| 1. |
- Abdellah, Mohamed, et al.
(författare)
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Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1−xS1−y quantum dots
- 2017
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 9:34, s. 12503-12508
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast fluorescence spectroscopy was used to investigate the hole injection in CdxSeyZn1-xS1-y gradient core-shell quantum dot (CSQD) sensitized p-type NiO photocathodes. A series of CSQDs with a wide range of shell thicknesses was studied. Complementary photoelectrochemical cell measurements were carried out to confirm that the hole injection from the active core through the gradient shell to NiO takes place. The hole injection from the valence band of the QDs to NiO depends much less on the shell thickness when compared to the corresponding electron injection to n-type semiconductor (ZnO). We simulate the charge carrier tunneling through the potential barrier due to the gradient shell by numerically solving the Schrodinger equation. The details of the band alignment determining the potential barrier are obtained from X-ray spectroscopy measurements. The observed drastic differences between the hole and electron injection are consistent with a model where the hole effective mass decreases, while the gradient shell thickness increases.
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| 2. |
- Chang, Ya-Ting, et al.
(författare)
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Perlecan heparan sulfate deficiency impairs pulmonary vascular development and attenuates hypoxic pulmonary hypertension
- 2015
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Ingår i: Cardiovascular Research. - : Oxford University Press (OUP). - 0008-6363 .- 1755-3245. ; 107:1, s. 20-31
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Tidskriftsartikel (refereegranskat)abstract
- Aims Excessive vascular cell proliferation is an important component of pulmonary hypertension (PH). Perlecan is the major heparan sulfate (HS) proteoglycan in the vascular extracellular matrix. It binds growth factors, including FGF2, and either restricts or promotes cell proliferation. In this study, we have explored the effects of perlecan HS deficiency on pulmonary vascular development and in hypoxia-induced PH. Methods and results In normoxia, Hspg2(Delta 3/Delta 3) mice, deficient in perlecan HS, had reduced pericytes and muscularization of intra-acinar vessels. Pulmonary angiography revealed a peripheral perfusion defect. Despite these abnormalities, right ventricular systolic pressure (RVSP) and myocardial mass remained normal. After 4 weeks of hypoxia, increases in the proportion of muscularized vessels, RVSP, and right ventricular hypertrophy were significantly less in Hspg2(Delta 3/Delta 3) compared with wild type. The early phase of hypoxia induced a significantly lower increase in fibroblast growth factor receptor-1 (FGFR1) protein level and receptor phosphorylation, and reduced pulmonary artery smooth muscle cell (PASMC) proliferation in Hspg2(Delta 3/Delta 3). At 4 weeks, FGF2 mRNA and protein were also significantly reduced in Hspg2(Delta 3/Delta 3) lungs. Ligand and carbohydrate engagement assay showed that perlecan HS is required for HS-FGF2-FGFR1 ternary complex formation. In vitro, proliferation assays showed that PASMC proliferation is reduced by selective FGFR1 inhibition. PASMC adhesion to fibronectin was higher in Hspg2(Delta 3/Delta 3) compared with wild type. Conclusions Perlecan HS chains are important for normal vascular arborization and recruitment of pericytes to pulmonary vessels. Perlecan HS deficiency also attenuates hypoxia-induced PH, where the underlying mechanisms involve impaired FGF2/FGFR1 interaction, inhibition of PASMC growth, and altered cell-matrix interactions.
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| 3. |
- Chi, Xiaoming, et al.
(författare)
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Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity
- 2018
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Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 43:20, s. 5017-5020
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.
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| 4. |
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| 5. |
- GUAN, WEN, et al.
(författare)
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Frequency tuning behaviour of terahertz quantum cascade lasers revealed by a laser beating scheme
- 2021
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 29:14, s. 21269-21279
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Tidskriftsartikel (refereegranskat)abstract
- In the terahertz frequency range, the commercialized spectrometers, such as the Fourier transform infrared and time domain spectroscopies, show spectral resolutions between a hundred megahertz and a few gigahertz. Therefore, the high precision frequency tuning ability of terahertz lasers cannot be revealed by these traditional spectroscopic techniques. In this work, we demonstrate a laser beating experiment to investigate the frequency tuning characteristics of terahertz quantum cascade lasers (QCLs) induced by temperature or drive current. Two terahertz QCLs emitting around 4.2 THz with identical active regions and laser dimensions (150 μm wide and 6 mm long) are employed in the beating experiment. One laser is operated as a frequency comb and the other one is driven at a lower current to emit a single frequency. To measure the beating signal, the single mode laser is used as a fast detector (laser self-detection). The laser beating scheme allows the high precision measurement of the frequency tuning of the single mode terahertz QCL. The experimental results show that in the investigated temperature and current ranges, the frequency tuning coefficients of the terahertz QCL are 6.1 MHz/0.1 K (temperature tuning) and 2.7 MHz/mA (current tuning) that cannot be revealed by a traditional terahertz spectrometer. The laser beating technique shows potential abilities in high precision linewidth measurements of narrow absorption lines and multi-channel terahertz communications.
