Nanocrystalline Films Research Articles

Local structure of hydrated nanocrystalline films of the proton conductor BaZr1-xScxO3-x/2 studied by infrared spectroscopy

We report results from a study of the local structure of hydrated nanocrystalline 2 μm films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.

Effect of a Novel sputtering process on the chemical and biological properties of silver-gold alloys.

Silver-gold nanocrystalline films were sputtered on HDPE substrates by a physical vapour deposition process using alloys with a nominal composition of 65% silver/35% gold or 35% silver/65% gold by weight, with comparison to a 100% silver target. Novel process conditions were introduced to include both water and oxygen as reactive gases. X-ray diffraction and chemical digests were used to assess the structure and chemical composition of the films. Log reductions and corrected zone of inhibition tests were used to measure the biological properties. Despite a range of physical and chemical properties, biological tests showed that the bactericidal properties of all silver-gold films were comparable with silver-only films in the short term and 65% silver films made with Novel sputtering conditions had comparable bacteriostatic abilities to silver-only over a 7-day period. The benefit of including gold may be seen in future studies of anti-inflammatory activity.

Bacterial MgSe complex nanoparticle synthesis and electrical characterization of fabricated Ag/MgSe/p-Si hetero-structure under dark and illumination

The Pseudomonas aeruginosa OG1 strain was used in the bacterial synthesis of MgSe compound nanoparticles. The obtained samples were subsequently shaped into nanocrystalline MgSe films, and their optical, structural, morphological, and electrical properties were assessed on glass and p-Si substrates. Structural and morphological characterizations showed that the fabricated thin film samples have a polycrystalline structure with high quality and uniform grain sizes. The MgSe films produced on glass substrates exhibit a direct spectral band gap of 2.53 eV, according to optical measurements. The Ag/MgSe/p-Si layered diode structure was fabricated using the produced MgSe nanoparticles and then characterized by electrical properties. Electrical measurements were carried out under these two conditions to assess the effects of dark and illumination conditions on the band dynamics of the heterostructure devices. Under illumination, the barrier height decreased while the interface density states distribution increased. These measurements showed that using bacterial-assisted grown MgSe nanocrystalline films, the developed Ag/MgSe/p-Si device structure exhibited a remarkable photoresponse and stable rectifying property. Green synthesis methods for the production of these nanocrystalline materials have the potential to offer low-cost alternatives for photosensitive applications.

Ultra-high growth rate of boron-doped diamond films with optimized growth parameters using in-liquid microwave plasma CVD

In this work, boron doped diamond (BDD) films were deposited onto a silicon substrate using the in-liquid microwave plasma chemical vapor deposition (IL-MPCVD) method. During the synthesis of BDD films, the effect of solvent, pressure, power and distance between the substrate and the microwave antenna on the growth rate of BDD films was studied. Pressure varied from 20 to 80 kPa at the interval of 20 kPa, power from 500 to 600 W at the interval of 50 W and distance from 1 to 1.5 mm. These different conditions resulted in the formation of both nanocrystalline and microcrystalline BDD films. Synthesized BDD films were characterized by Raman spectroscopy, laser microscopy, and optical emission spectroscopy. The highest growth rate of 410 μm/h is obtained as compared to the previous literature. Good synthesis parameters were used to deposit large area BDD films and the surface area expanded from 7 to 35 mm2. Along with this, the electrochemical properties of BDD films were studied in two different electrolytes. Concerning the growth rate, larger redox potential difference, IL-MPCVD is an effective method than the conventional microwave plasma chemical vapor deposition (MPCVD) method for the fabrication of high growth BDD films. Prime novelty statementIn this research, we synthesized BDD films with a B/C ratio of 1000 ppm by adjusting pressure, microwave power, and the substrate-to-electrode distance to determine the optimal synthesis conditions. This enabled us to determine the optimal synthesis conditions while examining variables like boron concentration and growth rate. By employing these optimized synthesis conditions, we successfully expanded the surface area of the BDD film from 7 to 35 mm2, which represents a fivefold increase. Most importantly, this is the first time reported the highest growth rate of 410 μm/h is achieved using this technique with to obtain highly crystalline BDD films. Additionally, we conducted an investigation into the electrochemical properties of BDD films in various electrolytes.

