Graphene Substrate Research Articles

Ultra-Low Loading of Iron Oxide and Platinum on CVD-Graphene Composites as Effective Electrode Catalysts for Solid Acid Fuel Cells

We propose a new design for electrocatalysts consisting of two electrocatalysts (platinum and iron oxide) that are deposited on the surfaces of an oxidized graphene substrate. This design is based on a simple structure where the catalysts were deposited separately on both sides of oxidized graphene substrate; while the iron oxide precipitated out of the etching solution on the bottom-side, the surface of the oxidized graphene substrate was decorated with platinum using the atomic layer deposition technique. The Fe2O3-decorated CVD-graphene composite exhibited better hydrogen electrooxidation performance (area-normalized electrode resistance (ANR) of ~600 Ω·cm−2) and superior stability in comparison with bare-graphene samples (ANR of ~5800 Ω·cm−2). Electrochemical impedance measurements in humidified hydrogen at 240 °C for (Fe2O3|Graphene|Platinum) electrodes show ANR of ~0.06 Ω·cm−2 for a platinum loading of ~60 µgPt·cm−2 and Fe2O3 loading of ~2.4 µgFe·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. This ANR value is ~30% lower than the charge transfer resistance of the same electrode composition in the absence of Fe2O3 nanoparticles. Detailed study of the Fe2O3 electrocatalytic properties reveals a significant improvement in the electrode’s activity and performance stability with the addition of iron ions to the platinum-decorated oxidized graphene cathodes, indicating that these hybrid (Fe2O3|Graphene|Platinum) materials may serve as highly efficient catalysts for solid acid fuel cells and beyond.

Graphene Hollow Micropatterns via Capillarity-Driven Assembly for Drug Storage and Neural Cell Alignment.

Electrical conductivity, cell-guided surface topology, and drug storage capacity of biomaterials are attractive properties for the repair and regeneration of anisotropic tissues with electrical sensitivity, such as nerves. However, designing and fabricating implantable biomaterials with all these functions remain challenging. Herein, we developed a freestanding graphene substrate with micropatterned surfaces by a simple templating method. Importantly, the raised surface micropatterns had an internal hollow structure. The morphology results showed that the template microgroove width and the graphene nanosheet size were important indicators of the formation of the hollow structures. Through real-time monitoring and theoretical analysis of the formation process, it was found that the main formation mechanism was the delamination and interlayer movement of the graphene nanosheets triggered by the evaporation-induced capillary force. Finally, we achieved the controlled release of loaded microparticles and promoted the orientation of rat dorsal root ganglion neurons by applying an electric field to the hollow micropatterns. This capillarity-induced self-assembly strategy paves the way for the development of high-performance graphene micropatterned films with a hollow structure that have potential for clinical application in the repair of nerve injury.

Imaging Field-Driven Melting of a Molecular Solid at the Atomic Scale.

Solid-liquid phase transitions are basic physical processes, but atomically-resolved microscopy has yet to capture their full dynamics. We have developed a new technique for controlling the melting and freezing of self-assembled molecular structures on a graphene field-effect transistor (FET) that allows phase transition behavior to be imaged using atomically-resolved scanning tunneling microscopy. This is achieved by applying electric fields to F4 TCNQ-decorated FETs to induce reversible transitions between molecular solid and liquid phases at the FET surface. Nonequilibrium melting dynamics are visualized by rapidly heating the graphene substrate with electrical current and imaging the resulting evolution toward new 2D equilibrium states. An analytical model has been developed that explains observed mixed-state phases based on spectroscopic measurement of solid and liquid molecular energy levels. The observed non-equilibrium melting dynamics are consistent with Monte Carlo simulations. This article is protected by copyright. All rights reserved.

Graphene/Heterojunction Composite Prepared by Carbon Thermal Reduction as a Sulfur Host for Lithium-Sulfur Batteries.

An interlayer nanocomposite (CC@rGO) consisting of a graphene heterojunction with CoO and Co9S8 was prepared using a simple and low-cost hydrothermal calcination method, which was tested as a cathode sulfur carrier for lithium-sulfur batteries. The CC@rGO composite comprises a spherical heterostructure uniformly distributed between graphene sheet layers, preventing stacking the graphene sheet layer. After the introduction of cobalt heterojunction on a graphene substrate, the Co element content increases the reactive sites of the composite and improves its electrochemical properties to some extent. The composite exhibited good cycling performance with an initial discharge capacity of 847.51 mAh/g at 0.5 C and a capacity decay rate of 0.0448% after 500 cycles, which also kept 452.91 mAh/g at 1 C and in the rate test from 3 C back to 0.1 C maintained 993.27 mAh/g. This article provides insight into the design of cathode materials for lithium-sulfur batteries.

