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  1. Article ; Online: Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation.

    Roy, Manosi / Sarkar, Kaushik / Som, Jacob / Pfeifer, Mark A / Craciun, Valentin / Schall, J David / Aravamudhan, Shyam / Wise, Frank W / Kumar, Dhananjay

    ACS applied materials & interfaces

    2023  Volume 15, Issue 3, Page(s) 4733–4742

    Abstract: Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × ... ...

    Abstract Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10
    Language English
    Publishing date 2023-01-10
    Publishing country United States
    Document type Journal Article
    ISSN 1944-8252
    ISSN (online) 1944-8252
    DOI 10.1021/acsami.2c18926
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

    Roy, Manosi / Sarkar, Kaushik / Som, Jacob / Pfeifer, Mark A. / Crăciun, V. / Schall, J. David / Aravamudhan, Shyam / Wise, Frank W. / Kumar, Dhananjay

    ACS Applied Materials & Interfaces. 2023 Jan. 10, v. 15, no. 3 p.4733-4742

    2023  

    Abstract: Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10-⁶ T). This vacuum contains enough residual ... ...

    Abstract Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10-⁶ T). This vacuum contains enough residual oxygen to allow a time-independent gas phase oxidation of the ablated species as well as a time-dependent regulated surface oxidation of TiN to TiON films. The time-dependent surface oxidation is controlled by means of film deposition time that, in turn, is controlled by changing the number of laser pulses impinging on the polycrystalline TiN target at a constant repetition rate. By changing the number of laser pulses from 150 to 5000, unoxidized (or negligibly oxidized) and oxidized TiN films have been obtained with the thickness in the range of four unit cells to 70 unit cells of TiN/TiON. X-ray photoelectron spectroscopy (XPS) investigations reveal higher oxygen content in TiON films prepared with a larger number of laser pulses. The oxidation of TiN films is achieved by precisely controlling the time of deposition, which affects the surface diffusion of oxygen to the TiN film lattice. The lattice constants of the TiON films obtained by x-ray diffraction (XRD) increase with the oxygen content in the film, as predicted by molecular dynamics (MD) simulations. The lattice constant increase is explained based on a larger electrostatic repulsive force due to unbalanced local charges in the vicinity of Ti vacancies and substitutional O. The bandgap of TiN and TiON films, measured using UV-visible spectroscopy, has an asymmetric V-shaped variation as a function of the number of pulses. The bandgap variation following the lower number of laser pulses (150-750) of the V-shaped curve is explained using the quantum confinement effect, while the bandgap variation following the higher number of laser pulses (1000-5000) is associated with the modification in the band structure due to hybridization of O₂ₚ and N₂ₚ energy levels.
    Keywords X-ray diffraction ; X-ray photoelectron spectroscopy ; energy ; hybridization ; molecular dynamics ; nitrides ; oxidation ; oxygen ; titanium ; ultraviolet-visible spectroscopy ; thin films ; pulsed laser deposition ; controlled oxidation ; bandgap energy ; oxynitrides ; transition metal nitrides
    Language English
    Dates of publication 2023-0110
    Size p. 4733-4742.
    Publishing place American Chemical Society
    Document type Article ; Online
    ISSN 1944-8252
    DOI 10.1021/acsami.2c18926
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  3. Article ; Online: Forming Anisotropic Crystal Composites: Assessing the Mechanical Translation of Gel Network Anisotropy to Calcite Crystal Form.

    Palin, Damian / Style, Robert W / Zlopaša, Jure / Petrozzini, Jonathan J / Pfeifer, Mark A / Jonkers, Henk M / Dufresne, Eric R / Estroff, Lara A

    Journal of the American Chemical Society

    2021  Volume 143, Issue 9, Page(s) 3439–3447

    Abstract: The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel ... ...

    Abstract The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.
    MeSH term(s) Anisotropy ; Calcium Carbonate/chemical synthesis ; Calcium Carbonate/chemistry ; Crystallization ; Gels/chemistry ; Sepharose/chemistry
    Chemical Substances Gels ; Sepharose (9012-36-6) ; Calcium Carbonate (H0G9379FGK)
    Language English
    Publishing date 2021-03-01
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.0c12326
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  4. Article ; Online: Three-dimensional mapping of a deformation field inside a nanocrystal.

    Pfeifer, Mark A / Williams, Garth J / Vartanyants, Ivan A / Harder, Ross / Robinson, Ian K

    Nature

    2006  Volume 442, Issue 7098, Page(s) 63–66

    Abstract: Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density ... ...

    Abstract Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals. Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate. When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a 'complex' crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative three-dimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials. Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers.
    Language English
    Publishing date 2006-07-06
    Publishing country England
    Document type Journal Article
    ZDB-ID 120714-3
    ISSN 1476-4687 ; 0028-0836
    ISSN (online) 1476-4687
    ISSN 0028-0836
    DOI 10.1038/nature04867
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  5. Article ; Online: Phase-diverse coherent diffractive imaging: high sensitivity with low dose.

    Putkunz, Corey T / Clark, Jesse N / Vine, David J / Williams, Garth J / Pfeifer, Mark A / Balaur, Eugeniu / McNulty, Ian / Nugent, Keith A / Peele, Andrew G

    Physical review letters

    2011  Volume 106, Issue 1, Page(s) 13903

    Abstract: This Letter demonstrates that coherent diffractive imaging (CDI), in combination with phase-diversity methods, provides reliable and artefact free high-resolution images. Here, using x rays, experimental results show a threefold improvement in the ... ...

