Alexei Gaidarzhy

Controllable nanomechanical memory element

We report the realization of a completely controllable high-speed nanomechanical memory element fabricated from single-crystal silicon wafers. This element consists of a doubly-clamped suspended nanomechanical beam structure, which can be made to switch controllably between two stable and distinct states at a single frequency in the megahertz range. Because of their sub-micron size and high normal-mode frequencies, these nanomechanical memory elements offer the potential to rival the current state-of-the-art electronic data storage and processing.

High quality factor gigahertz frequencies in nanomechanical diamond resonators

We report actuation and detection of gigahertz-range resonance frequencies in nanocrystalline diamond mechanical resonators. High order transverse vibration modes are measured in coupled-beam resonators exhibiting frequencies up to 1.441GHz. The cantilever-array design of the resonators translates the gigahertz-range resonant motion of micron-long cantilever elements to the displacement of the central supporting structure. Use of nanocrystalline diamond further increases the frequency compared to single crystal silicon by a factor of 3. High clamping losses usually associated with micron-sized straight beams are suppressed in the periodic geometry of our resonators, allowing for high quality factors exceeding 20 000 above 500MHz.

Evidence for quantized displacement in macroscopic nanomechanical oscillators.

We report the observation of discrete displacement of nanomechanical oscillators with gigahertz-range resonance frequencies at millikelvin temperatures. The oscillators are nanomachined single-crystal structures of silicon, designed to provide two distinct sets of coupled elements with very low and very high frequencies. With this novel design, femtometer-level displacement of the frequency-determining element is amplified into collective motion of the entire micron-sized structure. The observed discrete response possibly results from energy quantization at the onset of the quantum regime in these macroscopic nanomechanical oscillators.

Scaling of dissipation in megahertz-range micromechanical diamond oscillators

The authors report frequency and dissipation scaling laws for doubly clamped diamond resonators. The device lengths range from 10to19μm corresponding to frequency and quality-factor ranges of 17to66MHz and 600–2400, respectively. The authors find that the resonance frequency scales as 1∕L2 confirming the validity of the thin-beam approximation. The dominant dissipation comes from two sources: for the shorter beams, clamping loss is the dominant dissipation mechanism, while for the longer beams, surface losses provide a significant source of dissipation. The authors compare and contrast these mechanisms with other dissipation mechanisms to describe the data.

Quantum friction in nanomechanical oscillators at millikelvin temperatures

We report low-temperature measurements of dissipation in megahertz-range, suspended, single-crystal nanomechanical oscillators. At millikelvin temperatures, both dissipation (inverse quality factor) and shift in the resonance frequency display reproducible features, similar to those observed in sound attenuation experiments in disordered glasses and consistent with measurements in larger micromechanical oscillators fabricated from single-crystal silicon. Dissipation in our single-crystal nanomechanical structures is dominated by internal quantum friction due to an estimated number of roughly 50 two-level systems, which represent both dangling bonds on the surface and bulk defects.

Spectral response of a gigahertz-range nanomechanical oscillator

We report the measurement and simulation of the transverse displacement spectrum of a multi-element nanomechanical oscillator at previously inaccessible frequencies of up to 3GHz. The detected displacement signal is enhanced in the high-frequency range by the presence of high-order resonance modes generated by coherent motion of individual elements. The spectrum reveals a rich structure with groups of peaks forming quasibands. The spectral structure is qualitatively analogous to atomic emission spectra.

Temperature dependence of a nanomechanical switch

We present the effect of temperature on the switching characteristics of a bistable nonlinear nanomechanical beam. At megahertz-range frequencies, we find that it is possible to controllably change the state of the system between two stable mechanical states defined by the hysteresis brought on by nonlinear excitation. We find that the introduction of increased temperature results in a loss of switching fidelity, and that temperature acts as an effective source of external noise on the dynamics of the system.

Energy measurement in nonlinearly coupled nanomechanical modes

We report direct measurements of average vibration energy in a high frequency flexural resonance mode achieved via an-harmonic elastic coupling to a fundamental vibration mode of a nanomechanical resonator. The second order coupling effect produces a frequency shift of the read-out mode as a function of the mean square of the excitation amplitude of the high order mode. We measure frequency shifts at the lowest driving amplitudes, down to the noise floor of the experimental setup. With implementation of existing ultra-sensitive amplifiers, the reported technique will enable direct measurements of quantized energy transitions in low-thermal occupation number nanomechanical resonators.

Response spectrum of coupled nanomechanical resonators

We develop a simple continuum model to analyze the vibrational modes of a nanomechanical multielement structure. In this model, arrays of submicron cantilevers located symmetrically on both sides of the central clamped-clamped nanobeam are replaced by a continuum. In this approach, the equations of motion of the structure become exactly solvable. Our analytical results capture the main features of the vibrational modes observed both numerically and experimentally and can be applied to a general class of scale-independent elasticaly coupled resonator structures.

Arbitrary distribution and nonlinear modal interaction in coupled nanomechanical resonators

We propose a general one-dimensional continuous formulation to analyze the vibrational modes of antennalike nanomechanical resonators consisting of two symmetric arrays of cantilevers affixed to a central nanobeam. The cantilever arrays can have arbitrary density and length profile along the beam. We obtain the secular equation that allows for the determination of their frequency spectrum and illustrate the results on the particular examples of structures with constant or alternating cantilever length profiles. We show that our analytical results capture the vibration spectrum of such resonators and elucidate key relationships that could prove advantageous for experimental device performance. Furthermore, using a perturbative approach to treat the nonlinear and dissipative dynamics of driven structures, we analyze the anharmonic coupling between two specific widely spaced modes of the coupled-element device, with direct application to experiments.