Journal of Nano Research Vol. 10

Abstract: Thin film samples of multi-walled carbon nanotubes (MWCNTs) were irradiated with 120 MeV gold ions. Transmission electron microscopy (TEM) images of the pristine and irradiated samples were obtained. TEM pictures show that in the irradiated sample, the CNTs are in general shorter and some have their inner cores filled, unlike in the pristine sample. We also find from these images that average inner and outer tube diameters change as a result of ion irradiation. The films were also characterized using Raman spectrometry. Modifications of the disorder mode (D mode) and the tangential mode (G mode) under different irradiation fluences were studied in detail. As fluence increases, the MWCNTs first show damage, then healing under somewhat higher fluences and again amorphization under still higher fluence of ion irradiation.

Abstract: There are several known severe plastic deformation (SPD) methods, which allow receiving nano-grained structure of materials. One of the methods is called the KOBO method (the name is composed of the first two letters of the surnames of the inventors: KOrbel and BOchniak). The method was used for extrusion of copper alloys at room temperature to manufacture thin-wall tubes. During the KOBO extrusion, reversible cyclic torsion of the material results in multiple changing the deformation path. Hence, a heavy localized plastic flow leads to shear bands development that reduces the total strain hardening effect and results in effective structure refinement. In particular, thin-wall tubes produced from single-phase copper alloys, intensively cooled close to the die outlet, had homogeneous structure consisting of fine grains/subgrains of a few hundreds nanometers in size. The final structure of the material is practically independent on the initial structure of processed billets. If the accelerated cooling of extruded material was omitted, grain coarsening to the size of dozens of micrometers was observed. In multi-phase copper alloys, the grain refinement was limited to about 1 μm, both for intensively cooled and air-cooled products.

Abstract: M-type strontium hexaferrite nanocrystals of radar absorbing material (NRAM) i.e. SrFe12O19 were synthesized by modified flux method that combine the controlled chemical co-precipitation process for nucleation and complete uniform growth during annealing with NaCl flux. Uniform structural morphological transformation of nanocrystals from needle to hexagonal prism faces were noticed after annealing with increasing of heat treatment (HT) temperature from 800 to 1200°C for 4h. X-ray diffraction (XRD) results show the formation of various phases with increase in annealing temperature. The crystallinity and crystallite size are found to increase with increase in heat treatment temperature (15-40nm). The superparamagnetic behavior of strontium hexaferrite is confirmed by vibrating sample magnetometer (VSM) wherein it was noticed that magnetic field (10000 gauss max) did not have any effect on these materials. The transformation of magnetic properties i.e. from superparamagnetic to ferromagnetic behaviour after heating at various HT temperatures have been revealed by hysteresis loops under VSM study. The increase in saturation magnetization from 2.44 to 75.03 emu/gm is observed. Formation of ultrafine particles has been confirmed through field emission scanning electron microscope (FESEM). About 5 to10% of the needle like crystals in the ‘as synthesized’ condition were transformed to hexagonal pyramidal structure and most of the crystals are found to have plate like hexagonal structures with increase in heat treatment temperatures. The effect of such systematic morphological transformation of nanocrystals was observed in reflection loss properties in X band (8-12 GHz). The maximum reflection loss of -20.05, -24.31, -24.16, -25.22, -25.12, -24.01 dB at 8.1, 8.6, 9.2, 9.6, 10.7, and 12 GHz respectively are observed for the material heat treated at 1200°C. A significant increment from - 6.5 to -25.22 dB at 9.6 GHz in reflection loss (RL) is noticed due to symmetric morphological growth of RAM nanocrystal during annealing.

Abstract: Silver nanoparticles are of interest due to their unique physicochemical and antimicrobial properties. The nanoparticles were produced by chemical reduction using short chain polyethylene glycol (PEG) as reducing agent, solvent and stabilizer in absence of other chemicals. Silver nanoparticles were separated from colloidal dispersion by ultra centrifuge at 14000 rpm. The reduction of silver ion (Ag+) to silver nanoparticles (Agº) was monitored by pH measurement and UV-visible spectroscopy of colloidal dispersion at fixed intervals. Silver nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and diphenyl-picrylhydrazyl (DPPH) radical scavenging method. Antimicrobial activity of silver nanoparticles was investigated against Escherichia coli, Staphylococcus aureus and Vibrio parahaemolyticus by agar plate test. Results indicated 51.5% conversion efficiency of silver ions to silver nanoparticles. Colloidal dispersion containing 4.12 mg/ml silver nanoparticles showed uniform size of 5.5 ± 1.1 nm with a typical visible spectra band at 447 nm. Silver nanoparticles showed significant (p < 0.05) antimicrobial efficiency and with concentration of 100 ppm resulted in 46.22%, 66.51% and 69.06% inhibition against S. aureus, E. coli and V. parahaemolyticus, respectively. The nanoparticles were also found to reduce DPPH free radical up to 88.9%. Results of this study proved that the silver nanoparticles produced by polyethylene glycol possess antimicrobial and antioxidant activity.

