Mass production of graphene nanoscrolls and their application in high rate performance supercapacitors

Calculating and analyzing time delay in zigzag graphene nanoscrolls based complementary metal-oxide-semiconductors

Graphene Nano Scrolls (GNSs) and Zigzag graphene nanoscrolls (ZGNSs) are semi-one-dimensional materials with exceptional electrical and optical properties, making them attractive to be used in nanoelectronics and complementary metal-oxide-semiconductor (CMOS) technology. With in CMOS device technology, time delay is a crucial issue in the design and implementation of CMOS based ZGNSs. Current paper focus is on ZGNSs application in the channel area of metal-oxide-semiconductor field-effect transistors (MOSFETs) in CMOS technology. We studied analytically, the importance of different parameters on time delay reduction, resulting in faster switching and higher frequency in integrated circuits (ICs). The results of this research demonstrates that, the ZGNS-based CMOS proves considerable variations in the current due to the geometrical parameters, such as chirality number, channel length, and nanoscroll length which can be engineered to produce faster ICs.

Formation and stability of nanoscrolls composed of graphene and hexagonal boron nitride nanoribbons: insights from molecular dynamics simulations

CONTEXT

Nanoscrolls are tube-shaped structures formed when a sheet or ribbon of material is rolled into a cylinder, creating a hollow tube with a diameter on the nanoscale, similar to the papyrus. Carbon nanoscrolls have unique properties that make them useful in various applications, such as energy storage, catalysis, and drug delivery. In this study, we employed classical molecular dynamics simulations to investigate the formation and stability of nanoscrolls composed of graphene and hexagonal boron nitride (hBN) nanoribbons. Using a carbon nanotube (CNT) as a template to trigger their collapsing, we found that graphene/graphene, graphene/hBN, and hBN/hBN could form CNT-wrapped nanoscrolls at ultrafast speeds. We also confirmed that these nanoscrolls are thermally stable and discussed the other products formed from the interaction of these complexes and their temperature dependence. Gr/Gr and hBN/Gr nanoscrolls exhibit similar interlayer distances, while hBN/hBN nanoscrolls have wider interlayer distances than the other two composite nanoscrolls. These features suggest that hBN/hBN composite nanoscrolls could more efficiently capture small molecules because of their greater interlayer spacing.

METHODS

We conducted molecular dynamics simulations using the Forcite package in the Biovia Materials Studio software, which employs the Universal and Dreiding force fields. We considered an NVT ensemble with a fixed time step of 1.0 fs for a duration of 500 ps. The velocity Verlet algorithm was adopted to integrate the equations of motion of the entire system. We employed the Nosé-Hoover-Langevin thermostat to control the system temperature. The simulations were carried out without periodic boundary conditions, so there was no pressure coupling.

Recent Advances in Rolling 2D TMDs Nanosheets into 1D TMDs Nanotubes/Nanoscrolls

Transition metal dichalcogenides (TMDs) van der Waals (vdW) 1D heterostructures are recently synthesized from 2D nanosheets, which open up new opportunities for potential applications in electronic and optoelectronic devices. The most recent and promising strategies in regards to forming 1D TMDs nanotubes (NTs) or nanoscrolls (NSs) in this review article as well as their heterostructures that are produced from 2D TMDs are summarized. In order to improve the functionality of ultrathin 1D TMDs that are coaxially combined with boron nitride nanotubes and single-walled carbon nanotubes. 1D heterostructured devices perform better than 2D TMD nanosheets when the two devices are compared. The photovoltaic effect in WS₂ or MoS₂ NTs without a junction may exceed the Shockley-Queisser limit for the above-band-gap photovoltage generation. Photoelectrochemical hydrogen evolution is accelerated when monolayer WS₂ or MoS₂ NSs are incorporated into a heterojunction. In addition, the photovoltaic performance of the WSe₂ /MoS₂  NSs junction is superior to that of the performance of MoS₂ NSs. The summary of the current research about 1D TMDs can be used in a variety of ways, which assists in the development of new types of nanoscale optoelectronic devices. Finally, it also summarizes the current challenges and prospects.

