Amit Kumar

Ordering of fullerene and carbon nanotube thin films under energetic ion impact

We report the ordering of carbon nanostructures under energetic ion irradiation at low fluence (<5×1011ions∕cm2). Fullerene thin films and multiwalled carbon nanotube (MWCNT) films were irradiated with 200MeV Au and 60MeV Ni ions at different ion fluences, respectively. The changes in the irradiated films have been investigated by means of Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, and Raman spectroscopy. FTIR and Raman spectroscopy show the improvement of vibration strength in low fluence irradiated fullerene and MWCNT films. X-ray diffraction analysis on low fluence irradiated fullerene films revealed the structural order along the (220) atomic planes.

Fabrication of carbon nanostructures (nanodots, nanowires) by energetic ion irradiation

Carbon nanostructures were synthesized by energetic ion irradiation of Si-based gel films. These polymer-like films with different side groups and C concentrations were prepared by sol–gel chemistry and irradiated with Si or Au ions of different energies in the range 3 MeV–2 GeV. The shape and size of the formed carbon nanostructures was studied by energy filtered transmission electron microscopy. They exhibited a visible photoluminescence emission, due to their semiconducting nature and the confinement of excitons. The changes in the optical properties were correlated with the structural transformation of films, investigated by means of Fourier transformed infrared (FTIR) and Raman spectroscopies. The role of carbon concentration, structure and energy transferred by ions on the luminescence properties are discussed.

Hydrogen-induced passivation of boron acceptors in monocrystalline and polycrystalline diamond

This paper presents a review of the properties induced by the presence of hydrogen in monocrystalline boron-doped diamond (BDD) and proposes a comparison with results obtained on polycrystalline materials. Hydrogen diffusion, luminescence and electrical properties show the passivation of boron acceptors in diamond by the formation of (B,H) complexes, in both monocrystalline and polycrystalline forms, but at a different level. This behaviour raises open questions concerning the role of structural defects in the passivation of boron impurities by hydrogenation. Based on the assessment of the high thermal stability of (B,H) complexes, this approach leads to a route to provide patterned diamond conductive structures for micro as well as for nanotechnology applications.

Boron-deuterium complexes in diamond: How inhomogeneity leads to incorrect carrier type identification

The electrical properties of boron doped diamond layers after deuterium diffusion have been investigated by Hall effect and capacitance voltage measurements. It is found that (i) the deuterated boron doped diamond layers are inhomogeneous after the deuterium diffusion, resulting in conducting and insulating areas; (ii) negative and positive Hall voltages are measured on the same boron doped sample after deuterium diffusion, depending on the contact geometry (negative with van der Pauw and positive with mesa etched Hall bar); and (iii) in the conducting area, the majority of the boron-deuterium complexes are not ionized after the deuterium diffusion. The detailed electrical measurements using mesa-insulating Hall bar structures revealed that the existence of inhomogeneous regions with conducting and insulating areas is the most probable source of wrong n-type conductivity in deuterated boron doped diamond layers of this work. In the light of this result, the possibility of an incorrect assignment of a shal...

Conducting carbon nanopatterns (nanowire) by energetic ion irradiation

This work reports the formation of conducting carbon nanopatterns (nano-wires) in a semi-inorganic polymer by irradiation with energetic ions. The conducting nano-patterns/wires are evidenced by conducting atomic force microscopy. The typical diameter of the conducting wires is observed to be about ~50–200 nm. The density (spacing), growth direction and length of these carbon nanowires can be changed simply by ion fluence, angle of irradiation and the film thickness, respectively. The formation of conducting nanopatterns in an insulating matrix (polymers/gels) is correlated with the structural transformation of films, investigated by means of Raman spectroscopy.

