Abstract
The nanocone-shaped carbon nanotubes field-emitter array (NCNA) is a near-ideal field-emitter array that combines the advantages of geometry and material. In contrast to previous methods of field-emitter array, laser ablation is a low-cost and clean method that does not require any photolithography or wet chemistry. However, nanocone shapes are hard to achieve through laser ablation due to the micrometer-scale focusing spot. Here, we develop an ultraviolet (UV) laser beam patterning technique that is capable of reliably realizing NCNA with a cone-tip radius of ≈300 nm, utilizing optimized beam focusing and unique carbon nanotube–light interaction properties. The patterned array provided smaller turn-on fields (reduced from 2.6 to 1.6 V/μm) in emitters and supported a higher (increased from 10 to 140 mA/cm2) and more stable emission than their unpatterned counterparts. The present technique may be widely applied in the fabrication of high-performance CNTs field-emitter arrays.
Highlights
Aligned carbon nanotubes (VACNT) provide a much simpler, cheaper, as well as more scalable, manufacturable, and deployable platform upon which to build future electron sources
Bar: 10 nm). (c) Energy distribution diagram of the laser beam. (d) Gaussian distribution of laser beam energy. (e) The (e) The process of laser beam energy acting on Vertically aligned carbon nanotubes (VACNT) to form its shape. (f) Nanocone and (g) Nanocone array formation process of laser beam energy acting on VACNT to form its shape. (f) Nanocone and (g) Nanocone array formation process
The C 1s, O 1s, and N 1s peaks of processed VACNT and the C 1s and O 1s peaks of unprocessed VACNT are clearly visible in the X-ray photoelectron spectroscopy (XPS) survey scan spectrum
Summary
Aligned carbon nanotubes (VACNT) provide a much simpler, cheaper, as well as more scalable, manufacturable, and deployable platform upon which to build future electron sources. The photons of low wavelength ultraviolet (UV) light have high energy, and the single photons of high energy (>3 eV) can directly break (requires 3–10 eV) the chemical bonds of materials (photolytic process) [10]. This is a highly nonlinear process, which make it possible to process materials with sharp edges. The almost perfect absorption of VACNTs [13,14] for light in a wide wavelength range further reduces the heat-affected zone in the processing process [15] These factors together make it possible for the laser to process in pattern micron or even nanoscale CNTs structures, which have high and stable current under low electric field intensity. To explore the impacts of the microscale geometry on the emission characteristics of the VACNT thin films, three-dimensional finite element simulations were undertaken on unpatterned and patterned emitters
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