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| 6. |
- Hao, Xian, et al.
(författare)
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Direct measurement and modulation of single-molecule coordinative bonding forces in a transition metal complex
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Coordination chemistry has been a consistently active branch of chemistry since Werner’s seminal theory of coordination compounds inaugurated in 1893, with the central focus on transition metal complexes. However, control and measurement of metal–ligand interactions at the single-molecule level remain a daunting challenge. Here we demonstrate an interdisciplinary and systematic approach that enables measurement and modulation of the coordinative bonding forces in a transition metal complex. Terpyridine is derived with a thiol linker, facilitating covalent attachment of this ligand on both gold substrate surfaces and gold-coated atomic force microscopy tips. The coordination and bond breaking between terpyridine and osmium are followed in situ by electrochemically controlled atomic force microscopy at the single-molecule level. The redox state of the central metal atom is found to have a significant impact on the metal–ligand interactions. The present approach represents a major advancement in unravelling the nature of metal–ligand interactions and could have broad implications in coordination chemistry.
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| 7. |
- Hu, Xiaolong, et al.
(författare)
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Fractal superconducting nanowire single-photon detectors and their applications in polarimetric imaging
- 2024
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Ingår i: Advanced Photon Counting Techniques XVIII. - : SPIE-Intl Soc Optical Eng.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we review the research and development of the fractal superconducting nanowire single-photon detectors (SNSPDs), including our demonstrations of high-performance devices and systems with over 80% system detection efficiency, negligibly low residual polarization sensitivity, and low timing jitter. Using the fractal SNSPDs, we demonstrate full-Stokes polarimetric imaging LiDAR.
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| 8. |
- Hu, Xiaolong, et al.
(författare)
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Superconducting nanowire single-photon detectors at the infrared spectrum range : detection efficiency and timing jitter
- 2019
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Ingår i: TERAHERTZ, RF, MILLIMETER, AND SUBMILLIMETER-WAVE TECHNOLOGY AND APPLICATIONS XII. - : SPIE. - 9781510624771
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Konferensbidrag (refereegranskat)abstract
- This paper reviews some recent research progress in superconducting nanowire single-photon detectors (SNSPDs) at the infrared spectrum range, with particular emphasis on detection efficiency and timing jitter. For detection efficiency, we present fractal SNSPDs with reduced polarization sensitivity; for timing jitter, we present two mechanisms of device timing jitter - vortex-crossing-induced timing jitter and spatial-inhomogeneity-induced timing jitter.
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| 9. |
- Hu, Xiaolong, et al.
(författare)
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Timing properties of superconducting nanowire single-photon detectors
- 2019
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Ingår i: Quantum Optics and Photon Counting 2019. - : SPIE - International Society for Optical Engineering. - 9781510627215
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Konferensbidrag (refereegranskat)abstract
- In this paper, we review theoretical and experimental research progress on timing properties of superconducting nanowire single-photon detectors, including six possible mechanisms that induce timing jitter and experiments towards ultra-low timing jitter.
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| 10. |
- Li, Qing, et al.
(författare)
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Hierarchical Dehydrogenation Reactions on a Copper Surface
- 2018
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 140:19, s. 6076-6082
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchical control of chemical reactions is being considered as one of the most ambitious and challenging topics in modern organic chemistry. In this study, we have realized the one-by-one scission of the X-H bonds (X = N and C) of aromatic amines in a controlled fashion on the Cu(lll) surface. Each dehydrogenation reaction leads to certain metal-organic supramolecular structures, which were monitored in single-bond resolution via scanning tunneling microscopy and noncontact atomic force microscopy. Moreover, the reaction pathways were elucidated from X-ray photoelectron spectroscopy measurements and density functional theory calculations. Our insights pave the way for connecting molecules into complex structures in a more reliable and predictable manner, utilizing carefully tuned stepwise on-surface synthesis protocols.
