It has been generally accepted that the resolution of a lens-based optical microscope is limited to about > 200 nm in the focal plane and > 500 nm along the optic axis, with NA denoting the numerical aperture of the lens and the wavelength of light. The discovery in the 1990’s that elementary transitions between the states of a fluorophore can be used to eliminate the limiting role of diffraction has led to light microscopy concepts with resolution on the nanometer scale. Currently, all existing and successfully applied nanoscopy methods share a common enabling element: they switch fluorescence on or off, so that adjacent features are registered sequentially in time.For example, in a typical Stimulated Emission Depletion (STED) microscope, the fluorophores are switched off (=kept dark) by overlapping the excitation beam with a de-exciting (STED) beam which effectively confines the fluorophores to the ground state everywhere in the focal region except at a tiny area where the STED beam is close to zero. Fluorophores that are located in this subdiffraction-sized smaller area are registered. Scanning the beams further in space registers those fluorophores that had been switched off. An image of the whole object is assembled by sequential registration. The resolution is now given by the smaller diameter d of this area in which the fluorophores are still fluorescent. I is the intensity of the STED beam, which, for I >> Is, entails d→0, meaning that the resolution is conceptually no longer limited by lamda.STED microscopy has been used to investigate the fate of synaptic vesicle proteins after exocytosis, thus demonstrating the potential of emerging ‘fluorescence nanoscopy’ for the life sciences. A video-rate STED microscope was used to describe the mobility of vesicles inside the axons of cultured living neurons. Live-cell STED microscopy has also been used to image activity-dependent morphological plasticity of dendritic spines, while in another study, it revealed that single sphingolipids, but not phospholipids, are transiently (< 10 ms) and locally (< 20 nm) trapped in a living cell membrane, mediated by cholesterol.The concept of STED microscopy has been expanded to low intensity operation by switching the fluorophore to a long-lived dark (triplet) state or between a ‘fluorescence activated’ and a ‘deactivated’ (conformational) state as encountered in switchable fluorescent proteins. More recent but seminal nanoscopy schemes such as PALM, STORM and also GSDIM, switch the molecules individually and stochastically to a state that emits m >>1 detectable photons in a row before returning to a dark state, allowing the calculation of their position. Altogether, lens-based optical nanoscopy is an unexpected and fascinating development in the physical sciences that is poised to impact several areas of science, in particular the life sciences, in the near future.

Nitrogen-Vacancy (NV) color center in diamond has a perfectly stable photoluminescence in the red and near infrared spectral region.Diamond nanoparticles (size~20 nm) containing NV color centers (fluorescent NanoDiamonds, fNDs) are therefore perfectly suited for cellular and tissues imaging in this low absorption window, and for long-term tracking.We will show that fNDs are spontaneously internalized in different cell lines including primary neurons and do not induce cytotoxicity even at high concentrations.Thanks to NV center perfect photostability, fNDs are ideal for STimulated Emission Depletion Microscopy (STED) super-resolution microscopy which requires the combination of the fluorescence excitation by a usual Gaussian intensity shape beam (wavelength 532 nm) with the high power STED beam having a doughnut shaped intensity to stimulate the emission efficiently from the excited state (wavelength 735 nm). We will present preliminary observations of super-resolution imaging of fNDs in cells using cw lasers.Such super-resolution microscopy will be used in particular to image neuronal dendritic spines morphology, which disorders are associated to numerous neurodegenerative diseases.

Detection of weak magnetic fields with nanoscale spatial resolution is an outstanding problem in the biological and physical sciences. For example, at a distance of 10 nm, the spin of a single electron produces a magnetic field of about 1 micro Tesla, and the corresponding field from a single proton is a few nano Tesla. A sensor able to detect such magnetic fields with nanometer spatial resolution would enable powerful applications, ranging from the detection of magnetic resonance signals from individual electrons or nuclear spins in complex biological molecules to readout of classical or quantum bits of information encoded in an electron or nuclear spin memory. Recently we experimentally demonstrated an approach to such nanoscale magnetic sensing, using coherent manipulation of an individual electronic spin qubit associated with a nitrogen-vacancy impurity in diamond at room temperature. Using an ultra-pure diamond sample, we achieve detection of 30 nT magnetic fields at kilohertz frequencies after 1s of averaging. In this talk I will review some of the recent advances in the development of such a scanning magnetometer.

