• Bulletin of the Korean Chemical Society
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• v.32 no.spc8
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• pp.2941-2948
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• 2011

A nanogap formed by a metal nanoparticle and a flat metal substrate is one kind of "hot site" for surface-enhanced Raman scattering (SERS). The characteristics of a typical nanogap formed by a planar Au and either an Au and Ag nanoparticle have been well studied using 4-aminobenzenethiol (4-ABT) as a probe. 4-ABT is, however, an unusual molecule in the sense that its SERS spectral feature is dependent not only on the kinds of SERS substrates but also on the measurement conditions; thus further characterization is required using other adsorbate molecules such as 1,4-phenylenediisocyanide (1,4-PDI). In fact, no Raman signal was observable when 1,4-PDI was selfassembled on a flat Au substrate, but a distinct spectrum was obtained when 60 nm-sized Au or Ag nanoparticles were adsorbed on the pendent -NC groups of 1,4-PDI. This is definitely due to the electromagnetic coupling between the localized surface plasmon of Au or Ag nanoparticle with the surface plasmon polariton of the planar Au substrate, allowing an intense electric field to be induced in the gap between them. A higher Raman signal was observed when Ag nanoparticles were attached to 1,4-PDI, irrespective of the excitation wavelength, and especially the highest Raman signal was measured at the 632.8 nm excitation (with the enhancement factor on the order of ${\sim}10^3$), followed by the excitation at 568 and 514.5 nm, in agreement with the finite-difference timedomain calculation. From a separate potential-dependent SERS study, the voltage applied to the planar Au appeared to be transmitted without loss to the Au or Ag nanoparticles, and from the study of the effect of volatile organics, the voltage transmission from Au or Ag nanoparticles to the planar Au also appeared as equally probable to that from the planar Au to the Au or Ag nanoparticles in a nanogap electrode. The response of the Au-Ag nanogap to the external stimuli was, however, not the same as that of the Au-Au nanogap.

• Nuclear Engineering and Technology
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• v.44 no.8
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• pp.971-976
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• 2012

Silica-coated Au with Ag, Co, Cu, and Ir bimetallic radioisotope nanoparticles were synthesized by neutron irradiation, after coating $SiO_2$ onto the bimetallic particles by the sol-gel St$\ddot{o}$ber process. Bimetallic nanoparticles were synthesized by irradiating aqueous bimetallic ions at room temperature. Their shell and core diameters were recorded by TEM to be 100 - 112 nm and 20 - 50 nm, respectively. The bimetallic radioisotope nanoparticles' gamma spectra showed that they each contained two gamma-emitting nuclides. The nanoparticles could be used as radiotracers in petrochemical and refinery processes that involve temperatures that would decompose conventional organic radioactive labels.

• Journal of the Korean Chemical Society
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• v.57 no.5
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• pp.618-624
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• 2013

We demonstrated unique inter- and intra-plasmonic coupling effects in bimetallic Au@Ag core-shell NP arrays which are regularly or randomly arranged on self-assembled block copolymer (BCP) inverse micelle monolayers. Polyvinylpyrrolidone (PVP)-stabilized Au@Ag core-shell NP arrays in regular or disordered configuration were incorporated and assembled on reconstructed PS-b-P4VP inverse micelle templates through two types of processes. The intensively enhanced LSPR coupling properties of individual and assembled Au@Ag NPs were evaluated by UV-visible spectroscopy in terms of the type of ligand stabilizer, coupling between Au and Ag, thickness of Ag shell, and type of array configuration. Finally, Au@Ag core-shell NP arrays were employed as active substrates for surface enhanced Raman spectroscopy (SERS) and a significantly enhanced signal enhancement was observed in accordance with the coupling intensity of Au@Ag NPs patterns.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.365-369
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• 2018

We perform density functional theory calculations to study the CO and $O_2$ adsorption chemistry of Pt@X core@shell bimetallic nanoparticles (X = Pd, Rh, Ru, Au, or Ag). To prevent CO-poisoning of Pt nanoparticles, we introduce a Pt@X core-shell nanoparticle model that is composed of exposed surface sites of Pt and facets of X alloying element. We find that Pt@Pd, Pt@Rh, Pt@Ru, and Pt@Ag nanoparticles spatially bind CO and $O_2$, separately, on Pt and X, respectively. Particularly, Pt@Ag nanoparticles show the most well-balanced CO and $O_2$ binding energy values, which are required for facile CO oxidation. On the other hand, the $O_2$ binding energies of Pt@Pd, Pt@Ru, and Pt@Rh nanoparticles are too strong to catalyze further CO oxidation because of the strong oxygen affinity of Pd, Ru, and Rh. The Au shell of Pt@Au nanoparticles preferentially bond CO rather than $O_2$. From a catalysis design perspective, we believe that Pt@Ag is a better-performing Pt-based CO-tolerant CO oxidation catalyst.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.209-209
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• 2010

