arXiv subjects

Soumen Mandal

Publications and source records attributed to Soumen Mandal.

At least 37 records · Page 2Linked to original sources

arXiv2018

Superconducting Diamond on Silicon Nitride for Device Applications

Chemical vapour deposition (CVD) grown nanocrystalline diamond is an attractive material for the fabrication of devices. For some device architectures, optimisation of its growth on silicon nitride is essential. Here, the effects of three pre-growth surface treatments, often employed as cleaning methods of silicon nitride, were investigated. Such treatments provide control over the surface charge of the substrate through modification of the surface functionality, allowing for the optimisation of electrostatic diamond seeding densities. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) were used to analyse the silicon nitride surface following each treatment. Exposing silicon nitride to an oxygen plasma offered optimal surface conditions for the electrostatic self-assembly of a hydrogen-terminated diamond nanoparticle monolayer. The subsequent growth of boron-doped nanocrystalline diamond thin films on modified silicon nitride substrates under CVD conditions produced coalesced films for oxygen plasma and solvent treatments, whilst pin-holing of the diamond film was observed following RCA-1 treatment. The sharpest superconducting transition was observed for diamond grown on oxygen plasma treated silicon nitride, demonstrating it to be of the least structural disorder. Modifications to the substrate surface optimise the seeding and growth processes for the fabrication of diamond on silicon nitride devices.

cond-mat.mtrl-sci↗

arXiv2018

Production of Metal-free Diamond Nanoparticles

In this paper, the controlled production of high quality metal-free diamond nanoparticles is demonstrated. Milling with tempered steel is shown to leave behind iron oxide contamination which is difficult to remove. Milling with SiN alleviates this issue but generates more non diamond carbon. Thus the choice of milling materials is critically determined by the acceptable contaminants in the ultimate application. The removal of metal impurities, present in all commercially available nanoparticles, will open new possibilities towards the production of customised diamond nanoparticles, covering the most demanding quantum applications.

cond-mat.mtrl-sci↗

arXiv2018

Strongly inhomogeneous distribution of spectral properties of silicon-vacancy color centers in nanodiamonds

The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that the SiV center in nanodiamond exhibits a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range of approximatly 730 nm to 742 nm and broad linewidths between 5 nm and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 nm and 835 nm, but narrow linewidths from below 1 nm up to 4 nm. Supported by ab initio Kohn-Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of modified SiV centers. Whereas single photon emission is demonstrated for SiV centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.

quant-ph↗

arXiv2018

A simple, space constrained NIRIM type reactor for chemical vapour deposition of diamond

In this paper the design of a simple, space constrained chemical vapour deposition reactor for diamond growth is detailed. Based on the design by NIRIM, the reactor is composed of a quartz discharge tube placed within a 2.45 GHz waveguide to create the conditions required for metastable growth of diamond. Utilising largely off-the-shelf components and a modular design, the reactor allows for easy modification, repair, and cleaning between growth runs. The elements of the reactor design are laid out with the CAD files, parts list, and control files made easily available to enable replication. Finally, the quality of nanocrystalline diamond films produced are studied with SEM and Raman spectroscopy, with the observation of clear faceting and a large diamond fraction suggesting the design offers deposition of diamond with minimal complexity.

physics.app-ph↗

arXiv2018

Battery-like Supercapacitors from Vertically Aligned Carbon Nanofibers Coated Diamond: Design and Demonstrator

