566 research outputs found
Geographical Survey of Nigerian Mineral Resources: A Step toward Planned Development
The geographical survey of Nigerian Mineral resources – A step toward planned development is the determination of mineral resources that are within her territory, and it exploited wisely become useful to man. The minerals are associated with two main types of rocks found in Nigeria. They are the basement rocks and the sedimentary rocks. Nigerian mineral resources have been classified into four main groups of the fossil fuel, metallic, non-metallic and radio-active minerals. Exploitation of these minerals can if properly organized, serve as tourist attraction, where tourist are attracted to such site or environment either for relaxation, recreation or for educational purpose. There are opening for the untapped minerals to be exploited for development of the entire country. Key words: Geographical survey, Mineral resources, Nigeria, development, Tourism.
Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor
Crucial to analyze phenomena as varied as plasmonic hot spots and the spread
of cancer in living tissue, nanoscale thermometry is challenging: probes are
usually larger than the sample under study, and contact techniques may alter
the sample temperature itself. Many photostable nanomaterials whose
luminescence is temperature-dependent, such as lanthanide-doped phosphors, have
been shown to be good non-contact thermometric sensors when optically excited.
Using such nanomaterials, in this work we accomplished the key milestone of
enabling far-field thermometry with a spatial resolution that is not
diffraction-limited at readout.
We explore thermal effects on the cathodoluminescence of lanthanide-doped
NaYF nanoparticles. Whereas cathodoluminescence from such lanthanide-doped
nanomaterials has been previously observed, here we use quantitative features
of such emission for the first time towards an application beyond localization.
We demonstrate a thermometry scheme that is based on cathodoluminescence
lifetime changes as a function of temperature that achieves 30 mK
sensitivity in sub-m nanoparticle patches. The scheme is robust against
spurious effects related to electron beam radiation damage and optical
alignment fluctuations.
We foresee the potential of single nanoparticles, of sheets of nanoparticles,
and also of thin films of lanthanide-doped NaYF to yield temperature
information via cathodoluminescence changes when in the vicinity of a sample of
interest; the phosphor may even protect the sample from direct contact to
damaging electron beam radiation. Cathodoluminescence-based thermometry is thus
a valuable novel tool towards temperature monitoring at the nanoscale, with
broad applications including heat dissipation in miniaturized electronics and
biological diagnostics.Comment: Main text: 30 pages + 4 figures; supplementary information: 22 pages
+ 8 figure
Systematic Determination of Absolute Absorption Cross-section of Individual Carbon Nanotubes
Determination of optical absorption cross-section is always among the central
importance of understanding a material. However its realization on individual
nanostructures, such as carbon nanotubes, is experimentally challenging due to
the small extinction signal using conventional transmission measurements. Here
we develop a technique based on polarization manipulation to enhance the
sensitivity of single-nanotube absorption spectroscopy by two-orders of
magnitude. We systematically determine absorption cross-section over broad
spectral range at single-tube level for more than 50 chirality-defined
single-walled nanotubes. Our data reveals chirality-dependent one-dimensional
photo-physics through the behaviours of exciton oscillator strength and
lifetime. We also establish an empirical formula to predict absorption spectrum
of any nanotube, which provides the foundation to determine quantum
efficiencies in important photoluminescence and photovoltaic processes
Symmetric Versus Nonsymmetric Structure of the Phosphorus Vacancy on InP(110)
The atomic and electronic structure of positively charged P vacancies on
InP(110) surfaces is determined by combining scanning tunneling microscopy,
photoelectron spectroscopy, and density-functional theory calculations. The
vacancy exhibits a nonsymmetric rebonded atomic configuration with a charge
transfer level 0.75+-0.1 eV above the valence band maximum. The scanning
tunneling microscopy (STM) images show only a time average of two degenerate
geometries, due to a thermal flip motion between the mirror configurations.
