Yeonhee Lee

Korea Advanced Institute of Science and Technology, Sŏul, Seoul, South Korea

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Publications (57)87.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Seals are traditionally used in the Far East Asia to stamp an impression on a document in place of a signature. In this study, an accuser claimed that a personal contract regarding mining development rights acquired by a defendant was devolved to the accuser because the defendant stamped the devolvement contract in the presence of the accuser and a witness. The accuser further stated that the seal ink stamped on the devolvement contract was the same as that stamped on the development rights application document. To verify this, the seals used in two documents were analyzed using micro-attenuated total reflectance Fourier transform infrared spectroscopy and infrared spectra. The findings revealed that the seals originated from different manufacturers. Thus, the accuser's claim on the existence of a devolvement contract was proved to be false.
    Journal of Forensic Sciences 05/2014; · 1.24 Impact Factor
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    ABSTRACT: For block copolymers, the chemical difference between the two blocks will result in a preferential segregation of one of the blocks to the interface, but the phase separation is only on a microscopic scale, forming micro-domain structures due to the influence of inter-segment linkages, which restricts the extent to which the phases can separate. In this study, we report the characterization of the morphology from the lower disorder–order transition diblock copolymer, polystyrene-b-poly(2-ethyl hexyl acrylate) (PS-PEHA) where the PS blocks are perdeuterated, using surface techniques. The molecular surface composition and microscopic morphology for the diblock copolymers were obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and atomic force microscopy (AFM). TOF-SIMS depth profiles of diblock copolymers showed consistently regular alternative patterns with a constant period that was the same size as the lamellar spacing structure, as determined by AFM images. Structural characterization of dPS-PEHA thin films by TOF-SIMS and AFM was also performed for different molecular weights and film thickness. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 05/2014; · 1.22 Impact Factor
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    ABSTRACT: Document authentication is one of the most important fields in forensic science and includes analysis of handwriting, seal imprint, and printed materials. In this study, we investigated intersection lines by pen inks, red stamping ink, and laser toner using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR). TOF-SIMS is very useful when the quantity of the sample is insufficient or the sample is very precious. Each ink showed specific ion peaks from inorganic species such as Al, Si, Ti, Cr, Mn, Fe, Zn, and Pb and from organic components at a mass range of m/z 200–450 in TOF-SIMS spectra. ATR FTIR results also revealed different spectra for ink and toner samples. The overlapped area of ballpoint pen writing, red sealing stamping, and laser printing in a document was investigated in order to identify the sequence of recording. The sequence relations for various cases were studied from TOF-SIMS mapping image and ATR FTIR spectra. This study indicated that TOF-SIMS and ATR FTIR are useful techniques to determine the sequence of writing and printing under question. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 04/2014; · 1.22 Impact Factor
  • Minhwa Kang, Jihye Lee, Yeonhee Lee
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    ABSTRACT: Poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and poly(styrene-b-ethyl hexylacrylate) (PS-b-PEHA) were used to investigate microphase separation in block copolymer films. Blend homopolymers were also used to compare their nanostructures on the surface with those of diblock copolymers. Atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to obtain the nanostructural information of the diblock copolymers and the blend homopolymers. The tapping mode AFM results provided information about the surface morphology, microphase-separated structure, and thickness of the films according to the annealing condition and concentration. TOF-SIMS was used to determine the lamellar nanostructures of the block copolymer films. The TOF-SIMS depth profiles demonstrate variations in the hydrogen, deuterium, carbon, oxygen, and molecular fragment ions of the block copolymer according to the depth. Accurate surface structure information on the block copolymers and blend homopolymers was obtained by the combined images of TOF-SIMS and AFM. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 04/2014; · 1.22 Impact Factor
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    ABSTRACT: Questioned documents examined in a forensic laboratory sometimes contain signatures written with ballpoint pen inks; these signatures were examined to assess the feasibility of micro-attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy as a forensic tool. Micro-ATR FTIR spectra for signatures written with 63 ballpoint pens available commercially in Korea were obtained and used to construct an FTIR spectral database. A library-searching program was utilized to identify the manufacturer, blend, and model of each black ballpoint pen ink based upon their FTIR peak intensities, positions, and patterns in the spectral database. This FTIR technique was also successfully used in determining the sequence of homogeneous line intersections from the crossing lines of two ballpoint pen signatures. We have demonstrated with a set of sample documents that micro-ATR FTIR is a viable nondestructive analytical method that can be used to identify the origin of the ballpoint pen ink used to mark signatures.
