457 research outputs found
Simulation of anisotropic wet-chemical etching using a physical model
We present a method to describe the orientation dependence of the etch rate of silicon, or any other single crystalline material, in anisotropic etching solutions by analytical functions. The parameters in these functions have a simple physical meaning. Crystals have a small number of atomically smooth faces, which etch (and grow) slowly as a consequence of the removal (or addition) of atoms by rows and layers. However, smooth faces have a roughening transition (well known in statistical physics); at increasing temperature they become rougher, and accordingly the etch and growth rates increase. Consequently, the basic physical parameters of our functions are the roughness of the smooth faces and the velocity of steps on these faces. This small set of parameters describes the etch rate in the two-dimensional space of orientations (on the unit sphere). We have applied our method to the practical case of etch rate functions for silicon crystals in KOH solutions. The maximum deviation between experimental data and simulation using only nine physically meaningful parameters is less than 5% of the maximum etch rate. This method, which in this study is used to describe anisotropic etching of silicon, can easily be adjusted to describe the growth or etching process of any crysta
On the mechanics of buckling-delamination in compliant laminates
Many modern electronic devices consist of multilayered stacks of functional materials with a wide range of mechanical properties. Under the influence of thermo-mechanical loading, some of these layers may experience a significant amount of compressive stress. If the adherence between the layers or the internal strength within them is insufficient, this stress may be relaxed by the simultaneous delamination and buckling of one or several layers. Such fractures obviously compromise the integrity and functionality of the device.The mechanics of buckling-driven delamination are reasonably well understood for films on stiff or thick substrates. However, in the thin compliant stacksconsidered here, additional mechanisms come into play, which are not captured by the existing theoretical framework. We explore these mechanisms using finiteelement simulations and a simplified analytical model. The latter gives insight in the contributing factors and can be used by engineers to design againstbuckling–delamination
Scaling Propensity of Water
The commonly used Saturation Index calculated at 10°C (SI10) is not suitable for practical situations. New parameters have been developed for simple and rapid analysis of calcium carbonate precipitation (scaling) phenomena which occur during the heating of drinking water: TPCC90 (Theoretically Precipitable Calcium Carbonate at 90°C) SI90 (Saturation Index at 90°C) NI (Nucleation Index) PPCC (Practically Precipitable Calcium Carbonate) Both TPCC90 and SI90 describe the hydrodynamic driven force for the scaling reaction. The nucleation index indicates at what rate calcium carbonate precipitation is accelerated by nuclei present in the water. Finally, the PPCC is a measurement under practical conditions, determining the rate of scaling. The suitability of these parameters for predicting scaling was assessed and detailed results are presented in this publication
170 Nanometer Nuclear Magnetic Resonance Imaging using Magnetic Resonance Force Microscopy
We demonstrate one-dimensional nuclear magnetic resonance imaging of the
semiconductor GaAs with 170 nanometer slice separation and resolve two regions
of reduced nuclear spin polarization density separated by only 500 nanometers.
This is achieved by force detection of the magnetic resonance, Magnetic
Resonance Force Microscopy (MRFM), in combination with optical pumping to
increase the nuclear spin polarization. Optical pumping of the GaAs creates
spin polarization up to 12 times larger than the thermal nuclear spin
polarization at 5 K and 4 T. The experiment is sensitive to sample volumes
containing Ga. These results
demonstrate the ability of force-detected magnetic resonance to apply magnetic
resonance imaging to semiconductor devices and other nanostructures.Comment: Submitted to J of Magnetic Resonanc
When the Right (Drug) Should Be Left:Prenatal Drug Exposure and Heterotaxy Syndrome
Background: Recent studies reported an association between prenatal propylthiouracil exposure and birth defects, including abnormal arrangement across the left-right body axis, suggesting an association with heterotaxy syndrome. Methods: This case-control and case-finding study used data from 1981 to 2013 from the EUROCAT birth defect registry in the Northern Netherlands. First, we explored prenatal exposures in heterotaxy syndrome (cases) and Down syndrome (controls). Second, we describe the specific birth defects in offspring of mothers using propylthiouracil (PTU) prenatally. RESULTS: A total of 66 cases with heterotaxy syndrome (incidence 12.1 per 100,000 pregnancies) and 783 controls with Down syndrome (143.3 per 100,000 pregnancies) were studied. No differences in intoxication use during pregnancy were found between cases and controls, including smoking (28.0% vs. 22.7%; p = 0.40), alcohol (14.0% vs. 26.9%; p = 0.052), and recreational drugs (0 vs. 0.3%; p = 1.00). We found an association between heterotaxy syndrome and prenatal drug exposure to follitropin-alfa (5.6% vs. 1.1%; p = 0.04), and drugs used in nicotine dependence (3.7% vs. 0.2%; p = 0.02). Five mothers used PTU during pregnancy and gave birth to a child with trisomy 18, renal abnormalities, or hypospadias and cardiac defects. Conclusion: This study identified follitropin-alfa and drugs used in nicotine dependence as possible teratogens of heterotaxy syndrome. Our data suggest the possibility that there is an increased risk of birth defects (including renal, urological, and cardiac abnormalities) in children born among mothers taking PTU prenatally, but not for heterotaxy syndrome. (C) 2016 Wiley Periodicals, Inc.</p
Bulk screening in core level photoemission from Mott-Hubbard and Charge-Transfer systems
We report bulk-sensitive hard X-ray ( = 5.95 KeV) core level
photoemission spectroscopy (PES) of single crystal VCrO
and the high- cuprate BiSrCaCuO (Bi2212).
