arXiv subjects

K. Ganesan

Publications and source records attributed to K. Ganesan.

33 records · Page 2Linked to original sources

arXiv2019

Role of microstructure and structural disorder on tribological properties of polycrystalline diamond films

Polycrystalline diamond films with systematic change in microstructure that varies from microcrystalline to nanocrystalline structure are synthesized on Si by hot filament chemical vapor deposition. The morphology and structural properties of the grown diamond films are analyzed using field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffraction and Raman spectroscopy. The average roughness and grain size of the diamond films decrease with increase in CH4 to H2 ratio from 0.5 to 3 %. Also, structural disorder in these diamond films increases with decrease in grain size as evidenced from Raman spectroscopy. The coefficient of friction (CoF) is found to be very low for all the films. However, the average CoF is found to increase from 0.011 +/-0.005 to 0.03 +/- 0.015 as the grain size decrease from ~ 1 micron down to ~20 nm. Post analysis of wear track by FESEM, AFM based nanoscale friction and Raman spectroscopy reveal that microcrystalline diamond undergoes shear induced amorphization with negligible wear rate while nanocrystalline diamond films undergo shear induced plastic deformation without amorphization. A comprehensive mechanism for the observed CoF is discussed in the framework of microstructure, structural disorder and shear induced tribo-chemical reactions at the sliding interface.

cond-mat.mtrl-sci↗

arXiv2019

Si and N - vacancy color centers in discrete diamond nanoparticles: Raman and fluorescence spectroscopic studies

The present study reports on an innovative method to prepare discrete diamond nanoparticles or nanodiamonds (NDs) with high structural and optical quality through top-down approach by controlled oxidation of pre-synthesized nanocrystalline diamond (NCD) film. These NDs are studied for their structural and optical properties using atomic force microscopy (AFM), Raman and fluorescence (FL) spectroscopy. While AFM analysis confirms uniform distribution of discrete NDs with different sizes varying from a few tens of nanometers to about a micron, spectroscopic investigations reveal the presence of impurity - vacancy related color centers exhibiting FL at 637 and 738 nm as a function of particle size. In addition, an intense emission originating from vacancy centers associated with N and Si (SiV-) is observed for all NDs at the temperature close to liquid nitrogen. A detailed spectral analysis is carried out on the structural defects in these NDs. The full width at half maximum of diamond Raman band ( ~ 1332 cm-1) is found to be as narrow as 1.5 cm-1 which reveals the superior structural quality of these NDs. Further, mapping of diamond Raman and FL spectra of SiV- confirm the uniform distribution of NDs throughout the substrate. The narrow line widths and a minimal shift in peak positions of Raman and FL spectra endorse this aspect.

cond-mat.mtrl-sci↗

arXiv2017

Single crystal diamond membranes for nanoelectronics

Single crystal, nanoscale diamond membranes are highly sought after for a variety of applications including nanophotonics, nanoelectronics and quantum information science. However, so far, the availability of conductive diamond membranes remained an unreachable goal. In this work we present a complete nanofabrication methodology for engineering high aspect ratio, electrically active single crystal diamond membranes. The membranes have large lateral directions, exceeding 500x500 um2 and are only several hundreds of nanometers thick. We further realize vertical single crystal p-n junctions, made from the diamond membranes that exhibit onset voltages of ~ 10V and a current of several mA. Moreover, we deterministically introduce optically active color centers into the membranes, and demonstrate for the first time a single crystal nanoscale diamond LED. The robust and scalable approach to engineer the electrically active single crystal diamond membranes, offers new pathways for advanced nanophotonics, nanoelectronics and optomechanics devices employing diamond.

physics.app-ph↗

arXiv2017

Flipping growth orientation of nanographitic structures by plasma enhanced chemical vapor deposition

