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Chan DPC, Wong NS, Wong HTH, Lee S, Lee SS. Impact of influenza A (H3N2) seasonal outbreak on the pattern of vaccination uptake in healthcare workers. J Hosp Infect 2015; 90:354-5. [PMID: 26054565 PMCID: PMC7134442 DOI: 10.1016/j.jhin.2015.04.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Accepted: 04/30/2015] [Indexed: 11/26/2022]
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Thompson MA, Lee SS, Seegmiller J, McGowan CP. Kinematic and kinetic comparison of barefoot and shod running in mid/forefoot and rearfoot strike runners. Gait Posture 2015; 41:957-9. [PMID: 25827681 DOI: 10.1016/j.gaitpost.2015.03.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Revised: 03/02/2015] [Accepted: 03/03/2015] [Indexed: 02/02/2023]
Abstract
Barefoot running has been associated with decreased stride length and switching from a rearfoot strike (RFS) pattern to a mid/forefoot strike (M/FFS) pattern. However, some individuals naturally contact the ground on their mid/forefoot, even when wearing cushioned running shoes. The purpose of this study was to determine if the mechanics of barefoot running by natural shod RFS runners differed from natural shod M/FFS runners. Twenty habitually shod runners (ten natural M/FFS and ten natural RFS) participated in this study. Three-dimensional motion analysis and ground reaction force data were captured as subjects ran at their preferred running speed in both barefoot and shod conditions. M/FFS experienced only a decrease in stride length when switching from shod to barefoot running. Whereas, when switching from shod to barefoot running, RFS individuals experienced a decrease in stride length, switched to a plantarflexed position at ground contact and saw reduced impact peak magnitudes. These results suggest that when barefoot, the RFS group ran similar to the M/FFS group running barefoot or shod.
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Lee SM, Guan LL, Eun JS, Kim CH, Lee SJ, Kim ET, Lee SS. The effect of anaerobic fungal inoculation on the fermentation characteristics of rice straw silages. J Appl Microbiol 2015; 118:565-73. [PMID: 25495284 DOI: 10.1111/jam.12724] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 12/08/2014] [Accepted: 12/08/2014] [Indexed: 11/29/2022]
Abstract
AIMS To identify whether the supplement of anaerobic fungi isolates with cellulolytic activities accelerates the silage fermentation. METHODS AND RESULTS Three fungal isolates with the highest cellulolytic activities among 45 strains of anaerobic fungal stock in our laboratory were selected and used as silage inoculants. The rice straw (RS) was ensiled for 10, 30, 60, 90 and 120 days with four treatments of anaerobic fungi derived from the control (no fungus), Piromyces M014 (isolated from the rumen of the Korean native goat), Orpinomyces R001 (isolated from the duodenum of Korean native cattle) and Neocallimastix M010 (isolated from the guts of termites), respectively. The silages inoculated with pure strains of fungi showed a higher fungal population (P < 0.05) when compared to the control silage. In situ ruminal DM disappearance of RS silage (RSS) was improved with fungal treatment. SEM observation showed live fungal cells inoculated in RS could survive during the ensiling process. Overall, this study indicated that the inoculation of anaerobic fungi decreased the cell wall content of the RSS and increased in situ dry matter disappearance. CONCLUSIONS The supplementation of anaerobic fungi isolates to RSS as a silage inoculant improves the RSS quality. SIGNIFICANCE AND IMPACT OF THE STUDY This is the first study showing the potential application of supplement of anaerobic fungi isolated from the guts may be applied industrially as an alternate feed additive that improves the silage quality.
