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  • 1. Avdeef, Alex
    et al.
    Artursson, Per
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Neuhoff, Sibylle
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Lazorova, Lucia
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Tavelin, Staffan
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Caco-2 permeability of weakly basic drugs predicted with the Double-Sink PAMPA pK flux a method.2005In: Eur J Pharm Sci, ISSN 0928-0987, Vol. 24, no 4, p. 333-49Article in journal (Refereed)
  • 2. Aziz, Emad F
    et al.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Forsberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Andersson, Egil
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Zhang, Wenhua
    Yang, Jinglong
    Eisebitt, Stefan
    Bergström, Christel
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Luo, Yi
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Eberhardt, Wolfgang
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Photoinduced Formation of N2 Molecules in Ammonium Compounds2007In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 39, p. 9662-9669Article in journal (Refereed)
    Abstract [en]

    Via fluorescence yield (FY) and resonant inelastic scattering spectroscopy in the soft X-ray range we find that soft X-rays induce formation of N2 molecules in solid NH4Cl and in related compounds. The nitrogen molecules form weak bonds in NH4Cl, so that a substantial fraction of the molecules remains in the sample. From measurements of the FY as a function of exposure and temperature, the rates for the photochemical processes are estimated. At elevated temperatures (363 K), several nitrogen atoms are removed from the sample per incoming photon. At lower temperatures (233 K), the rate is reduced to around 0.02 nitrogen atoms for each incoming photon. Virtually all these atoms form N2 molecules which are bound in the sample. The generality and implications of these results are briefly discussed.

  • 3. Chatzigeorgiou, E
    et al.
    Århammar, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Resonant Inelastic X-ray Scattering on Mesoporous Magnesium Carbonate2019In: The 40th International Conference on Vacuum Ultraviolet and X-ray Physics, San Fransisco, 2019Conference paper (Refereed)
  • 4. Chatzigeorgiou, Evanthia
    et al.
    Århammar, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ekholm, Victor
    Såthe, Conny
    Olovsson, Weine
    Bittencourt, Rafael
    Agåker, Marcus
    Yin, Zhong
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Soft X-ray Spectroscopy on  amorphous and crystalline magnesium carbonate2019In: EUROMAT 2019, 2019, article id 14135Conference paper (Refereed)
  • 5.
    Edueng, Khadijah
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Bergström, Christel
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Mahlin, Denny
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Long-term physical (in)stability of spray-dried amorphous drugs: relationship with glass-forming ability and physicochemical properties2019In: Pharmaceutics, ISSN 1999-4923, E-ISSN 1999-4923, Vol. 11, no 9, article id 425Article in journal (Other academic)
  • 6.
    Edueng, Khadijah
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. International Islamic University Malaysia.
    Mahlin, Denny
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Astra Zeneca.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Nylander, Olivia
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Thakrani, Manish
    Department of Pharmacy, University College London, UK.
    Bergström, Christel
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Supersaturation Potential of Amorphous Active Pharmaceutical Ingredients after Long-Term Storage2019In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 24, no 15, article id 2731Article in journal (Refereed)
    Abstract [en]

    This study explores the effect of physical aging and/or crystallization on the supersaturation potential and crystallization kinetics of amorphous active pharmaceutical ingredients (APIs). Spray-dried, fully amorphous indapamide, metolazone, glibenclamide, hydrocortisone, hydrochlorothiazide, ketoconazole, and sulfathiazole were used as model APIs. The parameters used to assess the supersaturation potential and crystallization kinetics were the maximum supersaturation concentration (Cmax,app), the area under the curve (AUC), and the crystallization rate constant (k). These were compared for freshly spray-dried and aged/crystallized samples. Aged samples were stored at 75% relative humidity for 168 days (6 months) or until they were completely crystallized, whichever came first. The solid-state changes were monitored with differential scanning calorimetry, Raman spectroscopy, and powder X-ray diffraction. Supersaturation potential and crystallization kinetics were investigated using a tenfold supersaturation ratio compared to the thermodynamic solubility using the µDISS Profiler. The physically aged indapamide and metolazone and the minimally crystallized glibenclamide and hydrocortisone did not show significant differences in their Cmax,app and AUC when compared to the freshly spray-dried samples. Ketoconazole, with a crystalline content of 23%, reduced its Cmax,app and AUC by 50%, with Cmax,app being the same as the crystalline solubility. The AUC of aged metolazone, one of the two compounds that remained completely amorphous after storage, significantly improved as the crystallization kinetics significantly decreased. Glibenclamide improved the most in its supersaturation potential from amorphization. The study also revealed that, besides solid-state crystallization during storage, crystallization during dissolution and its corresponding pathway may significantly compromise the supersaturation potential of fully amorphous APIs.

