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The demand for graphene-based devices is rapidly growing but there are significant challenges for developing scalable and repeatable processes for the manufacturing of graphene devices. Basic research on understanding and controlling growth mechanisms have recently enabled various mass production approaches over the past decade. However, the integration of graphene with Micro-Nano Electromechanical Systems (MEMS/NEMS) has been especially challenging due to performance sensitivities of these systems to the production process. Therefore, ability to produce graphene-based devices on a large scale with high repeatability is still a major barrier to the commercialization of graphene. In this review article, we discuss the merits of integrating graphene into Micro-Nano Electromechanical Systems, current approaches for the mass production of graphene integrated devices, and propose solutions to overcome current manufacturing limits for the scalable and repeatable production of integrated graphene-based devices.

This study presents chemical vapor deposition (CVD) growth of high-quality monolayer graphene on 100 nm-thick Pt thin films deposited on TiO2-coated silicon wafers. Conventional graphene growth on ...

Growth of high quality and monolayer graphene on copper thin films on silicon wafers is a promising approach to massive and direct graphene device fabrication in spite of the presence of potential dewetting issues in the copper film during graphene growth. Current work demonstrates roles of a nickel adhesion coupled with the copper film resulting in mitigation of dewetting problem as well as uniform monolayer graphene growth over 97 % coverage on films. The feasibility of monolayer graphene growth on Cu-Ni alloy films as thin as 150 nm in total is also demonstrated. During the graphene growth on Cu-Ni films, the nickel adhesion layer uniformly diffuses into the copper thin film resulting in a Cu-Ni alloy, helping to promote graphene nucleation and large area surface coverage. Furthermore, it was found that the use of extremely thin metal catalyst films also constraint the total amount of carbon that can be absorbed into the film during growth, which helps to eliminate adlayer formation and promote monolayer growth regardless of alloying content, thus improving the monolayer fraction of graphene coverage on the thinner films. These results suggest a path forward for the large scale integration of high quality, monolayer graphene into nanoelectronic and nanomechanical devices.

This paper presents graphene growth on Pt deposited on four different adhesion layers such as Ti, Cr, Ta, and Ni. During the graphene growth at 1000 °C using conventional Chemical Vapor Deposition method, these adhesion layers diffuse into and alloy with Pt layer resulting graphene to grow on different alloys. Therefore, Pt layer on different adhesion layers induces different quality and number of layer(s) of graphene grown on the film. Monolayer graphene was produced on majority of metal layers except on Pt/Ta layer where bilayer graphene is observed. The lowest defects were found on graphene grown on Pt/Ni film where slightly higher number of wrinkles are observed compared to other alloys. We characterized graphene using SEM images of transferred graphene, of Pt grains after the growth of graphene, and of in-depth profiles of thin film via TOF-SIMS. Our paper states feasibility of graphene growth on Pt thin film on various adhesion layers and obstacles to overcome to enhance graphene transfer from Pt thin film. We address one of the major difficulties of graphene growth and transfer to implement graphene in NEMS/MEMS devices.

Monolayer graphene is commonly grown on Cu substrates due to the self-limiting nature of graphene synthesis by chemical vapor deposition (CVD). Consequently, the growth of multilayer graphene by CVD has proven to be relatively difficult. This study demonstrates that the number of layers in graphene synthesized on a copper substrate can be precisely set by controlling the partial pressure of hydrogen gas used in the CVD process. This study also shows that a pressure threshold exists for a distinct transition from monolayer to multilayer graphene growth. This threshold is shown to be the boundary where the graphene growth process on Cu by CVD is no longer a self-limiting process. In addition, the multilayer graphene synthesized through the pressure control method forms in the Volmer-Weber mode with an AB stacking structure.

This paper demonstrates the electrothermal tuning of a nanoelectromechanical resonator correlated with the mechanical properties of an Al/SiC bilayer beam structure at radio frequencies under the moderate conditions. This study confirms a relatively low change in the quality factor (Q-factor) over a wide range of frequency tuning (Δfr = 2.4 MHz). The effective stress of the beam plays an important role in the resonance frequency modulation and is critical to the Q-factor during electrothermal tuning. The Q-factor was decreased with the stress variation. However, the resonant frequency is linearly tuned on the basis of varied effective beam stresses and no major scarification of the Q-factor was observed.