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Kim ET, Park CG, Lim DH, Kwon EG, Ki KS, Kim SB, Moon YH, Shin NH, Lee SS. Effects of Coconut Materials on In vitro Ruminal Methanogenesis and Fermentation Characteristics. ASIAN-AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES 2014; 27:1721-5. [PMID: 25358365 PMCID: PMC4213683 DOI: 10.5713/ajas.2014.14216] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 05/19/2014] [Accepted: 08/31/2014] [Indexed: 11/27/2022]
Abstract
The objective of this study was to evaluate the in vitro effects of coconut materials on ruminal methanogenesis and fermentation characteristics, in particular their effectiveness for mitigating ruminal methanogenesis. Fistulated Holstein cows were used as the donor of rumen fluid. Coconut materials were added to an in vitro fermentation incubated with rumen fluid-buffer mixture and timothy substrate for 24 h incubation. Total gas production, gas profiles, total volatile fatty acids (tVFAs) and the ruminal methanogens diversity were measured. Although gas profiles in added coconut oil and coconut powder were not significantly different, in vitro ruminal methane production was decreased with the level of reduction between 15% and 19% as compared to control, respectively. Coconut oil and coconut powder also inhibited gas production. The tVFAs concentration was increased by coconut materials, but was not affected significantly as compared to control. Acetate concentration was significantly lower (p<0.05), while propionate was significantly higher (p<0.05) by addition of the coconut materials than that of the control. The acetate:propionate ratio was significantly lowered with addition of coconut oil and coconut powder (p<0.05). The methanogens and ciliate-associated methanogens in all added coconut materials were shown to decrease as compared with control. This study showed that ciliate-associated methanogens diversity was reduced by more than 50% in both coconut oil and coconut powder treatments. In conclusion, these results indicate that coconut powder is a potential agent for decreasing in vitro ruminal methane production and as effective as coconut oil.
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Congly SE, Lee SS. Editorial: can we afford the new direct-acting antivirals for treatment of genotype 1 hepatitis C? Aliment Pharmacol Ther 2014; 40:983-4. [PMID: 25229813 DOI: 10.1111/apt.12927] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 07/30/2014] [Indexed: 12/13/2022]
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Kim WY, Hanigan MD, Lee SJ, Lee SM, Kim DH, Hyun JH, Yeo JM, Lee SS. Effects of Cordyceps militaris on the growth of rumen microorganisms and in vitro rumen fermentation with respect to methane emissions. J Dairy Sci 2014; 97:7065-75. [PMID: 25200786 DOI: 10.3168/jds.2014-8064] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Accepted: 08/07/2014] [Indexed: 11/19/2022]
Abstract
This experiment was designed to investigate the effects of different concentrations (0.00, 0.10, 0.15, 0.20, 0.25, and 0.30 g/L) of dried Cordyceps militaris mushroom on in vitro anaerobic ruminal microbe fermentation and methane production using soluble starch as a substrate. Ruminal fluids were collected from Korean native cattle, mixed with phosphate buffer (1:2), and incubated anaerobically at 38 °C for 3, 6, 9, 12, 24, 36, 48, and 72 h. The addition of C. militaris significantly increased total volatile fatty acid and total gas production. The molar proportion of acetate was decreased and that of propionate was increased, with a corresponding decrease in the acetate:propionate ratio. As the concentration of C. militaris increased from 0.10 to 0.30 g/L, methane and hydrogen production decreased. The decrease in methane accumulation relative to the control was 14.1, 22.0, 24.9, 39.7, and 40.9% for the 0.10, 0.15, 0.20, 0.25, and 0.30 g/L treatments, respectively. Ammonia-N concentration and numbers of live protozoa decreased linearly with increasing concentrations of C. militaris. The pH of the medium significantly decreased at the highest level of C. militaris compared with the control. In conclusion, C. militaris stimulated mixed ruminal microorganism fermentation and inhibited methane production in vitro. Therefore, C. militaris could be developed as a novel compound for antimethanogenesis.
