Graphene Patterns Research Articles

Residue-free photolithographic patterning of graphene

Photolithography of graphene using an organic photoresist (PR), whereby the graphene film is patterned into a desired geometry, is required for the fabrication of graphene-based sensors and electronic devices. However, because the PR hardens during the O2 plasma etching process, its complete removal is difficult. Herein, we present a new route to obtain residue-free patterned graphene by introducing a buffer layer between graphene and the PR. The modified photolithography process allows complete removal of the hardened PR and eliminates poly(methyl methacrylate) residues on the graphene surface during the wet transfer process. Density functional theory calculations revealed that the binding strength between the buffer layer and graphene is weaker than that between the PR and graphene. This led to a clean graphene surface without PR and other organic residues. The graphene films patterned using the modified photolithography process are of superior quality; they have the lowest surface roughness, natural hydrophobicity, and the highest transmittance of 94.1% at the wavelength of 550 nm. In addition, graphene-based field-effect transistors fabricated using the new process present the electron mobility of 800 cm2 V−1 s−1, and their charge neutrality point is located near zero bias, indicating that the unintended doping effect was effectively eliminated. This work demonstrates a new process that is compatible with silicon-based nanosystems and can be readily applied in the mass production of residue-free graphene electronics.

Interfacial Laser-Induced Graphene Enabling High-Performance Liquid-Solid Triboelectric Nanogenerator.

Laser-induced graphene (LIG) has emerged as a promising and versatile method for high-throughput graphene patterning; however, its full potential in creating complex structures and devices for practical applications is yet to be explored. In this study, an in-situ growing LIG process that enables to pattern superhydrophobic fluorine-doped graphene on fluorinated ethylene propylene (FEP)-coated polyimide (PI) is demonstrated. This method leverages on distinct spectral responses of FEP and PI during laser excitation to generate the environment preferentially for LIG formation, eliminating the need for multistep processes and specific atmospheres. The structured and water-repellant structures rendered by the spectral-tuned interfacial LIG process are suitable as the electrode for the construction of a flexible droplet-based electricity generator (DEG), which exhibits high power conversion efficiency, generating a peak power density of 47.5 W m-2 from the impact of a water droplet 105µL from a height of 25cm. Importantly, the device exhibits superior cyclability and operational stability under high humidity and various pH conditions. The facile process developed can be extended to realize various functional devices.

A comprehensive multiparametric Raman analysis of graphene evolution under prolonged near-IR femtosecond laser irradiation

Laser processing is a promising technique for graphene modification and patterning, with applications in the development of several electronic devices. In-situ Raman spectroscopy allows monitoring laser processing, providing information on numerous perturbations of the graphene lattice, such as disorder, strain, and doping, among others. This work focuses on the study of a graphene layer under prolonged irradiation with a femtosecond near-infrared laser at different average powers below the ablation threshold. The temporal evolution of the spectral parameters is analyzed, including the central position, width, and area of the main Raman bands attributed to graphene and silicon substrate, as well as the background signal. In addition, we present the correlation curves between most of these parameters. Our results show an initial instantaneous effect, linear with irradiation power, in which mainly p-type doping occurs. With prolonged fs-laser irradiation, the evolution of the spectral parameters can be divided into several intervals associated with different doping and strain stages. At each stage, the parameters present multiple time dependencies, nevertheless, several correlations between them are revealed. This work highlights the complexity of the evolution of the complete Raman spectrum of graphene and the relevance of a comprehensive multiparametric analysis.

A Simplified Method for Patterning Graphene on Dielectric Layers.

The large-scale formation of patterned, quasi-freestanding graphene structures supported on a dielectric has so far been limited by the need to transfer the graphene onto a suitable substrate and contamination from the associated processing steps. We report μm scale, few-layer graphene structures formed at moderate temperatures (600–700 °C) and supported directly on an interfacial dielectric formed by oxidizing Si layers at the graphene/substrate interface. We show that the thickness of this underlying dielectric support can be tailored further by an additional Si intercalation of the graphene prior to oxidation. This produces quasi-freestanding, patterned graphene on dielectric SiO2 with a tunable thickness on demand, thus facilitating a new pathway to integrated graphene microelectronics.