Nanographitic structures (NGSs) with multitude of morphological features are grown on SiO2/Si substrates by electron cyclotron resonance - plasma enhanced chemical vapor deposition (ECR-PECVD). CH4 is used as source gas with Ar and H2 as dilutants. Field emission scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy are used to study the structural and morphological features of the grown films. Herein, we demonstrate, how the morphology can be tuned from planar to vertical structure using single control parameter namely, dilution of CH4 with Ar and/or H2. Our results show that the competitive growth and etching processes dictate the morphology of the NGSs. While Ar-rich composition favors vertically oriented graphene nanosheets, H2-rich composition aids growth of planar films. Raman analysis reveals dilution of CH4 with either Ar or H2 or in combination helps to improve the structural quality of the films. Line shape analysis of Raman 2D band shows nearly symmetric Lorentzian profile which confirms the turbostratic nature of the grown NGSs. Further, this aspect is elucidated by HRTEM studies by observing elliptical diffraction pattern. Based on these experiments, a comprehensive understanding is obtained on the growth and structural properties of NGSs grown over a wide range of feedstock compositions.

cond-mat.mtrl-sci↗

arXiv2017

The role of substrate bias and nitrogen doping on the structural evolution and local elastic modulus of diamond-like carbon films

Diamond-like carbon (DLC) films are synthesized on Si using plasma enhanced chemical vapor deposition. The role of substrate bias and nitrogen doping on the structural evolution and local elastic modulus of DLC films are systematically investigated. Raman spectroscopic studies reveal that the amount of graphitic C=C sp2 bonding increases with substrate bias and nitrogen doping. The density and hydrogen concentration in the films are found to vary from 0.7 to 2.2 g/cm3 and 16 to 38 atomic %, respectively, depending upon the substrate bias and nitrogen concentration in the DLC films. Atomic force acoustic microscopic (AFAM) analysis shows a direct correlation between local elastic modulus and structural properties estimated by Raman spectroscopy, Rutherford back scattering and elastic recoil detection analysis. AFAM analysis further confirms the evolution of soft second phases at high substrate biases (> -150V) in undoped DLC films. Further, N doping leads to formation of such soft second phases in DLC films even at lower substrate bias of -100 V. The AFAM studies provide a direct microscopic evidence for the "sub-implantation growth model" which predicts the formation of graphitic second phases in DLC matrix at high substrate biases.

cond-mat.mtrl-sci↗

arXiv2016

An upper limit on the lateral vacancy diffusion length in diamond

Ion implantation is widely used to modify the structural, electrical and optical properties of materials. By appropriate masking, this technique can be used to define nano- and micro-structures. However, depending on the type of mask used, experiments have shown that vacancy-related substrate modification can be inferred tens of microns away from the edge of the mask used to define the implanted region. This could be due to fast diffusion of vacancies from the implanted area during annealing or to a geometric effect related to ion scattering around the mask edges. For quantum and single-atom devices, stray ion damage can be deleterious and must be minimized. In order to profile the distribution of implantation-induced damage, we have used the nitrogen-vacancy colour centre as a sensitive marker for vacancy concentration and distribution following MeV He ion implantation into diamond and annealing. Results show that helium atoms implanted through a mask clamped to the diamond surface are scattered underneath the mask to distances in the range of tens of micrometers from the mask edge. Implantation through a lithographically defined and deposited mask, with no spacing between the mask and the substrate, significantly reduces the scattering to <5 m but does not eliminate it. These scattering distances are much larger than the theoretically estimated vacancy diffusion distance of 260 nm under similar conditions. This paper shows that diffusion, upon annealing, of vacancies created by ion implantation in diamond is limited and the appearance of vacancies many tens of micrometers from the edge of the mask is due to scattering effects.

cond-mat.mtrl-sci↗

arXiv2016

A comparative study on defect estimation using XPS and Raman spectroscopy in few layer nanographitic structures