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Kim DH, Kim KH, Nam IS, Lee SS, Choi CW, Kim WY, Kwon EG, Lee KY, Lee MJ, Oh YK. Effect of indigenous herbs on growth, blood metabolites and carcass characteristics in the late fattening period of hanwoo steers. ASIAN-AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES 2014; 26:1562-8. [PMID: 25049742 PMCID: PMC4093822 DOI: 10.5713/ajas.2013.13132] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 03/03/2013] [Revised: 06/27/2013] [Accepted: 05/29/2013] [Indexed: 11/27/2022]
Abstract
This study was conducted to evaluate the effects of indigenous herbal supplements on growth, blood metabolites and carcass characteristics in the late fattening period of Hanwoo steers. In a 6 month feeding trial, thirty Hanwoo steers (647±32 kg) were allotted to one of 5 treatment groups, control (basal diet contained lasalocid), licorice, clove, turmeric and silymarin, with six steers per pen. All groups received ad libitum concentrate and 1 kg rice straw/animal/d throughout the feeding trial. Blood samples were collected at the beginning, middle, and the end of the experiment and the steers were slaughtered at the end. Blood glucose, triglyceride, total protein, and albumin concentrations were higher in the turmeric treatment compared with other treatments. Blood urea nitrogen and creatinine concentrations were highest (p<0.003 and p = 0.071, respectively) in steers treated with silymarin. Alanine aminotransferase activity was lower (p<0.06) for licorice and silymarin compared with the control group. There were no alterations in serum aspartate aminotransferase and gamma glutamyltransferase activities as a consequence of herb treatments (p = 0.203 and 0.135, respectively). Final body weight, body weight gain, average dairy gain and dry matter intake were not significantly different among treatments. Yield grade, marbling score and quality grade were higher for silymarin group than those of the control group (p<0.05). Therefore, the results suggest that silymarin can be used an effective dietary supplement as an alternative to antibiotic feed additive and a productivity enhancer, providing safe and more consumer acceptable alternative to synthetic compounds during the late fattening period of steers.
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Alam M, Cho KH, Lee SS, Choy YH, Kim HS, Cho CI, Choi TJ. Effect of carcass traits on carcass prices of holstein steers in Korea. ASIAN-AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES 2014; 26:1388-98. [PMID: 25049722 PMCID: PMC4093074 DOI: 10.5713/ajas.2013.13109] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Revised: 05/26/2013] [Accepted: 04/11/2013] [Indexed: 11/27/2022]
Abstract
The present study investigated the contribution of carcass traits on carcass prices of Holstein steers in Korea. Phenotypic data consisted of 76,814 slaughtered Holsteins (1 to 6 yrs) from all over Korea. The means for live body weight at slaughter (BWT), chilled carcass weight (CWT), dressing percentage (DP), quantity grade index (QGI), eye muscle area (EMA), backfat thickness (BF) and marbling score (MS), carcass unit price (CUP), and carcass sell prices (CSP) were 729.0 kg, 414.2 kg, 56.79%, 64.42, 75.26 cm2, 5.77 mm, 1.98, 8,952.80 Korean won/kg and 3,722.80 Thousand Korean won/head. Least squares means were significantly different by various age groups, season of slaughter, marbling scores and yield grades. Pearson’s correlation coefficients of CUP with carcass traits ranged from 0.12 to 0.62. Besides, the relationships of carcass traits with CSP were relatively stronger than those with CUP. The multiple regression models for CUP and CSP with carcass traits accounted 39 to 63% of the total variation, respectively. Marbling score had maximum economic effects (partial coefficients) on both prices. In addition, the highest standardized partial coefficients (relative economic weights) for CUP and CSP were calculated to be on MS and CWT by 0.608 and 0.520, respectively. Path analyses showed that MS (0.376) and CWT (0.336) had maximum total effects on CUP and CSP, respectively; whereas BF contributed negatively. Further sub-group (age and season of slaughter) analyses also confirmed the overall outcomes. However, the relative economic weights and total path contributions also varied among the animal sub-groups. This study suggested the significant influences of carcass traits on carcass prices; especially MS and CWT were found to govern the carcass prices of Holstein steers in Korea.
