One-step transfer and doping of large area graphene by ultraviolet curing adhesive

The application of graphene as transparent conductive electrodes remains to be a challenge mainly due to the difficulties in transfer and doping of large-area graphene. Here we report a new one-step transfer and doping method using chemical modified ultraviolet curing adhesive. This method enables faster transfer of monolayer graphene onto polyethylene terephthalate (PET) substrates up to 17 in., with a sheet resistance of 205 Ω/□ without any additional surface doping. The sheet resistances stay stable both at 20 and 80 °C in air for 50 days. Moreover, the transmittance of the graphene/PET is 90.8%, which is only 0.9% less than that of PET substrate. Finally, a well behaved capacitive-type touch panel based on this transferred method is demonstrated.     

Direct dry transfer of chemical vapor deposition graphene to polymeric substrates

We demonstrate the direct dry transfer of large area chemical vapor deposition graphene to several polymers (low density polyethylene, high density polyethylene, polystyrene, polylactide acid and poly(vinylidenefluoride-co-trifluoroethylene) by means of only moderate heat and pressure, and the later mechanical peeling of the original graphene substrate. Simulations of the graphene–polymer interactions, rheological tests and graphene transfer at various experimental conditions show that controlling the graphene–polymer interface is the key to controlling graphene transfer. Raman spectroscopy and optical microscopy were used to identify and quantify graphene transferred to the polymer substrates. The results showed that the amount of graphene transferred to the polymer can be achieved by fine tuning the transfer conditions. As a result of the direct dry transfer technique, the graphene–polymer adhesion being stronger than graphene to Si/SiO₂ wafer.     

Controllable growth of 1–7 layers of graphene by chemical vapour deposition

We report that graphene films with thickness ranging from 1 to 7 layers can be controllably synthesized on the surface of polycrystalline copper by a chemical vapour deposition method. The number of layers of graphene is controlled precisely by regulating the flow ratio of CH₄ and H₂, the reaction pressure, the temperature and the reaction time. The synthesized graphene films were characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. In addition, the graphene films transferred from copper to other substrates are found to have a good optical transmittance that makes them suitable for transparent conductive materials.     

Non-destructive electrochemical graphene transfer from reusable thin-film catalysts

We demonstrate an electrochemical method – which we term oxidative decoupling transfer (ODT) – for transferring chemical vapor deposited graphene from physically deposited copper catalyst layers. This copper oxidation-based transfer technique is generally applicable to copper surfaces, and is particularly suitable where the copper is adhered to a substrate such as oxidized silicon. Graphene devices produced via this technique demonstrate 30% higher mobility than similar devices produced by standard catalyst etching techniques. The transferred graphene films cover more than 94% of target substrates – up to 100 mm diameter films are demonstrated here – and exhibit a low Raman D:G peak ratio and a homogenous and continuous distribution of sheet conductance mapped by THz time-domain spectroscopy. By applying a fixed potential of −0.4 V vs. an Ag/AgCl reference electrode – significantly below the threshold for hydrogen production by electrolysis of water – we avoid the formation of hydrogen bubbles at the graphene–copper interface, preventing delamination of thin sputtered catalyst layers from their supporting substrates. We demonstrate the reuse of the same growth substrate for five growth and transfer cycles and prove that this number is limited by the evaporation of Cu during growth of graphene. This technique therefore enables the repeated use of the highest crystallinity and purity substrates without undue increase in cost.     

Large scale atmospheric pressure chemical vapor deposition of graphene

We demonstrate that large scale high quality graphene synthesis can be performed using atmospheric pressure chemical vapor deposition (CVD) on Cu and illustrate how this procedure eliminates major difficulties associated with the low pressure CVD approach while allowing straightforward expansion of this technology to the roll-to-roll industrial scale graphene production. The detailed recipes evaluating the effects of copper foil thicknesses, purity, morphology and crystallographic orientation on the graphene growth rates and the number of graphene layers were investigated and optimized. Various foil cleaning protocols and growth conditions were evaluated and optimized to be suitable for production of large scale single layer graphene that was subsequently transferred on transparent flexible polyethylene terephthalate (PET) polymer substrates. Such “ready to use” graphene–PET sandwich structures were as large as 40″ in diagonal and >98% single layer, sufficient for many commercial and research applications. Synthesized large graphene film consists of domains exceeding 100 μm. Some curious behavior of high temperature graphene etching by oxygen is described that allows convenient visualization of interdomain boundaries and internal stresses.     