Selective Growth of van der Waals Heterostructures Enabled by Electron-Beam Irradiation.

Van der Waals heterostructures (vdWHSs) enable the fabrication of complex electronic devices based on two-dimensional (2D) materials. Ideally, these vdWHSs should be fabricated in a scalable and repeatable way and only in the specific areas of the substrate to lower the number of technological operations inducing defects and impurities. Here, we present a method of selective fabrication of vdWHSs via chemical vapor deposition by electron-beam (EB) irradiation. We distinguish two growth modes: positive (2D materials nucleate on the irradiated regions) on graphene and tungsten disulfide (WS2) substrates, and negative (2D materials do not nucleate on the irradiated regions) on the graphene substrate. The growth mode is controlled by limiting the air exposure of the irradiated substrate and the time between irradiation and growth. We conducted Raman mapping, Kelvin-probe force microscopy, X-ray photoelectron spectroscopy, and density-functional theory modeling studies to investigate the selective growth mechanism. We conclude that the selective growth is explained by the competition of three effects: EB-induced defects, adsorption of carbon species, and electrostatic interaction. The method here is a critical step toward the industry-scale fabrication of 2D-materials-based devices.

Design and optimization of a graphene-enhanced tunable wire-grid-like polarizer operating in the 0.5–0.75 THz band

Wireless networks are experiencing a surge in demand for data bandwidth, necessitating higher performance and faster data rates. However, conventional signal processing techniques are inadequate for potential future developments that require the use of higher carrier frequencies. The terahertz region of the spectrum has become an increasingly prominent area of research for wireless communication applications. However, components commonly utilized for lower frequency ranges exhibit inefficiencies and significant losses when operating at terahertz frequencies. Furthermore, the miniaturization of antenna sizes to the micrometer scale has made the concept of perfect electric conductor ineffective in the terahertz range. Therefore, it is imperative to establish a reference system of electromagnetic devices. Due to the essential role of polarization in wireless communication and the convenient and widely used properties of wire-grid polarizers, this article establishes a reference for the polarization effect of wire grid polarizers and obtains their optimal parameters. The optimal parameters are 61.58 μm distance, 20 μm thickness and 20 μm width within the frequency band from 0.5 THz to 0.75 THz. We proposed a three-layer structure consisting of copper wire-grids, monolayer graphene, and silicon dioxide substrate to combine the remarkable electromagnetic properties of graphene with wire-grids polarizer. The resulting graphene-enhanced polarizer achieved excellent polarization improvement, with a strongly reduced S21 transmission magnitude up to −55 dB compared to the case without graphene, representing an approximately 20 dB decrease.

Remediation of Amitriptyline Pharmaceutical Wastewater by Heteroatom-Doped Graphene Oxide: Process Optimization and Packed-Bed Studies

Amitriptyline residue released into the aquatic ecosystem can have detrimental consequences on marine organisms and human wellbeing via consumption of polluted water. With a uniquely large surface area and abundant functionalities, graphene oxide adsorption offers a remediation solution for such water pollution. This study focused on synthesizing a novel graphene-based adsorbent via ice-templating of boron-doped graphene substrate. The batch adsorption performance of the as-synthesized adsorbent was explored by central composite design (CCD), while its potential large-scale application was evaluated with a packed-bed column study. The CCD optimized conditions of 12.5 mg dosage, 32 min adsorption time, 30 °C operating temperature and 70 ppm concentration produced the highest removal efficiency of 87.72%. The results of the packed-bed study indicated that continuous adsorption of amitriptyline was best performed at a graphene bed of 3.5 cm in height, with 100 ppm of the pharmaceutical solution flowing at 2 mL/min. Furthermore, the breakthrough curve was effectively portrayed by the Log Bohart–Adams model. The as-synthesized adsorbent showed a high regeneration potential using ethanol eluent via multiple adsorption–desorption cycles. The results suggest the boron-doped graphene adsorbent in packed-bed as a highly effective system to remediate amitriptyline in an aqueous environment.

