We report the first experimental results on the electromagnetic interference (EMI) shielding effectiveness (SE) of monolayer graphene. The monolayer CVD graphene has an average SE value of 2.27 dB, corresponding to ~40% shielding of incident waves. CVD graphene shows more than seven times (in terms of dB) greater SE than gold film. The dominant mechanism is absorption rather than reflection, and the portion of absorption decreases with an increase in the number of graphene layers. Our modeling work shows that plane-wave theory for metal shielding is also applicable to graphene. The model predicts that ideal monolayer graphene can shield as much as 97.8% of EMI. This suggests the feasibility of manufacturing an ultrathin, transparent, and flexible EMI shield by single or few-layer graphene.
Recently, a flexible resistive switching memory device using graphene oxide was successfully demonstrated. In this work, the new findings on the switching mechanism of the graphene oxide memory are presented through a comprehensive study on the switching phenomena. It has been found that the switching operation of graphene oxide resistive switching memory (RRAM) is governed by dual mechanism of oxygen migration and Al diffusion. However, the Al diffusion into the graphene oxide is the main factor to determine the switching endurance property which limits the long term lifetime of the device. The electrode dependence on graphene oxide RRAM operation has been analyzed as well and is attributed to the difference in surface roughness of graphene oxide for the different bottom electrodes.
The large synthesis of graphene films by chemical vapor deposition (CVD) is expected to enable various applications. However, the transfer process of graphene from metal to dielectric substrate becomes a practical limitation in CVD method because of various chemical and mechanical stresses. In this paper, we have studied the critical factor of degradation and thereby to improve the electrical performance of graphene by CVD. It has been found that O=C-OH bonding is related to mobility degradation and doping effect. The removal of O=C-OH improves the carrier mobility by 30%.Graphene, a two-dimensional monolayer of sp 2 -bonded carbon atoms, has been intensively studied due to its useful electrical and mechanical properties, including extremely high mobility, high elasticity, and electromechanical modulation. 1-4 Since the discovery of graphene prepared by mechanical exfoliation, many electrical and chemical approaches to synthesize large-scale graphene have been developed. Recent advances in large-area synthesis of graphene films by chemical vapor deposition (CVD) on Cu or Ni substrates 5-9 are expected to enable various macroscopic applications such as graphene FETs on a wafer scale and transparent conducting films for flexible/stretchable electronics. However, the transfer 10 of graphene grown via CVD from a seed metal to a dielectric presents a practical limitation in such applications, because various chemical and mechanical damages to graphene layers are unavoidable during this step. In this work, we have carefully studied each transfer step to identify the critical factors on electronic performance degradation and thereby improve the performance of graphene. ExperimentalWe grew a large-scale graphene layer on a Cu substrate inside a CVD chamber, because the low solubility of the metal prevents stacking of multiple carbon layers and generates monolayer graphene. To facilitate graphene growth at low temperature, we used an induction coupled plasma (ICP)-CVD method, employing plasma to decompose the reaction gas, such as C 2 H 2 or CH 4 , in a low temperature ambient at 750 • C. After the reaction gas flow, the samples were cooled to room temperature, and monolayer graphene was then synthesized on the Cu substrate. An XPS analysis was conducted to compare the carbon states of the graphene in order to determine the effects of the transfer process. Additionally, a thermal annealing step was applied after the transfer to enhance the electrical performance, including the mobility and sheet resistance variation. Results and DiscussionThe overall process of the conventional graphene transfer method is summarized in Figure 1. In the transfer process, 10 polymethyl-methacrylate (PMMA) was spin-coated on the graphene layer to protect the graphene from mechanical breakage, and the PMMA/graphene/Cu film was then mechanically peeled off from the SiO 2 substrate. After the peeling step, the Cu substrate, which primarily had been in contact with the SiO 2 substrate, is exposed, and then can be easily etched by a Cu etchant, F...
A graphene thermoacoustic loudspeaker with a thin polymer mesh is fabricated using screen-printing. An experiment with substrates of various free-standing areas shows that a higher sound pressure level can be achieved as compared to previously reported graphene thermoacoustic loudspeakers. Moreover, a modified equation to predict the sound pressure level of the thermoacoustic loudspeaker with a thin and patterned substrate is proposed and verified by experimental results.
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