Multiband tunable perfect metamaterial absorber realized by different graphene patterns

In this paper, the absorption performance of a proposed metamaterial (MM) absorber based on a three-layer graphene structure working in the terahertz (THz) frequency band is studied. By using different types of combined graphene patterns, dual-band, tri-band, and quad-band absorption can be achieved. In the case of tri-band absorption, three absorption peaks with absorption rates of 99.7%, 99.9%, and 99.9% can be found at frequencies of 4.64 THz, 6.45 THz, and 9.71 THz, respectively. In addition, the proposed structure is polarization independent and has the absorption characteristic of wide incident angles. The frequency and the intensity of the absorption peaks can be adjusted by changing the chemical potential and the relaxation time of the graphene and the structural parameters. Therefore, we believe that the proposed graphene MM absorber structure provides flexible design ideas for a multibandwidth MM perfect absorber, and the proposed absorber also can be applied to subwavelength integrated sensors and optoelectronic devices in the terahertz range.

The role of graphene patterning in field-effect transistor sensors to detect the tau protein for Alzheimer's disease: Simplifying the immobilization process and improving the performance of graphene-based immunosensors

We report the improvement in the sensing performance of electrolyte-gated graphene field-effect transistor (FET) sensors capable of detecting tau protein through a simplified, linker-free, anti-tau antibody immobilization process. For most of the graphene-based immunosensor, linkers, such as pyrenebutanoic acid, succinimidyl ester (PSE) must be used to the graphene surface, while the other side of linkers serves to capture the antibodies that can specifically interact with the target biomarker. In this study, graphene was patterned into eight different types and linker-free patterned graphene FET sensors were fabricated to verify their detection performance. The linker-free antibody immobilization to patterned graphene exhibited that the antibody was immobilized to the edge defect and had a doping-like behaviors on graphene. As the tau protein concentration in the electrolyte increased from 10 fg/ml to 1 ng/ml, the performances, charge neutral point shift and current change rate of the patterned graphene sensors without linkers were enhanced 2–3 times compared to a pristine graphene sensor with the PSE linker. Moreover, tau protein in the plasma of five Alzheimer's disease patients was measured using a linker-free patterned graphene sensor. It shows a 3–4 times higher current change rate than that of pristine graphene sensor with the PSE linker. Since the antibody is immobilized directly without a linker, a patterned graphene sensor without a linker can operate more sensitively in higher ionic concentration electrolyte.

Stacking and gate-tunable topological flat bands, gaps, and anisotropic strip patterns in twisted trilayer graphene

Trilayer graphene with a twisted middle layer has recently emerged as a new platform exhibiting correlated phases and superconductivity near its magic angle. A detailed characterization of its electronic structure in the parameter space of twist angle $\ensuremath{\theta}$, interlayer potential difference $\mathrm{\ensuremath{\Delta}}$, and top-bottom layer stacking $\mathbit{\ensuremath{\tau}}$ reveals that flat bands with large Coulomb energy versus bandwidth $U/W>1$ are expected within a range of $\ifmmode\pm\else\textpm\fi{}0.{2}^{\ensuremath{\circ}}$ near $\ensuremath{\theta}\ensuremath{\simeq}1.{5}^{\ensuremath{\circ}}$ and $\ensuremath{\theta}\ensuremath{\simeq}1.{2}^{\ensuremath{\circ}}$ for ${\mathbit{\ensuremath{\tau}}}_{\mathrm{AA}}$ top-bottom layer stacking, between a wider ${1}^{\ensuremath{\circ}}--1.{7}^{\ensuremath{\circ}}$ range for ${\mathbit{\ensuremath{\tau}}}_{\mathrm{AB}}$ stacking, whose bands often have finite valley Chern numbers thanks to the opening of primary and secondary band gaps in the presence of a finite $\mathrm{\ensuremath{\Delta}}$, and below $\ensuremath{\theta}\ensuremath{\lesssim}0.{6}^{\ensuremath{\circ}}$ for all $\mathbit{\ensuremath{\tau}}$ considered. The largest $U/W$ ratios are expected at the magic angle $\ensuremath{\sim}1.{5}^{\ensuremath{\circ}}$ when $|\mathrm{\ensuremath{\Delta}}|\ensuremath{\sim}0$ meV for AA, and slightly below near $\ensuremath{\sim}1.{4}^{\ensuremath{\circ}}$ for finite $|\mathrm{\ensuremath{\Delta}}|\ensuremath{\sim}25$ meV for AB stackings, and near $\ensuremath{\theta}\ensuremath{\sim}0.{4}^{\ensuremath{\circ}}$ for both stackings. When $\mathbit{\ensuremath{\tau}}$ is the saddle point stacking vector between AB and BA we observe pronounced anisotropic local density of states (LDOS) strip patterns with broken triangular rotational symmetry. We present optical conductivity calculations that reflect the changes in the electronic structure introduced by the stacking and gate tunable system parameters.