Chemically synthesized nanoparticles, such as fluorescent dyes and colloidal quantum dots, are commonly used as nanoprobes for biological and chemical sensing applications and single photon emitters in integrated optical devices. More recently, diamond nanoparticles (DNPs) have emerged as promising candidates for these applications, owing to their excellent physical and chemical properties, which include structural stability, chemical inertness, optical transparency, biocompatibility, and surface functionalizability. Additionally, DNPs can be made optically active by the host of color centers from defects in diamond that arise either naturally or via implantation. The fluorescence from DNPs is stable at room temperature and can have wavelengths from the green to the infrared. We present results on the optical characterization of size-controlled DNPs containing the nitrogen-vacancy (NV) defect center. DNPs from commercially obtained diamond slurries have been purified and size separated using analytical ultracentrifugation, resulting in narrow size distributions of ±13nm. As demonstration of their remarkable photo- and structural stabilities in chemical sensing applications, we have subjected the DNPs to harsh chemical and physical conditions, i.e. boiling in brine, and shown that their morphology, size distribution, and luminescence remain unchanged.Meanwhile, we propose the use of DNPs containing single NV centers as ideal single photon emitters for coupling to passive optical resonators fabricated in transparent thin films such as titania. We have designed high Q/V titania nanobeam cavities (with theoretical Q ~ 10^6 and V~0.4(λ/n)^3) that operate near the zero phonon line (637 nm) of the NV fluorescence and fabricated these structures in sputtered titania, using electron beam lithography and reactive ion etching. Finally, we have studied the optical and charge transfer dynamics of various nanoparticles integrated with titania thin films, by measuring the spectra and time traces of single emitter fluorescence using confocal microscopy. In contrast to CdSe/ZnS quantum dots, which exhibit photobleaching and blinking behavior with prolonged dark states that are consistent with the transfer of charges into the lower bandgap titania host matrix, fluorescence from DNPs are stable and non-blinking.

Development of the next generation of diamond devices for chemical and biological sensing requires techniques for surface modification under ambient conditions. Single crystal (100) substrates have been treated with a hydrogen plasma to maximise the (100) terrace width and produce high quality surfaces. Thermal oxidation, in dry O2, yielded monolayer oxygen coverage with a high proportion of 'on-top' (>C=O)oxygen.Covalent binding of 4-trifluoromethylbenzylamine, in solution at room temperature, to the surface carbonyl group was accomplished to form the water sensitive imine bond. Reductive animation created a water stable amine functional group on the diamond (100) surface.

Fluorescent diamond nanoparticles (fNDs) carrying nitrogen-vacancy (N-V) colored centers hold great promises for biomedical applications [1]. They combine some of the outstanding properties of bulk diamond, such as the chemical resilience or the carbon surface chemistry, as well as the benefits of a fluorescent center emitting in the far-red with an ultrahigh photostability [2]. Furthermore, their low cytotoxicity is reported [3] and their mass production is now well controlled [4].The use of fNDs to label biomolecules and track their fate in-vivo or to deliver bioactive molecules implies the addition of specific functionalities to the bare fNDs. Stability in biological media, targeting or drug-release mechanisms go through a surface functionalization of the particles with, e.g. PEG chains, proteins, ionic moieties... However, after post-synthesis purifications treatments and irradiation/annealing steps to create N-V centers, fNDs surface chemistry remains highly inhomogeneous, with amorphous carbon, graphite shells and various oxidized terminations. Here we report on the chemical preparation of NDs. Methods for surface homogenization by exposures to reactive atmospheres (plasma treatments, annealings) in order to rationalize the surface chemistry are detailed. Then, new functionalization routes are proposed as efficient ways to bind bioactive molecules on these pre-treated fNDs. The surface modifications of the NDs are characterized using X-ray Photoelectron Spectroscopy, Auger electron Spectroscopy, Fourier Transformed Infra-Red Spectroscopy, Dynamic Light Scattering and Zeta Potential measurements. By our preparation and grafting methods, novel surface properties are given to NDs, such as e.g. cationic sites, self-adhesive spots, useful for biomedical applications.[1]A. M. Schrand et al., Crit. Rev. Sol. State, 34 (2009) 18[2]S.-J. Yu et al., J. Am. Chem. Soc., 127 (2005) 17604[3]V. Vaijayanthimala et al., Nanotechnol., 20 (2009) 425103[4]Y.-R. Chang et al., Nanotechnol., 3 (2008) 284

