Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout

The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the MHz range. The strong dependence of the resonant frequency on applied gate voltage can be fit to a membrane model, which yields the mass density and built-in strain. Upon removal and addition of mass, we observe changes in both the density and the strain, indicating that adsorbates impart tension to the graphene. Upon cooling, the frequency increases; the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, these studies lay the groundwork for applications, including high-sensitivity mass detectors

Review on carbon-derived, solid-state, micro and nano sensors for electrochemical sensing applications

The aim of this review is to summarize the most relevant contributions in the development of electrochemical sensors based on carbon materials in the recent years. There have been increasing numbers of reports on the first application of carbon derived materials for the preparation of an electrochemical sensor. These include carbon nanotubes, diamond like carbon films and diamond film-based sensors demonstrating that the particular structure of these carbon material and their unique properties make them a very attractive material for the design of electrochemical biosensors and gas sensors. Carbon nanotubes (CNT) have become one of the most extensively studied nanostructures because of their unique properties. CNT can enhance the electrochemical reactivity of important biomolecules and can promote the electron-transfer reactions of proteins (including those where the redox center is embedded deep within the glycoprotein shell). In addition to enhanced electrochemical reactivity, CNT-modified electrodes have been shown useful to be coated with biomolecules (e.g., nucleic acids) and to alleviate surface fouling effects (such as those involved in the NADH oxidation process). The remarkable sensitivity of CNT conductivity with the surface adsorbates permits the use of CNT as highly sensitive nanoscale sensors. These properties make CNT extremely attractive for a wide range of electrochemical sensors ranging from amperometric enzyme electrodes to DNA hybridization biosensors. Recently, a CNT sensor based fast diagnosis method using non-treated blood assay has been developed for specific detection of hepatitis B virus (HBV) (human liver diseases, such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma caused by hepatitis B virus). The linear detection limits for HBV plasma is in the range 0.5–3.0 μL−1 and for anti- HBVs 0.035–0.242 mg/mL in a 0.1 M NH4H2PO4 electrolyte solution. These detection limits enables early detection of HBV infection in suspected serum samples. Therefore, non-treated blood serum can be directly applied for real-time sensitive detection in medical diagnosis as well as in direct in vivo monitoring. Synthetic diamond has been recognized as an extremely attractive material for both (bio-) chemical sensing and as an interface to biological systems. Synthetic diamond have outstanding electrochemical properties, superior chemical inertness and biocompatibility. Recent advances in the synthesis of highly conducting nanocrystalline-diamond thin films and nano wires have lead to an entirely new class of electrochemical biosensors and bio-inorganic interfaces. In addition, it also combines with development of new chemical approaches to covalently attach biomolecules on the diamond surface also contributed to the advancement of diamond-based biosensors. The feasibility of a capacitive field-effect EDIS (electrolyte-diamond-insulatorsemiconductor) platform for multi-parameter sensing is demonstrated with an O-terminated nanocrystalline-diamond (NCD) film as transducer material for the detection of pH and penicillin concentration. This has also been extended for the label-free electrical monitoring of adsorption and binding of charged macromolecules. One more recent study demonstrated a novel bio-sensing platform, which is introduced by combination of a) geometrically controlled DNA bonding using vertically aligned diamond nano-wires and b) the superior electrochemical sensing properties of diamond as transducer material. Diamond nanowires can be a new approach towards next generation electrochemical gene sensor platforms. This review highlights the advantages of these carbon materials to promote different electron transfer reactions specially those related to biomolecules. Different strategies have been applied for constructing carbon material-based electrochemical sensors, their analytical performance and future prospects are discussed

Carbon nanomaterial based vapor sensors.

