Electrically excited infrared emission from InN nanowire transistors

We report electrically excited infrared emission from a single InN nanowire transistor. We report on: (1) the generation of IR emission by impact excitation of carriers under a high electrical field, (2) the size of the fundamental band gap of InN NW by measuring its emission spectra, (3) the observation of interband and conduction-band to conduction-band hot-carrier emission, and the carrier relaxation rate, and finally, (4) we present evidence that suggests that the electron accumulation layer at the InN NW surface forms a surface plasmon that couples to and enhances radiative electron-hole pair recombination.     

Phonon-assisted electron emission from individual carbon nanotubes

A question of how electrons can escape from one-atom-thick surfaces has seldom been studied and is still not properly answered. Herein, lateral electron emission from a one-atom-thick surface is thoroughly studied for the first time. We study electron emission from side surface of individual electrically biased carbon nanotubes (CNTs) both experimentally and theoretically and discover a new electron emission mechanism named phonon-assisted electron emission. A kinetic model based on coupled Boltzmann equations of electrons and optical phonons is proposed and well describes experimentally measured lateral electron emission from CNTs. It is shown that the electrons moving along a biased CNT can overflow from the one-atom-thick surface due to the absorption of hot forward-scattering optical phonons. A low working voltage, high emission density, and side emission character make phonon-assisted electron emission primarily promising in electron source applications.     

Electrically driven gallium movement in carbon nanotubes

Electrically driven gallium movement in carbon nanotubes is discussed. A higher current (~15 mA) makes the gallium migrate sharply toward the anode, which increases its mass transport speed with time in the range of 0 to more than 10.345 fg s(-1). In contrast, a lower current (~2 mA) only drives gallium to contact the anode, which decreases the resistance of the nanocomposite sharply, from 2.564 kΩ to 0.4 Ω. These results are valuable for designing electrically driven nanomass delivery and nanoswitches, respectively.     

Role of many body shake-up in core-valence-valence electron emission from single wall carbon nanotubes

Auger core-valence-valence transitions from single wall Carbon nanotubes are studied using a tight-binding calculational scheme with nearest neighbor overlap, hopping interactions, and a double-zeta basis set. The resulting Hamiltonian approximates the unperturbed pi and sigma bands of the nanomaterials coupled with the free electron states outside the solid and the core-hole. As a first step, the Fermi's golden rule is applied to determine the so called one-electron spectrum of emitted electrons from different tubes, in which either the neutralizing or the ejected electrons, in the initial state, lie within nearest neighboring atomic sites to the core-hole. Many-body corrections are effectively modeled using a broadening function, which accounts for dynamic screening effects involving the initial and final states. Particular attention is paid to the asymmetric component of the broadening function, responsible for the shake-up of pi electrons. Finally, the Cini-Sawatzky distortion function is used to describe the final state effect of the hole-hole interaction. A quantitative estimation of the interplay of shake-up processes is proposed by adjusting the asymmetric parameters of the broadening function to reproduce measurements of Auger electrons ejected from bundles of single wall Carbon nanotubes.     

High-Current-Density field emission from self-heating printed carbon nanotubes

High-current-density field emitters are considered as the potential and necessary components for compact high definition x-ray sources and high-power cold cathode microwave amplifiers. In this report, high-current-density field emission from self-heating printed carbon nanotubes is introduced. Large emission current causes large heat that increases the temperature of the emitters. The temperature is estimated to be more than ~1600 K. Localized surface field and high temperature both drive more electrons escaping from the emitters, and the maximum current density is larger than ~2.7 A/cm² that will satisfy the need of most vacuum electron devices including x-ray sources and microwave electron devices.     