Solvent-Free Preparation of Closely Packed MoS2 Nanoscrolls for Improved Photosensitivity

Due to their enhanced light absorption efficiency, one-dimensional (1D) transition metal dichalcogenide (TMDC) nanoscrolls derived from two-dimensional (2D) TMDC nanosheets have shown excellent optoelectronic properties. Currently, organic solvent and alkaline droplet-assisted scrolling methods are popular for preparing TMDC nanoscrolls. Unfortunately, the adsorption of organic solvent or alkaline impurities on TMDC is inevitable during the preparation, which affects the optoelectronic properties of TMDC. In this work, we report a solvent-free method to prepare closely packed MoS₂ nanoscrolls by dragging a deionized water droplet onto the chemical vapor deposition grown monolayer MoS₂ nanosheets at 100 °C (referred to as MoS₂ NS-W). The as-prepared MoS₂ NS-W was well characterized by optical microscopy, atomic force microscopy, and ultralow frequency (ULF) Raman spectroscopy. After high temperature annealing, the height of MoS₂ nanoscrolls prepared using an ethanol droplet (referred to as MoS₂ NS-E) greatly decreased, indicating the loss of encapsulated ethanol in MoS₂ NS-E. While the height of MoS₂ NS-W was almost unchanged under the same conditions, implying that no water was embedded in the scroll. Compared to the MoS₂ NS-E, the MoS₂ NS-W shows more ULF breathing mode peaks, confirming the stronger interlayer interaction. In addition, the MoS₂ NS-W shows a higher Young's modulus than MoS₂ NS-E, which could arise from the closely packed scroll structure. Importantly, the MoS₂ NS-W device showed a photosensitivity 1 order of magnitude higher than that of the MoS₂ NS-E device under blue, green, and red lasers, respectively. The decreased photosensitivity of MoS₂ NS-E was attributed to the larger dark current, which might be assigned to the adsorbed ethanol between the adjacent layers in MoS₂ NS-E. Our work provides a solvent-free method to prepare closely packed MoS₂ nanoscrolls at large scale and demonstrates their great potential for high-performance optoelectronic devices.

Low reflectance of carbon nanotube and nanoscroll-based thin film coatings: a case study

Research on carbon material-based thin films with low light reflectance has received significant attention for the development of high absorber coatings for stray light control applications. Herein, we report a method for the successful fabrication of stable thin films comprised of carbon nanotubes (CNTs) and nanoscrolls (CNS) on an aluminium (Al) substrate, which exhibited low reflectance of the order of 2-3% in the visible and near-infrared (NIR) spectral bands. Changes in the structural and chemical composition of pristine single-walled carbon nanotube (SWCNT) samples were analyzed after each processing step. Spectroscopy, microscopy and microstructural studies demonstrated emergence of CNS and multi-walled carbon nanotubes (MWCNTs) due to the sequential chemical processing of the sample. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies revealed the formation of CNS via curling and folding of graphene sheets. Microstructural investigations including SEM and atomic force microscopy (AFM) confirmed the presence of microcavities and pores on the surface of the film. These cavities and pores significantly contribute to the observed low reflectance value of CNTs, CNS compound films by trapping the incident light. Fundamental space environmental simulation tests (SEST) were performed on the coated films, that showed promising results with reflectance values almost unaltered in the visible and NIR spectral bands, demonstrating the durability of these films as potential candidates to be used in extreme space environmental conditions. This study describes the preparation, characterization, and testing of blended CNT and CNS coatings for low-light scattering applications.