光学透明胶膜CEF0807的性能研究

光学透明胶膜(CEF0807)是一种用于粘接光学透明元件的特种PSA(压敏胶),其对被粘基材的力学性能、透光性能、雾度、色彩失真度和可靠性等影响很大。研究结果表明:CEF0807是一种粘接性能优异的压敏胶,其对玻璃、聚碳酸酯(PC)、聚甲基丙烯酸甲酯(PMMA)和聚对苯二甲酸乙二醇酯(PET)等基材的180°剥离强度分别为141、117、108、103 N/100 mm;CEF0807具有优异的光学性能,其透光率为94.3%,而雾度和色差(ΔE)仅分别为0.80%和1.48;CEF0807经环境可靠性测试后性能优异,非常适合于光学元件、光学视窗等材料的粘接。     

pH-Mediated fine-tuning of optical properties of graphene oxide membranes

We demonstrate a pH-mediated fine-tuning method for the transmittance and optical properties of graphene oxide membranes (GOMs) which are assembled at liquid/air interface starting from graphene oxide (GO) hydrosols. The transmittance of GOM continuously decreases with the increase of the pH value of the parent hydrosol. The size and surface chemistry of GO nanosheets are discussed to how to influence the transmittance of GO hydrosol and the optical properties of the resulting membrane since a size classification occurs in acidic condition and a deoxygenate reaction is initiated by basic environment. This study indicates an easy strategy for precisely adjusting the optical properties of graphene-based membrane, which is very important for developing novel optical devices.     

Nanomechanical properties of graphene on poly(ethylene terephthalate) substrate

A graphene film was synthesized using chemical vapor deposition and then transferred to a flexible poly(ethylene terephthalate) (PET) substrate. The nanomechanical properties of the graphene/PET (G/PET) system were investigated by nanoindentation. The hardness (H) and reduced modulus (E_r) of PET and G/PET were calculated using the Oliver–Pharr method with corrections for creep and material pile-up around the contact. The H and E_r of the G/PET were 97% and 16% higher respectively than on the PET substrate. The increase in E_r can be attributed to the high in-plane elastic modulus of graphene, the smaller increase in E_r than H merely reflecting the far-field nature of the elastic stress field compared to the plastic stress field. The creep behavior of the PET is strongly hindered by the presence of the graphene overlayer. A simple volume contribution model was adopted to calculate the elastic modulus of the graphene overlayer and the computed values were of the right magnitude for graphene film.     

Synthesis of transfer-free graphene films on dielectric substrates with controllable thickness via an in-situ co-deposition method for electrochromic devices

The solutions and polymer supported materials in graphene transfer process would introduce lots of containments, defects and wrinkles, which weakens the performance of graphene. Herein, an in-situ co-deposition method is carried out to obtain transfer-free graphene films with controllable thickness on several dielectric substrates. The amorphous carbon (carbon source) and copper (catalyst) are co-deposited on dielectric substrates. Followed by an in-situ annealing process, the amorphous carbon is transformed to few-layer graphene. High co-deposition temperature could promote the decomposition of Cu(acac)₂ precursors, leading to the controllable thickness of amorphous carbon layer in Cu@C films. Finally, 3-, 5-, 8- and 10- layers graphene films with transmittance of up to 93.5% and square resistance of 0.8 kΩ·sq^?1 are obtained and a high-performance electrochromic device is fabricated using 3 layers graphene films as electrodes. The “color” and “bleach” time of the electrochromic device is 16.6 s and 6.8 s with the transmittance of 26.8% and 79.7% separately. This method paves an alternative way for the batch production of transfer-free graphene film as electrode materials.     

Enhancement of integrity of graphene transferred by interface energy modulation

We report on the systematic studies of the parameters governing the integrity of graphene film during general “wet” transfer from a thermodynamic point of view. We chose polystyrene (PS) as a test carrier material and attempted to use eight different solvents to find optimal conditions for the graphene transfer from a catalyst film to a desired substrate without defects. When parameterizing the conventional chemical properties of solvents, the boiling points and surface tension were found to be critical in determining the quality of the transferred graphene. During the formation step of a conformal PS film on a graphene surface before catalyst etching, a solvent with a boiling point over ∼140 °C was essential. During the following PS film removal step, a solvent with surface tension higher than approximately 29 dyn/cm led to the formation of a continuous graphene film without cracks and holes. In addition, a high spin-coating velocity and lower concentration of PS in the solvent enhanced the quality of a transferred graphene film. The UV treatment of Si/SiO₂ (100 nm) was also found to improve the adhesion of the graphene on substrates. By electrical characterization, morphological differences were found to affect the electrical properties markedly.     

