Biomedical subjects

Haiwon Lee

Publications and source records attributed to Haiwon Lee.

6 recordsLinked to original sources

PubMed2005

Surface functional group effect on atomic force microscope anodization lithography.

The lithographic effect of surface chemical functional groups of organic resists on atomic force microscope (AFM) anodization lithography is investigated using mixed self-assembled monolayers (SAMs). The SAM resist films were prepared with 1,12-diaminododecane dihydrochloride (DAD.2HCl), n-tridecylamine hydrochloride (TDA.HCl), and 1,12-diaminododecane hydrochloride (DAD.HCl), and their film characteristics were evaluated by ellipsometry, zeta-potential measurements, and AFM. The lithographic results indicate that the most dominant factor of the surface functional group effect is the electrochemical property of the surface groups as an anode surface in the anodization reaction, and the dimensions of the protruded patterns are critically determined by the wetting property of the resist surface. By controlling the surface chemical groups with considerations of their effects, high-speed patterning at 2 mm/s was achieved successfully using the mixed SAM resist of DAD.2HCl and TDA.HCl.

Journal Article↗

PubMed2004

Acid-catalyzed rearrangement of diaryl hydrazides for the efficient synthesis of functionalized 2,2'-diamino-1,1'-biaryls.

Diaryl hydrazides prepared from the Pd(0)- or Cu(I)-catalyzed coupling reactions of aryl hydrazides and aryl halides underwent the acid-catalyzed rearrangements to a series of previously unknown 2,2'-diaminobiaryls in good overall yields. The mildness of the reaction conditions allows the presence of various functional groups.

Journal Article↗

PubMed2003

Tandem or sequential coupling-IMDA cycloaddition approach to highly fused polycarbocycles.

The Diels-Alder cycloadduct made from 3,5-dibromo-2-pyrone and 2-bromo-styrene was successfully transformed stereoselectively into a series of novel benzotetracycles via a tandem or sequential Pd-catalyzed coupling-intramolecular Diels-Alder (IMDA) cycloaddition. The resulting polycarbocycles can be readily converted into a bicyclo[3.3.1]nonane system upon ozonolysis of the internal double bond.

Journal Article↗

PubMed2002

Diels-Alder cycloadditions of 3,5-dibromo-2-pyrone: a new ambident diene.

D-A cycloadditions of 3,5-dibromo-2-pyrone were investigated with a series of electronically and sterically distinct dienophiles. Our results showed that it is a highly potent ambident diene, being more reactive and stereoselective than monobromo-2-pyrones, and thus capable of generating a variety of bicycloadducts in much higher chemical yields and endo/exo ratios than monobromo-2-pyrones. Another interesting feature of this study is that the two bromine groups on the cycloadducts could be independently manipulated to produce other synthetically useful bicyclolactones.

Alkadienes↗

PubMed2002

A study of positive charge effect on AFM anodization lithography using metal phosphate monolayers.

Monolayer films of metal phosphate were prepared by sequential adsorption of phosphoric acid (PA) and metal ions (Zr4+ or Ca2+). The monolayer formation was confirmed and characterized by ellipsometry and atomic force microscopy (AFM). Nanometer-scale patterning on the self-assembled metal phosphate films has been achieved using AFM. The difference in AFM lithography on positively charged surfaces in the case of Zr4+ and Ca2+ ions was investigated and summarized. Since the presence of the positive charges allows electrons to move from a tip to a layer easily, the lithographic process initiates at a lower voltage in the layer of Zr2+ phosphate than in the layer of Ca phosphate or PA. Other lithographic results on metal phosphate layers were compared with those on a monolayer of PA.

Journal Article↗

PubMed2002

AFM nanolithography on a mixed LB film of hexadecylamine and palmitic acid.

An evenly mixed Langmuir film of hexadecylamine (HDA) and palmitic acid (PA) was prepared on the air-water interface and transferred to a Si substrate for the fabrication of nano-sized patterns. Vibrational spectrum of the transferred film shows that all acid groups of PAs were deprotonated and amine groups of HDAs were protonated by an acid-base reaction. The effect of mixing ratios in atomic force microscopy anodization lithography on the mixed films was investigated in terms of the line width of the protruded pattern. While the line width fabricated on PA film was 221 nm, the width on the mixed film was reduced to 84 nm under the same lithographic conditions. It is believed that the phenomenon was originated from the mixed structure from the interaction of HDA and PA. The chemical composition difference caused by the presence of ammonium cation in resist resulted in reducing the line width fabricated in the mixed Langmuir-Blodgett film.

Journal Article↗