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Kim ET, Min KS, Kim CH, Moon YH, Kim SC, Lee SS. The Effect of Plant Extracts on In-vitro Ruminal Fermentation, Methanogenesis and Methane-related Microbes in the Rumen. ASIAN-AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES 2014; 26:517-22. [PMID: 25049817 PMCID: PMC4093393 DOI: 10.5713/ajas.2012.12480] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 12/12/2012] [Accepted: 10/25/2012] [Indexed: 11/30/2022]
Abstract
The effect on methanogens attached to the surface of rumen ciliate protozoa by the addition of plant extracts (pine needles and ginkgo leaves) was studied with particular reference to their effectiveness for decreasing methane emission. The plant extracts (pine needles and ginkgo leaves) were added to an in vitro fermentation incubated with rumen fluid. The microbial population including bacteria, ciliated-associated methanogen, four different groups of methanogens and Fibrobacter succinogenes were quantified by using the real-time PCR. Gas profiles including methane, carbon dioxide and hydrogen, and runinal fermentation characteristics were observed in vitro. The methane emission from samples with an addition of individual juices from pine needles, ginkgo leaves and 70% ethanol extract from ginko leaves was significantly lower (p<0.05, 27.1, 28.1 and 28.1 vs 34.0 ml/g DM) than that of the control, respectively. Total VFAs in samples with an addition of any of the plant extracts were significantly lower than that of the control (p<0.05) as well. The order Methanococcales and the order Methanosarcinales were not detected by using PCR in any incubated mixtures. The ciliate-associated methanogens population decreased from 25% to 49% in the plant extacts as compared to control. We speculate that the supplementation of juice from pine needles and ginkgo leaves extract (70% ethanol extract) decreased the protozoa population resulting in a reduction of methane emission in the rumen and thus inhibiting methanogenesis. The order Methanobacteriales community was affected by addition of all plant extracts and decreased to less than the control, while the order Methanomicrobiales population showed an increase to more than that of the control. The F. succinogenes, the major fibrolytic microorganism, population in all added plant extracts was increased to greater than that of the control. In conclusion, pine needles and ginkgo leaves extracts appear to have properties that decrease methanogenesis by inhibiting protozoa species and may have a potential for use as additives for ruminants.
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Coffin CS, Lee SS. Editorial: Anti-viral therapy for prevention of perinatal HBV transmission--extending therapy beyond birth and the risk of post-partum flare. Aliment Pharmacol Ther 2014; 40:115-6. [PMID: 24903430 DOI: 10.1111/apt.12793] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Accepted: 04/21/2014] [Indexed: 12/08/2022]
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Naftalin CM, Chan KCW, Wong KH, Cheung SW, Chan RCY, Lee SS. CYP2B6-G516T genotype influences plasma efavirenz concentration in a Hong Kong population, allowing potential individualization of therapy. HIV Med 2014; 15:63-4. [PMID: 24299220 DOI: 10.1111/hiv.12076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Shtukenberg AG, Lee SS, Kahr B, Ward MD. Manipulating Crystallization with Molecular Additives. Annu Rev Chem Biomol Eng 2014; 5:77-96. [DOI: 10.1146/annurev-chembioeng-061312-103308] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Sadler MD, Lee SS. Letter: Treatment of HBeAg+ chronic hepatitis B--is tenofovir truly superior to entecavir? Aliment Pharmacol Ther 2014; 39:1339. [PMID: 24803253 DOI: 10.1111/apt.12732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Accepted: 03/13/2014] [Indexed: 12/08/2022]
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Congly SE, Lee SS. Commentary: the ss469415590 SNP--an IL28B marker looking for a home. Aliment Pharmacol Ther 2014; 39:339. [PMID: 24397320 DOI: 10.1111/apt.12597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 12/10/2013] [Indexed: 12/08/2022]
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91
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Mativetsky JM, Wang H, Lee SS, Whittaker-Brooks L, Loo YL. Face-on stacking and enhanced out-of-plane hole mobility in graphene-templated copper phthalocyanine. Chem Commun (Camb) 2014; 50:5319-21. [DOI: 10.1039/c3cc47516f] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lee SS. Benefits of early detection and treatment of human immunodeficiency virus infections. Hong Kong Med J 2013; 19:472-3. [DOI: 10.12809/hkmj134162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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93