The discovery of carbon nanotubes and subsequently graphene has led to an interest in carbon materials as sensing elements due to their unique properties. Graphene is a 2-dimensional material that has a large surface area that can be exposed to surface adsorbates from a target gas. This enables studies on the interaction of gas molecules with the graphene surface and subsequent changes in its properties. Graphene also exhibits high conductivity and low noise and has low crystal defects. Due to its high electron mobility at room temperature, graphene exhibits high sensitivity (in tune of detecting ppm) which is a required trait in environmental and industrial sensing applications, making graphene a good candidate for sensors. Several models of sensors based on graphene as sensing element have been put forth previously based on high-resolution lithographic techniques and for individual electrode attachment to the sensing film with e-beam lithography. These techniques can produce small numbers of devices that explore the limits of molecular scale sensing, but the methods are currently impractical for large scale production of low cost sensors. The work presented here counters this labor-intensive process and puts forth a practical lowcost sensor. Graphene sheets grown using chemical vapor deposition are transferred onto an acrylic chip designed for gas sensing. The working principle of the sensor is the electrical conductivity change exhibited by the graphene when molecules adsorb onto the material while the sensor chip is exposed to the target gas in a controlled environment. We present our graphene based sensor with the focus on designing small, cost effective and reliable sensors with high sensitivity towards the target gas, detailing the assembly of graphene/acrylic based devices, their characterization and investigation of their performance as resistive chemical sensors using different substrates as graphene supports

Non-silicon Microfabricated Nanostructured Chemical Sensors For Electric Nose Application

A systematic investigation has been performed for Electric Nose , a system that can identify gas samples and detect their concentrations by combining sensor array and data processing technologies. Non-silicon based microfabricatition has been developed for micro-electro-mechanical-system (MEMS) based gas sensors. Novel sensors have been designed, fabricated and tested. Nanocrystalline semiconductor metal oxide (SMO) materials include SnO2, WO3 and In2O3 have been studied for gas sensing applications. Different doping material such as copper, silver, platinum and indium are studied in order to achieve better selectivity for different targeting toxic gases including hydrogen, carbon monoxide, hydrogen sulfide etc. Fundamental issues like sensitivity, selectivity, stability, temperature influence, humidity influence, thermal characterization, drifting problem etc. of SMO gas sensors have been intensively investigated. A novel approach to improve temperature stability of SMO (including tin oxide) gas sensors by applying a temperature feedback control circuit has been developed. The feedback temperature controller that is compatible with MEMS sensor fabrication has been invented and applied to gas sensor array system. Significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient conditions. Single walled carbon nanotube (SWNT) has been studied to improve SnO2 gas sensing property in terms of sensitivity, response time and recovery time. Three times of better sensitivity has been achieved experimentally. The feasibility of using TSK Fuzzy neural network algorithm for Electric Nose has been exploited during the research. A training process of using TSK Fuzzy neural network with input/output pairs from individual gas sensor cell has been developed. This will make electric nose smart enough to measure gas concentrations in a gas mixture. The model has been proven valid by gas experimental results conducted

