Nanocrystalline Graphite Research Articles

Vertically Aligned Nanocrystalline Graphite Nanowalls for Flexible Electrodes as Electrochemical Sensors for Anthracene Detection

Plasma-enhanced chemical vapor deposition (PECVD) was used to obtain several graphite nanowall (GNW)-type films at different deposition times on silicon and copper to achieve various thicknesses of carbonic films for the development of electrochemical sensors for the detection of anthracene. The PECVD growth time varied from 15 min to 30 min to 45 min, while scanning electron microscopy (SEM) confirmed the changes in the thickness of the GNW films, revealing a continuous increase in the series. X-ray diffraction (XRD) analysis revealed that the crystallinity of the GNW film samples increased with increasing crystallite size and decreasing dislocation density as the deposition time increased. Electrochemical characterization of the GNW-based electrodes indicated that the electroactive area and heterogeneous electron transfer rate constant were greater for the GNW 45 min film in the carbonic material series. We present the transfer of GNW films on flexible polyethylene substrates for achieving flexible electrochemical sensors for further use in anthracene determination. The flexible GNW-based electrodes were investigated using differential pulse voltammetry (DPV) in the presence of anthracene. The results showed that the highest sensitivity in anthracene detection was provided by the sensor with the GNW film obtained after 45 min of PECVD growth. The optimization of the GNW film thickness for the development of flexible electrochemical sensors on polyethylene substrates represents a successful approach for enhancing the electrochemical performance of carbonic materials.

Growth of nanocrystalline graphite and vertically aligned graphite nanowalls thin films and their transfer on flexible substrates for applications as electrochemical sensors for anthracene detection

Plasma-enhanced chemical vapor deposition (PECVD) allows the growth of nanocrystalline graphite (NCG)-type materials, such as N-doped bulk NCG and graphite nanowalls (GNW), on different substrates (silicon and copper) to develop flexible electrochemical sensors for anthracene detection. The carbonic materials were investigated using different techniques, including X-ray diffraction, small-angle X-ray scattering, scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential pulsed voltammetry (DPV). XRD analysis revealed different crystallinity features for both graphitic materials, as the N-NCG film presented higher lattice strain (1 %) and dislocation density (5.2 × 1012 cm−2), compared to the GNW film with a lattice strain of 0.2 % and dislocation density of 7 × 1011 cm−2. We also present a successful approach for developing flexible electrodes via transfer process from Cu to polyethylene (PE) substrate. The carbonic films were transferred onto flexible substrates via thermal treatment of the Cu foils with the PE layers, followed by Cu etching to reveal the carbon material as the sensing area of the flexible sensors. Electrodes based on N-NCG and GNW grown on silicon and those transferred to PE substrates were investigated at different anthracene concentrations by DPV. The results showed greater performance for anthracene determination in the case of N-NCG/Si, showing a sensibility of 0.8 A⋅M−1 than that of GNW/Si (0.0625 A⋅M−1). However, the flexible GNW/PE electrode exhibited an increased response in DPV in the presence of anthracene, resulting in a higher sensitivity (0.23 A⋅M−1) than that of N-NCG/PE (0.19 A⋅M−1). This behavior suggests the good electrochemical compatibility of the GNW film with the flexible polymeric substrate to obtain a flexible electrochemical sensor for anthracene detection.

Bilayer-favored intercalation induced low-voltage electrochemical production of nano-graphene oxide in neutral phosphate

