• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.215-215
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• 2011

The bonding configuration and adsorption stability of alanine and leucine adsorbed on Ge(100)-2${\times}$1 surface were investigated and compared using core-level photoemission spectroscopy (CLPES) and density functional theory (DFT) calculations. The bonding configuration, stability, and adsorption energies were evaluated for two different coverage levels. In both cases, the C 1s, N 1s, and O 1s core-level spectra at a low coverage (0.30 ML) indicated that the carboxyl and amine groups participated in bonding with the Ge(100) surface in an "O-H dissociated-N dative bonded structure". At high coverage levels (0.60 ML), both this structure and an "O-H dissociation bonded structure" were present. As a result, we found that alanine adsorbs more easily (lower adsorption energy) than leucine on Ge(100) surfaces due to less steric hindrance of side chain.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.212-212
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• 2012

The Coverage dependent attachment of multifunctional groups included in threonine molecules adsorbed to Ge (100)$-2{\times}1$ surface was investigated using core-level photoemission spectroscopy (CLPES) and density functional theory (DFT) calculations. The core-level spectra at a low coverage indicated that the both carboxyl and amine groups participated in the bonding with the Ge (100) surface by "O-H dissociated and N-dative bonded structure". However, at high coverage level, additional adsorption geometry of "O-H dissociation bonded structure" appeared possibly to minimize the steric hindrance between adsorbed molecules. Moreover, the C 1s, N 1s, and O 1s core level spectra confirmed that the carboxyl oxygen is more competitive against the hydroxymethyl oxygen in the adsorption reaction. The adsorption energies calculated using DFT methods suggested that four of six adsorption structures were plausible. These structures were the "O-H dissociated-N dative bonded structure", the "O-H dissociation bonded structure", the "Om-H dissociated-N dative bonded structure", and the "Om-H dissociation bonded structure" (where Om indicates the hydroxymethyl oxygen). These structures are equally likely, according to the adsorption energies alone. Conclusively, we investigate in threonine on Ge (100) surface system that the "O-H dissociated-N dative bonded structure" and the "O-H dissociation bonded structure" are preferred at low coverage and high coverage.

• Journal of dental hygiene science
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• v.9 no.2
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• pp.153-160
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• 2009

The purposed of this study was to investigate the effect of Gold bonding agent as intermediate layer between metal substrate and ceramic coating. Gold bonding agent used to seal off any surface porosity, to mask the greyish color of the metal, and to provide an underlying bright golden hue to the ceramic coverage. The adhesion between metal substrate and ceramic is related to diffusion of oxygen during ceramic firing. The oxide layer produced on non-precious alloy anti titanium was considered to have a potentially adverse effect on metal-ceramic bonding. The oxidation characteristics of titanium and non-precious alloys are the main problem. Every group were divided into test and control groups. Control groups are carried out process of degassing for product oxide layer. Au coating was applied on each Ni-Cr, Co-Cr alloys and cp-Ti specimens with difference surface condition or degassing. Specimens surfaces and cutting plane was characterized by SEM/EDS. Results suggested that Au coating is effective barriers to protect metal oxidation during ceramic firing.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.155-155
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• 2000

Adsorption of alkali metals on a silicon surface has attracted much attention due to its importance in metal-semiconductor interface technology, In particular, the bonding nature of alkali metal to silicon substrate has been a focus of fundamental research efforts. We examined the adsorbed layer of Cs on a Si(111)-(7$\times$) surface by reactive ion scattering (RIS) of hyperthermal Cs+ beams. RIS from a Cs-adsorbed surface gives rise to Cs, representing pickup of surface Cs by Cs projectile. The Cs intensity is proportional to surface coverage of Cs at a high substrate temperature (473 K), while it varies anomalously with Cs coverage at low temperatures (130-170 K). This observation indicates that RIS selectively detects metallic Cs on surface, but discriminates ionic Cs. Transition from ionic to metallic Cs adlayer is driven by thermal diffusion of Cs and their clustering process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.137-137
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• 2013

The most stable adsorption structures and their corresponding energies of 4-pyridone, 4-hydroxypyridine, 2-pyridone and 2-hydroxypyridine have been investigated by Density Functional Theory (DFT) calculation method and high-resolution photoemission spectroscopy (HRPES). We confirmed that between the two reaction centers of 4- and 2-pyridone, only O atom of carbonyl functional group can act as a Lewis base and thus, O dative bonding structure is the most stable. On the other hand, we clarified that both the two reaction centers (the cyclic N atom and the O atom of hydroxyl functional group) of 4- and 2-hydroxypyridine (tautomers of 4- and 2-pyridone) can successfully function as a Lewis base. Through the interpretation of the N 1s and O 1s core level spectra obtained using HRPES, we could confirm the electronic structures and bonding configurations of these molecules with a coverage dependence on the Ge(100) surface.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.1 no.1
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• pp.50-57
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• 1992