Study on particle size and field effect with sp2/sp3 ratio of hydrogenated diamond-like carbon

Hydrogenated diamond-like carbon (HDLC) films were synthesized through a reactive gas-plasma process employing methane (CH4) and hydrogen (H2) as precursor gases on a silicon (100) wafer substrate, conducted at room temperature. The deposition process utilized a biased enhanced nucleation technique, varying the flow rate ratio of hydrogen and methane. The investigations revealed that increasing the methane flow rate led to a reduction in grain size and an augmented nucleation density of HDLC, as evidenced by contact-mode atomic force microscopy (AFM) images. This study demonstrated the effective control of diamond grain growth by introducing high-methane-concentration pulses during deposition. The field emission characteristics of HDLC samples were analyzed, revealing threshold fields of 12.2 V/μm for nanocrystalline films, 8.5 V/μm for subcrystalline films and 4.1 V/μm for microcrystalline films, corroborated by Raman spectra. Surface energy measurements indicated hydrophobic behavior in the samples. Notably, a decrease in the hydrogen/methane ratio was found to increase the sp2 character, which correlated with the emission field. AFM analysis of HDLC samples yielded surface roughness values ranging from 0.2 nm to approximately 0.01 nm, confirming the continuous, non-porous and smooth nature of the surfaces.

Metal Halide Perovskite Light-Emitting Transistor with Tunable Emission Based on Electrically Doped Semiconductor Nanocrystal-Based Microcavities

Electroluminescence of metal halide perovskites has been widely reported via the fabrication and optimization of light-emitting diodes and light-emitting transistors. Light-emitting transistors are particularly interesting owing to the additional control of the gate voltage on the electroluminescence. In this work, the design of a microcavity, with a defect mode that can be tuned with an applied voltage, integrated with a metal halide light-emitting transistor is shown. The optical properties of the device have been simulated with the transfer matrix method, considering the wavelength-dependent refractive indexes of all the employed materials. The tunability of the microcavity has been obtained via the employment of doped semiconductor nanocrystalline films, which show a tunable plasma frequency and, thus, a tunable refractive index as a function of the applied voltage. Consequently, the tunability of the electroluminescence of the metal halide perovskite light-emitting transistor has been demonstrated.

Investigation of temperature dependant current transport mechanism in Ag/In2O3/p-Si/Al heterojunction

Employing the pulsed laser ablation technique nano-crystalline thin films of Indium oxide (In2O3) are deposited successfully on boron doped silicon substrate. The structural and morphological parameters of the films are investigated by using X-ray diffraction and atomic force microscopic (AFM) spectroscopy, respectively. The deposited films are the crystalline nanostructures with (400) as preferred diffraction peak and grain size of 56.56 nm approximately. The computed roughness (Rq) of In2O3 film is 1.02 nm. The AFM analysis validated the deposition of homogeneous smooth In2O3 films with surface roughness of the order of nanometer. UV–vis spectroscopy was used to study the optical properties of the films. Greater than 80% transparency in visible region was exhibited by the films. The value of the optical band gap was found to be 3.89 eV. The electrical parameters dominating the mechanism of current transport in n-In2O3/p-Si heterojunction were explored by observing the temperature-dependent current–voltage (I–V) properties. In the temperature range of 80–300 K, the ideality factor and barrier height were found to be strongly temperature dependent. It was noticed that with the decrease in temperature there is increase in ideality factor whereas decrease in barrier height which confirm the interfacial imperfections and inhomogeniety in potential barrier height distributions. The temperature dependence of I–V data has revealed the existence of double Gaussian distribution of barrier heights with mean values of 0.85eV and 0.78eV with standard deviation of 0.014 V and 0.012 V respectively. The modified Richardson's plot gives the average barrier height and Richardson's coefficient as 0.86eV and 4.7 × 105 Am−2K−2 in the temperature range 300 K–180 K and 0.77eV and 5.2 × 105 Am−2K−2, respectively in the temperature range 160 K–80 K. The values of Richardson's constants are of the order of known theoretical value of 3.2 × 105 Am−2 K−2.

