Silicon nanowires: where mechanics and optics meet at the nanoscale (original) (raw)
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Nature Nanotechnology, 2010
One-dimensional nanomechanical resonators based on nanowires and nanotubes have emerged as promising candidates for mass sensors 1-6 . When the resonator is clamped at one end and the atoms or molecules being measured land on the other end (which is free to vibrate), the resonance frequency of the device decreases by an amount that is proportional to the mass of the atoms or molecules. However, atoms and molecules can land at any position along the resonator, and many biomolecules have sizes that are comparable to the size of the resonator, so the relationship between the added mass and the frequency shift breaks down 7-10 . Moreover, whereas resonators fabricated by top-down methods tend to vibrate in just one dimension because they are usually shaped like diving boards, perfectly axisymmetric one-dimensional nanoresonators can support flexural vibrations with the same amplitude and frequency in two dimensions 11 . Here, we propose a new approach to mass sensing and stiffness spectroscopy based on the fact that the nanoresonator will enter a superposition state of two orthogonal vibrations with different frequencies when this symmetry is broken. Measuring these frequencies allows the mass, stiffness and azimuthal arrival direction of the adsorbate to be determined.
High Sensitivity Deflection Detection of Nanowires
2010
A critical limitation of Nano-electromechanical systems (NEMS) is the lack of a high sensitivity position detection mechanism. We introduce a non-interferometric optical approach to determine the position of nanowires with high sensitivity and bandwidth. Its physical origins and limitations are determined by Mie scattering analysis. This enables a dramatic miniaturization of detectable cantilevers, with attendant reductions to the fundamental minimum force noise in highly damping environments. We measure the force-noise of an 80nm radius Ag2Ga nanowire-cantilever in water at 1.9 f N/ √ Hz.
High throughput optical readout of dense arrays of nanomechanical systems for sensing applications
Review of Scientific Instruments, 2010
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Optomechanics with Silicon Nanowires by Harnessing Confined Electromagnetic Modes
Nano Letters, 2012
The optomechanical coupling that emerges in an optical cavity in which one of the mirrors is a mechanical resonator has allowed sub-Kelvin cooling with the prospect of observing quantum phenomena, and self-sustained oscillators with very high spectral purity. Both applications clearly benefit from the use of the smallest possible mechanical resonator. Unfortunately, the optomechanical coupling largely decays when the size of the mechanical system is below the light wavelength. Here, we propose to exploit the optical resonances associated to the light confinement in subwavelength structures to circumvent this limitation, efficiently extending optomechanics to nanoscale objects. We demonstrate this mechanism with suspended silicon nanowires. We are able to optically cool the mechanical vibration of the nanowires from room temperature to 30-40 K or to obtain regenerative mechanical oscillation with a frequency stability of about one part per million. The reported optomechanical phenomena can be exploited for developing cost-optimized mass sensors with sensitivities in the zeptogram range.
Ultralow Dissipation Patterned Silicon Nanowire Arrays for Scanning Probe Microscopy
In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sensitive cantilevers in a number of unique scanning probe microscopy (SPM) settings. We describe the fabrication of ultra-low dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning probe applications. Our fabrication process produces, with high yield, ultra-high aspect ratio vertical SiNWs that exhibit exceptional force sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited force sensitivity of 9.7 ± 0.4 aN/ √ Hz at room temperature and 500 ± 20 zN/ √ Hz at 4 K. To facilitate their use in SPM, the SiNWs are patterned within 7 µm from the edge of the substrate, allowing convenient optical access for displacement detection.
Low-concentration mechanical biosensor based on a photonic crystal nanowire array
Nature Communications, 2011
The challenge for new biosensors is to achieve detection of biomolecules at low concentrations, which is useful for early-stage disease detection. Nanomechanical biosensors are promising in medical diagnostic applications. For nanomechanical biosensing at low concentrations, a suffi cient resonator device surface area is necessary for molecules to bind to. Here we present a low-concentration (500 aM sensitivity) DNA sensor, which uses a novel nanomechanical resonator with ordered vertical nanowire arrays on top of a Si / SiO 2 bilayer thin membrane. The high sensitivity is achieved by the strongly enhanced total surface area-to-volume ratio of the resonator (10 8 m − 1) and the state-of-the-art mass-per-area resolution (1.8 × 10 − 12 kg m − 2). Moreover, the nanowire array forms a photonic crystal that shows strong light trapping and absorption over broad-band optical wavelengths, enabling high-effi ciency broad-band optothermo-mechanical remote device actuation and biosensing on a chip. This method represents a mass-based platform technology that can sense molecules at low concentrations.
