The effect of surface passivation and crystallite size on the photoluminescence of porous silicon is reported. Oxygen-free porous silicon samples with medium to ultra high porosities have been prepared by using electr...
The effect of surface passivation and crystallite size on the photoluminescence of porous silicon is reported. Oxygen-free porous silicon samples with medium to ultra high porosities have been prepared by using electrochemical etching followed by photoassisted stain etching. As long as the samples were hydrogen-passivated the PL could be tuned from the red (750nm) to the blue (400nm) by increasing the porosity. We show that when surface oxidation occurred, the photoluminescence was red-shifted. For sizes smaller than 2.8nm, the red shift can be as large as 1eV but for larger sizes no shift has been observed. Comparing the experimental results with theoretical calculations, we suggest that the decrease in PL energy upon exposure to oxygen is related to recombination involving an electron or an exciton trapped in Si=O double bonds. This result clarifies the recombination mechanisms in porous silicon.
Manufacturing of drug delivery systems through the extrusion process is of great interest in academia and pharmaceutical industry alike. Even though significant amount of research has been conducted in this field, the...
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Manufacturing of drug delivery systems through the extrusion process is of great interest in academia and pharmaceutical industry alike. Even though significant amount of research has been conducted in this field, there are still many challenges to be addressed such as: thermal stability of drugs, difficult downstream handling of extrudates and high density of the extrudates. Recently, the foaming process is being seen as an answer for some of these problems. This paper reviews the role of polymeric foams in the manufacture of oral drug delivery systems. A case study analyzing the influence of foaming on the dissolution profile of a polymeric excipient in water is discussed in more detail.
Octanethiol-stabilized Si nanocrystals, ranging from 2 to 8 nm in diameter, were synthesized in cyclohexane heated and pressurized above its critical point at temperatures ranging from 400°C to 500°C. The na...
Octanethiol-stabilized Si nanocrystals, ranging from 2 to 8 nm in diameter, were synthesized in cyclohexane heated and pressurized above its critical point at temperatures ranging from 400°C to 500°C. The nanocrystals exhibit crystalline cores and photoluminesce with relatively high efficiencies. These nanocrystals are suitable for single particle spectroscopic measurements that reveal optical information about the individual chromophores that are buried in ensemble measurements. The sterically-stabilized Si nanocrystals emit with relatively narrow emission spectra at room temperature, characteristic of molecules.
Ordered structures of Ba(Cd1/3Ta2/3)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-or...
Ordered structures of Ba(Cd1/3Ta2/3)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-ordered structure of 1:2 with hexagonal symmetry for Ba(Cd1/3Ta2/3)O3 with boron additive. No significant changes in ordered structures were observed after long-period annealing. The 1:2 ordered domain structures (average domain size ∼18 nm) and high-density domain boundaries induced by ordering were observed for Ba(Cd1/3Ta2/3)O3 without boron additive sintered at relatively high temperature. The sintering process has a profound influence on the microstructure of Ba(Cd1/3Ta2/3)O3 ceramics.
We have investigated the nucleation and growth of gallium nitride (GaN) films on silicon and sapphire substrates using halide vapor phase epitaxy (HVPE). GaN growth was carried out on bare Si and sapphire surfaces, as...
We have investigated the nucleation and growth of gallium nitride (GaN) films on silicon and sapphire substrates using halide vapor phase epitaxy (HVPE). GaN growth was carried out on bare Si and sapphire surfaces, as well as on MOVPE-grown GaN buffer layers. HVPE growth on MOVPE GaN/AIN buffer layers results in lower defect densities as determined by x-ray than growth directly on sapphire. HVPE GaN films grown directly on sapphire exhibit strong near-edge photoluminescence, a pronounced lack of deep level-based luminescence, and x-ray FWHM values of 16 arcsec by an x-ray θ-2θ scan. The crystallinity of GaN films on sapphire is dominated by the presence of rotational misorientation domains, as measured by x-ray ω-scan diffractometry, which tend to decrease with increasing thickness or with the use of a homoepitaxial MOVPE buffer layer. The effect of increasing film thickness on the defect density of the epilayer was studied. In contrast, the HVPE growth of nitride films directly on silicon is complicated by mechanisms involving the formation of silicon nitrides and oxides at the initial growth front.
We have investigated the MOVPE growth of InxGa1-xAs metamorphic buffer layer (MBL) structures with a focus on techniques to improve the surface morphology and determine the influence of morphology on subsequently grow...
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In the present work,we examined the performance of 36 density functionals,including the newly developed doubly hybrid density functional XYG3(***,***,and *** Ⅲ,***,USA,2009,106,4963),to calculate ionization energies(...