  • 7.
    Ekholm, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Dong, Minjie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Såthe, Conny
    Uppsala University.
    Chatzigeorgiou, Evanthia
    Agåker, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Harada, Yoshihisa
    Miyawaki, Jun
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Aqueous carbonate and bicarbonate ions studied by RIXS at the O K-edgeManuscript (preprint) (Other academic)
  • 8.
    Englund, Gunilla
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Rorsman, Fredrik
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences.
    Rönnblom, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences.
    Karlbom, Urban
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences.
    Lazorova, Lucia
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Kindmark, Andreas
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences.
    Artursson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Regional levels of drug transporters along the human intestinal tract: Co-expression of ABC and SLC transporters and comparison with Caco-2 cells2006In: European Journal of Pharmaceutical Sciences, ISSN 0928-0987, E-ISSN 1879-0720, Vol. 29, no 3-4, p. 269-277Article in journal (Refereed)
    Abstract [en]

    A vast number of drugs are subjected to active or facilitated transport and multiple transport mechanism may contribute to the net flux during drug absorption. The main objective of this study was to quantify the regional mRNA expression and determine the co-expression of drug transporters from the ABC (Pgp, BCRP, MRP2, MRP3) and SLC (PEPT1, MCT1, OATPB, OCTN2, OCT1) families along the human intestine (duodenum, jejunum, ileum, and colon). A second objective was to compare the transporter expression between the different intestinal regions and Caco-2 cells. Eight out of nine of the investigated transporters exhibited significant regional differences in expression. OATPB was the only transporter that did not show a region-dependency in the expression along the human intestinal canal. The expression of Pgp, BCRP, OCTN2 and MCT1 differed along the small intestine, but the expression differences were greater than five-fold only for Pgp. The rank order of transcript prevalence was identical in the ileum and the jejunum. Between the ileum and colon, seven transcripts were differentially expressed, and MCT1, OCTN2 and MRP3 were expressed at higher levels in the colon than in the small intestine. The expression of transporters in Caco-2 was closest to the expression pattern in the small intestine, although the expression of OATPB, BCRP and MRP2 differed more than five-fold between the Caco-2 cells and ileum. In conclusion, this study provides quantitative data on the expression of transporters from the ABC and SLC families along the human intestine, which can be useful in the interpretation of clinical studies where more than one intestinal transporter contribute to the net transport and in the computer modelling of drug absorption.

  • 9.
    Frenning, Göran
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Hansson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    The Release of Catanionic Mixtures Embedded in Gels: An Approximate Analytical Analysis2011In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 57, no 6, p. 1402-1408Article in journal (Refereed)
    Abstract [en]

    We present an approximate analytical analysis of the release of catanionic mixtures from gels. The starting points are the monomer-mixed micelle equilibrium, described by using regular solution theory, and the one-dimensional diffusion equation. Focusing on a half-infinite planar system, we first point out an exact reduction of the problem to a system of ordinary differential equations. By using the pseudo-steady-state approximation and the integral-balance method, we then derive a single nonlinear equation for the mole fraction of drug in micelles at the extraction front. This equation may be readily solved numerically (or graphically), and once the solution is found, all quantities of interest may be determined in closed form. Comparisons with numerical solutions of the fully nonlinear problem indicate that the errors resulting from the approximations typically do not exceed 10%.

  • 10.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Molecular Arrangement, Electronic Structure and Transport Properties in Surfactant Gel- and Related Systems Studied by Soft X-ray and Dielectric Spectroscopy2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns studies of aqueous soft matter systems, especially surfactant micelle systems.