    Journal of Forensic Sciences 03/2014; · 1.24 Impact Factor
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    ABSTRACT: The compound semiconductor Cu(In,Ga)Se2 (CIGS) is well known as the next-generation solar cell material because of its high absorption coefficient for solar radiation, suitable band gap, ability to be deposited on flexible substrate materials, and producing highly flexible and lightweight solar panels. In order to improve the performance of solar cells, a quantitative and depth-resolved elemental analysis of photovoltaic thin films is strongly required. In this study, we determined the average concentration of the major elements, Cu, In, Ga, and Se in fabricated CIGS thin films, using inductively coupled plasma atomic emission spectrometry, X-ray fluorescence, and electron probe microanalysis. Depth profiling results for CIGS samples using AES, XPS, magnetic sector SIMS, and time of flight SIMS were also obtained to compare their atomic concentration results. In the SIMS technique, detection of MCs+ clusters reduced possible matrix effects because of the variant concentrations of In and Ga. The reproducibility and accuracy of quantitative analysis were investigated as a function of ion sputtering energy. The compositional distributions of CIGS absorber layers as measured by MCs+–SIMS showed good agreement with those of AES and XPS. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 03/2014; · 1.22 Impact Factor
  • Jihye Lee, Seon Hee Kim, Yeonhee Lee
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    ABSTRACT: Polycrystalline copper–indium–gallium–diselenide (CIGS) is used as an absorber in thin-film solar cells because of its appropriate band gap and high absorption coefficient for solar radiation. Many research groups have determined the CIGS compositions related to solar cell efficiency. In this work, three different Cu(In,Ga)Se2 thin films were prepared on molybdenum back contacts deposited on soda-lime glass substrates via a three-stage evaporation or, alternatively, a two-step selenized process. Surface analyses via AES, XPS, and SIMS were used to characterize the CIGS thin films and compare their depth profiles. The MCs+ clusters were detected to improve the quantification of major compositions in the CIGS thin films while suppressing the matrix effect in the SIMS depth profiles. The compositional distribution in the MCs+-SIMS was in good agreement with the AES and XPS depth profiles. The MCs+-SIMS results proved more quantitatively accurate than those from the elemental SIMS while comparing to ICP-AES data. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 03/2014; · 1.22 Impact Factor
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    ABSTRACT: An NMR method is reported for the determination of sesamin to verify the authenticity of sesame oil. The intensity of the well-resolved H2′ sesamin signal resonating at approximately 5.95 ppm is strongly correlated with the amounts of other types of vegetable oils present in the adulterated sesame oil using the relationship, y = 4.020x + 1.516 (r 2 = 0.9967). The H2′ peak intensity of sesamin was measured for sesame oil extracted directly from the mill-sourced sesame seeds because the sesame oils purchased from local markets could be adulterated. Additionally, the oils used were obtained from the seeds native to China and the Republic of Korea, because the sesamin concentrations may vary from region to region. The proposed 1H NMR method allows for the simple identification and determination of cheaper vegetable oils used as adulterants in sesame oil. High-performance liquid chromatography was used to confirm the validity of the results obtained by NMR.