Effect of graphene on solid–liquid coexistence in Cu nanodroplets

The microstructure determines the macro properties, so the chemical and physical properties of nanoparticles can be tuned by changing their structures. A molecular dynamics simulation for the rapid solidification of Cu nanodroplets on the graphene sheet is conducted to investigate the effect of substrate on nanoparticles. The phase transition, structure evolution, and crystallinity are quantified by the potential energy, the largest standard cluster analysis, and Bond-orientation order parameters. It is found that the solidification is inhomogeneous and stepwise crystallization. Interestingly, originating from the graphene wettability, different solid–liquid coexistence states are obtained that may have the potential to modify the chemical and physical reactions on nanoparticles. The temperature of this solid–liquid coexistence state depends strongly on the structural evolution of crystallization and thus can be regulated by the wetting properties of the graphene substrate. These results significantly extend the fundamental understanding of heterogeneous nucleation in nanodroplets, providing important insights for designing and fabricating composite materials with multifunctional properties.

CO2 reduction performance of Cu/Er supported on N-doped graphene: A first principles study

A high atomic utilization and excellent catalytic activity distinguish atomic dispersion catalysts from the others, which are frequently utilized in CO2 reduction. Compared with single-atom catalysts (SACs), diatomic catalysts (DACs) have more dispersed active sites and different electronic structures, which could show different catalytic properties. Here, the CO2 reduction reaction (CO2RR) to C1 products process was systematically investigated for five different graphene-supported catalysts, including monatomic CuNC and ErNC, diatomic CuNC-ErNC, CuErNC-I, and CuErNC-II, using first principles calculations. Their free-energy diagrams were created, and the limit-potential /overpotential of different products were determined. It was shown that the minimum overpotential for CO2RR to CO/CH4 was 0.28/0.91 V on CuErNC-I(Er), to HCOOH was 1.01 V on CuErNC-I(Cu/Er), and to CH3OH was 0.81 V on CuErNC-I(Cu), respectively. At the same time, CuErNC-I displayed better electrochemical activity than others, and CuNC-ErNC had high selectivity comparing CO2RR with hydrogen evolution reaction (HER). This work provided a successful example to design high performance and selectivity catalysts by anchoring metal dimers to N-doped graphene substrates.

Conductivity Enhancement of Graphene and Graphene Derivatives by Silver Nanoparticles

In this article, a facile way for the doping of graphene and graphene derivatives with silver nanoparticles at different Ag ratios is described. Ag nanoparticles were formed directly on the surface of two different graphene substrates dispersed in dimethylformamide by the reduction of Ag cations with NaBH4. A few layered graphene nanosheets (FLG) produced from graphite and reduced graphene oxide functionalized with amino arylsulfonates (f-rGO) were used as substrates. The final graphene/Ag nanoparticle hybrid in the form of solid, dense spots showed enhanced electrical conductivity, which can be attributed to the formation of conductive interconnections between the 2D nanosheets. Importantly, electrical conductivities of 20 and 167 103 S m−1 were measured for the hybrids of f-rGO and FLG, respectively, with the higher Ag percentage without an annealing process. A representative hybrid f-rGO with Ag nanoparticles was used for the development of a highly conductive water-based gravure ink with excellent printing properties.

Enhancing the Mechanical Stability of 2D Fullerene with a Graphene Substrate and Encapsulation.

Recent advancements have led to the synthesis of novel monolayer 2D carbon structures, namely quasi-hexagonal-phase fullerene (qHPC60) and quasi-tetragonal-phase fullerene (qTPC60). Particularly, qHPC60 exhibits a promising medium band gap of approximately 1.6 eV, making it an attractive candidate for semiconductor devices. In this study, we conducted comprehensive molecular dynamics simulations to investigate the mechanical stability of 2D fullerene when placed on a graphene substrate and encapsulated within it. Graphene, renowned for its exceptional tensile strength, was chosen as the substrate and encapsulation material. We compared the mechanical behaviors of qHPC60 and qTPC60, examined the influence of cracks on their mechanical properties, and analyzed the internal stress experienced during and after fracture. Our findings reveal that the mechanical reliability of 2D fullerene can be significantly improved by encapsulating it with graphene, particularly strengthening the cracked regions. The estimated elastic modulus increased from 191.6 (qHPC60) and 134.7 GPa (qTPC60) to 531.4 and 504.1 GPa, respectively. Moreover, we observed that defects on the C60 layer had a negligible impact on the deterioration of the mechanical properties. This research provides valuable insights into enhancing the mechanical properties of 2D fullerene through graphene substrates or encapsulation, thereby holding promising implications for future applications.

