Graphene-Dielectric Integration for Graphene Transistors

Engineering the future: Unveiling novel paths in heavy metal wastewater remediation with advanced carbon-based nanomaterials - Beyond performance comparison, tackling challenges, and exploring opportunities

This review addresses the pressing issue of heavy metal pollution in water, specifically focusing on the application of adsorption technology utilizing carbon materials such as biochar, carbon nanotubes, graphene, and carbon quantum dots. Utilizing bibliometric analysis with VOSviewer based on Web of Science core dataset, this study identifies research hotspots related to carbon-based materials in heavy metal applications over the past decade. However, existing literature still lacks sufficient comparative analysis of the potential of carbon-based materials' structural characteristics and inherent advantages in heavy metal applications. This review strategically addresses this gap, offering a comprehensive comparative analysis of these four materials from an engineering application perspective. It offers a thorough evaluation of their suitability for various water treatment applications, providing a detailed examination of their advantages and limitations in heavy metal application. Additionally, the review provides insights into performance comparisons, addresses challenges, and explores emerging opportunities in this field. Insights into potential application fields based on structural characteristics and inherent advantages are presented. This unique focus on a comprehensive comparative analysis distinguishes the article, offering a nuanced perspective on the strengths and future possibilities of carbon materials in tackling the global challenge of heavy metal pollution in water.

Reusable Electronic Tongue Based on Transient Receptor Potential Vanilloid 1 Nanodisc-Conjugated Graphene Field-Effect Transistor for a Spiciness-Related Pain Evaluation

The sense of spiciness is related to the stimulation of vanilloid compounds contained in the foods. Although, the spiciness is commonly considered as the part of taste, it is more classified to the sense of pain stimulated on a tongue, namely, pungency, which is described as a tingling or burning on the tongue. Herein, first, a reusable electronic tongue based on a transient receptor potential vanilloid 1 (TRPV1) nanodisc conjugated graphene field-effect transistor is fabricated and spiciness-related pain evaluation with reusable electrode is demonstrated. The pungent compound reactive receptor TRPV1 is synthesized in the form of nanodiscs to maintain stability and reusability. The newly developed platform shows highly selective and sensitive performance toward each spiciness related vanilloid compound repeatably: 1 aM capsaicin, 10 aM dihydrocapsaicin, 1 fM piperine, 10 nM allicin, and 1 pM AITC. The binding mechanism is also examined by simulation. Furthermore, the elimination of the burning sensation on the tongue after eating spicy foods is not investigated. Based on the synthesis of micelles composed of casein protein (which is contained in skim milk) that remove pungent compounds bound to TRPV1 nanodisc, the deactivation of TRPV1 is investigated, and the electrode is reusable that mimics electronic tongue.

Passivating Graphene and Suppressing Interfacial Phonon Scattering with Mechanically Transferred Large-Area Ga2O3

We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga₂O₃ synthesized on liquid Ga metal. A comparison of temperature-dependent electrical measurements of millimeter-scale passivated and bare graphene on SiO₂/Si indicates that the passivated graphene maintains its high field effect mobility desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in passivated graphene over a range of temperatures below 220 K, due to the interplay of screening of the surface optical phonon modes of the SiO₂ by high-dielectric-constant Ga₂O₃ and the relatively high characteristic phonon frequencies of Ga₂O₃. Raman spectroscopy and electrical measurements indicate that Ga₂O₃ passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al₂O₃.

Functionalized and Platinum-Decorated Multi-Layer Oxidized Graphene as a Proton, and Electron Conducting Separator in Solid Acid Fuel Cells

In the present article, electrodes containing a composite of platinum on top of a plasma-oxidized multi-layer graphene film are investigated as model electrodes that combine an exceptional high platinum utilization with high electrode stability. Graphene is thereby acting as a separator between the phosphate-based electrolyte and the platinum catalyst. Electrochemical impedance measurements in humidified hydrogen at 240 °C show area-normalized electrode resistance of 0.06 Ω·cm−2 for a platinum loading of ∼60 µgPt·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. The presented platinum decorated graphene electrodes enable stable operation over 60 h with a non-optimized degradation rate of 0.15% h−1, whereas electrodes with a similar design but without the graphene as separator are prone to a very fast degradation. The presented results propose an efficient way to stabilize solid acid fuel cell electrodes and provide valuable insights about the degradation processes which are essential for further electrode optimization.