Graphene oxide (GO) exhibits great potential in various fields such as catalysis, wastewater treatment, and energy storage. However, traditional top-down GO preparation methods based on graphite exfoliation often suffer from high energy consumption and inevitably environmental pollution. In this work, an environmentally benign and low-voltage electrochemical exfoliation approach to fabricate nanoscale GO employing carbon fiber-based materials as the precursor using phosphate was proposed. Under neutral phosphate electrolyte, bilayer graphene oxide with a lateral size of ∼500 nm, thickness of ∼1.5 nm, and C/O ratio of 2.96 could be obtained via a constant potential process. By adjusting the pH to 12 to intensify the exfoliation reaction, the lateral size of the graphene oxide was controllable, decreasing to ∼50 nm, while the C/O ratio decreased to 0.9. Due to the further decrease in C/O ratio, the thickness increased slightly to 2–3 nm. The exfoliation potential (1.6–2.5 V vs. Ag/AgCl) and electrolyte concentration (50–500 mM) had an obvious impact on the yield of graphene oxide. Through electrochemical analysis such as linear sweep voltammetry, as well as density functional theory calculations, the exfoliation mechanism of phosphate is elucidated in detail, demonstrating that the stepwise ionized phosphate anions possess more robust intercalation capability than sulfate, thus enabling efficient exfoliation to the intertwined nanocrystalline graphite structure of carbon fibers. The DFT results revealed the bilayer-favored intercalation of phosphate, which accords well with experiments. This work provides a new controllable and green approach for GO synthesis, demonstrated by life cycle assessment. It could assist subsequent studies exploring the size effects of GO and its applications in environmental remediation and energy storage.

Enhanced current phenomenon in nanocrystalline graphite nanopore

Enhanced current phenomenon in nanocrystalline graphite nanopore

Shear-promoted graphite-to-diamond phase transition at the grain boundary of nanocrystalline graphite

High pressure has traditionally been considered essential for the transformation of graphite into diamond. However, reducing the transition pressure required for this graphite-to-diamond (G2D) conversion holds significant appeal in both scientific research and engineering applications. In this study, we conducted large-scale molecular dynamics (MD) simulations using an environment-dependent interaction potential (EDIP) to examine the shear deformation of nanocrystalline graphite (n-graphite) with a grain size of approximately 6.5 nm. We discovered that the G2D transition pressure in n-graphite can be reduced to 2–3 GPa, significantly lower than the ∼90 GPa uniaxial stress required in crystalline graphite. This reduction is primarily due to concentrated local shear stresses at grain boundaries (GBs), which induce substantial rotations of graphite layers. These rotations facilitate the initial formation of diamond bonds at sites of pre-existing imperfections at the GBs, assisted by shear. Once initiated at the GBs, the G2D transition rapidly propagates within grains aligned parallel to the shear components, resulting in the formation of nanocrystalline diamond. Our findings underscore the critical roles of GBs and shear stress in enabling the G2D transition in n-graphite.

Biomimetic construction and preparation of high-strength carbon‑carbon composites reinforced with highly disordered nanocrystalline graphite and reduced graphene oxide

With the wide application of graphite products, the low strength has become a key influencing factor hindering the application of the functionalized graphite. Taking inspiration from the phenomenon of the pericarp preventing fruit cracking in nature, we proposed a biomimetic structure based on the pomegranate, and successfully fabricated a pomegranate-like carbon‑carbon composite (PL-C/rGO-1700) at 1700 °C by spark plasma sintering (SPS), using nanodiamonds and graphene oxide (GO) as precursors, respectively. The disordered nanocrystalline graphite derived from nanodiamonds and the reduced graphene oxide (rGO) can be considered as “pomegranate seeds” and “membrane”, respectively. The addition of rGO effectively deflected the crack extension path to enhance the flexural strength of the samples. Moreover, nanodiamond-derived disordered stacked nanocrystalline graphite improved the hardness, Young's modulus, and indentation elastic recovery of graphite bulk materials. The obtained PL-C/rGO-1700 exhibited a microhardness, flexural strength, indentation elastic recovery rate, and compressive strength of 2.7 GPa, 78.1 MPa, 81.0%, and 259.0 MPa. Therefore, our work provided a simple and rapid method for the preparation of high-strength carbon‑carbon composites.

On the mechanism of piezoresistance in nanocrystalline graphite.

Strain sensors are sensitive to mechanical deformations and enable the detection of strain also within integrated electronics. For flexible displays, the use of a seamlessly integrated strain sensor would be beneficial, and graphene is already in use as a transparent and flexible conductor. However, graphene intrinsically lacks a strong response, and only by engineering defects, such as grain boundaries, one can induce piezoresistivity. Nanocrystalline graphene (NCG), a derivative form of graphene, exhibits a high density of defects in the form of grain boundaries. It holds an advantage over graphene in easily achieving wafer-scale growth with controlled thickness. In this study, we explore the piezoresistivity in thin films of nanocrystalline graphite. Simultaneous measurements of sheet resistance and externally applied strain on NCG placed on polyethylene terephthalate (PET) substrates provide intriguing insights into the underlying mechanism. Raman measurements, in conjunction with strain applied to NCG grown on flexible glass, indicate that the strain is concentrated at the grain boundaries for smaller strain values. For larger strains, mechanisms such as grain rotation and the formation of nanocracks might contribute to the piezoresistive behavior in nanocrystalline graphene.

