Sunmee Kim

Ultrasonically Enhanced Diesel Removal from Soil

In this study, we investigated the effect of ultrasound on diesel removal from soils. Lab-scale soil flushing experiments were conducted for various conditions involving ultrasonic power, particle size, and diesel concentration, using specially designed and fabricated equipment. The test results indicated that the rate of contaminant extraction increased significantly with increasing ultrasonic power. The degree of enhancement varies with test conditions. Physical imaging of the specimens during tests was realized using a microscope. The images showed the disintegration of soil grains and oil drops resulting in a variation in contaminant removal efficiency.

Direct Transport Measurements Through An Ensemble Of Inas Self-Assembled Quantum Dots

Direct transport measurement results of an InAs self-assembled quantum dot system have been reported. The differential conductance characteristics measured from the metal-semiconductor-metal diodes incorporating InAs self-assembled quantum dots show conductance peaks. The energy spectrum of the dots is obtained from the peak positions.

Self-Assembled Quantum Dot Single Electron Devices

Single electron tunneling and its application to future VLSI systems has been an important subject extensively studied for the last decade [l]. Many types of materials and ideas have been applied to fabricate and implement single electron devices operating at high temperatures. The self-assembled quantum dot (SAQD) system is one of the attractive candidates for single electron devices since high quality Coulomb islands can be obtained in one-step growth processes. Furthermore, the characteristic energy scale of the devices would enhance because the quantum energy is expected to be added to the classical charging energy. on InGaAs SAQDs. lever-arms with nm spacings. staircases at 77 K and higher temperatures. Figure 1 (a) and (b) show an AFM photos of typical SAQD single electron devices fabricated by the lever-arm technique. The InGaAs SAQDs we have used were grown by an MOCVD technique and the typical diameter of the dots is approximately 20 nm [2]. The aluminum lever-arms with spacings from 200 to 40 nm were fabricated by a standard ebeam exposure and a lift-off process. Figure 2 (a) and (b) show the 77 K current-voltage (I V) and its differential conductance - voltage characteristics.(dUdV - V) of lever - arm device with the gap of 40 nm. Several staircases are clearly identified in both the I-V and the dVdV-V. dI/dV-V of the device with the gap of 150 nm. Clear staircases are also seen. These staircases are originated from the single electron tunneling through SAQDs located in the shortest current path between two lever - arms. In conclusion, self-assembled guantum dot single electron devices are made by the lever-arm technique with the minimum gap spacing of 40 nm and clear staircases are observed in the I-V characteristics. The result of more complicated devices with multiple lever-arms will also be presented at the conference.

Electrical Properties Of E-Beam Exposed Silicon Dioxides And Their Application To Nano-Devices

It has been well known that carbon contamination layers build up on thin films when they are exposed by high energy electron beams [l]. Such contamination layers were commonly used as etch-masks in earlier e-beam lithography and pattern transfer processes [2]. However, the electrical properties of the e-beam induced contamination layers and their application to nano-device fabrication have not been focused so far. We would like to present the electrical properties of e-beam induced carbon contamination layers on SiO,. It has been found that the aluminum can make electrical contacts to the contamination layers, and the current-voltage (I-V) characteristics of various Al/contamination layer/Al structures have been measured. Figure 1 (a) and (b) show in-situ scanning Auger electron spectroscopic data for the bare and the e-beam exposed SiO, films, respectively. The carbon layer with the thickness of 3 nm can be clearly identified in the case of the e-beam exposed S O z film. Figure 2 shows the SEM photo of a typical sample structure for the electrical measurements. The 40 pm long, 1 pm wide line patterns have been exposed between two aluminum pads. Figure 3 (a) and (b) show the current-voltage (I-V) and the differential conductance-voltage (dI/dV-V) characteristics of 3 samples with different ebeam doses. While the current measured between A1 pads on bare SiO, is negligible, the I-V from all 3 exposed samples exhibit conducting properties. Furthermore, both the I and the dI/dV systematically increase with the amount of the e-beam dose, as is summarized in Fig. 4 plotting dI/dV at 1 V as a function of the dose. In conclusion, the electrical measurement of carbon contamination layers on SiO, has been systematically performed. The conducting properties of thin carbon layer can be utilized in the one step fabrication of nano-meter sized wire structures and barrier structures. Characterization results of such e-beam induced nano-structures will also be presented at the conference.