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| 11. |
- Sun, Jinghao, et al.
(författare)
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On the Volume Calculation for Conditional DAG Tasks : Hardness and Algorithms
- 2020
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Ingår i: PROCEEDINGS OF THE 2020 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION (DATE 2020). - NEW YORK, USA. - 9783981926347 ; , s. 204-209
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Konferensbidrag (refereegranskat)abstract
- The hardness of analyzing conditional directed acyclic graph (DAG) tasks remains unknown so far. For example, previous researches asserted that the conditional DAG's volume can be solved in polynomial time. However, these researches all assume well-nested structures that are recursively composed by single-source-single-sink parallel and conditional components. For conditional DAGs in general that do not comply with this assumption, the hardness and algorithms of volume computation are still open. In this paper, we construct counterexamples to show that previous work cannot provide a safe upper bound of the conditional DAG's volume in general. Moreover, we prove that the volume computation problem for conditional DAGs is strongly NP-hard. Finally, we propose an exact algorithm for computing the conditional DAG's volume. Experiments show that our method can significantly improve the accuracy of the conditional DAG's volume estimation.
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| 12. |
- Tseng, Chi-Nan
(författare)
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Interactions between leukocytes, platelets and the endothelium in vein graft failure
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Autologous venous grafts are preferred conduits in bypass surgery due to their length, easy harvesting, and feasibility. However, development of intimal hyperplasia decreases long-term patency rate in venous grafts prompting close clinical surveillance and further intervention. Mechanical forces, inflammation, and shear stress responses in venous grafts after surgical transfer may be involved in the development of intimal hyperplasia. This thesis focuses on inflammatory reactions in venous grafts. We hypothesized that interactions between leukocytes, platelets and endothelial cells induce intimal hyperplasia resulting in venous graft failure. We demonstrate that VGs obtained by end-to-end anastomosis of the inferior vena cava (IVC) from donor mice grafted to the abdominal aorta in recipients suffer extensive endothelial injury, platelet deposition and leukocyte invasion early after grafting. Re-endothelialization of interposed venous grafts was completed after 4 weeks. Regenerated endothelium displayed normal resistance to recruitment of leukocytes. Thus, we found that there is a time window during the first weeks following grafting in which venous grafts are susceptible to vessel injury and inflammation. Leukocyte recruitment on inflammatory endothelium initiates with margination, capture followed by rolling, firm adhesion and transmigration. We hypothesized that absence or functionblockage of leukocyte adhesion molecules P-selectin and E-selectin that are important for rolling may influence development of intimal hyperplasia in venous grafts by reduction of the recruitment of leukocytes. Indeed, intimal hyperplasia was significantly reduced in E- and P-selectin double deficient mice compared to WT both at 28 days and 63 days after VG transfer. This was paralleled by a reduction in the recruitment of leukocytes to the graft wall. Similar findings were made in WT mice treated with a combination of function-blocking antibodies against P- and E-selectin. The effect of P-selectin alone was addressed using P-selectin deficient mice. We found that intimal hyperplasia was significantly attenuated in mice deficient in P-selectin compared to WT mice 28 days after surgery concomitant with decreased leukocyte invasion. Interestingly, single-dose blockage of P-selectin or its leukocytic ligand PSGL-1 at the time of surgery could block the function of these molecules for up to 10 days and reduced later formation of intimal hyperplasia. Hence, early inhibition of these molecules has potential therapeutic effects on long-term vein graft failure. Platelets strongly influence haemostasis, inflammation and tissue regeneration after vascular injury, which are all represented in the period of re-endothelialization after venous graft transfer. We tested whether absence or function-blockage of platelets could influence intimal hyperplasia in venous grafts. We first used antiserum depletion of platelets for 12 days following surgical grafting. Indeed, IH and leukocyte invasion were reduced in platelet-depleted mice. Moreover, inhibition of integrin αIIbβ3, the main aggregation receptor on platelets, also reduced IH and leukocyte recruitment in the graft wall. The reduction of intimal hyperplasia in mice treated with the antibody against integrin αIIbβ3 was paralleled by radical reductions of the number of adherent platelets and leukocytes on the luminal surface of grafts one hour following grafting. In summary, our work emphasizes the role of interactions between leukocytes, platelets and the vessel wall in venous grafts during their adaptation to the arterial circulation. These mechanisms constitute attractive targets for the development of further preventive pharmacological strategies against vein graft failure.