Abstract: The main goal of the work presented in this paper is to develop and characterize a manufacturing process that introduces a novel technology for manufacturing magnetic polyvinylchloride (PVC) nanocomposites, from stacked PVC foils, with intermediate sandwiched layers of uniformly dispersed ferro magnetic nanoparticles, by means of solid-state surface ultrasonic welding. Laboratory analysis of nanocomposite samples to investigate their behavior, is performed by microscopic, magnetic, and mechanical testing. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are employed for measuring nanoparticle dispersions and their distribution in the polymer matrix. The magnetic properties of the composites are measured by a physical property measurement system (PPMS), while mechanical behavior is studied by dynamic mechanical analyzer (DMA) and a universal mechanical testing system. The resulting materials are nanocomposite foils with very high ferromagnetic behavior.

Abstract: Starting from a three-dimensional transport model in the Landauer-Buttiker formalism we derive a scale-invariant expression for the drain current in a nano-transistor. Apart from dimensionless external parameters representing temperature, gate-, and drain voltage the normalized drain current depends on two dimensionless transistor parameters which are the characteristic length l and -width w of the electron channel. The latter quantities are the physical length and -width of the channel in units of the scaling length  = ~(2mF )􀀀1=2. Here F is the Fermi energy in the source contact and m is the eective mass in the electron channel. In the limit of wide transistors and low temperatures we evaluate the scale-invariant ID􀀀VD characteristics as a function of the characteristic length. In the strong barrier regime, i. e. for l & 20 long-channel behavior is found. At weaker barriers source-drain tunneling leads to increasingly signicant deviations from the long-channel behavior. We compare with experimental results.

Abstract: Copper is one of the most important metals in modern electronic technology. Keeping in view its role in nanoelectronics, we have fabricated copper nanowires of diameters 100 and 200nm using Anodic Alumina and polymer membranes as templates. Electrodeposition technique based on the principle of electroplating was adopted for copper nanowire fabrication in an electrochemical cell designed in our laboratory. SEM micrographs are used to calculate the aspect ratio of nanowires. The morphology of nanowires shows some interesting features.

Abstract: Cadmium oxide (CdO) quantum dots were synthesized in the laboratory by quenching method using CdO powder sintered at 9000C and ethyl alcohol kept at ice cold temperature. X-ray diffraction investigations reveal the NaCl cubic structure of CdO quantum dots. Addition of ethylenediamine to a portion of reaction mixture containing quantum dots results in the conversion of nanoparticles to nanorods. Heavy ion irradiation using 90 MeV Carbon (C+6) ion beam accelerated at 15 UD Pelletron, with fluence varying from 1011 to 1013 ions/cm2 , produced enlargement in the size of quantum dots revealed by TEM investigations. Heavy ion irradiation effects need to be investigated further, in view of industrial applications of quantum dots.

Abstract: Three types of nanolayered Pd-based metal/p-4H SiC systems, Au/Pd, Au/Pd/Al and Au/Pd/Ti/Pd have been investigated and compared to Pd monolayered metallization regarding the electrical and thermal properties. The lowest contact resistivity of 2.8x10-5 .cm2 has been achieved with the Au/Pd/Ti/Pd contact. This contact exhibits excellent thermal stability during long-term heating at temperature of 700oC and at operating temperatures up to 450oC. The surface morphology investigation has shown that despite the observed decrease, the palladium agglomeration has been not avoided completely in the same contact. The dominated surface roughness was measured to be 75 nm. However, the formation of dendrites in certain places leads to increase the surface roughness to 125 nm. The structural analysis revealed that palladium silicides are formed at the interface metal/p-4H SiC which affects on decrease of the barrier height in more than two times and conversion of the contact from Schottky into ohmic.

Abstract: The electron and hole energy states and oscillator strengths for interband transitions of two interacting Quantum dots (QDs) are theoretically studied. We explore how the properties of the system depend on the distance between them. Calculations are done for InAs QDs which are embedded in GaAs. The QDs have cylindrical form and are situated one on top of the other in such way that their symmetry axes coincide. The calculations are done in the envelope function approximation using position dependent effective masses. Finite Element Method (FEM) is utilized to find energy spectra, wavefunctions and oscillator strengths. We find that the hole states show less tunneling compared to the electron states, transitions in general show some anisotropy which decreases as the distance between the dots decrease and that the total oscillator strength for each particular transition is constant.