Nano Grains Research Articles

Comprehensive investigation on ruthenium doped Sn2S3 thin films for photo sensing applications

This study investigates the deposition of tin trisulfide (Sn2S3) films onto glass substrates through the nebulizer spray technique, employing aqueous solutions of SnCl2 and SC (NH2)2 at a molar ratio of Sn to S of 1:2 under various doping concentrations of ruthenium (1, 2, 3, 4, and 5 wt %). The crystallography, morphology, chemical, optical and photo sensing characteristics of deposited thin films has been comprehensively analysed using an X-ray diffractometer, Field emission scanning electron microscope annexed with energy dispersive X-ray analyser, UV-VIS spectrometer, Photoluminescence spectroscopy and a digital Keithley source meter. The X-ray diffraction investigation clearly establishes the polycrystalline nature of the films possessing orthorhombic crystal structure. The surface morphology was visualized via Field Emission Scanning Electron Microscope which confirmed the existence of spherical nano grains at 3 % Ru doping concentration. The energy dispersive X-ray analyser spectrum was used to probe the elements present in the prepared thin film and it supports the presence of Sn, S and Ru. The optical absorption and transmittance spectra were observed in the wavelength range between 450 and 900 nm for all the samples. Enhanced absorption in the visible region is observed from the absorption spectra. Direct allowed band gap values ranging around 2.05 eV–1.92 eV is observed for these Ru doped spray pyrolyzed Sn2S3 thin films. The I–V characteristics of the samples, studied under both light and dark conditions, demonstrate an increase in current values with higher concentrations of Ru doping. The highest value of the photo current (36 μA) was observed for 3 wt % ruthenium doped film. Highest responsivity of 67.6 × 10−2 A/W was observed for 3 % Ru doped Sn2S3 film. The same sample showed a highest detectivity and external quantum efficiency values of 8.70 × 109 Jones and 157 % respectively. The quick response of the detector can be affirmed from the short rise and fall time of 1.22 s and 1.21 s, respectively. Therefore, the Sn2S3 material doped with 3 % ruthenium, produced via the current economical method, emerges as a promising candidate for application in photo-detectors.

Formation mechanism and mechanical behavior of gradient nanograin structure in directional solidified Ti3Al alloy: Atomic-scale study

The formation mechanism of Ti3Al alloy during a directional solidification process was systemically investigated by means of molecular dynamics (MD) simulations, and its mechanical behavior was explored by comparing with its nanograined (NG), coarse-grained (CG) and gradient nanograined (GNG) counterparts. It is found that the solidified front forms equiaxed crystals first, then they transform into columnar crystals, and the GNG structure is formed finally. Noticeably, the grains will grow preferentially in the direction parallel to the solidification direction. Besides, it is also found that the directional solidified alloy with the GNG structure has higher tensile strength and better ductility than its NG and CG counterparts. The GNG structure not only suppresses strain localization and grain growth in its small grain regions, but also promotes more cross dislocations in the large grain regions, resulting in a better mechanical performance.

Unveiling the correlation between anomalous hardening and grain boundary diffusional transformation in ω single-phase nano-grained Ti-Fe alloy

A metastable ω single-phase nanograined (NG) Ti-Fe alloy was synthesized using laser inert-gas condensation (IGC). Upon being annealed at 360 °C, the NG Ti-Fe alloy exhibited a remarkable ultra-hardening, increasing the hardness from 4.7 to 8.6 GPa. Subsequent findings revealed an unexpected hardness enhancement, rising from 6.6 GPa at 420 °C to 7.6 GPa at 460 °C, despite the occurrence of grain growth. In-depth investigations into the strengthening mechanisms of the NG Ti-Fe alloy were conducted using in-situ synchrotron high-energy X-ray diffraction (XRD) and transmission electron microscopy (TEM). The comprehensive analysis unveiled that the diffusion-controlled structure evolution during annealing played a pivotal role in enhancing the alloy’s mechanical properties. This study not only presents the synthesis of a novel metastable alloy but also provides valuable insights into the intricate relationship between diffusion-controlled structure evolution and the resulting superior mechanical properties.