Mass sensing with graphene and carbon nanotube mechanical resonators

In recent years, carbon nanotube and graphene mechanical resonators have attracted considerable attention because of their unique properties. Their high resonance frequencies, high quality factors and their ultra-low mass turn them into exceptional sensors of minuscule external forces and masses. Their sensing capabilities hold promise for scanning probe microscopy, magnetic resonance imaging and mass spectrometry. Moreover, they are excellent probes for studying mechanical motion in the quantum regime, investigating nonlinear dynamics and carrying out surface science experiments on crystalline low-dimensional systems. A goal for fully exploiting the potential of mechanical resonators remains: Reaching the fundamental limit of the resolution of mass sensing imposed by the thermomechanical noise of the resonator. Currently, limitations are typically due to noise in the motion transduction. Nanotube and graphene resonators are particularly sensitive to noise in the detection since their intrinsically small dimensions result in minuscule transduced electrical or optical signals. This thesis researches ways for improving the mass resolution of the intrinsically smallest mechanical resonator systems, which are based on suspended graphene and carbon nanotubes. For this, we follow two complementary pathways. We first see how far we can go in terms of mass resolution with graphene resonators by reducing their size. We fabricate double clamped graphene resonators with submicron lengths and measure their mechanical properties at 4.2 K. The frequency stability of the resonators allows us to evaluate their mass resolution. We show that the frequency stability of graphene resonators is limited by the imprecision of the detection of the mechanical motion. We then develop a new electrical downmixing scheme to read-out the mechanical motion with a lower noise compared to previous techniques. It utilizes a RLC resonator together with an amplifier based on a high electron mobility transistor operated at 4.2 K. The signal to noise ratio is improved thanks to signal read-out at higher frequency (1.6 MHz compared to 1-10 kHz) and low temperature amplification. We observe an improved frequency stability measuring a carbon nanotube mechanical resonator with this read-out. The stability is no longer limited by the measurement instrumentation noise but by the device itself. Observing the intrinsic fluctuations of the resonator allows in future experiments to study surface science phenomena. We present some preliminary results that hint to the observation of the diffusion of xenon atoms on the surface of the resonator and to the adsorption of single fullerene molecules.En los últimos años, los resonadores mecánicos de nanotubos de carbono y grafeno han atraído una atención considerable debido a sus propiedades únicas. Sus altas frecuencias de resonancia, sus factores de calidad altos y su masa extremadamente baja los convierten en sensores excepcionales de fuerzas externas y masas minúsculas. Sus capacidades de detección son prometedoras para la microscopía con sonda de barrido, la tomografía por resonancia magnética y la espectrometría de masas. Además, son sondas excelentes para estudiar el movimiento mecánico en el régimen cuántico, investigar la dinámica no lineal y llevar a cabo experimentos de ciencia de superficie en sistemas cristalinos de baja dimensión. La explotación de todo el potencial de los resonadores mecánicos sigue siendo un objetivo: alcanzar el límite fundamental de la resolución de la detección de masas impuesta por el ruido termomecánico del resonador. Actualmente, las limitaciones se deben normalmente al ruido en la transducción de movimiento. Los resonadores de nanotubos y grafeno son particularmente sensibles al ruido en la detección, ya que sus dimensiones intrínsecamente pequeñas producen señales eléctricas u ópticas transducidas minúsculas. Esta tesis investiga formas de mejorar la resolución de masa de los sistemas de resonadores mecánicos intrínsecamente más pequeños, que se basan en grafeno suspendido y nanotubos de carbono. Para esto, seguimos dos caminos complementarios. Primero vemos hasta dónde podemos llegar en términos de resolución de masa con resonadores de grafeno al reducir su tamaño. Fabricamos resonadores de grafeno de doble sujeción con longitudes submicrométricas y medimos sus propiedades mecánicas a 4,2 K. La estabilidad de la frecuencia de los resonadores nos permite evaluar su resolución de masa. Mostramos que la estabilidad de la frecuencia de los resonadores de grafeno está limitada por la imprecisión de la detección del movimiento mecánico. Luego desarrollamos un nuevo esquema de downmixing eléctrico para leer el movimiento mecánico con un ruido más bajo en comparación con las técnicas anteriores. Utiliza un resonador RLC junto con un amplificador basado en un transistor de alta movilidad de electrones operado a 4,2 K. La relación señal / ruido se mejora gracias a la lectura de la señal a mayor frecuencia (1,6 MHz en comparación con 1-10 kHz) y a la amplificación a temperatura baja. Observamos una mejor estabilidad de la frecuencia midiendo un resonador mecánico de nanotubos de carbono con esta lectura. La estabilidad ya no está limitada por el ruido de la instrumentación de medición, sino por el propio dispositivo. Observar las fluctuaciones intrínsecas del resonador permite en futuros experimentos estudiar fenómenos de ciencia de superficie. Presentamos algunos resultados preliminares que apuntan a la observación de difusión de átomos de xenón en la superficie del resonador y a la adsorción de moléculas individuales de fulereno