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| 13. |
- Wang, Lina, et al.
(författare)
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Tailoring Alkane Uniaxial Self-Assembly via Polymer Modified Step Edges
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 123:47, s. 28811-28815
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Tidskriftsartikel (refereegranskat)abstract
- Controlling the orientations of molecules in self-assembled monolayers on surfaces is an effective means to construct high quality organic devices. Herein, we utilize linear polymer-modified step edges as a simple and peculiar template for regulating the subsequent self-assembly of alkane molecules (n-C32H66). With this strategy, all the alkane molecules orientate along the step edge ([011] directions). Combining with systematical DFT calculations, we demonstrated that it is the van der Waals interactions between the molecules that leads to (1) the initially adsorbed alkane monomers lie parallel to the polymers; (2) the adjacent alkane molecules show a parallel configuration. Since the polymers anchor on the surface along an exclusive [011] direction, all the adsorbed molecules in the self-assembly islands are regulated along the [011] directions as well.
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| 14. |
- Yang, Biao, et al.
(författare)
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Abiotic Formation of an Amide Bond via Surface-Supported Direct Carboxyl-Amine Coupling
- 2022
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 61:5
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Tidskriftsartikel (refereegranskat)abstract
- Amide bond formation is one of the most important reactions in biochemistry, notably being of crucial importance for the origin of life. Herein, we combine scanning tunneling microscopy and X-ray photoelectron spectroscopy studies to provide evidence for thermally activated abiotic formation of amide bonds between adsorbed precursors through direct carboxyl-amine coupling under ultrahigh-vacuum conditions by means of on-surface synthesis. Complementary insights from temperature-programmed desorption measurements and density functional theory calculations reveal the competition between cross-coupling amide formation and decarboxylation reactions on the Au(111) surface. Furthermore, we demonstrate the critical influence of the employed metal support: whereas on Au(111) the coupling readily occurs, different reaction scenarios prevail on Ag(111) and Cu(111). The systematic experiments signal that archetypical bio-related molecules can be abiotically synthesized in clean environments without water or oxygen.
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| 15. |
- Zhang, Zhenzong, et al.
(författare)
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Internal electric field engineering step-scheme–based heterojunction using lead-free Cs3Bi2Br9 perovskite–modified In4SnS8 for selective photocatalytic CO2 reduction to CO
- 2022
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 313
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on improving photocatalytic CO2 reduction reaction (CRR) activity and modulating product selectivity. An In4SnS8/Cs3Bi2Br9-X (ISS/CBB-X) heterojunction is prepared using novel lead-free Cs3Bi2Br9 perovskite quantum dot–modified In4SnS8, which shows considerable potential as photocatalysts for CRRs under visible light. The optimised ISS/CBB photocatalyst exhibits high activity and CO selectivity with a CO yield and selectivity of 9.55 μmol g−1 h−1 and 92.9%, respectively, 3.8 and 1.5 times higher than those of pristine ISS, respectively. Moreover, the step-scheme (S-scheme) mechanism can be fully confirmed via in situ irradiated X-ray photoelectron spectroscopy, in situ electron spin resonance, femtosecond time-resolved absorption spectroscopy and density functional theory calculations. Based on in situ diffuse reflectance spectra and theoretical investigations, the ISS/CBB shows a decreased energy barrier towards CO2 reduction to CO through an adsorbed ⁕COOH intermediate. This study contributes to the further understanding of fabricating efficient S-scheme-based photocatalysts for selective CRR.
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| 16. |
- Zheng, Kaibo, et al.
(författare)
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Directed Energy Transfer in Films of CdSe Quantum Dots: Beyond the Point Dipole Approximation
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:17, s. 6259-6268
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of Forster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of QDs, so that the simple point dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using ultrafast transient absorption spectroscopy and theoretical modeling. Pairwise interdot transfer time was determined in the range of 1.5 to 2 ns by spectral analyses which enable separation of the FRET contribution from intrinsic exciton decay. A rational model is suggested by taking into account the distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate dynamics of directed energy transfer in ordered multilayer QD films, which we also observe experimentally. The Monte Carlo simulations reveal that three ideal QD monolayers can provide exciton funneling efficiency above 80% from the most distant layer. Thereby, utilization of directed energy transfer can significantly improve light harvesting efficiency of QD devices.
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| 17. |
- Zhu, Nan, et al.
(författare)
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Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production.
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 10(9) s(-1). Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.
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