Mask-free and programmable patterning of graphene by ultrafast laser direct writing

Production of Large-Area Nucleus-Free Single-Crystal Graphene-Mesh Metamaterials with Zigzag Edges

In addition to conventional monolayer or bilayer graphene films, graphene-mesh metamaterials have attracted considerable research attention within the scientific community owing to their unique physical and optical properties. Currently, most graphene-mesh metamaterials are fabricated using common lithography techniques on exfoliated graphene flakes, which require the deposition and removal of chemicals during fabrication. This process may introduce contamination or doping, thereby limiting their production size and application in nanodevices. Herein, the controlled production of wafer-scale high-quality single-crystal nucleus-free graphene-mesh metamaterial films with zigzag edges is demonstrated. The ¹³ C-isotopic labeling graphene-growth approach, large-area Raman mapping techniques, and a uniquely designed high-voltage localized-space air-ionization etching method are utilized to directly remove the graphene nuclei. Subsequently, a hydrogen-assisted anisotropic etching process is employed for transforming irregular edges into zigzag edges within the hexagonal-shaped holes, producing a large-scale single-crystal high-quality graphene-mesh metamaterial film on a Cu(111) substrate. The carrier mobilities of the fabricated field-effect transistors on the as-produced films are measured. The findings of this study enable the large-scale production of high-quality low-dimensional graphene-mesh metamaterials and provide insights for the application of integrated circuits based on graphene and other 2D metamaterials.

Laser Patterning a Graphene Layer on a Ceramic Substrate for Sensor Applications

This paper describes a method for patterning the graphene layer and gold electrodes on a ceramic substrate using a Nd:YAG nanosecond fiber laser. The technique enables the processing of both layers and trimming of the sensor parameters. The main aim was to develop a technique for the effective and efficient shaping of both the sensory layer and the metallic electrodes. The laser shaping method is characterized by high speed and very good shape mapping, regardless of the complexity of the processing. Importantly, the technique enables the simultaneous shaping of both the graphene layer and Au electrodes in a direct process that does not require a complex and expensive masking process, and without damaging the ceramic substrate. Our results confirmed the effectiveness of the developed laser technology for shaping a graphene layer and Au electrodes. The ceramic substrate can be used in the construction of various types of sensors operating in a wide temperature range, especially the cryogenic range.

Modification of graphene oxide film properties using KrF laser irradiation

Modification of various properties of graphene oxide (GO) films on SiO2/Si substrate under KrF laser radiation was extensively studied. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and the electrical resistance measurements were employed to correlate the effects of laser irradiation on structural, chemical and electrical properties of GO films under different laser fluences. Raman spectroscopy shows reduced graphene oxide patterns with increased I 2D/I G ratios in irradiated samples. X-ray photoelectron spectroscopy shows a high ratio of carbon to oxygen atoms in the reduced graphene oxide (rGO) films compared to the pristine GO films. X-ray diffraction patterns display a significant drop in the diffraction peak intensity after laser irradiation. Finally, the electrical resistance of irradiated GO films reduced by about four orders of magnitudes compared to the unirradiated GO films. Simultaneously, reduction and patterning of GO films display promising fabrication technique that can be useful for many graphene-based devices.

Albumin (BSA) adsorption onto graphite stepped surfaces

Nanomaterials are good candidates for the design of novel components with biomedical applications. For example, nano-patterned substrates may be used to immobilize protein molecules in order to integrate them in biosensing units. Here, we perform long MD simulations (up to 200 ns) using an explicit solvent and physiological ion concentrations to characterize the adsorption of bovine serum albumin (BSA) onto a nano-patterned graphite substrate. We have studied the effect of the orientation and step size on the protein adsorption and final conformation. Our results show that the protein is stable, with small changes in the protein secondary structure that are confined to the contact area and reveal the influence of nano-structuring on the spontaneous adsorption, protein-surface binding energies, and protein mobility. Although van der Waals (vdW) interactions play a dominant role, our simulations reveal the important role played by the hydrophobic lipid-binding sites of the BSA molecule in the adsorption process. The complex structure of these sites, that incorporate residues with different hydrophobic character, and their flexibility are crucial to understand the influence of the ion concentration and protein orientation in the different steps of the adsorption process. Our study provides useful information for the molecular engineering of components that require the immobilization of biomolecules and the preservation of their biological activity.

3D nanostructured inkjet printed graphene via UV-pulsed laser irradiation enables paper-based electronics and electrochemical devices

Emerging research on printed and flexible graphene-based electronics is beginning to show tremendous promise for a wide variety of fields including wearable sensors and thin film transistors. However, post-print annealing/reduction processes that are necessary to increase the electrical conductivity of the printed graphene degrade sensitive substrates (e.g., paper) and are whole substrate processes that are unable to selectively anneal/reduce only the printed graphene-leaving sensitive device components exposed to damaging heat or chemicals. Herein a pulsed laser process is introduced that can selectively irradiate inkjet printed reduced graphene oxide (RGO) and subsequently improve the electrical conductivity (Rsheet∼0.7 kΩ□(-1)) of printed graphene above previously published reports. Furthermore, the laser process is capable of developing 3D petal-like graphene nanostructures from 2D planar printed graphene. These visible morphological changes display favorable electrochemical sensing characteristics-ferricyanide cyclic voltammetry with a redox peak separation (ΔEp) ≈ 0.7 V as well as hydrogen peroxide (H2O2) amperometry with a sensitivity of 3.32 μA mM(-1) and a response time of <5 s. Thus this work paves the way for not only paper-based electronics with graphene circuits, it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells, and theranostic devices.

Direct Growth of Patterned Graphene

The direct growth of single-layer graphene patterns via electron irradiation of aromatic self-assembled monolayers and subsequent annealing is demonstrated. In this way, a reduction in the number of necessary manufacturing steps is achieved. The formed micro- and nanostructures can be arbitrarily shaped and eventually implemented in a manifold of applications.