Tribochemical Behaviors of Onion-like Carbon Films as High-Performance Solid Lubricants with Variable Interfacial Nanostructures

Onion-like carbon (OLC), spherical nanoparticles consisting of carbon shells, is capable of providing exceptional lubrication effects. Nevertheless, the underlying mechanism, especially the tribo-induced evolution of interfacial nanostructures and their correlation with the friction states, is not clear. In this work, OLC films with a thickness of ∼1 μm were synthesized by electrophoretic deposition on the mirror-polished stainless steel. The lubricity was evaluated by tailoring the sliding aspects including applied normal load, contact time, and counterface materials. It is found that the friction reduction level is highly dependent on the material transfer and transformation of the OLC surface and the physicochemical nature of the as-formed tribolayer in the contact areas. The subsurface of the OLC film always undergoes a deep amorphization transformation upon sliding. It is interesting to note that the tribolayer formed on the bare steel ball is mainly composed of highly ordered graphene-like nanoflakes derived from the sliding-induced degradation of OLC nanospheres. In comparison, the nanospherical carbon structure can be retained in the topmost subsurface of the tribolayer formed on the ceramic Si₃N₄ ball. Such a nanosphere-/amorphization-coupled interface is capable of providing a robust lubrication state under high contact stresses. The findings identify a new lubrication mechanism for the spherical carbon nanostructure, rendering them effective solid lubricants.

Impact of pH on Regulating Ion Encapsulation of Graphene Oxide Nanoscroll for Pressure Sensing

Recently, graphene oxide nanoscroll (GONS) has attracted much attention due to its excellent properties. Encapsulation of nanomaterials in GONS can greatly enhance its performance while ion encapsulation is still unexplored. Herein, various ions including hydronium ion (H₃O⁺), Fe³⁺, Au³⁺, and Zn²⁺ were encapsulated in GONSs by molecular combing acidic graphene oxide (GO) solution. No GONS was obtained when the pH of the GO solution was greater than 9. A few GONSs without encapsulated ion were obtained at the pH of 5–8. When the pH decreased from 5 to 0.15, high-density GONSs with encapsulated ions were formed and the average height of GONS was increased from ~50 to ~190 nm. These results could be attributed to the varied repulsion between carboxylic acid groups located at the edges of GO nanosheets. Encapsulated metal ions were converted to nanoparticles in GONS after high-temperature annealing. The resistance-type device based on reduced GONS (rGONS) mesh with encapsulated H₃O⁺ showed good response for applied pressure from 600 to 8700 Pa, which manifested much better performance compared with that of a device based on rGONS mesh without H₃O⁺.

Highly Promoted Carrier Mobility and Intrinsic Stability by Rolling Up Monolayer Black Phosphorus into Nanoscrolls

Rolling up two-dimensional (2D) materials into nanoscrolls could not only retain the excellent properties of their 2D hosts but also display intriguing physical and chemical properties that arise from their 1D tubular structures. Here, we report a new class of black phosphorus nanoscrolls (bPNSs), which are stable at room-temperature and energetically more favorable than 2D bP. Most strikingly, these bPNSs hold tunable direct band gaps and extremely high mobilities (e.g., the mobility of the double-layer bPNS is about 20-fold higher than that of 2D bP monolayer). Their unique self-encapsulation structure and layer-dependent conduction band minimum can largely prevent the entrance of O₂ and the production of O₂^- and thereby suppress the possible environmental degradation as well. The enhanced intrinsic stability and promoted electronic properties render bPNSs great promise in many advanced electronics or optoelectronics applications.

A facile and general approach for production of nanoscrolls with high-yield from two-dimensional nanosheets

Nanoscrolls (NSs) assembled from two-dimensional nanosheets have emerged as a novel type of one-dimensional nanomaterials because of their unique topological features and properties. The scale-up preparation of the NSs is crucial for their foundational and applied research. Herein, we report a general and straightforward approach for efficiently converting two-dimensional nanosheets into the NSs with high yield. We demonstrated the converting process by illustrating the formation of the graphene nanoscrolls through characterizing their morphology and structure using a scanning electron microscope, transmission electron microscope, Raman spectra, and X-ray diffraction spectra. The graphene sheets with a few-lay number were converted immediately and entirely into the graphene nanoscrolls when they mixed with an ethanol solution of silver nitrate at room temperature. The as-prepared graphene nanoscrolls were confirmed to be formed via the layer-by-layer assembly of graphene triggered by silver cyanide formed in site. Also, we extended this approach to construct the nanoscrolls of the hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide, respectively, from their corresponding two-dimensional nanomaterials. In a broader context, this approach paves a significant new way for the large production of the NSs with cost-efficiency.