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Haam SJ, Lee SS, Lee DY, Paik HC. The effects of the climatic elements on occurrence of the spontaneous pneumothorax. J Cardiothorac Surg 2013. [PMCID: PMC3845070 DOI: 10.1186/1749-8090-8-s1-p153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
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Lee TH, Moon JH, Kim JH, Park DH, Lee SS, Choi HJ, Cho YD, Park SH, Kim SJ. Primary and revision efficacy of cross-wired metallic stents for endoscopic bilateral stent-in-stent placement in malignant hilar biliary strictures. Endoscopy 2013; 45:106-13. [PMID: 23212727 DOI: 10.1055/s-0032-1325928] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND AND STUDY AIMS Endoscopic bilateral drainage for inoperable malignant hilar biliary strictures (HBS) using metal stents is considered to be technically difficult. Furthermore, endoscopic revision of bilateral stenting after occlusion can be challenging. This study was performed to evaluate the long-term efficacy of endoscopic bilateral stent-in-stent placement of cross-wired metallic stents in high-grade malignant HBS and planned endoscopic bilateral revision. PATIENTS AND METHODS A total of 84 patients with inoperable high-grade malignant HBS were enrolled from three academic tertiary referral centers. Two cross-wired metal stents were inserted using a bilateral stent-in-stent placement method. Bilateral endoscopic revision was also performed during follow-up using either identical metal stents or plastic stents. The main outcome measurements were technical and functional success, complications, stent patency, and endoscopic revision efficacy. RESULTS The technical and clinical success rates of endoscopic bilateral stent-in-stent placement of cross-wired metallic stents were 95.2% (80/84) and 92.9% (78/84), respectively. Median patency (range) and survival were 238 days (10-429) and 256 days (10-1130), respectively. Obstruction of primary bilateral stents occurred in 30.8% (24/78) of patients with functionally successful stent placement. The technical and clinical success rates of planned bilateral endoscopic revision for occluded stents were 83.3% (20/24) and 79.2% (19/24), respectively. For revision, bilateral metallic stents were placed in 11 patients (55.0%); the remaining patients received plastic stents. CONCLUSIONS Palliative endoscopic bilateral stent-in-stent placement of cross-wired metallic stents was effective in patients with inoperable HBS. Revision endoscopic bilateral stenting may be feasible and successful in cases where the primary deployed metal stents are occluded.
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Kang SJ, Kim JB, Chiu CY, Ahn S, Schiros T, Lee SS, Yager KG, Toney MF, Loo YL, Nuckolls C. Corrigendum: A Supramolecular Complex in Small-Molecule Solar Cells based on Contorted Aromatic Molecules. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/anie.201303818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kang SJ, Kim JB, Chiu CY, Ahn S, Schiros T, Lee SS, Yager KG, Toney MF, Loo YL, Nuckolls C. Berichtigung: A Supramolecular Complex in Small-Molecule Solar Cells based on Contorted Aromatic Molecules. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Liu Y, Wang HH, Bian G, Zhang Z, Lee SS, Fenter PA, Tischler JZ, Hong H, Chiang TC. Interfacial bonding and structure of Bi2Te3 topological insulator films on Si(111) determined by surface x-ray scattering. PHYSICAL REVIEW LETTERS 2013; 110:226103. [PMID: 23767736 DOI: 10.1103/physrevlett.110.226103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 04/25/2013] [Indexed: 06/02/2023]
Abstract
Interfacial topological states are a key element of interest for topological insulator thin films, and their properties can depend sensitively on the atomic bonding configuration. We employ in situ nonresonant and resonant surface x-ray scattering to study the interfacial and internal structure of a prototypical topological film system: Bi2Te3 grown on Si(111). The results reveal a Te-dominated buffer layer, a large interfacial spacing, and a slightly relaxed and partially strained bottom quintuple layer of an otherwise properly stacked bulklike Bi2Te3 film. The presence of the buffer layer indicates a nontrivial process of interface formation and a mechanism for electronic decoupling between the topological film and the Si(111) substrate.
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Chen Y, Lee B, Yi HT, Lee SS, Payne MM, Pola S, Kuo CH, Loo YL, Anthony JE, Tao YT, Podzorov V. Dynamic character of charge transport parameters in disordered organic semiconductor field-effect transistors. Phys Chem Chem Phys 2013; 14:14142-51. [PMID: 22868385 DOI: 10.1039/c2cp41823a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this perspective article, we discuss the dynamic instability of charge carrier transport in a range of popular organic semiconductors. We observe that in many cases field-effect mobility, an important parameter used to characterize the performance of organic field-effect transistors (OFETs), strongly depends on the rate of the gate voltage sweep during the measurement. Some molecular systems are so dynamic that their nominal mobility can vary by more than one order of magnitude, depending on how fast the measurements are performed, making an assignment of a single mobility value to devices meaningless. It appears that dispersive transport in OFETs based on disordered semiconductors, those with a high density of localized trap states distributed over a wide energy range, is responsible for the gate voltage sweep rate dependence of nominal mobility. We compare such rate dependence in different materials and across different device architectures, including pristine and trap-dominated single-crystal OFETs, as well as solution-processed polycrystalline thin-film OFETs. The paramount significance given to a single mobility value in the organic electronics community and the practical importance of OFETs for applications thus suggest that such an issue, previously either overlooked or ignored, is in fact a very important point to consider when engaging in fundamental studies of charge carrier mobility in organic semiconductors or designing applied circuits with organic semiconductors.
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Hiszpanski AM, Lee SS, Wang H, Woll AR, Nuckolls C, Loo YL. Post-deposition processing methods to induce preferential orientation in contorted hexabenzocoronene thin films. ACS NANO 2013; 7:294-300. [PMID: 23228001 DOI: 10.1021/nn304003u] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The structuring in organic electrically active thin films critically influences the performance of devices comprising them. Controlling film structure, however, remains challenging and generally requires stringent deposition conditions or modification of the substrate. To this end, we have developed post-deposition processing methods that are decoupled from the initial deposition conditions to induce different out-of-plane molecular orientations in contorted hexabenzocoronene (HBC) thin films. As-deposited HBC thin films lack any long-range order; subjecting them to post-deposition processing, such as hexanes-vapor annealing, thermal annealing, and physical contact with elastomeric poly(dimethyl siloxane), induces crystallization with increasing extents of preferential edge-on orientation, corresponding to greater degrees of in-plane π-stacking. Accordingly, transistors comprising HBC thin films that have been processed under these conditions exhibit field-effect mobilities that increase by as much as 2 orders of magnitude with increasing extents of molecular orientation. The ability to decouple HBC deposition from its subsequent structuring through post-deposition processing affords us the unique opportunity to tune competing molecule-molecule and molecule-solvent interactions, which ultimately leads to control over the structure and electrical function of HBC films.
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Lee SS, Mativetsky JM, Loth MA, Anthony JE, Loo YL. Quantifying resistances across nanoscale low- and high-angle interspherulite boundaries in solution-processed organic semiconductor thin films. ACS NANO 2012; 6:9879-9886. [PMID: 23020587 DOI: 10.1021/nn303446h] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The nanoscale boundaries formed when neighboring spherulites impinge in polycrystalline, solution-processed organic semiconductor thin films act as bottlenecks to charge transport, significantly reducing organic thin-film transistor mobility in devices comprising spherulitic thin films as the active layers. These interspherulite boundaries (ISBs) are structurally complex, with varying angles of molecular orientation mismatch along their lengths. We have successfully engineered exclusively low- and exclusively high-angle ISBs to elucidate how the angle of molecular orientation mismatch at ISBs affects their resistivities in triethylsilylethynyl anthradithiophene thin films. Conductive AFM and four-probe measurements reveal that current flow is unaffected by the presence of low-angle ISBs, whereas current flow is significantly disrupted across high-angle ISBs. In the latter case, we estimate the resistivity to be 22 MΩμm(2)/width of the ISB, only less than a quarter of the resistivity measured across low-angle grain boundaries in thermally evaporated sexithiophene thin films. This discrepancy in resistivities across ISBs in solution-processed organic semiconductor thin films and grain boundaries in thermally evaporated organic semiconductor thin films likely arises from inherent differences in the nature of film formation in the respective systems.
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