Manipulating pattern periods via external bias for graphene‐based THz Dual‐Band absorber

AbstractElectrical control of terahertz (THz) radiation for high‐performance THz imaging is the key point. The spectrum suffers from a lack of active and available materials such as graphene have a severely limited bias range leading to restricted tuning. Therefore, here we demonstrated an efficient tunable device exploiting a triple bias layer for patterned graphene ribbons. Here, the patterned graphene acts as a tunable surface impedance leads to electrically controlled impedance matching between the device and free space. So, a dual‐band absorption is obtained which is appropriately robust against incident angle and capable of adjusting absorption peaks. The major contribution of the design is capability of manipulating patterns periods via gate biasing. This causes providing additional degree of freedom compared to conventional graphene patterns. According to the simulation results, the proposed device shows excellent tuning operation via gate bias voltages.

Moire Is Different

Graphene, as the thinnest material ever found, exhibits unconventionally relativistic behaviour of Dirac fermions. However, unusual phenomena (such as superconductivity) arise when stacking two graphene layers and twisting the bilayer graphene. The relativistic Dirac fermion in graphene has been widely studied and understood, but the large change observed in twisted bilayer graphene (TBG) is intriguing and still unclear because only van der Waals force (vdW) interlayer interaction is added from graphene to TBG and such a very weak interaction is expected to play a negligible role. To understand such dramatic variation, we studied the electronic structures of monolayer, bilayer and twisted bilayer graphene. Twisted bilayer graphene creates different moiré patterns when turned at different angles. We proposed tight-binding and effective continuum models and thereby drafted a computer code to calculate their electronic structures. Our calculated results show that the electronic structure of twisted bilayer graphene changes significantly even by a tiny twist. When bilayer graphene is twisted at special “magic angles”, flat bands appear. We examined how these flat bands are created, their properties and the relevance to some unconventional physical property such as superconductivity. We conclude that in the nanoscopic scale, similar looking atomic structures can create vastly different electronic structures. Like how P. W. Anderson stated that similar looking fields in science can have differences in his article “More is Different”, similar moiré patterns in twisted bilayer graphene can produce different electronic structures.

High-Quality Transferred GaN-Based Light-Emitting Diodes through Oxygen-Assisted Plasma Patterning of Graphene.

Two-dimensional (2D) release layers are commonly used to realize flexible nitride films. Here, high-quality, large-area, and transferable nitride films can be precisely controlled grown on O2-plasma-assisted patterned graphene. The first-principles calculation indicates that the patterned graphene introduced by O2 plasma changes the original wettability of sapphire and the growth behavior of Al atoms is related with layer number of graphene, which is consistent with experimental results. The as-fabricated violet GaN-based light-emitting diodes (LEDs) show high stability and high light output power (LOP). This work provides a general rule for the growth of high-quality and transferable III-nitride films on graphene from the atomic scale and provide actual demonstration in LED. The advantages of the proposed new growth method can supply new ways for electronic and optoelectronic flexible devices of group III nitride semiconductors.

