Nanoscale Films Research Articles

Superhydrophobic Anticorrosive Phosphonate-Siloxane Films Formed on Zinc with Different Surface Morphology.

The composition, structure, and protective and hydrophobic properties of nanoscale films formed layer-by-layer in solutions of sodium dodecylphosphonate (SDDP) and vinyltrimethoxysilane or n-octyltriethoxysilane (OTES) on the zinc surface with different morphologies were studied by SEM, XPS, water contact angle measurements, and electrochemical and corrosion tests. The protective, hydrophobic properties of phosphonate–siloxane films on zinc and their stability in a corrosive media are determined both by the initial surface morphology and composition of the surface oxide layer, and by the nature of inhibitors. It was shown that preliminary laser texturing of the zinc surface is preferable than chemical etching to enhance the anticorrosive properties of the resulting thin films. The most stable films with excellent superhydrophobic and protective properties in atmospheres of high humidity and salt spray are formed on the zinc surface with fractal morphology during layer-by-layer passivation with SDDP and OTES.

Nonreciprocal propagation of spin waves in a bilayer magnonic waveguide based on yttrium-iron garnet films

Objectives. Nonreciprocal spin wave effects can manifest themselves in metalized films of ferrite garnets. By studying the dynamics of spin waves in micro- and nano-scale magnetic films, the possibility of using multilayer dielectric films of yttrium iron garnet (YIG) to ensure the manifestation of the nonreciprocity effect is demonstrated. This approach offers advantages compared to the use of a layered YIG/metal structure due to significantly lower spin-wave losses in the two-layer YIG film consisting of layers with different values of magnetization. Such films can be used in logical elements to create controllable Mach-Zehnder interferometers based on magnonic principles. The purpose of this work is to reconcile the concept of nonreciprocal spin-wave propagation of a signal with the simultaneous manifestation of the effects arising from the propagation of spin waves in microwave guides formed by finite-width YIG films.Methods. We used an experimental microwave spectroscopy method based on a vector network analyzer along with a finite difference method to perform a numerical simulation of the dispersion characteristics of spin waves in two-layer magnonic microwave guides. An analytical model was also used to obtain a dispersion equation based on the magnetostatic approximation.Results. Based on measurements of the amplitude and phase responses, the possible coexistence of two frequency ranges for the propagation of a spin-wave signal in a two-layer magnon microwave guide based on a YIG film formed by two layers with different values of saturation magnetization was demonstrated. Regimes of nonreciprocal propagation of a spin-wave signal were revealed. A numerical model was using to study the formation mechanisms of spin wave modes in the spectrum of a two-layer structure formed due to the finite dimensions of the microwave guide. An analytical model was used to evaluate the transformation of the mode spectrum. The experimental data are in good agreement with the results of the proposed numerical and analytical models.Conclusions. The possibility of frequency-selective propagation of spin waves in a magnon microwaveguide consisting of two layers with different saturation magnetization values is demonstrated. Multimode propagation of spin waves can occur inside a two-layer structure in two frequency ranges. At the same time, this process is accompanied by a strong nonreciprocity of spin-wave signal propagation, which manifests itself in a change in the amplitude and phase responses when the direction of the external magnetic field is reversed. The proposed two-layer spin-wave waveguide concept can be used in the manufacture of magnon interconnects and magnon interferometers with the support of multiband regimes of operation.

Surface Doping in Poly(3,4-ethylenedioxythiophene)-Based Nanoscale Films: Insights for Polymer Electronics

Conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) are widely researched for application in electronic devices. Researcher’s look to exploit the ability of these polymers to conduct electrical charge. To induce conductivity, the polymers are doped with counterions; for PEDOT, this is typically done with poly(styrenesulfonate) or tosylate (Tos). The Tos anions inserted within the PEDOT nanostructure stabilize positive defects (holes) on the polymer’s conjugated backbone, which, in turn, facilitates electrical conduction. In this study, we use X-ray photoelectron spectroscopy to investigate the Tos doping of PEDOT within the outermost region (<15 nm) of electrochemically oxidized or reduced PEDOT:Tos nanoscale films. Computation of the predicted density of states from density functional theory studies is also conducted to aid in interpreting the ultraviolet photoelectron spectroscopy spectra. We observe that the doping of PEDOT:Tos is more complex than first thought, likely involving the nonionic triblock copolymer used during PEDOT’s oxidative polymerization. This hypothesis is corroborated by time-of-flight secondary-ion mass spectrometry measurements on the outer 2 nm of the oxidized and reduced PEDOT:Tos. The observation of complex and heightened doping near the surface opens opportunities for the deliberate surface engineering of PEDOT:Tos nanofilms in polymer electronic applications such as electrochemical transistors and electrical connections.

Nano-scale Wetting Film Impact on Multiphase Transport Properties in Porous Media

Nano-scale Wetting Film Impact on Multiphase Transport Properties in Porous Media

Nonlinear Optical Absorption in Nanoscale Films Revealed through Ultrafast Acoustics.

Herein we describe a novel spinning pump-probe photoacoustic technique developed to study nonlinear absorption in thin films. As a test case, an organic polycrystalline thin film of quinacridone, a well-known pigment, with a thickness in the tens of nanometers range, is excited by a femtosecond laser pulse which generates a time-domain Brillouin scattering signal. This signal is directly related to the strain wave launched from the film into the substrate and can be used to quantitatively extract the nonlinear optical absorption properties of the film itself. Quinacridone exhibits both quadratic and cubic laser fluence dependence regimes which we show to correspond to two- and three-photon absorption processes. This technique can be broadly applied to materials that are difficult or impossible to characterize with conventional transmittance-based measurements including materials at the nanoscale, prone to laser damage, with very weak nonlinear properties, opaque, or highly scattering.

Deposition of metal nanofilms on cylinder-shaped items

The use of the magnetron sputtering method ensures high adhesion of the applied thin nanoscale films and allows deposition of metal coatings (Cu, Ni, Ti, Ag, Au, etc.) on various substrates. The disadvantage of planar magnetron sputtering devices is the inability to apply coatings to the inner surface of cylindrical parts (for example, silvering of the inner walls of waveguides). The formation of such films is possible with the use of a rod cathode-target and a cylindrical anode-substrate coaxially located with it. In the space between the target cathode and the anode substrate, a low-temperature gas discharge plasma is created by applying a constant electric voltage, and a magnetic induction field perpendicular to the electric field is created by permanent magnets or solenoids located outside the cylindrical anode substrate. The disadvantages of such a device include the inability to control the characteristics of the permanent magnetic induction field in the case of permanent magnets and the inhomogeneous characteristics of the magnetic induction field in the case of solenoids. A significant disadvantage is the need to rebuild the entire system of external magnets in the event of a change in the requirements for the parameters of the magnetic induction field or a change in the configuration of the substrate. Therefore, it is necessary to exclude external sources of the magnetic induction field. In the proposed device, the magnetic induction field is created due to the flow of a constant current of the required value through the cathode. The use of alternating and direct current sources and a system of capacitors and chokes allows creating a controlled magnetic field of the required configuration and implementing a discharge in the crossed fields. This makes it possible to obtain a high-quality coating with heterogeneity of about 3% throughout the product.This paper was recommended for publication by the Organizing Committee&nbsp;of the International Conference Nanophysics and Nanomaterials (24&ndash;25 November&nbsp;2021, Saint Petersburg, Mining University).

Chalcogenide optomemristors for multi-factor neuromorphic computation

Neuromorphic hardware that emulates biological computations is a key driver of progress in AI. For example, memristive technologies, including chalcogenide-based in-memory computing concepts, have been employed to dramatically accelerate and increase the efficiency of basic neural operations. However, powerful mechanisms such as reinforcement learning and dendritic computation require more advanced device operations involving multiple interacting signals. Here we show that nano-scaled films of chalcogenide semiconductors can perform such multi-factor in-memory computation where their tunable electronic and optical properties are jointly exploited. We demonstrate that ultrathin photoactive cavities of Ge-doped Selenide can emulate synapses with three-factor neo-Hebbian plasticity and dendrites with shunting inhibition. We apply these properties to solve a maze game through on-device reinforcement learning, as well as to provide a single-neuron solution to linearly inseparable XOR implementation.

Investigation of Interfacial Microstructures of TiN/AlN Multilayers by Neutron Reflectometry

Three alternate TiN/AlN nanostructured multilayers with the TiN layer thicknesses of 60, 70, and 120 Å and the AlN layer thickness of 10 Å were fabricated using dc reactive magnetron sputtering. Microstructural characterizations of the three nano-scale films were performed using nonpolarized specular neutron reflectometry. The results showed that the three TiN/AlN multilayer thin films were typical superlattice films and the thicknesses of the TiN layer and AlN layer in the multilayers were consistent with the design thickness nearly. The interface roughness was asymmetric in all the samples. The interface of AlN growing on TiN was much sharper than that of TiN growing on AlN and the latter was the diffusion interface in the TiN/AlN multilayer films.