Numerical investigation of internal damage in heterogeneous-structured laminates using a 3D multiple physical mechanisms based constitutive model

Heterogeneous-structured laminates (HSLs), which consist of multiple layers of metallic materials arranged in successive pairs of coarse-grained (CG) and nano-grained (NG) layers, have been recently reported to display excellent balance of strength and ductility. However, it is argued that accompanying state-of-art numerical models developed to simulate the deformation of this specific class of composite materials have limitations for investigating their underlying damage evolution. Addressing this issue is essential to support the rational design, optimisation and application of HSLs, especially when subjected to contact and dynamic processes. For this reason, a novel 3D numerical framework for HSLs is proposed and tested in this research considering published experimental findings and dislocation theories. This framework comprehensively considers the evolution of various types of dislocations and back stress while being coupled with the Johnson Cook damage criterion. The HSL specimens simulated here were made of alternating layers of CG and NG copper separated by interface affected zones. Following initial microhardness and uniaxial tensile simulations on homogenous copper with different grain sizes, simulations of HSLs were conducted to study the effect of different layer thickness and the volume fraction of the NG layer. Overall, a good correlation between numerical and experimental results was achieved. An important and distinguishing characteristic of this research is that the proposed model enables the evolution of internal damage and the synergetic effect between the CG and NG layers to be investigated. Through the evaluation of the damage accumulation factor in the NG layer, the simulations results yielded quantitative information which aligned with the following known experimental observations: 1) the smaller the layer thickness, then the smaller the internal damage and 2) the internal damage increases with the increase in volume content of the NG layer. In addition, for a set simulated strain of 10%, the developed model could be used to show that the damage accumulation factor in the NG layer was 10 times lower than that in its counterpart, i.e., a stand-alone NG layer not sandwiched between two CG layers.

The investigation of synthesis and textured properties of in situ formed hBN with spark plasma sintering

Hexagonal boron nitride (hBN) exhibits high thermal conductivity within the in-plane direction and significantly lower thermal conductivity in the cross-plane direction because of its anisotropic nature. When the texture properties of bulk hBN are strong, it is a potentially promising application area for the insulating heat spreaders and heat sinks. In this study, hBN was synthesized in situ with the spark plasma sintering (SPS) technique and the effects of sintering temperature on the orientation of hBN grains were investigated. The precursor was prepared by chemically reacting urea and boric acid in heat treatment at 850 °C. The hBN was produced using the previous precursor in a SPS at 1500, 1700, and 1900 °C. The samples were characterized using XRD, FTIR, SEM and Raman spectroscopy. The properties of the samples were further determined through measurements of density, DSC and thermal diffusivity. The hBN samples obtained through the SPS process have nano and micron-size grains. The hBN was highly crystalline and homogeneous, as determined by the XRD pattern, Raman spectra and Raman maps. The orientation of hBN grains has been revealed in the c-axis of hBN crystallites and was preferably arranged within a plane parallel to the SPS pressing direction. The hBN orientation preference index (IOP) value of −19925.5 at 1700 °C indicates the highest quality texture orientation. Increasing the temperature to 1900 °C decreased the orientation in the direction parallel to the pressing direction. The highest thermal conductivity calculated according to the thermal diffusivity perpendicular to the sintering pressure direction was 8.86 W m−1K−1 at 1900 °C.

Influence of multilayer nanoarchitecture on phase transformations in the Ti-Cr-Zr system

Nanocrystalline thin films find extensive applications due to their high mechanical strength and wear resistance. However, the challenge is to prevent unwanted grain growth during operation, especially at high temperatures, due to the increased grain boundary volume, which elevates the system's overall energy. Addressing this issue necessitates identifying optimal heat treatment conditions and selecting appropriate chemistry to stabilize grain boundaries. This study investigates the grain growth and phase evolution within Ti-Cr-Zr magnetron sputtered nano multilayers with 5 and 10 nm individual layer thickness, subjected to vacuum heat treatment at 1100 °C for 5 and 10 min. Characterization involved X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). During deposition, evidence of diffusion was observed as the multilayers formed Cr4TiZr, TiCr2, and Cr2Zr, phases. The Ti-Cr-Zr nanoscale system multilayers with 10 nm individual layer thickness also exhibited the emergence of Ti0.3Zr0.7 phase. During heat treatment grain growth occurred, after 10 min an average grain size of 173.7 nm and 119.1 nm was noted for the Ti-Cr-Zr nanoscale system multilayer with 5 nm and 10 nm individual layer thickness, respectively. The different growth rates are attributed to their distinct interfacial volumes, influencing the reaction velocity due to the variations in nano-layer thickness. No new phases were formed after heat treatment for the case of 10 nm individual layer thickness coating. However, 5 nm individual layer coatings showed the emergence of Ti0.3Zr0.7 phase, not present after deposition. In conclusion, this research achieved the desired nano grain stabilization of the Ti-Cr-Zr system nanoscale multilayers after heat treatment at 1100 °C for 10 min. This process led to the complete decomposition of the multilayer structure, resulting in the formation of grains smaller than 200 nm, marking a significant step toward the effective control of grain growth in nanocrystalline materials.

