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81.
Sun Z Boneschanscher MP Swart I Vanmaekelbergh D Liljeroth P 《Physical review letters》2011,106(4):046104
Noncontact atomic force microscopy (AFM) has recently progressed tremendously in achieving atomic resolution imaging through the use of small oscillation amplitudes and well-defined modification of the tip apex. In particular, it has been shown that picking up simple inorganic molecules (such as CO) by the AFM tip leads to a well-defined tip apex and to enhanced image resolution. Here, we use the same approach to study the three-dimensional intermolecular interaction potential between two molecules and focus on the implications of using molecule-modified AFM tips for microscopy and force spectroscopy experiments. The flexibility of the CO at the tip apex complicates the measurement of the intermolecular interaction energy between two CO molecules. Our work establishes the physical limits of measuring intermolecular interactions with scanning probes. 相似文献
82.
N. Eassa D.M. Murape J.H. Neethling R. Betz E. Coetsee H.C. Swart A. Venter J.R. Botha 《Surface science》2011,605(11-12):994-999
A sulphur based chemical, ([(NH4)2S/(NH4)2SO4]) to which S has been added not previously reported for the treatment of (111)A InAs surfaces is introduced and benchmarked against the commonly used passivants Na2S·9H2O and ((NH4)2S + S), using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It has been found that the native oxide layer present on the InAs surface is more effectively removed when treated with ([(NH4)2S/(NH4)2SO4] + S) than with ((NH4)2S + S) or Na2S·9H2O. AES depth profiles of the sulphurized layers revealed the formation of a thin (less than 8.5 nm) In–S surface layer for both ((NH4)2SO4 + S) and ([(NH4)2S/(NH4)2SO4] + S) treatments. No evidence for the formation of As―S bonds was found. Treatment with ([(NH4)2S/(NH4)2SO4] + S) also affected a significant improvement compared to the more established sulphur treatments in the surface morphology of the otherwise poor as-received n-InAs (111)A surface. 相似文献
83.
Dr. Olga A. Stasyuk Prof. Dr. Miquel Solà Prof. Dr. Marcel Swart Prof. Dr. Célia Fonseca Guerra Prof. Dr. Tadeusz Marek Krygowski Prof. Dr. Halina Szatylowicz 《Chemphyschem》2020,21(18):2112-2126
For many years, non-covalently bonded complexes of nucleobases have attracted considerable interest. However, there is a lack of information about the nature of hydrogen bonding between nucleobases when the bonding is affected by metal coordination to one of the nucleobases, and how the individual hydrogen bonds and aromaticity of nucleobases respond to the presence of the metal cation. Here we report a DFT computational study of nucleobase pairs interacting with alkali metal cations. The metal cations contribute to the stabilization of the base pairs to varying degrees depending on their position. The energy decomposition analysis revealed that the nature of bonding between nucleobases does not change much upon metal coordination. The effect of the cations on individual hydrogen bonds were described by changes in VDD charges on frontier atoms, H-bond length, bond energy from NBO analysis, and the delocalization index from QTAIM calculations. The aromaticity changes were determined by a HOMA index. 相似文献
84.
Metal-sulphur phase-based semiconductor materials are often investigated in the field of nanotechnology. Herein, we describe the synthetic route to obtain Mo2S3 nanocrystals from MoS2 via a laser-furnace technique. These nanocrystals have been tested for cytotoxicity against the monocytic leukemic THP-1 cell line. The synthetic process caused a phase change from MoS2 to Mo2S3 at a temperature of 1100 °C and a pressure of 400 Torr. Powder X-ray diffraction analysis confirmed the crystallinity and structure and X-ray photoelectron spectroscopy confirmed the chemical composition and oxidation states of the Mo2S3 nanocrystals. The morphology of the Mo2S3 has been observed by using field emission scanning electron microscopy and high-resolution transmission electron microscopy. The in vitro cytotoxicity evaluation of the Mo2S3 nanocrystals was determined in the THP-1 cell line. The cytotoxic potential of the Mo2S3 against THP-1 cells was assessed by the WST-1 assay and intracellular caspase activities. The caspase activities were significantly elevated indicating the initiation of both the intrinsic and extrinsic apoptotic pathways when compared to untreated cells. Field emission scanning electron microscopy revealed that the Mo2S3 NCs compromised the cell membrane integrity resulting in a loss of THP-1 cell viability and apoptosis. Thus, Mo2S3 is an aqueous nanocrystal which shows promising cytotoxicity effect against THP-1 with good photoluminescent properties. 相似文献
85.
