaterials have garnered considerable attention due to their unique properties, such as thinness and excellent electronic properties. The inherent anisotropy of 2D nanomaterials, which is characterized by their high aspect ratio, can maximize the directional functionality to enhance the conductivity and utilization of edges. Here, we demonstrate how to utilize the edges of titanium carbide (Ti3C2Tx) MXene nanosheet to control the linear polarization in the terahertz (THz) frequency range. By a simple and unique vertical alignment exploiting the high surface charge and excellent colloidal dispersibility of MXene nanosheets, MXene nanosheets are vertically oriented along an applied AC electric field. The well-aligned edges justify the THz polarizing effect, revealing outstanding performances such as the broadband coverage in 0.2–1.5 THz and an exceptional extinction ratio reaching 20 dB. Furthermore, we vary the local orientation of the vertical MXene nanosheets by tailoring the applied electric field, enabling spatially controllable polarization capabilities. Our results can provide a generic tool for the utilization of 2D nanomaterials in diverse potential applications in optics and electronics.

Nanoscale Local Contacts Enable Inverted Inorganic Perovskite Solar Cells with 20.8 % Efficiency.

Inorganic perovskite solar cells (IPSCs) have gained significant attention due to their excellent thermal stability and suitable band gap (~1.7 eV) for tandem solar cell applications. However, the defect-induced non-radiative recombination losses, low charge extraction efficiency, energy level mismatches, and so on render the fabrication of high-efficiency inverted IPSCs remains challenging. Here, the use of 3-amino-5-bromopyridine-2-formamide (ABF) in methanol was dynamically spin-coated on the surface of CsPbI2.85Br0.15 film, which facilitates the limited etching of defect-rich subsurface layer, resulting in the formation of vertical PbI2 nanosheet structures. This enabled localized contacts between the perovskite film and the electron transport layer, suppress the recombination of electron-hole and beneficial to electron extraction. Additionally, the C=O and C=N groups in ABF effectively passivated the undercoordinated Pb2+ at grain boundaries and on the surface of CsPbI2.85Br0.15 film. Eventually, we achieved a champion efficiency of 20.80 % (certified efficiency of 20.02 %) for inverted IPSCs with enhanced stability, which is the highest value ever reported to date. Furthermore, we successfully prepared p-i-n type monolithic inorganic perovskite/silicon tandem solar cells (IPSTSCs) with an efficiency of 26.26 %. This strategy provided both fast extraction and efficient passivation at the electron-selective interface.

Nanoscale Local Contacts Enable Inverted Inorganic Perovskite Solar Cells with 20.8 % Efficiency

AbstractInorganic perovskite solar cells (IPSCs) have gained significant attention due to their excellent thermal stability and suitable band gap (~1.7 eV) for tandem solar cell applications. However, the defect‐induced non‐radiative recombination losses, low charge extraction efficiency, energy level mismatches, and so on render the fabrication of high‐efficiency inverted IPSCs remains challenging. Here, the use of 3‐amino‐5‐bromopyridine‐2‐formamide (ABF) in methanol was dynamically spin‐coated on the surface of CsPbI2.85Br0.15 film, which facilitates the limited etching of defect‐rich subsurface layer, resulting in the formation of vertical PbI2 nanosheet structures. This enabled localized contacts between the perovskite film and the electron transport layer, suppress the recombination of electron‐hole and beneficial to electron extraction. Additionally, the C=O and C=N groups in ABF effectively passivated the undercoordinated Pb2+ at grain boundaries and on the surface of CsPbI2.85Br0.15 film. Eventually, we achieved a champion efficiency of 20.80 % (certified efficiency of 20.02 %) for inverted IPSCs with enhanced stability, which is the highest value ever reported to date. Furthermore, we successfully prepared p‐i‐n type monolithic inorganic perovskite/silicon tandem solar cells (IPSTSCs) with an efficiency of 26.26 %. This strategy provided both fast extraction and efficient passivation at the electron‐selective interface.