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In the present work,we examined the performance of 36 density functionals,including the newly developed doubly hybrid density functional XYG3(***,***,and *** Ⅲ,***,USA,2009,106,4963),to calculate ionization energies(IEs)and electron affinities(EAs).We used the well-established G2-1 set as reference,which contains 14 atoms and 24 molecules for IE,along with 7 atoms and 18 molecules for ***3 leads to mean absolute deviations(MADs)of 0.057 and 0.080 eV for IEs and EAs,respectively,using the basis set of 6-311+G(3df,2p).In comparison with some other functionals,MADs for IEs are 0.109(B2PLYP),0.119(M06-2X),0.159(X3LYP),0.161(PBE),0.162(B3LYP),0.165(PBE0),0.173(TPSS),0.200(BLYP),and 0.215 eV(LC-BLYP).MADs for EAs are 0.090(X3LYP),0.090(B2PLYP),0.102(PBE),0.103(M06-2X),0.104(TPSS),0.105(BLYP),0.106(B3LYP),0.126(LC-BLYP),and 0.128 eV(PBE0).
作者：
Jian WuQing GePatrick T Matherwujian@mail.pse.umass.edu
University of Connecticut Chemical Engineering DepartmentPolymer Program Institute of Materials Science 97 North Eagleville Road Storrs CT 06269 United States Qing@***
University of Connecticut Chemical Engineering Departmentand Polymer ProgramInstitute of Materials Sciece Storrs CT 06269 United States ptmather@syr.edu
University of Connecticut Chemical Engineering Departmentand Polymer ProgramInstitute of Materials Sciece Storrs CT 06269 United States
A series of unique hybrid thermoplastic polyurethanes (TPUs) was synthesized using PEG as soft segment and incorporating an isobutyl-functionalized POSS diol (TMP POSS diol) in the hard segment. The molecular weight o...
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A series of unique hybrid thermoplastic polyurethanes (TPUs) was synthesized using PEG as soft segment and incorporating an isobutyl-functionalized POSS diol (TMP POSS diol) in the hard segment. The molecular weight of PEG was systematically varied to include 10, 20, and 35 kDa, while the mole ratio of POSS diol (as chain extender) to PEG was in range from 3:1 to 8:1 with samples featuring a PEG molecular weight of 10 kDa. The diisocyanate employed for TPU polymerization was 4,4'-methylenebis(phenyl-isocyanate) (MDI). We found that the hydrophobic hard segments (POSS) can form crystalline structures driven by micro-phase separation, this being due to significant thermodynamic incompatibility between POSS and ethylene oxide units. The POSS nano-crystals thus formed serve as physical crosslinking sites within an inorganic-organic hybrid network. This affords a new hybrid organic-inorganic hydrogel in the water-swollen state. The equilibrium swelling ratio increased monotonically with PEG loading and ranged from ∼70% to ∼600%. The shear modulus, G, of the hybrid hydrogels was observed to span 0.3 < G < 4.0 MPa – C values commonly found for elastomers, not hydrogels. Indeed, the hydrogel stiffness can be finely tuned through the POSS:PEG molar ratio, as this predictably controls swelling in water.
Temperature programmed desorption (TPD) studies in ultra high vacuum revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These p...
Temperature programmed desorption (TPD) studies in ultra high vacuum revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe. Dimethylcadmium partially decomposes to produce Cd adatoms; a large fraction of the excess Cd atoms desorb upon heating. In contrast, DETe desorbs without decomposing, suggesting that the rate limiting step in CdTe MOCVD on CdTe(111)A is surface decomposition of the tellurium alkyl.
Trypsin-coated magnetic nanoparticles (EC-TR/NPs), prepared via a simple multilayer random crosslinking of the trypsin molecules onto magnetic nanoparticles, were highly stable and could be easily captured using a mag...
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Trypsin-coated magnetic nanoparticles (EC-TR/NPs), prepared via a simple multilayer random crosslinking of the trypsin molecules onto magnetic nanoparticles, were highly stable and could be easily captured using a magnet after the digestion was complete. EC-TR/NPs showed a negligible loss of trypsin activity after multiple uses and continuous shaking, whereas the conventional immobilization of covalently attached trypsin on NPs resulted in a rapid inactivation under the same conditions due to the denaturation and autolysis of trypsin. A single model protein, a five-protein mixture, and a whole mouse brain proteome were digested at atmospheric pressure and 37°C for 12?h or in combination with pressure cycling technology at room temperature for 1?min. In all cases, EC-TR/NPs performed equally to or better than free trypsin in terms of both the identified peptide/protein number and the digestion reproducibility. In addition, the concomitant use of EC-TR/NPs and pressure cycling technology resulted in very rapid (～1?min) and efficient digestions with more reproducible digestion results.
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