One of the major challenges in producing highly accurate graphene-based nanoelectromechanical (NEMS) resonators is the poor fabrication repeatability of graphene-based NEMS devices due to small variations in the residual stress and initial tension of the graphene film. This has meant that graphene-based nanoelectromechanical resonators tend to have large variations in natural frequency and quality factor from device to device. This poor repeatability makes it impossible to use these resonators to make accurate, high-precision force and displacement sensors or electromechanical filters. However, by actively controlling the tension on the graphene resonator it is possible both to increase repeatability between devices and to increase the force/mass sensitivity of the nanoelectromechanical resonators produced. Such tension control makes it possible to produce electrometrical filters that can be precisely tuned over a frequency range of up to several orders-of-magnitude. In order to controllably strain the graphene resonator, a microelectromechanical system (MEMS) is be used to apply tension to the graphene. The MEMS device consists of a graphene resonator connected between a set of gold electrodes. Each gold electrode is located on a different MEMS stage. Each stage is connected to a set of flexural bearings which are used to guide the motion of the stage. The displacement stage is actuated using a thermal actuator that allows a uniform and constant tension to be applied to the graphene resonator. The displacement of the actuator and the tension applied to the graphene are measured using a pair of differential capacitive actuators. The resonator is actuated electrostatically using the electrical back gate, and the resonant frequency is measured from the change in conductance of the graphene as it approaches resonance. Using this setup, it is possible to tune the natural frequency of the graphene resonator with high precision and accuracy. In addition to designing devices that can compensate for manufacturing errors in nanomanufactured devices, this paper will present several methods that can greatly expand the scope and rate at which nanomaterials-based devices can be fabricated. For example, this paper will present a transfer-free, wafer-scale manufacturing process that can be used to produce suspended graphene-based devices such as the graphene-based NEMS resonators. This new method involves the growth of graphene directly on the device wafer and release of the graphene-based device through etching of the copper catalyst layer. This method replaces traditional graphene fabrication methods, such as mechanical exfoliation, electron beam lithography, or transfer from copper foils, which are slow and require a transfer step that is the source of much of inconsistency in suspended graphene-based devices. Therefore, these new transfer-free, wafer-scale fabrication methods offer the potential to increase the throughput, yield, and repeatability of manufacturing processes for graphene resonators while reducing manufacturing costs and complexity.

Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves.

To achieve high performance of nanoelectromechanical resonators in room-temperature and low-vacuum conditions, the precise control of electrothermal power is critical in not only frequency tuning but also regulating nonlinearity in the radio-frequency range. This study presents theoretical analysis and experimental results for controlling nonlinearity of nanoelectromechanical resonators using nonlinear damping and stiffness terms. Experiments show that, with increasing electrothermal power, critical amplitude increases up to where the resonators display linear harmonic oscillation. As a result, the linearity of the resonator that has been driven into the nonlinear regime can be reclaimed.

We demonstrate the effect of nanoresonator geometry on the resonance property using a magnetomotive transduction technique for SiC nanoresonators in moderate conditions of pressure, temperature, and magnetic intensity. These trials were performed in conditions similar to those useful for practical applications to assist in the deployment of SiC-based nanoelectromechanical system prototype devices. This letter confirms that the resonant properties of a nanoscaled electromechanical resonator in moderate conditions are similar to those found during tests in ideal conditions. The resonance characteristics were analyzed based on the geometrical changes of the nanoresonator. The radio-frequency performance parameters such as the critical amplitude and dynamic range, which are crucial in the determination of linear operation range of nanoresonators, were maintained at a level comparable to those found under laboratory conditions. This letter brings this technology closer to practical applications in sensors, filters, and the oscillation of nanoscaled electromechanical devices.

Differential interference contrast microscopy is designed to image unstained and transparent specimens by enhancing the contrast resulting from the Nomarski prism-effected optical path difference. Retinitis pigmentosa, one of the most common inherited retinal diseases, is characterized by progressive loss of photoreceptors. In this study, Differential interference contrast microscopy was evaluated as a new and simple application for observation of the retinal photoreceptor layer and retinitis pigmentosa diagnostics and monitoring. Retinal tissues of Royal College of Surgeons rats and retinal-degeneration mice, both well-established animal models for the disease, were prepared as flatmounts and histological sections representing different elapsed times since the occurrence of the disease. Under the microscopy, the retinal flatmounts showed that the mosaic pattern of the photoreceptor layer was irregular and partly collapsed at the early stage of retinitis pigmentosa, and, by the advanced stage, amorphous. The histological sections, similarly, showed thinning of the photoreceptor layer at the early stage and loss of the outer nuclear layer by the advanced stage. To count and compare the number of photoreceptors in the normal and early-retinitis pigmentosa-stage tissues, an automated cell-counting program designed with MATLAB, a numerical computing language, using a morphological reconstruction method, was applied to the differential interference contrast microscopic images. The number of cells significantly decreased, on average, from 282 to 143 cells for the Royal College of Surgeons rats and from 255 to 170 for the retinal-degeneration mouse. We successfully demonstrated the potential of the differential interference contrast microscopy technique's application to the diagnosis and monitoring of RP.

We represent differential interference contrast (DIC) microscopy as a new and simple application for diagnostics of RP. We show the possibility that DIC technique may distinguish the RP disease in vivo.