    The aim has been to study the molecular arrangement and electronic structure of the constituents of, as well as transport properties in such a system. The molecular arrangement and electronic structure has been studied by means of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray spectroscopy (RIXS). The transport properties have been investigated by low-frequency dielectric spectroscopy (LFDS) and small angle X-ray scattering (SAXS) as well as a theoretical modelling. The latter was based on Fick’s laws of the release from binary surfactant system and was validated by experiments.

    The RIXS and XAS measurements show the electronic structure in bulk water and the influence of the chemical surrounding of the water molecule in bulk water and of the water molecules confined in a micelle lattice. The spectra are highly dependent on the molecular arrangement in such systems. For glycine and sodium polyacrylate RIXS and XAS spectra show features which are unique for carboxyl and carboxylate groups and such measurements can thus be used for fingerprinting.

    The LFDS and SAXS measurements show a strong correlation between structure in a surfactant/poly-ion system and apparent mobility of surfactants. This conclusion is in line with earlier observations.

    By the theoretical modelling a predictive model for the surfactant release from a binary surfactant micelle system has been obtained and the importance of different factors for surfactant release has been further clarified.

    List of papers
    1. Angular anisotropy in resonant inelastic soft X-ray scattering of liquid water
    Open this publication in new window or tab >>Angular anisotropy in resonant inelastic soft X-ray scattering of liquid water
    Show others...
    2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 13, p. 132203-Article in journal (Refereed) Published
    Abstract [en]

    Resonantly excited soft x-ray emission spectra of liquid water have been measured at two different angles relative to the polarization direction of the exciting radiation. The results demonstrate that the emission is much more isotropic than expected for the free water   molecule but that the trends in the remaining anisotropy qualitatively agree. It is found that the two sharp oxygen peaks at high emission energy correspond to states of different symmetry.

     

    Keywords
    liquid structure, resonant states, water, X-ray emission spectra, X-ray scattering
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-98012 (URN)10.1103/PhysRevB.79.132203 (DOI)000265942800013 ()
    Available from: 2009-02-06 Created: 2009-02-06 Last updated: 2017-12-14Bibliographically approved
    2. Electronic structure of water molecules confined in a micelle lattice
    Open this publication in new window or tab >>Electronic structure of water molecules confined in a micelle lattice
    Show others...
    2009 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 24, p. 8201-8205Article in journal (Refereed) Published
    Abstract [en]

    Oxygen K absorption and emission spectra of water molecules confined in dodecyltrimethyl ammonium chloride micelle structures are presented. The local electronic structure of the water molecules is found to be dramatically different from the electronic structure of water molecules in the gas-phase as well as in liquid water. Hybridization with states of the ions in the surrounding ions is directly observed, and evidence for stabilization of the water molecules relative to molecules in bulk water is found.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-109461 (URN)10.1021/jp902058w (DOI)000266930200001 ()19473020 (PubMedID)
    Available from: 2009-10-15 Created: 2009-10-15 Last updated: 2017-12-12Bibliographically approved
    3. Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution
    Open this publication in new window or tab >>Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution
    Show others...
    2009 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 49, p. 16002-16006Article in journal (Refereed) Published
    Abstract [en]

    Nitrogen and oxygen K emission spectra of glycine in the form of  anions, zwitterions, and cations in aqueous solution are presented. It  is shown that protonation has a dramatic influence on the local   electronic structure and that the functional groups give a distinct  spectral fingerprint.

     

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-121091 (URN)10.1021/jp905998x (DOI)000272083000012 ()
    Available from: 2010-03-18 Created: 2010-03-18 Last updated: 2017-12-12Bibliographically approved
    4. Ion mobility and gel complex structure in dodecyl trimethylammonium/polyacrylate gel complexes
    Open this publication in new window or tab >>Ion mobility and gel complex structure in dodecyl trimethylammonium/polyacrylate gel complexes
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In the present study dielectric spectroscopy and small angle x-ray scattering were employed to evaluate temperature dependent ionic mobility and structural features in a dodecyltrimethylammonium/polyacrylate gel complex. A gradually transition of  the gel complex from a structure exclusively consisting of discrete micelles arranged on a hexagonal close-packed lattice at 25 °C to a structure mainly consisting of a hexagonal phase of long rod-like micelles at ~ 65 °C was revealed. As well it was found that the mobility of the dodecyltrimethylammonium surfactant ions increased with an increasing fraction of hexagonal phase domains, something which was most likely due to a “residence time-hopping distance” mechanism of monomer ions moving between the micelles. The present findings should be useful for the understanding of the gel structure influence on the mechanisms for surfactant transport and shell formation in surfactant polyion gel complexes.