Hierarchical FeOxHy@Ni3B hybrid for efficient alkaline oxygen evolution at high current density

Electrocatalysts with high activity and long-term durability are vital toward large-scale hydrogen production from electrocatalytic water splitting. Here, the self-supported electrode (FeOxHy@Ni3B/NF) with hierarchical heterostructure was simply prepared by using Ni3B chunks grown on nickel foam as substrate to in situ form vertical FeOxHy nanosheets. Such hybrid shows efficient oxygen evolution reaction activity with overpotentials as low as 267 and 249 mV at 100 mA cm−2 in 1 M KOH solution and 30 wt% KOH solution, respectively. Meanwhile, it also exhibits excellent catalytic stability, sustaining catalysis at 500 mA cm−2 in 1 M KOH solution for 200 h, and even for 200 h at 1000 mA cm−2 in 30 wt% KOH solution. Further experimental results reveal that the FeOxHy@Ni3B/NF is endowed with superhydrophilic and superaerophobic surface properties, which not only provide more mass transport channels, as well as facilitated the diffusion of reaction intermediates and gas bubbles. Also, it holds faster reaction kinetics, more accessible active sites and accelerated electron transfer rates due to strong synergistic interactions at the heterogeneous interface.

Directional guiding of mass and charge transfer via vertically aligned graphite nanosheets for high-rate and ultralong lifespan Dual-ion batteries

Cathode materials based on graphite for dual-ion batteries (DIBs) demonstrate multifarious merits, such as abundant resources and high anion interaction potential etc. However, the traditional irregular spherical graphite cathodes suffer from uneven anion migration through the highly tortuous pathways and the inductive anisotropic electric fields, leading to mass transfer non-uniformity and sluggish reaction kinetics. Simultaneously, large-sized anions and solvent co-intercalation restrict the anion intercalation behavior and cause severe intercalation volume expansion. To address these challenges, the vertical graphite nanosheets (VGNs) were designed to guide the anion transport directionally for the first time. The perpendicular open structures of VGNs regulate the uniform ion gradient and electric field for rapid anion diffusion by the directional and shortened ion channels with low electrode tortuosity. Meanwhile, the ordered tunnels buffer the intercalation volume expansion, enhancing the structural stability. Consequently, the DIBs with the VGNs as cathodes deliver an impressive discharge specific capacity of ∼ 220 mAh/g at 300 mA g−1, superior rate capability of up to 2000 mA g−1, and excellent cycling stability without obvious degradation after 2000 cycles, which surpasses those of reported DIBs based on anion intercalation cathodes significantly. This investigation on vertically aligned graphite nanosheets provides insights for the development of highly efficient nanomaterials for energy storage systems.

Efficient CO2 electroreduction to formate using Bi–Pb bimetallic catalysts with 2D vertical nanosheets

2D vertical Bi–Pb bimetallic nanosheets with an electron transfer effect were used to broaden the potential window of the CO2RR.

The photocatalyst with a strong internal electric field grown in situ on the surface of copper foam collaborates with peroxymonosulfate to enhance directional charge transfer and achieve ultra-fast Mn+/M(n+1)+ cycling

To address three pressing problems that limit the application of photocatalytic synergic peroxymonosulfate (PMS) technology, namely difficult reuse, low photogenerated carrier separation efficiency, and sluggish metallic ions redox cycle, we utilized an in-situ growth method to construct a vertical nanosheet heterojunction on the surface of copper foam (CF). This heterojunction is characterized by a strong internal electric field (IEF) that serves as both a “pump” for the rapid and efficient migration of electrons and a driving force for the activation of PMS by these electrons. In the CF@CCS@CO-3/7/Vis/PMS system, the photoelectrons generated by photocatalysis quickly replenish the high valence metals activated by PMS, allowing for highly efficient cycling of differently valenced metal ions and reducing the dissolution of high valence metal ions produced by PMS. As a result, close to 100 % of ciprofloxacin (CIP) was degraded within 60 min in the CF@CCS@CO-3/7/Vis/PMS system with a reaction rate constant k of 0.0621 min−1, which is about 3.22 times higher than that of the CF@CCS@CO-3/7/Vis system and 2.65 times higher than that of the CF@CCS@CO-3/7/PMS system. Moreover, the in-situ growth of active ingredients with vertical nanosheet structure on the CF surface can well maintain structure and reactivity in complex environments, allowing more than 10 cycles to be realized. The results of the free radical burst assay and EPR analysis indicated that SO4∙−, ∙O2− and h+ were the main reactive species involved in the catalytic process. Building upon CF@CCS@CO-3/7, we assembled a fixed-bed continuous treatment device that enables high mineralization flow treatment of pharmaceutical wastewater (after Secondary biological treatment).