Stereotactic adrenal medullary transplantation into the striatum was performed in 5 patients with severe Parkinson's disease. Four patients had previously been treated with thalamotomies and all were on L-dopa therapy with significant side effects. All 5 patients had shown marked disability before the procedure. Autologous adrenal medullary tissue was sliced into 20-30 fragments and transplanted into two sites of the caudate nucleus, one at the ventricular surface and the other in the head of the nucleus. The cases were followed for 4-5 years (mean 4.5 years), except for 1 patient who died of unrelated causes 22 months after the procedure. Initial bilateral symptom improvement was observed in all cases for 9-21 months (mean 15.2 months) after transplantation without L-dopa therapy. Later, these improvements progressively deteriorated. L-dopa therapy had to be resumed for all. MRI on the long-term follow-up showed the transplanted tissue as a low signal intensity area surrounded by high intensity spots in T1- and T2-weighted images. Compared to previous MR studies, the transplanted tissue was shrunken and presumed nonviable.

Growing interests on carbon nanotubes (CNTs) and ZnO film let us consider radio frequency characteristics for future employment in electronic devices. Prior to the deployment and development for RF devices, the fundamentals about two materials are investigated. Multi-walled CNTs are characterized up to 50 GHz. Using the measured S-parameters Telegrapher's equivalent circuit models are extracted. And, for the ZnO film the equivalent circuit parameters are obtained as well. The circuit parameters provide the useful criterion to evaluate RF performance.

Graphene is a two-dimensional monolayer comprised of carbon atoms. By its unique intrinsic properties, graphene has many advantages for gas sensing. In this paper, we find results of the gas sensing performance using uniform single crystal structure graphene by mechanical exfoliation method measured under room temperature, atmospheric pressure. Also, we discuss the effects of various thermal treatments on the graphene at atmospheric pressure. The sensitivity increases and recovery time decreases as measurement temperature increases.

Electrical characteristics of single ZnO nanowire with various diameters at the high-frequency range are presented. Transmission characteristics were measured as S-parameter and RLC circuit simulation to deduce passive circuit elements. The result showed that the contact parameters were dominant as frequency increases. This study discovered the parasitic effects supposed to be minimised, contribute significantly to major signal transmission of ZnO nanowire and are crucial in developing such nano-electronic devices.

During the period from March 1992 to June 1996, we performed percutaneous radiofrequency (RF) facet rhizotomy in 324 patients with low back pain. Employing the lesion generator, we coagulated branches of the zygapophyseal nerve to treat low back pain. The follow-up period was 6-51 months (average: 22.5 months). There were no complications during the procedure and the follow-up period and no poor results were observed. Two-hundred and thirty-one patients (103 females and 128 males) had mechanical low back pain syndrome and showed marked improvement of pain after the procedure, including 29 cases with previous spinal surgery. We concluded that percutaneous RF facet rhizotomy is a safe and effective procedure for low back pain patients, especially for those with mechanical low back pain syndrome.

We investigated the radio-frequency transmission properties of reduced graphene oxide (GO) sheets including contact effects with the metal electrodes. GO sheets were prepared by dielectrophoresis and their structural characteristics were analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy. The contact resistance was much higher than the intrinsic resistance over the entire frequency range, thus the contact resistance was considered as a dominant component of impedance in the radio-frequency regime. In the radio-frequency regime, GO sheets showed a drastic decrease in impedance based on a consistent decrease in the intrinsic and contact resistance. These results support the potential of GO as a radio-frequency interconnector with a solution-based fabrication method.

We confirm graphene oxide, a two-dimensional carbon structure at the nanoscale level can be a strong candidate for high-efficient interconnector in radio-frequency range. In this paper, we investigate high frequency characteristics of graphene oxide in range of 0.5–40 GHz. Radio-frequency transmission properties were extracted as S-parameters to determine the intrinsic ac transmission of graphene sheets, such as the impedance variation dependence on frequency. The impedance and resistance of graphene sheets drastically decrease as frequency increases. This result confirms graphene oxide has high potential for transmitting signals at gigahertz ranges.

The nonlinear oscillations of nanoelectromechanical resonators have previously been studied both experimentally and analytically. Nanoresonators have achieved superior sensitivity and high quality factors in many applications. However, the linear operating range of nanoresonators is significantly limited because of the small dimensions and thus the linear regime of nanoresonators may be required to expand performance in various conditions. In order to increase the linear operating range, we proposed that proper adjustments of simultaneous application of drive and electrothermal power can be used to optimize the resonance performance, providing a wider linear range as well as to tune the resonance frequency. For a nanoresonator operated by simultaneous drive and electrothermal power, experimental data are theoretically supported using nonlinear damping and spring terms. In the transition between linearity and nonlinearity by proper combinations of ac drive and dc electrothermal power, the experimental data can be better fitted, by theoretical study, with newly derived nonlinear damping terms. We believe that better understanding of these effects with different ac/dc combinations on radio frequency oscillation is crucial for utilizing nanoresonators for various applications such as sensors, oscillators and filters.