Extending the Depth of Focus of an Infrared Microscope Using a Binary Axicon Fabricated on Barium Fluoride.

Axial resolution is one of the most important characteristics of a microscope. In all microscopes, a high axial resolution is desired in order to discriminate information efficiently along the longitudinal direction. However, when studying thick samples that do not contain laterally overlapping information, a low axial resolution is desirable, as information from multiple planes can be recorded simultaneously from a single camera shot instead of plane-by-plane mechanical refocusing. In this study, we increased the focal depth of an infrared microscope non-invasively by introducing a binary axicon fabricated on a barium fluoride substrate close to the sample. Preliminary results of imaging the thick and sparse silk fibers showed an improved focal depth with a slight decrease in lateral resolution and an increase in background noise.

Mechanical and Optical Properties of Cr2O3 Thin Films Grown by Atomic Layer Deposition Method Using Cr(thd)3 and Ozone.

Cr2O3 thin films were grown on a Si (1 0 0) substrate using Cr(thd)3 and O3 by atomic layer deposition (ALD) at substrate temperatures (TG) from 200 to 300 °C. X-ray amorphous films were deposited at a TG ≤ 225 °C, whereas at higher temperatures (TG ≥ 250 °C), the eskolaite phase was observed in the films. The growth rate of the films increased from 0.003 to 0.01 nm/cycle by increasing TG from 200 to 275 °C. The relatively low growth rate of Cr(thd)3-O3 makes it appropriate for the ALD of precisely controllable solid solution-type ternary-component thin films. The Ti-doped Cr2O3 film showed higher hardness (16.7 GPa) compared with that of the undoped film (12.8 GPa) with similar thickness. The band gap values of the pure Cr2O3 corresponding to the indirect transition model showed no dependence on TG; however, doping the Cr2O3 with Ti decreased its band gap energy value from 3.1 to 2.2 eV.

Nanostructures Stacked on Hafnium Oxide Films Interfacing Graphene and Silicon Oxide Layers as Resistive Switching Media.

SiO2 films were grown to thicknesses below 15 nm by ozone-assisted atomic layer deposition. The graphene was a chemical vapor deposited on copper foil and transferred wet-chemically to the SiO2 films. On the top of the graphene layer, either continuous HfO2 or SiO2 films were grown by plasma-assisted atomic layer deposition or by electron beam evaporation, respectively. Micro-Raman spectroscopy confirmed the integrity of the graphene after the deposition processes of both the HfO2 and SiO2. Stacked nanostructures with graphene layers intermediating the SiO2 and either the SiO2 or HfO2 insulator layers were devised as the resistive switching media between the top Ti and bottom TiN electrodes. The behavior of the devices was studied comparatively with and without graphene interlayers. The switching processes were attained in the devices supplied with graphene interlayers, whereas in the media consisting of the SiO2-HfO2 double layers only, the switching effect was not observed. In addition, the endurance characteristics were improved after the insertion of graphene between the wide band gap dielectric layers. Pre-annealing the Si/TiN/SiO2 substrates before transferring the graphene further improved the performance.

Memory Effects in Nanolaminates of Hafnium and Iron Oxide Films Structured by Atomic Layer Deposition.

HfO2 and Fe2O3 thin films and laminated stacks were grown by atomic layer deposition at 350 °C from hafnium tetrachloride, ferrocene, and ozone. Nonlinear, saturating, and hysteretic magnetization was recorded in the films. Magnetization was expectedly dominated by increasing the content of Fe2O3. However, coercive force could also be enhanced by the choice of appropriate ratios of HfO2 and Fe2O3 in nanolaminated structures. Saturation magnetization was observed in the measurement temperature range of 5-350 K, decreasing towards higher temperatures and increasing with the films' thicknesses and crystal growth. Coercive force tended to increase with a decrease in the thickness of crystallized layers. The films containing insulating HfO2 layers grown alternately with magnetic Fe2O3 exhibited abilities to both switch resistively and magnetize at room temperature. Resistive switching was unipolar in all the oxides mounted between Ti and TiN electrodes.

Structure and Electrical Behavior of Hafnium-Praseodymium Oxide Thin Films Grown by Atomic Layer Deposition.

Crystal structure and electrical properties of hafnium-praseodymium oxide thin films grown by atomic layer deposition on ruthenium substrate electrodes were characterized and compared with those of undoped HfO2 films. The HfO2 reference films crystallized in the stable monoclinic phase of HfO2. Mixing HfO2 and PrOx resulted in the growth of nanocrystalline metastable tetragonal HfO2. The highest relative permittivities reaching 37-40 were measured for the films with tetragonal structures that were grown using HfO2:PrOx cycle ratio of 5:1 and possessed Pr/(Pr + Hf) atomic ratios of 0.09-0.10. All the HfO2:PrOx films exhibited resistive switching behavior. Lower commutation voltages and current values, promising in terms of reduced power consumption, were achieved for the films grown with HfO2:PrOx cycle ratios of 3:1 and 2:1 and showing Pr/(Pr + Hf) atomic ratios of 0.16-0.23. Differently from the undoped HfO2 films, the Pr-doped films showed low variability of resistance state currents and stable endurance behavior, extending over 104 switching cycles.

Atomic layer deposition and properties of ZrO2/Fe2O3 thin films.

Thin solid films consisting of ZrO2 and Fe2O3 were grown by atomic layer deposition (ALD) at 400 °C. Metastable phases of ZrO2 were stabilized by Fe2O3 doping. The number of alternating ZrO2 and Fe2O3 deposition cycles were varied in order to achieve films with different cation ratios. The influence of annealing on the composition and structure of the thin films was investigated. Additionally, the influence of composition and structure on electrical and magnetic properties was studied. Several samples exhibited a measurable saturation magnetization and most of the samples exhibited a charge polarization. Both phenomena were observed in the sample with a Zr/Fe atomic ratio of 2.0.

Nanoscale characterization of TiO(2) films grown by atomic layer deposition on RuO(2) electrodes.

Topography and leakage current maps of TiO2 films grown by atomic layer deposition on RuO2 electrodes using either a TiCl4 or a Ti(O-i-C3H7)4 precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl4-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti(O-i-C3H7)4-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction.

Electrochemical modification of gold electrodes with azobenzene derivatives by diazonium reduction.

An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X-ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi-reversible voltammogram of the Fe(CN)6 (3-/4-) redox couple on bare Au and a sigmoidal shape for the GBC- and FBK-modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)6 (3-/4-) response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)6 (3-/4-) redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge-transfer rates to the Fe(CN)6 (3-) probe for the GBC- and FBK-modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.