Soumen Mandal

Chemical mechanical polishing of thin film diamond

The demonstration that Nanocrystalline Diamond (NCD) can retain the superior Young’s modulus (1100 GPa) of single crystal diamond twinned with its ability to be grown at low temperatures (<450 °C) has driven a revival into the growth and applications of NCD thin films. However, owing to the competitive growth of crystals the resulting film has a roughness that evolves with film thickness, preventing NCD films from reaching their full potential in devices where a smooth film is required. To reduce this roughness, films have been polished using Chemical Mechanical Polishing (CMP). A Logitech Tribo CMP tool equipped with a polyurethane/polyester polishing cloth and an alkaline colloidal silica polishing fluid has been used to polish NCD films. The resulting films have been characterised with Atomic Force Microscopy, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. Root mean square roughness values have been reduced from 18.3 nm to 1.7 nm over 25 μm2, with roughness values as low as 0.42 nm over ∼0.25 μm2. A polishing mechanism of wet oxidation of the surface, attachment of silica particles and subsequent shearing away of carbon has also been proposed.

The Diamond Superconducting Quantum Interference Device

Diamond is an electrical insulator in its natural form. However, when doped with boron above a critical level (∼0.25 atom %) it can be rendered superconducting at low temperatures with high critical fields. Here we present the realization of a micrometer-scale superconducting quantum interference device (μ-SQUID) made from nanocrystalline boron-doped diamond (BDD) films. Our results demonstrate that μ-SQUIDs made from superconducting diamond can be operated in magnetic fields as large as 4 T independent of the field direction. This is a decisive step toward the detection of quantum motion in a diamond-based nanomechanical oscillator.Soumen Mandal ∗ , Tobias Bautze, Oliver A. Williams, Cécile Naud, Étienne Bustarret, Franck Omnès, Pierre Rodière, Tristan Meunier, Christopher Bäuerle ∗ , and Laurent Saminadayar Institut Néel, CNRS et Université Joseph Fourier, F-38042 Grenoble, France Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastraße 72, 79108 Freiburg, Germany and Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France

Silica based polishing of {100} and {111} single crystal diamond

Abstract Diamond is one of the hardest and most difficult to polish materials. In this paper, the polishing of {111} and {100} single crystal diamond surfaces by standard chemical mechanical polishing, as used in the silicon industry, is demonstrated. A Logitech Tribo Chemical Mechanical Polishing system with Logitech SF1 Syton and a polyurethane/polyester polishing pad was used. A reduction in roughness from 0.92 to 0.23 nm root mean square and 0.31 to 0.09 nm rms for {100} and {111} samples respectively was observed.Diamond is one of the hardest and most difficult to polish mate ri ls. In this paper, the polishing of {111} and {100} single crystal diamond surface s by standard Chemical Mechanical Polishing, as used in the silicon industry, is demonstr ated. A Logitech Tribo Chemical Mechanical Polishing system with Logitech SF1 Syton and a po lyurethane/polyester polishing pad was used. A reduction in roughness from 0.92 to 0.23 nm roo t mean square (RMS) and 0.31 to 0.09 nm RMS for {100} and {111} samples respectively w as observed.

Battery-like supercapacitors from diamond networks and water-soluble redox electrolytes

Enhanced performance of electrochemical capacitors can be achieved by larger capacitances as well as higher power and energy densities. In this work, such battery-like supercapacitors were fabricated using a three-dimensional and conductive diamond network as the capacitor electrode and water-soluble redox couples as the electrolyte. In 0.05 M Fe(CN)63−/4− + 1.0 M Na2SO4 aqueous solution, a capacitance of 73.42 mF cm−2 was obtained at a current density of 1 mA cm−2. This value is 10u2006000 times higher than the capacitance of diamond electric double layer capacitors (EDLCs). The energy and power densities of a fabricated diamond network symmetric pseudocapacitor were up to 56.50 W h kg−1 and 13.7 kW kg−1, respectively. Compared with those of diamond EDLCs obtained with the same cell voltage, they are enhanced about 3500 and 1440 fold, respectively. Therefore the combination of diamond networks and water-soluble redox electrolytes is a novel approach to construct electrochemical capacitors and thus bridges the gap between normal dielectric capacitors and rechargeable batteries.

