JAPAN NANONET BULLETIN - 67th Issue - March 30, 2006

YOUNG RESEARCHERS’ INTRODUCTION

Shojiro KOMATSU
Chief Researcher, National Institute for Materials Science (NIMS)

Electron field emission from self-organized micro emitters of new-type boron nitride films

(Issued in Japanese: December 8, 2004)

Negative electron affinity (NEA) and geometrical enhancement factor are distinctly important to promote electron field emission (eFE), and it must be possible to control them in the fabrication of electron emitting devices. NEA occurs in semiconductors when the vacuum level lies below the conduction band minimum mainly due to a surface electronic dipole, which is known for doped diamond surfaces terminated with hydrogen. Wide band gap materials such as diamond, AlN, and BN are empirically known to show NEA. The geometrical enhancement factor β is defined as a constant characteristic of an electron field emitter in the Fowler-Nordheim equation. It is related to the local electric field enhancement caused by protruded shapes, which is prominent in carbon nanotubes (CNT) and fabricated electron field emitters employing shapes with high aspect ratio.

Here, we report on self-organized electron emitters with high β, cone-shape structures and micrometer dimensions made of sp³-bonded 5H-BN. Emission density (Id) generation began at 90 mA/cm² with a threshold of 6 V/μm, which is comparable to that of CNT, and the Id rapidly reached ~0.9 A/cm² with an applied electric field (E) of 8.6 V/μm. This value of Id was very high considering the low applied E in comparison with those of CNT. The films were grown by plasma-assisted chemical vapor deposition with the assistance of 193 nm laser irradiation of the surface. The work function of this material was ~5 eV while the band gap was estimated to be ~6 eV. The known robustness of sp³-bonded BN with its excellent electron emission characteristics and the self-organization of the emitter shaped structures may provide new applications for electron emitting devices.

Shojiro KOMATSU

Chief Researcher, National Institute for Materials Science (NIMS)

1986	Dr. Engineering, The university of Tokyo.
1986 ~present	National Institute for Materials Science (NIMS) (formerly known as National Institute for Inorganic Materials)

Awards and Prizes
2004	Plasma electronics award, Japan Society of Applied Physics

E-mail:

Fig. 1 Large Image

A. Scanning electron microscopy (SEM) image of the emitters with dimensions of ~10 μM. B. The cone-shaped emitters are aligned towards the incident 193 nm laser light irradiated during the growth by plasma-assisted chemical vapor deposition from diborane and ammonia.


Fig. 2 Large Image
B. Electron field emission from the sample as a function of the applied field. Two and three measurements for the sample points A and B were made, respectively, with different gap distances between the probe anode tip and the sample surface which served as the cathode. A. Fowler-Nordheim plots of the data corresponding to Fig.2B. The field enhancement factors β were evaluated by employing a representative work function of 5 eV in these plots.

Fig. 2 Large Image

B. Electron field emission from the sample as a function of the applied field. Two and three measurements for the sample points A and B were made, respectively, with different gap distances between the probe anode tip and the sample surface which served as the cathode.
A. Fowler-Nordheim plots of the data corresponding to Fig.2B. The field enhancement factors β were evaluated by employing a representative work function of 5 eV in these plots.

Relevant papers

Komatsu, S., Okudo, K., Kazami, D., Golberg, D., Li, Y., Moriyoshi, Y., Shiratani, M. & Okada, K.
Electron Field Emission from Self-Organized Micro-Emitters of sp³-Bonded 5H Boron Nitride with Very High Current Density at Low Electric Field
J. Phys. Chem. B ,108-17, 5182-5184 (2004).
Komatsu, S., Kurashima, K., Kanda, H., Okada, K., Moriyoshi, Y., Shimizu, Y., Shiratani, M., Nakano, T. & Samukawa, S.
Highly Crys-talline 5H-polytype of sp³-bonded Boron Nitride Prepared by Plasma-Packets-Assisted Pulsed-Laser Deposition: An Ultraviolet Light Emitter at 225nm
Appl. Phys. Lett. 81-24, 4547-4549 (2002).
Komatsu, S., Okada, K., Shimizu, Y. & Moriyoshi, Y
New Phase of sp³-bonded BN: The 5H Polytype
J. Phys. Chem. B, 103-17, 3289-3291 (1999).