Enhancement in field emission current density of Ni nanoparticles embedded in thin silica matrix by swift heavy ion irradiation
TL;DR: In this paper, the field emission properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au+7 ions at various fluences are studied and a large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart.
Abstract: The field emission (FE) properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au+7 ions at various fluences are studied here. A large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart. The dependence of FE properties on irradiation fluence is correlated with surface roughness, density of states of valence band and size distribution of nanoparticles as examined with atomic force microscope, X-ray photoelectron spectroscopy, and grazing incidence small angle x-ray scattering. A current density as high as 0.48 mA/cm2 at an applied field 15 V/μm has been found for the first time for planar field emitters in the film irradiated with fluence of 5.0 × 1013 ions/cm2. This significant enhancement in the current density is attributed to an optimized size distribution along with highest surface roughness of the same. This new member of field emission family meets most of the requirements of cold cathodes for vacuum micro/nanoelectronic devices.
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TL;DR: In this paper, the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorod, quasi-aligned nanowires, and nanowire) was investigated.
Abstract: Highly ordered CdS nanostructure arrays were successfully fabricated via a simple two-step metal-organic chemical vapor deposition process. Both stimulated emission and field-emission measurements were carried out in an attempt to understand the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorods, quasi-aligned nanowires, and nanowires). The 1D CdS nanostructures of various types displayed notable differences in stimulated and field-emission performances. The stimulated emission strongly correlated with the structure alignment: the better the alignment, the lower the threshold. Both of the alignments and aspect ratios greatly affected the field-emission properties; the CdS emitters of higher aspect ratio and better alignment exhibited better field-emission performance. Thus the well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.
175 citations
TL;DR: In this paper, field emission studies of lanthanum hexaboride (LaB6) coated multiwalled carbon nanotube (MWCNT) films, pristine LaB6 films, and pristine MWCNT films are reported.
Abstract: Detailed results from field emission studies of lanthanum hexaboride (LaB6) coated multiwalled carbon nanotube (MWCNT) films, pristine LaB6 films, and pristine MWCNT films are reported. The films have been synthesized by a combination of chemical and physical deposition processes. An impressive increase in field enhancement factor and temporal stability as well as a reduction in turn-on field and threshold field are observed in LaB6-coated MWCNTs compared to pristine MWCNT and pristine LaB6 films. Surface morphology of the films has been examined by scanning electron microscopy. Introduction of LaB6 nanoparticles on the outer walls of CNTs LaB6-coated MWCNTs films is confirmed by transmission electron microscopy. The presence of LaB6 was confirmed by X-ray photoelectron spectroscopy results and further validated by the Raman spectra. Raman spectroscopy also shows 67% increase in defect concentration in MWCNTs upon coating with LaB6 and an upshift in the 2D band that could be attributed to p-type doping. Ultraviolet photoelectron spectroscopy studies reveal a reduction in the work function of LaB6-coated MWCNT with respect to its pristine counterpart. The enhanced field emission properties in LaB6-coated MWCNT films are correlated with a change in microstructure and work function.
24 citations
TL;DR: It is concluded from theoretical analysis that change in fluence alters the co-ordination chemistry followed by the charge distribution and spin alignment, which influence the VB DOS and concurrent FE as evident from the authors' experiment.
Abstract: This work is driven by the vision of engineering planar field emitters with ferromagnetic metal-insulator nanocomposite thin films, using swift heavy ion (SHI) irradiation method. FeCo nanoparticles inside SiO2 matrix, when subjected to SHI get elongated. Using this, we demonstrate here a planar field emitter with maximum current density of 550 μA/cm(2) at an applied field of 15 V/μm. The film, irradiated with 5 × 10(13) ions/cm(2) fluence (5e13) of 120 MeV Au(9+) ions, shows very high electron emitting quantum efficiency in comparison to its unirradiated counterpart. Surface enhanced Raman spectroscopy analysis of unirradiated and 5e13 films further confirms that the field emission (FE) enhancement is not only due to surface protrusions but also depends on the properties of entire matrix. We find experimental evidence of enhanced valence band density of states (VB DOS) for 5e13 film from XPS, which is verified in the electronic structure of a model FeCo cluster from first-principles based calculations combining density functional theory (DFT) and molecular dynamics (MD) simulations. The MD temperature is selected from the lattice temperature profile inside nanoparticles as deduced from thermal spike model. Increasing the irradiation fluence beyond 5e13, results in reduced VB DOS and melting of surface protrusions, thus causing reduction of FE current density. We finally conclude from theoretical analysis that change in fluence alters the co-ordination chemistry followed by the charge distribution and spin alignment, which influence the VB DOS and concurrent FE as evident from our experiment.
11 citations
TL;DR: In this article, the formation of nanoscale voids in amorphous-germanium (a-Ge), and their size and shape evolution under ultra-fast thermal spikes within an ion track of a swift heavy ion, is meticulously expatiated using experimental and theoretical approaches.
