Thermionic Emission From Potassium-Intercalated Carbon Nanotube Arrays

2007 ◽  
Author(s):  
Tyler L. Westover ◽  
Glen Powell ◽  
Timothy S. Fisher
Keyword(s):  
Work Function ◽  
Electrical Power ◽  
Thermionic Emission ◽  
Nanotube Arrays ◽  
Energy Distributions ◽  
Emission Data ◽  
Carbon Nanotube Arrays ◽  
Experimental Apparatus ◽  
Work Functions ◽  
Efficient Power

Vacuum and solid-state thermionic emission have long been proposed as a means of converting heat or solar energy directly into electrical power. However, low work function materials must be developed before a reasonably efficient power generation device can be realized. In this work, thermionic emission energy distributions were measured for four samples including a single-crystal tungsten (100) sample, a pristine CNT mat, and two potassium-intercalated CNT mats. One of the potassium-intercalated CNT mats was composed largely of randomly oriented CNTs while the other CNT sample was grown in templated anodized alumina to align the growth pattern. Thermionic emission data obtained from the tungsten sample validated the experimental apparatus and method. The pristine CNT mat exhibited an emission distribution with a work function of 4.7 eV, while the potassium-intercalated samples exhibited work functions of approximately 3.1 and 3.4 eV for the randomly oriented and the templated meshes, respectively. The differences in the measured work function values for intercalated samples may be due to emitter tip differences. Both intercalated CNT samples showed some degradation after cooling from 510°C and reheating to the same temperature.

Thermionic Emission From Alkali Potassium-Intercalated Carbon Nanotube Arrays for Direct Energy Conversion

2007 ◽  
Author(s):  
Tyler L. Westover ◽  
Aalap Dighe ◽  
Placidus Amama ◽  
Nicholas Lilovich ◽  
Timothy S. Fisher
Keyword(s):  
Carbon Nanotube ◽  
Work Function ◽  
Electrical Power ◽  
Thermionic Emission ◽  
Energy Analyzer ◽  
Energy Distributions ◽  
Carbon Nanotube Arrays ◽  
Direct Energy ◽  
Cnt Arrays ◽  
Work Functions

Vacuum and solid-state thermionic electron emission are potentially efficient means for converting heat or solar energy directly into electrical power. However, low work function materials must be developed before reasonable efficiency can be realized with a power generation device based on thermionic emission. In this work, carbon nanotube (CNT) arrays have been doped with potassium atoms using a two-zone vapor method to lower their work functions to 2–4 eV. We have previously shown that carbon nanotube emitters prepared in this way are stable in atmospheric air although undesirable oxide compounds can form on the carbon nanotube surface. Using a hemispherical electron energy analyzer to obtain thermionic emission energy distributions, we show that low work function emitters can be prepared from potassium-intercalated CNT mats at temperatures as low as 400°C and that emitters prepared in this way can be stable at temperatures up to 620°C.

Photo- and Thermionic Emission From Potassium-Intercalated Single-Walled Carbon Nanotube Arrays

2008 ◽  
Author(s):  
Tyler L. Westover ◽  
Aaron D. Franklin ◽  
Timothy S. Fisher ◽  
Ronald G. Reifenberger
Keyword(s):  
Work Function ◽  
Elevated Temperatures ◽  
Electrical Power ◽  
Small Diameter ◽  
Thermionic Emission ◽  
Theoretical Models ◽  
Thermal Excitation ◽  
Single Walled Carbon Nanotube ◽  
Wide Range ◽  
Generation Capacity

Vacuum thermionic electron emission has been considered for many years as a means to convert heat or solar energy directly into electrical power. However, an emitter material has not yet been identified that has a sufficiently low work function and that is stable at the elevated temperatures required for thermionic emission. Recent theoretical models predict that photonic and thermal excitation can combine to significantly increase overall efficiency and power generation capacity beyond that which is possible with thermionic emission alone. Carbon nanotubes (CNTs) intercalated with potassium have demonstrated work functions as low as 2.0 eV, and low electron scattering rates observed in small diameter CNTs offer the possibility of efficient photoemission. This study uses a Nd:YAG laser to irradiate potassium-intercalated single-walled CNTs (K/SWCNTs), and the resultant energy distributions of photo- and thermionic emitted electrons are measured using a hemispherical electron energy analyzer for a wide range of temperatures. We observe that the work function of K/SWCNTs is temperature dependent and has a minimum of approximately 2.0 eV at approximately 600 K. At temperatures above 600 K, the measured work function K/SWCNTs increases with temperature, presumably due to deintercalation of potassium atoms.

