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Dark field microscopy

A Ramm, N Sakib, A Bhasin, M C Downer
We use near-infrared dark-field optical microscopy to probe isothermal time variation of the volume fraction of naturally-occurring, subsurface microstructures in PG 64-22 asphalt binders at temperature T=30∘C, following a rapid heating (cooling) increment |ΔT|=20∘C from initial temperature T0=10∘C(50∘C). We compare these microstructure variations with isothermal time variations of the magnitude |G30∗(t)| of the bulk complex shear modulus measured for identical sample conditions with a Dynamic Shear Rheometer...
May 22, 2018: Journal of Microscopy
S Trautmann, M Richard-Lacroix, A Dathe, H Schneidewind, J Dellith, W Fritzsche, V Deckert
The optical response of realistic 3D plasmonic substrates composed of randomly shaped particles of different size and interparticle distance distributions in addition to nanometer scale surface roughness is intrinsically challenging to simulate due to computational limitations. Here, we present a Finite Element Method (FEM)-based methodology that bridges in-depth theoretical investigations and experimental optical response of plasmonic substrates composed of such silver nanoparticles. Parametrized scanning electron microscopy (SEM) images of surface enhanced Raman spectroscopy (SERS) active substrate and tip-enhanced Raman spectroscopy (TERS) probes are used to simulate the far-and near-field optical response...
May 18, 2018: Nanoscale
Takumi Hamaoka, Chih-Yu Jao, Masaki Takeguchi
Annular dark-field scanning confocal electron microscopy (ADF-SCEM) has been studied using multislice simulations. Thermal diffuse scattering was considered in the calculations. Geometric aberrations of the lenses were introduced. A finite-sized pinhole was taken into consideration, in addition to an ideal point pinhole. ADF-SCEM images of Al crystals aligned along a zone-axis exhibit elongated contrast along the optic axis. Results of simulations suggest that if geometric aberrations of an imaging lens are corrected, depth resolution in ADF-SCEM can be improved by employing a large collection semi-angle of an annular aperture, even with a finite pinhole...
May 14, 2018: Microscopy
Shanshan Wang, Hidetaka Sawada, Xiaoyu Han, Si Zhou, Sha Li, Zheng Xiao Guo, Angus I Kirkland, Jamie H Warner
We show that Pt nanoclusters preferentially nucleate along the grain boundaries (GBs) in polycrystalline MoS2 monolayer films, with dislocations acting as the seed site. Atomic resolution studies by aberration-corrected annular dark-field scanning transmission electron microscopy reveal periodic spacing of Pt nanoclusters with dependence on GB tilt angles and random spacings for the antiphase boundaries ( i.e., 60°). Individual Pt atoms are imaged within the dislocation core sections of the GB region, with various positions observed, including both the substitutional sites of Mo and the hollow center of the octahedral ring...
May 15, 2018: ACS Nano
Philippe Kowalczyk, Françoise Hippert, Nicolas Bernier, Cristian Mocuta, Chiara Sabbione, Walter Batista-Pessoa, Pierre Noé
Van der Waals layered GeTe/Sb2 Te3 superlattices (SLs) have demonstrated outstanding performances for use in resistive memories in so-called interfacial phase-change memory (iPCM) devices. GeTe/Sb2 Te3 SLs are made by periodically stacking ultrathin GeTe and Sb2 Te3 crystalline layers. The mechanism of the resistance change in iPCM devices is still highly debated. Recent experimental studies on SLs grown by molecular beam epitaxy or pulsed laser deposition indicate that the local structure does not correspond to any of the previously proposed structural models...
May 14, 2018: Small
Jun-Zhou Chen, Guo-Ai Li, Xin Cai, Jian-Tang Jiang, Wen-Zhu Shao, Li Yang, Liang Zhen
A non-isothermal ageing process was proposed for an Al-Zn-Mg-Cu alloy aiming to accommodate the slow heating/cooling procedure during the ageing of large components. The evolution of microstructure and microchemistry was analyzed by using transmission electron microscopy, high-angle annular dark field imaging, and energy dispersive spectrometry. The age-hardening of the alloy was examined to evaluate the strengthening behavior during the non-isothermal process. The corrosion behavior was investigated via observing the specimens immersed in EXCO solution (solution for Exfoliation Corrosion Susceptibility test in 2xxx and 7xxx series aluminum alloys, referring ASTM G34-01)...
