People often say that technology develops in the twinkling of an eye. However, there are still those who slowly and steadily push forward through their research in order to create a paradigm shift. One of them is Professor Cheol Jin Lee at the School of Electrical Engineering in KU, who has worked for 21 years to develop a new technology that can replace the filament-based hot-cathode X-ray tube that has been used for 120 years.

Carbon nanotube, a novel nanomaterial discovered in 1991, has attracted much attention, but researchers have struggled with it for years because the process of inducing electron emission from the material has not been as efficient as expected. In 1988, Professor Lee, who had previously studied new semiconductor materials and devices, began researching carbon nanotube synthesis and field emission characteristics in order to develop a new technology that could be useful to humankind. Of course, it was not Professor Lee’s group alone that was attempting to develop a carbon nanotube-based electron emitter. However, believing that he could never obtain productive results unless he left research into traditional methods behind, he devoted himself to the pursuit of this goal, animated by an original and creative idea. “While most researchers were structuring a carbon nanotube-based field emitter by using carbon nanotube paste, I was searching for a unique structuring and preparation method. Eventually, I hit on a method of vertically aligning carbon nanotubes at a high density in order to maximize the electron beam density. This method enables one to form a high-density carbon nanotube structure without incorporating an organic substance into the preparation of an electron emitter, and thus enables the manufacture of a high-efficiency electron emitter with excellent characteristics.”


▲Schematic diagram of nanomaterial-based cold cathode X-ray tube.

Besides the carbon nanotube-based emitter, Professor Lee also developed a type of gate electrode technology that had never been attempted before by using graphene, which is another new nanomaterial. He continued his R&D work on the carbon nanotube-based emitter, the graphene gate electrode, an electron beam focus lens, and an anode, and sealed the individual components in a glass vacuum tube, the completed technology designed to enable the production of a high-performance cold cathode X-ray tube. He presented his new technology at the 32nd International Vacuum Nanoelectronics Conference (IVNC 2019) held in Cincinnati, Ohio, on July 22-26, in a paper entitled “Nanomaterial-Based High-Performance Cold Cathode X-ray Tube Technology.” This new technology enables a novel method of generating high-quality X-rays by using carbon nanotube and graphene, and the cold cathode X-ray tube based on it is the first of its type in the world. In the course of Professor Lee’s research over the last two decades, he has published 202 articles in international SCI journals, had 12,770 citations in international SCI journals (h-index 63, i10-index 143), given 220 presentations at international conferences, been granted 18 international patents and 60 Korean patents, and applied additionally for two international patents and one Korean patent.


▲Schematic diagram of nanomaterial-based cold cathode X-ray tube.

Professor Lee explains the impetus behind his current work. “The conventional X-ray apparatus for medical imaging devices has several problems. First of all, since a filament must be heated to a temperature of over 2000℃ to enable it to emit an electron beam, it takes a long time to prepare it for its normal operation. In addition, only 5% of the input energy is used in the emission of the electron beam, and the rest is lost as thermal energy. In other words, the energy efficiency of the conventional apparatus is very low. Moreover, as the electrons are emitted by means of heat, the X-ray dose is difficult to control. In practice, the dose should be adjusted to a variety of levels to obtain clear X-ray images of different body parts with the varying bone structures, thicknesses and densities of a range of men and women, young and old. The difficulties involved in the dosage control of the conventional X-ray apparatus make it challenging to acquire high-resolution images. Another problem is that patients may be exposed to an excessive dose of X-ray.