Analytical theory of enhanced Bose–Einstein condensation in thin films

We present an analytically solvable theory of Bose–Einstein condensation (BEC) in thin film geometries. Analytical closed-form expressions for the critical temperature are obtained in both the low-to-moderate confinement regime (where the film thickness L is in the order of microns) as well as in the strong confinement regime where the thickness is in the order of few nanometers or lower. The possibility of high-temperature BEC is predicted in the strong confinement limit, with a square-root divergence of the critical temperature T c ∼ L −1/2. For cold Bose gases, this implies an enhancement up to two orders of magnitude in T c for films on the nanometer scale. Analytical predictions are also obtained for the heat capacity and the condensate fraction. A new law for the heat capacity of the condensate, i.e. C ∼ T 2, is predicted for nano-scale films, which implies a different λ-point behavior with respect to bulk systems, while the condensate fraction is predicted to follow a law.

Novel Method of Measuring the Thickness of Nanoscale Films Using Energy Dispersive X‐Ray Spectroscopy Line Scan Profiles

AbstractThe cross‐sectional transmission electron microscopy (TEM) imaging method is widely used to determine the nanoscale thickness of thin films. However, thin films to be analyzed within TEM samples often have a curved or distorted shape, or poor alignment with the electron beam direction, which can easily overestimate the thickness due to TEM projection artifacts. This study develops a novel method to measure the thickness of thin films using a TEM energy‐dispersive X‐ray spectroscopy (EDS) line scan. This method is based on the constant integration of the quantitative line scan profile regardless of geometric configuration, making it possible to overcome the projection problem. The proposed method is experimentally validated with a Si/Ti/Si stacked sample. The EDS line scan is performed at various tilt angles at the same location, and it is confirmed that the integration of each quantification profile has the same value, thus providing a consistent thickness value. This method is effective in measuring the thickness of the thin film more accurately and reliably regardless of the inclination angle of the thin film.

Nanoscale-Resistive Switching in Forming-Free Zinc Oxide Memristive Structures.

This article presents the results of experimental studies of the impact of electrode material and the effect of nanoscale film thickness on the resistive switching in forming-free nanocrystalline ZnO films grown by pulsed laser deposition. It was demonstrated that the nanocrystalline ZnO film with TiN, Pt, ZnO:In, and ZnO:Pd bottom electrodes exhibits a nonlinear bipolar effect of forming-free resistive switching. The sample with Pt showed the highest resistance values RHRS and RLRS and the highest value of Uset = 2.7 ± 0.4 V. The samples with the ZnO:In and ZnO:Pd bottom electrode showed the lowest Uset and Ures values. An increase in the number of laser pulses from 1000 to 5000 was shown to lead to an increase in the thickness of the nanocrystalline ZnO film from 7.2 ± 2.5 nm to 53.6 ± 18.3 nm. The dependence of electrophysical parameters (electron concentration, electron mobility, and resistivity) on the thickness of the forming-free nanocrystalline ZnO film for the TiN/ZnO/W structure was investigated. The endurance test and homogeneity test for TiN/ZnO/W structures were performed. The structure Al2O3/TiN/ZnO/W with a nanocrystalline ZnO thickness 41.2 ± 9.7 nm was shown to be preferable for the manufacture of ReRAM and memristive neuromorphic systems due to the highest value of RHRS/RLRS = 2307.8 ± 166.4 and low values of Uset = 1.9 ± 0.2 V and Ures = −1.3 ± 0.5 V. It was demonstrated that the use of the TiN top electrode in the Al2O3/TiN/ZnO memristor structure allowed for the reduction in Uset and Ures and the increase in the RHRS/RLRS ratio. The results obtained can be used in the manufacturing of resistive-switching nanoscale devices for neuromorphic computing based on the forming-free nanocrystalline ZnO oxide films.

Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.