FeTiB nanocrystalline films: Static and dynamic magnetic properties in accordance with phase composition and magnetic structure

Nanocrystalline Fe100–56.8Ti0–13.5B0–34.2 films 1.4 µm thick are prepared by dc magnetron deposition on glass substrates. The structure and magnetic properties of the films are comprehensively characterized and analyzed. The lattice parameter and the grain size of the bcc Fe-based phase (2-25 nm), parameters of the stochastic magnetic structure (the relative size and the effective anisotropy field of stochastic domains D1/2<Ha> and the local magnetic anisotropy field at the grain scale), saturation magnetization Ms, coercive field Hc, static permeability mst, and ferromagnetic resonance frequency fr of the films are quantitatively estimated and their interrelations are studied. As Ti and B contents increase, the phase composition of the films changes in accordance with the sequence αFe - αFe(Ti) - αFe(Ti) + TiB2 - amorphous, wherein Ms decreases from 2.1 to 0.3 T. The Hc values vary in the interval 7–70 Oe determined by the D1/2 <Ha> field or by other magnetic anisotropy sources. The μst values vary in the interval 20–140. The μst values obtained by the Lorentzian dispersion law adequately fall within the range of the calculated permeabilities, which is limited by the coercive field obtained from the hysteresis loops and the anisotropy field determined by Kittel equation. The μst values of the films are kept up to the frequencies of at least 1.5 GHz. The frequency dependences of the permeability of the films are analyzed taking into account the influence of skin effect and are considered in terms of Acher’s law. The obtained values of the Acher’s constant (less than 0.3) indicate the possibility of reaching the higher values of μst and fr at the expense of elimination of the perpendicular anisotropy, in particular, via the formation of thinner films as compared to the films under study (1.4 µm thick). According to the available literature data, the presented investigations, using the FeTiB films as an example, were performed for the first time.

Investigation of linear and non-linear optical features of crystalline and non-crystalline iron oxide thin films for optoelectronic purposes

Spray pyrolysis at various temperatures was employed to produce non-crystalline and crystalline iron oxide (α-Fe2O3) thin films on glass. The amorphous and crystalline characteristics of α-Fe2O3 thin films were affirmed via X-ray diffraction analysis. With low deposition times (5 min) and at various substrate temperatures, iron oxide seems almost in a non-crystalline structure. As for the increase in deposition time (40 min), the crystallinity’s degree was enhanced. According to Tauc’s law, the direct gap energy Ed for both the amorphous and the crystalline phases, were found to be 1.95 and 2.125 eV, respectively. Moreover, the indirect gap energy, Ein = 1.65 and 1.71 eV were obtained for the amorphous phases and the crystalline phases, respectively. The linear and non-linear optical features of amorphous and crystalline structure were meticulously and adaptably detailed. It is observed that the behavior of the refractive index n (λ) and extinction coefficient k (λ) of the crystalline state was lower than that of the amorphous state. The real and imaginary linear dielectric constant and also the thin film quality factor were estimated for both the amorphous and crystalline states as well as the volume and surface energy loss functions for the crystalline and amorphous states. In conclusion, amorphous and crystalline α-Fe2O3 nanocrystalline films improved their optical properties, making them potential candidates for multifunctional applications such as optoelectronics and spintronics electronics devices.