Defects in planar and vertically oriented nanographitic structures (NGSs) synthesized by plasma enhanced chemical vapor deposition (PECVD) has been investigated using Raman and X-ray photoelectron spectroscopy. While Raman spectra reveal the dominance of vacancy and boundary type defects respectively in vertical and planar NGSs, XPS provides additional information on vacancy related defect peaks at C 1s spectrum that originate from non-conjugated carbon atoms in hexagonal lattice. Although an excellent correlation prevails between these two techniques, our results show that estimation of surface defects by XPS is more accurate than Raman analysis. Nuances of these techniques are discussed in the context of assessing defects in nanographitic structures.

cond-mat.mtrl-sci↗

arXiv2016

Optical and electronic properties of sub-surface conducting layers in diamond created by MeV B-implantation at elevated temperatures

Boron implantation with in-situ dynamic annealing is used to produce highly conductive sub-surface layers in type IIa (100) diamond plates for the search of a superconducting phase transition. Here we demonstrate that high-fluence MeV ion-implantation, at elevated temperatures avoids graphitization and can be used to achieve doping densities of 6 at.%. In order to quantify the diamond crystal damage associated with implantation Raman spectroscopy was performed, demonstrating high temperature annealing recovers the lattice. Additionally, low-temperature electronic transport measurements show evidence of charge carrier densities close to the metal-insulator-transition. After electronic characterization, secondary ion mass spectrometry was performed to map out the ion profile of the implanted plates. The analysis shows close agreement with the simulated ion-profile assuming scaling factors that take into account an average change in diamond density due to device fabrication. Finally, the data show that boron diffusion is negligible during the high temperature annealing process.

cond-mat.mtrl-sci↗

arXiv2016

A route towards controlling the morphology of vertical graphene nanosheets

Herein, an effort has given to sheds light on the effects of plasma process parameters on the growth of vertical graphene nanosheets (VGNs) by plasma enhanced chemical vapor deposition (PECVD. The parameters include substrate temperature, microwave power and distance between plasma sources to substrate. The significant influence of these variable parameters is observed on the morphology, growth rate and crystallinity. Thus these parameters are found to be deciding factors, which determine the surface reaction and growth kinetics that governed the final structure and controlled morphology of VGNs. The activation energy of the VGNs grown by PECVD is found to be 0.57 eV. A direct evidence of vertical growth through the nanographitic island is observed from temperature dependent growth of VGNs. Such understanding on growth of VGNs is not only useful for growth mechanism under plasma chemistry but also beneficial to get controlled and desired structure for field emission and energy storage application.

cond-mat.mtrl-sci↗

arXiv2014

Evolution and defect analysis of vertical graphene nanosheets

We report catalyst-free direct synthesis of vertical graphene nanosheets (VGNs) on SiO2/Si and quartz substrates using microwave electron cyclotron resonance - plasma enhanced chemical vapor deposition. The evolution of VGNs is studied systematically at different growth stages. Raman analysis as a function of growth time reveals that two different disorder-induced competing mechanisms contributing to the defect band intensity. The VGNs grown on SiO2/Si substrates predominantly consists of both vacancy-like and hopping defects. On the other hand, the VGNs grown on quartz substrates contain mainly boundary-like defects. XPS studies also corroborate Raman analysis in terms of defect density and vacancy-like defects for the VGNs grown on SiO2/Si substrates. Moreover, the grown VGNs exhibit a high optical transmittance from 95 to 78 % at 550 nm and the sheet resistance varies from 30 to 2.17 kohms/square depending on growth time.