Nano-diamond particles obtained from the purification of detonation products are found tightly aggregated and with a diverse array of contaminants. This aggregation is due to sp2 carbon shells which are formed during the cooling cycle of the detonation shock wave. The de-aggregation of such material is difficult and various techniques have been proposed each with their relative merits and flaws. For example, milling techniques based on zirconia beads result in significant contamination while burning in air results in substantial material loss. In this work we present a complimentary technique based on the surface shell reactivity of these particles that has none of the above drawbacks.By heating detonation nano-diamond particles in hydrogen gas at 500 °C (10 mbar, 5 hours), we are able to produce mono-disperse colloids with particle sizes between 3-4 nm. The zeta potential of these colloids changes from negative for the untreated particles to positive for the treated material. The negative zeta potential originates from acidic groups on the untreated product that are displaced by hydrogen in the treated material. The change in zeta potential and particle size demonstrates that the particle surfaces are able to react with molecular hydrogen at relatively low temperatures. This is due to the sp2 nature of the surfaces which we have confirmed with TEM and analogous experiments on carbon black. Positive zeta potentials are a common feature of hydrogenated carbon black and larger diamond particles with less sp2 do not show this effect. Thus, we conclude that the effect is based on the sp2 nature of the detonation nano-diamond surfaces.

The facile surface chemistry of diamond nanoparticles with a variety of different functional groups has made these systems attractive for many different applications in the materials and bio-medical sciences. To better understand and predict the covalent bonding of surface species to diamond nanoparticles, we have been using a semi-empirical electronic method to calculate surface binding energies for –NH2 and -COOH groups on hydrogen terminated 4.5 nm octahedral diamond nanoparticles as a function of binding site. The calculations predict that both functional groups prefer binding at apex sites, followed by edge and then terrace sites. For the amino group, the energy difference between bonding to an apex and edge site is ~0.3 eV, while the difference between the edge and terrace site is only ~0.1 eV. The energy difference between the apex and edge sites for the carboxylic acid group is also ~0.3 eV, but the energy difference between the edge and terrace site is ~0.7 eV. The differences in binding energies between the different sites are attributed to geometric effects that reduce steric repulsion between the functional groups and surface hydrogen for the apex and edge sites compared to the terrace sites. The larger difference in binding energy between the edge and terrace sites for the carboxylic acid compared to the amino group is attributed to the larger size of the former. This prediction of a relatively large dependence of binding energy on binding site suggests very different thermal lifetimes of these sites, and the possibility of using thermal cycling in different plasma environments to create nanoparticles with spatially heterogeneous chemical activity. Results of Monte Carlo simulations intended to test this hypothesis will be presented.

Nanodiamond powder (ND) produced by detonation on an industrial scale is an attractive nanomaterial for reinforcing polymer matrices due to its superior mechanical, thermal and chemical properties. Composite materials are widely used for industrial and consumer applications ranging from the aerospace industry to electronic and biomedical applications. Specifically, desirable mechanical properties of the composite materials in combination with low specific weight can lead to an increased performance and fuel economy, which are major issues in the modern economy. Therefore, there exists an ongoing interest in creating composites which are stronger and lighter than pure polymers or metals. A careful selection of the composite components is of importance to achieve the desired properties. Nanodiamond is an excellent candidate for reinforcing polymer matrices due to its unique properties. Combined with a variety of chemical functionalizations, made possible due to a presence of a large number of functional groups on its surface, this material can be tailored to engineer new composites with enhanced mechanical properties. In this study, ND has been incorporated into an epoxy matrix. High concentration (up to 50%) ND samples have been produced using hot pressing and tested by depth sensing indentation with a spherical diamond indenter. An increase of up to 350% in Young’s modulus has been observed as well as an increase in hardness of up to 300% percent as compared to neat epoxy. Also, scratch tests show a significant increase in wear resistance of the composite were both piled-up and the amount of removed material have been reduced by 50%. Additionally thermal conductivity of ND epoxy samples with concentration of 30wt. % or higher has been improved. Both mechanical and thermal conductivity data suggest the formation of an interconnected network of ND particles. To further improve mechanical properties at low concentrations of ND, research on surface functionalization of ND is ongoing.