Transforming Monolayer Transition-Metal Dichalcogenide Nanosheets into One-Dimensional Nanoscrolls with High Photosensitivity

One-dimensional (1D) nanoscrolls derived from two-dimensional (2D) nanosheets own unusual physical and chemical properties that arise from the spiraled 1D morphology and the atomic thin 2D building blocks. Unfortunately, preparation of large-sized nanoscrolls of transition-metal dichalcogenides (TMDCs) remains a big challenge, which greatly restricts the fabrication of single-scroll devices for their fundamental studies and further applications. In this work, we report a universal and facile method, by making use of the evaporation process of volatile organic solvent, to prepare TMDC (e.g., MoS₂ and WS₂) nanoscrolls with lengths of several tens to one hundred micrometers from their 2D precursors presynthesized by chemical vapor deposition on Si/SiO₂. Both atomic force microscopy and electron microscopy characterizations confirmed the spirally rolledup structure in the resulting nanoscrolls. An interlayer spacing of as small as ∼0.65 nm was observed, suggesting the strong coupling between adjacent layers, which was further evidenced by the emergence of new breathing mode peaks in the ultralow frequency Raman spectrum. Importantly, compared with the photodetector fabricated from a monolayer MoS₂ or WS₂ nanosheet, the device based on an MoS₂ or WS₂ nanoscroll showed the much enhanced performance, respectively, with the photosensitivity greatly increased up to 2 orders of magnitude. Our work suggests that turning 2D TMDCs into 1D scrolls is promising in achieving high performances in various electronic/optoelectronic applications, and our general method can be extended to the preparation of large-sized nanoscrolls of other kinds of 2D materials that may bring about new properties and phenomena.

Rolling up transition metal dichalcogenide nanoscrolls via one drop of ethanol

Two-dimensional transition metal dichalcogenides (TMDs) have attracted lots of interest because of their potential for electronic and optoelectronic applications. Atomically thin TMD flakes were believed capable to scroll into nanoscrolls (NSs) with distinct properties. However, limited by mechanical strength and chemical stability, production of high-quality TMD NSs remains challenging. Here, we scroll chemical vapor deposition-grown monolayer TMD flakes into high-quality NSs in situ in 5 s with a nearly 100% yield by only one droplet of ethanol solution. An obvious photoluminescence is demonstrated in NSs and the self-encapsulated structure makes NSs more insensitive to external factors in optical and electrical properties. Furthermore, based on the internal open topology, NSs hybridized with a variety of functional materials have been fabricated, which is expected to confer TMD NSs with additional properties and functions attractive for potential application.

Nanoscrolls (NSs) have interesting properties due to papyrus-like rolled-up geometry but their synthesis is difficult. Here Cui et al. show that vapor deposited monolayer transition metal dichalcogenide flakes form patternable arrays of NSs with the assistance of one droplet of ethanol solution.

Cellulose Nanocrystal Templated Graphene Nanoscrolls for High Performance Supercapacitors and Hydrogen Storage: An Experimental and Molecular Simulation Study

Graphene nanoscrolls (GNS), due to their remarkably interesting properties, have attracted significant interest with applications in various engineering sectors. However, uncontrolled morphologies, poor yield and low quality GNS produced through traditional routes are major challenges associated. We demonstrate sustainable approach of utilizing bio-derived cellulose nanocrystals (CNCs) as template for fabrication of GNS with tunable morphological dimensions ranging from micron-to-nanoscale(controlled length < 1 μm or >1 μm), alongwith encapsulation of catalytically active metallic-species in scroll interlayers. The surface-modified magnetic CNCs acts as structural-directing agents which provides enough momentum to initiate self-scrolling phenomenon of graphene through van der Waals forces and π-π interactions, mechanism of which is demonstrated through experimental and molecular simulation studies. The proposed approach of GNS fabrication provides flexibility to tune physico-chemical properties of GNS by simply varying interlayer spacing, scrolling density and fraction of encapsulated metallic nanoparticles. The hybrid GNS with confined palladium or platinum nanoparticles (at lower loading ~1 wt.%) shows enhanced hydrogen storage capacity (~0.2 wt.% at~20 bar and ~273 K) and excellent supercapacitance behavior (~223–357 F/g) for prolonged cycles (retention ~93.5–96.4% at ~10000 cycles). The current strategy of utilizing bio-based templates can be further extended to incorporate complex architectures or nanomaterials in GNS core or inter-layers, which will potentially broaden its applications in fabrication of high-performance devices.