    Analytical Letters 01/2014; 47(7). · 0.97 Impact Factor
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    ABSTRACT: Analytical identification of dyes in excavated textiles is an indispensable task for conservation research and restoration of ancient remains. However, excavated textiles have changed in color because of the burial environment and their centuries of burial; also, the color gradually fades after excavation. Furthermore, the low amount and limited availability of samples make it extremely difficult to identify the dyes. Therefore, in this study, non-destructive analytical instruments such as time-of-flight secondary ion mass spectrometry (TOF-SIMS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used for dye detection, and analysis results are compared. In order to compare a dye to another dye, standard samples of dyed silk were prepared using dye compounds such as curcumin, berberine, quercetin, and indigo. These samples were then analyzed with TOF-SIMS and FTIR. After the methodology to determine the dyes in the textiles was established, surface analytical techniques were also performed on three ancient textiles coming from 18th century Joseon Dynasty tombs. From the TOF-SIMS and the FTIR spectra, indigo was detected on the blue textile, and indigo and berberine were detected on the green and brown textiles. The results suggest that TOF-SIMS and FTIR are efficient and complementary non-destructive techniques for the characterization of excavated fabrics. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 01/2014; · 1.22 Impact Factor
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    ABSTRACT: A sensitive and selective colorimetric method for determination of nitrite ion in aqueous samples was developed using 1-(2-mercaptoethyl)-1, 3, 5-triazinane-2, 4, 6-trione-functionalized gold nanoparticles (MTT-GNPs). The nitrite ion seems to be used as a "molecular bridge", which can form NH---N and NH---O hydrogen bonds with the MTT-GNPs, shorten the interparticle distance, and induce the aggregation of the MTT-GNPs. This aggregation results in a dramatic change from wine-red to purple-gray color. Therefore, the concentration of nitrite ion in environmental samples can be quantitatively detected using the MTT-GNPs sensor by the naked eyes or UV-vis spectrometer. Moreover, investigations have revealed the sensitivity of the detection could be clearly improved by modulating pH of the solution, which led to a more rapid color change in the optimized GNPs system. The absorption ratios (A790/A535) of the modified GNPs solution exhibited a linear correlation with nitrite ion concentrations and the limit of detection was 1ppm. This cost effective sensing system allows for the rapid and facile determination of the concentration of [Formula: see text] ions in aqueous samples.
    Talanta 01/2014; 125:153–158. · 3.50 Impact Factor
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    ABSTRACT: The chalcopyrite semiconductor, Cu(InGa)Se2 (CIGS), is popular as an absorber material for incorporation in high-efficiency photovoltaic devices because it has an appropriate band gap and a high absorption coefficient. To improve the efficiency of solar cells, many research groups have studied the quantitative characterization of the CIGS absorber layers. In this study, a compositional analysis of a CIGS thin film was performed by depth profiling in secondary ion mass spectrometry (SIMS) with MCs+ (where M denotes an element from the CIGS sample) cluster ion detection, and the relative sensitivity factor of the cluster ion was calculated. The emission of MCs+ ions from CIGS absorber elements, such as Cu, In, Ga, and Se, under Cs+ ion bombardment was investigated using time-of-flight SIMS (TOF-SIMS) and magnetic sector SIMS. The detection of MCs+ ions suppressed the matrix effects of varying concentrations of constituent elements of the CIGS thin films. The atomic concentrations of the CIGS absorber layers from the MCs+-SIMS exhibited more accurate quantification compared to those of elemental SIMS and agreed with those of inductively coupled plasma atomic emission spectrometry. Both TOF-SIMS and magnetic sector SIMS depth profiles showed a similar MCs+ distribution for the CIGS thin films.
    Applied Physics A 10/2013; · 1.69 Impact Factor
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    ABSTRACT: We investigate the dynamics and the mechanism of flame retardants in polycarbonate matrices to explore for a way of designing efficient and environment-friendly flame retardants. The high phosphorous content of organic phosphates has been considered as a requirement for efficient flame retardants. We show, however, that one can enhance the efficiency of flame retardants even with a relatively low phosphorous content by tuning the dynamics and the intermolecular interactions of flame retardants. This would enable one to design bulkier flame retardants that should be less volatile and less harmful in indoor environments. UL94 flammability tests indicate that even though the phosphorous content of 2,4-di-tert-butylphenyl diphenyl phosphate (DDP) is much smaller with two bulky tertiary butyl groups than that of triphenyl phosphate (TPP), DDP should be as efficient a flame retardant as TPP, which is a widely-used flame retardant. On the other hand, the 2-tert-butylphenyl diphenyl phosphate (2-tBuDP), with a less phosphorous content than TPP but with a more phosphorous content than DDP, is less efficient as a flame retardant than both DDP and TPP. Dynamic secondary ion mass spectrometry and molecular dynamics simulations reveal that the diffusion of DDP is slower by an order of magnitude at low temperature than that of TPP but becomes comparable to that of TPP at ignition temperature. This implies that DDP should be much less volatile than TPP at low temperature, which is confirmed by thermogravimetric analysis. We also find from Fourier transform infrared spectroscopy that Fries rearrangement and char formation are suppressed more by DDP than by TPP. The low volatility and the suppressed char formation of DDP suggest that the enhanced flame retardancy of DDP should be attributed to its slow diffusivity at room temperature and yet sufficiently high diffusivity at high temperature.
