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Register a new userFull stress tensor measurement using colour centres in diamond
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Stress and strain are important factors in determining the mechanical, electronic, and optical properties of materials, relating to each other by the materials elasticity or stiffness. Both are represented by second rank field tensors with, in general, six independent components. Measurements of these quantities are usually achieved by measuring a property that depends on the translational symmetry and periodicity of the crystal lattice, such as optical phonon energies using Raman spectroscopy, the electronic band gap using cathodoluminescence, photoelasticity via the optical birefringence, or Electron Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists between the maximum sensitivity of the measurements and the spatial resolution. Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy allow measurement of all six components of the stress tensor, but neither is able to provide full 3D maps. Here we demonstrate a method for measuring the full stress tensor in diamond, using the spectral and optical polarization properties of the photoluminescence from individual nitrogen vacancy (NV) colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local fluctuations in the stress in the sample, and corresponding to a strain of about 10^-5, comparable with the best sensitivity provided by other techniques. By using the colour centres as built-in local sensors, the technique overcomes the reciprocal relationship between spatial resolution and sensitivity and offers the potential for measuring strains as small as 10^-9 at spatial resolution of order 10 nm. Furthermore it provides a straightforward route to volumetric stress mapping. Aside from its value in understanding strain distributions in diamond, this new approach to stress and strain measurement could be adapted for use in micro or nanoscale sensors.
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Optically active point defects in crystals have gained widespread attention as photonic systems that can find use in quantum information technologies. However challenges remain in the placing of individual defects at desired locations, an essential element of device fabrication. Here we report the controlled generation of single nitrogen-vacancy (NV) centres in diamond using laser writing. The use of aberration correction in the writing optics allows precise positioning of vacancies within the diamond crystal, and subsequent annealing produces single NV centres with up to 45% success probability, within about 200 nm of the desired position. Selected NV centres fabricated by this method display stable, coherent optical transitions at cryogenic temperatures, a pre-requisite for the creation of distributed quantum networks of solid-state qubits. The results illustrate the potential of laser writing as a new tool for defect engineering in quantum technologies.
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Single-photon sources represent a key enabling technology in quantum optics, and single colour centres in diamond are a promising platform to serve this purpose, due to their high quantum efficiency and photostability at room temperature. The widely studied nitrogen vacancy centres are characterized by several limitations, thus other defects have recently been considered, with a specific focus of centres emitting in the Near Infra-Red. In the present work, we report on the coupling of native near-infrared-emitting centres in high-quality single crystal diamond with Solid Immersion Lens structures fabricated by Focused Ion Beam lithography. The reported improvements in terms of light collection efficiency make the proposed system an ideal platform for the development of single-photon emitters with appealing photophysical and spectral properties.
Strain engineering allows the physical properties of materials and devices to be widely tailored, as paradigmatically demonstrated by strained transistors and semiconductor lasers employed in consumer electronics. For this reason, its potential impact on our society has been compared to that of chemical alloying. Although significant progress has been made in the last years on strained nanomaterials, strain fields (which are of tensorial nature, with six independent components) are still mostly used in a scalar and/or static fashion. Here we present a new class of strain actuators which allow the three components of the in-plane stress tensor in a nanomembrane to be independently and reversibly controlled. The actuators are based on monolithic piezoelectric substrates, which are micro-machined via femtosecond-laser processing. Their functionality is demonstrated by programming arbitrary stress states in a semiconductor layer, whose light emission is used as a local and sensitive strain gauge. The results shown in this work open a new route to investigate and make use of strain effects in materials and devices.
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 sub-micrometer spatial resolution and a sensitivity of the order of 1 MPa (corresponding to a strain of less than $10^{-6}$). To illustrate the effectiveness and versatility of the technique, we apply it to a broad range of experimental situations, including mapping the elastic stress induced by localized implantation damage, nano-indents 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.
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