Limits...
A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron

View Article: PubMed Central - PubMed

ABSTRACT

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

No MeSH data available.


Cross-sectional SEM and TEM micrographs of the CNT cold-cathode showing the overview of the interfacial structure, where (a) SEM image and (b) high magnitude image of an initially-grown CNT directly connects with the substrate, (c) TEM image and (d) HRTEM image of one CNT grows from the stainless steel.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5017026&req=5

f5: Cross-sectional SEM and TEM micrographs of the CNT cold-cathode showing the overview of the interfacial structure, where (a) SEM image and (b) high magnitude image of an initially-grown CNT directly connects with the substrate, (c) TEM image and (d) HRTEM image of one CNT grows from the stainless steel.

Mentions: To answer why the individual CNT can sustain very high current and uniform emission over large area, we also studied the interface between CNTs and stainless steel substrate by SEM and TEM. The interface, full of importance, relates to the contact resistance and adherence of the nanotubes to the substrate and is a weak point where destructive vacuum breakdown may initiate18. After a long period time of growth, the CNT films often cover on the whole stainless steel. Not likes a silicon substrate which can be easily broken by a force at the edge, the stainless steel is difficult to be cut for observing the cross section of interface. To solve such a problem, we prepared samples with short growth time while keeping the other conditions same, so that the sample can be sectioned using the method developed by J B Park19. The CNTs were found being of around a micrometer long (Fig. 5a,b). The cross-section specimen was put into the TEM chamber for observation at 80 kV. We can see that the bottom of a CNT directly contacts with the stainless steel substrate without amorphous carbon layer (Fig. 5c). The high resolution TEM (HRTEM) shows the CNT walls are parallel to each other with a spacing of 0.34 nm and perpendicular to the substrate (Fig. 5d). Such near ideal contact interface between CNT and substrate is not seen before. Thus the CNTs have excellent electrical and mechanical contact, able to deliver large electron current from and dissipate heat to substrate under high-density large emission current operation.


A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron
Cross-sectional SEM and TEM micrographs of the CNT cold-cathode showing the overview of the interfacial structure, where (a) SEM image and (b) high magnitude image of an initially-grown CNT directly connects with the substrate, (c) TEM image and (d) HRTEM image of one CNT grows from the stainless steel.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5017026&req=5

f5: Cross-sectional SEM and TEM micrographs of the CNT cold-cathode showing the overview of the interfacial structure, where (a) SEM image and (b) high magnitude image of an initially-grown CNT directly connects with the substrate, (c) TEM image and (d) HRTEM image of one CNT grows from the stainless steel.
Mentions: To answer why the individual CNT can sustain very high current and uniform emission over large area, we also studied the interface between CNTs and stainless steel substrate by SEM and TEM. The interface, full of importance, relates to the contact resistance and adherence of the nanotubes to the substrate and is a weak point where destructive vacuum breakdown may initiate18. After a long period time of growth, the CNT films often cover on the whole stainless steel. Not likes a silicon substrate which can be easily broken by a force at the edge, the stainless steel is difficult to be cut for observing the cross section of interface. To solve such a problem, we prepared samples with short growth time while keeping the other conditions same, so that the sample can be sectioned using the method developed by J B Park19. The CNTs were found being of around a micrometer long (Fig. 5a,b). The cross-section specimen was put into the TEM chamber for observation at 80 kV. We can see that the bottom of a CNT directly contacts with the stainless steel substrate without amorphous carbon layer (Fig. 5c). The high resolution TEM (HRTEM) shows the CNT walls are parallel to each other with a spacing of 0.34 nm and perpendicular to the substrate (Fig. 5d). Such near ideal contact interface between CNT and substrate is not seen before. Thus the CNTs have excellent electrical and mechanical contact, able to deliver large electron current from and dissipate heat to substrate under high-density large emission current operation.

View Article: PubMed Central - PubMed

ABSTRACT

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

No MeSH data available.