Mechanism of Efficient Field Emission from Carbon Nanotubes

1999 ◽  
Vol 558 ◽  
Author(s):  
W. Zhu ◽  
C. Bower ◽  
O. Zhou ◽  
G. P. Kochanski ◽  
S. Jin
Keyword(s):  
Carbon Nanotubes ◽  
Electric Fields ◽  
Emission Characteristics ◽  
Emission Pattern ◽  
Cold Cathodes ◽  
Microelectronic Devices ◽  
Large Current ◽  
Large Current Density ◽  
Vacuum Microelectronic ◽  
Current Densities

ABSTRACTWe report observation of electron emission from individual carbon nanotubes. Two classes of emitters are observed, one emitting electrons with momentum nearly parallel to the nanotube axis, the other emitting electrons with nonzero momentum perpendicular to the tube axis. The emission pattern reflects the electronic structure of a particular tube and allows us to distinguish between structurally different nanotubes. These nanotube emitters exhibit excellent macroscopic emission properties; they can operate at a very large current density, as high as 4 A/cm2. At electric fields as low as 4-7 V/μm, they emit technologically useful current densities, e.g. 10 mA/cm2. The emission characteristics and durability of the carbon nanotube cold cathodes offer promising applications for vacuum microelectronic devices.

scholarly journals Engineering active sites on hierarchical transition bimetal oxides/sulfides heterostructure array enabling robust overall water splitting

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Panlong Zhai ◽  
Yanxue Zhang ◽  
Yunzhen Wu ◽  
Junfeng Gao ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Water Splitting ◽  
Active Sites ◽  
Rational Design ◽  
Large Scale ◽  
Grand Challenge ◽  
Long Term Stability ◽  
Large Current ◽  
Electrode Cell ◽  
Large Current Density ◽  
Current Densities

Abstract Rational design of the catalysts is impressive for sustainable energy conversion. However, there is a grand challenge to engineer active sites at the interface. Herein, hierarchical transition bimetal oxides/sulfides heterostructure arrays interacting two-dimensional MoOx/MoS2 nanosheets attached to one-dimensional NiOx/Ni3S2 nanorods were fabricated by oxidation/hydrogenation-induced surface reconfiguration strategy. The NiMoOx/NiMoS heterostructure array exhibits the overpotentials of 38 mV for hydrogen evolution and 186 mV for oxygen evolution at 10 mA cm−2, even surviving at a large current density of 500 mA cm−2 with long-term stability. Due to optimized adsorption energies and accelerated water splitting kinetics by theory calculations, the assembled two-electrode cell delivers the industrially relevant current densities of 500 and 1000 mA cm−2 at record low cell voltages of 1.60 and 1.66 V with excellent durability. This research provides a promising avenue to enhance the electrocatalytic performance of the catalysts by engineering interfacial active sites toward large-scale water splitting.

Metal-ionic-conductor potassium ferrite nanocrystals with intrinsic superhydrophilic surfaces for electrocatalytic water splitting at ultrahigh current densities

2021 ◽  
Vol 9 (12) ◽  
pp. 7586-7593
Author(s):  
Juan Jian ◽  
Wei Chen ◽  
Decheng Zeng ◽  
Limin Chang ◽  
Ran Zhang ◽  
...  
Keyword(s):  
Water Splitting ◽  
Current Density ◽  
Nickel Foam ◽  
Ionic Conductor ◽  
Large Current ◽  
Binder Free ◽  
Large Current Density ◽  
Current Densities ◽  
Superhydrophilic Surfaces

Metal-ionic-conductor K2Fe4O7 (KFO) with instinct superhydrophilic properties was hydrothermally grown on nickel foam (NF), the formed binder-free nano-KFO/NF can deliver extremely large current density for water splitting.

Industrially promising NiCoP nanorod arrays tailored with trace W and Mo atoms for boosting large-current-density overall water splitting

Nanoscale ◽  
2021 ◽  
Author(s):  
Xin Guo ◽  
Menggang Li ◽  
Lin He ◽  
Shuo Geng ◽  
Fenyang Tian ◽  
...  
Keyword(s):  
Water Splitting ◽  
Current Density ◽  
Nanorod Arrays ◽  
Overall Water Splitting ◽  
Large Current ◽  
Large Current Density ◽  
High Overpotentials ◽  
Current Densities

Nanoarray catalysts supported on the substrates provide an opportunity for industrially promising overall water splitting at large-current-densities. However, most of the present electrocatalysts show high overpotentials at a large current...