(Invited) Tuning Photocatalytic Activity with Energetic and Kinetic Asymmetry at Coating-Stabilized Particulate Semiconductors

Semiconductor photocatalysts coevolve reductive and oxidative reactions at nanoscale proximity. The local charge separation and local coevolution have unique advantages: i) photocatalysts can operate in neutral pH water or water vapor instead of strong acid or base; ii) most semiconductors form a self-passivating layer at corroded surfaces to prevent corrosion propagation; and iii) nanoparticulate photoabsorbers or nanocrystalline films have achieved near-unity quantum efficiency, promising scale-up solar-to-chemical conversion. Despite the near-unity quantum efficiency achieved for SrTiO3 particles, the Edisonian approach is applied to the vast majority of photocatalysts, thus limiting progress. Technologically important semiconductors of 1.1 – 2.3 eV bandgaps and properly adjusted band edges, such as GaP and Si, can be ball milled into powder, followed by chemical passivation and protective coating processes. Thus, we introduce the Hu-lab-invented charge-transport coatings to protect semiconductors, such as silicon and gallium indium phosphide. We tune their photocatalytic activity by varying and measuring the energetics and kinetics at local reactive sites, in the following case studies.First, we combine photoelectrochemical cells with local potential-sensing probe microscopy to elucidate photocatalytic processes. In particular, we focus on local energetics and kinetics of multiple concurrent redox processes, i.e., two-redox chemistry. Figure 1A illustrates such a three-terminal photo-electro-catalytic cell setup, where the photoelectrode materials are photocatalysts by themselves. We showcase the efficient charge-separation design by fabricating photocatalysts with particulate semiconductors (e.g., commercial CdS powders, GaInP2 epitaxial layers, and ball-milled GaP nanoparticles), TiO2 coatings, and Rh cocatalysts for the concurring reduction of water and oxidation of reversible redox mediators or sacrificial reagents.We discovered that nanoscale site energetics are mutually dependent on local charge-transfer kinetics.[1] Besides, all known visible-light active photocatalysts of 1.1 – 2.3 eV bandgap photo-oxidize or corrode in water.[2] We discovered multi-functional protective coatings that i) allow for both electrons and holes to transport at tunable energy levels;[3] ii) shift band edges favorably, [4]; iii) reduce charge trapping and recombination,[5] and iv) tune water-oxidation selectivity between O2 and hydrogen peroxide production. [6] We show that in the presence of quinone redox couples in a bicarbonate solution, CO is produced with a 1-atm CO2-free Ar-purged headspace where the only source of CO2 is the (bi)carbonate anions, whilst the quinone redox couples can systematically vary the band edge positions of GaInP photoabsorbers.As shown in Figure 1B, CO evolution rate for both Fe(CN)6 3-/4- and H2BQ/BQ are higher at pH 7 than pH 8.5. The local CO2 concentration at pH 8.5 limited CO production rates. This observation corroborates our hypothesis that photocatalytic redox reactions locally drive pH swing to release CO2 at the oxidative sites, whereas the nearby reductive sites reduce in-situ generated CO2 into CO2R products. We envision direct solar fuel production from natural resources such as sunlight, bicarbonates from the ocean, or moisture in the air in a durable particle reactor.[7] We also processed wood and leaves into pulps and performed photocatalytic H2 production from the CdS/TiO2/Rh/CoOx panel (Figure 1C) using bottom LED illumination, as the glucose solution became colored.In summary, we show the rational design of photocatalysts. These coating-stabilized semiconductor particles present a scalable pathway for making H2 while effectively activating water and biomass as the two most abundant oxidants. We address the timescale mismatch between light absorption and catalysis by effectively accumulating electrons and holes at the respective reductive and oxidative sites.[8] The study paves the way for utilizing biomass to obtain bioenergy with carbon capture and storage.

Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells.

The small nanoparticle size and long-chain ligands in colloidal metal halide perovskite quantum dots (PeQDs) cause charge confinement, which impedes exciton dissociation and carrier extraction in PeQD solar cells, so they have low short-circuit current density Jsc , which impedes further increases in their power conversion efficiency (PCE). Here, a re-assembling process (RP) is developed for perovskite nanocrystalline (PeNC) films made of colloidal perovskite nanocrystals to increase Jsc in PeNC solar cells. The RP of PeNC films increases their crystallite size and eliminates long-chain ligands, and thereby overcomes the charge confinement in PeNC films. These changes facilitate exciton dissociation and increase carrier extraction in PeNC solar cells. By use of this method, the gradient-bandgap PeNC solar cells achieve a Jsc = 19.30mA cm-2 without compromising the photovoltage, and yield a high PCE of 16.46% with negligible hysteresis and good stability. This work provides a new strategy to process PeNC films and pave the way for high performance PeNC optoelectronic devices.

