KEYWORDSNitrogen-vacancy center, diamond, spin-mechanical interaction, nanomechancial sensing, NEMS 2 ABSTRACT Nanomechanical sensors and quantum nanosensors are two rapidly developing technologies that have diverse interdisciplinary applications in biological and chemical analysis and microscopy.For example, nanomechanical sensors based upon nanoelectromechanical systems (NEMS) have demonstrated chip-scale mass spectrometry capable of detecting single macromolecules, such as proteins. Quantum nanosensors based upon electron spins of negatively-charged nitrogen-vacancy (NV) centers in diamond have demonstrated diverse modes of nanometrology, including single molecule magnetic resonance spectroscopy. Here, we report the first step towards combining these two complementary technologies in the form of diamond nanomechanical structures containing NV centers. We establish the principles for nanomechanical sensing using such nano-spinmechanical sensors (NSMS) and assess their potential for mass spectrometry and force microscopy. We predict that NSMS are able to provide unprecedented AC force images of cellular biomechanics and to, not only detect the mass of a single macromolecule, but also image its distribution. When combined with the other nanometrology modes of the NV center, NSMS potentially offer unparalleled analytical power at the nanoscale. TEXTNanomechanical sensors based upon nanoelectromechanical systems (NEMS) are a burgeoning nanotechnology with diverse microscopy and analytical applications in biology and chemistry. Two applications with particular promise are force microscopy in geometries that transcend the constraints of conventional atomic force microscopy (AFM) 1-3 and on-chip mass spectrometry with single molecule sensitivity. [4][5][6] Another burgeoning nanotechnology is quantum nanosensors based upon the electron spin of the NV center in diamond. The NV center has been 3 used to locate single elementary charges, 7 to perform thermometry within living cells 8 and to realize nanoscale MRI in ambient conditions. 9-11 However, there is yet to be a nanosensing application of the NV center that exploits its susceptibility to local mechanical stress/ strain.Here, we propose that the mechanical susceptibility of the NV center's electron spin can be exploited together with the extreme mechanical properties of diamond nanomechanical structures to realize nano-spin-mechanical sensors (NSMS) that outperform the best available technology. Such NSMS will be capable of both high-sensitivity nanomechanical sensing and the quantum nanosensing of electric fields, magnetic fields and temperature. NSMS will thereby constitute the unification of two burgeoning nanotechnologies and have the potential to perform such unparalleled analytical feats as mass-spectrometry and MRI of single molecules. As the first step towards realizing NSMS, we report the complete characterization of the spin-mechanical interaction of the NV center. We use this to establish the design and operating principles of diamond NSMS and to perfor...

Significant attention has been recently focussed on the realization of high precision nanothermometry using the spin-resonance temperature shift of the negatively charged nitrogen-vacancy (NV − ) center in diamond. However, the precise physical origins of the temperature shift is yet to be understood. Here, the shifts of the center's optical and spin resonances are observed and a model is developed that identifies the origin of each shift to be a combination of thermal expansion and electron-phonon interactions. Our results provide new insight into the center's vibronic properties and reveal implications for NV − thermometry.PACS numbers: 63.20.kp, 61.72.jn, 76.70.hb The negatively charged nitrogen-vacancy (NV − ) center in diamond [1] is an important quantum technology platform for a range of new applications exploiting quantum coherence. Beyond quantum information processing, the prospect of employing the NV − center as a room temperature nanoscale electric and magnetic field sensor has attracted considerable interest [2][3][4][5][6][7]. Recently, the effects of temperature on the center's ground state spin resonance have been investigated [9], which enabled the influence of temperature on existing NV − metrology applications to be characterized and new thermometry applications to be proposed [8][9][10][11] and demonstrated [12][13][14]. However, the temperature shift of the center's spin resonance is not well understood and previous attempts at modelling the shift have been largely unsuccessful [9][10][11]. It is evident that the implementation of the NV − center as a nano-thermometer, magnetometer or electrometer requires a thorough understanding of the temperature shifts of its resonances, particularly if these implementations are designed for ambient conditions [15]. Here, the temperature shifts of the center's visible, infrared and spin resonances are observed and a model is developed that identifies the origin of each shift to be a combination of thermal expansion and electron-phonon interactions. This new insight reveals implications for NV − metrology.The NV − center is a C 3v point defect in diamond consisting of a substitutional nitrogen atom adjacent to a carbon vacancy that has trapped an additional electron (refer to Fig. 1a). As depicted in Fig. 1b, the oneelectron orbital level structure of the NV − center contains three defect orbital levels (a 1 , e x and e y ) deep within the diamond bandgap. Electron paramagnetic resonance (EPR) observations and ab initio calculations indicate that these defect orbitals are highly localized to the center [16][17][18][19][20]. Figure 1c shows the center's manyelectron electronic structure generated by the occupation of the three defect orbitals by four electrons [21,22], including the low-temperature zero phonon line (ZPL) energies of the visible (E V ∼1.946 eV) [23] and infrared (E IR ∼1.19 eV) [24][25][26] transitions. The energy separations of the spin triplet and singlet levels ( 3 A 2 ↔ 1 E and 1 A 1 ↔ 3 E) are unknown. As depicted in the inset of Fig...

With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV − -N + pairs. There can be a small percentage of neutral charge NV 0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV − zero-phonon has been altered. The alteration arises from a change of the distribution of N + ions and a modification of the average electric field at the NV − sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV − centres enhances the density of close N + ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N 0 in the lattice results in more distant distribution of N + ions and a narrowing of the ZPL. The competition between NV − and N 0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV − and N 0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV − -N + pairs in diamond. There is a critical dependence on pair separation. When the NV − -N + pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A 0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NVto N + and an optical cycle that involves NV 0 . The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV − in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV − are required. As well as extensive measurements of the NV − optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported.

The precise measurement of mechanical stress at the nanoscale is of fundamental and technological importance. In principle, all six independent variables of the stress tensor, which describe the direction and magnitude of compression/tension and shear stress in a solid, can be exploited to tune or enhance the properties of materials and devices. However, existing techniques to probe the local stress are generally incapable of measuring the entire stress tensor. Here, we make use of an ensemble of atomic-sized in situ strain sensors in diamond (nitrogen-vacancy defects) to achieve spatial mapping of the full stress tensor, with a submicrometer spatial resolution and a sensitivity of the order of 1 MPa (10 MPa) for the shear (axial) stress components. To illustrate the effectiveness and versatility of the technique, we apply it to a broad range of experimental situations, including mapping the stress induced by localized implantation damage, nanoindents, and scratches. In addition, we observe surprisingly large stress contributions from functional electronic devices fabricated on the diamond and also demonstrate sensitivity to deformations of materials in contact with the diamond. Our technique could enable in situ measurements of the mechanical response of diamond nanostructures under various stimuli, with potential applications in strain engineering for diamond-based quantum technologies and in nanomechanical sensing for on-chip mass spectroscopy.

The characteristic transition of the − NV centre at 637 nm is between A 3 2 and E 3 triplet states. There