Electron Transport and Anode Heating Due to Field Emission From Carbon Nanotubes

2002 ◽  
Author(s):  
D. G. Walker ◽  
T. S. Fisher
Keyword(s):  
Carbon Nanotubes ◽  
Field Emission ◽  
Anode Surface ◽  
Electron Trajectory ◽  
Coulomb Interactions ◽  
Turn On ◽  
Large Current ◽  
Ring Diameter ◽  
Current Densities ◽  
Vacuum Gap

Carbon nanotubes (CNT) are being considered for field emission applications because of their low turn-on voltage and ability to support large current densities. The localization of emission and large currents from CNTs result in significant anode heating. The present work investigates the electron energy distribution at the anode surface through simulation of the field emission process and the trajectory of electrons across the vacuum gap. Field emission is modeled by Fowler-Nordheim-like expressions where the emission site is assumed to be a ring with the diameter of a nanotube. The electron trajectory is determined through a Monte Carlo simulation including Coulomb interactions between electrons. Results indicate that the electron beam spreads due to Coulomb interaction, but that the initial ring is preserved. In fact, the ring diameter at the anode spreads to 3μ per 10μ of vacuum gap in a field of 10 Vμm. This estimate matches well with reported observations. Further, the spreading becomes more significant with increased fields due to the higher current density of field emitted electrons.

Carbon Nanotubes as Potential Cold Cathodes for Vacuum Microelectronic Applications

2006 ◽  
Vol 963 ◽  
Author(s):  
Sanju Gupta
Keyword(s):  
Carbon Nanotubes ◽  
Physical Properties ◽  
Field Emission ◽  
Electron Emission ◽  
Cold Cathodes ◽  
Electron Field ◽  
Length Changes ◽  
Vacuum Microelectronic ◽  
Insight Into ◽  
Nanotube Films

ABSTRACTMaterials science is playing a dramatic role in discovering new materials with tailored physical properties. Cold cathodes/field emitters are one of the examples. Electron field emitting materials are of vital importance for a variety of vacuum microelectronic devices including field emission displays for flat panel displays, electron microscopes, X-ray generators, and vacuum lamps. This is the driving force to investigate the advanced nanostructured carbons as cold cathodes as one of the potential candidates. Recently, they are also being proposed for thermionic power generators. The rationale is that reducing one or more dimensions of a system below some critical length changes the systems' physical properties, where carbon nanotubes (CNTs) in the class of carbon nanostructures serve as a model example. In this paper, synthesis and characterization of vertically aligned multiwall and single-/double-wall carbon nanotube films using a microwave plasma-assisted chemical vapor deposition technique for vacuum microelectronics is presented. Recent advances in their synthesis, processing, and characterization indicate that the above mentioned potential is slowly being realized. Experiments showed that by continuous reduction in the thickness of the catalyst film produces hollow concentric tubes in contrast to bamboo-like multiwalled tubes with larger thickness. To assess the electron field emission properties, besides the traditional field emission (I-V) properties, temperature dependent field electron emission microscopy (T-FEEM) enabling real-time imaging of electron emission providing information on emission site density, temporal variation of the emission intensity, and insight into the role of adsorbates from nanotube films will be discussed. Physics based models (such as negative or low electron affinity, geometric enhancement, surface dipole, tunneling due to adsorbates, structure modification due to doping etc.) will be described to support the experimental observations in addition to weak thermionic field emission contribution. These findings provided a great insight into the field emission mechanism and a contrasting comparison between small and large diameter carbon nanotubes.

scholarly journals Blinding in electric current stimulation in subacute neglect patients with current densities of 0.8 A/m2: a cross-over pilot study

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Anna Gorsler ◽  
Ulrike Grittner ◽  
Nadine Külzow ◽  
Torsten Rackoll
Keyword(s):  
Pilot Study ◽  
Electric Fields ◽  
Standard Care ◽  
Small Sample Size ◽  
Small Sample ◽  
Related Factors ◽  
Attentional Deficits ◽  
Age Related ◽  
Current Densities ◽  
Improve Standard

Abstract Objective Neglect after stroke is a disabling disorder and its rehabilitation is a major challenge. Transcranial direct current stimulation (tDCS) seems to be a promising adjuvant technique to improve standard care neglect therapy. Since electric fields are influenced by age-related factors, higher current densities are probably needed for effective treatment in aged stroke patients. Validation of treatment efficacy requires sham-controlled experiments, but increased current densities might comprise blinding. Therefore, a pilot study was conducted to test sham adequacy when using current density of 0.8 A/m2. Whether especially neglect patients who mainly suffer from perceptual and attentional deficits are able to differentiate beyond chance active from sham tDCS was investigated in a randomized cross-over design (active/sham stimulation) in 12 early subacute patients with left-sided hemineglect. Stimulation (0.8 A/m2) was performed simultaneous to standard care neglect therapy. Results Odds ratio of correct guessing an atDCS condition compared to wrongly judge an atDCS condition as sham was 10.00 (95%CI 0.65–154.40, p = 0.099). However, given the small sample size and high OR, although likely somewhat overestimated, results require careful interpretation and blinding success in neglect studies with current densities of 0.8 A/m2 should be further confirmed.

Industrially promising IrNi-FeNi3 hybrid nanosheets for overall water splitting catalysis at large current density

2021 ◽  
Vol 286 ◽  
pp. 119881
Author(s):  
Yamei Wang ◽  
Guangfu Qian ◽  
Qinglian Xu ◽  
Hao Zhang ◽  
Fang Shen ◽  
...  
Keyword(s):  
Water Splitting ◽  
Current Density ◽  
Overall Water Splitting ◽  
Large Current ◽  
Large Current Density
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