Battery-like supercapacitors feature high power and energy densities as well as long-term capacitance retention. The utilized capacitor electrodes are thus better to have large surface areas, high conductivity, high stability, and importantly be of binder free. Herein, vertically aligned carbon nanofibers (CNFs) coated boron-doped diamonds (BDD) are employed as the capacitor electrodes to construct battery-like supercapacitors. Grown via a thermal chemical vapor deposition technique, these CNFs/BDD hybrid films are binder free and own porous structures, resulting in large surface areas. Meanwhile, the containment of graphene layers and copper metal catalysts inside CNFs/BDD leads to their high conductivity. Electric double layer capacitors (EDLCs) and pseudocapacitors (PCs) are then constructed in the inert electrolyte (1.0 M H2SO4 solution) and in the redox-active electrolyte (1.0 M Na2SO4 + 0.05 M Fe(CN)63-/4-), respectively. For assembled two-electrode symmetrical supercapacitor devices, the capacitances of EDLC and PC devices reach 30 and 48 mF cm-2 at 10 mV s-1, respectively. They remain constant even after 10 000 cycles. The power densities are 27.3 kW kg-1 and 25.3 kW kg-1 for EDLC and PC devices, together with their energy densities of 22.9 Wh kg-1 and 44.1 Wh kg-1, respectively. The performance of formed EDLC and PC devices is comparable to market-available batteries. Therefore, the vertically aligned CNFs/BDD hybrid film is a suitable capacitor electrode material to construct high-performance battery-like and industry-orientated supercapacitors for flexible power devices.

physics.app-ph↗

arXiv2018

Redox agent enhanced chemical mechanical polishing of thin film diamond

The chemical nature of the chemical mechanical polishing of diamond has been examined by adding various redox agents to the alkaline SF1 polishing slurry. Three oxidizing agents namely, hydrogen peroxide, potassium permanganate and ferric nitrate, and two reducing agents, oxalic acid and sodium thiosulfate, were added to the SF1 slurry. Oxalic acid produced the fastest polishing rate while hydrogen peroxide had very little effect on polishing, probably due to its volatile nature. X-ray photoelectron spectroscopy (XPS) reveals little difference in the surface oxygen content on the polished samples using various slurries. This suggests that the addition of redox agents do not increase the density of oxygen containing species on the surface but accelerates the process of attachment and removal of Si or O atoms within the slurry particles to the diamond surface.

cond-mat.mtrl-sci↗

arXiv2017

Surface zeta potential and diamond seeding on gallium nitride films

Measurement of zeta potential of Ga and N-face gallium nitride has been carried out as function of pH. Both the faces show negative zeta potential in the pH range 5.5-9. The Ga face has an isoelectric point at pH 5.5. The N-face shows higher negative zeta potential due to larger concentration of adsorbed oxygen. Zeta potential data clearly showed that H-terminated diamond seed solution at pH 8 will be optimal for the self assembly of a monolayer of diamond nanoparticles on the GaN surface. Subsequent growth of thin diamond films on GaN seeded with H-terminated diamond seeds produced fully coalesced films confirming a seeding density in excess of 10$^{12}$ cm$^{-2}$. This technique removes the requirement for a low thermal conduction seeding layer like silicon nitride on GaN.

cond-mat.mtrl-sci↗

arXiv2014

Polishing of {100} and {111} single crystal diamond through the use of Chemical Mechanical Polishing

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 (RMS) and 0.31 to 0.09 nm RMS for {100} and {111} samples respectively was observed.

cond-mat.mtrl-sci↗

arXiv2014

Superconducting nano-mechanical diamond resonators

In this work we present the fabrication and characterization of superconducting nano-mechanical resonators made from nanocrystalline boron doped diamond (BDD). The oscillators can be driven and read out in their superconducting state and show quality factors as high as 40,000 at a resonance frequency of around 10 MHz. Mechanical damping is studied for magnetic fields up to 3 T where the resonators still show superconducting properties. Due to their simple fabrication procedure, the devices can easily be coupled to other superconducting circuits and their performance is comparable with state-of-the-art technology.

cond-mat.mes-hall↗

arXiv2013

Chemical mechanical polishing of thin film diamond

The demonstration that Nanocrystalline Diamond (NCD) can retain the superior Young's modulus (1,100 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 μm$^2$, with roughness values as low as 0.42 nm over ~ 0.25 μm$^2$. A polishing mechanism of wet oxidation of the surface, attachment of silica particles and subsequent shearing away of carbon has also been proposed.