Characterization of fluidized bed chemical vapor deposition ZrC coatings on PyC/YSZ kernels deposited under differing conditions

Coated fuel particle architectures with ZrC coatings are candidate fuels for advanced power reactors and space nuclear propulsion (SNP) concepts. Owing to its relevance to SNP, the composition, microstructure, and mechanical properties of eight ZrC coatings prepared by fluidized bed chemical vapor deposition were evaluated. Evaluation by SEM and EBSD showed that all grains were columnar. Across the various examined samples, minor axis diameters varied between 0.3 and 1.1 μm, and major axis diameters varied between 0.4 and 2.3 μm. Major and minor diameters increased with thickness particularly at higher deposition temperatures in which the major grain axis (from an ellipse fit to the grain shape) increased by 2.5 μm over the entire coating. Coatings with higher reactive gas flows and Zr/C concentrations closer to 1 were observed to contain nanocrystalline graphite deposits. Reactive gas flow doubling led to increases in coating thickness from around 10–15 μm to around 22–27 μm.

Sugar-Derived Nanocrystalline Graphite Matrix C/C Composites with Excellent Ablative Resistance at 3000°C.

Sugars are renewable resources essential to human life, but they are rarely used as raw materials for the industrial production of carbon-based materials, especially for the preparation of carbon fiber-reinforced carbon-matrix (C/C) composites, which are extremely useful for the semiconductor and aerospace sectors. Herein, a method utilizing sugar-derived carbon to replace petrochemicals as dense matrix to preparing C/C composites is reported. The matrix from sugar-derived C/C (S-C/C) composites has a nanocrystalline graphite structure that is highly thermally stable and effectively bonded to the carbon fibers. The mechanical properties of the S-C/C composite are comparable to those prepared from petrochemical sources; significantly, it exhibits a linear ablation rate of 0.03 mm s-1 after 200 s of ablation at 3000°C in 10 MW m-2 heat flux. This new class of S-C/C is promising for use in a broad range of fields, ranging from semiconductor to aerospace.

Nanoscale Chemical Diversity of Coke Deposits on Nanoprinted Metal Catalysts Visualized by Tip-Enhanced Raman Spectroscopy.

Coke formation is the prime cause of catalyst deactivation, where undesired carbon wastes block the catalyst surface and hinder further reaction in a broad gamut of industrial chemical processes. Yet, the origins of coke formation and their distribution across the catalyst remain elusive, obstructing the design of coke-resistant catalysts. Here, the first-time application of tip-enhanced Raman spectroscopy (TERS) is demonstrated as a nanoscale chemical probe to localize and identify coke deposits on a post-mortem metal nanocatalyst. Monitoring coke at the nanoscale circumvents bulk averaging and reveals the local nature of coke with unmatched detail. The nature of coke is chemically diverse and ranges from nanocrystalline graphite to disordered and polymeric coke, even on a single nanoscale location of a top-down nanoprinted SiO2 -supported Pt catalyst. Surprisingly, not all Pt is an equal producer of coke, where clear isolated coke "hotspots" are present non-homogeneously on Pt which generate large amounts of disordered coke. After their formation, coke shifts to the support and undergoes long-range transport on the surrounding SiO2 surface, where it becomes more graphitic. The presented results provide novel guidelines to selectively free-up the coked metal surface at more mild rejuvenation conditions, thus securing the long-term catalyst stability.