Abstract: The formation of nanoscale voids in amorphous-germanium (a-Ge), and their size and shape evolution under ultra-fast thermal spikes within an ion track of swift heavy ion, is meticulously expatiated using experimental and theoretical approaches. Two step energetic ion irradiation processes were used to fabricate novel and distinct embedded nanovoids within bulk Ge. The 'bow-tie' shape of voids formed in a single ion track tends to attain a spherical shape as the ion tracks overlap at a fluence of about 1 × 1012 ions cm−2. The void assumes a prolate spheroid shape with major axis along the ion trajectory at sufficiently high ion fluences. Small angle x-ray scattering can provide complementary information about the primary stage of void formation hence this technique is applied for monitoring simultaneously their formation and growth dynamics. The results are supported by the investigation of cross-sectional transmission and scanning electron micrographs. The multi-time-scale theoretical approach corroborates the experimental findings and relates the bow-tie shape void formation to density variations as a result of melting and resolidification of Ge within the region of thermal spike generated along an ion track, plus non-isotropic stresses generated towards the end of the thermal spike.
9 citations
TL;DR: In this paper, the role of the electronic spin of individual atoms in controlling particle shape is investigated, and the lattice temperature profiles derived from thermal spike model is carried out to understand the structural distortion at higher temperatures.
8 citations
Cites background from "Enhancement in field emission curre..."
...From our photo emission data (not shown) we found that upon irradiation the surface of the NPs gets partially oxidized [7]....
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...[7]) can be replicated only in Ni38 cluster where a closed-shell structure is formed....
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...The formation of equally separated large arrays of nano-crystals inside a matrix [3], change in crystallographic phases [4], alterations in easy axis of magnetization [5], tuning plasmonic properties [6], enhanced field emission [7,8] are a...
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TL;DR: In this article, the main features of the extraction of electrons from cold metals by intense electric fields are well known, and an approximate theory of the effect was first developed by Schottky.
Abstract: 1. Introduction .—The main features of the phenomenon of the extraction of electrons from cold metals by intense electric fields are well known, and an approximate theory of the effect was first developed by Schottky. More recently the experimental data have been much improved, notably by Millikan and Eyring, and Millikan and Lauritsen. The theory has been considered afresh by O. W. Richardson and by Houston working with Sommerfeld. It seems to us, however, that there is still room for improvement in the theoretical exposition and its correlation with the experiments. Neither O. W. Richardson nor Houston really treat the theory in the simple straightforward way which is now possible in the new mechanics, using the revived electron theory of metals which we owe to Sommerfeld. Again, while Millikan and Lauritsen seem to have established quite definitely the laws of dependence of the emission on the field strength F, they speak of the implications of their result in a way which is hard to justify and might in certain circumstances prove to be definitely misleading. Millikan and Lauritsen show that a plot of log I, where I is the current, against 1/F yields a good straight line whenever the experimental conditions are sufficiently stable. At ordinary temperatures these currents are completely independent of the temperature. The formula for these current is I = C e ─a /F, (1) Which is, of course, indistinguishable from I = CF2 e ─a /F. (2) Millikan and his associates have also shown that as the higher temperatures, at which ordinary thermionic emission begins, are approached, the strong field emission does become sensitive to temperature and finally blends into the thermionic.
5,151 citations
TL;DR: In this paper, a scheme for fitting the Ni 2p spectra using multiplet envelopes is proposed, based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd 9 L and the unscreened cd 8 final state configurations, respectively.
1,589 citations
TL;DR: Field emission of electrons from individually mounted carbon nanotubes has been found to be dramatically enhanced when the nanotube tips are opened by laser evaporation or oxidative etching, in a process that resembles unraveling the sleeve of a sweater.
Abstract: Field emission of electrons from individually mounted carbon nanotubes has been found to be dramatically enhanced when the nanotube tips are opened by laser evaporation or oxidative etching. Emission currents of 0.1 to 1 microampere were readily obtained at room temperature with bias voltages of less than 80 volts. The emitting structures are concluded to be linear chains of carbon atoms, Cn, (n = 10 to 100), pulled out from the open edges of the graphene wall layers of the nanotube by the force of the electric field, in a process that resembles unraveling the sleeve of a sweater.
1,538 citations
TL;DR: The large-scale preparation of FeCo nanoparticles boosts the potential of magnetic nanoparticles for data storage and medicinal imaging applications.
Abstract: Magnetic nanoparticles are useful for a wide range of applications from data storage to medicinal imaging The large-scale preparation of FeCo nanoparticles boosts this potential
474 citations
TL;DR: In this article, a Fortran program, IsGISAXS, is described for the simulation and analysis of grazing-incidence small-angle X-ray scattering of islands supported on a substrate.
Abstract: This paper describes a Fortran program, IsGISAXS, for the simulation and analysis of grazing-incidence small-angle X-ray scattering (GISAXS) of islands supported on a substrate. As is usual in small-angle scattering of particles, the scattering cross section is expressed in terms of an island form factor and interference function. However, the emphasis is placed on the specificity of the grazing-incidence geometry, in particular in the evaluation of the island form factor in the distorted-wave Born approximation. A library of simple geometrical shapes is available. A full account of size and possible shape distributions is given in the decoupling approximation, where sizes and positions are not correlated, and in the local monodisperse approximation. Two types of island repartitions on the substrate are considered: disordered systems characterized by their particle–particle pair correlation functions, and bidimensional crystalline or paracrystalline systems of particles.
434 citations