Molecular dynamics simulation of crack propagation in very small grain size nanocopper with different grain size gradients.

In this paper, we use molecular dynamics to simulate the crack propagation behavior of gradient nano-grained (GNG) copper models with different grain size gradients, compare the crack propagation rates of different models, and analyze the microstructural changes and the mechanism of crack propagation. The simulation results show that the increase of the grain size gradient of the GNG copper model can improve the fracture resistance of the material, and the crack propagation mode undergoes a transition from brittle propagation along the grain boundaries to the formation of pores at the grain boundaries, and then to ductile fracture along the inclined plastic shear zone. The number of dislocations increases with the grain size gradient, while the crack passivation is more serious, indicating that a larger grain size gradient is more effective in inhibiting crack propagation. The introduction of gradient grain size promotes crack propagation and weakens the plasticity of the material relative to the nano-grained (NG) copper model.

Ru-doped nano grain hydrophilic copper hydroxide electrodes for supercapacitor application

Ru-doped nano grain hydrophilic copper hydroxide electrodes for supercapacitor application

The significant role of bimodal lamellar heterostructure for Lüders deformation and TRIP effect in 18Cr–8Ni austenitic stainless steel

A series of 18Cr–8Ni ASSs with homogeneous or heterogeneous structures were prepared to reveal the unique deformation mechanism of hetero-deformation-induced (HDI) hardening in lamellar heterostructure. By adjusting the annealing temperature, the nano-grained (NG) and coarse-grained (CG) unimodal homogeneous structures were obtained by annealing at 600 °C and 1000 °C, respectively, while the nano-grained/ultrafine-grained (NG/UFG) and ultrafine-grained/fine-grained (UFG/FG) bimodal heterogeneous structures were achieved by annealing at 700 °C and 800 °C. Compared to the conventional bimodal homogeneous structure (UFG/FG), the hetero-zone boundaries (HBs) of bimodal lamellar heterostructure (NG/UFG) can not only provide extra HDI hardening effect, but also coordinate the inhomogeneous deformation for Lüders deformation. The HDI hardening and Lüders deformation greatly facilitate the transformation induced plasticity (TRIP) effect to achieve. This is due to the lower austenite stability in soft region (coarser grain), leading to the formation of deformation-induced martensite (DIM) under lower stress, on the other hand, the Lüders deformation achieved a dynamic balance between both sides of hetero-boundary, avoiding the stress concentration and promoting the TRIP effect. Consequently, the DIM content of the NG/UFG specimen is considerably higher than that of the UFG/FG specimen (78 vol% to 27 vol%).

Origin mechanism of heterostructure nanograins with gradient grain size suppressing strain localization

Strain localization is a common deformation induced instability in many nanograined metals. Gradient nanograined metals are known to suppress the strain localization by inner coarse grains (CGs) coordinating plastic deformation. However, in this study, we found that using micropillar compression, heterostructure nanograins (NGs) with gradient grain size could suppress the strain localization and thus provide extra strain hardening without the CGs coordinating the plastic deformation. The gradient distribution of the grain size in Ti–6Al–4V alloy with heterostructure NGs plays a significant role in suppressing the strain localization. First, the gradient grain size distribution in NGs causes shear band delocalization by activating the stress-driven grain boundary migration and dislocation slip, which largely suppresses shear band localization at the low strain level. Second, when the gradient grain size distribution disappears, gradient nanograins (GNGs) change to homogeneous ultrafine grains (UFGs) stored with a large number of dislocations at the high strain level. This can refine the UFGs to NGs by dislocation-induced dynamic recrystallization and coordinate the plastic deformation in the shear bands, thereby suppressing the shear band localization at the high strain level. Hence, heterostructure NGs with gradient grain size contribute to the extra strain hardening by suppressing the strain localization. This study not only provides new insights into how GNGs suppress the strain localization, but also offers a new strategy for designing heterostructure NGs using grain boundary engineering (gradient distribution of the grain size) to improve the ductility of nanograined metals.

Optimisation of deposition voltage of zirconium-doped chromium telluride via typical three-electrode cell electrochemical deposition technique

ABSTRACT The electrochemical deposition approach has been used to successfully produce CrTe and Zr/CrTe materials. The surface morphology of the films has shown a stone-like micro-grain. When the deposition voltage rises to 14 V, the stone-like nano grain transforms into a white well-pack precipitate and spreads. The surface of the doped CrTe material displayed uniform nano-grain deposition. The films are polycrystalline with hexagonal phases. The film had two strong peaks: one at orientation (112), which corresponds to a 2theta value of 32.72°, and others at orientations (111), (112), (121), and (200), which correspond to 2theta values of 21.57°, 32.72°, 46.65°, and 60.58°. The crystal lattice is indicated by a peak intensity reduction that occurs at higher 2theta degree values; an unindexed peak results from the substrate utilised for the deposition. The energy bandgap of the synthesised Zr/CrTe created at different deposition voltages ranges from 1.15 to 1.43 eV, while its energy band gap of the pristine CrTe is 1.62 eV, demonstrating that the energy bandgap decreases as the voltage rises.

Study of ageing and size effects in Nickel–Titanium shape memory alloy using molecular dynamics simulations

ABSTRACT The effect of ageing process at 1073.15 K on the athermal phase transformation in different nanograins (4.5, 6 and 9 nm) of Nickel–Titanium shape memory alloy is studied using molecular dynamics simulations. The martensitic transformation start temperature and transformed martensite volume decrease with decreasing grain size. The two-stage phase transformation with intermediate phase formation is observed only in the smallest grain (4.5 nm) where a single martensite variant is formed. On the contrary, larger grains show a self-accommodated twinned martensite variants with one-stage transformation from austenite to martensite. The ageing process hardly influences the morphology of the martensite phase, however, it rises the martensite start temperature and reduces the austenite start temperature. The nano grain size models demonstrate the constrained transformation due to the transformation barrier and the accumulation of internal stress, while the ageing process shows the tendency for stress relaxation.

Interface formation and defect elimination mechanism of T2/304L interface during electromagnetic pulse welding process

Experimental and numerical methods are carried out to analyze the interface formation and defect elimination mechanism during electromagnetic pulse welding T2 to 304L tube by changing the inner tube morphology from original scheme to stage scheme, ramp stage, and location stage. When the original scheme is operated with 13mm lap length, the morphology of interface is divided into four zones containing end unwelded zone, first welded zone, central unwelded zone, and second welded zone due to the different impact velocity and angle during the initial impact process, parallel impact process, and final impact process. The parallel impact leads to the formation of the central unwelded zone, containing (Cu, Fe) solid solution, oxides, nano grains, and amorphous phase. By providing a suitable impact angle, the ramp scheme (α = 7°) and location scheme (L = 6.5 mm) can eliminate the defect in the central unwelded zone.

Effect of dopant on the energy bandgap on strontium sulphide doped silver for optoelectronic application

ABSTRACT In this study, strontium chloride hexahydrate (SrCl2.6 H2O), silver nitrate (AgNO3), and thioacetamide (C2H5NS) were employed as cationic and anionic precursors in the electrochemical deposition technique for the synthesis and characterisation of strontium sulphide doped silver (SrS/Ag) thin films. The spectrum reveals the polycrystalline nature of the materials. The film displayed a significant peak at orientation (111), which corresponds to 2theta values of 26.69° for undoped SrS, and a flawless crystalline peak with a cubic phase indexed at orientations (111), (112), (200), and (211). SrS/Ag of 0.01, 0.02, and 0.03 mol correspond to 2theta values of (26.45, 33.79, 37.60, and 51.77) o respectively. Clove-like material with precipitate is visible in the SrS material’s micrograph; the big nano grain on the surface of the substrate exhibits photon absorption but lacks any signs of pinholes. The materials show an increase in thickness from 126.01 to 122.02 nm and an increase in film resistivity from 1.58 × 109 to 1.69 × 109 cm, which further led to a decrease in conductivity from 6.32 × 108 to 5.91 × 108 S/m. The bandgap energy of 1.35 to 2.00 eV was obtained.

