-
ACS Nano 07/2012; · 10.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the growth of ultrathin diamond nanorods (DNRs) by a microwave plasma assisted chemical vapor deposition method using a mixture gas of nitrogen and methane. DNRs have a diameter as thin as 2.1 nm, which is not only smaller than reported one-dimensional diamond nanostructures (4-300 nm) but also smaller than the theoretical value for energetically stable DNRs. The ultrathin DNR is encapsulated in tapered carbon nanotubes (CNTs) with an orientation relation of (111)diamond//(0002)graphite. Together with diamond nanoclusters and multilayer graphene nanowires/nano-onions, DNRs are self-assembled into isolated electron-emitting spherules and exhibit a low-threshold, high current-density (flat panel display threshold: 10 mA/cm2 at 2.9 V/microm) field emission performance, better than that of all other conventional (Mo and Si tips, etc.) and popular nanostructural (ZnO nanostructure and nanodiamond, etc.) field emitters except for oriented CNTs. The forming mechanism of DNRs is suggested based on a heterogeneous self-catalytic vapor-solid process. This novel DNRs-based integrated nanostructure has not only a theoretical significance but also has a potential for use as low-power cold cathodes.
ACS Nano 05/2009; 3(4):1032-8. · 10.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Enhanced electron field emission (EFE) behavior was observed in ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films upon irradiation with 100 MeV Ag <sup>9+</sup> -ions in a fluence of 5×10<sup>11</sup> ions / cm <sup>2</sup> . Transmission electron microscopy indicated that while the overall crystallinity of these films remained essentially unaffected, the local microstructure of the materials was tremendously altered due to heavy ion irradiation, which implied that the melting and recrystallization process have occurred along the trajectory of the heavy ions. Such a process induced the formation of interconnected nanocluster networks, facilitating the electron conduction and enhancing the EFE properties for the materials. The enhancement in the EFE is more prominent for MCD films than that for UNCD films, reaching a low turn-on field of E<sub>0</sub>=3.2 V /μ m and large EFE current density of J<sub>e</sub>=3.04 mA / cm <sup>2</sup> for 5×10<sup>11</sup> ions / cm <sup>2</sup> heavy ion irradiated samples.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nanocrystalline diamond films prepared by microwave plasma enhanced chemical vapor deposition (MPECVD) were implanted using 110 keV nitrogen ions under fluence ranging from 10(13)-10(14) ions/cm2. Scanning Electron Microscopy (SEM) and Raman spectroscopy were used to analyze the changes in the surface of the films before and after ion implantation. Results show that with nitrogen ion implantation in nanocrystalline diamond film cause to decrease in diamond crystallinity. The field emission measurement shows a sharp increase in current density with increase in dose. The ion implantation also alters the turn on field. It is observed that the structural damage caused by ion implantation plays a significant role in emission behaviour of nanocrystalline diamonds.
Journal of Nanoscience and Nanotechnology 09/2008; 8(8):4141-5. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Different forms of diamond have been shown to have qualities as field emission sources. As a consequence, much effort has been focused on both the synthesis of diamond nanostructures to increase the field enhancement factor and understanding the emission mechanism in these nominally insulating materials. In our recent study, we have grown ultrananocrystalline diamond (UNCD) coated nanocrystalline diamond (NCD) tips on NCD films for field emitters. The films were characterized using field emission scanning electron microscopy and Raman spectroscopy to identify the quality of the films. The fabricated different sizes of pyramid tips and their field emission properties are reported. It has been observed that with increase in tip size, the turn on voltage also increases.
Journal of Nanoscience and Nanotechnology 09/2008; 8(8):4198-201. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Different forms of diamond have been shown to have qualities as field emission sources. As a consequence, much effort has been focused on both the synthesis of diamond nanostructures to increase the field enhancement factor and understanding the emission mechanism in these nominally insulating materials. In our recent study, we have grown ultrananocrystalline diamond (UNCD) coated nanocrystalline diamond (NCD) tips on NCD films for field emitters. The films were characterized using field emission scanning electron microscopy and Raman spectroscopy to identify the quality of the films. The fabricated different sizes of pyramid tips and their field emission properties are reported. It has been observed that with increase in tip size, the turn on voltage also increases.
Journal of Nanoscience and Nanotechnology 07/2008; 8(8):4198-4201. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Diamond windows prepared using hot filament chemical vapor deposition (CVD) were irradiated with Au and Ag ions of energy 100 and 130 MeV, respectively with fluence in the range 10 10 to 3 Â 10 13 ions/cm 2 . Scanning electron microscopy (SEM) images showed substantial damage at the surface of the windows irradiated with Au + of energy 100 MeV and fluence of 3 Â 10 13 ions/cm 2 . At some locations on the diamond windows deposited at 16 kPa, the surface layer appeared to have melted and flowed like a liquid exposing small crystallites underneath. Raman spectra of windows after irradiation showed i) a decrease in the intensity of the one-phonon line at 1332 cm À 1 along with an increase in its half width; ii) substantial reduction in the intensity of the graphite G band; and, iii) the appearance of a new band at 667 cm À 1 . The band at 667 cm À 1 did not have a corresponding Stokes line and was therefore identified as a photoluminescence (PL) band. The ion induced damage and localized melting of CVD diamond windows are discussed in terms of the thermal spike model. D 2005 Elsevier B.V. All rights reserved.