VCrO exhibits low binding energy "satellites" to the V
"main lines" in the metallic phase, which are suppressed in the
antiferromagnetic insulator phase. In contrast, the Cu spectra of Bi2212
do not show temperature dependent features, but a comparison with soft X-ray
PES indicates a large increase in the "satellites" or weight
in the bulk. Cluster model calculations, including full multiplet structure and
a screening channel derived from the coherent band at the Fermi energy, give
very satisfactory agreement with experiments
Resonant Inelastic X-ray Scattering Studies of Elementary Excitations
In the past decade, Resonant Inelastic X-ray Scattering (RIXS) has made
remarkable progress as a spectroscopic technique. This is a direct result of
the availability of high-brilliance synchrotron X-ray radiation sources and of
advanced photon detection instrumentation. The technique's unique capability to
probe elementary excitations in complex materials by measuring their energy-,
momentum-, and polarization-dependence has brought RIXS to the forefront of
experimental photon science. We review both the experimental and theoretical
RIXS investigations of the past decade, focusing on those determining the
low-energy charge, spin, orbital and lattice excitations of solids. We present
the fundamentals of RIXS as an experimental method and then review the
theoretical state of affairs, its recent developments and discuss the different
(approximate) methods to compute the dynamical RIXS response. The last decade's
body of experimental RIXS data and its interpretation is surveyed, with an
emphasis on RIXS studies of correlated electron systems, especially transition
metal compounds. Finally, we discuss the promise that RIXS holds for the near
future, particularly in view of the advent of x-ray laser photon sources.Comment: Review, 67 pages, 44 figure
The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
(Ultra) Luminous Infrared Galaxies ((U)LIRGs) are objects characterized by
their extreme infrared (8-1000 m) luminosities (L and L). The Herschel Comprehensive ULIRG
Emission Survey (HerCULES; PI van der Werf) presents a representative
flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of
these objects (10). With the \emph{Herschel
Space Observatory}, we observe [CII] 157 m, [OI] 63 m, and [OI] 145
m line emission with PACS, CO J=4-3 through J=13-12, [CI] 370 m, and
[CI] 609 m with SPIRE, and low-J CO transitions with ground-based
telescopes. The CO ladders of the sample are separated into three classes based
on their excitation level. In 13 of the galaxies, the [OI] 63 m emission
line is self absorbed. Comparing the CO excitation to the IRAS 60/100 m
ratio and to far infrared luminosity, we find that the CO excitation is more
correlated to the far infrared colors. We present cooling budgets for the
galaxies and find fine-structure line flux deficits in the [CII], [SiII], [OI],
and [CI] lines in the objects with the highest far IR fluxes, but do not
observe this for CO . In order to study the heating of the
molecular gas, we present a combination of three diagnostic quantities to help
determine the dominant heating source. Using the CO excitation, the CO J=1-0
linewidth, and the AGN contribution, we conclude that galaxies with large CO
linewidths always have high-excitation CO ladders, and often low AGN
contributions, suggesting that mechanical heating is important
Transfer of Spectral Weight in Spectroscopies of Correlated Electron Systems
We study the transfer of spectral weight in the photoemission and optical
spectra of strongly correlated electron systems. Within the LISA, that becomes
exact in the limit of large lattice coordination, we consider and compare two
models of correlated electrons, the Hubbard model and the periodic Anderson
model. The results are discussed in regard of recent experiments. In the
Hubbard model, we predict an anomalous enhancement optical spectral weight as a
function of temperature in the correlated metallic state which is in
qualitative agreement with optical measurements in . We argue that
anomalies observed in the spectroscopy of the metal are connected to the
proximity to a crossover region in the phase diagram of the model. In the
insulating phase, we obtain an excellent agreement with the experimental data
and present a detailed discussion on the role of magnetic frustration by
studying the resolved single particle spectra. The results for the periodic
Anderson model are discussed in connection to recent experimental data of the
Kondo insulators and . The model can successfully explain
the different energy scales that are associated to the thermal filling of the
optical gap, which we also relate to corresponding changes in the density of
states. The temperature dependence of the optical sum rule is obtained and its
relevance for the interpretation of the experimental data discussed. Finally,
we argue that the large scattering rate measured in Kondo insulators cannot be
described by the periodic Anderson model.Comment: 19 pages + 29 figures. Submitted to PR
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