Cu+ redox activation and polyselenide stabilization via strong Se-C interaction for superior magnesium storage

Copper selenides have been recognized as one of the most promising Mg2+ host materials due to their high electrical conductivity and unique ionic displacement mechanism, yet they suffer from low magnesium storage capacity and inferior cycling stability caused by insufficient Cu+ conversion and inevitable polyselenide dissolution. Herein, the graphene-supported CuSe (CuSe@G) with strong Se-C interaction is prepared as the high-performance cathode material for rechargeable magnesium batteries. The strong Se-C interaction between CuSe monomers and graphene substrate can not only immobilize the Se species but also boost the electrochemical replacement reaction between Cu2+ and Mg2+. The highly dispersed CuSe nanoparticles on graphene can also accelerate Mg2+ diffusion rate at the cathode-electrolyte interfaces and further regulate the electrochemical reaction kinetics. Such well-designed method can significantly improve the reversible capacity from 167 to 233.7 mAh g–1 at 0.1 A g–1 current density and cycling stability (63 mAh g–1 after 1000 cycles with 0.039% capacity decay per cycle) of copper selenide cathode materials. This work presents an in-depth insight into graphene bonding strategy for fabricating superior conversion-type selenide cathodes for rechargeable magnesium batteries.

Synthesis of Axially Coordinated Cobalt Porphyrin/graphene Oxide Nanocomposite for Enhanced Electrocatalytic CO2 Reduction to CO

The electrocatalysts containing cobalt-pyrrolic nitrogen-carbon (Co-N4-C) moiety for CO2 reduction reaction (CO2RR) have caught much attention. However, the effects of Co valence state and its synergy with graphene substrate are not clear yet. In this work, cobalt porphyrin (CoTPP) molecule with the intrinsic Co-N4-C moiety is successfully combined with graphene oxide (GO) via three kinds of liquid-phase methods. The ratio of CoTPP to GO and the valence state of Co atom are studied to explore their catalysis for CO2RR to CO. It is found that axially-coordinated Co(III)TPPCl/GO nanocomposites synthesized via a chemical method exhibit better ability for CO2RR, as compared with Co(II)TPP+GO and/or Co(III)TPPCl+GO nanocomposites obtained via a physically mixing way. After optimizing the ratio of CoTPP to GO, the Faradaic efficiency (FE) is more than 90% for CO2RR to CO between –0.7 and –0.8 V vs. reversible hydrogen electrode (RHE) in Co(III)TPPCl/GO75. The synergy between CoTPP and GO and the effect of Co valence state are systematically investigated, indicating that their strong interaction plays the key role in electrocatalytic CO2RR.

Direct mapping of bending and torsional dynamics in individual nanostructures

Investigating coherent acoustic vibrations in nanostructured materials provides fundamental insights into optomechanical responses and microscopic energy flow. Extensive measurements of vibrational dynamics have been performed for a wide variety of nanoparticles and nanoparticle assemblies. However, virtually all of them show that only the dilation modes are launched after laser excitations, and the acoustic bending and torsional motions, which are commonly observed in photoexcited chemical bonds, are absent. Unambiguous identification and refined characterization of these "missing" modes have been a long-standing issue. In this report, we investigated the acoustic vibrational dynamics of individual Au nanoprisms on free-standing graphene substrates using an ultrafast high-sensitivity dark-field imaging approach in four-dimensional transmission electron microscopy. Following optical excitations, we observed low-frequency multiple-mode oscillations and higher superposition amplitudes at nanoprism corners and edges on the subnanoparticle level. In combination with finite-element simulations, we determined that these vibrational modes correspond to out-of-plane bending and torsional motions, superimposed by an overall tilting effect of the nanoprisms. The launch and relaxation processes of these modes are highly pertinent to substrate effects and nanoparticle geometries. These findings contribute to the fundamental understanding about acoustic dynamics of individual nanostructures and their interaction with substrates.