Intrinsic discoloration of permanent anterior teeth is a continuing esthetic problem. Tetracycline ingested during amelogenesis has long been recognized as predisposing factor in intrinsic staining. Methods for restoring original tooth color have included (1) complete PFM crown coverage (2) porcelain laminate veneers (3) direct bonding of composite resin, and (4) bleaching. In the case of tetracycline-stained upper anterior teeth, We authors, obtained the satisfactory results by means of gingivectomy, preliminary bleaching and porcelain laminate veneer restoration.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.188-188
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• 1999

The embedded atom method (EAM) of Daw and Baskes as a semiempirical method, has been successfully applied to the fcc or nearly filled d-band transition metals due to its computational feasibility and its methodological simplicity. Then Baskes modified the EAM (MEAM) to include directional bonding and applied it to metals, semiconductors, and diatomic gases, all of which have different types of bondings. Here, we present a detailed study of the energetics of adsorption on the fcc(111) surfaces and binary system within the framework of MEAM. In adsorption on fcc(111) surfaces, there are two energetically favored sites, so called, fcc site and hcp site, which may trigger stacking fault in the growth of films and might switch growth mode between 3D growth and layer by layer growth. We scrutinized the role of the hcp sites, which would offer dynamic growth pathways although the dynamics are not yet clear within the limited experimental resolution. Featuring these transient motions in the atomic level should contribute to the understanding the growth mechanisms on fcc(111) surface. And we also applied MEAM for initial stage energetics at the Cr coverage of sub- monolayer on W(110). We hope that recently observed extraordinary growth behavior at the Cr coverage of 0.7 monolayer, self- organized nano-scale lines, can be resolved in this MEAM binary system calculation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.216-216
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• 2011

We will investigate the bonding configurations of phenylalanine and tyrosine adsorbed on the Ge(100) surface using CLPES and DFT calculations. First, the C 1s, N 1s, and O 1s spectra obtained at 300 K revealed that both the amine and carboxyl groups of phenylalanine and tyrosine concurrently participated in adsorption on the Ge(100) surface without bond breaking using CLPES, depending on the extent of coverage. In the second place, we confirmed that the "O-H dissociated-N dative bonded structure" is the most stable structure implying kinetically favorable structure, and the "O-H dissociation bonded structure" is another stable structure manifesting thermodynamically advantageous structure using DFT calculations. This tendency turns up both phenylalanine and tyrosine, similarly. Furthermore, through the CLPES data and DFT calculation data, we discovered that the "O-H dissociated-N dative bonded structure" and the "O-H dissociation bonded structure" are preferred at 0.30 ML and 0.60 ML, respectively. Moreover, we found that the phenyl ring of phenylalanine is located in axial position to Ge(100) surface, but the phenyl ring of tyrosine is located in parallel to Ge(100) surface using DFT calculations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.248-250
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• 2017

The Mar-M-247 alloy is one of the most widely used materials for gas turbine components in aerospace filed and it shows excellent high temperature strength properties. Hot section parts, such as turbine nozzle and blade, are difficult to manufacture because of their complicated shape. So, the joining process usually applies to them. In this study, the high-temperature behavior of Mar-M-247 alloy at liquid diffusion bonding was investigated. Thus, we performed the diffusion bonding at $1,121^{\circ}C$ for 7 minutes, and observed changes in high temperature strength. As a result, the strength of the bonded specimens decreased by about 70% at $649^{\circ}C$, 60% at $825^{\circ}C$, and 45% at $1,000^{\circ}C$ compared to the base metal. As a result of observing the strength change with bonding time, the specimen bonded for 720 minutes showed a similar strength with the base metal at $649^{\circ}C$. Inferring this result, the joint is considered to be the one-body part.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.8 no.1
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• pp.64-74
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• 1999

The use of fluoride and other preventive methods caused a dramatic decline in dental caries and the need for restorative dentistry. In our modern society that places a high value on appearance, emphasis is now shifting towards esthetic dentistry which has experienced a high popularity with the development of bonding techniques and materials including porcelain and composite. To satisfy patients wanting whiter teeth and a better looking smile, there are many treatment options ranging from full crown coverage to conservative procedures such as bleaching. Whether bleaching should be combined with other esthetic procedures or used alone depends on the type of discoloration and the patient's willingness to accept the various treatment options. Therefore, in order to obtain a successful esthetic outcome, careful diagnosis and treatment planning followed by consultation with the patient is of utmost importance.