Swift heavy ion irradiation of polyaniline-graphene nanocomposite films: Structural and optical properties

In this study, we investigate the use of swift heavy ions to modify the structural and optical properties of PANI-graphene nanocomposite (PANI-G NC) films. PANI-G NC films were synthesized on Indium Tin Oxide (ITO)-coated glass by electrochemical polymerization of aniline in the presence of CVD-grown graphene. The films were then irradiated with 36 MeV Cu8+ ions at fluences between 5.4 × 1012 and 6.4 × 1013 ions/cm2. SEM results show that irradiation up to 1.6 × 1013 ions/cm2 leads to the formation of a porous interconnected network, with graphene nanoparticles adhering to the PANI matrix. Beyond this fluence, a dense and compact granular structure appears. Raman spectroscopy reveals enhanced Raman scattering of the polaronic lattice and the introduction of defects in graphene. At fluences exceeding 2.1 × 1013 ions/cm2, the obtained spectra reveal a distinctive broad envelope centered at the D and G positions of graphene, characteristic of nanocrystalline graphite. X-ray diffraction shows an increase in both crystallinity and crystallite size of the PANI-G NC film with increasing fluence, followed by a decrease beyond a critical ion fluence. Optical modifications were characterized by a red shift in the UV–Vis spectrum with increased fluence. The optical band gap shows a decreasing trend with ion dose, attributed to the formation of carbonaceous clusters along the latent tracks of energetic ions. In short, this study demonstrates that swift heavy ion irradiation could be an effective tool for enhancing the structural and optical properties of PANI-G NC films and tailoring them for specific applications.

Enhanced Broadband Photodetection with Geometry and Interface Engineered Nanocrystalline Graphite

AbstractPhotodetection across the near‐infrared (NIR) to short‐wavelength infrared (SWIR) spectrum is important for many applications. This study explores photodetection using nanocrystalline graphite (NCG) in a suspended, narrow constriction configuration for improved performance. Bowtie constrictions are fabricated in both suspended and substrate‐supported NCG devices, allowing for accurate comparison. It shows that the suspended constriction enhances the bolometric photoresponse and sensor detectivity by several orders of magnitude compared to the substrate‐supported counterparts, attributed to reduced thermalization and electric field concentration. The suspended configuration preserves a spectrally flat photoresponse while reducing operating voltage through a tailored NCG layer thickness. Chromatic aberration‐corrected photocurrent spectroscopy is used to measure the photoresponse from 1100 to 1700 nm, and diffraction‐limited hyperspectral photocurrent imaging is conducted to measure the local photocurrent generation across the device. Bolometric and photo‐thermoelectric currents are restricted to the suspended central constriction due to electric field concentration and thermal decoupling and the direction of the photocurrents within the sensor is revealed. The experimental data is complemented by simulations of the light absorption and the electric field distribution. This work indicates the importance of geometry and thermal decoupling for boosting device performance, offering promising prospects for sensitive and low‐power NCG‐based photodetectors in the NIR‐SWIR range.

Microstructure, mechanical properties and high-speed dry-cutting performance of AlCrSiCN composite coatings

AlCrSiCN specimens with different carbon contents were fabricated by cathodic vacuum arc technique, and the microstructures, mechanical property, tribological and high-speed dry-cutting performance were investigated. The results show that the structural transformation from dense and fine nanocomposite to coarse columnar structures was found for the AlCrSiCN coatings when increasing the C content. The excess carbon was presented in the form of nanocrystalline graphite and/or amorphous carbon. Addition of C also reduces the surface roughness and the micro-hardness. The adhesive strengths of AlCrSiCN coatings (such as C10 and C20 coatings) with a low C content were enhanced, whereas it decreased to a value of Lc2 of 17.7 N when the C content increased to 5.58 at. % for C30 coating. Tribological experiments showed that C atoms reduced the coefficient of friction due to the lubricating effect of nanocrystalline graphite and/or amorphous carbon. The high-speed dry-cutting results also showed that AlCrSiCN-coated tools performed better than those with an AlCrSiN coating, and the coatings (C10) with a lower C content possessed the greatest wear resistance.