Local current analysis on defective zigzag graphene nanoribbons devices for biosensor material applications

In this contribution, we aim at investigating the mechanism of biosensing in graphene-based materials from first principles. Inspired by recent experiments, we construct an atomistic model composed of a pyrene molecule serving as a linker fragment, which is used in experiment to attach certain aptamers, and a defective zigzag graphene nanoribbons (ZGNRs). Density functional theory including dispersive interaction is employed to study the energetics of the linker absorption on the defective ZGNRs. Combining non-equilibrium Green's function and the Landauer formalism, the total current-bias voltage dependence through the device is evaluated. Modifying the distance between the linker molecule and the nanojunction plane reveals a quantitative change in the total current-bias voltage dependence, which correlates to the experimental measurements. In order to illuminate the geometric origin of these variation observed in the considered systems, the local currents through the device are investigated using the method originally introduced by Evers and co-workers. In our new implementation, the numerical efficiency is improved by applying sparse matrix storage and spectral filtering techniques, without compromising the resolution of the local currents. Local current density maps qualitatively demonstrate the local variation of the interference between the linker molecule and the nanojunction plane.

Selectively Metallized 2D Materials for Simple Logic Devices

We herein demonstrate, for the first time, transparent, flexible, and large-area monolithic MoS₂ transistors and logic gates. Each single transistor consists of only two components: a monolithic chemical vapor deposition-grown MoS₂ and an ion gel. Additional electrode materials are not required. The uniqueness of the device configuration is attributed to two factors. One is that a MoS₂ layer is a semiconductor, but it can be doped degenerately; monolithic MoS₂ can thus serve as both the electrodes and the channel of a transistor via selective doping of the material at certain positions. The other is the use of an electrolyte gate dielectric that permits effective gating (<3 V) even from an electrode coplanar with the channel. The resulting monolithic MoS₂ transistors yield excellent device performance, including a maximum mobility of 1.5 cm²/V s, an on-off ratio of 10⁵, and a turn-on voltage of -0.69 V. This unique transistor architecture was successfully applied to various semiconductors such as ReS₂ and indium-gallium-zinc oxide. Furthermore, the presented devices exhibit excellent mechanical, operational, and environmental stabilities. Fabrication of complex logic circuits (NOT, NAND, and NOR gates) by integration of the monolithic MoS₂ transistors is demonstrated. Finally, the monolithic MoS₂ transistor was connected to drive red, green, and blue light-emitting diode pixels, which yielded high luminance at a low voltage (<3 V). We believe that the unique architecture of the devices provides a facile way for low-cost, flexible, and high-performance two-dimensional electronics.

Graphene Field-Effect Transistors Employing Different Thin Oxide Films: A Comparative Study

In this work, we report on a comparison among graphene field-effect transistors (GFETs) employing different dielectrics as gate layers to evaluate their microwave response. In particular, aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and hafnium oxide (HfO₂) have been tested. GFETs have been fabricated on a single chip and a statistical analysis has been performed on a set of 24 devices for each type of oxide. Direct current and microwave measurements have been carried out on such GFETs and short circuit current gain and maximum available gain have been chosen as quality factors to evaluate their microwave performance. Our results show that all of the devices belonging to a specific group (i.e., with the same oxide) have a well-defined performance curve and that the choice of hafnium oxide represents the best trade-off in terms of dielectric properties. Graphene transistors employing HfO₂ as the dielectric layer, in fact, exhibit the best performance in terms of both the cutoff frequency and the maximum frequency of oscillation.

ZnO Nanomembrane/Expanded Graphite Composite Synthesized by Atomic Layer Deposition as Binder-Free Anode for Lithium Ion Batteries

A zinc oxide (ZnO)/expanded graphite (EG) composite was successfully synthesized by using atomic layer deposition with dimethyl zinc as the zinc source and deionized water as the oxidant source. In the composite structure, EG provides a conductive channel and mechanical support to ZnO nanomembranes, which effectively avoids the electrode pulverization caused by the volume change of ZnO. The anodes made from the flexible composite films without using binder, conductive agent, and current collector show high stable capacities especially for that with a moderate ZnO concentration. The highest capacity stayed at 438 mAh g^-1 at a current rate of 200 mA g^-1 after 500 cycles. The good performance is considered to be due to the co-effects of the high capacity of ZnO and the support of the EG framework. Such composite structures may have great potential in low-cost and flexible batteries.

