Yoon Taek Jang

Tungsten nanowires and their field electron emission properties

We report the fabrication of tungsten nanowires, by simple thermal treatment of W films, that behave as self-catalytic layers and their excellent electron field emission properties as well. The obtained nanowires have a diameter ranging from 10 to 50 nm, showing perfect straightness and neat appearance. Typical turn-on field for the electron emission is about 5 V/μm, and the field enhancement factor β becomes 38 256, which is very close to that of the high efficient single-wall carbon nanotube emitters. The most exciting result is the possibility of easy fabrication of perfectly straight nanowires as promising building blocks for terabit-level interconnection and nanomachine components without the intentional use of any heterogeneous catalysts.

Fabrication and characteristics of field emitter using carbon nanotubes directly grown by thermal chemical vapor deposition

We experimentally present the effects of vertical alignment and density of carbon nanotubes on the emission current level. For practical display application, we have fabricated the triode type emitter using directly grown nanotubes as emission tip, and characterized their basic field emission properties. The triode type emitter exhibited a turn-on voltage of 37 V and an anode current density of 1.7 μA with gate voltage at 47 V. The vertical alignment of nanotubes does not play a key role in improving the emission properties in triode type nanotubes emitter.

Direct nano-wiring carbon nanotube using growth barrier: A possible mechanism of selective lateral growth

In this work we report the direct nano-bridging of carbon nanotubes (CNT) between micro-sized islands using conventional photolithography technique necessary for the nanomachining and the molecular device applications compatible with the Si-based process. The most distinct feature in this work is to use a growth barrier of Nb metal or insulating layer on the top of the catalytic metal to prevent the growth of CNT from the vertical direction to the substrate. As a result, CNTs of either “straight line” or a perfect “Y shape” were selectively grown between lateral sides of the catalytic metals or pre-defined electrodes without any trace of vertical growth. The length of the CNTs was 500–1000 nm and the diameter thinner than about 20 nm. We suggest that magnetic and crystallographic characteristics due to the unique interaction between the Nb overlayer and ferromagnetic Ni catalysts and nano-granulation of Ni layer during the growth process are important for the lateral (i.e., parallel to the substrate) CNTs...

Coulomb blockade devices of Co dot arrays on tungsten-nanowire templates fabricated by using only a thin film technique

A simple fabrication of gate-controlled nanodevices made of the Co nanodots on tungsten (W)-nanowire templates by using conventional photolithography and a thin film technique is reported. The combined multiple grain nanobridge allows the observation of the Coulomb gap up to a temperature as high as 200 K and shows nonlinear current–voltage characteristics up to 250 K. The combination of Co dots with straight W-nanowire templates opens possibilities of reproducible blockade devices.

Gated field emitter using carbon nanotubes for vacuum microelectronic devices

We have fabricated a gated field emitter using directly grown carbon nanotubes (CNTs) as an electron emission source. Vertically aligned CNTs were grown at the center of the gate hole using thermal chemical vapor deposition. In order to reduce the leakage current due to flowing current along CNTs grown on the sidewalls of the gate hole, we adopted a new process scheme such as sidewall protector. The leakage current of gated CNT emitter with sidewall protector shows a decrease of 85.8 % compared to that of a conventional structure.

Selective lateral nano-bridging of carbon nanowire between catalytic contact electrodes

We report selective lateral nano-bridging of carbon nanowire (CNW) between microsized islands using conventional photolithography technique necessary for the nanomachining and the molecular device applications compatible with Si-based process. Most distinct feature in this work is to use a growth barrier of Nb metal or insulating layer on the top of the catalytic Ni metal to prevent the growth of CNW from vertical direction to the substrate. As a result, CNWs of either “straight line” or a “Y-junction” were selectively grown between lateral sides of the catalytic metals or pre-defined electrodes without any trace of vertical growth. These results clearly indicate that this method would be one of the most feasible fabrication techniques for the nanomachines or the electronic applications with high integration level through process optimization.

Decrease of electron paramagnetic defect density and enhancement of electron field emission in annealed carbon films

We have studied the effect of the paramagnetic defects in carbon films on the field-emission properties. The paramagnetic defects in carbon films originating from the carbon dangling bonds were measured using electron spin resonance (ESR). We found a reduction of the dangling bond density in the annealed carbon films in N2/H2 atmosphere from ESR spectroscopy. The annealed films with lower defect densities, i.e., dangling bonds, showed an improved characteristic of higher emission current density as well as a lower turn-on electric field in the Fowler–Nordheim type tunneling. Also in the annealed carbon films a correlation is observed between the decrease of band gap estimated from the electrical conductivity and the reduction of dangling bond density. The earlier results indicate that the enhancement of the emission current level in the annealed carbon films is related to the decrease of the ESR centers.

A novel micro-gas sensor using laterally grown carbon nanotubes

We experimentally present the multiwalled carbon (MWNT) based gas sensor by a direct nano-wiring between Nb electrodes. Upon exposure MWNT to NH/sub 3/, the electrical resistance of the MWNTs is found to increase. The increase of temperature and gas concentration actually reduces the response time and increases the sensitivity to introduction of gas, respectively. Our results show a promising technique for forming CNT bridges between electrodes for chemical gas sensor at room temperature.