    Keywords
    Dielectric Spectroscopy, SAXS, Dodecyltrimethyl ammonium ion, polyacrylate ion, surfactant-poly ion complexes, mobility
    National Category
    Natural Sciences
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-205020 (URN)
    Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2014-01-08
    5. Determining the static dielectric permittivity of ion conducting materials
    Open this publication in new window or tab >>Determining the static dielectric permittivity of ion conducting materials
    2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 9, p. 092901-1Article in journal (Refereed) Published
    Abstract [en]

    A method is derived for the determination of the static dielectric permittivity of ion conducting materials when this parameter is obscured by electrode polarization in as-recorded low frequency dielectric spectra. The method requires permittivity measurements at two different electrode separations, and is applicable when the electric fields created by charge separation near the electrode surfaces do not induce nonlinear effects in the frequency region where electrode polarization begins to affect the dielectric response. The performance of the method is illustrated by the analysis of an ion conducting cellulose gel biosynthesized by the Acetobacter. xylinum bacterium. The method opens up possibilities to obtain more detailed information about dynamic processes in ion conducting materials from dielectric spectroscopy.

    National Category
    Other Engineering and Technologies
    Research subject
    Engineering Science with specialization in Nanotechnology and Functional Materials
    Identifiers
    urn:nbn:se:uu:diva-17822 (URN)10.1063/1.2977861 (DOI)000258975800043 ()
    Available from: 2008-09-03 Created: 2008-09-03 Last updated: 2017-12-08Bibliographically approved
    6. Implications of regular solution theory on the release mechanism of catanionic mixtures from gels
    Open this publication in new window or tab >>Implications of regular solution theory on the release mechanism of catanionic mixtures from gels
    Show others...
    2009 (English)In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 71, no 2, p. 214-225Article in journal (Refereed) Published
    Abstract [en]

    The aim of this study was to apply the regular solution theory of mixed  micelles to gain new insights on the drug release mechanism, when using   catanionic mixtures as a method of obtaining prolonged release from   gels. Synergistic effects were investigated at equilibrium and   quantified in terms of regular solution theory interaction parameters.  The drug release from catanionic aggregates was studied both in a polymer free environment, using dialysis membranes, and in gels, using  a modified LISP paddle method. The drug release kinetics was modelled   theoretically by combining the regular solution theory with Fick's   diffusion laws assuming a contribution to the transport only from monomeric species (stationary aggregates). The theoretical predictions were found to be in reasonably good agreement with experiments. An analysis of the calculated distribution of species between aggregated and monomeric states was shown to provide further insights into the release mechanism.

    Keywords
    Vesicle, Micelle, Catanionic, Regular solution theory, Diffusion
    National Category
    Pharmaceutical Sciences
    Identifiers
    urn:nbn:se:uu:diva-96417 (URN)10.1016/j.colsurfb.2009.02.008 (DOI)000266897900008 ()19286357 (PubMedID)
    Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2018-01-13Bibliographically approved
    7. The Release of Catanionic Mixtures Embedded in Gels: An Approximate Analytical Analysis
    Open this publication in new window or tab >>The Release of Catanionic Mixtures Embedded in Gels: An Approximate Analytical Analysis
    2011 (English)In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 57, no 6, p. 1402-1408Article in journal (Refereed) Published
    Abstract [en]

    We present an approximate analytical analysis of the release of catanionic mixtures from gels. The starting points are the monomer-mixed micelle equilibrium, described by using regular solution theory, and the one-dimensional diffusion equation. Focusing on a half-infinite planar system, we first point out an exact reduction of the problem to a system of ordinary differential equations. By using the pseudo-steady-state approximation and the integral-balance method, we then derive a single nonlinear equation for the mole fraction of drug in micelles at the extraction front. This equation may be readily solved numerically (or graphically), and once the solution is found, all quantities of interest may be determined in closed form. Comparisons with numerical solutions of the fully nonlinear problem indicate that the errors resulting from the approximations typically do not exceed 10%.