The Landscape of Gold Nanocrystal Surface Chemistry.

ConspectusGold nanoparticles (AuNPs) exhibit unique size- and shape-dependent properties not obtainable at the macroscale. Gold nanorods (AuNRs), with their morphology-dependent optical properties, ability to convert light to heat, and high surface-to-volume ratios, are of great interest for biosensing, medicine, and catalysis. While the gold core provides many fascinating properties, this Account focuses on AuNP soft surface coatings, which govern the interactions of nanoparticles with the local environments. Postmodification of AuNP surface chemistry can greatly alter NP colloidal stability, nano-bio interactions, and functionality. Polyelectrolyte coatings provide controllable surface-coating thickness and charge, which impact the composition of the acquired corona in biological settings. Covalent modification, in which covalently bound ligands replace the original capping layer, is often performed with thiols and disulfides due to their ability to replace native coatings. N-heterocyclic carbenes and looped peptides expand the possible functionalities of the ligand layer.The characterization of surface ligands bound to AuNPs, in terms of ligand density and dynamics, remains a challenge. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for understanding molecular structures and dynamics. Our recent NMR work on AuNPs demonstrated that NMR data were obtainable for ligands on NPs with diameters up to 25 nm for the first time. This was facilitated by the strong proton NMR signals of the trimethylammonium headgroup, which are present in a distinct regime from other ligand protons' signals. Ligand density analyses showed that the smallest AuNPs (below 4 nm) had the largest ligand densities, yet spin-spin T2 measurements revealed that these smallest NPs also had the most mobile ligand headgroups. Molecular dynamics simulations were able to reconcile these seemingly contradictory results.While NMR spectroscopy provides ligand information averaged over many NPs, the ligand distribution on individual particles' surfaces must also be probed to fully understand the surface coating. Taking advantage of improvements in electron energy loss spectroscopy (EELS) detectors employed with scanning transmission electron microscopy (STEM), a single-layer graphene substrate was used to calibrate the carbon K-edge EELS signal, allowing quantitative imaging of the carbon atom densities on AuNRs with sub-nanometer spatial resolution. In collaboration with others, we revealed that the mean value for surfactant-bilayer-coated AuNRs had 10-30% reduced ligand density at the ends of the rods compared to the sides, confirming prior indirect evidence for spatially distinct ligand densities.Recent work has found that surface ligands on nanoparticles can, somewhat surprisingly, enhance the selectivity and efficiency of the electrocatalytic reduction of CO2 by controlling access to the active site, tuning its electronic and chemical environment, or denying entry to impurities that poison the nanoparticle surface to facilitate reduction. Looking to the future, while NMR and EELS are powerful and complementary techniques for investigating surface coatings on AuNPs, the frontier of this field includes the development of methods to probe the surface ligands of individual NPs in a high-throughput manner, to monitor nano-bio interactions within complex matrices, and to study structure-property relationships of AuNPs in biological systems.

Graphene Oxide Facilitates Transformation of Waste PET into MOF Nanorods in Ionic Liquids.

Although though ionic liquids (IL) are rapidly emerging as highly efficient reagents for the depolymerization of waste plastics, their high cost and adverse impact on the environment make the overall process not only expensive but also environmentally harmful. In this manuscript, we report that graphene oxide (GO) facilitates the transformation of waste polyethylene terephthalate (PET) to Ni-MOF (metal organic framework) nanorods anchored on reduced graphene oxide (Ni-MOF@rGO) through NMP (N-Methyl-2-pyrrolidone)-based coordination in ionic liquids. Morphological studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed mesoporous three-dimensional structures of micrometer-long Ni-MOF nanorods anchored on reduced graphene substrates (Ni-MOF@rGO ), whereas structural studies using XRD and Raman spectra demonstrated the crystallinity of Ni-MOF nanorods. Chemical analysis of Ni-MOF@rGO carried out using X-ray photoelectron spectroscopy demonstrated that nickel moieties exist in an electroactive OH-Ni-OH state, which was further confirmed by nanoscale elemental maps recorded using energy-dispersive X-ray spectroscopy (EDS). The applicability of Ni-MOF@rGO as an electro-catalyst in a urea-enhanced water oxidation reaction (UOR) is reported. Furthermore, the ability of our newly developed NMP-based IL to grow MOF nanocubes on carbon nanotubes and MOF nano-islands on carbon fibers is also reported.