The High Energy Ion Irradiation Impact on Carbon Nanotubes

High-energy ion irradiation can create defects, defects annealing depending on various parameters such as ion fluence and the energy loss of ions in the materials. The present report is concerned with the field emission properties of ion-irradiated multiwalled carbon nanotubes (MWCNTs) and double-walled carbon nanotubes (DWCNTs). The carbon nanotubes synthesized by a chemical vapor deposition method were irradiated by high-energy (90 MeV) Au ions with different ion fluence from 4 × 1011 to 1 × 1013 ions/cm2. After ion irradiation, the field emission properties of MWCNTs and DWCNTs were greatly influenced. The change in the emission characteristics is due to structural defects caused by the high-energy ion irradiation. The emission characteristic of MWCNTs was improved and turn-on field decreased from 5.43 to 3.10 V/μm by ion irradiation. Noticeable improvement in emission characteristics of MWCNTs was observed at a fluence of 1 × 1013 ions/cm2. The emission characteristics of DWCNTs deteriorated and the turn-on field was increased from 2.44 to 7.76 V/μm. This results show the distinctly different behavior of ion-irradiated MWCNTs and DWCNTs.

Nanotechnology: A Boon to Dentistry

they are found in osseous sites, they almost exclusively manifest in the jaws and were first described by Thoma and Goldman in 1947.1 Odontogenic myxoma (OM) is a nonencapsulated benign tumor of the jaws with a very rare occurrence rate. The tumor grows gradually with accumulation of mucoid ground substance with minimal collagen. The origin of OM is believed to be the mesenchyme of a developing tooth or the periodontal ligament.2 There are variable reports on the relative frequency of OM in the available literature. In Asia, Europe, and America, OM frequencies between 0.5 and 17.7% of all odontogenic tumors have been reported.1,3 Others report the frequency to be around 3 to 6% of all odontogenic tumors. The tumor mostly affects young patients in their second and third decade of life.4 It occurs across an age group that varies from 22.7 to 36.9 years. It is rarely seen in patients younger than 10 years or older than 50 years.5 The OM is usually a slow and painless swelling occurring more often in the mandible than maxilla, especially in the molar region. Displacement of teeth and paresthesia are uncommon clinical features. When located in the maxilla, OM often involves the maxillary sinus.6 Despite the benign nature of these lesions, there is a high rate of local recurrence after curettage alone and in certain cases it requires a resection of the surgical area.7 It therefore reaches considerable size before being detected, and perforation of the cortices of the involved bone may be seen.5,8 The radiographic features of OM are not pathognomonic, but the most common presentation is a multilocular radiolucency frequently described as honeycombed, soap bubble, or tennis racket appearance. Unilocular appearance may be seen more commonly in children and in the anterior part of the jaws.9 Although OM presents as an asymptomatic expansion, due to the accumulation of mucoid or gelatinous gray-whitish tissue that replaces the cancellous bone, it sometimes results in perforation of the cortical borders of the affected bone. In view of its rarity, the present case of OM of the maxilla in a 24-year-old male infiltrating the maxillary antrum and adjacent tissues is herewith reported.

Design of 2.4 GHz differential low noise amplifier using 0.18 μm CMOS technology

In this paper the inductive degenerated Differential Low Noise Amplifier (DLNA) is designed with operating frequency 2.4 GHz using 0.18 μm CMOS Technology. The DLNA is biased at 1.8 V supply and perfectly matched with input impedance of 50 Ω. Designed DLNA provides power gain of 21.59 dB with a noise figure of 398.1 mdB.

Area optimization of two-stage amplifier using modified particle swarm optimization algorithm

Modern era cannot be consider without an electronics circuits. If Signal strength at the receiving antenna is very weak then there must be required a device that increase the strength of the received signal (power), known as Amplifier. Output of an amplifier is always stronger than its input. So amplifiers are the simplest yet one of the most important parts of electronic circuits. This is why the designing of amplifiers is crucial in analog circuit designing. This paper investigated to minimize the area of a two stage amplifier using modified particle swarm optimization (MPSO) method considering other constraints. The total transistor area obtain using MPSO in this paper is 2.61×10-10 m2 and it is the best of my knowledge, also the power dissipation is much lesser, 1492 μW. Obtained values are verified by the CADENCE simulator and validated. The results proved that the use of modified particle swarm optimization made it possible to achieve better results.