Kichul Kim

Flexible and Transparent Gas Molecule Sensor Integrated with Sensing and Heating Graphene Layers

Graphene leading to high surface-to-volume ratio and outstanding conductivity is applied for gas molecule sensing with fully utilizing its unique transparent and flexible functionalities which cannot be expected from solid-state gas sensors. In order to attain a fast response and rapid recovering time, the flexible sensors also require integrated flexible and transparent heaters. Here, large-scale flexible and transparent gas molecule sensor devices, integrated with a graphene sensing channel and a graphene transparent heater for fast recovering operation, are demonstrated. This combined all-graphene device structure enables an overall device optical transmittance that exceeds 90% and reliable sensing performance with a bending strain of less than 1.4%. In particular, it is possible to classify the fast (≈14 s) and slow (≈95 s) response due to sp(2) -carbon bonding and disorders on graphene and the self-integrated graphene heater leads to the rapid recovery (≈11 s) of a 2 cm × 2 cm sized sensor with reproducible sensing cycles, including full recovery steps without significant signal degradation under exposure to NO2 gas.

Latin squares for parallel array access

A parallel memory system for efficient parallel array access using perfect latin squares as skewing functions is discussed. Simple construction methods for building perfect latin squares are presented. The resulting skewing scheme provides conflict free access to several important subsets of an array. The address generation can be performed in constant time with simple circuitry. The skewing scheme can provide constant time access to rows, columns, diagonals, and N/sup 1/2/*N/sup 1/2/ subarrays of an N*N array with maximum memory utilization. Self-routing Benes networks can be used to realize the permutations needed between the processing elements and the memory modules. Two skewing schemes that provide conflict free access to three-dimensional arrays are also discussed. Combined with self-routing Benes networks, these schemes provide efficient access to frequently used subsets of three-dimensional arrays. >

Perfect latin squares

Abstract We introduce new latin squares called perfect latin squares which have desirable properties for parallel array access. These squares provide conflict free access to various subsets of an n2×n2 array using n2 memory modules. We present a general construction method for building perfect latin squares of order n2 for all n. Some useful properties of the latin squares built by our construction method for parallel array access are also identified.

Facile fabrication of properties-controllable graphene sheet

Graphene has been received a considerable amount of attention as a transparent conducting electrode (TCE) which may be able to replace indium tin oxide (ITO) to overcome the significant weakness of the poor flexibility of ITO. Given that graphene is the thinnest 2-dimensional (2D) material known, it shows extremely high flexibility, and its lateral periodic honeycomb structure of sp2-bonded carbon atoms enables ~2.3% of incident light absorption per layer. However, there is a trade-off between the electrical resistance and the optical transmittance, and the fixed absorption rate in graphene limits is use when fabricating devices. Therefore, a more efficient method which continuously controls the optical and electrical properties of graphene is needed. Here, we introduce a method which controls the optical transmittance and the electrical resistance of graphene through various thicknesses of the top Cu layers with a Cu/Ni metal catalyst structure used to fabricate a planar mesh pattern of single and multi-layer graphene. We exhibit a continuous transmittance change from 85% (MLG) to 97.6% (SLG) at an incident light wavelength of 550 nm on graphene samples simultaneously grown in a CVD quartz tube. We also investigate the relationships between the sheet resistances.

Dielectric Characteristics of Pb(Zr, Ti)O3 Films on MgO Single Crystal Substrate by Terahertz Time Domain Spectroscopy

Lead zirconium titanate (PbZr0.52Ti0.48 O3 and PbZr0.30Ti0.70O3) films were prepared on MgO (100) substrate by the sol-gel method. Film Thickness, microstructure and crystalline structure of the films were investigated by scanning electron microscope (SEM) and X-ray diffraction analysis, respectively. Terahertz time-domain spectroscopy has been used to investigate the dielectric properties of ferroelectric Pb(Zr, Ti)O3 thin films in the frequency range of 0.2 to 2.0 THz.