Enhanced electron emission from titanium coated multiwalled carbon nanotubes

Enhanced field emission properties and improved crystallinity of titanium (Ti) coated multiwalled carbon nanotubes (MWCNTs), prepared by microwave plasma enhanced chemical vapour deposition have been observed. Ti films of extremely low thicknesses (0.5 nm, 1.0 nm and 1.5 nm) were coated over carbon nanotubes (CNTs) and their field emission behaviour was investigated. The turn on field of Ti coated CNTs was found to be low (~ 0.8 V/μm) as compared to pristine CNTs (~ 1.8 V/μm). The field enhancement factor for Ti coated CNTs was quite large (~ 1.14 × 10⁴) as compared to pristine CNTs (~ 6 × 10³). This enhancement in electron emission is attributed to the passivation of defects and improved crystallinity of CNTs. Surface morphological and microstructural studies were carried out to investigate the growth of pristine and Ti coated CNTs. It was observed that Ti nanoclusters adsorb on the edges of MWCNTs and increase their crystallinity. This increase is directly correlated with the thickness of Ti film deposited. Micro Raman spectroscopy confirmed the improved crystallanity of Ti coated CNTs.     

Field emission from multi-walled carbon nanotubes with various fillers

Pastes for field emission test were prepared by 3-roll milling of multi-walled carbon nanotubes (MWNTs) and UV-sensitive binder solution. The effects of four filler additives, namely two types of indium tin oxide (ITO) powder, glass frit and Ag on the field emission properties of the screen-printed paste were investigated and compared to those without filler using a diode-type configuration. The paste formulation was shown to be adequate for fine patterning using a UV-lithography technique. MWNT pastes containing any type of filler showed better emission properties than the paste without filler, thereby confirming the importance of the filler. The MWNT paste with 1 wt.% glass frit showed the best results with the lowest turn-on field of 1.75 V/μm at 1 μA/cm², highest emission current density of 78 μA/cm² at 5 V/μm, and β-factor of 17,000 approximately, which are satisfactory for practical application.     

Field emission from carbon nanotubes in DC and pulsed mode

Multi-wall Carbon Nanotube (CNT) emitters were tested in a combined diode-RF electron gun. Field emission of the nanotubes was observed at 5-30 MV/m, using a 250 ns FWHM long pulse with a peak voltage of 80-470 kV. The field emission threshold is compatible with that found from previous DC testing. We have extracted from a continuous field emitter up to a nanoCoulomb of charge and measured an emittance of 4 mm mrad with a 2 pC electron beam. The total charge emission during RF operation, using the 1.5 GHz, 2 cell RF structure, was found dependent on its period. RF operation showed that back bombarding electrons with up to 5 MeV did not impair the emission stability of the CNTs.     

Enhancement of field emission property from hills-like carbon nanotubes film

Improved field emission property of carbon nanotubes (CNTs) is achieved by using NiTi alloy film as catalyst under optimized condition. The NiTi alloy films are prepared by magnetron co-sputtering process and the CNTs films are synthesized by thermal chemical vapor deposition. With the increase of the Ni/Ti ratio from 19 at.% to 95 at.%, the CNTs density increases from discrete cluster to dense network, and the optimized field emission property of CNTs film is found at the medium density. However, the field emission property is significantly enhanced when the Ni/Ti ratio is about 76 at.%, and it is supposed to attribute to the combined effect of the hills-like surface enhancement and the intrinsic emission properties of CNTs.     

Analysis of localized failure of single-wall carbon nanotubes

A method is developed to determine the conditions for the onset of localized failure of carbon nanotubes. Examples of failure modes include ductile necking under tension or localized crushing under compression. A nanoscale continuum theory for carbon nanotube is adapted. The onset of localized failure is identified by the singularity point of the acoustic tensor derived from continuum energy function based on Tersoff–Brenner potential. The analysis predicts 35–44% of breaking strains for tension and 18–25% compressive strain for plastic collapse. The results are in agreement with molecular dynamics simulations and experimental estimations reported in the literature.     

Screening of excitons in single, suspended carbon nanotubes

Resonant Raman spectroscopy of single carbon nanotubes suspended across trenches displays red-shifts of up to 30 meV of the electronic transition energies as a function of the surrounding dielectric environment. We develop a simple scaling relationship between the exciton binding energy and the external dielectric function and thus quantify the effect of screening. Our results imply that the underlying particle interaction energies change by hundreds of meV.     

Fluorescent volumetric display excited by a single infrared beam

A volumetric display technique that uses fluorescence excited by a single infrared beam is proposed. A convergent laser beam is used to activate ions locally around the focal point. Three-dimensional scanning by the focal point is achieved by moving an inclined image plane in the direction perpendicular to an optical axis. Preliminary experimental results of three-dimensional image generation in an Er(3+)-doped fluoride glass excited by a laser beam of 810 nm wavelength are presented.     