    Keywords
    controlled drug delivery, release, drug release, mathematical modeling, diffusion, catanionic mixtures
    National Category
    Pharmaceutical Sciences
    Identifiers
    urn:nbn:se:uu:diva-154684 (URN)10.1002/aic.12368 (DOI)000290616500004 ()
    Available from: 2011-06-09 Created: 2011-06-09 Last updated: 2018-01-12Bibliographically approved
  • 11.
    Gråsjö, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Andersson, Egil
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Forsberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Aziz, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Johansson, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Hansson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Oxygen K-edge studies of water poor surfactant gel systems2008Conference paper (Other (popular science, discussion, etc.))
  • 12.
    Gråsjö, Johan
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Hansson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Ion mobility and gel complex structure in dodecyl trimethylammonium/polyacrylate gel complexesManuscript (preprint) (Other academic)
    Abstract [en]

    In the present study dielectric spectroscopy and small angle x-ray scattering were employed to evaluate temperature dependent ionic mobility and structural features in a dodecyltrimethylammonium/polyacrylate gel complex. A gradually transition of  the gel complex from a structure exclusively consisting of discrete micelles arranged on a hexagonal close-packed lattice at 25 °C to a structure mainly consisting of a hexagonal phase of long rod-like micelles at ~ 65 °C was revealed. As well it was found that the mobility of the dodecyltrimethylammonium surfactant ions increased with an increasing fraction of hexagonal phase domains, something which was most likely due to a “residence time-hopping distance” mechanism of monomer ions moving between the micelles. The present findings should be useful for the understanding of the gel structure influence on the mechanisms for surfactant transport and shell formation in surfactant polyion gel complexes.

  • 13.
    Gråsjö, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Welch, Ken
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Determining the static dielectric permittivity of ion conducting materials2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 9, p. 092901-1Article in journal (Refereed)
    Abstract [en]

    A method is derived for the determination of the static dielectric permittivity of ion conducting materials when this parameter is obscured by electrode polarization in as-recorded low frequency dielectric spectra. The method requires permittivity measurements at two different electrode separations, and is applicable when the electric fields created by charge separation near the electrode surfaces do not induce nonlinear effects in the frequency region where electrode polarization begins to affect the dielectric response. The performance of the method is illustrated by the analysis of an ion conducting cellulose gel biosynthesized by the Acetobacter. xylinum bacterium. The method opens up possibilities to obtain more detailed information about dynamic processes in ion conducting materials from dielectric spectroscopy.

  • 14. Jederstrom, Gustaf
    et al.
    Andersson, Arne
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Medicine, Department of Medical Cell Biology.
    Gråsjö, Johan
    Sjöholm, Ingvar
    Formulating Insulin for Oral Administration: Preparation of Hyaluronan-Insulin Complex2004In: Pharmaceutical Research, Vol. 21, no 11, p. 2040-2047Article in journal (Refereed)
  • 15.
    Jederström, Gustaf
    et al.
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Nordin, Astrid
    Faculty of Medicine, Department of Medical Cell Biology.
    Sjöholm, Ingvar
    Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Andersson, Arne
    Faculty of Medicine, Department of Medical Cell Biology.
    Blood glucose-lowering activity of a hyaluronan-insulin complex after oral administration to rats with diabetes.2005In: Diabetes Technol Ther, ISSN 1520-9156, Vol. 7, no 6, p. 948-57Article in journal (Refereed)
  • 16.
    Jonsson, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Frenning, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Mechanical behaviour of ideal elastic-plastic particles subjected to different triaxial loading conditions2017In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 315, p. 347-355Article in journal (Refereed)
    Abstract [en]