Optical Transduction for Vertical Nanowire Resonators
We describe an optical transduction mechanism to measure the flexural mode vibrations of vertically aligned nanowires on a flat substrate with high sensitivity, linearity, and ease of implementation. We demonstrate that the light reflected from the substrate when a laser beam strikes it parallel to the nanowires is modulated proportionally to their vibration, so that measuring such modulation provides a highly efficient resonance readout. This mechanism is applicable to single nanowires or arrays without specific requirements regarding their geometry or array pattern, and no fabrication process besides the nanowire generation is required. We show how to optimize the performance of this mechanism by characterizing the split flexural modes of vertical silicon nanowires in their full dynamic range and up to the fifth mode order. The presented transduction approach is relevant for any application of nanowire resonators, particularly for integrating nanomechanical sensing in functional substrates based on vertical nanowires for biological applications.
Mechanical resonance of clamped silicon nanowires measured by optical interferometry
Journal of Applied Physics, 2008
The mechanical resonance of laterally grown silicon nanowires measured by an optical interferometric technique is reported. The lengths and diameters of the nanowires ranged from L = 2 to 20 m and D = 39 to 400 nm, respectively. The wires showed resonant frequencies in the f 0 =1-12 MHz range and resonant quality factors Q at low pressure ranging from Q = 5000 to Q = 25 000. The dependence of resonant frequency on the ratio of diameter to length squared, D / L 2 , yielded a ratio of ͱ E / = 9400Ϯ 450 m / s. Assuming a density of = 2330 kg/ m 3 , this experimental result yields an experimental Young modulus of E = 205Ϯ 10 GPa, consistent with that of a bulk silicon. As the wires were cooled from T = 270 K to T = 77 K, a 0.35% increase of resonant frequency was observed. This increase of resonant frequency with cooling resulted from a change in Young's modulus and from the thermal contraction of silicon. The quality factor did not vary significantly from P =10 −4 to 10 2 Torr, suggesting that viscous damping does not dominate the dissipative processes in this pressure range. Although viscous damping became important above P =10 2 Torr, relatively high quality factors of Q = 7000 were still observed at atmospheric pressure.
Multimode laser cooling and ultra-high sensitivity force sensing with nanowires
Nature Communications, 2014
Photo-induced forces can be used to manipulate and cool the mechanical motion of oscillators. When the oscillator is used as a force sensor, such as in atomic force microscopy, active feedback is an enticing route to enhancing measurement performance. Here, we show broadband multimode cooling of −23 dB down to a temperature of 8 ± 1 K in the stationary regime. Through the use of periodic quiescence feedback cooling, we show improved signalto-noise ratios for the measurement of transient signals. We compare the performance of real feedback to numerical post-processing of data and show that both methods produce similar improvements to the signal-to-noise ratio of force measurements. We achieved a room temperature force measurement sensitivity of < 2 × 10 −16 N with integration time of less than 0.1 ms. The high precision and fast force microscopy results presented will potentially benefit applications in biosensing, molecular metrology, subsurface imaging and accelerometry. 1 arXiv:1502.03506v1 [physics.optics] 12 Feb 2015 dates for mass and force sensing [1-3], biomaterial sensing by means of Kelvin probe force microscopy [4], and single-spin and charge detection [5]. Miniaturized oscillators, however, are more susceptible to thermal noise and their use can be challenging as it entails low-noise high-frequency electronics to monitor and control the vibrational modes. Passive cooling is not always an option, particularly in biomaterial sensing applications where samples are dependent on specific environmental conditions. Active feedback cooling can instead be used to reduce the Brownian motion of the oscillators. To date, effective optical cooling of micro/nano-mechanical resonators has been achieved via cavity cooling [6-8] and active optical feedback cooling [9] through radiation pressure [10-13]
A local optical probe for measuring motion and stress in a nanoelectromechanical system
Nature Nanotechnology, 2012
1 Nanoelectromechanical systems 1 can be operated as ultrasensi-2 tive mass sensors 2,3 and ultrahigh-frequency resonators 4 , and 3 can also be used to explore fundamental physical phenomena 4 such as nonlinear damping 5 and quantum effects in macro-5 scopic objects 6 . Various dissipation mechanisms are known to 6 limit the mechanical quality factors of nanoelectromechanical 7 systems and to induce aging due to material degradation, so 8 there is a need for methods that can probe the motion of 9 these systems, and the stresses within them, at the nanoscale. 10 Here, we report a non-invasive local optical probe for the quan-11 titative measurement of motion and stress within a nanoelec-12 tromechanical system, based on Fizeau interferometry and 13 Raman spectroscopy. The system consists of a multilayer gra-14 phene resonator that is clamped to a gold film on an oxidized 15 silicon surface. The resonator and the surface both act as 16 mirrors and therefore define an optical cavity. Fizeau interfero-17 metry provides a calibrated measurement of the motion of the 18 resonator, while Raman spectroscopy can probe the strain 19 within the system and allows a purely spectral detection of 20 mechanical resonance at the nanoscale.