There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Nanoelectromechanical systems were fabricated from single- and multilayer graphene sheets by mechanically exfoliating thin sheets from graphite over trenches in silicon oxide. Vibrations with fundamental resonant frequencies in the megahertz range are actuated either optically or electrically and detected optically by interferometry. We demonstrate room-temperature charge sensitivities down to 8 × 10 –4 electrons per root hertz. The thinnest resonator consists of a single suspended layer of atoms and represents the ultimate limit of two-dimensional nanoelectromechanical systems.

https://science.sciencemag.org/content/sci/315/5811/490.full.pdf

Electromechanical Resonators from Graphene Sheets

The dynamic back-action caused by electromagnetic forces (radiation pressure) in optical and microwave cavities is of growing interest. Back-action cooling, for example, is being pursued as a means of achieving the quantum ground state of macroscopic mechanical oscillators. Work in the optical domain has revolved around millimetre- or micrometre-scale structures using the radiation pressure force. By comparison, in microwave devices, low-loss superconducting structures have been used for gradient-force-mediated coupling to a nanomechanical oscillator of picogram mass. Here we describe measurements of an optical system consisting of a pair of specially patterned nanoscale beams in which optical and mechanical energies are simultaneously localized to a cubic-micron-scale volume, and for which large per-photon optical gradient forces are realized. The resulting scale of the per-photon force and the mass of the structure enable the exploration of cavity optomechanical regimes in which, for example, the mechanical rigidity of the structure is dominantly provided by the internal light field itself. In addition to precision measurement and sensitive force detection, nano-optomechanics may find application in reconfigurable and tunable photonic systems, light-based radio-frequency communication and the generation of giant optical nonlinearities for wavelength conversion and optical buffering.

/pdf/a-picogram-and-nanometre-scale-photonic-crystal-3c87ztdlya.pdf

A picogram- and nanometre-scale photonic-crystal optomechanical cavity

Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.

http://cau.ac.kr/~jjang14/BioMEMS/Waggoner_LOC_Cantilever_Sensors_Bio_detection_Review_2007.pdf

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

Advances in technology have allowed chemical sampling with high spatial resolution and the manipulation and measurement of individual molecules. Adaptation of these approaches to lab-on-a-chip formats is providing a new class of research tools for the investigation of biochemistry and life processes.

Future lab-on-a-chip technologies for interrogating individual molecules

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...

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

Resonant nanoelectromechanical systems (NEMS) are being actively investigated as sensitive mass detectors for applications such as chemical and biological sensing. We demonstrate that highly uniform arrays of nanomechanical resonators can be used to detect the binding of individual DNA molecules through resonant frequency shifts resulting from the added mass of bound analyte. Localized binding sites created with gold nanodots create a calibrated response with sufficient sensitivity and accuracy to count small numbers of bound molecules. The amount of nonspecifically bound material from solution, a fundamental issue in any ultra-sensitive assay, was measured to be less than the mass of one DNA molecule, allowing us to detect a single 1587 bp DNA molecule.

Enumeration of DNA molecules bound to a nanomechanical oscillator.

We report a method of optical excitation of nanomechanical cantilever-type oscillators. The periodic driving signal with a controlled modulation amplitude was provided by a 415 nm diode laser, wherein the laser spot was located at some distance away from the clamped end of the cantilever. The measured resonant response of the cantilever was obtained at distances in excess of 160μm with varying oscillator dimensions. The effectiveness of the driving mode is studied for different combinations of materials, namely Si–SiO2 and Si3N4–SiO2. These observations were considered within the theoretical framework of the mechanism of heat transfer. We show that measurable amplitudes of vibrations can be obtained at temperature changes much less than 1°.

Optical excitation of nanoelectromechanical oscillators

Limit cycle, or self-oscillations, can occur in a variety of NEMS devices illuminated within an interference field. As the device moves within the field, the quantity of light absorbed and hence the resulting thermal stresses changes, resulting in a feedback loop that can lead to limit cycle oscillations. Examples of devices that exhibit such behavior are discussed as are experimental results demonstrating the onset of limit cycle oscillations as continuous wave (CW) laser power is increased. A model describing the motion and heating of the devices is derived and analyzed. Conditions for the onset of limit cycle oscillations are computed as are conditions for these oscillations to be either hysteretic or nonhysteretic. An example simulation of a particular device is discussed and compared with experimental results.

/pdf/limit-cycle-oscillations-in-cw-laser-driven-nems-2mnhnwm1oy.pdf

Limit cycle oscillations in CW laser-driven NEMS

Two-dimensional arrays of coupled nanomechanical plate-type resonators were fabricated in single crystal silicon using e-beam lithography Collective modes were studied using a double laser setup with independent positioning of the point laser drive and interferometric motion detector The formation of a wide acoustic band has been demonstrated Localization due to disorder (mistune) was identified as a parameter that limits the propagation of the elastic waves We show that all 400 resonators in our 20×20 array participate in the extended modes and estimate group velocity and density of states Applications utilizing the resonator arrays for radio frequency signal processing are discussed

Robert B. Reichenbach

Papers

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

Enumeration of DNA molecules bound to a nanomechanical oscillator.

Optical excitation of nanoelectromechanical oscillators

Limit cycle oscillations in CW laser-driven NEMS

Two-dimensional array of coupled nanomechanical resonators