Hypervalent Iodine Compounds as Versatile Reagents for Extremely Efficient and Reversible Patterning of Graphene with Nanoscale Precision.

Rational patterning and tailoring of graphene relies on the disclosure of suitable reagents for structuring the target functionalities on the 2D-carbon network. Here, a series of hypervalent iodine compounds, namely, 1-chloro-1,2-benziodoxol-3(1H)-one, 1,3-dihydro-1-hydroxy-3,3-dimethyl-1,2-benziodoxole, and 3,3-dimethyl-1-(trifluoromethyl)-1,2-benziodoxole is reported to be extremely efficient for a diversified graphene patterning. The decomposition of these compounds generates highly reactive Cl, OH, and CF3 radicals exclusively in the irradiated areas, which subsequently attach onto the graphene leading to locally controlled chlorination, hydroxylation, and trifluoromethylation, respectively. This is the first realization of a patterned hydroxylation of graphene, and the degrees of functionalization of the patterned chlorination and trifluoromethylation are both unprecedented. The usage of these mild reagents here is reasonably facile compared to the reported methods using hazardous Cl2 or ICl and allows for sophisticated pattern designs with nanoscale precision, promising for arbitrary nanomanipulation of graphene's properties like hydrophilicity and conductivity by the three distinct functionalities (Cl, OH, and CF3 ). Moreover, the attachment of functional entities to these highly functionalized graphene nanoarchitectures is fully reversible upon thermal annealing, enabling a full writing/storing/reading/erasing control over the chemical information stored within graphene. This work provides an exciting clue for target 2D functionalization and modulation of graphene by using suitable hypervalent iodine compounds.

Three-Dimensional (3D) Laser-Induced Graphene: Structure, Properties, and Application to Chemical Sensing.

Notwithstanding its relatively recent discovery, graphene has gone through many evolution steps and inspired a multitude of applications in many fields, from electronics to life science. The recent advancements in graphene production and patterning, and the inclusion of two-dimensional (2D) graphenic materials in three-dimensional (3D) superstructures, further extended the number of potential applications. In this Review, we focus on laser-induced graphene (LIG), an intriguing 3D porous graphenic material produced by direct laser scribing of carbonaceous precursors, and on its applications in chemical sensors and biosensors. LIG can be shaped in different 3D forms with a high surface-to-volume ratio, which is a valuable characteristic for sensors that typically rely on phenomena occurring at surfaces and interfaces. Herein, an overview of LIG, including synthesis from various precursors, structure, and characteristic properties, is first provided. The discussion focuses especially on transport and surface properties, and on how these can be controlled by tuning the laser processing. Progresses and trends in LIG-based chemical sensors are then reviewed, discussing the various transduction mechanisms and different LIG functionalization procedures for chemical sensing. A comparative evaluation of sensors performance is then provided. Finally, sensors for glucose detection are reviewed in more detail, since they represent the vast majority of LIG-based chemical sensors.

Tunable quad-band perfect metamaterial absorber on the basis of monolayer graphene pattern and its sensing application

In this paper, a classic three-layer metamaterial absorber (MA) is designed to achieve quad-band perfect absorption. The unit cell of the top graphene pattern layer is made up of a periodically arranged graphene split-ring nested with a cross-like graphene structure formed by four L-shaped strips. The middle dielectric spacer layer is SiO2 and the ground layer is gold. Simulation results show that four absorption bands with near unity peak absorption rate will occur in the interested frequency range of 3–11 THz. The absorption mechanism and the parameter dependency are discussed at first, which will provide guiding significances for the actual fabrication. Meanwhile, when the Fermi level of graphene is increased, the four absorption bands will have different degrees of blue-shift, and when the relaxation time of graphene is increased, the four absorption peaks will increase first and then decreases. As a result, dynamical tunability of the absorption properties can be achieved by changing the Fermi level or the relaxation time of the graphene without changing the geometry of the proposed MA. Further investigation indicates that the proposed absorber is independent of the polarization of the input electromagnetic (EM) wave and can maintain well absorption properties when the incident angle is changed within a broader range. Considering the potential sensing applications, it is shown that the proposed MA can be operated as a type of refractive index sensor with highest sensitivity of 2.97THz/RIU, and the maximum figure of merit (FOM) is 47.5. In terms of these unique performances, the proposed MA has broad application prospects in multispectral optical stealth, optical filtering, integrated photo detecting, sensing and so on.