A novel method for quantifying irradiation damage in nuclear graphite using Raman spectroscopy

Raman spectroscopy has long been used in studying irradiation damage in carbon/graphite materials. It is however unclear if the measurements from different types of materials are directly comparable. Further, decoupling the contribution from irradiation temperature and fluence to the total damage in nuclear graphite possessing irradiation damage gradient is currently not readily feasible as it requires a complete set of test reactor irradiation experiments over the relevant temperature and fluence range. A novel methodology has therefore been proposed and developed to quantify total irradiation damage evolution at crystal level based on graphite Raman G-band position shift. Specifically, G-band positions derived from a large number of spectra collected from the fractured surface of microfine-grained POCO ZXF-5Q graphite possessing proton irradiation damage gradient were plotted with open literature Raman data on HOPG, BEPO (AXGP graphite), PCEA and IG-110 graphite as a function of dpa. The total damage level within 2σ beam radius in this POCO graphite was estimated to be equivalent to ∼2–5 dpa at ∼350–370 °C. Derived G-band positions were then mapped to the three-stage amorphization trajectory model indicating beam centre area has entered the second stage, i.e., transitioning from nanocrystalline graphite into amorphous carbon. G-band position relative shift (ΔG) curve with a ‘turn-around’ peak as a function of total damage can be used for in-service lifetime prediction. The developed methodology has the potential to ‘unify’ total damage levels across different grades of nuclear graphite caused by ion, neutron and proton irradiation at different temperatures.

Investigation of charge storage in admixture of dextrose derived interconnected carbon spheres and micro-sized silicon

This work reports the investigations and electrochemical properties of a material, prepared by micro-sized Si (mSi) (upto 50 μm) which were partially coated with upto ~7 μm sized carbon microspheres (CS). The mixture of mSi enwrapped with CS ([email protected]) was fabricated using a low temperature and facile hydrothermal carbonization (HTC) of dextrose. XRD and Raman study revealed an amorphous phase due to carbon/SiO2 and a highly disordered nanocrystalline graphite respectively. Also, FTIR suggested the SiO bending and symmetric stretching of linear SiOSi. The electrochemical investigation with three cell assembly of fabricated [email protected] as an electrode material for supercapacitor application exhibited a maximum specific capacitance of 278.79 F g−1 at 5 mV s−1 scan rate which is around 7 times as calculated for pristine mSi powder. In [email protected], conducting, amorphous and nano crystalline carbon combined with mSi exhibited enhanced specific capacitance and a low equivalent series resistance (ESR). mSi served as anchor and contributed to enhancing specific capacitance and providing 2 V voltage window. This work opens the possibility of designing energy materials with the waste Si and pseudocapacitive materials.

Field-Effect Transistors Based on Single-Layer Graphene and Graphene-Derived Materials.

The progress of advanced materials has invoked great interest in promising novel biosensing applications. Field-effect transistors (FETs) are excellent options for biosensing devices due to the variability of the utilized materials and the self-amplifying role of electrical signals. The focus on nanoelectronics and high-performance biosensors has also generated an increasing demand for easy fabrication methods, as well as for economical and revolutionary materials. One of the innovative materials used in biosensing applications is graphene, on account of its remarkable properties, such as high thermal and electrical conductivity, potent mechanical properties, and high surface area to immobilize the receptors in biosensors. Besides graphene, other competing graphene-derived materials (GDMs) have emerged in this field, with comparable properties and improved cost-efficiency and ease of fabrication. In this paper, a comparative experimental study is presented for the first time, for FETs having a channel fabricated from three different graphenic materials: single-layer graphene (SLG), graphene/graphite nanowalls (GNW), and bulk nanocrystalline graphite (bulk-NCG). The devices are investigated by scanning electron microscopy (SEM), Raman spectroscopy, and I-V measurements. An increased electrical conductance is observed for the bulk-NCG-based FET, despite its higher defect density, the channel displaying a transconductance of up to ≊4.9×10-3 A V-1, and a charge carrier mobility of ≊2.86×10-4 cm2 V-1 s-1, at a source-drain potential of 3 V. An improvement in sensitivity due to Au nanoparticle functionalization is also acknowledged, with an increase of the ON/OFF current ratio of over four times, from ≊178.95 to ≊746.43, for the bulk-NCG FETs.