Thin Solid Films 02/2006; 503:121. · 1.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Self-supported diamond sheets of the thickness ranging from 15 to 30 μm were prepared using hot filament chemical vapor deposition technique. The controlled variation of the deposition parameters resulted in the sheets with varying amount of nondiamond impurities. Routine characterization of the sheets was carried out using scanning electron microscopy, x-ray diffractometry, Raman spectroscopy, Fourier transform infrared spectroscopy, and Positron annihilation spectroscopy techniques. Detailed measurements of room temperature electrical conductivity (σ300), current–voltage (I–V) characteristics, and annealing studies on the sheets deposited with various structural disorder have yielded useful information about the electrical conduction in this interesting material. σ300 and I–V characteristic measurements were done in sandwiched configuration taking care off the surface effects. The diamond sheets deposited at low deposition pressure (Pd<60 Torr) contain negligible nondiamond impurities and show σ300≅10−6–10−7 S.cm−1. The I–V characteristics in these sheets show space charge limited conduction behavior with I∝Vn and n>1, in high voltage range. In contrast the sheets deposited at higher pressure (60 Torr and higher), containing high concentration of nondiamond impurities, show a sharp reduction in the values of σ300. Interestingly, the conduction in these sheets is ohmic with n values nearly equal to unity. Similarly the sheets deposited with nitrogen also show a sharp reduction in σ300. Annealing of all types of diamond sheets results in a decrease in σ300 values by several orders of magnitude. In the sheets deposited at low Pd, the n values increase sharply with annealing. On the other hand the values of n in the sheets deposited at higher pressure remain constant with annealing. The above results are explained in terms of hydrogen abstraction from the traps and compensation of donor–acceptor pairs. © 2001 American Institute of Physics.
Journal of Applied Physics. 07/2001; 90(3):1642-1649.
-
[show abstract]
[hide abstract]
ABSTRACT: Enhanced field emission is observed in nanocrystalline diamond (NCD) films upon irradiation with 100 MeV Ag9+ ions in the range of fluences from 5 × 1010 to 5 × 1011 ions/cm2. Field emission characteristics monotonically changes with the ion beam fluence, but does not show any correlation with sp2 cluster size induced. Enhancement of field emission is presumed to result from the formation of interconnected sp2 cluster network. The turn-on field (E0) for inducing the electron field emission (EFE) has been lowered from 28 to 3.2 V/μm, whereas the EFE current density has been increased from 1.4 × 10− 6 to 2.086 mA/cm2. Such EFE properties are comparable with those of carbon nanotubes.
Diamond and Related Materials. 18:164-168.
-
Pawan K. Tyagi,
M.K. Singh,
Abha Misra, Umesh Palnitkar,
D.S. Misra,
E. Titus,
N. Ali,
G. Cabral,
J. Gracio,
M. Roy,
S.K. Kulshreshtha
[show abstract]
[hide abstract]
ABSTRACT: Carbon nanotubes (CNTs) filled with ferromagnetic materials have the potentials for use in magnetic scanning probe microscopy and as an assembly of aligned high density magnetic nanocores for future magnetic data storage devices. Highly ordered and uniform Ni-filled CNTs were deposited by chemical vapour deposition. As-grown Ni-filled CNTs were characterized using transmission electron microscopy, Raman spectroscopy and nano-area diffraction. The magnetic properties of Ni-filled CNTs were investigated using superconducting quantum interference device analysis. Magnetisation characterization, performed at temperature 2 K with magnetic field up to 2 T, showed better ferromagnetism compared to the bulk Ni.
Thin Solid Films.
-
[show abstract]
[hide abstract]
ABSTRACT: Multiwalled carbon nanotubes are grown by microwave plasma chemical vapor deposition with CH4 and H2 as precursor gases. Ni and Ni/Pt electroplated layers are used as catalysts for the synthesis of the tubes. We observe that a very efficient filling of the tubes takes place with Ni. In some cases Ni/Pt filling is also observed inside the tubes. High-resolution transmission electron microscopy (HRTEM) studies, coupled with energy-dispersive X-ray analyses of the tubes, indicate Ni nanorods with a highly symmetrical cylindrical structure. The diameter of the cylindrical nanorods is on the order of 40 nm, and their length is 660 nm. The nano area diffraction pattern of the nanorods reveals the cubic structure of nickel, and electron diffraction spots corresponding to (111), (200), (220) planes are evident. The lattice constant of Ni measured from the diffraction spots was found to be 0.347 +/- 0.0013 nm. This should be compared with 0.352 nm, the value of "a" in bulk Ni. The decrease in the lattice constant may be due to the strain experienced inside the tubes. Raman spectroscopy shows the typical signature of the tangential breathing mode present in the tubes at 1580 cm-1 that shifts to a new position when the C12 is replaced by 13C. The shift, however, is too small and is difficult to explain on the basis of mass difference. HRTEM experiments indicate the presence of Ni3C in the samples dominantly in the interfacial region.
Journal of Nanoscience and Nanotechnology 3(1-2):165-70. · 1.56 Impact Factor