Actively tunable dual-broadband graphene-based terahertz metamaterial absorber* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11504006 and 61805072) and the Key Scientific Research Project of Colleges and Universities in Henan Province, China (Grant No. 22A140001).

A tunable metamaterial absorber (MA) with dual-broadband and high absorption properties at terahertz (THz) frequencies is designed in this work. The MA consists of a periodic array of flower-like monolayer graphene patterns at top, a SiO2 dielectric spacer in middle, and a gold ground plane at the bottom. The simulation results demonstrate that the designed MA has two wide absorption bands with an absorption of over 90% in frequency ranges of 0.68 THz–1.63 THz and 3.34 THz–4.08 THz, and the corresponding relative bandwidths reach 82.3% and 20%, respectively. The peak absorptivity of the absorber can be dynamically controlled from less than 10% to nearly 100% by adjusting the graphene chemical potential from 0 eV to 0.9 eV. Furthermore, the designed absorber is polarization-insensitive and has good robustness to incident angles. Such a high-performance MA has broad application prospects in THz imaging, modulating, filtering, etc.

(Invited) Graphene Field-Effect Transistors As Bioanalytical Sensors: Advances in Design, Fabrication and Characterization

Graphene field-effect transistors (GFETs) are emerging as bioanalytical sensors, in which their responsive electrical conductance is used to perform quantitative analyses of biologically-relevant molecules such as DNA, proteins, ions and small molecules. In this presentation, I will report on key principles and recent developments in the design, fabrication and performance of such GFET biomolecular sensors. In particular, I will discuss approaches for surface functionalization and patterning of graphene to optimize its coupling with molecules. I will also describe hardware and software developments for wafer-scale fabrication and multiplexed analyses of GFET sensor devices. Finally, I will discuss our work in developing such sensors for applications in fundamental biophysics and cancer diagnostics.

Multicomponent Covalent Chemical Patterning of Graphene.

The chemical patterning of graphene is being pursued tenaciously due to exciting possibilities in electronics, catalysis, sensing, and photonics. Despite the intense efforts, spatially controlled, multifunctional covalent patterning of graphene has not been achieved. The lack of control originates from the inherently poor reactivity of the basal plane of graphene, which necessitates the use of harsh chemistries. Here, we demonstrate spatially resolved multicomponent covalent chemical patterning of single layer graphene using a facile and efficient method. Three different functional groups could be covalently attached to the basal plane in dense, well-defined patterns using a combination of lithography and a self-limiting variant of diazonium chemistry requiring no need for graphene activation. The layer thickness of the covalent films could be controlled down to 1 nm. This work provides a solid foundation for the fabrication of chemically patterned multifunctional graphene interfaces for device applications.

Multi-bias graphene-based THz super absorber

The terahertz frequency band becomes a growth platform of various applications from medical imaging to indoor communications. Emerging new materials such as graphene and developing reliable models paved the design way for graphene-based microstructures. This paper proposes a relatively comprehensive design methodology for graphene-based multi-layers structures. The procedure includes forming device geometry, finding graphene patterns, material types, and optimizing control parameters. In this way, a reconfigurable THz wave absorber is introduced. Exploiting a multi bias scheme for a single graphene layer provide opportunity to affect device reaction via bias itself and patterns period simultaneously which increase adjustability of device response. Also using two different graphene patterns turns the device complex regarding design optimizations and simulations. So a well-known and simple circuit representation is used to design the proposed methodology and the proposed device. Knowing equivalent circuit models for the device elements triggers developing an evolutionary algorithm to search for a desirable response. In this context, the paper suggests using a weighted binary matrix in the design process. The matrix determines bias schemes for each layer. Then an evolutionary algorithm optimizes whole biases values. The expectation is more in-depth control over the device behavior via biases values. This is verified by exploited circuit model formulations and Finite Element Method (FEM) as numerical simulation for a unique three layers device.