Asymmetric Sandwich Janus Structure for High‐Performance Textile‐Based Thermo–Hydroelectric Generators Toward Human Health Monitoring

AbstractTextile‐based generators that can convert low‐grade energy from the human body or environment into sustainable electricity have generated immense scientific interest in self‐powered wearable applications. However, their low power density and environmental suitability have extremely restricted their portable applications in complex and mutable environments. Herein, an asymmetric sandwich structure between molybdenum disulfide (MoS2)‐carbonized silks (MCs) and MoS2/MXene–Cottons (MMCs) to construct efficient thermo–hydroelectric generators (THEGs) that synergistically harvest heat‐moisture energy to generate considerable electricity is rationally designed. Notably, the large surface area of MoS2/MXene van der Waals heterojunctions (vdWhs) enables efficient charge collection, and the vertical MoS2 nanosheet arrays supply abundant nanochannels for a highly efficient hydration effect, generating an output power density of 32.26 µW cm−2 after wetting with deionized water. Combined with the sensitive temperature recognition ability with a Seebeck coefficient of 23.5 µV K−1, the application possibilities of these prepared THEGs in the mutual conversion of fingertip temperature/language, and the monitoring of the human physiological state is foresee.

Optical signature of the formation of vertical HfS2 nanosheets grown on sapphire substrate

Semiconducting hafnium disulfide (HfS2), a group IVB two-dimensional transition metal dichalcogenide (TMD), has been investigated extensively due to its predicted superior physical properties. Herein, we investigate the formation of vertical HfS2 nanosheets on a sapphire substrates with diffuse reflectance. The samples were grown using chemical vapor deposition (CVD) by varying HfCl4 supply to control the evolution of the HfS2 nanosheets. There is an increase in diffuse reflectance in the range of 400–800 nm, with a peak at 498 nm, once vertical HfS2 nanosheets are successfully grown with sufficient HfCl4 supply. Raman scattering spectroscopy, scanning electron microscopy, and 2θ X-ray diffraction measurements confirmed the formation of HfS2 nanosheets. Our observations can provide guidance on a quantitative and non-destructive route to monitor the evolution and formation of vertical HfS2 nanosheets.

Vertical and porous MoS2-CoS2 heterojunction nanosheet arrays as highly efficient bifunctional electrocatalysts for oxygen and hydrogen evolutions

Highly efficient water electrolytic agents are restricted by the lack of cheap and Earth-abundant catalysts that can manipulate at unharsh conditions and be prepared with a simple procedure. Here, hierarchically vertical and porous MoS2-CoS2 heterojunction nanosheet arrays are designed and fabricated. The MoS2-CoS2 nanosheets are composed of ultrasmall nanocrytallites with the dimension of ∼62 nm. This special and novel architecture presents synergistic properties to create excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), where high density active sites generated by ultrasmall nanocrytallites with heterostructures, and the vertical and porous structure accelerates electrolyte transport with luxuriant channels while this hierarchically collaborative framework guarantees completely exposed active sites to electrolytes. This electrode shows low overpotentials of 295 and 103 mV at 10 mA cm−2, small Tafel slopes of 70 and 78 mV dec−1, and long stability for OER and HER, respectively. This work indicates that vertical and porous heterojunction nanosheet arrays with hierarchically ultrasmall secondary nanostructures are a promising catalyst for widespread application.