Modeling of Nanolubricant-Assisted Machining Process by using Multiple Regression Analysis

Graphite, due to its hexagonally arranged crystal structure, is a preferred lubricant. The crystal structure within a planar condensed ring system indicates that the layers are stacked in a direction that is parallel to each other. Researchers have reported that the use of graphite powder as a lubricant during machining has exhibited promising results. Mixture of graphite in a carrying medium demonstrated multifunctional lubrication performance due to the separation of sliding surfaces by a liquid lubricant film and protected by solid powder. Scientific literature has pointed out that graphite powder at the nanoscale has been used in various mechanical operations exhibiting promising results. It is found that nanolevel graphite powder has been used previously by researchers in the metal-forming operations and tribological tests. This emphasizes the significance of the present work, which investigates the impact of nanoscale differences in the particle size of graphite powder has on the machining of hardened steel. With SAE 40 oil functioning as the carrying medium and nanocrystalline graphite of various size range performing as the lubricant, the current work attempts to determine the effects of solid-lubricant-assisted machining. It is observed experimentally that the machining parameters have improved with respect to the particle size of the nanopowder. The experimental results show that the cutting forces, tool temperatures, and surface roughness are found to increase as the size of the nanocrystalline graphite powder is reduced from 70–90 to 5–10 nm. Using the experimental values, regression analysis is carried out to develop nonlinear expressions between the input and output variables using SPSS statistical tool. The data are used to develop the models to predict cutting forces, tool temperatures, and surface roughness for the input parameters like size of the nanocrystalline graphite powder, depth of cut, feed rate, and cutting velocity for a considerably good range in a scientific way so that further researchers can use it. Further, the outputs obtained from the experimentation and the regression equations are compared and analysis is carried out in terms of the error percentage.

Sustainable Preparation of Graphene Quantum Dots for Metal Ion Sensing Application

Over the past several years, graphene quantum dots (GQDs) have been extensively studied in water treatment and sensing applications because of their exceptional structure-related properties, intrinsic inert carbon property, eco-friendly nature, etc. This work reported on the preparation of GQDs from the ethanolic extracts of eucalyptus tree leaves by a hydrothermal treatment technique. Different heat treatment times and temperatures were used during the hydrothermal treatment technique. The optical, morphological, and compositional analyses of the green-synthesized GQDs were carried out. It can be noted that the product yield of GQDs showed the maximum yield at a reaction temperature of 300 °C. Further, it was noted that at a treatment period of 480 min, the greatest product yield of about 44.34% was attained. The quantum yields of prepared GQDs obtained after 480 min of treatment at 300 °C (named as GQD/300) were noted to be 0.069. Moreover, the D/G ratio of GQD/300 was noted to be 0.532 and this suggested that the GQD/300 developed has a nano-crystalline graphite structure. The TEM images demonstrated the development of GQD/300 with sizes between 2.0 to 5.0 nm. Furthermore, it was noted that the GQD/300 can detect Fe3+ in a very selective manner, and hence the developed GQD/300 was successfully used for the metal ion sensing application.

Design of carbon fiber with nano accuracy for enrichment interface

The interface is the pivot of the mechanical properties of Carbon fiber reinforced plastic composites (CFRP). Presently, interface researches are numerous but few involve carbonized interface. Herein, the effect of temperature on the physicochemical properties of the carbonized interface is investigated using PDA as a precursor. The results show that the high temperature causes the amorphous carbon structure in the carbon coating to transform into nanocrystalline graphite structure, and the polarity of the fiber surface is reduced. The increase in surface roughness due to temperature fails to compensate for the negative effect of reduced polarity on the interfacial bonding properties. Both the tensile strength of carbon fiber and ILSS of CFRP decreased with the increase in temperature. This study will have interesting implications for the construction of the model in the carbonized interface.

Evolution of Nanocrystalline Graphite’s Physical Properties during Film Formation

Nanocrystalline graphite (NCG) layers represent a good alternative to graphene for the development of various applications, using large area, complementary metal-oxide semiconductor (CMOS) compatible technologies. A comprehensive analysis of the physical properties of NCG layers—grown for different time periods via plasma-enhanced chemical vapour deposition (PECVD)—was conducted. The correlation between measured properties (thickness, optical constants, Raman response, electrical performance, and surface morphology) and growth time was established to further develop various functional structures. All thin films show an increased grain size and improved crystalline structure, with better electrical properties, as the plasma growth time is increased. Moreover, the spectroscopic ellipsometry investigations of their thickness and optical constants, together with the surface roughness extracted from the atomic force microscopy examinations and the electrical properties resulting from Hall measurements, point out the transition from nucleation to three-dimensional growth in the PECVD process around the five-minute mark.