Covalent 2D Patterning, Local Electronic Structure and Polarization Switching of Graphene at the Nanometer Level.

A very facile and efficient protocol for the covalent patterning and properties tuning of graphene is reported. Highly reactive fluorine radicals were added to confined regions of graphene directed by laser writing on graphene coated with 1‐fluoro‐3,3‐dimethylbenziodoxole. This process allows for the realization of exquisite patterns on graphene with resolutions down to 200 nm. The degree of functionalization, ranging from the unfunctionalized graphene to extremely high functionalized graphene, can be precisely tuned by controlling the laser irradiation time. Subsequent substitution of the initially patterned fluorine atoms afforded an unprecedented graphene nanostructure bearing thiophene groups. This substitution led to a complete switch of both the electronic structure and the polarization within the patterned graphene regions. This approach paves the way towards the precise modulation of the structure and properties of nanostructured graphene.

Flexible Graphene Textile Temperature Sensing RFID Coils Based on Spray Printing

Radio frequency identification (RFID) is a well-established technology utilized in inventory management, security, logistics, product marketing as well as next generation smart flexible sensor platforms. This work reports the development of printed, wearable graphene temperature sensor on flexible textile substrates with structural configuration of RFID coil. Patterning of graphene in the form of sensing RFID coils on textile surfaces was achieved with cost-effective and scalable spray printing of graphene oxide and sequential reduction to reduced graphene oxide. Graphene RFID coil operating at 13.56 MHz with temperature sensing capability, are printed on flexible, ordinary fabrics to enable wearable and flexible electronics applications. The demonstration of reduced graphene oxide on textile as temperature sensitive layer is the distinct feature of this work. Good sensitivity of 0.0125°C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> is achieved with linear response in the range of 25°C to 45°C and ~12% decrease in resistance was observed over the measured temperature span. Induced voltage of 100 mV peak-to-peak at an area of 30.25 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is measured. RFID performance of the sensor coil under different bending radii starting from fully flat (0°) to complete bending (90°) was also studied, showing that sensor coil performs well during flat operation (100 mV) and stays above noise floor even under fully bended condition (12 mV). Finally, flexible temperature sensing RFID antenna attached to human body to investigate performance for wearable applications, indicating that the sensor can effectively monitor temperatures in the range of 25°C to 45°C.

Wave propagation in elliptic graphene sheet for energy harvesting

Wave propagation of elliptic graphene sheets was investigated using the molecular dynamic (MD) simulation method for efficient energy harvesting. The displacement wave propagation pattern, wave focusing, and energy transportation of elliptic graphene sheets with different aspect ratios under various loading conditions are comprehensively studied. Results show that displacement wave energy concentrates at focal points of the elliptic graphene under impulse loadings. And the wave propagation patterns of elliptic graphene under the impulse and sinusoidal loading are different because of different frequency components in the loading. Compared with rectangular graphene sheets, elliptic graphene sheets can harvest more energy at the lower and upper focal points when line impulse loadings act at different locations. Moreover, the energy harvesting time of elliptic graphene is less than that of rectangular graphene for gathering the same amount of kinetic energy. It is found that the energy harvesting efficiency of elliptic graphene sheets outperforms those of rectangular graphene sheets with three aspect ratios, demonstrating the superiority of elliptic graphene sheets for energy harvesting. The elliptic graphene sheet with an aspect ratio of 2 has the optimal kinetic energy harvesting performance by considering both the energy harvesting time and efficiency. Our findings will be valuable for designing and fabricating the emerging two-dimensional material-based energy harvesters, mass sensors, and gas detectors.