Investigating the Broadband Microwave Absorption of Nanodiamond Impurities

Broadband microwave complex permittivity measurements of nanodiamond powders are presented. Previous studies show that measurements of dielectric loss strongly correlate with the presence of nondiamond surface impurities. In this study, the frequency dependence of these losses is investigated using the microwave cavity perturbation (MCP) and broadband coaxial probe (BCP) methods. This allowed further understanding as to what mechanisms contribute to the microwave absorption (free electron conduction or dielectric loss from the disordered surfaces). A multimode MCP system is used which utilizes TM0np modes to provide partial spectral characterization. The MCP results revealed minimal frequency dependence, unlike any static conduction-related mechanism. The BCP measurements corroborate the MCP results with much higher spectral resolution, and further demonstrate that disorder related loss may dominate over free electron conduction from 1-10 GHz. From 0.1-1 GHz, free electron conduction has a greater influence with a characteristic 1/f dependence implying that conduction may dominate at lower frequencies. However, the BCP method, while repeatable, lacks in precision compared to the cavity method. Nonetheless, the major conclusion in this paper is that through simple microwave permittivity measurements, nondiamond carbon impurities in nanodiamond powders are measurable most likely because of disorder related losses as opposed to free electron conduction.

Observation of conduction electron spin resonance in boron-doped diamond

We observe the electron spin resonance of conduction electrons in boron-doped (6400 ppm) superconducting diamond (Tc=3.8 K). We clearly identify the benchmarks of conduction electron spin resonance (CESR): the nearly temperature independent electron spin resonance signal intensity and its magnitude, which is in good agreement with that expected from the density of states through the Pauli spin susceptibility. The temperature dependent CESR linewidth weakly increases with increasing temperature, which can be understood in the framework of the Elliott-Yafet theory of spin relaxation. An anomalous and yet unexplained relation is observed between the g-factor, CESR linewidth, and the resistivity using the empirical Elliott-Yafet relation.

Fluctuation spectroscopy as a probe of granular superconducting diamond films

We present resistance versus temperature data for a series of boron-doped nanocrystalline diamond films. Upon extracting the fluctuation conductivity near the critical temperature we observe three distinct scaling regions—three-dimensional (3D) intragrain, quasi-0D, and 3D intergrain—in confirmation of the prediction of Lerner, Varlamov, and Vinokur. The location of the dimensional crossovers between these scaling regions allows us to determine the tunneling energy and the Thouless energy directly. This is a demonstration of the use of fluctuation spectroscopy to determine the properties of a superconducting granular system.

Spectroscopic Ellipsometry of Nanocrystalline Diamond Film Growth

With the retention of many of the unrivaled properties of bulk diamond but in thin-film form, nanocrystalline diamond (NCD) has applications ranging from micro-/nano-electromechanical systems to tribological coatings. However, with Young’s modulus, transparency, and thermal conductivity of films all dependent on the grain size and nondiamond content, compositional and structural analysis of the initial stages of diamond growth is required to optimize growth. Spectroscopic ellipsometry (SE) has therefore been applied to the characterization of 25–75 nm thick NCD samples atop nanodiamond-seeded silicon with a clear distinction between the nucleation and bulk growth regimes discernable. The resulting presence of an interfacial carbide and peak in nondiamond carbon content upon coalescence is correlated with Raman spectroscopy, whereas the surface roughness and microstructure are in accordance with values provided by atomic force microscopy. As such, SE is demonstrated to be a powerful technique for the characterization of the initial stages of growth and hence the optimization of seeding and nucleation within films to yield high-quality NCD.

Pure nanodiamonds for levitated optomechanics in vacuum

Optical trapping at high vacuum of a nanodiamond containing a nitrogen vacancy centre would provide a test bed for several new phenomena in fundamental physics. However, the nanodiamonds used so far have absorbed too much of the trapping light, heating them to destruction (above 800 K) except at pressures above ~10 mbar where air molecules dissipate the excess heat. Here we show that milling diamond of 1000 times greater purity creates nanodiamonds that do not heat up even when the optical intensity is raised above 700 GW m−2 below 5 mbar of pressure.Levitated nanodiamonds containing nitrogen vacancy centres in high vacuum are a potential test bed for numerous phenomena in fundamental physics. However, experiments so far have been limited to low vacuum due to heating arising from optical absorption of the trapping laser. We show that milling pure diamond creates nanodiamonds that do not heat up as the optical intensity is raised above 700 GW/m

Impact of chemical vapour deposition plasma inhomogeneity on the spatial variation of sp 2 carbon in boron doped diamond electrodes

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