Enhanced field emission characteristics of zinc oxide mixed carbon nano-tubes

J.Y. Pan, C.C. Zhu, Y. L. Gao. Enhanced field emission characteristics of zinc oxide mixed carbon nano-tube films. Applied Surface Science 254(2008) 3787-3792.

Purpose of The Study

To improve the field emission characteristics by mixing Zinc oxide and carbon nano tubes(CNT) in a composite material. CNT are potential cathode materials in flat emission display. CNT FED are expected to be candidate of a flat plane display. However CNT have a high turn-on electric field, low emission stability and emission uniformity. These factors are slowing the progress of CNT. This study is a proposed method to reduce the turn-on electric field and increase emission stability and uniformity.

Methods

Using Chemical Vapor Deposition (CVD) to synthesize multi-wall CNTs, these CNTs were used as emitters of screen printed cathode films. CNT were mixed with ZnO, Terpineol(dispersant) and ethyl cellulose(binder) heated to 120 celcius and stirred. The CNT film is prepared by screen printing the solution on indium tin oxide (ITO) coated glass. Dried and baked to remove organic binder. The printing area is 2.5 cm x 2.5cm. Field-emission scanning electron microscopy was used to analyze the morphologies of the prepared films.

Key Findings

1. ZnO grains fill into the interspaces of CNTs (shown by SEM images).

2. Potential emitters in ZnO-CNT film would also increase due to the distribution of ZnO flakes.

3. Compared to usual CNTs, ZnO-CNT film has a lower turn-on electric field.(from 1.70 to 1.17 V/micrometer)

4. The emission current of ZnO-CNTs is 505 microamps, which is higher compared to the usual CNT (60 microamps).

5. ZnO is helpful as a field emission material to improve field emission characteristics of CNT films.

The UV-nanoimprint lithography equipment with multi-head imprinting unit for sub-50 nm half-pitch patterns

JaeJong Lee, KeeBong Choi, GeeHong Kim, SeungWoo Lee. The UV-nanoimprint lithography equipment with multi-head imprinting unit for sub 50-nm half pitch patterns. Microelectronic Engineering 84 (2007) p.963-966.

Purpose of the Study: Nanoimprinting lithography (NIL) is a promising technology to produce sub-50 nm half pitch features on silicon and/or quartz-based substrates. It is considered the next generation lithography.  The fundamental procedure is replicating the patterns defined on the stamp to any deformable materials such as photo resist. In this paper, chip-size multi-head imprinting unit with compliance stage adn overlay/alignment system with moire and dual grating unit are presented to fabricate 50 nanometer half-pitch patterns.

Methods:

To fabricate nanoscale patterns by UV-NIL tool there are two methods: single-step and step and repeat imprinting approach. Single-step can fabricate nanoscale patterns using a large size stamp that is the same size as the wafer. Step and repeat can fabricate nanoscale patterns using the small size stamp one inch square. Each approach has its disadvantages and advantages. However, the single-step has the advantages of short imprinting time and high throughput because of the large stamp size that is the same as the wafer.  Using single-step nanoimprinting lithography tool (ANT-4) with a multi-head imprinting unit, the passive compliant stage, UV system with wavelength of 365 nm, and fine stage with 3 nm resolution.

Key Findings:

1. The key issues of  uniform contact method between the stamp and the substrate, the overlay and alignment unit between the stamp and the substrate for fabrication are resolved by using the chip-size multi-head imprinting unit for above 4 inch wafer.

2. 50 nm dot adn 100 nm half-pitch channels for biosensor and 50 nm grating patterns for optical tele-communication device are clearly transferred to the Si substrate using the UV-NIL tool.

New system for secondary electron detection in variable-pressure scanning electron microscopy

Slowko, W. New system for secondary electron detection in variable-pressure scanning electron microscopy. Journal of Microscopy, Vol. 224. Pt. 1. October 2006. pp. 97-99.

Purpose of Study

Presenting a new secondary electron detection system that elimates the need for gas ionization and combines a two-stage detector head and a differential pumping system.

Methods

By adding a microsphere plate (MSP) to the standard Everhart-Thornley detector head in the scanning electron microscope. The MSP is an electron multipler used to view clearer images of the secondary electrons in various gas pressure and with various types of samples including biological samples.

Key Findings

1. The detector can work in high pressure or low pressure conditions.

2. To avoid scattering the electron beam, the distance d to the sample can be reduced.

3. Gas ionization is not needed. This elimates the poor images obtained in main approach to producing images of secondary electrons.

4. The new system is faster than previous systems as far as scanning rates.

The Role of Surface Energy in the Growth of Boron Crystals

Hayami, Wataru; Otani, Shigeki. The Role of Surface Energy in the Growth of Boron Crystals. Journal of Physical Chemistry. C (2007), 111 688-692

Purpose of the study

Surface energies were calculated to determine their role in growing nanowire of  alpha-tetragonal Boron. To determine the existence of pure alpha – tetragonal polymorph of Boron by calculating the surface energies of alpha-rhombohedral, beta-rhombohedral and alpha-tetragonal.  

Methods

Using a CPMD code, calculation of total surface energy and geometrical optimization were evaluated. The total energy of the bulk was first calculated in order to evaluate the surface energy. Surface energies were calculated at various surfaces.

Key Findings

1. The alpha-tetragonal structure has a much smaller cohesive energy than those of the other structures. (alpha-rh, beta-rh)

2. The surface energy plays a key role in stabilizing the phase. Alpha-tetragonal was a lower surface energy than alpha-rh, beta-rh.

3. According to the Wulff’s theorem, a low-energy surface is closer to the center and, as a result, exhibits a larger surface area. The total energy of the crystal, Etot is equal to :

                                    Etot = -CvN + CsN ^2/3

4. The pure alpha-tetragonal nanowire is in a metastable state since, thickness of the nanowires in the experiments are several tens of nanometers larger than the maximum size of the alpha-tetragonal crystal.

5. Two growth processes are proposed for the growth of alpha-tetragonal nanowires. Vapor-solid (VS) & Vapor-liquid-solid (VLS).

6. Laser ablation is a better method than chemical vapor deposition for making alpha-tetragonal Boron nanowires.

Definitions:

CPMD (Car-Parrihello Molecular Dynamics)

Laser ablation: process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam.