Geneva, 19 June 2009. At the 151st session of the CERN* Council today,
CERN Director General Rolf Heuer confirmed that the Large Hadron
Collider (LHC) remains on schedule for a restart this autumn, albeit
about 2-3 weeks later than originally foreseen. Following the incident
of 19 September 2008 that brought the LHC to a standstill, a great deal
of work has been done to understand the causes of the incident and
ensure that a similar incident cannot happen again.
“Many new tests have been developed,” said CERN’s Director for
accelerators, Steve Myers. “That’s given us a wealth of information
about the LHC splices, and confidence that we will be in good shape for
running this year.”
Nanoscale charging hysteresis measurement using multifrequency electrosctatic force spectroscopy
Dana group has developed a scanning probe technique that can be used
to measure charging of localized states on conducting or partially
insulating substrates at room temperature under ambient conditions.
Electrostatic interactions in the presence of a charged particle
between the tip and the sample is monitored by the second order
flexural mode, while the fundamental mode is used for stabilizing the
tip-sample separation
In a cyclic voltage sweep,
measuring the amplitude of the electrostatic excitation, it is possible
to obtain linear curves symmetric around the contact potential
difference value as shown in the figure. Charging of the surface
states, or states between the tip and the ground plane effectively
shifts the surface potential causing a hysteresis.
Figure: (a) Electrostatic excitation of the second order mode during a
voltage sweep on a clean silicon surface. The arrows denote voltage
sweep directions. No hysteresis can be observed. (b) Electrostatic
excitation of the second order mode during a voltage sweep on silicon
nitride layer with silicon nanocrystals embedded. Significant
hysteresis is observable, indicating charging of nanocrystals. The
arrows denote onset of charging and discharging events. The insets show
capacitance-voltage traces of macroscopic capacitors fabricated using
silicon nitride films without and with nanocrystals.
Reference: Bostanci et al., Applied Physics Letters 92, 093108 2008
Source: Institute of Materials Science and Nanotechnology - Turkey
Electronic and magnetic properties of 3d transition-metal atom adsorbed graphene and graphene nanoribbons
Graphene
is an example of a truly two dimensional crystal with interesting
properties. Carbon based materials are expected to be building block of
tomorrow's technology. Carbon nanotubes can be metallic or
semiconducting, depending on their chirality. This could lead to a
fully carbon-based elecronics. However, the lack of control on the
chirality prevents carbon nanotubes from electronic application. Recent
studies indicate that graphene nanoribbons can be produced in a highly
controlable manner unlike CNTs. Graphene nanoribbons appear to be
superior to nanotubes. Functionalization of graphene by adatoms can
also provide several different applications. Chemical functionalization
and substitutional doping have been investigated for many years in
nanotubes with the aim of tailoring their properties for sensing,
transport, and chemical and optical applications. It is thus natural to
do a similar investigation for graphene. In this study, we studied
electronic and magnetic properties of graphene and graphene ribbons
functionalized by 3d-transition metal (TM) atoms. The binding
energies, electronic and magnetic properties of TM atoms adsorbed to a
single side and double sides of graphene are investigated according to
a well-defined pattern of absorbtion. We find that 3d-TM atoms can be
adsorbed on graphene with binding energies ranging between 0.10 to 1.95
eV depending on their species and coverage density. Upon TM-atom
adsorption graphene becomes magnetic metal. Graphene nanoribbons with
armchair edge shapes also adsorb TM-atoms. Binding to the edge
hexagons yield the minimum energy state for all TM-atom species
examined in this work, and all ribbon widths under consideration.
Energy band structures of 3d-TM atom adsorbed graphene nanoribbons
display different magnetic properties. Fe and Ti adsorbed ribbons
become half-metallic whereas depending on the ribbon width and the
adsorption atom species, AGNRs also become FM or AFM metals, magnetic
semiconductors.
UNAM researchers engineer laser fibers for medical operations
UNAM researchers engineer laser fibers for medical operations
UNAM
researchers created an infrared fiber that can be used in hospitals for
laser surgery. The fibers deliver intense laser light inside the body
where it can be used to remove malignant tissues with high precision.
The
specialty fibers are designed and developed fully at UNAM, which has
its own fiber tower custom built for the project. After the completion
of the 3.5 meter high fiber tower in August last year, the researchers
are now able to draw tens of meters of photonic band gap fibers from
polymer-chalcogenide glass composites.
In
distinction to the regular optical fibers, these new generation fibers
guide electromagnetic radiation by a dielectric mirror structure
embedded inside the hollow core. The mirror structure consists of
micrometer sized alternating layer materials. Also, the hollow core of
the fiber enables high power laser light transmission that would easily
melt solid-core fibers.
The transmission wavelength of
the fiber is determined by the multilayer thickness and thus can be
scaled for a wide range of wavelengths. Currently fibers are targeted
for CO2 (10.6 μm) and Holmium (2.1 μm) laser radiation delivery, which
is frequently used in medical operations such as laryngology, urology
(prostate removals).
UNAM researchers discover a new medium for high-capacity hydrogen storage
Graphene, a single atomic layer of graphite, display several unusual
properties originating from its honeycomb structure that can allow
physicists to observe strange relativistic effects at a speed much
slower than the speed of light. Researchers from UNAM, Bilkent
University predicted that graphene flakes with both sides covered by
Ca monolayers can also be used for high-capacity hydrogen storage
medium.
Developing safe and efficient hydrogen storage
is essential for hydrogen economy. Recently efforts have been devoted
to develop carbon based nanostructures, which can absorb H2 molecules
with high storage capacity, but can release them easily in the course
of consumption in fuel cells.
Hydrogen being lightest
element in the universe does not allow an efficient storage in
pressured tanks. The storage mechanism predicted through high
performance computations based on quantum mechanics appears to be
feasible using graphene flakes. This work also reveals another
interesting aspect of graphene.
C. Ataca, E. Aktürk, and S. Ciraci Phys. Rev. B Rapid Comm. 79, xxxx (2009)
Source: Institute of Materials Science and Nanotechnology - Turkey
Scientists design a molecule that must perform a logic
computation before it can go about killing cancer cells via
photodynamic therapy
Researchers in Turkey are reporting a first attempt to marry molecular computing with photodynamic cancer therapy (J. Am. Chem. Soc. 2009, 131,
48). The idea is to design a molecule that must perform a logic
computation before it can help kill cancer cells. In this case, the
logic function for the sensitizer molecule (shown) has to recognize two
characteristics inherent to cancer cells. In this case, the logic
function for the sensitizer molecule (shown) has to recognize two
characteristics inherent to cancer cells: high concentrations of H+ and
Na+. When the conditions are satisfied, which in computing terminology
is referred to as “AND” logic, the molecule, in the presence of light,
generates singlet oxygen (diamagnetic O2), a reactive oxygen species
that destroys cells. The proof-of-principle work was undertaken by
Suriye Ozlem of Middle East Technical University and Engin U. Akkaya of
Bilkent University, both in Ankara. “As the field of molecular
computing grows, it needs applications in areas where conventional
silicon computing cannot go—such as inside biological cells,” comments
A. Prasanna de Silva, a chemist at Queen’s University of Belfast, in
Northern Ireland. The work adds to the growing evidence that “this goal
is attainable,” de Silva says, although getting the new molecule across
cell membranes may require adding water-soluble groups.
One of the many gifted and renowned Muslim scientists Abu Ali Hasan ibn al-Hasan al-Haytham was bom around 965AD in Basrah. He is sometimes called al-Basri, meaning from the city of Basra in Iraq, and sometinies called al-Misri, meaning that he came from Egypt. in Latin he is known as Alhazen because of the Latinised version of his first name “al-Hasan”. An eminent physician, especially optics, he made his mark as the “father of modem optics.”
Strain Calculations from Hall Measurements in Undoped Al0.25Ga0.75N/GaN HEMT Structures
Abstract
The transport properties of undoped Al0.25Ga0.75N/GaN HEMT structures grown by MOCVD were investigated in a temperature range of 20 K–350 K. With Quantitative Mobility Spectrum Analysis (QMSA) method; it was found that, all conduction in undoped Al0.25Ga0.75N/GaN HEMT structures belong to the two dimensional electron gas (2DEG). With the acception of Hall sheet carrier density is the total polarization induced charge density, strains of 2DEG interfaces were calculated. Calculated strain values are in good agreement with the literature. Effects of the growth parameters of the nucleation layers of samples on the mobility and density of the 2DEG are listed.
S. B. Lisesivdin, A. Yildiz, M. Kasap, and E. Ozbay AIP Conf. Proc. 899 623 (2007).
UNAM
researchers created an infrared fiber that can be used in hospitals for
laser surgery. The fibers deliver intense laser light inside the body
where it can be used to remove malignant tissues with high precision. 