| 1. |
- Kananizadeh, Negin, et al.
(författare)
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Deposition of titanium dioxide nanoparticles onto engineered rough surfaces with controlled heights and properties
- 2019
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Ingår i: Colloids and Surfaces A. - : ELSEVIER SCIENCE BV. - 0927-7757 .- 1873-4359. ; 571, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the influence of surface roughness on the deposition of nanoparticles is important to a variety of environmental and industrial processes. In this work, slanted columnar thin films (SCTFs) were engineered to serve as an analogue for rough surfaces with controlled height and surface properties. The deposition of titanium dioxide nanoparticles (TiO(2)NPs) onto alumina-or silica-coated SCTFs (Al2O3-Si-SCTF, SiO2-Si-SCTF) with varying heights (50 nm, 100 nm, and 200 nm) was measured using a combined quartz crystal microbalance with dissipation monitoring (QCM-D) and generalized ellipsometry (GE) technique. No TiO2NP deposition was observed on flat, silica-coated QCM-D sensors or rough, 100 nm thick SiO2-Si-SCTF. TiO2NP deposition onto Al2O3-Si-SCTFs in ultra-pure water was significantly higher than on the flat alumina-coated QCM-D sensor, and deposition increased as the roughness height increased. The nanoparticle attachment was sensitive to the local flow field and the interaction energy between nanoparticles and the QCM-D sensor. At a higher ionic strength condition (100 mM NaCl), TiO2NP aggregates with varying sizes formed a rigid layer on top of SCTFs. For the first time, deposition of nanoparticles was measured as a function of roughness height, and the impact of roughness on the properties of the attached nanoparticle layers was revealed. This finding indicates that key parameters describing surface roughness should be explicitly included into models to accurately predict the transport of nanoparticles in the subsurface.
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| 2. |
- Kilic, Ufuk, et al.
(författare)
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Critical-point model dielectric function analysis of WO3 thin films deposited by atomic layer deposition techniques
- 2018
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 124:11
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Tidskriftsartikel (refereegranskat)abstract
- WO3 thin films were grown by atomic layer deposition and spectroscopic ellipsometry data gathered in the photon energy range of 0.72-8.5 eV, and from multiple samples were utilized to determine the frequency dependent complex-valued isotropic dielectric function for WO3. We employ a critical-point model dielectric function analysis and determine a parameterized set of oscillators and compare the observed critical-point contributions with the vertical transition energy distribution found within the band structure of WO3 calculated by the density functional theory. The surface roughness was investigated using atomic force microscopy, and compared with the effective roughness as seen by the spectroscopic ellipsometry. Published by AIP Publishing.
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| 3. |
- Kilic, Ufuk, et al.
(författare)
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Precursor-surface interactions revealed during plasma-enhanced atomic layer deposition of metal oxide thin films by in-situ spectroscopic ellipsometry
- 2020
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- We find that a five-phase (substrate, mixed native oxide and roughness interface layer, metal oxide thin film layer, surface ligand layer, ambient) model with two-dynamic (metal oxide thin film layer thickness and surface ligand layer void fraction) parameters (dynamic dual box model) is sufficient to explain in-situ spectroscopic ellipsometry data measured within and across multiple cycles during plasma-enhanced atomic layer deposition of metal oxide thin films. We demonstrate our dynamic dual box model for analysis of in-situ spectroscopic ellipsometry data in the photon energy range of 0.7-3.4eV measured with time resolution of few seconds over large numbers of cycles during the growth of titanium oxide (TiO2) and tungsten oxide (WO3) thin films, as examples. We observe cyclic surface roughening with fast kinetics and subsequent roughness reduction with slow kinetics, upon cyclic exposure to precursor materials, leading to oscillations of the metal thin film thickness with small but positive growth per cycle. We explain the cyclic surface roughening by precursor-surface interactions leading to defect creation, and subsequent surface restructuring. Atomic force microscopic images before and after growth, x-ray photoelectron spectroscopy, and x-ray diffraction investigations confirm structural and chemical properties of our thin films. Our proposed dynamic dual box model may be generally applicable to monitor and control metal oxide growth in atomic layer deposition, and we include data for SiO2 and Al2O3 as further examples.
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| 4. |
- Kilic, Ufuk, et al.
(författare)
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Tunable plasmonic resonances in Si-Au slanted columnar heterostructure thin films
- 2019
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous Si-Au slanted columnar heterostructures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is observed in the vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like mode frequency within the near-infrared spectral range by varying the geometry of Si-Au slanted columnar heterostructures. In addition, coupled-plasmon-like and inter-band transition-like modes occur in the visible and ultra-violet spectral regions, respectively. We elucidate an example for the potential use of Si-Au slanted columnar heterostructures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water.
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| 5. |
- Mock, Alyssa, et al.
(författare)
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Anisotropy, band-to-band transitions, phonon modes, and oxidation properties of cobalt-oxide core-shell slanted columnar thin films
- 2016
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 108:5, s. 051905-
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Tidskriftsartikel (refereegranskat)abstract
- Highly ordered and spatially coherent cobalt slanted columnar thin films (SCTFs) were deposited by glancing angle deposition onto silicon substrates, and subsequently oxidized by annealing at 475 degrees C. Scanning electron microscopy, Raman scattering, generalized ellipsometry, and density functional theory investigations reveal shape-invariant transformation of the slanted nanocolumns from metallic to transparent metal-oxide core-shell structures with properties characteristic of spinel cobalt oxide. We find passivation of Co-SCTFs yielding Co-Al2O3 core-shell structures produced by conformal deposition of a few nanometers of alumina using atomic layer deposition fully prevents cobalt oxidation in ambient and from annealing up to 475 degrees C. (C) 2016 AIP Publishing LLC.
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| 6. |
- Rice, Charles, et al.
(författare)
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Control of slanting angle, porosity, and anisotropic optical constants of slanted columnar thin films via in situ nucleation layer tailoring
- 2017
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Ingår i: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 421, s. 766-771
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Tidskriftsartikel (refereegranskat)abstract
- Electron-beam evaporation at a glancing angle of 85 is utilized to fabricate highly ordered, spatially coherent titanium slanted columnar thin films. Prior to deposition of the slanted columnar thin films, a titanium nucleation layer is deposited using electron-beam deposition at normal incidence with various intended nucleation layer thicknesses of 0 nm, 5 nm, 7.5 nm, 10 nm, 20 nm, and 50 nm. Structural and optical properties of the anisotropic porous thin films are studied by scanning electron microscopy, atomic force microscopy, and Mueller matrix generalized spectroscopic ellipsometry in the near infrared to ultra-violet spectral regions. An anisotropic effective medium approximation is employed for analysis of the ellipsometry data in order to determine slanting angle and porosity model parameters. We find that the slanting angle and titanium volume fraction are strongly influenced by the nucleation layer thickness. Structural parameters of SCTFs deposited on 50 nm nucleation layers are similar to those from SCTFs with no nucleation layer. For small nucleation layer thicknesses, the corresponding SCTF slanting angle and titanium volume fraction decrease reaching a minimum of approximate to 33 degrees and approximate to 12% respectively, at 10 nm nucleation layer thickness. In accordance with the strong decrease in volume fraction we observe substantial reduction of the effective anisotropic thin film optical constants. We find the slanting angle and porosity variation reproducible and suggest use of a nucleation layer for control of slanting angle and porosity of slanted columnar thin films. (C) 2017 Published by Elsevier B.V.
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| 7. |
- Sekora, Derek, et al.
(författare)
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Optical and structural properties of cobalt-permalloy slanted columnar heterostructure thin films
- 2017
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Ingår i: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 421, s. 783-787
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Tidskriftsartikel (refereegranskat)abstract
- Optical and structural properties of sequential Co-column-NiFe-column slanted columnar heterostructure thin films with an A1203 passivation coating are reported. Electron-beam evaporated glancing angle deposition is utilized to deposit the sequential multiple-material slanted columnar heterostructure thin films. Mueller matrix generalized spectroscopic ellipsometry data is analyzed with a best-match model approach employing the anisotropic Bruggeman effective medium approximation formalism to determine bulk-like and anisotropic optical and structural properties of the individual Co and NiFe slanted columnar material sub-layers. Scanning electron microscopy is applied to image the Co-NiFe sequential growth properties and to verify the results of the ellipsometric analysis. Comparisons to single-material slanted columnar thin films and optically bulk solid thin films are presented and discussed. We find that the optical and structural properties of each material sub-layer of the sequential slanted columnar heterostructure film are distinct from each other and resemble those of their respective single-material counterparts. (C) 2016 Elsevier B.V. All rights reserved.
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| 8. |
- Sekora, Derek, et al.
(författare)
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Structural and optical properties of alumina passivated amorphous Si slanted columnar thin films during electrochemical Li-ion intercalation and deintercalation observed by in situ generalized spectroscopic ellipsometry
- 2017
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Ingår i: Journal of Vacuum Science & Technology B. - : A V S AMER INST PHYSICS. - 1071-1023 .- 1520-8567. ; 35:3
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the structural and optical property changes of alumina passivated amorphous Si slanted columnar thin films during electrochemical Li-ion intercalation and deintercalation determined by in situ generalized spectroscopic ellipsometry. The cyclic voltammetry investigations versus Li/Li+ are performed at a rate of 1mV/s, while Mueller matrix generalized spectroscopic ellipsometry data are collected. Through a best-match model analysis utilizing the homogeneous biaxial layer approach, temporal anisotropic optical constants are obtained. The authors observe a strong anisotropic electrochromic response with maximum changes of similar to 18% in the anisotropic refractive indices and similar to 750% in the anisotropic extinction coefficients. Furthermore, the thin films reversibly expand and contract by similar to 35%. A comparative analysis of the temporal optical constant response to the changes in overall optical anisotropy of the electrode reveals six transient regions throughout the Li-ion intercalation and deintercalation cycle of the highly ordered three-dimensional nanostructures. The transients correspond to electrochemical potential regions which show limited charge transfer, metalization or demetalization, and swelling or deswelling of the nanostructures. Furthermore, the electrochemical potential regions in which the transients are observed here are very similar to those previously reported for Li-ion intercalation and deintercalation of silicon nanowires using structural analysis techniques, where four distinct phases of Li-Si alloy formation were revealed. The authors find that at low Li contributions, swelling and deswelling occur preferentially along the slanted columns, while at high Li contributions, swelling and deswelling occur preferentially within the intercolumnar space. (C) 2017 American Vacuum Society.
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