Modeling the Effect of Grain Boundary Segregations on the Fracture Toughness of Nanocrystalline and Ultrafine-Grained Alloys

A theoretical two-dimensional (2D) model is proposed that describes the effect of grain boundary (GB) segregations on the fracture toughness of nanocrystalline or ultrafine-grained alloys. It is shown that GB segregations can lead to crack curvature, providing both crack surface roughness and crack deflection near the crack tip. Within the model, the growth of cracks along GBs under the action of a tensile load is considered. The effects of brittle GB segregations on the crack surface roughness and crack deflection near the crack tip are analyzed, and the associated increase in the fracture toughness of the material is calculated. It is shown that toughening can be achieved if segregations are very brittle and occupy a moderate proportion of GBs. In particular, a sufficiently large (up to 50%) fraction of GBs containing very brittle segregations can increase the fracture toughness by 30–35%. The results of the model can be applied to thin nanocrystalline or ultrafine-grained films.

Effect of calcination temperature on phase composition and optical properties of Al-ZnO nanocrystalline films

Nanocrystalline Al-ZnO films were successfully synthesized by thermal decomposition method. The method includes two stages: synthesis from the melt of organic salts and the films production. The effect of the calcination temperature varying from 600 to 800 °C on the crystallite sizes, phase composition and optical properties of the synthesized films was also investigated. X-ray diffraction (XRD) showed the formation of a hexagonal wurtzite crystal structure with a distorted lattice upon the introduction of Al3+ ions. Based on calculations and scanning electron microscopy (SEM) images, the crystallites size increased from 18 to 28 nm with the calcination temperature increasing. Optical properties of Al-ZnO films were studied by optical transmission spectra. An increase in the calcination temperature leads to a decrease in the ZnO band gap. It was shown that the proposed method makes it possible to obtain optically transparent Al-ZnO films consisting of nanocrystallites. By varying the calcination temperature, the optical properties can be adjusted, which will significantly expand the application range of these materials.

Formation of a nanostructured film at the “hydrocarbon — graphene nanofluid” interface

The interaction mechanisms between graphene nanoparticles (GN) and oil molecules are crucial for successful oil recovery. More than a hundred studies appear in the press each year showing the effectiveness of using nanofluids based on graphene-like nanoparticles to enhance oil recovery in various reservoirs. Increased oil recovery with nanofluid injection is explained by changes in wettability, reduction of interfacial tension and changes in viscosity. Therefore, knowledge of the interaction mechanisms between graphene nanoparticles and hydrocarbons is an urgent task of modern science, both fundamental and applied. A comprehensive study of the interaction of graphene nanoparticles and hydrocarbons was carried out in order to understand the mechanisms that affect the formation of microheterophase state at the interface of hydrocarbons and graphene nanofluids (GNF). Using the methods of X-ray analysis it was found that the structure of the microheterophase state is a nanocrystalline film. The paper presents the results of the film formation at the “hydrocarbon — graphene nanofluid” interface. It was found that both slow and fast growth of nanostructured films could be observed under different modes of heat sinking from the interface. At fast heat sinking a slow growth of the film with the formation of fractal structures of Mandelbrot set type is observed. With slow heat dissipation, rapid film growth is observed with the formation of a continuous homogeneous structure which is not a fractal.

