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.

Properties of tin oxide films grown by atomic layer deposition from tin tetraiodide and ozone.

Polycrystalline SnO2 thin films were grown by atomic layer deposition (ALD) on SiO2/Si(100) substrates from SnI4 and O3. Suitable evaporation temperatures for the SnI4 precursor as well as the relationship between growth per cycle and substrate temperature were determined. Crystal growth in the films in the temperature range of 225-600 °C was identified. Spectroscopic analyses revealed low amounts of residual iodine and implied the formation of single-phase oxide in the films grown at temperatures above 300 °C. Appropriateness of the mentioned precursor system to the preparation of SnO2 films was established.

3D incoherent imaging using an ensemble of sparse self-rotating beams.

Interferenceless coded aperture correlation holography (I-COACH) is one of the simplest incoherent holography techniques. In I-COACH, the light from an object is modulated by a coded mask, and the resulting intensity distribution is recorded. The 3D image of the object is reconstructed by processing the object intensity distribution with the pre-recorded 3D point spread intensity distributions. The first version of I-COACH was implemented using a scattering phase mask, which makes its implementation challenging in light-sensitive experiments. The I-COACH technique gradually evolved with the advancement in the engineering of coded phase masks that retain randomness but improve the concentration of light in smaller areas in the image sensor. In this direction, I-COACH was demonstrated using weakly scattered intensity patterns, dot patterns and recently using accelerating Airy patterns, and the case with accelerating Airy patterns exhibited the highest SNR. In this study, we propose and demonstrate I-COACH with an ensemble of self-rotating beams. Unlike accelerating Airy beams, self-rotating beams exhibit a better energy concentration. In the case of self-rotating beams, the uniqueness of the intensity distributions with depth is attributed to the rotation of the intensity pattern as opposed to the shifts of the Airy patterns, making the intensity distribution stable along depths. A significant improvement in SNR was observed in optical experiments.

Enhanced design of multiplexed coded masks for Fresnel incoherent correlation holography.

Fresnel incoherent correlation holography (FINCH) is a well-established incoherent digital holography technique. In FINCH, light from an object point splits into two, differently modulated using two diffractive lenses with different focal distances and interfered to form a self-interference hologram. The hologram numerically back propagates to reconstruct the image of the object at different depths. FINCH, in the inline configuration, requires at least three camera shots with different phase shifts between the two interfering beams followed by superposition to obtain a complex hologram that can be used to reconstruct an object's image without the twin image and bias terms. In general, FINCH is implemented using an active device, such as a spatial light modulator, to display the diffractive lenses. The first version of FINCH used a phase mask generated by random multiplexing of two diffractive lenses, which resulted in high reconstruction noise. Therefore, a polarization multiplexing method was later developed to suppress the reconstruction noise at the expense of some power loss. In this study, a novel computational algorithm based on the Gerchberg-Saxton algorithm (GSA) called transport of amplitude into phase (TAP-GSA) was developed for FINCH to design multiplexed phase masks with high light throughput and low reconstruction noise. The simulation and optical experiments demonstrate a power efficiency improvement of ~ 150 and ~ 200% in the new method in comparison to random multiplexing and polarization multiplexing, respectively. The SNR of the proposed method is better than that of random multiplexing in all tested cases but lower than that of the polarization multiplexing method.

Influence of Annealing on Mechanical Behavior of Alumina-Tantala Nanolaminates.

Mechanical properties of thin films are significant for the applicability of nanodevices. Amorphous Al2O3-Ta2O5 double and triple layers were atomic layer-deposited to the thickness of 70 nm with constituent single-layer thicknesses varying from 40 to 23 nm. The sequence of layers was alternated and rapid thermal annealing (700 and 800 °C) was implemented on all deposited nanolaminates. Annealing caused changes in the microstructure of laminates dependent on their layered structure. Various shapes of crystalline grains of orthorhombic Ta2O5 were formed. Annealing at 800 °C resulted in hardening up to 16 GPa (~11 GPa prior to annealing) in double-layered laminate with top Ta2O5 and bottom Al2O3 layers, while the hardness of all other laminates remained below 15 GPa. The elastic modulus of annealed laminates depended on the sequence of layers and reached up to 169 GPa. The layered structure of the laminate had a significant influence on the mechanical behavior after annealing treatments.

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.

Mechanical and Magnetic Properties of Double Layered Nanostructures of Tin and Zirconium Oxides Grown by Atomic Layer Deposition.