    The contact force development for two types of polymeric elastoplastic particles subjected to different triaxial loading conditions was studied experimentally utilising a unique triaxial testing apparatus. In order to evaluate the experimental results, a finite element analysis was performed. The experimental findings highlighted the importance of contact dependence, which manifested itself in two principally different ways. Firstly, a reduced stiffness was observed when plastic deformation ceased to be fully contained, which, depending on the loading conditions, occurred at an engineering strain of about 5-10%. Secondly, a markedly increased stiffness was observed when particle confinement inhibited further plastic deformation, making elastic volume reduction the predominant deformation mode. The experimental results could be well reproduced by the numerical simulations, provided that isotropic hardening was included in the elastoplastic model. In an attempt to invariantly describe the data, a nominal contact pressure was determined as a function of the volumetric constraint of the particle. This resulted in an adequate collapse of results obtained for different loading conditions onto a single master curve at large volumetric constraint. In summary, this paper should be considered as a step along the pathway towards our long term goal of introducing novel and improved contact models.

  • 17.
    Jonsson, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Nordström, Josefina
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Johansson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Frenning, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    An apparatus for confined triaxial testing of single particles2015In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 270, p. 121-127Article in journal (Refereed)
    Abstract [en]

    A novel triaxial apparatus employing overlapping rigid boundaries has been designed and constructed for experimental measurement of contact forces under confined compression of single granules in the mm-scale. The performance of the apparatus was evaluated by performing uniaxial and triaxial compression experiments on ideal elastic-plastic materials. Compression curves were compared with the fully plastic Abbott-Firestone contact model and with results from FEM simulations. The increase in contact force associated with confined conditions was observed in the compression curves from triaxial compression experiments, as supported by predictions from simulations using single particle contact models. Hence, a new method for the assessment of mechanical behaviour of single particles under confined compression can be considered as established.

  • 18.
    Nilsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Frenning, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Alderborn, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Conductivity percolation in loosely compacted microcrystalline cellulose: An in situ study by dielectric spectroscopy during densification2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 41, p. 20502-20506Article in journal (Refereed)
    Abstract [en]

    The present study aims at contributing to a complete understanding of the water-induced ionic charge transport in cellulose. The behavior of this transport in loosely compacted microcrystalline cellulose (MCC) powder was investigated as a function of density utilizing a new type of measurement setup, allowing for dielectric spectroscopy measurement in situ during compaction. The ionic conductivity in MCC was found to increase with increasing density until a leveling-out was observed for densities above similar to 0.7 g/cm(3). Further, it was shown that the ionic conductivity vs density followed a percolation type behavior signifying the percolation of conductive paths in a 3D conducting network. The density percolation threshold was found to be between similar to 0.2 and 0.4 g/cm(3), depending strongly on the cellulose moisture content. The observed percolation behavior was attributed to the forming of interparticulate bonds in the MCC and the percolation threshold dependence on moisture was linked to the moisture dependence of particle rearrangement and plastic deformation in MCC during compaction. The obtained results add to the understanding of the density-dependent water-induced ionic transport in cellulose showing that, at given moisture content, the two major parameters determining the magnitude of the conductivity are the connectedness of the interparticluate bonds and the connectedness of pores with a diameter in the 5-20 nm size range. At densities between similar to 0.7 and 1.2 g/cm(3) both the bond and the pore networks have percolated, facilitating charge transport through the MCC compact.

  • 19.
    Pazesh, Samaneh
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Berggren, Jonas
    Recipharm Pharmaceut Dev AB, Solna, Sweden.
    Alderborn, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Comminution-amorphisation relationships during ball milling of lactose at different milling conditions2017In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 528, no 1-2, p. 215-227Article in journal (Refereed)
    Abstract [en]

    The purpose of the study was to investigate the relationship between comminution and amorphisation of alpha-lactose monohydrate particles during ball milling under different milling conditions, including ball-to-powder mass ratio, milling time and ball diameter. The results revealed that at a constant ball filling ratio, ball-to-powder mass ratio of 25:1 resulted in the lowest minimum particle diameter of similar to 5 mu m and the highest degree of apparent amorphous content of 82%. The rate of comminution was high during early stage of milling whereas the degree of apparent amorphous content increased gradually at a slow rate. An increased ball-to-powder mass ratio during milling increased both the rate of comminution and the rate of amorphisation. Using a given ball-to-powder mass ratio, the ball diameter affected the degree of apparent amorphous content of the particles while the particle diameter remained unchanged. The relationship between comminution and amorphisation could be described as consisting of two stages, i.e. comminution dominated and amorphisation dominated stage. It was proposed that the rate constant of comminution and amorphisation are controlled by stress energy distribution in the milling jar and the stress energy distribution is regulated by the ball motion pattern that can be affected by the process parameter used.