Rolling up graphene oxide sheets through solvent-induced self-assembly in dispersions

Herein we report a new approach to fabricating nanoscrolls through the self-assembly of graphene oxide (GO) sheets in a dispersion. The assembly process for GO nanosheets was induced by the dropwise addition of an appropriate organic solvent such as N,N-dimethylformamide (DMF) into the aqueous dispersion. The results show that nanoscrolls were gradually formed from the GO sheets by rolling-up in a piece-by-piece manner with the increase of the DMF content. The transmission electron microscopic analysis indicates that for a typical case, the nanoscrolls have an average diameter of 242 ± 102 nm at the central part and the interlayer spacing between adjacent GO layers is 0.58 nm. The scrolls were estimated to have 207 turns and include on average 42 pieces of GO sheets per scroll. By this method, GO sheets with different sizes and oxidation degrees were proved to be able to form GO nanoscrolls in a similar way. Moreover, it is interesting that the diffraction efficiency of surface-relief-gratings photoinduced on the film of azo molecular glass was significantly enhanced by doping the GO nanoscrolls with a very low content (0.5 wt%); this suggests a possible new application for the GO scrolls in optical devices. This facile approach, which is also feasible by using other organic solvents such as ethanol, can be used to fabricate GO nanoscrolls for large scale applications in supercapacitors, sensors and other devices.

Fabrication of Metal Molybdate Micro/Nanomaterials for Electrochemical Energy Storage

Currently, metal molybdates compounds can be prepared by several methods and are considered as prospective electrode materials in many fields because the metal ions possess the ability to exist in several oxidation states. These multiple oxidation states contribute to prolonging the discharge time, improving the energy density, and increasing the cycling stability. The high electrochemical performance of metal molybdates as electrochemical energy storage devices are discussed in this review. According to recent publications and research progress on relevant materials, the investigation of metal molybdate compounds are discussed via three main aspects: synthetic methods, material properties and measured electrochemical performance of these compounds as electrode materials. The recent progress in general metal molybdate nanomaterials for LIBs and supercapacitors are carefully presented here.

Scrolling up graphene oxide nanosheets assisted by self-assembled monolayers of alkanethiols

We report a simple and novel method for the fabrication of high-quality nanoscrolls of graphene oxide (GO) and graphene oxide decorated with silver nanoparticles (GO-Ag) on a gold substrate through a scrolling process assisted by the self-assembly of alkanethiol monolayers. The yield and rate of the scrolling process were highly dependent on the lengths of the alkanethiol molecules, and could be well described by power law functions. Importantly, compared to nanosheets, nanoscrolls of GO and GO-Ag showed superior performance in humidity sensing due to their unique scrolled structures.

Vertically Oriented Graphene Nanoribbon Fibers for High-Volumetric Energy Density All-Solid-State Asymmetric Supercapacitors

Graphene fiber based micro-supercapacitors (GF micro-SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π-π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined-hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as-obtained fiber shows high length specific capacitance of 3.2 mF cm^-1 and volumetric capacitance of 234.8 F cm^-3 at 2 mV s^-1 , as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all-solid-state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO₂ coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm^-3 and 5.7 mWh cm^-3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro-SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.

Nitrogen-Doped Graphene Nanoscroll Foam with High Diffusion Rate and Binding Affinity for Removal of Organic Pollutants

A nitrogen-doped 3D graphene foam assembled with nanoscroll structure is constructed via a facile mild-heating methodology using a polar molecule of formamide as the driving regent. The as-prepared graphene nanoscroll foam exhibits promising performance in organic pollutant removal with improved adsorption rate and high binding affinity, and is thought to be a novel adsorption material.