Study of the ability to field emission from diamond-like carbon layers and carbon nanotubes

The aim of this work was to study the relationship between parameters of the electron field emission and the film deposition method. In this study two methods were applied: classical radio frequency plasma-assisted chemical vapor deposition (RF PACVD) to produce diamond-like carbon (DLC) layers and chemical vapor deposition (CVD) to produce carbon nanotubes (CNT). DLC layers were grown on n-type silicon substrates and CNT were grown on n-type and p-type silicon substrates.Atomic force microscopy (AFM) and Raman spectroscopy were used to investigate the physical and chemical parameters of DLC films after deposition process. The electrical parameters of capacitors with the DLC layer as an insulator were extracted from the capacitance-voltage (C-V) and current-voltage (I-V) characteristics. Measurements of the field emission were performed after characterization of the layer properties.     

Highly selective sorting of semiconducting single wall carbon nanotubes exhibiting light emission at telecom wavelengths

Single wall carbon nanotubes (SWNTs) are known for their exceptional electronic properties.However,most of the synthesis methods lead to the production of a mixture of carbon nanotubes having different chiralities associated with metallic (m-SWNTs) and semiconducting (s-SWNTs) characteristics.For application purposes,effective methods for separating these species are highly desired.Here,we report a protocol for achieving a highly selective separation of s-SWNTs that exhibit a fundamental optical transition centered at 1,550 nm.We employ a polymer assisted sorting approach,and the influence of preparation methods on the optical and transport performances of the separated nanotubes is analyzed.As even traces of m-SWNTs can critically affect performances,we aim to produce samples that do not contain any detectable fraction of residual m-SWNTs.     

Enhancement of photoluminescence from ZnO film by single wall carbon nanotubes

Optical emissions from ZnO films were enhanced by a formation of hybrid structures with single wall carbon-nanotubes (SWCNTs). The SWCNTs were characterized by the presence of the associated fibers and islands together with many carbon nanotube structures and their average height was about < or = 40 nm from atomic force microscope and scanning electron microscope measurements. The intensities of photoluminescence on ZnO films with SWCNTs were increased up to about 30 and 60% in the region of 3.3 eV (near band edge) and 2.3 eV (deep-level) bands, respectively. It was considered that the enhancement of optical emissions from ZnO might be resulted from the effects of an excitation light scattering by SWCNTs and a surface plasmon resonance between bandgap of ZnO and SWCNTs. The surface plasmon resonance mode in the ultra-violet regions is smaller than the deep-level region relatively. This result showed that the commercial ZnO/carbon nanotubes have a feasibility of application to optoelectronic device.     

Molecular discriminators using single wall carbon nanotubes

The interaction between single wall carbon nanotubes (SWNTs) and amphiphilic molecules has been studied in a solid phase. SWNTs are allowed to interact with different amphiphilic probes (e.g.?lipids) in a narrow capillary interface. Contact between strong hydrophobic and amphiphilic interfaces leads to a molecular restructuring of the lipids at the interface. The geometry of the diffusion front and the rate and the extent of diffusion of the interface are dependent on the structure of the lipid at the interface. Lecithin having a linear tail showed greater mobility of the interface as compared to a branched tail lipid like dipalmitoyl phosphatidylcholine, indicating the hydrophobic interaction between single wall carbon nanotube core and the hydrophobic tail of the lipid. Solid phase interactions between SWNT and lipids can thus become a very simple but efficient means of discriminating amphiphilic molecules in general and lipids in particular.     

碳纳米管场发射阴极的制备及其场发射特性

采用电泳法将碳纳米管组装到电化学淀积的银台阵列上作为场发射阴极并研究了它的场发射特性.场发射特性测试结果表明:该阴极具有优异的场发射特性,开启电场为2.8V/μm,在应用电场为5.5V/μm时,发射电流密度达到1.7mA/cm2.具有优异的发射性能的原因可以归结到银台的边缘和银台类山状的表面增强了碳纳米管的场致电子发射.该阴极制备工艺简单、发射特性优异,且容易实现大面积制备,可以应用到大面积场发射显示器件中.