Copyright (c) 2011 All rights reserved. http://works.bepress.com/byung_kim Recent documents in Byung I. Kim en-us Wed, 07 Dec 2011 01:40:44 PST 3600 http://works.bepress.com/byung_kim/8 http://works.bepress.com/byung_kim/8 Mon, 05 Dec 2011 15:48:35 PST We observed remarkable oscillatory forces with amplitude of 60-90 nN and periodicity of 3–4 water molecule diameters in an ambient environment between two silicon surfaces as the tip-sample distance decreased using the cantilever-based optical interfacial force microscope with lateral modulation. As the humidity increased, the oscillatory forces changed from being large at lower relative humidities, below 40%, to progressively becoming smaller as the humidity went higher than 40%. The frequency of oscillatory forces increased with the existence of lateral tip-modulation and with the slower approaching tip-speed. Its starting point distance has been found to originate from the topographic water structure.

]]> Byung I. Kim et al. http://works.bepress.com/byung_kim/7 http://works.bepress.com/byung_kim/7 Mon, 05 Dec 2011 15:48:33 PST An asymmetric planar molecule, 4-trans-2-(pyrid-4-yl-vynyl) benzoic acid (PVBA), has been used to establish the organic chiral recognition on fcc(111) metal surfaces. The strong correlation between the orientation and chiral recognition of PVBA on both Ag(111) and Pd(111) guides the choice of a model potential, which determines the relative binding energy of PVBA on fcc(111). An angle-dependent calculation of relative binding energy reproduces the experimental observation of the chiral recognition of PVBA on Ag(111) but not on Pd(111).

]]> Byung I. Kim http://works.bepress.com/byung_kim/6 http://works.bepress.com/byung_kim/6 Mon, 05 Dec 2011 15:48:30 PST The search for an ideal magnetic semiconductor with tunable ferromagnetic behaviour over a wide range of doping or by electrical gating is being actively pursued as a major step towards realizing spin electronics. A magnetic semiconductor having a high Curie temperature, capable of independently controlled carrier density and magnetic doping, is crucial for developing spin-based multifunctional devices. Cr-doped In₂O₃ is such a unique system, where the electrical and magnetic behaviour—from ferromagnetic metal-like to ferromagnetic semiconducting to paramagnetic insulator—can be controllably tuned by the defect concentration. An explicit dependence of magnetic interaction leading to ferromagnetism on the carrier density is shown. A carrier-density-dependent high Curie temperature of 850–930 K has been measured, in addition to the observation of clear magnetic domain structures in these films. Being optically transparent with the above optimal properties, Cr-doped In₂O₃ emerges as a viable candidate for the development of spin electronics.

]]> Alex Punnoose et al. http://works.bepress.com/byung_kim/5 http://works.bepress.com/byung_kim/5 Mon, 05 Dec 2011 15:48:27 PST Long-term stability of plasmid DNA (pDNA) conformations is critical in many research areas, especially those concerning future gene therapy. Despite its importance, the time-evolution of pDNA structures has rarely been studied at a molecular resolution. Here, the time-evolution of pDNA solutions spanning four years was observed with atomic force microscopy (AFM). The AFM data show that the pDNA molecules changed over time from isolated supercoiled structures, to aggregated supercoiled structures, to thin, branched network structures, and finally to wider, branched network structures. Additional topographical analysis of the AFM data suggests that the actions of residual proteins could be the main mechanism for the structural changes in our laboratory-prepared pDNA.

]]> Byung I. Kim et al. http://works.bepress.com/byung_kim/4 http://works.bepress.com/byung_kim/4 Wed, 17 Aug 2011 13:06:33 PDT We measured normal and friction forces simultaneously using a recently developed cantilever-based optical interfacial force microscope (COIFM) technique for studies of interfacial structures and mechanical properties of nanoscale materials. We derived how the forces can be incorporated into the detection signal using the classical Euler equation for beams. A lateral modulation with the amplitude of one nanometers was applied to create the friction forces between tip and sample. We demonstrated its capability by measuring normal and friction forces of interfacial water at the molecular scale over all distance ranges.

]]> Byung I. Kim et al. http://works.bepress.com/byung_kim/3 http://works.bepress.com/byung_kim/3 Mon, 06 Jul 2009 14:24:10 PDT We developed a cantilever based optical interfacial force microscopy (COIFM) that employs a microactuated silicon cantilever and optical detection method to establish the measurement of the single molecular interactions using the force feedback technique. Through the direct measurement of the COIFM force-distance curves, we have demonstrated that the COIFM is capable of unveiling structural and mechanical information on interfacial water at the single molecular level over all distances between two hydrophilic surfaces.

]]> Jeremy R. Bonander et al. http://works.bepress.com/byung_kim/1 http://works.bepress.com/byung_kim/1 Mon, 06 Jul 2009 14:24:09 PDT Separation of topographic features from magnetic images has been an issue for the past two decades in magnetic force microscopy (MFM). The frequent pickups of the topographic features are interpreted as transitions of the tip between bistable states of the tip-sample assembly in the noncontact and tapping regions. MFM using electrostatic force modulation demonstrates the separation of the topographic features from the magnetic images by removing the tapping state from the bistable states through the introduction of a capacitive coupling.

]]> Byung K. Kim http://works.bepress.com/byung_kim/2 http://works.bepress.com/byung_kim/2 Mon, 06 Jul 2009 14:24:09 PDT I have demonstrated the advantage of the phase locked oscillator (PLO) over the conventional direct resonance oscillator (DRO) in noncontact mode atomic force microscopy (AFM) under ultrahigh vacuum. Direct comparison between PLO and DRO has been made in terms of background noise level, temporal response, and stability. Compared to the DRO method without phase coherence, the experimental results show that the PLO method is more effective in reducing the noise level and enhancing the stability over all force regimes in UHV noncontact AFM. The noise reduction and stability enhancement in PLO indicate the important role of the phase coherent effect in improving the capability of noncontact imaging in UHV.

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