The influence of precursor temperature on strontium sulphide doped silver for optoelectronic application

This research aims at the study of strontium sulphide doped silver using 0.1 mol of strontium chloride hexahydrate (SrCl2.6H2O), Thioacetamide (C2H5NS), and 0.01 mol of silver nitrate (AgNO3) as the cationic, anionic, and dopant concentrations via electrochemical deposition technique. The film had a strong peak at (111) and (211) which corresponds to 2theta values of 26.69° and 51.77° for undoped SrS and doped SrS respectively, and a flawless crystalline peak with a cubic phase that is indexed at orientations (111), (112), (200), and (211). SrS/Ag of deposited different precursor temperatures (room, 35, 40, and 45)o correspond to 2theta values of 26.69°, 33.79°, 37.60°, and 51.77° respectively. The crystal lattice is shown by the rise in peak intensity with higher 2theta degree values; the appearance of an unindexed peak is caused by the substrate utilized for the deposition. Clove-like material with precipitate is visible in the SrS material's micrograph; the big nano grain on the surface of the substrate exhibits photon absorption but lacks any signs of pinholes. At the introduction of dopant and heating the precursor at 35 °C, 40 °C, and 45 °C there is a drastic change in the micrograph of the films, for the films at 35 °C the nanoparticle clave together with a melted wax with a sharp large white precipitate which is very visible on the surface of the film and the material deposited at 40 °C and 45 °C there is no visible precipitate on the film which show that as the precursor temperature increases it eliminate lattice strain and improve the photovoltaic properties of the deposited material. The energy band gap of strontium sulphide (SrS) and strontium sulphide doped silver (SrS/Ag) at different precursor temperatures of 35 °C, 40 °C, 45 °C is 1.50–2.35 eV.

Grain size and piezoelectric effect on magnetoelectric coupling in BFO/PZT perovskite-perovskite composites

Magnetoelectric multiferroics are provoking much research activity for their potential applications in novel multifunctional devices. Compared with single-phase multiferroics, magnetoelectric composites have competitive advantages. The magnetoelectric coupling of composites is heavily influenced by composition and grain size. We prepared BFO/PZT composites with separate phases via the solid-state sintering method. We show that equal molar ratio composition has a better magnetoelectric coupling response than other compositions. The composites with nano bismuth ferrite have better magnetoelectric coupling performance, and these with both nano grain sizes present the highest magnetoelectric voltage coefficients (αE = 16.9 mV cm−1 Oe−1). The strain-mediated mechanism was confirmed via a comparison between strain response and polarization of nano/micro type composites with the composition of 3:7. We found that the magnetoelectric voltage coefficient αE positively correlates with strain response instead of polarization in BFO/PZT composites, which provides experimental evidence for the strain-mediated ME composite theory.

Influence of Deposition Voltage on Strontium Sulphide Doped Silver for Optoelectronic Application

In the research electrochemical deposition technique was use in deposition of undoped SrS and doped SrS with silver were 0.01 mol of thioacetamide (C2H5NS), 0.1 mol of strontium chloride hexahydrate (SrCl2.6H2O), and 0.01 mol of silver nitrate (AgNO3) were utilized as the cationic, anionic, and dopant concentrations. The XRD spectra of the SrS and SrS doped silver showed prominent crystalline peaks at angles of 26.69°, 37.97°, 51.39°, and 65.56° for SrS and 26.42°, 33.42°, 37.98°, and 51.32° for SrS/Ag, respectively, with corresponding diffraction planes (111), (112), (200), and (211). However, the diffraction pattern shows that the peak intensity increases as the deposition voltage increases. The undoped SrS material morphology has a clove-like substance with precipitate; the large nano grain on the substrate's surface exhibits photon absorption but shows no traces of pinholes. When doped SrS is deposited at various precursor voltages, it forms uniform surfaces devoid of pinholes. The cell also penetrates the substrate being used for the deposition, as seen by the elemental makeup of the films. It was observed that SrS/Ag at 10V and 12V had little precipitate on the surfaces; this is because a carbon electrode was utilized, which tends to react with electrolyte at low voltages but does not do so at 14V. The films show that when the deposition voltage increased, the electrical resistivity decreased from 1.42 x 109 to 1.37 x 109 Ω.m and the thickness decreased from 125.02 to 123.025nm. This further led to an increase in conductivity from 7.04 x 108 to 7.29 x 108 S/m. It was discovered that the absorbance decreases as the electromagnetic radiation's wavelength grows and the deposition voltage rises. According to research done on the deposited material, its energy bandgap lies between 1.55 and 2.51 eV.