Room temperature sputtering deposition of high-haze Ga-doped ZnO transparent conductive thin films on self-textured bio-based poly(ethylene 2, 5-furandicarboxylate) substrates

In this work, bio-based poly(ethylene 2,5-furandicarboxylate) (PEF) films were prepared by drop-casting method and used as substrates for depositing Ga-doped ZnO (GZO) transparent conductive thin films. Results showed that the 300-nm GZO thin films deposited on PEF substrates exhibited haze values above 65% at 550 nm without post-treatment. The high haze value was because of the large surface roughness of PEF films. The total optical transmittance and electrical properties of GZO thin films on PEF were comparable to those of GZO thin films on PET. The present study provides a simple way for the sputtering deposition of high-haze transparent conductive thin films on flexible substrates.     

Homogeneous bilayer graphene film based flexible transparent conductor

Graphene is considered as a promising candidate to replace conventional transparent conductors due to its low opacity, high carrier mobility and flexible structure. Multi-layer graphene or stacked single layer graphenes have been investigated in the past but both have their drawbacks. The uniformity of multi-layer graphene is still questionable, and single layer graphene stacks require many transfer processes to achieve sufficiently low sheet resistance. In this work, bilayer graphene film grown with low pressure chemical vapor deposition was used as a transparent conductor for the first time. The technique was demonstrated to be highly efficient in fabricating a conductive and uniform transparent conductor compared to multi-layer or single layer graphene. Four transfers of bilayer graphene yielded a transparent conducting film with a sheet resistance of 180 Ω(□) at a transmittance of 83%. In addition, bilayer graphene films transferred onto the plastic substrate showed remarkable robustness against bending, with sheet resistance change less than 15% at 2.14% strain, a 20-fold improvement over commercial indium oxide films.     

W18O49/PET-ITO柔性电致变色薄膜制备及其变色性能

采用溶剂热法制备W18O49纳米线电致变色材料，喷涂在聚对苯二甲酸乙二醇酯?氧化铟锡(PET?ITO)(方阻35 Ω)柔性透明导电基底上得到柔性电致变色薄膜。采用X射线衍射仪、扫描电子显微镜、高分辨场透射电子显微镜和X射线光电子能谱对W18O49的微观结构和价态等进行表征，用电化学工作站与紫外?可见光分光光度计对W18O49/PET?ITO柔性电致变色薄膜的光学调制范围、响应时间和循环稳定性等进行了表征和分析。结果表明，光谱扫描波长?=633 nm时，W18O49/PET?ITO柔性电致变色薄膜的光学调制范围ΔT=23%。薄膜透光率变化90%时，着色和褪色时间分别为12.8和10.6 s。W18O49/PET?ITO柔性电致变色薄膜具有优异的循环稳定性，连续着色褪色循环3000 s薄膜透光率仍达80.9%。     

Hybrid ZnO NR/graphene structures as advanced optoelectronic devices with high transmittance

A hybrid structure (HS) made of one-dimensional ZnO nanorods (NRs) and a two-dimensional synthesized graphene sheet was successfully constructed in this study. The uniform ZnO NRs were obtained by hydrothermal method and grown on a graphene surface that had been transferred to a polyethylene terephthalate substrate. The HS exhibited high transmittance (approximately 75%) over the visible wavelength range, even after cyclic bending with a small radius of curvature. Raman spectroscopy and Hall measurement were carried out to verify the chemical composition and electrical properties of the structure. Stable electrical conductance of the ZnO NR/graphene HS was achieved, and increase in carrier mobility decreased the resistance of the ZnO-with-graphene sheet in comparison with bare ZnO NRs.     

Controlled Synthesis of Monolayer Graphene Toward Transparent Flexible Conductive Film Application

We demonstrate the synthesis of monolayer graphene using thermal chemical vapor deposition and successive transfer onto arbitrary substrates toward transparent flexible conductive film application. We used electron-beam-deposited Ni thin film as a synthetic catalyst and introduced a gas mixture consisting of methane and hydrogen. To optimize the synthesis condition, we investigated the effects of synthetic temperature and cooling rate in the ranges of 850–1,000°C and 2–8°C/min, respectively. It was found that a cooling rate of 4°C/min after 1,000°C synthesis is the most effective condition for monolayer graphene production. We also successfully transferred as-synthesized graphene films to arbitrary substrates such as silicon-dioxide-coated wafers, glass, and polyethylene terephthalate sheets to develop transparent, flexible, and conductive film application.     

Multilayer graphene grown by precipitation upon cooling of nickel on diamond

Multilayer graphene is grown by precipitation upon cooling of a thin nickel film deposited by e-beam evaporation on single crystal diamond (0 0 1) oriented substrates. Nickel acts as a strong catalyst inducing the dissolution of carbon from diamond into the metal. Carbon segregation produces multilayers of graphene on the top surface. Characterization by Raman spectroscopy reveals that these thin layers display relatively narrow Raman phonon peaks that are typically associated with graphene. Atomic force microscope measurements reveal a multigrain structure that reproduces small domains in the nickel film. The multilayer graphene is transferred onto a optical microscope glass slide for further analysis. The thickness of the layers estimated from optical transmission measurements is 12 nm. The catalytic reaction found for nickel on diamond is not observed when glassy carbon is used as substrate. This method provides a venue for the fabrication of large area graphene films.     

