153 research outputs found
First-principles approach to rotational-vibrational frequencies and infrared intensity for H adsorbed in nanoporous materials
The absorption sites and the low-lying rotational and vibrational (RV) energy
states for H adsorbed within a metal-organic framework are calculated via
van der Waals density functional theory. The induced dipole due to bond
stretching is found to be accurately given by a first-principles driven
approximation using maximally-localized-Wannier-function analysis. The
strengths and positions of lines in the complex spectra of RV transitions are
in reasonable agreement with experiment, and in particular explain the
experimentally mysteriously missing primary line for para hydrogen
Analyzing the frequency shift of physiadsorbed CO2 in metal organic framework materials
Combining first-principles density functional theory simulations with IR and
Raman experiments, we determine the frequency shift of vibrational modes of CO2
when physiadsorbed in the iso-structural metal organic framework materials
Mg-MOF74 and Zn-MOF74. Surprisingly, we find that the resulting change in shift
is rather different for these two systems and we elucidate possible reasons. We
explicitly consider three factors responsible for the frequency shift through
physiabsorption, namely (i) the change in the molecule length, (ii) the
asymmetric distortion of the CO molecule, and (iii) the direct influence of
the metal center. The influence of each factor is evaluated separately through
different geometry considerations, providing a fundamental understanding of the
frequency shifts observed experimentally.Comment: 9 pages, 4 figure
Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro
Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K
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FTIR Study of Copper Agglomeration during Atomic Layer Deposition of Copper
The growth of of metallic copper by atomic layer deposition (ALD) using copper(I) di-sec-butylacetamidinate and molecular hydrogen on surfaces has been studied. The mechanisms for the initial surface reaction and chemical bonding evolutions with each ALD cycle are inferred from in situ Fourier transform infrared spectroscopy (FTIR) data. Spectroscopic evidence for Cu agglomeration on is presented involving the intensity variations of the LO/TO phonon modes after chemical reaction with the Cu precursor and after the precursor cycle. These intensity variations are observed over the first 20 ALD cycles at 185°C.Chemistry and Chemical Biolog
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