Rapid Fabrication of Graphene Field-Effect Transistors with Liquid-metal Interconnects and Electrolytic Gate Dielectric Made of Honey

Historically, graphene-based transistor fabrication has been time-consuming due to the high demand for carefully controlled Raman spectroscopy, physical vapor deposition, and lift-off processes. For the first time in a three-terminal graphene field-effect transistor embodiment, we introduce a rapid fabrication technique that implements non-toxic eutectic liquid-metal Galinstan interconnects and an electrolytic gate dielectric comprised of honey. The goal is to minimize cost and turnaround time between fabrication runs; thereby, allowing researchers to focus on the characterization of graphene phenomena that drives innovation rather than a lengthy device fabrication process that hinders it. We demonstrate characteristic Dirac peaks for a single-gate graphene field-effect transistor embodiment that exhibits hole and electron mobilities of 213 ± 15 and 166 ± 5 cm ²/V·s respectively. We discuss how our methods can be used for the rapid determination of graphene quality and can complement Raman Spectroscopy techniques. Lastly, we explore a PN junction embodiment which further validates that our fabrication techniques can rapidly adapt to alternative device architectures and greatly broaden the research applicability.

Retained Carrier-Mobility and Enhanced Plasmonic-Photovoltaics of Graphene via ring-centered η6 Functionalization and Nanointerfacing

Binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp² hybridized carbons to maintain its carrier-mobility, has remained a challenge. The conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via "carbon-centered" covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp² to tetrahedral sp³. This disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties. Here, we show large-area, vapor-phase, "ring-centered" hexahapto (η⁶) functionalization of graphene to create nucleation-sites for silver nanoparticles (AgNPs) without disrupting its sp² character. This is achieved by the grafting of chromium tricarbonyl [Cr(CO)₃] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η⁶-graphene)Cr(CO)₃ complex. This nondestructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 K); with AgNPs attached on graphene/n-Si solar cells, we report an ∼11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).

Continuous and ultrathin platinum films on graphene using atomic layer deposition: a combined computational and experimental study

Integrating metals and metal oxides with graphene is key in utilizing its extraordinary material properties that are ideal for nanoelectronic and catalyst applications. Atomic layer deposition (ALD) has become a key technique for depositing ultrathin, conformal metal(oxide) films. ALD of metal(oxide) films on graphene, however, remains a genuine challenge due to the chemical inertness of graphene. In this study we address this issue by combining first-principles density functional theory (DFT) simulations with ALD experiments. The focus is on the Pt ALD on graphene, as this hybrid system is very promising for solar and fuel cells, hydrogen technologies, microreactors, and sensors. Here we elucidate the surface reactions underpinning the nucleation stage of Pt ALD on pristine, defective and functionalized graphenes. The employed reaction mechanism clearly depends on (a) the available surface groups on graphene, and (b) the ligands accompanying the metal centre in the precursor. DFT calculations also indicate that graphene oxide (GO) can afford a stronger adsorption of MeCpPtMe₃, unlike Pt(acac)₂, as compared to bare (non-functionalized) graphene, suggesting that GO monolayers are effective Pt ALD seed layers. Confirming the latter, we evince that wafer-scale, continuous Pt films can indeed be grown on GO monolayers using a thermal ALD process with MeCpPtMe₃ and O₂ gas. Besides, the current in-depth atomistic insights are of practical use for understanding similar ALD processes of other metals and metal oxides on graphene.