    The Journal of Physical Chemistry B 06/2013; · 3.61 Impact Factor
  • Materials. 05/2013; 6(5):2007-2025.
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    ABSTRACT: The inverse-micellar preparation of Si nanoparticles (Nps) was improved by utilizing sodium naphthalide. The Si Nps were subsequently functionalized with 4-vinylbenzoic acid for their attachment onto TiO(2) films of dye-sensitized solar cells (DSSCs). The average diameter of the COOH-functionalized Si (Si-COOH) Nps was 4.6(±1.7) nm. Depth profiling by secondary-ion mass spectrometry revealed that the Si Nps were uniformly attached onto the TiO(2) films. The number of Ru(II) dye molecules adsorbed onto a TiO(2) film that was treated with the Si-COOH Nps was 42 % higher than that on the untreated TiO(2) film. As a result, DSSCs that incorporated the Si-COOH Nps exhibited higher short-circuit photocurrent density and an overall energy-conversion efficiency than the untreated DSSCs by 22 % and 27 %, respectively. This enhanced performance, mostly owing to the intramolecular charge-transfer to TiO(2) from the dye molecules that were anchored to the Si-COOH Nps, was confirmed by comparing the performance with two different Ru(II) -bipyridine dyes (N719 and N749).
    Chemistry - An Asian Journal 03/2012; 7(7):1624-9. · 4.57 Impact Factor
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    ABSTRACT: Some cosmetic products manufactured in Korea for the treatment of eczema, seborrhea and psoriasis have been suspected to contain anti-inflammatory corticosteroids such as prednisolone, hydrocortisone, betamethasone, dexamethasone and triamcinolone acetonide without these ingredients being indicated on the label. Due to their severe side effects such as permenent skin atopy, these corticosteroids have to be monitored in cosmetic products from a forensic point of view. Many cosmetic product samples (N=65) have been collected from both local and online markets in Korea. The corticosteroid content of these samples was analyzed by LC-MS/MS with diagnostic ions (m/z). Linearity was studied with 0.1-10 μg/mL range in all corticosteroids. Good correlation coefficients (r(2)≥0.997) were found and the limits of quantification were 4.68-7.97 ng/mL for each of the corticosteroids. At three different concentrations spanning the linear dynamic ranges, mean recoveries were 97.2-113.5%and precisions (RSD) for intra-day and inter-day analysis were less than 8.9%. Also, accuracy (Bias %) was less than 11.8%. The results showed that between 0.76-0.94 μg/g levels of prednisolone were detected in four cosmetic products and triamcinolone acetonidewas detected with a concentration in the range of 11.5-272 μg/g in nine samples. This fact reveals that some manufacturers have arbitrarily added these corticosteroids in their cosmetic products without indicating them on the label. Thus, these cosmetic products have to be monitored and if proven illegal preparations removed from the market.
    Forensic science international 01/2012; 220(1-3):e23-8. · 2.10 Impact Factor
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    ABSTRACT: In the title compound, C(22)H(21)ClO(2), the oxolane ring adopts a twisted conformation. The dihedral angles between the mean plane of the oxolane ring and the mean planes of the 4-chloro-phenyl, phenyl and cyclo-pentenyl rings are 71.81 (18), 76.9 (18) and 82.08 (18)°, respectively.
    Acta Crystallographica Section E Structure Reports Online 01/2012; 68(Pt 1):o45. · 0.35 Impact Factor
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    ABSTRACT: Within the field of archeology, textile research is of growing interest because of its potential to provide relevant information regarding either the development or the technological advancement of ancient populations or the socio-economic and religious purposes of textile production. It is of paramount importance in cultural heritage research to use non-destructive techniques. Therefore, dye analyses were performed using two non-destructive methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and Fourier transform infrared spectroscopy (FT-IR). In order to build a database, standard samples of dyed silk were prepared using several natural dye compounds; these samples were then analyzed with FT-IR and TOF-SIMS. Afterwards, spectroscopic analyses were carried out on five textile fragments coming from the 16th to the 18th century Korean tombs. FT-IR and TOF-SIMS spectra allowed the identification of fiber of the archeological textiles, making it possible to distinguish between the cotton and silk fibers. Furthermore, it was possible to identify indigo in three blue fabrics and to show its presence in a green textile. The results suggest that FT-IR and TOF-SIMS are two efficient and very helpful techniques for the characterization of excavated fabrics.