금(Au) 또는 은(Ag) 금속 나노입자의 모양, 크기, 분포 상태를 조절하여 가시광선과 적외선, 자외선 영역에서 강한 표면 플라즈몬 효과을 이용할 수 있는데, 최근 이러한 금속 나노입자의 표면플라즈몬 효과를 이용하여 태양광 소자의 성능을 향상시키는 연구가 매우 활발하게 이루어지고 있다. 그 중, 높은 효율과 낮은 제작비용 그리고 간단한 공정과정의 장점을 갖고 있어서 크게 주목 받고 있는 염료감응태양전지에서도 금(Au) 또는 은(Ag) 금속 나노입자을 이용하기 위한 많은 연구가 진행되고 있다. 그 예로, Au가 코팅된 $TiO_2$ 기반의 염료감응태양전지구조를 제작하여, 입사된 빛이 표면플라즈몬 효과를 통해, Au에서 여기된 전자들이 Au/$TiO_2$ 사에의 schottky 장벽을 통과하여 $TiO_2$의 전도대 전자들의 밀도가 증가하여, charge carrier generating rate을 높여 소자의 광변환 효율의 향상을 증명하였다. 이에 본 연구에서는, $TiO_2$보다 높은 전자 이동도(mobility)와 직선통로(direct path way)의 장점을 갖고 있는 ZnO nanorod에서의 charge carrier generating rate을 높일 수 있도록, 비교적 가격이 저렴한 Ag nanoparticle을 코팅하였다. ZnO nanorod 제작은 낮은 온도에서 간단하게 성장시킬 수 있는 hydrothermal 방법을 이용하였다. 기판위에 RF magnetron 스퍼터를 이용하여 AZO seed layer를 증착한 후, zinc nitrate $Zn(NO_3)_2{\cdot}6H_2O$과 hexamethylentetramines (HMT)으로 혼합된 용액을 사용해 ZnO nanorods를 성장시켰다. 이 후, Ag를 형성할 수 있도록 열증기증착법을 이용하여 코팅하였다. Ag의 증착시간에 따른 ZnO nanorods에서의 코팅된 구조와 형태를 관찰하기 위해 field emission scanning electron microscopy (FE-SEM)을 이용하여 측정하였으며, 결정성을 조사하기 위해 X-ray diffraction (XRD)을 이용하여 분석하였다. 또한 입사된 빛에 의해, 여기된 ZnO 전도대 전자들이 다시 재결합을 통해 방출되는 photoluminescence 양을 scanning PL 장비를 통해 측정하여 Ag가 코팅된 ZnO nanorod의 광특성을 분석하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.9.1-9.1
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• 2011

나노입자는 벌크에 비해 월등히 큰 비표면적(surface-to-volume ratio)과 작은 사이즈에서 오는 양자효과로 인해 촉매나 나노 전자 소자 등 여러 분야에서 응용되고 있다. 특히 백금 나노입자는 수소나 메탄올의 산화, 산소환원 반응의 독보적인 촉매로서 연료전지의 산화극과 환원극의 촉매로 널리 활용되고 있다. 본 연구에서는 높은 가격의 백금의 사용량을 줄일 수 있는 합금 나노입자 촉매에 대한 연구의 일환으로 Pd, Au, Cu, Ag 등의 원소를 활용한 합금 나노입자에 대한 구조 및 열역학적 안정성에 대한 연구를 수행하였다. 다양한 합금에 대한 원자간 포텐셜을 개발하였고, 이를 기반으로 몬테카를로 및 분자동력학 시뮬레이션을 수행하여 Pd-Pt, Cu-Pt, Ag-Pt, Au-Pt 이원계 합금 나노입자의 다양한 원자 구조 및 형상에 따른 결합에너지와 열역학적 특성에 대하여 분석하였다.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.69-75
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• 2008

Tautomerism of pyrimidine base cytosine has been comparatively examined on nanoparticle and roughened plate surfaces of silver, gold, and copper by surface-enhanced Raman scattering (SERS). The SERS spectrum was found to be different depending on the metals and their substrate conditions suggesting the dissimilar population of various tautomers of cytosine on the surfaces. The ab initio calculations were performed at the levels of B3LYP, HF, and MP2 levels of theory with the LanL2DZ basis set to estimate the energetic stability of the tautomers with the metal complexes as well as the gas phase state. The amino group and N3-coordinated tautomer was predicted to be more favorable for bonding to Au, whereas the hydroxyl and N1-coordinated zwitter ionic form is most stable with Ag and Cu as a bidentate form from the DFT calculation. The binding energy with the Ag atom is calculated to be smaller than those with the Au and Cu atoms in line with the temperature-dependent SERS spectra of cytosine.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.300-306
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• 2011