In Situ Observation of Initial Stage in Dielectric Growth and Deposition of Ultrahigh Nucleation Density Dielectric on Two-Dimensional Surfaces

Several proposed beyond-CMOS devices based on two-dimensional (2D) heterostructures require the deposition of thin dielectrics between 2D layers. However, the direct deposition of dielectrics on 2D materials is challenging due to their inert surface chemistry. To deposit high-quality, thin dielectrics on 2D materials, a flat lying titanyl phthalocyanine (TiOPc) monolayer, deposited via the molecular beam epitaxy, was employed to create a seed layer for atomic layer deposition (ALD) on 2D materials, and the initial stage of growth was probed using in situ STM. ALD pulses of trimethyl aluminum (TMA) and H2O resulted in the uniform deposition of AlOx on the TiOPc/HOPG. The uniformity of the dielectric is consistent with DFT calculations showing multiple reaction sites are available on the TiOPc molecule for reaction with TMA. Capacitors prepared with 50 cycles of AlOx on TiOPc/graphene display a capacitance greater than 1000 nF/cm(2), and dual-gated devices have current densities of 10(-7)A/cm(2) with 40 cycles.

Near-infrared electro-optic modulator based on plasmonic graphene

We propose a novel scheme for an electro-optic modulator based on plasmonically enhanced graphene. As opposed to previously reported designs where the switchable absorption of graphene itself was employed for modulation, here a graphene monolayer is used to actively tune the plasmonic resonance condition through the modification of interaction between optical field and an indium tin oxide (ITO) plasmonic structure. Strong plasmonic resonance in the near infrared wavelength region can be supported by accurate design of ITO structures, and tuning the graphene chemical potential through electrical gating switches on and off the ITO plasmonic resonance. This provides much increased electro-absorption efficiency as compared to systems relying only on the tunable absorption of the graphene.

Fluorinated graphene and hexagonal boron nitride as ALD seed layers for graphene-based van der Waals heterostructures

Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H2O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics.

Controlled, reversible, and nondestructive generation of uniaxial extreme strains (>10%) in graphene

Theoretical calculations have predicted that extreme strains (>10%) in graphene would result in novel applications. However, up to now the highest reported strain reached ∼1.3%. Here, we demonstrate uniaxial strains >10% by pulling graphene using a tensile-MEMS. To prevent it from slipping away it was locally clamped with epoxy using a femtopipette. The results were analyzed using Raman spectroscopy and optical tracking. Furthermore, analysis proved the process to be reversible and nondestructive for the graphene.

Boron nitride film as a buffer layer in deposition of dielectrics on graphene

As a two-dimensional material, graphene is highly susceptible to environmental influences. It is therefore challenging to deposit dielectrics on graphene without affecting its electronic properties. It is demonstrated that the effect of the dielectric deposition on graphene can be reduced by using a multilayer hexagonal boron nitride film as a buffer layer. Particularly, the boron nitride layer provides significant protection in magnetron sputtering deposition. It also enables growth of uniform and charge trapping free high-k dielectrics by atomic layer deposition. The doping effect of various deposition methods on graphene has been discussed.

Emerging Applications for High K Materials in VLSI Technology

The current status of High K dielectrics in Very Large Scale Integrated circuit (VLSI) manufacturing for leading edge Dynamic Random Access Memory (DRAM) and Complementary Metal Oxide Semiconductor (CMOS) applications is summarized along with the deposition methods and general equipment types employed. Emerging applications for High K dielectrics in future CMOS are described as well for implementations in 10 nm and beyond nodes. Additional emerging applications for High K dielectrics include Resistive RAM memories, Metal-Insulator-Metal (MIM) diodes, Ferroelectric logic and memory devices, and as mask layers for patterning. Atomic Layer Deposition (ALD) is a common and proven deposition method for all of the applications discussed for use in future VLSI manufacturing.

Self-induced gate dielectric for graphene field-effect transistor

We report the electronic characteristics of an avant-garde graphene-field-effect transistor (G-FETs) based on ZnO microwire as top-gate electrode with self-induced dielectric layer. Surface-adsorbed oxygen is wrapped up the ZnO microwire to provide high electrostatic gate-channel capacitance. This nonconventional device structure yields an on-current of 175 μA, on/off current ratio of 55, and a device mobility exceeding 1630 cm(2)/(V s) for holes and 1240 cm(2)/(V s) for electrons at room temperature. Self-induced gate dielectric process prevents G-FETs from impurity doping and defect formation in graphene lattice and facilitates the lithographic process. Performance degradation of G-FETs can be overcome by this avant-garde device structure.

