556 research outputs found
Backscattered Electrons and Their Influence on Contrast in the Scanning Electron Microscope
The backscattered electron (BSE) induced secondaries (SE2) emerge from an area that is usually many orders of magnitude larger than the area in which the impinging primary probe releases secondary electrons (SE1). These SE2 secondary electrons form a) an undesired background signal in high resolution scanning micrographs and b) are responsible for the well known proximity effect in electron beam lithography. In this paper we focus our attention on the first topic exclusively: we discuss the complex influence of the SE2 on contrast in SEM micrographs (neglecting the components SE3 and SE4). We do this on the basis of our emission-microscopic measurements of the spatial distributions of SE1 and SE2 emerging from flat bulk specimens. By integrating these distributions in two dimensions we calculate the total number of SE1 and SE2 electrons and deduce the signal to backgroud ratio SE1/(SE1+SE2), i.e., the maximum contrast in one pixel ( single pixel contrast ) and the contrast of two adjacent pixels 1 and 2 according to its usual definition C= (I1 -I2)/(I1 +I2). We calculate the enhanced secondary emission factor for backscattered electrons from our total numbers of SE1 and SE2 for Si, Ge and Ag to Si=2.58, Ge=1.46, Ag=1,23
Magnetism of Superconducting UPt3
The phase diagram of superconducting in pressure-temperature
plane, together with the neutron scattering data is studied within a two
component superconducting order parameter scenario. In order to give a
qualitative explanation to the experimental data a set of two linearly
independent antiferromagnetic moments which emerge appropriately at the
temperature \mbox{} and \mbox{} and
couple to superconductivity is proposed. Several constraints on the fourth
order coefficients in the Ginzburg-Landau free energy are obtained.Comment: 17 pages, figures available on request to
[email protected]
Silicon Superconducting Quantum Interference Device
We have studied a Superconducting Quantum Interference SQUID device made from
a single layer thin film of superconducting silicon. The superconducting layer
is obtained by heavily doping a silicon wafer with boron atoms using the Gas
Immersion Laser Doping (GILD) technique. The SQUID device is composed of two
nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at
low temperature and low magnetic field. The overall behavior shows very good
agreement with numerical simulations based on the Ginzburg-Landau equations.Comment: Published in Applied Physics Letters (August 2015
Theory of Neutron Diffraction from the Vortex Lattice in UPt3
Neutron scattering experiments have recently been performed in the
superconducting state of UPt3 to determine the structure of the vortex lattice.
The data show anomalous field dependence of the aspect ratio of the unit cell
in the B phase. There is apparently also a change in the effective coherence
length on the transition from the B to the C phases. Such observations are not
consistent with conventional superconductvity. A theory of these results is
constructed based on a picture of two-component superconductivity for UPt3. In
this way, these unusual observations can be understood. There is a possible
discrepancy between theory and experiment in the detailed field dependence of
the aspect ratio.Comment: 11 pages; uses REVTEX, APS and PRABIB styles; 2 Postscript figure
files include
A Scanning Hall Probe Microscope for high resolution, large area, variable height Magnetic Field Imaging
International audienceWe present a Scanning Hall Probe Microscope operating in ambient conditions. One of the unique features of this microscope is the use of the same stepper motors for both sample positioning as well as scanning, which makes it possible to have a large scan range (few mm) in x and y directions, with a scan resolution of 0.1 µm. Protocols have been implemented to enable scanning at different heights from the sample surface. The z range is 35 mm. Microstructured Hall probes of size 1-5 µm have been developed. A minimum probe-sample distance < 2 µm has been obtained by the combination of new Hall probes and probe-sample distance regulation using a tuning fork based force detection technique. The system is also capable of recording local B(z) profiles. We discuss the application of the microscope for the study of micro-magnet arrays being developed for applications in micro-system
Theory of 'which path' dephasing in single electron interference due to trace in conductive environment
A single-electron two-path interference (Young) experiment is considered
theoretically. The decoherence of an electron wave packet due to the 'which
path' trace left in the conducting (metallic) plate placed under the electron
trajectories is calculated using the many-body quantum description of the
electron gas reservoir.Comment: 11 pages, 5 figures, moderate changes, 1 new figure, updated
reference
Decoherence of electron beams by electromagnetic field fluctuations
Electromagnetic field fluctuations are responsible for the destruction of
electron coherence (dephasing) in solids and in vacuum electron beam
interference. The vacuum fluctuations are modified by conductors and
dielectrics, as in the Casimir effect, and hence, bodies in the vicinity of the
beams can influence the beam coherence. We calculate the quenching of
interference of two beams moving in vacuum parallel to a thick plate with
permittivity . In case of an
ideal conductor or dielectric the dephasing is suppressed
when the beams are close to the surface of the plate, because the random
tangential electric field , responsible for dephasing, is zero at the
surface. The situation is changed dramatically when
or are finite. In this case there exists a layer near
the surface, where the fluctuations of are strong due to evanescent
near fields. The thickness of this near - field layer is of the order of the
wavelength in the dielectric or the skin depth in the conductor, corresponding
to a frequency which is the inverse electron time of flight from the emitter to
the detector. When the beams are within this layer their dephasing is enhanced
and for slow enough electrons can be even stronger than far from the surface
General relativistic corrections to the Sagnac effect
The difference in travel time of corotating and counter-rotating light waves
in the field of a central massive and spinning body is studied. The corrections
to the special relativistic formula are worked out in a Kerr field. Estimation
of numeric values for the Earth and satellites in orbit around it show that a
direct measurement is in the order of concrete possibilities.Comment: REVTex, accepted for publication on Phys. Rev.
- …