May 3, 2018: Materials
Huiyan Ning, Yandong Yu, Bo Gao, Lirong Xiao, Lihua Wen, Zehua Yan, Li Li, Xuefei Chen
Grain refinement and precipitation are two effective ways to improve the mechanical properties of Mg-RE alloys. In this work, a two-step forming process is proposed. This includes cold rolling and subsequent annealing at high temperature for a short duration. By the two-step forming process, grains can be refined from 100 μm to 20 μm in compare with ~30 μm by common hot rolling at 450 °C for a reduction of 80%. The sample shows more distinct aging hardening, as the hardness amplification of 60 HV is twice that of the hot-rolled sample...
May 9, 2018: Materials
Xuewen He, Zheng Zhao, Ling-Hong Xiong, Peng Fei Gao, Chen Peng, Rong Sheng Li, Yu Xiong, Zhi Li, Herman H-Y Sung, Ian D Williams, Ryan T K Kwok, Jacky W Y Lam, Cheng Zhi Huang, Nan Ma, Ben Zhong Tang
Multimodality imaging is highly desirable for accurate diagnosis by achieving high sensitivity, spatial-temporal resolution and penetration depth with a single structural unit. However, it is still challenging to integrate fluorescent and plasmonic modalities into a single structure as they are naturally incompatible because of significant fluorescence quenching by plasmonic noble-metal nanoparticles. Herein, we report a new type of silver@AIEgen (aggregation-induced emission luminogen) core-shell nanoparticle (AACSN) with both strong aggregated-state fluorescence of AIEgen and distinctive plasmonic scattering of silver nanoparticle for multimodality imaging in living cells and small animals...
May 9, 2018: Journal of the American Chemical Society
Xiaoqin Chu, Qian Li, Shuangying Gui, Zhengguang Li, Jiaojiao Cao, Jianqin Jiang
This study developed a new transdermal delivery system for the improved delivery of sinomenine hydrochloride (SH). The delivery system utilized the advantages of lyotropic liquid crystals (LLC) creating an adaptable system that offers a variety of options for the field of transdermal delivery. The formulation was prepared, characterized, and evaluated for its skin penetration in vitro. In the study, the appearance of samples was characterized by visual observation, and these LLC gels were colorless and transparent...
May 8, 2018: AAPS PharmSciTech
Adam Ferrick, Mei Wang, Taylor J Woehl
Electric field directed assembly of colloidal nanoparticles (NPs) has been widely adopted for fabricating functional thin films and nanostructured surfaces. While first order electrokinetic effects on NPs are well-understood in terms of classical models, effects of second order electrokinetics that involve induced surface charge are still poorly understood. Induced charge electroosmotic phenomena, such as electrohydrodynamic (EHD) flow, have long been implicated in electric field directed NP assembly with little experimental basis...
May 4, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
N Baladés, D L Sales, M Herrera, C H Tan, Y Liu, R D Richards, S I Molina
The Bi content in GaAs/GaAs1 - x Bi x /GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content...
April 25, 2018: Nanoscale Research Letters
Tadahiro Yokosawa, Eric Prestat, Robert Polly, Muriel Bouby, Kathy Dardenne, Nicolas Finck, Sarah J Haigh, Melissa A Denecke, Horst Geckeis
Transformation products of two-line ferrihydrite associated with Lu(III) were studied after 12 years of aging using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), high-efficiency energy-dispersive X-ray spectroscopy (EDXS), and density functional theory (DFT). The transformation products consisted of hematite nanoparticles with overgrown goethite needles. High-efficiency STEM-EDXS revealed that Lu is only associated with goethite needles, and atomic-resolution HAADF-STEM reveals structural incorporation of Lu within goethite, partially replacing structural Fe sites...
April 18, 2018: Environmental Science and Pollution Research International
Xiaoli Yang, Qinggang Liu, Yaru Zhang, Xiong Su, Yanqiang Huang, Tao Zhang
We report here a facile strategy for encapsulating Pt clusters into MFI crystals via a dry gel conversion (DGC) method, by introducing Pt-immobilized Schiff-SiO2 as the silicon resource. This protocol involves a solid phase transformation process for crystallization which occurs without significant deconstruction of the structure of the Pt-containing precursor. High-angle annular dark-field scanning transmission electron microscopy images indicate that most of the Pt clusters are less than 1 nm in size and located in defective channels or voids of MFI...
April 12, 2018: Nanoscale
Wenjuan Bian, Yue Lin, Ting Wang, Xue Yu, Jianbei Qiu, Meng Zhou, Hongmei Luo, Siu Fung Yu, Xuhui Xu
Core-shell structure is an obvious concept to suppress surface-related deactivations in lanthanide-doped upconversion nanoparticles (UCNPs). However, no direct observation on the atomic-scale surface restoration, which can improve the upconversion photoluminescence, has been reported. Here, we use the aberration-corrected high angle annular dark field scanning transmission electron microscopy to study the surface condition of KLu2F7:Yb3+,Er3+ bare core UCNPs. Due to the very thin and uniform thickness of the UCNPs, we observe unambiguously that the recovery from surface defects enhances upconversion photoluminescence...
