Taehoon Lee

Roughness control of polycrystalline diamond films grown by bias-enhanced microwave plasma-assisted CVD

Abstract A simple growth technique to control the surface roughness of polycrystalline diamond films is proposed. The films are grown using a microwave plasma-assisted chemical vapor deposition method, with varying the methane (CH 4 ) concentration at the stage of bias-enhanced nucleation. It is found from the field-emission scanning electron microscope spectra that nanocrystalline diamond nuclei are formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. The RMS value of surface roughness for grown films, which is estimated from the atomic force microscope images, monotonically decreases from 165 to 53 nm with methane concentration. It is also observed that the surface roughness is closely related to the nucleation density. In addition, employing a two-step growth method, which consists of first-growth at 500 W and subsequent second-growth at 800 W, enables the as-grown polycrystalline diamond film to have a smaller roughness of approximately 46 nm. This is believed to be due to the secondary nucleation effect induced during the growth step.

Electron-emission from nano- and micro-crystalline diamond films: the effects of nitrogen and oxygen additives

Abstract Diamond films are grown on Si substrate by microwave plasma CVD using CH 4 +H 2 (for undoped) and additive N 2 (for nitrogen-incorporated) with/without O 2 as precursors. Crystal structures for grown films, such as micro- and nano-crystalline and surface morphologies are characterized in terms of growth condition by Raman and field-emission SEM, respectively. Cathodoluminescence (CL) spectra are monitored to identify the nitrogen-incorporation in grown diamond films. Relative intensity ratios of nitrogen-related band to band-A (denoted by I N / I A ) are also estimated from the CL characteristics and the influence of additive N 2 and O 2 precursors on the I N / I A ratio is analyzed. For all-grown films, electron-emission characteristics are measured, from which threshold fields for the emission are also estimated. Observed emission properties are correlated with crystal structures and morphologies obtained from grown films by considering the structural transformation from micro- to nano-crystalline as well as the nitrogen-induced defect states.

Growth of highly-oriented diamond films on 6H–SiC (0001) and Si (111) substrates and the effect of carburization

Abstract The growth of highly oriented diamond is performed on Si (111) and 6H–SiC (0001) substrates via two-step and three-step processes using microwave plasma CVD. The two-step process involves bias-enhanced nucleation (BEN) and deposition, and the three-step process involves carburization in addition to the two-step process. The diamond films grown on the Si (111) substrate exhibit high quality and desirable (111)-orientation under the carburization condition of 5.3×10 3 Pa in pressure with no bias applied. The mechanism for the formation of conversion layer during the carburization step is investigated on both the substrates through the Raman and X-ray photoelectron spectroscopy (XPS) studies. The results indicate that the carburization mainly composed of β-SiC, which plays a crucial role for the formation of the conversion layer and which eventually promotes the diamond nucleation. It is also suggested that a highly-oriented and high-quality diamond film can be successfully achieved by carburization.

Uniform dehydrogenation of amorphous silicon thin films using a wide thermal annealing system

To prevent ablation caused by sudden hydrogen eruption during crystallization of hydrogenated amorphous Si (a-Si:H) thin films, a wide dehydrogenation thermal annealing (wDTA) system was developed to reduce hydrogen content in a-Si:H film prior to its crystallization process. The annealed a-Si:H films were fully dehydrogenated and nanocrystallized by the wDTA system. Raman scattering measurement revealed that the dehydrogenation process lowers the hydrogen content through disappearance of the peak intensity at 2000 cm−1. The a-Si:H film was transformed into nanocrystallized Si with lower residual stress. The major advantage of this wDTA was the large area uniformity of the thermal and the resulting material properties for 8 generation display. The uniform material characteristics of the hydrogen content, thickness, energy bandgap, and transmittance of the annealed Si films in the overall area was confirmed by Raman spectroscopy, spectroscopic ellipsometry, and UV–vis spectrometer measurement.

GeOx interfacial layer scavenging remotely induced by metal electrode in metal/HfO2/GeOx/Ge capacitors

The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeOx interfacial layer (IL) between HfO2 dielectric and Ge substrate in metal/HfO2/GeOx/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeOx IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeOx IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by o...

Probing Amyloid β and the Antibody Interaction Using Atomic Force Microscopy

Amyloid β (Aβ) peptide is considered to be the critical causative factor in the pathogenesis of Alzheimers disease (AD) because the hydrophilic molecules accumulated outside of the neural cells and results in the formation of highly toxicity amyloid plaque. In this study, we probed the interaction between Aβ and the antibody using atomic force microscopy (AFM). We compared two kinds of antibodies which are the antibody for Aβ 1-42 (antibody42) and the antibody for Aβ 1-16 (antibody16). To detect the interaction between Aβ and the antibodies, the single molecular force spectroscopy was carried out using Aβ modified glass substrate and the antibodies modified AFM probes. In the results, the single Aβ-antibody42 dissociation constant was estimated to be 5.2 × 10-3 s-1 and the single Aβ-antibody16 dissociation constant was 2.8×10-2 s-1. The Aβ-antibody42 showed 5.3 times longer bond life time compare with Aβ-antibody16. It suggested that antibody42 is better choice for the Aβ sensor development.