cond-mat.mtrl-sci↗

arXiv2012

Ambient Nanoscale Sensing with Single Spins Using Quantum Decoherence

Magnetic resonance detection is one of the most important tools used in life-sciences today. However, as the technique detects the magnetization of large ensembles of spins it is fundamentally limited in spatial resolution to mesoscopic scales. Here we detect the natural fluctuations of nanoscale spin ensembles at ambient temperatures by measuring the decoherence rate of a single quantum spin in response to introduced extrinsic target spins. In our experiments 45 nm nanodiamonds with single nitrogen-vacancy (NV) spins were immersed in solution containing spin 5/2 Mn^2+ ions and the NV decoherence rate measured though optically detected magnetic resonance. The presence of both freely moving and accreted Mn spins in solution were detected via significant changes in measured NV decoherence rates. Analysis of the data using a quantum cluster expansion treatment of the NV-target system found the measurements to be consistent with the detection of ~2,500 motionally diffusing Mn spins over an effective volume of (16 nm)^3 in 4.2 s, representing a reduction in target ensemble size and acquisition time of several orders of magnitude over state-of-the-art electron spin resonance detection. These measurements provide the basis for the detection of nanoscale magnetic field fluctuations with unprecedented sensitivity and resolution in ambient conditions.

cond-mat.mes-hall↗

arXiv2012

Dynamic stabilization of the optical resonances of single nitrogen-vacancy centers in diamond

We report electrical tuning by the Stark effect of the excited-state structure of single nitrogen-vacancy (NV) centers located less than ~100 nm from the diamond surface. The zero-phonon line (ZPL) emission frequency is controllably varied over a range of 300 GHz. Using high-resolution emission spectroscopy, we observe electrical tuning of the strengths of both cycling and spin-altering transitions. Under resonant excitation, we apply dynamic feedback to stabilize the ZPL frequency. The transition is locked over several minutes and drifts of the peak position on timescales greater than ~100 ms are reduced to a fraction of the single-scan linewidth, with standard deviation as low as 16 MHz (obtained for an NV in bulk, ultra-pure diamond). These techniques should improve the entanglement success probability in quantum communications protocols.

quant-ph↗

arXiv2011

Depletion of nitrogen-vacancy color centers in diamond via hydrogen passivation

We show a marked reduction in the emission from nitrogen-vacancy (NV) color centers in single crystal diamond due to exposure of the diamond to hydrogen plasmas ranging from 700°C to 1000°C. Significant fluorescence reduction was observed beneath the exposed surface to at least 80mm depth after ~10 minutes, and did not recover after post-annealing in vacuum for seven hours at 1100°C. We attribute the fluorescence reduction to the formation of NVH centers by the plasma induced diffusion of hydrogen. These results have important implications for the formation of nitrogen-vacancy centers for quantum applications, and inform our understanding of the conversion of nitrogen-vacancy to NVH, whilst also providing the first experimental evidence of long range hydrogen diffusion through intrinsic high-purity diamond material.

cond-mat.mtrl-sci↗

arXiv2009

A Reliable Replication Strategy for VoD System using Markov Chain

In this paper we have investigated on the reliability of streams for a VoD system. The objective of the paper is to maximize the availability of streams for the peers in the VoD system. We have achieved this by using data replication technique in the peers. Hence, we proposed a new data replication technique to optimally store the videos in the peers. The new data replication technique generates more number of replicas than the existing techniques such as random, minimum request and maximize hit. We have also investigated by applying the CTMC model for the reliability of replications during the peer failures. Our result shows that the mean lifetime of replicas are more under various circumstances. We have addressed the practical issues of efficient utilization of overall bandwidth and buffer in the VoD system. We achieved greater success playback probability of videos than the existing techniques.

cs.MM↗

arXiv2009

Nano-manipulation of diamond-based single photon sources

The ability to manipulate nano-particles at the nano-scale is critical for the development of active quantum systems. This paper presents a new technique to manipulate diamond nano-crystals at the nano-scale using a scanning electron microscope, nano-manipulator and custom tapered optical fibre probes. The manipulation of a ~ 300 nm diamond crystal, containing a single nitrogen-vacancy centre, onto the endface of an optical fibre is demonstrated. The emission properties of the single photon source post manipulation are in excellent agreement with those observed on the original substrate.

quant-ph↗