Vertically molybdenum disulfide nanosheets on carbon cloth using CVD by controlling growth atmosphere for electrocatalysis

Molybdenum disulfide (MoS2) has been deemed as one of the promising noble-metal-free electrocatalysts for hydrogen evolution reaction (HER), but it suffers from the inert basal plane and low electronic conductivity. Regulating the morphology of MoS2 during the synthesis on conductive substrates is a synergistic strategy for enhancing the HER performance. In this work, vertical MoS2 nanosheets were fabricated on carbon cloth (CC) using an atmospheric pressure chemical vapor deposition method. The growth process could be effectively tuned through introducing hydrogen gas during vapor deposition process, resulting in nanosheets with increased edge density. The mechanism for edge-enriching through controlling the growth atmosphere is systematically studied. The as-prepared MoS2 exhibits excellent HER activity due to the combination of optimized microstructures and coupling with CC. Our findings provide new insights to design advanced MoS2-based electrocatalysts for HER.

High-Quality Recrystallization of Amorphous Silicon on Si (100) Induced via Laser Annealing at the Nanoscale

At sub-3 nm nodes, the scaling of lateral devices represented by a fin field-effect transistor (FinFET) and gate-all-around field effect transistors (GAAFET) faces increasing technical challenges. At the same time, the development of vertical devices in the three-dimensional direction has excellent potential for scaling. However, existing vertical devices face two technical challenges: “self-alignment of gate and channel” and “precise gate length control”. A recrystallization-based vertical C-shaped-channel nanosheet field effect transistor (RC-VCNFET) was proposed, and related process modules were developed. The vertical nanosheet with an “exposed top” structure was successfully fabricated. Moreover, through physical characterization methods such as scanning electron microscopy (SEM), atomic force microscopy (AFM), conductive atomic force microscopy (C-AFM) and transmission electron microscopy (TEM), the influencing factors of the crystal structure of the vertical nanosheet were analyzed. This lays the foundation for fabricating high-performance and low-cost RC-VCNFETs devices in the future.

Kinetically controlled composition of III-V ternary nanostructures

Controlling the composition of ternary III-V and III-nitride nanomaterials such as vertical nanowires, horizontal nanowires, nanosheets, and nanomembranes grown by different epitaxy techniques is essential for band gap engineering and fabrication of nanoheterostructures with tunable properties. Herein, we investigate the diffusion-induced growth process of III-V ternary materials in different geometries including planar layers, nanomembranes, and horizontal and vertical nanowires grown by selective area epitaxy or with a catalyst droplet on top and derive a rather general equation connecting the composition of ternary solid with the composition of vapor. The form of this vapor-solid distribution remains identical for a wide range of geometries, while the coefficients entering the equation contain thermodynamic factors, kinetic constants of the material transport, and geometrical parameters of the growth template. General properties of the vapor-solid distribution are investigated with respect to material constants, growth condition, and geometry, including the interplay of thermodynamics and growth kinetics leading to the suppression of the miscibility gaps in InGaAs and InGaN systems. A good correlation of the model with the data on the compositions of InGaAs, InGaP, and AlGaAs materials grown by different methods is demonstrated. Overall, these results give a simple analytical tool for understanding the compositional trends and compositional tuning of III-V ternary nanostructures, which should work equally well for Si-Ge and II-VI material systems.

