212 research outputs found
Electron Transport at Surfaces and Interfaces
Here we present two techniques which give insight on transport phenomena with atomic resolution. Ballistic electron emission microscopy is used to study the ballistic transport through layered heterogeneous systems. The measured ballistic fraction of the tunneling current provides information
about lossless transport channels through metallic layers and organic adsorbates. The transport characteristics of Bi(111)/Si Schottky devices and the influence of the organic adsorbates perylene tetracaboxylic dianhydride acid and C60 on the ballistic current are discussed. Scanning
tunneling potentiometry gives access to the lateral transport along a surface, thus scattering processes within two-dimensional electron systems for the Bi(111) surface and the Si(111)(?3 × ?3)-Ag surface could be visualized
Thermal expansion in photo-assisted tunneling: visible light versus free-space terahertz pulses
Photo-assisted tunneling in scanning tunneling microscopy has attracted
considerable interest to combine sub-picosecond and sub-nanometer resolutions.
The illumination of a junction with visible or infrared light, however, induces
thermal expansion of the tip and the sample, which strongly affects the
measurements. Employing free-space THz pulses instead of visible light has been
proposed to solve these thermal issues while providing photo-induced currents
of similar magnitude. Here we compared the impact of illuminating the same
tunneling junction, reaching comparable photo-induced current, with red light
and with THz radiations. Our data provide a clear and direct evidence of
thermal expansion with red light-illumination, while such thermal effects are
negligible with THz radiations
Variable-temperature lightwave-driven scanning tunneling microscope with a compact, turn-key terahertz source
We report on a lightwave-driven scanning tunneling microscope based on a
home-built microscope and a compact, commercial, and cost-effective
terahertz-generation unit with a repetition rate of 100 MHz. The measurements
are performed in ultrahigh vacuum at temperatures between 10 K and 300 K. The
cross-correlation of the pump and probe pulses indicate a temporal resolution
on the order of a picosecond. In terms of spatial resolution, CO molecules,
step edges and atomically resolved terraces are readily observed in terahertz
images, with sometimes better contrast than in the topographic and (DC) current
channels. The utilization of a compact, turn-key terahertz-generation system
requires only limited experience with optics and terahertz generation, which
may facilitate the deployment of the technique to further research groups
Face recognition based on the proximity measure clustering
In this paper problems of featureless face recognition are considered. The recognition is based on clustering the proximity measures between the distributions of brightness clusters cardinality for segmented images. As a proximity measure three types of distances are used in this work: the Euclidean, cosine and Kullback-Leibler distances. Image segmentation and proximity measure clustering are carried out by means of a software model of the recurrent neural network. Results of the experimental studies of the proposed approach are presented
Temperature dependence of the energy dissipation in dynamic force microscopy
The dissipation of energy in dynamic force microscopy is usually described in
terms of an adhesion hysteresis mechanism. This mechanism should become less
efficient with increasing temperature. To verify this prediction we have
measured topography and dissipation data with dynamic force microscopy in the
temperature range from 100 K up to 300 K. We used
3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both
materials exhibiting a strong dissipation signal at large frequency shifts. At
room temperature, the energy dissipated into the sample (or tip) is 1.9
eV/cycle for PTCDA and 2.7 eV/cycle for KBr, respectively, and is in good
agreement with an adhesion hysteresis mechanism. The energy dissipation over
the PTCDA surface decreases with increasing temperature yielding a negative
temperature coefficient. For the KBr substrate, we find the opposite behaviour:
an increase of dissipated energy with increasing temperature. While the
negative temperature coefficient in case of PTCDA agrees rather well with the
adhesion hysteresis model, the positive slope found for KBr points to a
hitherto unknown dissipation mechanism
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Reconstruction of Ultra-thin Alveolar-capillary Basement Membrane Mimics
Alveolar-capillary basement membrane (BM) is ultra-thin (<2 µm) extracellular matrix that maintains integral epithelial-endothelial cell layers. In vitro reconstructions of alveolar-capillary barrier supported on synthetic scaffolds closely resembling the fibrous and ultra-thin natural BM are essential in mimicking the lung pathophysiology. Although BM topology and dimensions are well known to significantly influence cellular behavior, conventionally used BM mimics fail to recreate this natural niche. To overcome this, electrospun ultra-thin 2 µm poly(caprolactone) (PCL) nanofibrous mesh is used to establish an alveolar-capillary barrier model of lung endothelial/epithelial cells. Transepithelial electrical resistance (TEER) and permeability studies reveal integral tight junctions and improved mass transport through the highly porous PCL meshes compared to conventional dense membranes with etched pores. The chemotaxis of neutrophils is shown across the barrier in presence of inflammatory response that is naturally impeded in confined regions. Conventional requirement of 3 µm or larger pore size can lead to barrier disruption due to epithelial/endothelial cell invasion. Despite high porosity, the interconnected BM mimic prevents barrier disruption and allows neutrophil transmigration, thereby demonstrating the physiological relevance of the thin nanofibrous meshes. It is envisioned that these bipolar cultured barriers would contribute to an organ-level in vitro model for pathological disease, environmental pollutants, and nanotoxicology. © 2021 The Authors. Advanced Biology published by Wiley-VCH Gmb
Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111)
The rates of a hindered molecular rotation induced by tunneling electrons are evaluated using scattering theory within the sudden approximation. Our approach explains the excitation of copper phthalocyanine molecules (CuPc) on Cu(111) as revealed in a recent measurement of telegraph noise in a scanning tunneling microscopy experiment. A complete explanation of the experimental data is performed by computing the geometry of the adsorbed system, its electronic structure, and the energy transfer between tunneling electrons and the molecule's rotational degree of freedom. The results unambiguously show that tunneling electrons induce a frustrated rotation of the molecule. In addition, the theory determines the spatial distribution of the frustrated rotation excitation, confirming the striking dominance of two out of four molecular lobes in the observed excitation process. This lobe selectivity is attributed to the different hybridizations with the underlying substrate. © 2013 American Physical Society.J.S., A.S., C.A.B., and R.M. gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft through the SFB616 ‘Energy Dissipation at Surfaces.’ N.L. is supported by the ICT-FET Integrated Project AtMol (http://www.atmol.eu). M.C.C. thanks the Studienstiftung desdeutschen Volkes.Peer Reviewe
Electrification using Decentralized Micro Hydropower Plants in North-eastern Afghanistan
Electricity supply database from the Afghan national authority for electricity supply shows that about only 20% of the population in Afghanistan had access to grid electricity by 2010. The national utility has a total capacity of about 842 MW, out of which about 696 MW was operational. Additionally, many decentralized units (Micro Hydropower (MHP) plants, diesel generators and solar home systems) supply electricity to about 7% of the population. The donors supported National Solidarity Programme (NSP) has promoted hundreds of rural electrification projects. MHP plants are the major renewable energy based projects among them. In order to identify the operational status of installed MHP plants in four North-eastern provinces (i.e. Badakhshan, Baghlan, Balkh and Takhar) and to assess their socio-economic impacts, an extensive field monitoring had been carried out. The major parameters studied were spatial distribution of MHP plants, investment costs, operational models, end user electricity tariffs, productive use of electricity, community satisfaction, etc. Altogether, 421 MHP installations (about 11 MW installed capacity) were visited. The outcomes obtained from those surveys are presented in detail in this paper
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