Microstructural and phase changes in alpha uranium investigated via in-situ studies and molecular dynamics

A deeper knowledge of thermally induced microstructural and phase evolution in nuclear metallic fuel can be obtained using novel in-situ microscopic analyses. Such studies can provide information on the dynamics of phase transitions which is not possible with conventional postmortem characterization (post-irradiation examination). In this work, the behavior of alpha uranium (α-U) was investigated via in-situ heating tests in a transmission electron microscope. The main objective is to understand the microstructural and phase changes, such as defect annihilation and β phase formation and retention, observed in reactor in-pile transient studies at the Transient Reactor Test facility. Indeed, defect migration and rearrangement were observed within the α phase starting at 673 K; α→β phase transition was observed between 773 K and 1,073 K during the heating ramp (which is in the temperature window reported for α→β transition temperatures). Recrystallization and formation of nano grains was observed at high temperatures (over 1,073 K). Such recrystallization was possibly related to the formation of the γ phase. Finally, it was indeed observed that the β phase (but not γ phase) was retained at room temperature upon rapid cooling. Molecular dynamics studies support these experimental results and shows that the γ phase of pure uranium cannot be retained at room temperature if not stabilized with the addition of an alloying element.

Columnar and nanocrystalline combined microstructure of the nitrided layer by active screen plasma nitriding on surface-nanocrystalline titanium alloy

The microstructure and formation mechanism of the nitrided layer by active screen plasma nitriding on surface-nanocrystalline TA17 titanium alloy were studied by TEM. The nitrided layer of both the original and shot-peened TA17 samples was composed of two sublayers: the outer TiN layer formed by deposition of titanium nitride particles and the inner Ti2N layer formed by nitrogen diffusion into the titanium substrate. The Ti2N layer was found to be an Al-depleted zone, which was a proof for its formation mode of nitrogen diffusion. Compared with the TiN layer of the original sample filled with columnar grains, the TiN layer of the shot-peened sample was composed of mainly equiaxed nanograins and a small amount of columnar grains. The large number of high-energy grain boundaries on the shot-peened surface provided numerous nucleation sites, resulting in the formation of equiaxed nanocrystalline TiN. During long term nitriding, most of the nano-scale TiN grains were maintained due to their high thermal stability, while the nano grains of the shot-peened substrate surface grew into microscale due to their low thermal stability. With the thickening of the nitrided layer, some equiaxed TiN nanograins grew into columns perpendicular to the substrate surface due to competitive growth.

Synergistic Strengthening of Dislocation and Heterodeformation Induced in Gradient Nanograined Copper Film: A Molecular Dynamics Study

Unlike conventional homogeneous nanograined (NG) materials, gradient structured materials combine high strength and ductility. The gradient nanograined (GNG) structures are divided into three zones by grain size: the small‐grained zone, the transition‐grained zone, and the large‐grained zone. Molecular dynamics (MD) simulation is performed to investigate the effect of the widths of zones on the strength of GNG structures with different grain sizes. The simulation results reveal the strengthening mechanism of GNG structures from the perspective of microstructure evolution. With the change in grain size, the dominant deformation mode changes from grain boundary (GB) activities in the mall‐grained zone to dislocation slip in the large one. The inverse Hall–Petch phenomenon is observed during plastic deformation. Synergistic strengthening of dislocation and heterodeformation induced (HDI) can be achieved in the structure by regulating the widths of zones with different grain sizes.