Nanotube field electron emission: principles, development, and applications

Abstract

There is a growing trend to apply field emission (FE) electron sources in vacuum electronic devices due to their fast response, high efficiency and low energy consumption compared to thermionic emission ones. Carbon nanotubes (CNTs) have been regarded as a promising class of electron field emitters since the 1990s and have promoted the development of FE technology greatly because of their high electrical and thermal conductivity, chemical stability, high aspect ratio and small size. Recent studies have shown that FE from CNTs has the potential to replace conventional thermionic emission in many areas and that it exhibits advanced features in practical applications. Consequently, FE from nanotubes and applications thereof have attracted much attention. This paper provides a comprehensive review of both recent advances in CNT field emitters and issues related to applications of CNT based FE. FE theories and principles are introduced, and the early development of field emitters is related. CNT emitter types and their FE performance are discussed. The current situation for applications based on nanotube FE is reviewed. Although challenges remain, the tremendous progress made in CNT FE over the past ten years indicates the field's development potential.

Physical electrostatics of small field emitter arrays/clusters

“…and, on substituting for the "R"s, using eqs (S1) and (S3): Since, from earlier, (δ 1 ) dir ≈ -4η 2 (ℓ/c) 3 , it follows from eq. (48) that (Ξ NF -1) ≈ (δ 0 ) NF -(δ 1 ) NF = + (7/4)η 2 (ℓ/c) 3 .…”

“…(33) can be neglected. In this case, δ NF is given adequately by δ NF ("scs") ≈ (r/nc) 3 = +η(ℓ /nc) 3 (35) In the case of widely separated emitters (r<<ℓ<<nc), expression (32) reduces to δ NF ("ws") ≈ (r − 2ℓ )r 2 /(nc) 3 ≈ −2ℓ r 2 /(nc) 3 ≈ −2η 2 (ℓ /nc) 3 (36) In this "widely separated" limit, the effect is always a decrease in apex FEF. Obviously, the size of this neighbor-field-induced FEF-decrease dies away as the separation nc increases.…”

“…(S59)When r<<c, this reduces to:(δ 1 ) NF ≈ 2[r 3 /c 3 -2r 2 ℓ/{c 2 +(2ℓ) 2 } 3/2 ](S60)For small separations (r<<c<<ℓ), this reduces to(δ 1 ) NF ≈ 2[r 3 /c 3 -(1/4)r 2 /ℓ 2 ] (S61) (δ 1 ) NF ≈ 2(r/c) 3 -(1/2)(r/ℓ) 2 . (S62)For sufficiently small separations [(r<<c<<ℓ) and (c 3 <<4rℓ 2 ) and (c>4r)](δ 1 ) NF ≈ +2(r/c) 3 = +(9/8)η 3 (ℓ/c)3 (S63)…”

“…For two widely spaced emitters, eq. (27) (with n=1) adequately gives the fractional reduction -δ two ("ws") in apex FEF as 2η (ℓ/c)3 . On a ln-ln plot, made against ln(c/ℓ), the large-c form would be the straight lineln(−δ two ) ≈ ln(2η) − 3ln(c/ℓ ) .(55)FIG.…”

Memristive model of hysteretic field emission from carbon nanotube arrays

“…In the past two decades, the study of field emission from carbon nanomaterials has attracted significant attention. [1][2][3] Potential applications for field-emission devices include X-ray tubes, 4 highluminance light sources 5 and field-emission displays. 6 While most of the attention has been focused on field emission from carbon nanotube (CNT) arrays, the field emission from carbon yarns, fibers and graphene flakes has also been reported.…”