Direct Growth of Patterned Vertical Graphene Using Thermal Stress Mismatch between Barrier Layer and Substrate

Vertical graphene (VG) combines the excellent properties of conventional graphene with a unique vertical nanosheet structure, and has shown tremendous promise in the field of electronics and composites. However, its complex surface morphology brings great difficulties to micro-nano fabrication, especially regarding photolithography induced nanosheet collapse and remaining chemical residues. Here, we demonstrate an innovative method for directly growing patterned VG on a SiO2/Si substrate. A patterned Cr film was deposited on the substrate as a barrier layer. The VG was synthesized by PECVD on both the patterned Cr film and the exposed SiO2/Si substrate. During the cooling process, the patterned Cr film covered by VG naturally peeled off from the substrate due to the thermal stress mismatch, while the VG directly grown on the SiO2/Si substrate was remained. The temperature-dependent thermal stress distribution in each layer was analyzed using finite element simulations, and the separation mechanism of the Cr film from the substrate was explained. This method avoids the contamination and damage caused by the VG photolithography process. Our work is expected to provide a convenient and reliable solution for the manufacture of VG-based electronic devices.

Enhanced non-layer-dependent piezo-response in sailboat-like vertical molybdenum disulfide nanosheets for piezo-catalytic hydrogen evolution and dye degradation: Effect of microstructure and phase composition

The piezo-response of two-dimensional molybdenum disulfide(MoS2) only exists at the edge of odd-number layers. It’s crucial to design reasonable micro/nano-structures and construct tight interfaces to weaken layer-dependence, enhance energy harvesting, charge transfer and active sites exposure to improve piezoelectricity. The novel sailboat-like-vertical-MoS2-nanosheets(SVMS), in which abundant vertical MoS2 nanosheets(∼20 nm, 1–5 layers) are uniformly distributed on horizontal substrate of MoS2, with abundant vertical interfaces and controllable phase composition are prepared by facile method. The larger geometric-asymmetry enhances mechanical energy capture. Experiment and theory revealed the enhanced in-/out-of-plane polarization, higher piezo-response in multi-directions and abundant active edge sites of SVMS, thereby eliminating the layer-dependence and generating higher piezo-potential. Cooperating with the Mo-S bonds at vertical interfaces, free electrons-holes are efficiently separated and migrated. The piezo-degradation of Rhodamine B(RhB) and hydrogen evolution rate under ultrasonic/stirring are 0.16 min−1 and 1598 μmolg−1h−1 for SVMS(2H) with the highest piezo-response (under ultrasonic wave, stirring and water flow), which are over 1.6 and 3.1 times than few-layer MoS2 nanosheets. 94% RhB(500 mL) is degraded under water-flow(60 min). The mechanism was proposed. Overall, the design of SVMS with enhanced piezoelectricity was studied and modulated by regulating microstructure and phase composition, which has excellent application potential in fields of environment, energy and novel materials.

Lithiophilic interface dynamic engineering to inhibit Li dendrite growth for intrinsically safe Li-metal batteries

Lithium (Li) metal is deemed as attractive anode due to its low electrochemical potential and high theoretical capacity. Nevertheless, the uncontrollable Li dendrite growth causes safety concern and battery failure, which severely impedes the commercialization of Li metal batteries (LMBs). Herein, 3D functional matrix comprising NiFe-layered-double-hydroxide nanosheet arrays (NiFe-LDH) evenly dispersed on acidified carbon cloth (NiFe-LDH@ACC) via hydrothermal method is designed to manipulate uniform Li electrodeposition morphology. Vertical NiFe-LDH nanosheets possess high accessible surface area to supply vast Li nucleation sites, thus effectively reducing the local current density and decreasing the nucleation energy barrier to suppress Li dendrites growth, which has been validated by simulation. Moreover, 3D structure of carbon cloth provides adequate space for storing Li metal, substantially abating volume fluctuation during repeated Li plating/stripping process. Consequently, the Li@NiFe-LDH@ACC electrode manifests ultra-long lifespan over 3500 h and low-voltage hysteresis in symmetric cells. Additionally, the full cell with limited Li@NiFe-LDH@ACC anode and commercial LiFePO4 cathode (mass loading: 8.35 mg cm−2) displays good rate capacity from 0.2 C to 5 C, and can steadily operate for 75 cycles at 2 C with a capacity of 131 mAh g−1, revealing the practical feasibility of the surface modification strategy for constructing advanced Li metal anode with high safety and appealing durability.