Facile preparation of high-quality Pt/reduced graphene oxide nanoscrolls for methanol oxidation

A simple and novel approach for the preparation of a Pt/reduced graphene oxide nanoscroll (Pt/RGOS) nanocatalyst is reported for the first time. The Pt/reduced graphene oxide (Pt/RGO) was fabricated by the co-reduction of GO and Pt salt using ethylene glycol under microwave irradiation, then the Pt/RGOSs were obtained by oxygen implosion in situ rolling up of the Pt/RGO using catalytic decomposition of Pt towards H2O2 under ultrasonication. Transmission electron microscopy shows that the Pt nanoparticles are uniformly dispersed on the reduced graphene oxide nanoscrolls with tubular structure, open edges and ends, and tubular diameter ranging from 10 to 100 nm. X-ray diffraction indicates that the crystal structure and diffraction intensity of the platinum practically remains unchanged, and the RGO has not been oxidized before or after rolling. Raman spectroscopy reveals that the Pt/RGOSs have a higher D/G ratio (1.2) than Pt/RGO (1.1). BET (Brunauer, Emmett and Teller) results exhibit that the Pt/RGOSs possess higher specific surface area and broader pore size range (188 m(2) g(-1), 25-45 nm) than Pt/RGO (122 m(2) g(-1), 30-38 nm). Additionally, the electrocatalytic performance of the Pt/RGOSs for methanol oxidation was evaluated, and the results show that the Pt/RGOSs possess significantly higher electrocatalytic activity and stability than Pt/RGO.

Quantitatively enhanced reliability and uniformity of high-κ dielectrics on graphene enabled by self-assembled seeding layers

The full potential of graphene in integrated circuits can only be realized with a reliable ultrathin high-κ top-gate dielectric. Here, we report the first statistical analysis of the breakdown characteristics of dielectrics on graphene, which allows the simultaneous optimization of gate capacitance and the key parameters that describe large-area uniformity and dielectric strength. In particular, vertically heterogeneous and laterally homogeneous Al2O3 and HfO2 stacks grown via atomic-layer deposition and seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride organic monolayer exhibit high uniformities (Weibull shape parameter β > 25) and large breakdown strengths (Weibull scale parameter, E(BD) > 7 MV/cm) that are comparable to control dielectrics grown on Si substrates.

Graphene: an emerging electronic material

Graphene, a single layer of carbon atoms in a honeycomb lattice, offers a number of fundamentally superior qualities that make it a promising material for a wide range of applications, particularly in electronic devices. Its unique form factor and exceptional physical properties have the potential to enable an entirely new generation of technologies beyond the limits of conventional materials. The extraordinarily high carrier mobility and saturation velocity can enable a fast switching speed for radio-frequency analog circuits. Unadulterated graphene is a semi-metal, incapable of a true off-state, which typically precludes its applications in digital logic electronics without bandgap engineering. The versatility of graphene-based devices goes beyond conventional transistor circuits and includes flexible and transparent electronics, optoelectronics, sensors, electromechanical systems, and energy technologies. Many challenges remain before this relatively new material becomes commercially viable, but laboratory prototypes have already shown the numerous advantages and novel functionality that graphene provides.

Ferroelectric memory based on nanostructures

In the past decades, ferroelectric materials have attracted wide attention due to their applications in nonvolatile memory devices (NVMDs) rendered by the electrically switchable spontaneous polarizations. Furthermore, the combination of ferroelectric and nanomaterials opens a new route to fabricating a nanoscale memory device with ultrahigh memory integration, which greatly eases the ever increasing scaling and economic challenges encountered in the traditional semiconductor industry. In this review, we summarize the recent development of the nonvolatile ferroelectric field effect transistor (FeFET) memory devices based on nanostructures. The operating principles of FeFET are introduced first, followed by the discussion of the real FeFET memory nanodevices based on oxide nanowires, nanoparticles, semiconductor nanotetrapods, carbon nanotubes, and graphene. Finally, we present the opportunities and challenges in nanomemory devices and our views on the future prospects of NVMDs.

Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone

Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.

Seeding atomic layer deposition of high-k dielectrics on epitaxial graphene with organic self-assembled monolayers

The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO(2) and Al(2)O(3) on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al(2)O(3) and 10 nm HfO(2) dielectric stack show high capacitance values of ∼700 nF/cm(2) and low leakage currents of ∼5 × 10(-9) A/cm(2) at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics.