Formation Dynamics of Carbon Atomic Chain from Graphene by Electron Beam Irradiation

Carbon has numerous allotropes and various crystalline forms with full dimensionalities such as diamond, graphite, fullerenes, and carbon nanotubes leading a wide range of applications. Since the emerge of graphene consisting of a single atomic layer of carbon atoms, a fabrication of all-carbon-based device with combination of one-, two-, and three-dimensional carbons has become a hot issue. Here, we introduce an ultimate one-dimensional carbon atomic chain. Carbon atomic chains were experimentally created by removing atoms from monolayer graphene sheet under electron beam inside transmission electron microscope (TEM). A series of TEM images demonstrate the dynamics of carbon atomic chains over time from the formation, transformation, and then breakage

Mechanism of Defect Formation and Defect-Driven Growth of Two-Dimensional Materials

Department of Materials Science and EngineeringThe extraordinary properties of graphene have led to intensive research on two-dimensional (2D) materials since the discovery of mechanically exfoliated graphene. Especially development of synthesis of large-area 2D materials films using chemical vapor deposition (CVD) has extremely enlarged the spectrum of potential applications of 2D materials in the fields of various nanotechnology. CVD methods, however, also produce various defective structures with slight modifications to the growth parameters which influence the intrinsic properties of 2D materials. Although defects on 2D materials were often considered as hindrance to degrade the intrinsic properties, if well adjusted, they have huge ability to modulate electromagnetic and mechanical property of the materials, with better performance as needed. Hence, in-depth knowledge of crystal structures with defects and their formation mechanisms must be established to understand the relationship between defects and properties of 2D materials. In this study, transmission electron microscopy (TEM) have made a significant contribution to understanding in the mechanism of defect formation and defect-driven growth of 2D materials, by directly imaging the features at atomic scale and dynamics of defect formation in real-time, and analyzing information of electron diffraction of crystals, and also examining corresponding change in electric property from the defect structure using electron energy loss spectroscopy. Among many 2D materials, I have focused on novel defective structures on hexagonal boron nitride (hBN). In contrast to the wide spectrum of proposed applications for graphene as an active component in nanodevices, hBN is often regarded as a passive material where the range of applications is largely confined to substrates or electron barriers for 2D material-based devices due to its electrically insulating feature with a large bandgap and thus received less attention. Herein, through a systematic study using TEM, I report many interesting features of hBN including controllable hole defects, spiral growth driven by screw dislocation at anti-phase boundary, and atomically sharp twin boundary as a promising one-dimensional hBN conducting channel.clos

Atomic Resolution Imaging of Rotated Bilayer Graphene Sheets Using a Low kV Aberration-corrected Transmission Electron Microscope

Modern aberration-corrected transmission electron microscope (TEM) with appropriate electron beam energy is able to achieve atomic resolution imaging of single and bilayer graphene sheets. Especially, atomic configuration of bilayer graphene with a rotation angle can be identified from the direct imaging and phase reconstructed imaging since atomic resolution Moir pattern can be obtained successfully at atomic scale using an aberration-corrected TEM. This study boosts a reliable stacking order analysis, which is required for synthesized or artificially prepared multilayer graphene, and lets graphene researchers utilize the information of atomic configuration of stacked graphene layers readily.ope

One-dimensional hexagonal boron nitride conducting channel

Hexagonal boron nitride (hBN) is an insulating two-dimensional (2D) material with a large bandgap. Although known for its interfacing with other 2D materials and structural similarities to graphene, the potential use of hBN in 2D electronics is limited by its insulating nature. Here, we report atomically sharp twin boundaries at AA???/AB stacking boundaries in chemical vapor deposition???synthesized few-layer hBN. We find that the twin boundary is composed of a 6???6??? configuration, showing conducting feature with a zero bandgap. Furthermore, the formation mechanism of the atomically sharp twin boundaries is suggested by an analogy with stacking combinations of AA???/AB based on the observations of extended Klein edges at the layer boundaries of ABstacked hBN. The atomically sharp AA???/AB stacking boundary is promising as an ultimate 1D electron channel embedded in insulating pristine hBN. This study will provide insights into the fabrication of single-hBN electronic devices

Production of α-Bisabolol from metabolically engineered Escherichia coli

α-Bisabolol is a natural-occurring sesquiterpenoid with applications in cosmetics as whitening and soothing agent. It is synthesized from the universal precursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are generated either through the mevalonate (MVA) pathway or the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway. Farnesyl pyrophosphate (FPP) synthase (IspA) then catalyzes the condensation of IPP and DMAPP to the linear FPP, which is rearranged and cyclized to α-bisabolol by bisabolol synthases. Here, we compared the capacity of 5 α-bisabolol synthases from Lippia dulcis, Streptomyces citricolor, Santalum spicatum, Matricaria recutita, and Artemisia annua for α-bisabolol production. MVA pathway and FPP synthase were also overexpressed to supply sufficient FPP for bisabolol synthesis in the recombinant E. coli. Bisabolol synthase from M. recutita (MrBBS) shows the highest activity of bisabolol synthesis, and 75 mg/L/OD600 of bisabolol was produced in a test-tube culture. We further optimized the expression level of IspA and MrBBS by modulation their RBS strength. The 24 bisabolol synthesis operons with different RBSs were assessed for their performance on bisabolol synthesis. By this approach, the best strain is able to produce bisabolol with a capacity of 220mg/L/OD600 in a test tube culture. The consequence of host strain optimization led to an increase in bisabolol production to 300 mg/L/OD600, which presents a 4-fold increase over the initial engineered strain. This work was supported by a grant (NRF-2016R1A2B2010678) from the National Research Foundation, MSIP, Korea

Controllable modification of transport properties of single-walled carbon nanotube field effect transistors with in situ Al decoration

We use an in situ Al decoration technique to control the transport characteristics of single-walled carbon nanotube field effect transistors (SWNT-FETs). Al nanoparticle decoration in a high vacuum caused the devices to change from p -type to n -type FETs, and subsequent exposure to the ambient atmosphere induced a gradual recovery of p -type character. In comparison with the bare SWNT-FETs under high vacuum, the channel-open devices with decorated Al particles exhibited reduced current under ambient conditions. However, selective Al decoration only at the contact resulted in an improved p -type current in ambient air.open182

Potentiated therapeutic angiogenesis by primed human mesenchymal stem cells in a mouse model of hindlimb ischemia

Background: Human bone marrow-derived mesenchymal stem cells (hMSCs) are advantageous for cell-based therapy to treat ischemic diseases owing to their capacity to secrete various paracrine factors with potent angiogenic activity. Materials methods: In this study, we describe a method to increase secreted levels of VEGF and HGF from hMSCs without genetic modification. Results: We demonstrated that transplantation of primed hMSCs into ischemic limbs led to significantly greater improvements in tissue perfusion and limb salvage by increasing capillary formation compared with nonprimed hMSCs. The primed hMSCs also exhibited greater survival in vivo and secreted human VEGF and HGF in the ischemic tissue, supporting enhanced angiogenesis and cell survival. Conclusion: These findings indicate that priming hMSCs via methods described in this study enhances secretion of critical proangiogenic factors resulting in an enhanced therapeutic effect of cells for the treatment of ischemic diseases.This research was supported by grants from the Korea Health Technology R&D Project (M-S Chang, A100823) and the Innovative Research Institute for Cell Therapy, National University Hospital (A062260), both sponsored by the Ministry of Health, Welfare and Family, Seoul, Republic of Korea.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000027724/1SEQ:1PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000027724ADJUST_YN:YEMP_ID:A075930DEPT_CD:862CITE_RATE:3.718FILENAME:첨부된 내역이 없습니다.DEPT_NM:치의과학과EMAIL:[email protected]_YN:YCONFIRM:

Effects of physical activity participation on cognitive impairment in older adults population with disabilities

BackgroundExisting research on the association between cognitive function and physical activity in the older adults population with disabilities is limited. Additionally, there is a need to explore avenues for enhancing the longevity and quality of life among these individuals.ObjectiveThis study aimed to investigate the independent and joint associations between cognitive function and levels of physical activity in the older adults population with disabilities.MethodsA total of 315 older adults adults (men = 182, women = 133), identified with disabilities based on medical evaluation, were recruited from the first survey of the Korean Longitudinal Study of Aging (KLoSA). Participants underwent assessments for cognitive function, physical activity (PA), activities of daily living (ADLs), instrumental activities of daily living (IADLs), and grip strength.ResultsADLs (p < 0.001) and IADLs (p < 0.001) scores were significantly higher in the male normal cognitive group compared to both the male and female cognitive impairment groups. In an unadjusted model, disabled older adults individuals who did not meet the recommended PA guidelines showed an increased odds ratio for cognitive dysfunction (OR = 2.29, 95% CI = 1.32–3.97). Those participating in PA at least 1 day per week also demonstrated an elevated odds ratio (OR = 1.22, 95% CI = 1.08–1.38) for cognitive dysfunction compared to those who engaged in regular PA. A negative correlation was observed between K-MMSE scores and grip strength (r = 0.448, p < 0.001).ConclusionThis study provides robust evidence that disabled older adults individuals who do not meet the recommended guidelines for PA or who do not participate in PA at least once a week have an increased likelihood of cognitive impairment compared to those who are regularly active