314 research outputs found
Unambiguous interpretation of atomically resolved force microscopy images of an insulator
The (111) surface of CaF 2 was imaged with dynamic mode scanning force microscopy and modeled using atomistic simulation. Both experiment and theory showed a clear triangular contrast pattern in images, and theory demonstrated that the contrast pattern is due to the interaction of a positive electrostatic potential tip with fluorine ions in the two topmost surface layers. We find a good agreement of position and relative height of scan line features between theory and experiment and thus establish for the first time an unambiguous identification of sublattices of an insulator imaged by force microscopy
Investigating Atomic Details of the CaF(111) Surface with a qPlus Sensor
The (111) surface of CaF has been intensively studied with
large-amplitude frequency-modulation atomic force microscopy and atomic
contrast formation is now well understood. It has been shown that the apparent
contrast patterns obtained with a polar tip strongly depend on the tip
terminating ion and three sub-lattices of anions and cations can be imaged.
Here, we study the details of atomic contrast formation on CaF(111) with
small-amplitude force microscopy utilizing the qPlus sensor that has been shown
to provide utmost resolution at high scanning stability. Step edges resulting
from cleaving crystals in-situ in the ultra-high vacuum appear as very sharp
structures and on flat terraces, the atomic corrugation is seen in high clarity
even for large area scans. The atomic structure is also not lost when scanning
across triple layer step edges. High resolution scans of small surface areas
yield contrast features of anion- and cation sub-lattices with unprecedented
resolution. These contrast patterns are related to previously reported
theoretical results.Comment: 18 pages, 9 Figures, presented at 7th Int Conf Noncontact AFM
Seattle, USA Sep 12-15 2004, accepted for publication in Nanotechnology,
http://www.iop.or
Unambiguous Interpretation of Atomically Resolved Force Microscopy Images of an Insulator
The (111) surface of CaF2 was imaged with dynamic mode scanning force microscopy and modeledusing atomistic simulation. Both experiment and theory showed a clear triangular contrast pattern in images, and theory demonstrated that the contrast pattern is due to the interaction of a positive electrostatic potential tip with fluorine ions in the two topmost surface layers. We find a good agreement of position and relative height of scan line features between theory and experiment and thus establish for the first time an unambiguous identification of sublattices of an insulator imaged by force microscopy.Peer reviewe
Talking everyday science to very young children: a study involving parents and practitioners within an early childhood centre
The acquisition of everyday scientific concepts by 3-6 year old children attending early childhood institutions has been widely studied. In contrast, research on science learning processes among younger children is less extensive. This paper reports on findings from an exploratory empirical study undertaken in a âstay and playâ service used by parents with children aged 0-3 and located within an East London early childhood centre. The research team collaborated with practitioners to deliver a programme of activities aimed at encouraging parentsâ confidence in their own ability to support emergent scientific thinking among their young children. The programme generated childrenâs engagement and interest. Parents and practitioners reported increased confidence in their ability to promote young childrenâs natural curiosity at home and in early childhood provision. The authors see no reason for positing qualitative differences between the way children acquire scientific and other concepts in their earliest years
Parents talking everyday science with young children
This report is the evaluation of an early years project which was developed by members of the Cass Early Childhood Studies Research Group with funding from the 2015 UEL Civic Engagement Fund. The project aimed to encourage parentsâ confidence in their own ability to support emergent scientific thinking among their young children. The project was modelled on an early years initiative undertaken a few years ago in rural Bangladesh. The original Bangladeshi project was pioneered by Dr Sue Dale Tunnicliffe, Reader in Science Education at University College Londonâs Institute of Education, and chair of CASTME, the Commonwealth Association of Science, Technology and Mathematics Educator
Transition Radiation Spectroscopy with Prototypes of the ALICE TRD
We present measurements of the transition radiation (TR) spectrum produced in
an irregular radiator at different electron momenta. The data are compared to
simulations of TR from a regular radiator.Comment: 4 pages, 5 Figures, Proceedings for "TRDs for the 3rd millennium"
(Sept. 4-7, 2003, Bari, Italy
Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of the TiO2(110) surface
Enevoldsen GH, Pinto HP, Foster AS, et al. Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of the TiO2(110) surface. Physical Review B. 2008;78(4):045416.The atomic-scale contrast in noncontact atomic force microscopy (nc-AFM) images is determined by the geometry and exact atomic structure of the tip apex. However, the tip state is an experimentally unknown parameter, and the lack of insight into the tip apex often limits the possibilities of extracting precise quantitative and qualitative atomistic information on the surface under inspection. From an interplay between simultaneously recorded nc-AFM and scanning tunneling microscopy (STM) data, and atomistic STM simulations based on multiple scattering theory, we demonstrate how the state of the scanning probe microscopy (SPM) tip in the experiments may be determined. The analysis of a large number of experimental SPM images recorded with different tips reveals that no general correlation exists between the contrast observed in the nc-AFM and the tunneling current (I-t) images on TiO2(110) surface. The exact state of the SPM tip must, therefore, be determined for each specific case, which is normally a very difficult endeavor. However, our analysis of the AFM contrast on TiO2(110) surface allows us to considerably reduce the number of tips to be considered in a full simulation. By carefully evaluating the contrast of a handpicked library of SPM tips, we manage to determine a very accurate model of the SPM tip used in an experiment for the first time. It is envisioned that the approach presented here may eventually be used in future studies to screen for and select a SPM tip with a special functionalization prior to imaging an unknown sample, and in that way facilitate precise modeling and chemical identification of surface species
Chemical identification of point defects and adsorbates on a metal oxide surface by atomic force microscopy
Lauritsen JV, Foster AS, Olesen GH, et al. Chemical identification of point defects and adsorbates on a metal oxide surface by atomic force microscopy. Nanotechnology. 2006;17(14):3436-3441.Atomic force microscopy in the non-contact mode (nc-AFM) can provide atom-resolved images of the surface of, in principle, any material independent of its conductivity. Due to the complex mechanisms involved in the contrast formation in nc-AFM imaging, it is, however, far from trivial to identify individual surface atoms or adsorbates from AFM images. In this work, we successfully demonstrate how to extract detailed information about defects and the chemical identity of adsorbates on a metal oxide surface from nc-AFM images. We make use of the observation that the apex of the AFM tip can be altered to expose either a positive or negative tip termination. The complementary set of images recorded with the two tip terminations unambiguously define the ionic sub-lattices and reveal the exact positions of oxygen vacancies and hydroxyl (OH) defects on a TiO2 surface. Chemical specificity is extracted by comparing the characteristic contrast patterns of the defects with results from comprehensive AFM simulations. Our methodology of analysis is generally applicable and may be pivotal for uncovering surface defects and adsorbates on other transition metal oxides designed for heterogeneous catalysis, photo-electrolysis or biocompatibility
Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials
Recent years witnessed a rapid growth of interest of scientific and
engineering communities to thermal properties of materials. Carbon allotropes
and derivatives occupy a unique place in terms of their ability to conduct
heat. The room-temperature thermal conductivity of carbon materials span an
extraordinary large range - of over five orders of magnitude - from the lowest
in amorphous carbons to the highest in graphene and carbon nanotubes. I review
thermal and thermoelectric properties of carbon materials focusing on recent
results for graphene, carbon nanotubes and nanostructured carbon materials with
different degrees of disorder. A special attention is given to the unusual size
dependence of heat conduction in two-dimensional crystals and, specifically, in
graphene. I also describe prospects of applications of graphene and carbon
materials for thermal management of electronics.Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxe
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