    Surface and Interface Analysis 01/2012; · 1.22 Impact Factor
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    ABSTRACT: The morphology from symmetric diblock copolymers of poly(styrene-b-propylmethacrylate) (PS-PPrMA), where polystyrene (PS) block was perdeuterated near the copolymer/air and copolymer/substrate interfaces and in the bulk, was characterized by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Elemental depth profiles measured in the negative ion mode by a Cs+ primary ion beam demonstrate variations in hydrogen, deuterium, carbon, oxygen and hydrocarbons within the diblock copolymer according to the depth. The annealed deuterated poly(styrene-b-propylmethacrylate) (dPS-PPrMA) copolymer samples showed a decrease in the deuterated PS secondary ion peak intensity as compared to the as-cast samples. TOF-SIMS depth profiling was obtained for the lamellar morphology of dPS-PPrMA which is found to orient parallel to the surface of the substrate. This preferential orientation resulted in a periodic variation in the composition of each block that continued through the entire copolymer film with thickness of 700 and 2100 Å. Temperature-dependent annealing studies on dPS-PPrMA thin film on the silicon substrates were performed to investigate the lower critical ordering transition (LCOT) properties of diblock copolymers. Copyright © 2010 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 12/2010; 43(1‐2):277 - 280. · 1.22 Impact Factor
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    ABSTRACT: A surface-induced orientation of symmetric, deuterated polystyrene/poly(propyl methacrylate) diblock copolymers, dPS-PPrMA with different molecular weights (Mn = 135 000, 119 600, and 75 300) was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Elemental depth profiles obtained in the negative ion mode by a Cs+ primary ion beam demonstrate variations in hydrogen, deuterium, carbon, oxygen, and hydrocarbons within the diblock copolymer according to the depth. Solution casting films of the copolymers with thicknesses of 700 and 2100 Å exhibited no preferential orientation of the microdomain morphology with respect to the surface at room temperature. Annealing the copolymer films at 215 °C for 4 h produced a dramatic orientation of the microdomains parallel to the surface of the film. This preferential alignment provided regular oscillation in the composition of both blocks, which continued through the entire film. The periodicity as determined from a depth profile of TOF-SIMS showed good agreement with the results of small-angle X-ray scattering. Positive and negative ion molecular depth profiles by a C60+ cluster ion beam also provide information pertaining to the lower disorder–order transition (LDOT) behavior of the dPS-PPrMA copolymer. Depth profile results indicate a PPrMA layer preferentially located at the copolymer/silicon substrate interface. The microdomain separation processes of dPS-PPrMA were investigated as a function of the annealing temperature and time. Copyright © 2010 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 07/2010; 42(8):1409 - 1416. · 1.22 Impact Factor
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    ABSTRACT: Red seal inks from Korea (6), Japan (1) and China (6) were studied to investigate the feasibility of micro-attenuated total reflectance (ATR) FTIR spectroscopy as a tool in the forensic study of questioned documents involving seal inks. The technique was able to differentiate red seal inks of similar colors and different manufacturers. Blind testing has shown that micro-ATR FTIR can identify the origin of the red seal inks with accuracy. Data gathered were converted to a database for future reference. Also, the technique was also successful in determining the sequence of heterogeneous line intersection from a personal seal and a ballpoint pen. The results show that micro-ATR FTIR can be a valuable non-destructive tool for the objective analysis of questioned documents involving different red seal inks.
    Forensic science international 06/2010; 199(1-3):6-8. · 2.10 Impact Factor

Publication Stats

179 Citations
87.49 Total Impact Points

Institutions

  • 2012–2014
    • Korea Advanced Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 1997–2014
    • Korea Institute of Science and Technology
      • Advanced Analysis Center
      Sŏul, Seoul, South Korea
  • 2002–2012
    • Korea University
      • Department of Chemistry
      Seoul, Seoul, South Korea