Hybrid nanomaterial and its applications: IR sensing and energy harvesting

In this dissertation, a hybrid nanomaterial, single-wall carbon nanotubes-copper sulfide nanoparticles (SWNTs-CuS NPs), was synthesized and its properties were analyzed. Due to its unique optical and thermal properties, the hybrid nanomaterial exhibited great potential for infrared (IR) sensing and energy harvesting. The hybrid nanomaterial was synthesized with the non-covalent bond technique to functionalize the surface of the SWNTs and bind the CuS nanoparticles on the surface of the SWNTs. For testing and analyzing the hybrid nanomaterial, SWNTs-CuS nanoparticles were formed as a thin film structure using the vacuum filtration method. Two conductive wires were bound on the ends of the thin film to build a thin film device for measurements and analyses. Measurements found that the hybrid nanomaterial had a significantly increased light absorption (up to 80%) compared to the pure SWNTs. Moreover, the hybrid nanomaterial thin film devices exhibited a clear optical and thermal switching effect, which could be further enhanced up to ten times with asymmetric illumination of light and thermal radiation on the thin film devices instead of symmetric illumination. A simple prototype thermoelectric generator enabled by the hybrid nanomaterials was demonstrated, indicating a new route for achieving thermoelectricity. In addition, CuS nanoparticles have great optical absorption especially in the near-infrared region. Therefore, the hybrid nanomaterial thin films also have the potential for IR sensing applications. The first application to be covered in this dissertation is the IR sensing application. IR thin film sensors based on the SWNTs-CuS nanoparticles hybrid nanomaterials were fabricated. The IR response in the photocurrent of the hybrid thin film sensor was significantly enhanced, increasing the photocurrent by 300% when the IR light illuminates the thin film device asymmetrically. The detection limit could be as low as 48mW mm-2. The dramatically enhanced sensitivity and detection limit were due to the temperature difference between the two junctions formed by the nanohybrid thin film and copper-wire electrodes under asymmetric IR illumination, and the difference between the effective Seebeck coefficient of the nanohybrid thin film and that of the Cu wires. The IR sensor embedded in polydimethylsiloxane (PDMS) layers was also fabricated and tested to demonstrate its potential application as a flexible IR sensor. In another application, energy harvesting, a new type of thermoelectric microgenerator enabled with the SWNTs-CuS nanoparticles hybrid nanomaterial, was fabricated. This type of microgenerator did not require any cooling or heat sink element to maintain the temperature difference or gradient in the device. Instead, the integrated nanomaterials in the device enhanced the local temperature and thus produced and maintained an intrinsic temperature difference or gradient across the microgenerator, thereby converting light and heat directly into electricity. In order to enhance the maximum output voltage, the incoming light had to be focused on the thin film region. A tunable lens was fabricated to collect and focus the ambient light on the thin film to enhance the output voltage of the microgenerators. The tunable lens was fabricated with a flexible polymer, PDMS. Therefore, the focal length of the tunable lens can be adjusted by pumping oil into the lens chamber to deform a PDMS membrane, resulting in the changed focus of the lens. In order to enhance the output power, two different arrays of thermoelectric generators in series and in parallel were fabricated. A hybrid nanomaterial thin film was also used to enhance the temperature gradient of the thermoelectric generators. For the devices in series, the generated voltage of all thermoelectric generators was combined together to enhance the output voltage. With the device in parallel, it can be used to combine all of the current of thermoelectric generators together to enhance the output current

Fully Integrated Biochip Platforms for Advanced Healthcare

Recent advances in microelectronics and biosensors are enabling developments of innovative biochips for advanced healthcare by providing fully integrated platforms for continuous monitoring of a large set of human disease biomarkers. Continuous monitoring of several human metabolites can be addressed by using fully integrated and minimally invasive devices located in the sub-cutis, typically in the peritoneal region. This extends the techniques of continuous monitoring of glucose currently being pursued with diabetic patients. However, several issues have to be considered in order to succeed in developing fully integrated and minimally invasive implantable devices. These innovative devices require a high-degree of integration, minimal invasive surgery, long-term biocompatibility, security and privacy in data transmission, high reliability, high reproducibility, high specificity, low detection limit and high sensitivity. Recent advances in the field have already proposed possible solutions for several of these issues. The aim of the present paper is to present a broad spectrum of recent results and to propose future directions of development in order to obtain fully implantable systems for the continuous monitoring of the human metabolism in advanced healthcare applications