The electrical properties of as deposited mono-dispersed detonation nanodiamonds(DNDs) have been studied; a resistivity of the order of 1012 Ω/sq has beendetermined, with only one significant conduction pathway being observed. The dielectric character of the DND particles is also good, with dielectric loss tangent values in the range 0.05-0.5 being recorded. These combined observations suggest DNDs behave in electrical terms similar to thin film diamond, and that electrical applications for DNDs are worthy of pursuit. Since a simple room temperature sonication process has been used for their deposition, coating a wide-range of three dimensional substrate materials will be possible. A limitation on the electrical use the mono-dispersed DNDs, at least in the untreated, as-deposited from solution form used here, is the catastrophic loss of diamond-like character at temperatures above 400C. In contrast H-terminated NDs show greater stability and strongly modified electrical characteristics. The results be discussed in terms of the surface electrical characteristics of this interesting form of diamond.

Current experimental configurations for MW PECVD diamond growth do not allow simple up-scaling towards large areas, which is essential for microelectronic industries and other applications. Another important issue is the reduction of the substrate temperature during diamond growth to enhance the compatibility with wafer processing technologies. Such advantages are provided by MW-Linear Antenna (LA) plasma applicators, allowing a scalable concept for diamond growing plasmas. In the present work we introduce a novel construction of LA MW applicators designed for nanodiamond growth by using plasmas ranging from continuous wave (CW) to pulsed modes of high repetition rates (up to 20 kHz).Using fast pulsing provides several advantages for diamond growth. Firstly, it allows the application of high power in short pulses, leading to non-linear MW absorption and consequently a reduction of total average input power to ~ 5W/cm2 compared to ~ 20 W/cm2 for CW LA-MWs or to typically 100-200W /cm2 for resonance cavity applicators. Despite the factor of 50 power reduction, the diamond growth rate that can be obtained at 450°C is comparable to or higher than that of resonance cavity systems. Secondly, the pulsed plasma concept brings improvements in diamond quality when compared to the CW mode. The resulting diamond films, grown by pulsed plasma, show clean grain boundaries with columnar growth, i.e. resembling classical nano-crystalline diamond (NCD) films of high crystallinity. This is achieved by the use of a tailored plasma chemistry. In fact the concentration of atomic hydrogen can be sustained with sufficiently high values during the power-off periods at the right pulse frequency, while the growth rates in the off-period is significantly reduced. This allows suppression of re-nucleation during the growth and preparation of high quality NCD films with 2-5% sp2 carbon (based on Raman measurements), for layer thicknesses ranging from 30 to 300 nm. We show how diamond quality, measured by Raman spectroscopy and by ellipsometry depends on the MW pulse frequency and CH4/CO2/H2 gas ratios. The plasma conditions are monitored by OES spectroscopy and by using plasma probing to measure the electron fluxes and the electron energy distribution function. We demonstrate highly uniform diamond films grown on Si wafers with a homogeneity < 5% over an 8 inch area.

Kinetic Monte Carlo (KMC) simulations of CVD diamond growth have been used to simulate 300 atomic layers of diamond growth. We have previously used this model to gain insight into the fundamental processes, including adsorption, surface migration, beta-scission and etching, that govern CVD diamond growth for a fixed set of deposition conditions. We now report new results obtained from using this model to predict the growth rates and morphology expected from gas phase conditions that experimentally give rise to single crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) films. Despite its simplicity, the KMC model predicts growth rates and surface roughness values for each of the diamond types that are consistent with experimental observations. The relative rates of surface H abstraction and hopping determine the average surface diffusion length, λ, and (in the absence of defect formation and renucleation) this is a key parameter in controlling surface morphology. When the hopping rate is more than ~100× greater than the H abstraction rate, λ becomes <2, which means that migration is limited by the lack of availability of surface radical sites, and the migrating surface species simply hop back and forth between 2 adjacent sites but do not travel far beyond their initial adsorption site. Thus, Eley-Rideal processes dominate the growth, leading to the rough surfaces seen in NCD and UNCD. Conversely, when the hopping rate <100× higher than the H abstraction rate, migration occurs over greater distances (λ > 2), leading to Langmuir-Hinshelwood processes dominating the growth producing the smoother surfaces of MCD and SCD. By extrapolation, we predict that atomically smooth surfaces over large areas should occur once migrating species can travel ~5 sites (λ = 5), which requires a gas-phase concentration ratio of [H]/[CHx] > 13400 at the growing surface. Finally, the predictions for UNCD deposition in a microwave system were found to be anomalous compared to all the other growth conditions, probably as a result of carbonaceous particulates being created in the plasma which affect the gas chemis