  • 20.
    Pietzsch, Annette
    et al.
    MAXlab, Lund University.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jamstorp, Erik
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Kennedy, Brian
    Hennies, Franz
    Arhammar, Cecilia
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Kaolinite: defect states define material properties-a soft x-ray and first principles study of the band gap2015In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 202, p. 11-15Article in journal (Refereed)
  • 21.
    Rubensson, Jan-Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Binggeli, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sathe, C.
    Hennies, F.
    Bisogni, V.
    Huang, Y.
    Olalde, P.
    Schmitt, T.
    Strocov, V. N.
    Fohlisch, A.
    Kennedy, B.
    Pietzsch, A.
    Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 13, article id 133001Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.

  • 22.
    Söderström, Johan
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Gråsjö, Johan
    Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Kashtanov, S
    Bergström, Christel
    Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Agåker, Marcus
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Schmitt, Thorsten
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Augustsson, Andreas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Duda, Laurent
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Guo, Jinghua
    Nordgren, Joseph
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Luo, Yi
    Artursson, Per
    Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy.
    Rubensson, Jan-Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    X-ray yield and selectively excited X-ray emission spectra of atenolol and nadolol.2005In: J Electr Spectr, Vol. 144-147, p. 283-285Article in journal (Refereed)
  • 23.
    Tunón, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Alderborn, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Effect of intragranular porosity on compression behaviour of and drug release from reservoir pellets2003In: European Journal of Pharmaceutical Sciences, ISSN 0928-0987, E-ISSN 1879-0720, Vol. 19, no 5, p. 333-344Article in journal (Refereed)
    Abstract [en]

    In this study, reservoir pellets were prepared and their compression behaviour as well as the importance of their porosity for compression-induced changes in drug release was investigated. Pellets of three different porosities, consisting of microcrystalline cellulose and salicylic acid, were prepared by extrusion-spheronisation and spray-coated with ethyl cellulose (ethanol solution). Lubricated reservoir pellets were compressed and retrieved by deaggregation of the tablets. The retrieved pellets were analysed regarding porosity, thickness, surface area, shape and drug release. It was found that the coating did not significantly affect their compression behaviour. Compaction of pellets of high original porosity considerably affected densification and degree of deformation, whereas the effect on drug release was minor. For low porosity pellets the influence of compaction on drug release was appreciable, but only slight regarding densification and degree of deformation. In conclusion, the porosity of pellets is a potential factor that the formulator can use to optimize drug release and one that can affect the robustness of a formulation during manufacture. Moreover, the coating may be able to adapt to the densification and deformation of the pellets.

  • 24.
    Århammar, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pietzsch, Annette
    MAX-lab, Lunds universitet, Lund.
    Bock, Nicolas
    Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
    Holmström, Erik
    Instituto di Fisica, Universidad Austral de Chile, Valdivia, Chile.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Zhao, Shuxi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Peery, T
    Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
    Hennies, Franz
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Amerioun, Shahrad
    Sandvik Tooling, R and D, Stockholm.
    Foehlisch, Alexander
    Insitute for Methods and Instrumentation in Synchrotron Radiation Research G-12, Helmhotz-Zentrum Berlin für Materialien und Energie, Berlin, Tyskland.
    Schlappa, Justine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schmitt, Thorsten
    Swiss Light Source, Paul Scherrer Institut, Villigen, Schweiz.
    Strocov, Vladimir N
    Swiss Light Source, Paul Scherrer Institut, Villigen, Schweiz.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wallace, Duane C
    Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Unveiling the complex electronic structure of amorphous metal oxides2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 16, p. 6355-6360Article in journal (Refereed)
    Abstract [en]

    Amorphous materials represent a large and important emerging area of material's science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today's integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5-10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

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