Search

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. Funding Agencies|National Science Foundation (NSF) through the Nebraska Materials Research Science and Engineering Center (MRSEC)National Science Foundation (NSF) [DMR-1420645, CMMI 1337856, DMR 1808715]; Air Force Research Office [FA9550-18-1-0360]; American Chemical SocietyAmerican Chemical Society [ACS PRF 59374-ND5]; University of Nebraska-Lincoln; J. A. Woollam Co., Inc.; J. A. Woollam Foundation

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 (TiO2NPs) 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.

Biological experiments involving isolated organs and tissues demand precise temperature monitoring and regulation. An automatic temperature control system was proposed and optimised on real isolated swine hearts and the prototype is described in this work. The traditional Langendorff apparatus consists of a heart holder, a reservoir of perfusion solution flowing to aortic cannula and a heating bath allowing passive heat transfer to the reservoir of perfusion solution. The commercial infrared camera FLIR T62101 was added to this basic set-up and used for very precise monitoring of the temperature kinetic of the organ and connected with an electronic feedback loop, which allowed real-time and precise regulation of heat transfer from the heating bath to the perfusion solution and in turn indirectly to the heart tissue. This provides real time control and active regulation of the myocardial tissue temperature. The infrared camera was tested in several modes and several variants of detection were optimised for ideal measurement of the region of interest of the ex vivo organ. The kinetics of the temperature changes and temperature stability of the tissue were recorded and calibrated by external electronic thermometers (type Pt100, inserted in tissue). The time lapse from the hang-up of the hypo termed organ (30 °C) until optimal warming (37 °C) was less than eight minutes in the final instrument prototype. The final stability of the 37 °C tissue temperature was approved; the temperature fluctuation of left ventricle tissue was characterised as 36.8 ± 0.5 °C. This upgraded traditional instrument could be used in specific preclinical and clinical transplantation and analytical projects in future.

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. Funding Agencies|National Science Foundation (NSF) through the Nebraska Materials Research Science and Engineering Center (MRSEC) [DMR-1420645, CMMI 1337856, EAR 1521428, DMR 1808715]; German Research Foundation [FE 1532/1-1]; Air Force Research Office [FA9550-18-1-0360]; American Chemical Society [ACS PRF 59374-ND5]; University of Nebraska-Lincoln; J.A. Woollam Co., Inc.; J.A. Woollam Foundation

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 ≈33° and ≈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.

The anisotropic optical dielectric functions of a metal (cobalt) slanted columnar thin film deposited by electron-beam glancing angle deposition are reported for the terahertz (THz) frequency domain before and after the slanted columnar thin film was passivated by a conformal alumina coating. A simple effective medium dielectric function homogenization approach which describes isolated, electrically conductive columns rendering the thin film biaxial (orthorhombic) is used to model the observed optical responses. Upon passivating the slanted columnar thin film with a 3 nm thick alumina film an increase of both the real and the imaginary part of the dielectric function for all major polarizability directions is found and attributed to screening effects within the spatially coherent metal nanocolumns.

Optical and structural properties of sequential Co-column–NiFe-column slanted columnar heterostructure thin films with an Al 2 O 3 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.

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 0.7-3.4 eV measured with time resolution of few seconds over large numbers of cycles during the growth of titanium oxide (TiO

Hypothesis A surface comprising spatially coherent columnar nanostructures is expected to retain intercolumnar liquid during a quartz crystal microbalance measurement due to the surface structure. Part of the liquid retained by the nanostructures may then be displaced by adsorbate. Experiments Slanted columnar nanostructure thin films were designed to vary in height but remain structurally similar, fabricated by glancing angle deposition, and characterized by generalized ellipsometry. A frequency overtone analysis, introduced here, was applied to analyze quartz crystal microbalance data for the exchange of isotope liquids over the nanostructured surfaces and determine the areal inertial mass of structure-retained liquid. The adsorption of cetyltrimethylammonium bromide onto nanostructures was investigated by simultaneous quartz crystal microbalance and generalized ellipsometry measurements. Findings The areal inertial mass of structure-retained liquid varies linearly with nanostructure height. The proportionality constant is a function of the surface topography and agrees with the generalized ellipsometry-determined nanostructure film porosity, implying that nearly all intercolumnar liquid is retained. We report that for adsorption processes within porous nanostructured films, the quartz crystal microbalance is sensitive not to the combined areal inertial mass of adsorbate and retained liquid but rather to the density difference between adsorbate and liquid due to the volume exchange within the nanostructure film.

Sculptured thin film (STF) substrates consist of nanocolumns with precise orientation, intercolumnar spacing, and optical anisotropy, which can be used as model biomaterial substrates to study the effect of homogenous nanotopogrophies on the three-dimensional distribution of adsorbed proteins. Generalized ellipsometry was used to discriminate between the distributions of adsorbed FN either on top of or within the intercolumnar void spaces of STFs, afforded by the optical properties of these precisely crafted substrates. Generalized ellipsometry indicated that STFs with vertical nanocolumns enhanced total FN adsorption two-fold relative to flat control substrates and the FN adsorption studies demonstrate different STF characteristics influence the degree of FN immobilization both on top and within intercolumnar spaces, with increasing spacing and surface area enhancing total protein adsorption. Mouse fibroblasts or mouse mesenchymal stem cells were subsequently cultured on STFs, to investigate the effect of highly ordered and defined nanotopographies on cell adhesion, spreading, and proliferation. All STF nanotopographies investigated in the absence of adsorbed FN were found to significantly enhance cell adhesion relative to flat substrates; and the addition of FN to STFs was found to have cell-dependent effects on enhancing cell–material interactions. Furthermore, the amount of FN adsorbed to the STFs did not correlate with comparative enhancements of cell–material interactions, suggesting that nanotopography predominantly contributes to the biocompatibility of homogenous nanocolumnar surfaces. This is the first study to correlate precisely defined nanostructured features with protein distribution and cell–nanomaterial interactions. STFs demonstrate immense potential as biomaterial surfaces for applications in tissue engineering, drug delivery, and biosensing.

The work deals with fabrication of iron oxide (α-Fe 2 O 3 ) hematite films by a novel high-power impulse magnetron sputtering method (HiPIMS). Hematite is regarded as a highly promising material for sustainable production of hydrogen via photoelectrochemical (PEC) water splitting. Some of the crucial issues of hematite are a large overpotential needed to develop the water oxidation photocurrent onset, high extent of surface defects acting as traps, and a short diffusion length (2–4 nm) of photogenerated holes. We report on minimizing these limits by deposition of highly photoactive nanocrystalline very thin (∼30 nm) absorbing hematite films by HiPIMS and their passivation by ultra-thin (∼2 nm) atomic layer deposited (ALD) isocrystalline alumina oxide (α-Al 2 O 3 ) films. A new approach of one-step annealing of this bilayer system is introduced. The films were judged on the basis of physical properties such as crystalline structure, optical absorption, surface topography, and electronic properties. The functional properties were investigated under simulated photoelectrochemical (PEC) water-splitting conditions. The shift by 1 V vs. RHE and the maximal photocurrent value of 0.48 mA cm −2 at 1.23 V vs. RHE were achieved.

The uniform pinhole-free iron disulfide (FeS2) pyrite thin films were fabricated. In the first step the FeO(OH)x xerogel solution was synthetized by means of a novel epoxy catalyzed sol–gel method and next spin-coated onto various substrates to form the thin films. In the second step the xerogel coatings were annealed to yield hematite (α-Fe2O3) films, which were transformed into pyrite by chemical sulfurization. Among the main deposition parameters studied were the temperature of xerogel–hematite transformation and the optimal sufulrization temperature and duration. It has been observed that 15 min sulfurization at the temperature of 450 °C provided the pyrite films of sufficient quality. The estimated optical band gap of 0.98 eV is very close to the theoretical value of 0.95 eV. Auger electron spectroscopy showed almost ideal stoichiometry of FeS2. However a trace amount of oxygen (approximately 0.5 at.%) present in the film was still detected. The photoinduced functionality of the films was assessed based on photoelectrochemical experiments. In order to demonstrate the ability of pyrite to photosensitize a large band gap semiconductor, a bilayer system of TiO2 anatase/FeS2 pyrite was prepared. The highest photocurrent reached was 45 μA cm−2 at the light intensity of 10.5 mW cm−2.