cond-mat.mtrl-sci↗

arXiv2013

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 ESR 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.

cond-mat.mtrl-sci↗

arXiv2013

A detailed analysis of the Raman spectra in superconducting boron doped nanocrystalline diamond

The light scattering properties of superconducting (Tc=3.8 K) heavily boron doped nanocrystalline diamond has been investigated by Raman spectroscopy using visible excitations. Fano type interference of the zone-center phonon line and the electronic continuum was identified. Lineshape analysis reveals Fano lineshapes with a significant asymmetry (q=-2). An anomalous wavelength dependence and small value of the Raman scattering amplitude is observed in agreement with previous studies.

cond-mat.mtrl-sci↗

arXiv2012

Growth of [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ - YBa$_{2}$Cu$_{3}$O$_{7}$ heterostructures

YBa$_{2}$Cu$_{3}$O$_{7}$ - La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ heterostructures of [110] orientation are grown to allow direct injection of spin polarized holes from the La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ into the CuO$_2$ superconducting planes. The magnetic response of the structure at T $<$ T$_{sc}$ shows both diamagnetic and ferromagnetic moments with [001] direction as magnetic easy axis. While the superconducting transition temperature (T$_{sc}$) of these structures is sharp ($Δ$T$_{sc} \simeq$ 2.5 K), the critical current density (J$_c$) follows a dependence of the type $J_c = J{_o}(1-\frac{T}{T_{sc}})^{3/2}$ with highly suppressed J$_o$ ($\simeq 2 \times 10^4$ A/cm$^2$) indicating strong pair breaking effects of the ferromagnetic boundary.

cond-mat.supr-con↗

arXiv2011

The Diamond SQUID

Diamond is an electrical insulator in its natural form. However, when doped with boron above a critical level (~0.25 at.%) 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 4T independent on the field direction. This is a decisive step towards the detection of quantum motion in a diamond based nanomechanical oscillator.

cond-mat.mes-hall↗

arXiv2011

Efficient Radio Frequency filters for space constrained cryogenic set-ups

Noise filtering is an essential part for measurement of quantum phenomena at extremely low temperatures. Here, we present the design of a filter which can be installed in space constrained cryogenic environment containing a large number of signal carrying lines. Our filters have a -3db point of 65kHz and its performance at GHz frequencies are comparable to the best available RF filters.

physics.ins-det↗

arXiv2010

A comparative study of angle dependent magnetoresistance in [001] and [110] $La_{2/3}Sr_{1/3}MnO_3$

The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.

cond-mat.mtrl-sci↗

arXiv2010

Nanostructures made from superconducting boron doped diamond

We report on the transport properties of nanostructures made from boron-doped superconducting diamond. Starting from nanocrystalline superconducting boron-doped diamond thin films, grown by Chemical Vapor Deposition, we pattern by electron-beam lithography devices with dimensions in the nanometer range. We show that even for such small devices, the superconducting properties of the material are well preserved: for wires of width less than $100\, nm$, we measure critical temperatures in the Kelvin range and critical field in the Tesla range.

cond-mat.mes-hall↗

arXiv2010

Magnetoresistance studies of $La_{2/3} Sr_{1/3} MnO_3$ - $YBa_2 Cu_3 O_7$ - $La_{2/3} Sr_{1/3} Mn O_3$ trilayers with ferromagnetic coupling along the nodal direction of $YBa_2 Cu_3 O_7$

I have successfully prepared (110) trilayers of \LSMO-\YBCO-\LSMO. Magnetization measurements on these samples reveal a stronger coupling between the ferromagnetic layers. The coupling is an order of magnitude higher than that seen in the case of (001) trilayers. Magnetoresistance measurements show a first order transition in the data coinciding with the antiferromagnetic regime deduced from the magnetization measurements. I have also measured the anisotropic magnetoresistance (AMR) of these samples revealing an unusually high AMR ($\sim 72000%$). I attribute such a high AMR to the pair breaking effects in these films.

cond-mat.supr-con↗