Sung Koo Kang

Aspect Ratio Controlled Synthesis of Gold Nanorods

Au nanorods were synthesized by using seed-mediated methods. The aspect ratio of the Au nanorods was controlled by temperature and the amount of surfactant used and the rods were characterized by TEM, HRTEM and UV-VIS spectrophotometer. Au nanorods with high aspect ratio could be prepared by decreasing the temperature used and controlling the surfactant concentration. The UV-VIS absorption spectra of the nanorods also showed variations in the aspect ratio. These results suggest that Au nanorods form, via an anisotropic growth mechanism, and that the surfactant plays a role in this process.

Dependence of image distortion in a liquid-cell atomic force microscope on fluidic properties

When the standard grating sample was tested in seven different fluids using a liquid atomic force microscope, it was observed that the images were significantly distorted. It was proposed as a modified squeeze-drag superposition model for the elucidation of image distortion. This model considers the net force between the cantilever and the sample for scanning with the y direction. It was found that the net force between the cantilever and the sample was strongly dependent on the kinematic viscosity of fluids. These image distortion phenomena were proven by the proposed model with the experiments.

Multifunctionalization of organosilanes on submicron-sized island-type electrodes for the selective detection of metal ions

A submicron-sized metal ion detector with two electrodes was fabricated by atomic force microscopy lithography. Two detection zones were functionalized with thiol (SH) and amine (NH2) groups, which have a high affinity for mercury and copper, respectively. Conductance with metal adsorption was measured by the forced contact of the tip (mobile electrode) with the gold-deposited center (fixed electrode) at a constant repulsive force (38nN). In Cu2+∕Hg2+ binary solutions, one electrode (thiol group) showed a high affinity for mercury, and the other for copper. This two-electrode system immobilized with different functional groups was used in the selective adsorption and detection of target materials.

Fabrication of submicron size electrode via nonetching method for metal ion detection

A metal ion detector with a submicron size electrode was fabricated by atomic force microscopy lithography using a pre-programmed voltage and a nonetching method. The square frame of the mesa pattern was functionalized by (aminopropyl)triethoxysilane for the metal ion detection, and the remaining portion was used as an electrode by the self-assembly of (3-mercaptopropyl)trimethoxysialne for Au metal deposition. In this module, no metal lining or lead line was required, because the conductive tip (mobile electrode) was in direct contact with the gold-deposited mesa portion (fixed electrode). The conductance changed with the quantity of adsorbed copper ions, due to electron tunneling between the mobile and surface electrodes.

Synthesis oftrans-substituted porphyrin building blocks containing two S-trityl or thiol groups

The synthesis of some linear structuredtrans-porphyrin bearing functional groups (S-trityl or thiol) was described. The rational synthetic pathway consisted of 6 reaction steps (up to S-trityl derivatized porphyrin, 5 steps), constituting a MacDonald-type 2+2 condensation and amine-carboxylic acid coupling. The completion of each step was confirmed by1H-NMR, UV/Vis adsorption, and FAM-MS. The resulting porphyrins would be applicable to the study of self-assembled gold-thiol structures, due to the reactive nature of the molecules with a gold surface.

Fabrication of submicron-sized copper structures on pre-patterned self-assembled monolayer and Langmuir-Blodgett films

The fabrication of a metal microstructure on pre-patterned organic templates, prepared using SAM and LB techniques is described. The OTS derivatized substrate was oxidized by AFM anodic oxidation at the threshold voltage. Site-selective copper structure was then fabricated on the locally modified monolayer based on pre-designed patterns. The sequential adsorption-reduction of copper ion was carried out, leading to improved metal coverage and a reduction in defects.

The effect of ultrasonic waves on the fabrication of TiO2 nanoparticles on a substrate using a self-assembly method

A method for enhancing surface uniformity was investigated during the formation of titania film. A self-assembling technique with ultrasonic applications was effectively used to fabricate titania nanoparticles on the solid substrate after surface functionalization by APTES (3-amino-propyl-tri-ethoxy-silane). Morphological changes associated with structural evolution were observed by using AFM (atomic force microscopy). Results showed that ultrasonic waves were very effective in both enhancing the surface uniformity and narrowing the particle size distribution of the titania nanoparticles.

Fabrication of 3D functionalized microstructure via scanning probe lithography and self-assembly methods.

A type of 2-dimensional planar pattern with spatial resolution can be easily produced using scanning probe lithography (SPL). However, it has not been used successfully for fabricating 3-dimensional (3D) structures due to the low aspect ratio of the resulting structure. Herein, we describe a method for fabricating a 3D functionalized structure via a combination of SPL and self-assembly techniques. In this study, a 3D structure was established on a Si surface with a passivated monolayer via SPL. The patterned layer was modified using a omega-functionalized organosilane. Lateral force microscopy (LFM) was applied to discriminate the chemical functionalities and gold nanoparticles were also used to clearly identify the modified layer.

Fast heating stage for open liquid-cell atomic force microscopy

A fast heating∕cooling stage designed for use in atomic force microscope imaging in liquid media was described. The proposed configuration was assembled by calculating the heat transfer coefficient for the heating∕cooling plate and the spacer. The air gap between the cooling jacket and scanner acted as a resist for the transfer of heat to the scanner, which induced by the thermal drift, cantilever bending, and nonlinearity of image. In this system, the tapping mode was negligibly affected by thermal stress of the heating stage, compared to the contact mode.