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R. D. Waldron

Bio: R. D. Waldron is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Infrared spectroscopy & Ionic bonding. The author has an hindex of 2, co-authored 2 publications receiving 1765 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the infrared spectra of 7 ferrites of the formula $M{\mathrm{Fe}}{2}{\mathrm {O}}_{4}, where $M$ designates a divalent metal, are presented and analyzed.
Abstract: The infrared spectra of 7 ferrites of the formula $M{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$, where $M$ designates a divalent metal, are presented and analyzed. Electronic absorption was observed in the visible and near-infrared regions. Two absorption bands arising from interatomic vibrations were measured and force constants calculated for the stretching of bonds between octahedral or tetrahedral metal ions and oxide ions. These force constants are in agreement with the elastic and thermodynamic properties of these compounds and are sensitive to distribution of metal ions between the alternate sites. The integrated vibrational band intensities were measured: they are compatible with predominantly ionic bonding for these structures.

1,957 citations

Journal ArticleDOI
TL;DR: In this article, the energy transport process for indirect illumination was studied by measuring the photocurrent pulses produced by high-intensity light flashes and by experiments with light transmission and electric fields.
Abstract: The spectral response of photoconductivity of ZnS and CdS for both single-crystal and sintered-powder samples was measured for several distances between the area of illumination and the electrode region. The energy transport process for indirect illumination was studied by measuring the photocurrent pulses produced by high-intensity light flashes and by experiments with light transmission and electric fields. These studies demonstrate energy transport by electrically neutral entities other than photons, which we interpret as diffusion of excitons or mobile electron-hole pairs.This indirect or transfer photocurrent occurs predominantly at frequencies below the absorption edge of the crystal, with the detailed response being sensitive to the impurity content of the samples. The diffusion parameters in this region generally lie in the following range: lifetime $\ensuremath{\tau}={10}^{\ensuremath{-}4} \mathrm{to} {10}^{\ensuremath{-}6}$ sec, diffusion constant $D={10}^{3} \mathrm{to} {10}^{4}$ ${\mathrm{cm}}^{2}$/sec, and diffusion length $L=0.1 \mathrm{to} 1$ cm.The transfer photocurrent for steady illumination shows a nearly linear dependence on the incident light intensity. The slow decay of the photocurrent indicates that trapping processes are important in the photocurrent mechanism. Measurement of photocurrent pulses for flash illumination shows a greater than linear dependence on intensity, indicating a second-order or bimolecular process. A proposed mechanism for the transfer photoeffect involves initial absorption of the light with creation of an exciton, which diffuses to a trap in the lattice. A second exciton reaching the trap then dissociates, using energy transferred from the trap.

32 citations


Cited by
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Journal ArticleDOI
16 Jun 2010-ACS Nano
TL;DR: The magnetite-graphene hybrids show a high binding capacity for As(III) and As(V), whose presence in the drinking water in wide areas of South Asia has been a huge problem.
Abstract: Magnetite−graphene hybrids have been synthesized via a chemical reaction with a magnetite particle size of ∼10 nm. The composites are superparamagnetic at room temperature and can be separated by an external magnetic field. As compared to bare magnetite particles, the hybrids show a high binding capacity for As(III) and As(V), whose presence in the drinking water in wide areas of South Asia has been a huge problem. Their high binding capacity is due to the increased adsorption sites in the M−RGO composite which occurs by reducing the aggregation of bare magnetite. Since the composites show near complete (over 99.9%) arsenic removal within 1 ppb, they are practically usable for arsenic separation from water.

1,806 citations

Journal ArticleDOI
Ming Ma1, Yu Zhang1, Wei Yu1, Hao-ying Shen1, Haiqian Zhang1, Ning Gu1 
TL;DR: In this paper, the magnetite nanoparticles were prepared by coprecipitation of Fe 2 and Fe 3 with NH4OH, and then, amino silane was coated onto the surface of magnetite particles.

803 citations

Journal ArticleDOI
TL;DR: Magnetite nanoparticles coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3 were prepared by silanization reaction and characterized by X-ray diffractometry, transmission electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy and magnetization measurements as mentioned in this paper.

727 citations

Journal ArticleDOI
TL;DR: In this paper, the degenerate four-wave mixing (DFWM) of visible radiation in borosilicate glasses doped with crystallites of the mixed semiconductor CdSxSe1−x was investigated.
Abstract: We report degenerate four-wave mixing (DFWM) of visible radiation in borosilicate glasses doped with crystallites of the mixed semiconductor CdSxSe1−x. These semiconductor-doped glasses—available commercially in the form of colored glass filters—exhibit third-order nonlinearities of ~10−9–10−8 esu for DFWM with short (~10-nsec) laser pulses at various visible wavelengths. Our studies on the temporal decay of the transient gratings indicate that the nonlinearity is not thermal in origin but may be attributed to the generation of a short-lived electron–hole plasma. In contrast with DFWM experiments in other semiconductors invoking gratings of optically generated carriers (or other mobile particles), we report unique diffusion-independent decay of the gratings in these glasses; this is deduced from the dependence of the intensity and polarization of the DFWM signal on the polarization combinations of the input beams. Finally, we report detailed data on the aberration-correction properties of these isotropic glasses.

686 citations

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TL;DR: The efficient removal of cationic dye, methylene blue (MB), from aqueous solution with the one-pot solvothermal synthesized magnetite-loaded multi-walled carbon nanotubes (M-MWCNTs) was demonstrated, and it was shown that the MB adsorption was pH-dependent.

602 citations