Double layered stacks of ZrO2 and SnO2 films, aiming at the synthesis of thin magnetic and elastic material layers, were grown by atomic layer deposition to thicknesses in the range of 20-25 nm at 300 °C from ZrCl4, SnI4, H2O, and O3 as precursors. The as-deposited nanostructures consisted of a metastable tetragonal polymorph of ZrO2, and a stable tetragonal phase of SnO2, with complementary minor reflections from the orthorhombic polymorph of SnO2. The hardness and elastic modulus of the stacks depended on the order of the constituent oxide films, reaching 15 and 171 GPa, respectively, in the case of top SnO2 layers. Nonlinear saturative magnetization could be induced in the stacks with coercive fields up to 130 Oe.

Atomic layer deposited nanolaminates of zirconium oxide and manganese oxide from manganese(III)acetylacetonate and ozone.

Atomic layer deposition method was used to grow thin films consisting of ZrO2and MnOxlayers. Magnetic and electric properties were studied of films deposited at 300 °C. Some deposition characteristics of the manganese(III)acetylacetonate and ozone process were investigated, such as the dependence of growth rate on the deposition temperature and film crystallinity. All films were partly crystalline in their as-deposited state. Zirconium oxide contained cubic and tetragonal phases of ZrO2, while the manganese oxide was shown to consist of cubic Mn2O3and tetragonal Mn3O4phases. All the films exhibited nonlinear saturative magnetization with hysteresis, as well as resistive switching characteristics.

Silicon oxide-niobium oxide mixture films and nanolaminates grown by atomic layer deposition from niobium pentaethoxide and hexakis(ethylamino) disilane.

Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 °C from Nb(OC2H5)5, Si2(NHC2H5)6, and O3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be observed in the form of characteristic current-voltage behavior. Switching parameters in the conventional regime were well defined only in a SiO2:Nb2O5 mixture at certain, optimized, composition with Nb:Si atomic ratio of 0.13, whereas low-reading voltage measurements allowed recording memory effects in a wider composition range.

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.

Magnetic and Electrical Performance of Atomic Layer Deposited Iron Erbium Oxide Thin Films.

Mixed films of a high-permittivity oxide, Er2O3, and a magnetic material, Fe2O3, were grown by atomic layer deposition on silicon and titanium nitride at 375 °C using erbium diketonate, ferrocene, and ozone as precursors. Crystalline phases of erbium and iron oxides were formed. Growth into three-dimensional trenched structures was demonstrated. A structure deposited using tens to hundreds subsequent cycles for both constituent metal oxide layers promoted both charge polarization and saturative magnetization compared to those in the more homogeneously mixed films.

Inert ambient annealing effect on MANOS capacitor memory characteristics.

In this work we report on the influence of nitrogen ambient thermal effects on the performance of Pt/Al2O3/Si3N4/SiO2/Si memory capacitors. Two post deposition annealing (PDA) furnace steps were employed, at 850 and 1050 °C both for 15 min. The alumina films were deposited by atomic layer deposition using TMA/H2O at 250 °C. The structural characteristics of the stacks were evaluated by transmission electron microscopy and x-ray reflectivity measurements. The memory performance of the stacks was evaluated by write/erase and erase/write measurements, endurance and retention testing. It was found that in as-deposited state the Al2O3 layer is defective resulting in strong leakage currents, controlled by deep defects states. Thus, this behavior inhibits the memory functionality of the stacks. PDA crystallizes and condenses the Al2O3 transforming the layer from amorphous to polycrystalline. During this transformation the Al2O3 electrical quality improves greatly indicating that a significant number of these deep defects have been removed during annealing. Physical reasoning implies that the most plausible origin of these deep defects is hydrogen. However, the polycrystalline Al2O3 films showed inferior retention characteristics which are attributed to grain boundary related shallow defects. The findings of this work could pave the way for more efficient annealing schemes, in which an important factor is the time interval for hydrogen out-diffusion from the Al2O3 layer.

Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes.

The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.

Atomic layer deposition of ruthenium films on strontium titanate.

Atomic layer deposition of ruthenium on SrTiO3 layers was investigated using (C2H5C5H4). (NC4H4)Ru and air as precursors. For comparison, the growth was studied also on ZrO2 films and SiO2/Si surfaces. Deposition temperature was 325 degrees C. Using rather short but intense air pulses, smooth and uniform Ru films were deposited on SrTiO3. The films were crystallized at early stages of the growth. The nucleation density and rate on SrTiO3 were notably lower compared to that on ZrO2 and SiO2, but the physical qualities including the film conductivity were considerably enhanced after reaching Ru film thickness around 10 nm.