    Abstract This Letter demonstrates that coherent diffractive imaging (CDI), in combination with phase-diversity methods, provides reliable and artefact free high-resolution images. Here, using x rays, experimental results show a threefold improvement in the available image contrast. Furthermore, in conditions requiring low imaging dose, it is demonstrated that phase-diverse CDI provides a factor of 2 improvement in comparison to previous CDI techniques.
    Language English
    Publishing date 2011-01-07
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.106.013903
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  6. Article ; Online: High-resolution X-ray imaging of Plasmodium falciparum-infected red blood cells.

    Williams, Garth J / Hanssen, Eric / Peele, Andrew G / Pfeifer, Mark A / Clark, Jesse / Abbey, Brian / Cadenazzi, Guido / de Jonge, Martin D / Vogt, Stefan / Tilley, Leann / Nugent, Keith A

    Cytometry. Part A : the journal of the International Society for Analytical Cytology

    2008  Volume 73, Issue 10, Page(s) 949–957

    Abstract: Methods for imaging cellular architecture and ultimately macromolecular complexes and individual proteins, within a cellular environment, are an important goal for cell and molecular biology. Coherent diffractive imaging (CDI) is a method of lensless ... ...

    Abstract Methods for imaging cellular architecture and ultimately macromolecular complexes and individual proteins, within a cellular environment, are an important goal for cell and molecular biology. Coherent diffractive imaging (CDI) is a method of lensless imaging that can be applied to any individual finite object. A diffraction pattern from a single biological structure is recorded and an iterative Fourier transform between real space and reciprocal space is used to reconstruct information about the architecture of the sample to high resolution. As a test system for cellular imaging, we have applied CDI to an important human pathogen, the malaria parasite, Plasmodium falciparum. We have employed a novel CDI approach, known as Fresnel CDI, which uses illumination with a curved incident wavefront, to image red blood cells infected with malaria parasites. We have examined the intrinsic X-ray absorption contrast of these cells and compared them with cells contrasted with heavy metal stains or immunogold labeling. We compare CDI images with data obtained from the same cells using scanning electron microscopy, light microscopy, and scanning X-ray fluorescence microscopy. We show that CDI can offer new information both within and at the surface of complex biological specimens at a spatial resolution of better than 40 nm. and we demonstrate an imaging modality that conveniently combines scanning X-ray fluorescence microscopy with CDI. The data provide independent confirmation of the validity of the coherent diffractive image and demonstrate that CDI offers the potential to become an important and reliable new high-resolution imaging modality for cell biology. CDI can detect features at high resolution within unsectioned cells.
    MeSH term(s) Animals ; Erythrocytes/diagnostic imaging ; Erythrocytes/parasitology ; Erythrocytes/ultrastructure ; Green Fluorescent Proteins/analysis ; Green Fluorescent Proteins/genetics ; Microscopy, Electron, Scanning Transmission ; Microscopy, Fluorescence ; Plasmodium falciparum/isolation & purification ; Radiography ; Transfection ; X-Ray Diffraction/methods
    Chemical Substances Green Fluorescent Proteins (147336-22-9)
    Language English
    Publishing date 2008-10
    Publishing country United States
    Document type Comparative Study ; Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2099868-5
    ISSN 1552-4930 ; 0196-4763 ; 1552-4922
    ISSN (online) 1552-4930
    ISSN 0196-4763 ; 1552-4922
    DOI 10.1002/cyto.a.20616
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  7. Article: High-resolution X-ray imaging of Plasmodium falciparum-infected red blood cells

    Williams, Garth J / Hanssen, Eric / Peele, Andrew G / Pfeifer, Mark A / Clark, Jesse / Abbey, Brian / Cadenazzi, Guido / de Jonge, Martin D / Vogt, Stefan / Tilley, Leann / Nugent, Keith A

    Cytometry. Part A. 2008 Oct., v. 73A, no. 10

    2008  

    Abstract: Methods for imaging cellular architecture and ultimately macromolecular complexes and individual proteins, within a cellular environment, are an important goal for cell and molecular biology. Coherent diffractive imaging (CDI) is a method of lensless ... ...

    Abstract Methods for imaging cellular architecture and ultimately macromolecular complexes and individual proteins, within a cellular environment, are an important goal for cell and molecular biology. Coherent diffractive imaging (CDI) is a method of lensless imaging that can be applied to any individual finite object. A diffraction pattern from a single biological structure is recorded and an iterative Fourier transform between real space and reciprocal space is used to reconstruct information about the architecture of the sample to high resolution. As a test system for cellular imaging, we have applied CDI to an important human pathogen, the malaria parasite, Plasmodium falciparum. We have employed a novel CDI approach, known as Fresnel CDI, which uses illumination with a curved incident wavefront, to image red blood cells infected with malaria parasites. We have examined the intrinsic X-ray absorption contrast of these cells and compared them with cells contrasted with heavy metal stains or immunogold labeling. We compare CDI images with data obtained from the same cells using scanning electron microscopy, light microscopy, and scanning X-ray fluorescence microscopy. We show that CDI can offer new information both within and at the surface of complex biological specimens at a spatial resolution of better than 40 nm. and we demonstrate an imaging modality that conveniently combines scanning X-ray fluorescence microscopy with CDI. The data provide independent confirmation of the validity of the coherent diffractive image and demonstrate that CDI offers the potential to become an important and reliable new high-resolution imaging modality for cell biology. CDI can detect features at high resolution within unsectioned cells. © 2008 International Society for Advancement of Cytometry
    Language English
    Dates of publication 2008-10
    Size p. 949-957.
    Publishing place Wiley Subscription Services, Inc., A Wiley Company
    Document type Article
    ISSN 1552-4922
    DOI 10.1002/cyto.a.20616
    Database NAL-Catalogue (AGRICOLA)

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