We report the surface distribution of metal (Ag, Au) nanoparticles grown on polarity-patterned ferroelectric substrates by photochemical reaction. Single crystal periodically polarity-patterned $LiNbO_3$(PPLN) was used as a ferroelectric substrate. The nanoparticles were grown by ultra-violet (UV) light exposure of the PPLN in the aqueous solutions including metas. The surface distribution of the grown nanoparticles were measured by atomic force microscopy and identification of the orientation of the polarity of the ferroelectric surface was performed by piezoelectric force microscopy. The Ag- and Au-nanoparticles grown on +z polarity regions are larger and denser than that on -z polarity regions. In particlur, the largest and denser Ag-nanoparticles were grwon on the polarity boundary regions of the PPLN while Au-nanoparticles were not specifically grown on the boundary regions. Thus, we found that the size and position of metal nanoparticles grown on ferroelectric surfaces can be controlled by UV-exposure time and polarity pattern structures. Also, we discuss the difference of the surface distribution of the metal nano-particles depending on the polarity of the ferroelectric surfaces in terms of surface band structures, reduced work fucntion, and inhomogeneous electric field distribution.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.126-126
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• 2011

수직으로 정렬된 1차원 ZnO nanorod arrays (NRAs)는 효율적인 반사방지 특성의 기하학적 구조를 갖고 있어, 크기와 모양 그리고 정렬형태의 다양한 설계를 통해 빛의 흡수율과 광 추출효율을 증가시켜 광전소자 및 태양광 소자의 성능을 향상시킬 수 있으며, 최근 이러한 연구에 대한 관심이 집중되고 있다. 본 연구에서는 ZnO NRAs의 넓은 표면적과 불연속적인 독특한 표면을 활용하여 광학적 특성을 효과적으로 개선하였다. 실험을 위해, thermal evaporator를 사용하여 Au와 Ag 그리고 e-beam evaporator를 사용하여 $SiO_2$를 ZnO NRAs 표면에 여러 가지 조건으로 증착하여, 독특한 계층 나노구조의 형성과 광학적 특성을 관찰하였다. 표면 roughness가 큰 FTO/glass 위에 수열합성법을 통해 끝이 뾰족하고, 비스듬히 정렬된 ZnO nano-tip array에 Au를 증착할 경우 ZnO/Au core/shell 구조가 형성되며, Au의 광 흡수율이 매우 크게 증가함을 관찰할 수 있었다. 반면 flat한 표면위에 빽빽하게 수직으로 정렬된 ZnO NRAs를 성장시켜 그 위에 Ag를 증착할 경우, evaporated Ag flux가 ZnO nanorod의 사이에 scattered 되어 ZnO nanorod 기둥의 측면에 직경이 50 nm 이하인 nanoparticles이 decorated 되어 국소표면플라즈몬 현상이 관찰되었으며, 이러한 효과를 통해 입사되는 빛의 흡수율을 효과적으로 증가시킬 수 있었다. 또한, ZnO NRAs의 표면에 $SiO_2$를 e-beam evaporator를 이용하여 증착할 경우, 자연적으로 vapor flux와 ZnO nanorod 사이에 oblique angle이 $80^{\circ}$ 이상으로 증가하여 $SiO_2$ nanorods가 자발적으로 형성되어 ZnO/$SiO_2$ branch 계층형태의 나노구조를 제작할 수 있었다. 이러한 구조는 유효 graded refractive index profile로 인해 기존의 ZnO NRAs보다 개선된 반사방지 특성을 나타냈다. 이러한 계층 나노구조의 광학적 특성을 시뮬레이션을 통해 이론적으로 분석을 통해 광전자 소자의 성능의 개선에 대한 적용 가능성을 조사하였다.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.625-628
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• 2012

We investigated the interaction between polyynes (linear carbon chains) and various metal nanoparticles (Ag, Au, and Cu) to provide insight into the optical properties of metal-polyynes systems prepared by different experimental techniques. Polyynes were produced by laser ablation in deionized water, metal nanoparticles solutions, and copper chloride solution. Metal nanoparticles complexes with polyynes were analyzed by Raman, surface-enhanced Raman scattering, and UV-vis spectroscopy.