335 research outputs found
High sensitive quasi freestanding epitaxial graphene gassensor on 6H-SiC
We have measured the electrical response to NO, N, NH and CO for
epitaxial graphene and quasi freestanding epitaxial graphene on 6H-SiC
substrates. Quasi freestanding epitaxial graphene shows a 6 fold increase in
NO2 sensitivity compared to epitaxial graphene. Both samples show a sensitivity
better than the experimentally limited 1 ppb. The strong increase in
sensitivity of quasi freestanding epitaxial graphene can be explained by a
Fermi-energy close to the Dirac Point leading to a strongly surface doping
dependent sample resistance. Both sensors show a negligible sensitivity to
N, NH and CO
Захисні лісові насадження – важливий структурний елемент у формуванні національної екологічної мережі
Описано роль і значення захисних лісових насаджень як важливого структурного елементу при формуванні національної екологічної мережі.Описана роль и значение защитных лесных насаждений как важного структурного элемента при формировании национальной экологической сети.Role and meaning of forest protective stands as an important structural element for national ecological network formation is described
Direct magneto-optical compression of an effusive atomic beam for high-resolution focused ion beam application
An atomic rubidium beam formed in a 70 mm long two-dimensional
magneto-optical trap (2D MOT), directly loaded from a collimated Knudsen
source, is analyzed using laser-induced fluorescence. The longitudinal velocity
distribution, the transverse temperature and the flux of the atomic beam are
reported. The equivalent transverse reduced brightness of an ion beam with
similar properties as the atomic beam is calculated because the beam is
developed to be photoionized and applied in a focused ion beam. In a single
two-dimensional magneto-optical trapping step an equivalent transverse reduced
brightness of A/(m sr eV) was
achieved with a beam flux equivalent to nA. The
temperature of the beam is further reduced with an optical molasses after the
2D MOT. This increased the equivalent brightness to A/(m sr eV). For currents below 10 pA, for which disorder-induced
heating can be suppressed, this number is also a good estimate of the ion beam
brightness that can be expected. Such an ion beam brightness would be a six
times improvement over the liquid metal ion source and could improve the
resolution in focused ion beam nanofabrication.Comment: 10 pages, 8 figures, 1 tabl
Digital alloy interface grading of an InAlAs/InGaAs quantum cascade laser structure studied by cross-sectional scanning tunneling microscopy
We have studied an InGaAs/InAlAs quantum cascade laser structure with cross-sectional scanning tunneling microscopy. In the quantum cascade laser structure digital alloy grading was used to soften the barriers of the active region. We show that due to alloy fluctuations, softening of the barriers occurs even without the digital gradin
The protective value of trait mindfulness for mothers' anxiety during the perinatal period
Objectives:Anxiety is highly prevalent in the perinatal period and can have negative consequences for the mother and the child. Extensive research has been done on risk factors for anxiety during the perinatal period, but less is known about protective factors. The current study aims to determine the relative contribution of trait mindfulness as a protective factor for anxiety.Methods: A longitudinal study design was used, with four measurement points: 12, 22, and 32 weeks of pregnancy (T0, T1, and T2, respectively), and 6 weeks postpartum (T3). General anxiety was measured at T1, T2, and T3, pregnancy-specific distress was measured at T1 and T2, mindfulness facets (acting with awareness, non-reacting, and non-judging) and partner involvement were measured at T1, and other known risk factors for anxiety were measured at T0. Multilevel regression models were used for statistical analyses.Results:Mindfulness facets measured at T1 were negatively associated with anxiety at T1, T2, and T3, and pregnancy-specific distress at T1 and T2. Of the mindfulness facets, non-judging was shown to have the largest protective effect against anxiety and pregnancy-specific distress. Also compared to partner-involvement and known risk factors, non-judging showed the largest effect on anxiety and pregnancy-specific distress.Conclusions:For pregnant women who are at risk for developing or experiencing high levels of anxiety, it may be beneficial to participate in a mindfulness training with special attention for the attitudinal aspects of mindfulness.</p
Real-space measurement of the potential distribution inside organic semiconductors
We demonstrate that the soft nature of organic semiconductors can be exploited to directly measure the potential distribution inside such an organic layer by scanning-tunneling microscope (STM) based spectroscopy. Keeping the STM feedback system active while reducing the tip-sample bias forces the tip to penetrate the organic layer. From an analysis of the injection and bulk transport processes it follows that the tip height versus bias trace obtained in this way directly reflects the potential distribution in the organic layer
Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs
We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm which is consistent with the observed electronic radius of QR structures.This work was partially supported by the GOA BOF UA 2000, IUAP, FWO-V projects G.0274.01N, G.0435.03, the WOG WO.035.04N (Belgium), the Spanish MCYT under NANOSELF project TIC2002-04096-C03-03 (Spain), the
European Commission GROWTH Programme, NANOMAT
project, contract No. G5RD-CT-2001-00545, and the European Commission SANDiE Network of Excellence, contract No. NMP4-CT-2004-500101.Peer reviewe
Boosting the Figure Of Merit of LSPR-based refractive index sensing by phase-sensitive measurements
Localized surface plasmon resonances possess very interesting properties for
a wide variety of sensing applications. In many of the existing applications
only the intensity of the reflected or transmitted signals is taken into
account, while the phase information is ignored. At the center frequency of a
(localized) surface plasmon resonance, the electron cloud makes the transition
between in- and out-of-phase oscillation with respect to the incident wave.
Here we show that this information can experimentally be extracted by
performing phase-sensitive measurements, which result in linewidths that are
almost one order of magnitude smaller than those for intensity based
measurements. As this phase transition is an intrinsic property of a plasmon
resonance, this opens up many possibilities for boosting the figure of merit
(FOM) of refractive index sensing by taking into account the phase of the
plasmon resonance. We experimentally investigated this for two model systems:
randomly distributed gold nanodisks and gold nanorings on top of a continuous
gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5
for the respective nanoparticles
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