This leads to an apparently symmetric STM image, although the ground state
atomic structure is nonsymmetric.Comment: 5 pages including 3 figures. related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides with experiment and theory
Chalcogen vacancies are considered to be the most abundant point defects in
two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors, and
predicted to result in deep in-gap states (IGS). As a result, important
features in the optical response of 2D-TMDs have typically been attributed to
chalcogen vacancies, with indirect support from Transmission Electron
Microscopy (TEM) and Scanning Tunneling Microscopy (STM) images. However, TEM
imaging measurements do not provide direct access to the electronic structure
of individual defects; and while Scanning Tunneling Spectroscopy (STS) is a
direct probe of local electronic structure, the interpretation of the chemical
nature of atomically-resolved STM images of point defects in 2D-TMDs can be
ambiguous. As a result, the assignment of point defects as vacancies or
substitutional atoms of different kinds in 2D-TMDs, and their influence on
their electronic properties, has been inconsistent and lacks consensus. Here,
we combine low-temperature non-contact atomic force microscopy (nc-AFM), STS,
and state-of-the-art ab initio density functional theory (DFT) and GW
calculations to determine both the structure and electronic properties of the
most abundant individual chalcogen-site defects common to 2D-TMDs.
Surprisingly, we observe no IGS for any of the chalcogen defects probed. Our
results and analysis strongly suggest that the common chalcogen defects in our
2D-TMDs, prepared and measured in standard environments, are substitutional
oxygen rather than vacancies
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Quasi-ternary nanoparticle superlattices through nanoparticle design
Individual nanoscale building blocks exhibit a wide range of size-dependent properties, since their size can be tuned over known characteristic length scales of bulk materials. In the last several years, the possibility of combining different materials in the form of two and three component nanoparticles (NPs) has been extensively explored. Also multi-component materials can be obtained via self-assembly of NPs from their binary colloidal mixtures. These new nanocrystal solids may possess tunable collective properties that originate from interactions between size and composition controlled building blocks. Exchange coupling between neighboring NPs of magnetically soft and hard materials enhances the magnetic energy product of the nanocomposite material. Randomly mixed solids of small and large semiconducting CdSe NPs revealed enhancement of photoluminescence intensity of large semiconductor particles accompanied by quenching of photoluminescence of the small particles because of long-range resonant transfer of electronic excitations from the more electronically confined small particles to higher excited states of the large particles. Recently, it was demonstrated that binary semiconducting composite materials can show strongly enhanced electronic properties with about 100-fold higher conductance as compared to the sum of individual conductances of single-component films. Creation of highly periodic superlattices is expected not just provide the control of the homogeneity of the sample but also affect their properties. It was shown that silver nanocrystals organized into periodic cubic structures vibrated coherently [20] and demonstrated a change in electronic transport properties
Wigs, disguises and child's play : solidarity in teacher education
It is generally acknowledged that much contemporary education takes place within a dominant audit culture, in which accountability becomes a powerful driver of educational practices. In this culture both pupils and teachers risk being configured as a means to an assessment and target-driven end: pupils are schooled within a particular paradigm of education. The article discusses some ethical issues raised by such schooling, particularly the tensions arising for teachers, and by implication, teacher educators who prepare and support teachers for work in situations where vocational aims and beliefs may be in in conflict with instrumentalist aims. The article offers De Certeau’s concept of ‘la perruque’ to suggest an opening to playful engagement for human ends in education, as a way of contending with and managing the tensions generated. I use the concept to recover a concept of solidarity for teacher educators and teachers to enable ethical teaching in difficult times
Mapping Local Charge Recombination Heterogeneity by Multidimensional Nanospectroscopic Imaging
As materials functionality becomes more dependent on local physical and electronic properties,
the importance of optically probing matter with true nanoscale spatial resolution has increased.
In this work, we mapped the influence of local trap states within individual nanowires on carrier
recombination with deeply subwavelength resolution. This is achieved using multidimensional
nanospectroscopic imaging based on a nano-optical device. Placed at the end of a scan probe,
the device delivers optimal near-field properties, including highly efficient far-field to near-field
coupling, ultralarge field enhancement, nearly background-free imaging, independence from
sample requirements, and broadband operation. We performed ~40-nanometer–resolution
hyperspectral imaging of indium phosphide nanowires via excitation and collection through
the probes, revealing optoelectronic structure along individual nanowires that is not accessible
with other methods
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