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 was 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 density functional theory. We investigate surface roughness with atomic force microscopy and compare to ellipsometric determined effective roughness layer thickness.

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 1 mV/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 ∼18% in the anisotropic refractive indices and ∼750% in the anisotropic extinction coefficients. Furthermore, the thin films reversibly expand and contract by ∼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 deinterc...

Highly-ordered and spatially-coherent cobalt slanted columnar thin films were deposited by glancing angle deposition onto silicon substrates, and subsequently oxidized by annealing at 475 $^{\circ}$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 CoAl$_2$O$_3$ 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 $^{\circ}$C., 5 pages, 5 figures, 2 tables

An antenna integration concept for carbon fibre reinforced plastics is presented, using the example of a thin conformal S-band annular slot antenna on a UAV. Instead of cutting large holes into the aircraft shell or a panel as usually done for conformal antennas, the antenna is moulded into the laminate. Smooth load transitions for maximum mechanical stability are created in this way. Simulation and measurement results of the antenna performance are shown. Additional advantages of the annular slot antenna over normal blade antennas are presented with regard to typical UAV applications.

Monophasic action potential (MAP) can be recorded from the heart surface by optical method via fluorescence measurement. The motion of isolated heart during experiment caused additional noise in recorded signal. The motion artifact can be eliminated by ratiometric fluorescence emission measurements. This study is based on experiments in which a new ratiometric recording setup is used for recording MAPs from isolated rabbit hearts perfused according to Langendorff. MAPs recorded by new ratiometric recording setup are compared with simple optical MAP measurement without ratiometry.

We use generalized spectroscopic ellipsometry to characterize the biaxial optical properties of porous polymer and slanted nanocolumnar template thin films. The porous polymer with inverse columnar structure was prepared via infiltrating polymer into the voids of the slanted nanocolumnar film and selectively removing the column material (cobalt). The anisotropic Bruggeman effective medium approximation was employed to analyze the ellipsometry data of the porous polymer film and nanocolumnar template. The classification and structure of optical anisotropy are found to be identical for both samples. The interchangeable optical behaviors between two complementary structures are attributed to the equivalency in their anisotropic polarizabilities.

Iron films deposited by direct current magnetron sputtering onto glass substrates were converted into FeS2 films by thermal sulfurization. Experiments were carried out to optimize the sulfurization process, and the formation of FeS2 thin films was investigated under different annealing temperatures and times. High quality FeS2 films were fabricated using this process, and single phase pyrite films were obtained after sulfurization in a sulfur and nitrogen atmosphere at 450 °C for 1 h. Film crystallinity and phase identification were determined by using x-ray diffraction. The cubic phase pyrite films prepared were p-type, and scanning electron microscopy studies exhibited a homogeneous surface of pyrite. The authors have found that the best Ohmic contact for their pyrite thin films, using inexpensive metals, was Ni. The following were chosen for the study: Al, Mo, Fe, and Ni, and the one that led to the lowest resistance, 333 Ω, was Ni.

WE have recently stated that if silk II (for example, silk of the cocoon filament1) is treated with hot alkali, there appears in X-ray diagrams at the equator one reflexion of 45 A., besides some additional higher orders (silk III2). Diagrams of higher-orientated samples show that the net plane with D= 45 A. coincides with the equator reflexions (D= 9.15 and 4.57 A.), which, as is well known, represent the plane of the flat micelles. The 45-A. reflexion is much more intense and sharp than the equator reflexions of 9.15 and 4.57 A.

THE filament of the silkworm Bombyx mori gives the well-known X-ray fibre diagram1, which can also be obtained by stretching the silk-gland taken from the animal2.

Coleman and Howitt1 have observed the interesting fact that if one dissolves denatured silk-fibroin in cupriethylene-diamine, a product is obtained which does not differ essentially from the native fibroin, and therefore they have called it the process of “renaturation”.

SINCE writing the communication entitled “An Unstable Lattice in Silk Fibroin”1, a further modification of silk has been found which can be prepared by treating ‘silk II’ with 0.5 per cent sodium hydroxide at 60–70° C. for about a minute. We suggest that this new type of silk be called ‘silk III’. It shows all the interferences of ‘silk II’ and in addition the equator net-plane distances shown in the accompanying table.