Efficient room temperature carbon dioxide gas sensor based on barium doped CuO thin films

For a safe environment, harmful-gas sensors of low cost and high performance are essential. For CO2 gas sensing applications, Ba-doped CuO thin films with 4 mol% and 6 mol% Ba were produced on glass substrates using the successive ionic layer adsorption and reaction approach. Utilizing various techniques, crystallographic structures, nanomorphologies, and elemental compositions were examined to assess the impact of doping on the characteristics of the films. According to the structural and morphological analyses, the nanocrystalline films consisted of irregularly shaped nanoparticles, which assembled to form a rough surface with unequal grain sizes. Because of its nanoporous nature, the CuO:6% Ba thin film exhibited the most substantial nanomorphological change and the highest gas sensing capability. At varied CO2 gas flow rates, the maximum sensor response (9.4%) and Rair/RCO2 ratio (1.12) at room temperature (RT = 30 °C) were observed at 100 SCCM. By optimizing the sensor’s operating temperature, the sensor response value reached 82.2% at 150 °C, which is approximately eight times the value at RT. Selectivity, reusability, repeatability, detection limit, and quantification limit were all tested. It shows excellent response and recovery times of 5.6 and 5.44 s. In comparison to prior literature, the improved sensor is suited for use in industrial applications.Graphical abstract

Influence of Exposure Cd1-xMgx Fe₂O4 Compound by RF Plasma

Background:&#x0D; The work focuses on enhancing the structural properties, where the Cd1-x Mgx Fe2O4 products prepared by sol-gel solution were characterized. Auto ignition approach using several automated equipment, as FESEM, XRD, for concentrations (x=0.0,0.8 and 1), post-synthesis plasmas were exposed in a low-pressure chamber using the RF Magnetron Sputtering System and the results compared. by X-ray diffraction analysis, confirms the configuration to the FCC cubic structure of the studied samples. Plasma treatment did not affect the crystallization but the crystal size (D) of the particle size decreases after exposure to plasma from (32.33- 27.083)nm . Morphological studies confirmed surface shape changes and particle size reduction upon exposure to plasma.&#x0D; Materials and Methods:&#x0D; The sol-gel method common and old a chemical process for the production of a variety of nanostructures, most notably nanoparticles of metal oxide. In which The molecular feedstock is combined with water or alcohol and then subjected to moderate heating while being agitated. The basic principle pertaining to the sol-gel technology is to manufacture a homogenous solution created from raw materials also then gelatinized . The powders are ground and sintered in a refractory oven at 1100 ° C for 6 hours. The powder was then pressed by a hydraulic press at a pressure of 150 kN into molds to form a disc with a diameter of 20 mm. The work will take place in two phases: before exposing it to the plasma, and then when the samples are placed into the RF Magnetron Sputtering.&#x0D; Results:&#x0D; The X-ray measurements showed that the un-exposure and plasma- exposure samples have a cubic spinel structure, and that the variation of the structural parameters with the exposure is irregular, Consequently enhancing the atoms' ability to diffuse after being put onto the substrate and grain size of the sample. The morphological analysis of the as-prepared ferrite Cd1-xMgxFe2O4 samples was performed using FE-SEM, which gives details on the size and structure of the particles that make up the nanocrystals. The surface exposed to the plasma shows a change in the positions of the crystals and their cohesion with each other , which may result from a decrease in supermagnetic effect and lattice defects in Ferrite nanocrystalline films.&#x0D; Conclusion:&#x0D; The aim of this work is to synthesize Cd1-xMgx Fe₂O4 ferrite nanoparticles in spinel cube structure by sol-gel self-combustion method. Then, the synthesis of thermal plasma using Radio frequency (RF) plasma, where the structural properties, surface shape, and interpretation were studied properties of ferrite nanoparticles produced before and after plasma exposure. According to the conducted XRD investigations the validity of the cubic spinel structure of ferrite and that the irregular difference in the size of the crystals before and after the exposure, the particle size decreases after exposure to plasma from (32.33- 27.083)nm, and the capillary parameter they were reduced from (8.892 to 8.743)nm for plasma-treated samples. the results obtained from shaping cubic spinel phase in both iron nanoparticles before and after plasma exposure supported by the XRD results. The morphological study revealed irregularity grain distribution and dominant agglomeration in ferrite before and after exposure.

