Nanoelectromechanical systems (NEMS) resonators can detect mass with exceptional sensitivity. Previously, mass spectra from several hundred adsorption events were assembled in NEMS-based mass spectrometry using statistical analysis. Here, we report the first realization of single-molecule NEMS-based mass spectrometry in real time. As each molecule in the sample adsorbs upon the NEMS resonator, its mass and the position-of-adsorption are determined by continuously tracking two driven vibrational modes of the device. We demonstrate the potential of multimode NEMS-based mass spectrometry by analyzing IgM antibody complexes in real-time. NEMS-MS is a unique and promising new form of mass spectrometry: it can resolve neutral species, provides resolving power that increases markedly for very large masses, and allows acquisition of spectra, molecule-by-molecule, in real-time.

Derivation of Eq. (2) in the main textPrecipitous downward shifts in the modal resonance frequencies of a nanomechanical device occur upon adsorption of individual analytes [1]. These measured frequency shifts can be used to calculate the mass, position, and molecular shape of individual analytes that adsorb upon a NEMS resonator -as described in the main text. Importantly, in the limit where the particle mass is much less than the device mass, the sequential measurement of multiple particles is unaffected by the mass loading due to previous particles.Previous analyses [1,2] have considered the analyte particles to be point masses. In this work, we model the individual particles as finite-sized objects with a spatial mass distribution that is initially unknown. We consider a general device of arbitrary composition that is loaded by an adsorbate with mass, m , which is much less than the device mass, M. We further assume that the particle size is small compared to the device dimensions (and the wavelengths of the vibrational modes) or, if not, that the particle is much more compliant than the device itself.Under such conditions, which are especially relevant for the case of soft biological molecules (of special interest to us), the vibrational mode shapes of the device are unaffected by the adsorbed analyte, and thus the strain energy of the device is also unchanged. It then follows that the maximum kinetic energy of the device, before and after mass loading, is invariant for the same oscillation amplitude, i.e.,

We herein report on the chemical and physical changes that occur in thin films of poly(methyl methacrylate), PMMA, induced by exposure to high-energy vacuum ultraviolet radiation and a supersonic beam of neutral, ground electronic state O((3)P) atomic oxygen. A combination of in situ quartz crystal microbalance and in situ Fourier-transform infrared reflection-absorption spectroscopy were used to determine the photochemical reaction kinetics and mechanisms during irradiation. The surface morphological changes were measured with atomic force microscopy. The results showed there was no enhancement in the mass loss rate during simultaneous exposure of vacuum ultraviolet (VUV) radiation and atomic oxygen. Rather, the rate of mass loss was impeded when the polymer film was exposed to both reagents. This study elucidates the kinetics of photochemical and oxidative reaction for PMMA, and shows that the synergistic effect involving VUV irradiation and exposure to ground state atomic oxygen depends substantially on the relative fluxes of these reagents.

We report the demonstration of strong coupling between single Cesium atoms and a high-Q chip-based microresonator. Our toroidal microresonators are compact, Si chip-based whispering gallery mode resonators that confine light to small volumes with extremely low losses, and are manufactured in large numbers by standard lithographic techniques. Combined with the capability to couple efficiently light to and from these microresonators by a tapered optical fiber, toroidal microresonators offer a promising avenue towards scalable quantum networks. Experimentally, laser cooled Cs atoms are dropped onto a toroidal microresonator while a probe beam is critically coupled to the cavity mode. When an atom interacts with the cavity, it modifies the resonance spectrum of the cavity, leading to rejection of some of the probe light from the cavity, and thus to an increase in the output power. By observing such transit events while systematically detuning the cavity from the atomic resonance, we determine the maximal accessible single-photon Rabi frequency of Ω 0 /2π ≈ (100 ± 24) MHz. This value puts our system in the regime of strong coupling, being significantly larger than the dissipation rates in our system.