April 4, 2018: ACS Nano
Peri Korshed, Lin Li, Duc-The Ngo, Tao Wang
Silver nanoparticles (AgNPs) are widely used as antibacterial agents, but their antibacterial durability and the influence by storage conditions have not been thoroughly investigated. In this study, AgNPs were produced using a picosecond laser and stored under three different conditions: daylight, dark and cold (4 °C). The antibacterial effects of the laser AgNPs were examined against Escherichia coli in either a 14-day interval (frequent air exposure) or a 45-day interval (less frequent air exposure) using a well-diffusion method until the antibacterial effects disappeared...
April 4, 2018: Nanomaterials
Anupama Bhat, Kewei Huan, Tiana Cooks, Hacene Boukari, Qi Lu
Noble metallic nanoparticles (NPs) such as gold and silver nanoparticles (AuNPs and AgNPs) have been shown to exhibit anti-tumor effect in anti-angiogenesis, photothermal and radio therapeutics. On the other hand, cell membranes are critical locales for specific targeting of cancerous cells. Therefore, NP-membrane interactions need be studied at molecular level to help better understand the underlying physicochemical mechanisms for future applications in cancer nanotechnology. Herein, we report our study on the interactions between citrate stabilized colloidal AuNPs/AgNPs (10 nm in size) and giant unilamellar vesicles (GUVs) using hyperspectral dark-field microscopy...
March 28, 2018: International Journal of Molecular Sciences
Arnaud Demortiere, Donovan Leonard, Valeri Petkov, Karena W Chapman, Soma Chattopadhyay, Chunxing She, David A Cullen, Tomohiro Shibata, Matthew Pelton, Elena V Shevchenko
Colloidal semiconductor nanocrystals are commonly grown with a shell of a second semiconductor material to obtain desired physical properties, such as increased photoluminescence quantum yield. However, the growth of a lattice-mismatched shell results in strain within the nanocrystal, and this strain has the potential to produce crystalline defects. Here, we study CdSe/CdS core/shell nanorods as a model system to investigate the influence of core size and shape on the formation of stacking faults in the nanocrystal...
March 28, 2018: Journal of Physical Chemistry Letters
Kunkun Li, Qing-Zhen Huang, Qinghua Zhang, Zewen Xiao, Toshio Kamiya, Hideo Hosono, Duanduan Yuan, Jiangang Guo, Xiaolong Chen
We report the synthesis and characterizations of a new FeSe-based compound CsFe4-δ Se4 , which is closely related to alkali intercalated FeSe superconductors while exhibits distinct features. It does not undergo phase separation and antiferromagnetic transition. Powder neutron diffractions, electron microscopy and high-angle annular-dark-field images confirm that CsFe4-δ Se4 possesses an ordered Cs arrangement as √2 × √2 superstructure, evidencing a B-centered orthorhombic lattice with a space group of Bmmm...
March 26, 2018: Inorganic Chemistry
Youkui Zhang, Chuanqiang Wu, Hongliang Jiang, Yunxiang Lin, Hengjie Liu, Qun He, Shuangming Chen, Tao Duan, Li Song
Developing highly efficient catalysts for oxygen evolution reaction (OER) in neutral media is extremely crucial for microbial electrolysis cells and electrochemical CO2 reduction. Herein, a facile one-step approach is developed to synthesize a new type of well-dispersed iridium (Ir) incorporated cobalt-based hydroxide nanosheets (nominated as CoIr) for OER. The Ir species as clusters and single atoms are incorporated into the defect-rich hydroxide nanosheets through the formation of rich Co-Ir species, as revealed by systematic synchrotron radiation based X-ray spectroscopic characterizations combining with high-angle annular dark-field scanning transmission electron microscopy measurement...
March 25, 2018: Advanced Materials
B I R Dhladhla, P Mwanza, M E Lee, S Moore, G B Dealtry
Enumeration techniques were compared for quantification of the South African isolate of Cryptophlebia leucotreta granulovirus (CrleGV-SA), used as a biopesticide to control false codling moth (Thaumatotibia leucotreta), an insect pest of various fruits and nuts, including citrus. The routine enumeration method for CrleGV-SA virus particles in experimentation and production of CrleGV-SA biopesticides is dark field microscopy. This method was compared with spectrophotometry, scanning electron microscopy (SEM) and real time quantitative polymerase chain reaction (qPCR)...
March 20, 2018: Journal of Virological Methods
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