Kyung Ho Kim

Uniform Graphene Quantum Dots Patterned from Self-Assembled Silica Nanodots

Graphene dots precisely controlled in size are interesting in nanoelectronics due to their quantum optical and electrical properties. However, most graphene quantum dot (GQD) research so far has been performed based on flake-type graphene reduced from graphene oxides. Consequently, it is extremely difficult to isolate the size effect of GQDs from the measured optical properties. Here, we report the size-controlled fabrication of uniform GQDs using self-assembled block copolymer (BCP) as an etch mask on graphene films grown by chemical vapor deposition (CVD). Electron microscope images show that as-prepared GQDs are composed of mono- or bilayer graphene with diameters of 10 and 20 nm, corresponding to the size of BCP nanospheres. In the measured photoluminescence (PL) spectra, the emission peak of the GQDs on the SiO(2) substrate is shown to be at ∼395 nm. The fabrication of GQDs was supported by the analysis of the Raman spectra and the observation of PL spectra after each fabrication step. Additionally, oxygen content in the GQDs is rationally controlled by additional air plasma treatment, which reveals the effect of oxygen content to the PL property.

Whole device printing for full colour displays with organic light emitting diodes

Whole device printing is presented for realizing full colour displays with red (R), green (G) and blue (B) organic light emitting diodes (OLEDs). In this process, the whole OLED structure is transferred from a patterned mould to a glass substrate. Therefore, a simple step and repeat of the transfer of each of R, G and B OLED for RGB pixels completes the fabrication of the full colour display over a given area. A difference in the work of adhesion at two interfaces enables the transfer. A rigiflex mould is used for the printing. It is rigid enough to allow sub-100 nm resolution and yet flexible enough for intimate contact with the glass substrate, which permits large area application.

Migration of neutrophils targeting amyloid plaques in Alzheimer's disease mouse model

Immune responses in the brain are thought to play a role in disorders of the central nervous system, but an understanding of the process underlying how immune cells get into the brain and their fate there remains unclear. In this study, we used a 2-photon microscopy to reveal that neutrophils infiltrate brain and migrate toward amyloid plaques in a mouse model of Alzheimers disease. These findings suggest a new molecular process underlying the pathophysiology of Alzheimers disease.

Quantitative atomic force measurement with a quartz tuning fork

The authors demonstrate a simple yet robust method for quantitative measurement of dynamic atomic force using the quartz tuning fork for both electrically driven mode and mechanically driven mode. It is shown that both modes can be made fully equivalent and also allow accurate force measurement. The quartz tuning fork is now expected to be widely employed as a quantitative force measurement probe in addition to its capability to surface image in the atomic scale.

Solution-based formation of multilayers of small molecules for organic light emitting diodes

We developed an approach for fabricating small molecule organic light emitting diodes by solution-based processing. The approach involves dissolving a small molecule organic in a solvent, spin coating it on a mold, and then transferring the layer onto the existing organic layer on a substrate. This ability to form multilayers of small molecule organics allows one to take advantage of both the efficiency offered by the multilayer structures and the low cost fabrication made possible by the solution processing.

Alternative to pentacene patterning for organic thin film transistor

A method is presented for patterning the pentacene active layer of organic thin film transistor. The method involves forming a metal pattern on a gate dielectric surface by transfer patterning, depositing pentacene over the whole surface, and then lifting off a bilayer of pentacene on the metal with a flat elastomeric mold. Compared with the method of direct pentacene transfer reported earlier [S. Y. Park, T. Kwon, and H. H. Lee, Adv. Mater. (Weinheim, Ger.) 18, 1861 (2006)], this alternative allows one to choose a surface for larger pentacene grain size and eliminates a high off-current associated with the direct transfer method. The rigid nature of a rigiflex mold allows the pentacene pattern size to be defined in submicrometer range and the flexible nature of rigiflex and elastomeric molds permits large area application.

Host-Guest Self-assembly in Block Copolymer Blends

Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their limited thin film morphologies. Here, we report that unusual and spontaneous positioning between host and guest BCP microdomains, even in the absence of H-bond linkages, can create hybridized morphologies that cannot be formed from a neat BCP. Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology. As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated. These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

Global changes of phospholipids identified by MALDI imaging mass spectrometry in a mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia; however, at the present time there is no disease-modifying drug for AD. There is increasing evidence supporting the role of lipid changes in the process of normal cognitive aging and in the etiology of age-related neurodegenerative diseases. AD is characterized by the presence of intraneuronal protein clusters and extracellular aggregates of β-amyloid (Aβ). Disrupted Aβ kinetics may activate intracellular signaling pathways, including tau hyperphosphorylation and proinflammatory pathways. We analyzed and visualized the lipid profiles of mouse brains using MALDI-TOF MS. Direct tissue analysis by MALDI-TOF imaging MS (IMS) can determine the relative abundance and spatial distribution of specific lipids in different tissues. We used 5XFAD mice that almost exclusively generate and rapidly accumulate massive cerebral levels of Aβ-42 (1). Our data showed changes in lipid distribution in the mouse frontal cortex, hippocampus, and subiculum, where Aβ plaques are first generated in AD. Our results suggest that MALDI-IMS is a powerful tool for analyzing the distribution of various phospholipids and that this application might provide novel insight into the prediction of disease.

Thrombospondin-1 prevents amyloid beta-mediated synaptic pathology in Alzheimer's disease.

Alzheimers disease (AD) is characterized by impaired cognitive function and memory loss, which are often the result of synaptic pathology. Thrombospondin (TSP) is an astrocyte-secreted protein, well known for its function as a modulator of synaptogenesis and neurogenesis. Here, we investigated the effects of TSP-1 on AD pathogenesis. We found that the level of TSP-1 expression was decreased in AD brains. When we treated astrocytes with amyloid beta (Aβ), secreted TSP-1 was decreased in autophagy-dependent manner. In addition, treatment with Aβ induced synaptic pathology, such as decreased dendritic spine density and reduced synaptic activity. These effects were prevented by coincubation of TSP-1 with Aβ, which acts through the TSP-1 receptor alpha-2-delta-1 in neurons. Finally, intrasubicular injection with TSP-1 into AD model mouse brains mitigated the Aβ-mediated reduction of synaptic proteins and related signaling pathways. These results indicate that TSP-1 is a potential therapeutic target in AD pathogenesis.

Shear-mode magnetic force microscopy with a quartz tuning fork in ambient conditions

We have demonstrated high-resolution shear-mode magnetic force microscopy (MFM) using a quartz tuning fork in ambient conditions. A commercial magnetic cantilever tip was attached to one prong of the tuning fork to realize shear-mode MFM operation. We have obtained MFM images with a spatial resolution of less than 100xa0nm and demonstrated a frequency resolution of ∼1xa0mHz, values which are achieved by phase shift detection methods.