J. M. Parpia

Impermeable Atomic Membranes from Graphene Sheets

We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the worlds thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick.

Measurement of mechanical resonance and losses in nanometer scale silicon wires

We present data on nanofabricated suspended silicon wires driven at resonance. The wires are electrostatically driven and detected optically. We have observed wires with widths as small as 45 nm and resonant frequencies as high as 380 MHz. We see a strong dependence of the resonant quality factor on the surface to volume ratio.

Large-Scale Arrays of Single-Layer Graphene Resonators

We fabricated large arrays of suspended, single-layer graphene membrane resonators using chemical vapor deposition (CVD) growth followed by patterning and transfer. We measure the resonators using both optical and electrical actuation and detection techniques. We find that the resonators can be modeled as flat membranes under tension, and that clamping the membranes on all sides improves agreement with our model and reduces the variation in frequency between identical resonators. The resonance frequency is tunable with both electrostatic gate voltage and temperature, and quality factors improve dramatically with cooling, reaching values up to 9000 at 10 K. These measurements show that it is possible to produce large arrays of CVD-grown graphene resonators with reproducible properties and the same excellent electrical and mechanical properties previously reported for exfoliated graphene.

High quality factor resonance at room temperature with nanostrings under high tensile stress

Quality factors as high as 207 000 are demonstrated at room temperature for radio-frequency silicon nitride string resonators with cross sectional dimensions on the scale of 100nm, made with a nonlithographic technique. A product of quality factor and surface to volume ratio greater than 6000nm−1 is presented, the highest yet reported. Doubly clamped nanostring resonators are fabricated in high tensile-stress silicon nitride using a nonlithographic electrospinning process. We fabricate devices with an electron beam process, and demonstrate frequency and quality factor results identical to those obtained with the nonlithographic technique. We also compare high tensile-stress doubly clamped beams with doubly clamped and cantilever resonators made of a lower stress material, as well as cantilever beams made of the high stress material. In all cases, the doubly clamped high stress beams have the highest quality factors. We therefore attribute the high quality factors to high tensile stress. Potential dominant...

Nanomechanical resonant structures in nanocrystalline diamond

We report the fabrication and the operation of nanomechanical resonant structures in nanocrystalline diamond. For this purpose, continuous diamond films as thin as 80 nm were grown using microwave plasma enhanced chemical vapor deposition. The lateral dimensions of the fabricated structures were as small as 50 nm and the measured mechanical resonant frequencies were up to 640 MHz. The mechanical quality factors were in the range of 2500–3000 at room temperature. The elastic properties of these films obtained via the resonant measurements indicate a Young’s modulus close to that of single-crystal diamond.

Nanofabrication and electrostatic operation of single-crystal silicon paddle oscillators

We report the fabrication and characterization of paddle oscillators featuring nanometer-scale supporting rods. The devices show two resonances in the 1–10 MHz range, which we attribute to the translational and torsional modes of motion. While the frequency response of the translational motion shows evidence of nonlinear behavior, the torsional response remains symmetric throughout the range of excitation. We present a model for the electrostatic excitation of the two modes. Torsional motion is induced via asymmetries of the system, and amplified by a modulation of the effective torsional constant. The model of the translational motion predicts a nonlinear behavior for displacements as small as 15 nm. Analysis of both modes of motion consistently suggests structures softer than expected from bulk silicon. Quality factors approaching 103 are measured.

Free-Standing Epitaxial Graphene

We report on a method to produce free-standing graphene sheets from epitaxial graphene on silicon carbide (SiC) substrate. Doubly clamped nanomechanical resonators with lengths up to 20 microm were patterned using this technique and their resonant motion was actuated and detected optically. Resonance frequencies of the order of tens of megahertz were measured for most devices, indicating that the resonators are much stiffer than expected for beams under no tension. Raman spectroscopy suggests that the graphene is not chemically modified during the release of the devices, demonstrating that the technique is a robust means of fabricating large-area suspended graphene structures.

A megahertz nanomechanical resonator with room temperature quality factor over a million

We demonstrate the fabrication and operation of high aspect ratio tensile stressed silicon nitride string resonators. We explore the parameter space of small cross sections, on the order of 100nm, and long lengths up to 325μm, demonstrating that such high aspect ratio resonators can be made with standard wet release processing using a material with internal tensile stress. Room temperature quality factors exceed one million at frequencies above 1MHz. The utility of such high quality factor flexural resonators to probe the interaction of high frequency nanoscale devices with rarefied gases is demonstrated.

High, Size-Dependent Quality Factor in an Array of Graphene Mechanical Resonators

Graphenes unparalleled strength, stiffness, and low mass per unit area make it an ideal material for nanomechanical resonators, but its relatively low quality factor is an important drawback that has been difficult to overcome. Here, we use a simple procedure to fabricate circular mechanical resonators of various diameters from graphene grown by chemical vapor deposition. In addition to highly reproducible resonance frequencies and mode shapes, we observe a striking improvement of the membrane quality factor with increasing size. At room temperature, we observe quality factors as high as 2400 ± 300 for a resonator 22.5 μm in diameter, about an order of magnitude greater than previously observed quality factors for monolayer graphene. Measurements of quality factor as a function of modal frequency reveal little dependence of Q on frequency. These measurements shed light on the mechanisms behind dissipation in monolayer graphene resonators and demonstrate that the quality factor of graphene resonators relative to their thickness is among the highest of any mechanical resonator demonstrated to date.

Parametric amplification in a torsional microresonator

We observe parametric amplification in a torsional micron-scale mechanical resonator. An applied voltage is used to make a dynamic change to the torsional spring constant. Oscillating the spring constant at twice the resonant frequency results in a phase dependent amplification of the resonant motion. Our results agree well with the theory of parametric amplification. By taking swept frequency measurements, we observe interesting structure in the resonant response curves.