Sensitive and Fast Direct Conversion X‐Ray Detectors Based on Single‐Crystalline HgI<sub>2</sub> Photoconductor and ZnO Nanowire Vacuum Diode

Deng

et al. 2021

Nanomaterials

Self Cite

A cold cathode has many applications in high frequency and high power electronic devices, X-ray source, vacuum microelectronic devices and vacuum nanoelectronic devices. After decades of exploration on the cold cathode materials, ZnO nanowire has been regarded as one of the most promising candidates, in particular for large area field emitter arrays (FEAs). Numerous works on the fundamental field emission properties of ZnO nanowire, as well as demonstrations of varieties of large area vacuum microelectronic applications, have been reported. Moreover, techniques such as modifying the geometrical structure, surface decoration and element doping were also proposed for optimizing the field emissions. This paper aims to provide a comprehensive review on recent progress on the ZnO nanowire cold cathode and its applications. We will begin with a brief introduction on the synthesis methods and discuss their advantages/disadvantages for cold cathode applications. After that, the field emission properties, mechanism and optimization will be introduced in detail. Then, the development for applications of large-area ZnO nanowire FEAs will also be covered. Finally, some future perspectives are provided.

Section: Applicationsmentioning

confidence: 99%

Section: Perspectivesmentioning

confidence: 99%

Recent Progress on ZnO Nanowires Cold Cathode and Its Applications

Deng

et al. 2021

Nanomaterials

Self Cite

“…[7][8][9] So far, the a-Se photo-using ZnO NW vacuum diode connected with HgI 2 crystal were proposed to achieve high sensitivity owing to the high X-ray absorption coefficient of HgI 2 and high operating electric field of vacuum diode. [19] However, the HgI 2 crystal is hard to be integrated with ZnO NW cold cathode, limiting their applications in flat-panel X-ray imaging. The flat-panel X-ray detectors formed by ZnO NW cold cathodes and Ga 2 O 3 photoconductor targets were proposed for sensitive direct-conversion X-ray detection using the EBIPC mechanism.…”

Section: Introductionmentioning

confidence: 99%

Highly Sensitive Direct‐Conversion Vacuum Flat‐Panel X‐Ray Detectors Formed by Ga₂O₃‐ZnO Heterojunction Cold Cathode and ZnS Target and their Photoelectron Multiplication Mechanism

Zhang

Wang

et al. 2022

Adv Materials Inter

Self Cite

“…Quasi-1D (Q1D) metal oxide nanostructures, such as zinc oxide (ZnO) nanowires, are regarded as a potential candidate for field emitter arrays (FEAs), which are applied in field emission photo detector, [1][2] parallel electron beam lithography [3] and flat panel X-ray source, [4][5][6] because of their advantages of high uniformity and excellent field emission characteristics. Numerous devices using Q1D ZnO nanostructures based FEAs have been demonstrated in the past decade.…”

Section: Introductionmentioning

confidence: 99%

“…Numerous devices using Q1D ZnO nanostructures based FEAs have been demonstrated in the past decade. [1][2][3][4][5][6][7][8][9][10] However, their performance still cannot meet commercialization requirements. How to further improve the emission current density of large-scale Q1D ZnO has a different field emission mechanism and different electrical characteristics, a model for its self-heating process that considers all these factors must be established.…”

Section: Introductionmentioning

confidence: 99%

Stable Heating Above 900 K in the Field Emission of ZnO Nanowires: Mechanism for Achieving High Current in Large Scale Field Emitter Arrays

Luo

Cao

et al. 2020

Adv Elect Materials

Self Cite

FEAs is particularly the major challenge that requires not only comprehensive knowledge on the intrinsic field emission mechanism of individual field emitter but also improvement on the actual proportion of field emitters that contribute to the FEAs. In addition to the screen effect, [11] thermal runaway is an important factor limiting the actual proportion of ZnO nanowire. [12] A general picture for the thermal runaway originated from the positive feedback of the self-heating characteristic of the Q1D field emitter on its thermal field emission current, which induces vacuum breakdown. Although several previous works have studied the thermal runaway mechanism for Q1D field emitter [13-15] and the melting of ZnO nanowire has been reported, suggesting the existence of thermal runaway, [12,16] the question of what temperature the individual Q1D ZnO field emitter can reach steadily, which determines the maximum emission current and breakdown field, remains unclear. With a high breakdown field, more emitters can be activated when increasing the applied field. One could also make better use of the ballasting effect usually existing in the ZnO nanowire field emitter itself [5] or equipped with an active driving device [17-18] and thus a highly uniform stable emission and a high emission current could be achieved. The field emission ring pattern was reported as a signature for the thermal field emission of the tungsten tip and the carbon nanotube (CNT). [19-21] It generally comprises the emission current from both the tip and the sidewall of the field emitter. Accordingly, one can obtain the thermal field emission current distribution along the emitter, which gives information on its temperature, by analyzing the ring pattern profile. [20] Compared to the field emission electron energy distribution that has been utilized to measure the temperature of individual CNT, [22] the method of field emission pattern is more simple. Furthermore, it can be applied in a large-scale substrate with potential application as a temperature monitor for FEAs. Although field emission ring patterns comprising several emission spots have been reported in ZnO nanowires, [23-24] they are different from those observed from the CNT, which is a continue ring. Their underlying mechanisms are due to the tip structure and the adsorbate instead of the thermal field emission. Considering that the ZnO nanowire The thermal runaway of a quasi-1D (Q1D) field emitter is an important cause of vacuum breakdown, which limits the field emission current density in field emitter arrays (FEAs). Comprehensive knowledge on the self-heating process of zinc oxide (ZnO) nanowires is important for obtaining a high breakdown field for activating more emitters. This work investigates the self-heating model of individual ZnO nanowire by considering the thermal field emission current distribution along the nanowire. Theoretical calculations suggest that the thermal field emission distribution along the nanowire can be reflected on the profile of the field emission pattern, ...