Induction heating-assisted repeated growth and electrochemical transfer of graphene on millimeter-thick metal substrates

Chemical vapor deposition in a hot wall reactor is the most common technique for the production of large area single layer graphene. However, growth in this type of reactors is time consuming and the results are limited by the surface quality of the widely used catalytic metal foils as growth substrates. In this work we demonstrate the use of millimeter-thick Cu and Pt substrates for graphene growth via inductive magnetic heating, which allows for fast temperature ramps during heat up and cooling. Based on a detailed growth study, a two-step growth process resulting in continuous monolayer graphene films of high crystal quality with grain size of larger than 90 μm is established. An electrochemical transfer process is used to separate the graphene film from the metallic substrate, yielding excellent results in terms of defect density, doping and residual contamination. Back-gated graphene field-effect transistors fabricated on Si/SiO₂ structures exhibit a high reproducibility with a peak mobility higher than 4000 cm²/Vs. The combination of the highly time efficient graphene growth and electrochemical transfer together with the reusability of the growth substrates and the possibility of applying novel surface pretreatments pave the way for the use of high quality substrates in industrial applications.     

Highly transparent low resistance ATO/AgNWs/ATO flexible transparent conductive thin films

Indium-free flexible transparent conductive thin films (TCFs) composed of silver nanowire (AgNW) networks and Sb doped SnO₂ (ATO) layers were prepared on polyethylene terephthalate (PET) substrates. The ATO layers were deposited via radio frequency (RF) magnetron sputtering at room temperature. The AgNWs were achieved via a modified polyol reduction method and embedded between the ATO layers. The effects of AgNW networks and ATO layers on electrical and optical properties of the ATO/AgNWs/ATO flexible tri-layer thin films are investigated. The ATO layers can improve the optical transmittance and reduce the resistivity of tri-layers, and the corresponding mechanisms are proposed. Typically, an ATO/AgNWs/ATO flexible tri-layers show a high figure of merit value (30.06 × 10^-3 Ω^-1) with a low sheet resistance of 7.1 Ω/sq. and a high transmittance of 85.7%. Meanwhile, the tri-layers present excellent mechanical flexibility, and the ATO layers acted as the protecting layers improve the adhesive and environmental stability at high temperature and humidity for the ATO/AgNWs/ATO flexible tri-layers. These results indicate that ATO/AgNWs/ATO flexible tri-layer thin films can be useful for the fabrication of wearable electronic devices.     

One-step metal electroplating and patterning on a plastic substrate using an electrically-conductive layer of few-layer graphene

Few-layer graphene (FLG) was investigated as an electrically-conductive interleaf layer for one-step electroplating and patterning of metal on nonconductive polymer substrates without using multiple and toxic pretreatment processes in traditional electroplating. An individual FLG (5–10 nm of thickness with 6.4% of oxygen content) was obtained by expanding graphite with microwave followed by exfoliating the expanded graphite with sonication in N-methyl-pyrrolidone. Stacking FLG in the in-plane direction, a robust FLG film was obtained by the vacuum-assisted filtering and drying methods, and transferred to a polyethylene terephthalate (PET) substrate via an intermediate transfer to the water surface. The sheet resistance of the FLG film on the PET substrate was 0.9 kΩ/sq with a thickness of 80 nm and the root-mean-square roughness of 29 nm. In the electroplating of nickel on the FLG film, hemisphere-shape metal seeds appeared in the early stage of electroplating and they subsequently grew up to 200–480 nm, which became connected to form a continuous nickel layer. The thickness of the continuous nickel layer increased linearly with electroplating time. The developed electroplating method demonstrated its capability of selective patterning on nonconductive substrates using a simple masking technique.     

Design correlations for the optical performance of the particle-diffusing bottom diffusers in the LCD backlight unit

Although the bottom diffuser film is one of the key components in the backlight unit in a liquid crystal display, the design equations for the optical performance of the bottom diffuser films were not reported in the literature. In this work, different narrow-size-distributed acrylic-styrene resin particles were mixed with the thermosetting acrylic resins and coated on the transparent poly(ethylene terephthalate) (PET) substrates to form particle-diffusing bottom diffusers with different optical performances. The correlations for the light transmittance and haze of a bottom diffuser as functions of the coating thickness/particle diameter ratio and beads/resin weight ratio were empirically developed as a power law model and an exponential model, respectively. The developed correlations may effectively reduce the time required for bottom diffuser designs in the backlight unit.