超音波援用ドップラーOCT（UA-OCDV）を用いた組織透水性のマイクロ断層評価

In recent years, the regenerative medicine has been being developed due to the improvement of tissue engineering, e.g. autologous regenerative tissue by three-dimensional culture. In this study, Ultrasound-assisted Doppler Velocigraphy (UA-OCDV) is constructed to measure the tissue displacement and the inerstitial fluid flow, tomographically, non-contactly and non-invasively at the micrometer resolution. This is based on Doppler OCT, which can visualize Doppler velocity inside tissue by applying phase analysis to low coherence interference signals. Furthermore, a High Intensity Focused Ultrasound (HIFU) transducer is introduced into Doppler OCT as a non-contact loading device of periodical acoustic radiation pressure. UA-OCDV was experimentally applied to flow field around scaffold. As a result, UA-OCDV was able to provide the tomographic visualization of periodical flow velocity field. Flow velocity through fibers of hydrophilic scaffold was observed to increase 140% compared to that of hydrophobic one. The nano-scale water film generated around hydrophilic surface is considered to reduce the flow resistance. In conclusion, it was therefore suggested that UA-OCDV had a potential of diagnosing tissue permeability non-contactly and non-inasively.

Template-free synthesis of a wafer-sized polyaniline nanoscale film with high electrical conductivity for trace ammonia gas sensing

We synthesized a large area ordered and conductive PANI film at the air–water interface. It can be used to prepare a flexible sensor for trace NH3 detection and discoloration test paper for NH3 detection to monitor the freshness of shrimp.

Strain Properties of Multicomponent Nanosize Film Materials

The results of the correlation between the longitudinal strain coefficient (SC) and the values of the Poisson coefficient and Grüneisen parameter for nanosize film multicomponent alloys (d ≅ 30–50 nm, ci ≅ 11–20 at%) are presented. It is established that in the region of elastic or quasi‐elastic deformation (less than or equal to 0.4%), the value of SC is insensitive to changes in the Grüneisen parameter in the range of 1.5–2.5 units during the transition to plastic formation (more than 0.4%). The value of SC decreases from 4–5 units to 3–1 units. Similarly, SC is insensitive to changes in the Poisson coefficient less than or equal 0.4 but decreases sharply in the region of plastic deformation. It is concluded that a sensitive element based on a multicomponent nanoscale film of a solid solution, including a high‐entropy one, has advantages over others due to phase stability in a wide temperature range. These materials may be used to develop the architecture of sensitive elements of sensors for various functional purposes.

Structural and Thermal Properties of Electrospun Whey Protein/PEO Nanofibers

Nano-scale fibers or films obtained by adding natural active agents to natural food proteins are promising materials for packaging purposes. Whey proteins (WPs) are one of the most popular matrices in application with their cheap and sustainable availability. They have many functional properties and their antimicrobial, antiviral and anticarcinogenic properties are highlighted as well. Enzymatic hydrolysis can increase their functionality such as inducing gelation and revealing bioactive peptides. These features can make whey proteins good candidates for the fabrication of talented fiber structures through electrospinning. Electrospinning technique based on the deposition of fine fibers on a collector surface under electrical forces can be used to form protein nanofibers. The purpose of this research is to produce whey-based protein nanofibers and determine their structural and thermal features by infra-red spectroscopy and thermogravimetric analysis. A high molecular polymer, polyethylene oxide (PEO) was used in combination with whey protein concentrate (WPC) to increase spinnability. Besides, enzymatic hydrolysis of WPC enhanced the viscosity of the protein/polymer solution and helped electrospinning ability. Both non-hydrolyzed and hydrolyzed WPC/PEO nanofibers exhibited promising morphological, structural and thermal properties for targeted use in food and biomedical applications. Further research will focus on the application of these protein nanofibers for food packaging purposes.

Plasmon resonance measurements in pool boiling, condensation and evaporation experiments on a nanostructured surface

Surface plasmon resonance (SPR) is used in a wide range of applications, including biology, physics and materials science, because of its ability to obtain sub-wavelength measurements from a simple white light source, in real time and non-invasively. Surprisingly, this technique is just beginning to be used in the field of phase change heat transfer, whereas fundamental phenomena occurring near interfaces, such as ice, liquid or vapour nucleation, require the development of innovative techniques capable of reaching this little-explored scale. In this paper, the grating-coupled SPR method is implemented on aluminium samples on which different liquid-vapour phase change phenomena take place. The first goal of this work was the study of the influence of the surface topography on the boiling phenomenon, in particular in the presence of geometrical patterns of micrometric and sub-micrometric scales, typical of those necessary for the implementation of the grating-coupled SPR method. The results show that mirror-polished surfaces covered with periodically structured sub-micrometric grooves have the best thermal characteristics amongst the different surfaces tested, similar to those of a mirror-polished surface with a small number of holes evenly distributed over the surface. Sub-micrometre scale corrugated surfaces being also ideally suited for SPR, they were also used in the second part of the paper to evaluate the potential of this method for the study of boiling, condensation and evaporation. Although our optical SPR test bench, limited by its acquisition frequency, was not able to detect the very fast birth of the first vapour nuclei at the beginning of nucleate boiling, the results yet show the interest of the method as a non-intrusive technique to measure the temperature of the liquid in the very vicinity of the wall, which is also an essential measurement. In addition, measurements from the condensation and evaporation experiments show that SPR provides a useful means to monitor the formation of a nanoscale condensation film and the evaporation of an acetone film in real time. This exploratory study opens perspectives to understand the small-scale phenomena that occur during phase changes and thus help develop functional surfaces that promote or delay their occurrence.

Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale

The intrinsic magnetic topological insulator MnBi2Te4 has attracted much attention due to its special magnetic and topological properties. To date, most reports have focused on bulk or flake samples. For material integration and device applications, the epitaxial growth of MnBi2Te4 film in nanoscale is more important but challenging. Here, we report the growth of self-regulated MnBi2Te4 films by the molecular beam epitaxy. By tuning the substrate temperature to the optimal temperature for the growth surface, the stoichiometry of MnBi2Te4 becomes sensitive to the Mn/Bi flux ratio. Excessive and deficient Mn resulted in the formation of a MnTe and Bi2Te3 phase, respectively. The magnetic measurement of the 7 SL MnBi2Te4 film probed by the superconducting quantum interference device (SQUID) shows that the antiferromagnetic order occurring at the Néel temperature 22 K is accompanied by an anomalous magnetic hysteresis loop along the c-axis. The band structure measured by angle-resolved photoemission spectroscopy (ARPES) at 80 K reveals a Dirac-like surface state, which indicates that MnBi2Te4 has topological insulator properties in the paramagnetic phase. Our work demonstrates the key growth parameters for the design and optimization of the synthesis of nanoscale MnBi2Te4 films, which are of great significance for fundamental research and device applications involving antiferromagnetic topological insulators.

Molecular study on anisotropic thermal conductivity of nanoscale liquid argon films with different configurations

The thermodynamic and transport properties of thin films may be substantially divergent from their bulk materials. This is especially distinguished for nanoscale liquid films, as demonstrated by prior work about the specific heat capacity of nanoscale water films. Furthermore, the forms of thin liquid films, either freestanding, sessile or confined, also exhibit apparent impact on the properties. In this investigation, the influence of size and solid/liquid interface on the thermal conductivities of nanoscale liquid argon films with these different forms is studied by employing the molecular dynamics method. The results show that the anisotropy of the thermal conductivity is closely related to the configuration, but weakened while the film thickness increases. The relationships between the anisotropic thermal conductivities and the thin film size are revealed by considering the contribution of a solid/liquid interface to the thermal conductivity. The reason is analyzed in the aspect of size and interface by comparison of the densities, potential energy distributions, and vibrational densities of state of argon atoms, which show asymmetry in the directions parallel and perpendicular to the sessile film. Thus, insight is provided into the interface effect on the anisotropic thermal conductivity of nanoscale liquid argon films with different forms which can be found in many applications including interface separation, evaporation, and distillation.

N-Type Digital Memory Characteristics of Diketopyrrolopyrrole-Based Narrow Bandgap Polymers

New π-conjugated polymers based on dithienyl-diketopyrrolopyrrole (dtDPP) were synthesized by direct arylation polymerization, that is, poly(dtDPP), poly(dtDPP-FL), and poly(dtDPP-TPA). They revealed extremely low bandgaps, which could be achieved by controlling the donor–acceptor powers among the backbone building blocks. They were all thermally stable up to 250 °C and, furthermore, solution-processible in conventional ways, producing good-quality thin films. Poly(dtDPP) favorably self-assembled, forming an edge-on layer structure in nanoscale films, whereas the others were preferentially oriented within the film plane without any regular packing structures. All the dt-DPP-based polymers as active layers in devices demonstrated high-performance n-type digital memories (low switching voltage, high ON/OFF current ratio, and high stability) because of the narrow bandgaps. Moreover, the memory modes (nonvolatile and volatile) could be tuned by adjusting the donor–acceptor powers in the backbone. Overall, the dtDPP-based polymers are suitable for the low-cost mass production of n-type nonvolatile and volatile high performing memory devices. In addition, this study provides a guideline on how to achieve high-performance n-type digital memories by balancing the donor and acceptor powers among the chemical building blocks.