Evolution of the Growth of a Micro-Nano Crystalline Diamond Film on an Axial Carbide Tool Model in Microwave Plasma

Conformal multilayer micro-nanocrystalline diamond coatings were grown on substrates of a hard alloy with 9% Co with a high aspect number in microwave plasma from gas mixtures CH4/H2 and CH4/H2/N2. The substrates were of a cylindrical axial tool model with a size ratio: d = 12 mm to l = 75 mm. An original tool holder made of molybdenum, in the form of a sector of the excessive ring with the axis of the hole parallel to the central conductive platform, protects part of the substrate from heating due to the edge effect of plasma. The uniformity of heating of the growth part, which is located inside the excessive ring, is calculated using mathematical modeling and is provided by rotation at a speed of at least 12 rpm, which ensures the uniformity of the coating. The average grain size of the nanocrystalline film measured along the cylinder forming was 41 nm.

Shear-induced directional grain growth in Ag nanocrystalline films under nanoindentation

Nanocrystalline metallic materials exhibit different mechanical properties compared with coarse-grained counterparts. In essence, the high density of grain boundaries contributes to significant portion of plasticity, which is more pronounced in thin films. Due to intrinsic geometric limitation, the responses of nanocrystalline films under shear-dominant loading are seldom understood. Here, we take Ag film as an example, with a larger indentation depth than film thickness, the deformation beneath the pyramidal surfaces of the indenter is considered to be dominated by in-plane shear stress with gradient distribution. The shear-dominant loading leads to directional grain elongation within indentation region, accompanied with frequent formation of nanotwins across the grain boundaries. These findings enrich our understanding of stress induced grain growth under nanoindentation, and provide a novel way to study shear-dominated plastic deformation in metallic nanocrystalline films.

Polarization Switching and Correlated Phase Transitions in Fluorite-Structure ZrO2 Nanocrystals.

Unconventional ferroelectricity in fluorite-structure oxides enables tremendous opportunities in nanoelectronics owing to their superior scalability and silicon compatibility. However, their polarization order and switching process remain elusive due to the challenges of visualizing oxygen ions in nanocrystalline films. In this work, the oxygen shifting during polarization switching and correlated polar-nonpolar phase transitions are directly captured among multiple metastable phases in freestanding ZrO2 thin films by low-dose integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM). Bidirectional transitions between antiferroelectric and ferroelectric orders and interfacial polarization relaxation are clarified at unit-cell scale. Meanwhile, polarization switching is strongly correlated with Zr-O displacement in reversible martensitic transformation between monoclinic and orthorhombic phases and two-step tetrahedral-to-orthorhombic phase transition. These findings provide atomic insights into the transition pathways between metastable polymorphs and unravel the evolution of polarization orders in (anti)ferroelectric fluorite oxides.

Influence of Thermal and Flash-Lamp Annealing on the Thermoelectrical Properties of Cu2ZnSnS4 Nanocrystals Obtained by "Green" Colloidal Synthesis.

The problem with waste heat in solar panels has stimulated research on materials suitable for hybrid solar cells, which combine photovoltaic and thermoelectric properties. One such potential material is Cu2ZnSnS4 (CZTS). Here, we investigated thin films formed from CZTS nanocrystals obtained by "green" colloidal synthesis. The films were subjected to thermal annealing at temperatures up to 350 °C or flash-lamp annealing (FLA) at light-pulse power densities up to 12 J/cm2. The range of 250-300 °C was found to be optimal for obtaining conductive nanocrystalline films, for which the thermoelectric parameters could also be determined reliably. From phonon Raman spectra, we conclude that in this temperature range, a structural transition occurs in CZTS, accompanied by the formation of the minor CuxS phase. The latter is assumed to be a determinant for both the electrical and thermoelectrical properties of CZTS films obtained in this way. For the FLA-treated samples, the film conductivity achieved was too low to measure the thermoelectric parameters reliably, although the partial improvement of the CZTS crystallinity is observed in the Raman spectra. However, the absence of the CuxS phase supports the assumption of its importance with respect to the thermoelectric properties of such CZTS thin films.