Investigation of bifunctionality of FePc-functionalized graphene for enhanced ORR/OER activity

Iron phthalocyanine monolayer supported on a graphene substrate (GFePc) is a promising Pt-free oxygen reduction reaction catalyst. The electronic properties of GFePc can be tuned via the ligand exchange of FePc, substate doping, and defect incorporation into the graphene substrate. Boron and nitrogen were chosen as substrate dopants due to their comparability to carbon in size. Two of the most common graphene defects, single and double (585) vacancies, were chosen to represent defects that can naturally occur on the graphene substrate. Tetra-substituted phthalocyanines (carboxy-, nitro-, and amino-) and hexadeca-substituted phthalocyanines (chloro‑, fluoro-, and amino-) were tested due to their availability in the current market. Utilizing ab initio spin polarized density functional theory (DFT) calculations, the dominating pathways of both the oxygen reduction (ORR) and oxygen evolution reactions (OER) have been simulated along with defining their rate-limiting step to quantify the ORR/OER overpotentials (indicator of catalyst reactivity/performance). The DFT results show that ∼1 at.% Boron doping in conjunction with a mono-vacancy graphene substrate offers the best ORR performance but a worse OER performance when compared to the pristine GFePc. Generally, an increase in ORR activity exhibited a decrease in OER activity. A qualitative volcano correlation between electronic descriptors and ORR overpotential for modified GFePc systems was observed. The present study allows for expanded understanding and definition of substituted iron phthalocyanine functionalized graphene and the effects of both substrate modification and ligand exchange on GFePc's performance as a potential bifunctional single-metal-atom based electro-catalyst.

Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial β-In2Se3 Thin Films.

Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In2Se3 has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of β-In2Se3 films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer β-In2Se3 is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer β-In2Se3/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In2Se3 film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality β-In2Se3 thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial β-In2Se3 films.

Substrate Effect on Band Bending of MoSe2 Monolayer Near Mirror‐Twin Domain Boundaries

AbstractBand bending near mirror twin domain boundaries (MTBs) in a MoSe2 monolayer grown on different substrates, i.e., highly oriented pyrolytic graphite (HOPG), graphene‐on‐SiC, and crystalline Au(110), is investigated by low temperature scanning tunneling microscopy/spectroscopy. Upshift bending of the valence band edge near MTB is observed on both graphene and HOPG substrates, whereas a downshift bending is found on Au(110). For the former, the magnitudes of bending are different. This is explained based on the static charge model, where an accumulative charge exists at MTBs due to both the electrical dipole discontinuity across the MTB as well as charge transfer between the substrate and MoSe2 epilayer. The relevance of the static electric model is further affirmed by noting a geometric effect on the band bending, where it is asymmetric across the vertex of an MTB loop.

Comparative Evaluation of Laser-Induced Graphene (LIG) Traces on Polyimide Under Soft and Hard Stress for IoT Applications

Laser-induced graphene (LIG) is an emerging manufacturing technique for engraving graphene patterns on precursor substrates. LIG has great potential applications to flexible eco-friendly and wrapping electronics devices such as on-skin sensors and antennas for human body physiological monitoring. Moreover, LIG-made electronic labels could be embedded into innovative food packages to reduce contamination and waste. As the so-obtained conducting graphene traces form a non-homogeneous and partly volatile structure, it strongly interacts with the external environment. This paper resumes a unitary experimental campaign to quantify the stability of the sheet resistance of LIG traces against several external stimuli, such as temperature and humidity gradients, contact with dry and wet objects, and cyclic bending. The results indicate that their effects depend on the tuning parameters of the laser and, in particular, on the power and beam defocusing. The sheet resistance variation during temperature and humidity stress is relatively modest and generally reversible by resorting to a 9 W beam with a few defocusing that generates a very compact and robust graphene substrate. The cyclic touch with dry and especially with wet objects can instead produce a more remarkable variation of the resistance and even permanent degradation of the surface depending on the specific lasing parameters. A conservative ±30% uncertainty of the nominal sheet resistance hence must be included in the electromagnetic simulations of LIG-based devices to account for unpredictable dynamic interactions with real-life objects.