Photo- and thermionic emission from potassium-intercalated carbon nanotube arrays

2010 ◽  
Vol 28 (2) ◽  
pp. 423-434 ◽  
Author(s):  
Tyler L. Westover ◽  
Aaron D. Franklin ◽  
Baratunde A. Cola ◽  
Timothy S. Fisher ◽  
Ronald G. Reifenberger
Keyword(s):  
Carbon Nanotube ◽  
Thermionic Emission ◽  
Nanotube Arrays ◽  
Carbon Nanotube Arrays

Efficient photo-thermionic emission from carbon nanotube arrays

Carbon ◽  
2016 ◽  
Vol 96 ◽  
pp. 641-646 ◽  
Author(s):  
Zhenjun Li ◽  
Bing Bai ◽  
Chi Li ◽  
Qing Dai
Keyword(s):  
Carbon Nanotube ◽  
Thermionic Emission ◽  
Nanotube Arrays ◽  
Carbon Nanotube Arrays

Hierarchical Nano- and Micro-engineered Interlaminar Reinforcement of Advanced Aerospace Grade Composites with Carbon Nanotube Arrays

2021 ◽  
Author(s):  
Jeonyoon Lee ◽  
Luiz H. Acauan ◽  
Estelle Kalfon-Cohen ◽  
Seth S. Kessler ◽  
Brian L. Wardle
Keyword(s):  
Carbon Nanotube ◽  
Nanotube Arrays ◽  
Carbon Nanotube Arrays

scholarly journals Substrate adhesion evolves non-monotonically with processing time in millimeter-scale aligned carbon nanotube arrays

Nanoscale ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 261-271
Author(s):  
Ashley L. Kaiser ◽  
Dale L. Lidston ◽  
Sophie C. Peterson ◽  
Luiz H. Acauan ◽  
Stephen A. Steiner ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Adhesion Strength ◽  
Processing Time ◽  
Effective Modulus ◽  
Work Of Adhesion ◽  
Process Time ◽  
Nanotube Arrays ◽  
Substrate Adhesion ◽  
Carbon Nanotube Arrays

Aligned carbon nanotube (CNT) array adhesion strength evolves with CNT process time, decreasing and then increasing during growth and annealing, as captured by models relating CNT diameter, array effective modulus, and CNT–substrate work of adhesion.

scholarly journals Optically Induced Field-Emission Source Based on Aligned Vertical Carbon Nanotube Arrays

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1810
Author(s):  
Mengjie Li ◽  
Qilong Wang ◽  
Ji Xu ◽  
Jian Zhang ◽  
Zhiyang Qi ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Electric Field ◽  
Field Emission ◽  
Field Enhancement ◽  
Absorption Efficiency ◽  
Photon Absorption ◽  
Nanotube Arrays ◽  
Carbon Nanotube Arrays ◽  
Induced Field ◽  
Optically Induced

Due to the high field enhancement factor and photon-absorption efficiency, carbon nanotubes (CNTs) have been widely used in optically induced field-emission as a cathode. Here, we report vertical carbon nanotube arrays (VCNTAs) that performed as high-density electron sources. A combination of high applied electric field and laser illumination made it possible to modulate the emission with laser pulses. When the bias electric field and laser power density increased, the emission process is sensitive to a power law of the laser intensity, which supports the emission mechanism of optically induced field emission followed by over-the-barrier emission. Furthermore, we determine a polarization dependence that exhibits a cosine behavior, which verifies the high possibility of optically induced field emission.

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