S. V. Motloung F. B. Dejene H. C. Swart O. M. Ntwaeaborwa 《Journal of Sol-Gel Science and Technology》2014,70(3):422-427
Undoped and Pb2+-doped ultrafine cubic zinc aluminate (ZnAl2O4) hosts were successfully prepared at a relatively low temperature (~80 °C) using the sol–gel method. The concentration of Pb2+ was varied from 0 to 5 mol%. The TGA showed that the minimum annealing temperature required to obtain single phase ZnAl2O4 must be above 400 °C. The XRD data revealed that all the annealed samples were single phase crystalline structures and the estimated crystallites size were in the range of 21–30 nm in diameter. The FTIR results suggest that heat-treating can destroy some of the bonds. The surface morphology of the phosphors was influenced by the Pb2+ mol%. Undoped and Pb2+-doped ZnAl2O4 nanoparticles exhibit the violet emission at slightly different positions. The slight peak shifts suggests the possibilities that the luminescence centre can either be due to the defects level in the host or Pb2+ ions. The emission peaks at 390 and 399 nm are ascribed to the typical UV transitions 3P0,1 → 1S0 in Pb2+ ion. At the higher Pb2+ mol%, the luminescence quenching behaviour occurs, which suggests that doping with Pb2+ ions is accompanied by the introduction of new defect sites that enhance non-radiative recombination of the excited electrons. 相似文献
86.
Exploring the Potential Energy Surface of E2P4 Clusters (E=Group 13 Element): The Quest for Inverse Carbon‐Free Sandwiches
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Abril C. Castro Dr. Edison Osorio Dr. José Luis Cabellos Dr. Erick Cerpa Dr. Eduard Matito Prof. Dr. Miquel Solà Prof. Dr. Marcel Swart Prof. Dr. Gabriel Merino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4583-4590
Inverse carbon‐free sandwich structures with formula E2P4 (E=Al, Ga, In, Tl) have been proposed as a promising new target in main‐group chemistry. Our computational exploration of their corresponding potential‐energy surfaces at the S12h/TZ2P level shows that indeed stable carbon‐free inverse‐sandwiches can be obtained if one chooses an appropriate Group 13 element for E. The boron analogue B2P4 does not form the D4h‐symmetric inverse‐sandwich structure, but instead prefers a D2d structure of two perpendicular BP2 units with the formation of a double B?B bond. For the other elements of Group 13, Al–Tl, the most favorable isomer is the D4h inverse‐sandwich structure. The preference for the D2d isomer for B2P4 and D4h for their heavier analogues has been rationalized in terms of an isomerization‐energy decomposition analysis, and further corroborated by determination of aromaticity of these species. 相似文献
87.
The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns,
vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and
are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist
of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex
wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML
models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control
methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method
used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller
was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex
dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved
for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional
and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially
varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order
CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle
map. 相似文献
88.
The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such
as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron
microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced
by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization
reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included. 相似文献
89.
After some introductory propositions, we give a dual characterization of those locally convex spaces which satisfy the Mackey
convergence condition or the fast convergence condition by means of Schwartz topologies. Making use of the universal Schwartz
space (l
∞
,τ(l
∞
,l
1)) we prove some representation theorems for bornological and ultrabornological spaces, that is, every bornological spaceE is a dense subspace of an inductive limit lim indE
a, a∈A, ofseparable Banach spacesE
a, and every Mackey null sequence inE is a null sequence in someE
a. IfE is ultrabornological, thenE can be represented as lim indE
a,a∈A, allE
a separable Banach spaces, such that every fast null sequence inE is a null sequence in someE
a. 相似文献
90.