Very high frequency (VHF) nanoelectromechanical systems (NEMS) provide unprecedented sensitivity for inertial mass sensing. We demonstrate in situ measurements in real time with mass noise floor approximately 20 zg. Our best mass resolution corresponds to approximately 7 zg, equivalent to approximately 30 xenon atoms or the mass of an individual 4 kDa molecule. Detailed analysis of the ultimate sensitivity of such devices based on these experimental results indicates that NEMS can ultimately provide inertial mass sensing of individual intact, electrically neutral macromolecules with single-Dalton (1 amu) resolution.

Mass spectrometry (MS) provides rapid and quantitative identification of protein species with relatively low sample consumption. Yet with the trend toward biological analysis at increasingly smaller scales, ultimately down to the volume of an individual cell, MS with few-to-single molecule sensitivity will be required. Nanoelectromechanical systems (NEMS) provide unparalleled mass sensitivity, which is now sufficient for the detection of individual molecular species in real time. Here we report the first demonstration of MS based on single-biological-molecule detection with NEMS. In our NEMS-MS system, nanoparticles and protein species are introduced by electrospray injection from fluid phase in ambient conditions into vacuum and subsequently delivered to the NEMS detector by hexapole ion optics. Precipitous frequency shifts, proportional to the mass, are recorded in real time as analytes adsorb, one-by-one, onto a phase-locked, ultrahigh frequency NEMS resonator. These first NEMS-MS spectra, obtained with modest mass sensitivity from only several hundred mass adsorption events, presage the future capabilities of this approach. We also outline the substantial improvements that are feasible in the near term, some of which are unique to NEMS-MS.

Crystal defects can confine isolated electronic spins and are promising candidates for solid-state quantum information. Alongside research focusing on nitrogen-vacancy centres in diamond, an alternative strategy seeks to identify new spin systems with an expanded set of technological capabilities, a materials-driven approach that could ultimately lead to ‘designer’ spins with tailored properties. Here we show that the 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including states in all three with room-temperature quantum coherence. The prevalence of this spin coherence shows that crystal polymorphism can be a degree of freedom for engineering spin qubits. Long spin coherence times allow us to use double electron–electron resonance to measure magnetic dipole interactions between spin ensembles in inequivalent lattice sites of the same crystal. Together with the distinct optical and spin transition energies of such inequivalent states, these interactions provide a route to dipole-coupled networks of separately addressable spins.

We demonstrate very high frequency (VHF) nanomechanical resonators based upon single-crystal silicon nanowires (SiNWs), which are prepared by the bottom-up chemical synthesis. Metallized SiNW resonators operating near 200 MHz are realized with quality factor Q ≈ 2000−2500. Pristine SiNWs, with fundamental resonances as high as 215 MHz, are measured using a VHF readout technique that is optimized for these high resistance devices. The pristine resonators provide the highest Q's, as high as Q ≈ 13 100 for an 80 MHz device. SiNWs excel at mass sensing; characterization of their mass responsivity and frequency stability demonstrates sensitivities approaching 10 zeptograms. These SiNW resonators offer significant potential for applications in resonant sensing, quantum electromechanical systems, and high frequency signal processing.Nanoelectromechanical systems (NEMS), particularly nanomechanical resonators vibrating at high frequencies, 1 are being actively explored for applications including resonant sensors for ultrahigh-resolution mass sensing, 2 force detection, 3 quantum electromechanics, 4 electromechanical signal generation and processing, 5 and high-speed logic and computation. 6 These NEMS resonators are usually made by topdown lithographic techniques and surface nanomachining, which together enable realization of nanomechanical devices with considerable complexity and functionality. By contrast, chemical-synthesis-based bottom-up approaches now provide nanowires with high crystalline quality, perfectly terminated surfaces, and sizes down to the molecular scale. These represent a new class of building blocks for NEMS resonators that offer unique attributes. Si nanowires (SiNWs) are, perhaps, among the most intriguing given silicon's preeminent role in micro-and nanoelectronics and as a structural material for micro-and nanoelectromechanical systems. Development of SiNW-NEMS, however, has been impeded by difficulties in suspending SiNWs to give them mechanical freedom and in subsequent device integration. Recently, a hybrid process has been developed to fabricate SiNWs suspended over microtrenches by employing vapor-liquidsolid (VLS) epitaxial growth.8 This device geometry facilitates the direct probing of mechanical properties of SiNWs via static deflection. 9,10 In this Letter, we describe the first demonstration of resonant mechanical devices operating at very high frequencies (VHF) that are based on such suspended SiNWs. We demonstrate robust SiNW resonators vibrating at frequencies greater than 200 MHz. Furthermore, comprehensive measurements of the resonance characteristics, quality factors, and resonator frequency stability show that these bottom-up SiNWs provide excellent performance. These devices expand and advance prospects for NEMS resonator technologies and enable new possibilities for applications. Parts a and b of Figure 1 show the typical suspended SiNWs in microtrenches. The detailed synthetic procedure via VLS epitaxial growth has been described in ref 8. Briefly, the SiNW begins cry...