Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride, and molybdenum sulfide (MoS2), have attracted considerable interest from the academia and industry because of their extraordinary properties. With the remarkable development of transmission electron microscope (TEM), nanolabs can be established inside the TEM to simulate a real environment by introducing external fields, such as electron irradiation, thermal excitation, electrical field, and mechanical force, into the system. In consequence, besides static structural characterization, in situ TEM can also realize dynamic observation of the evolution in structures and properties of 2D materials. This extension promises an enormous potential for manipulating and engineering 2D materials at the atomic scale with desired structures and properties for future applications. In this study, we review the recent progress of in situ electron microscopy studies of 2D materials, including atomic resolution characterization, in situ growth, nanofabrication, and property characterization.

The synthesis and texturization processes of fluorinated surfaces by means of atmospheric plasma are investigated and presented through an integrated study of both the plasma phase and the resulting material surface. Three methods enhancing the surface hydrophobicity up to the production of super-hydrophobic surfaces are evaluated: (i) the modification of a polytetrafluoroethylene (PTFE) surface, (ii) the plasma deposition of fluorinated coatings and (iii) the incorporation of nanoparticles into those fluorinated films. In all the approaches, the nature of the plasma gas appears to be a crucial parameter for the desired property. Although a higher etching of the PTFE surface can be obtained with a pure helium plasma, the texturization can only be created if O2 is added to the plasma, which simultaneously decreases the total etching. The deposition of CxFy films by a dielectric barrier discharge leads to hydrophobic coatings with water contact angles (WCAs) of 115°, but only the filamentary argon discharge induces higher WCAs. Finally, nanoparticles were deposited under the fluorinated layer to increase the surface roughness and therefore produce super-hydrophobic hybrid coatings characterized by the nonadherence of the water droplet at the surface.

A ternary Nickel foam (NF)–graphene/MnO2/polyaniline (PANI) nanocomposite has been synthesized using green chemistry approach (in situ polymerization). All reactants were dispersed homogeneously in precursor solution in the form of ions and molecules. PANI and MnO2 molecules on the NF–graphene contact each other and are arranged alternately in the composite. Alternative arrangement of PANI and MnO2 nanoparticles separates them and prevents the aggregation of PANI and MnO2 to decrease the particle size of the composite on the surface of NF–graphene. The intermolecule contact improves the conductivity of the composite. The composite showed excellent specific capacitance of 1081 F/g at a scan rate of 1 mV/s and specific capacitance of 815 F/g at a current density of 3 A/g, having excellent cycling stability. Current study provides an alternative pathway to improve the rate capability and cycling stability of nanostructured electrodes, by offering a great promise for their applications in supercapacitors.

Herein, we present a method for introducing β-cyclodextrin (β-CD) and Ferrocene (Fc) into the main chain of poly(acrylic acid) (PAA) to fabricate a novel supramolecular polymer, which was investigated by Fourier transform infrared spectroscopy and 1H Nuclear Magnetic Resonance (1H NMR). This polymer can self-assemble into interesting nanoparticles in aqueous solution. The redox-responsive Fc–CD host–guest interactions endow these nanoparticles with unique self-degradable and self-healable features under redox potential control. This redox behavior of the supramolecular polymer would open up an approach for redox-controlled biological materials with great application potential.

Compounds of poly(3-hydroxybutyrate) (PHB) and carbon black (CB) with CB content ranging between 0.5 and 10% were prepared in an internal mixer. The effect of heating and cooling rates on the crystallization and melting of PHB/CB compounds was investigated by differential scanning calorimetry (DSC), and its morphology analyzed by optical microscopy (OM). Results showed that PHB and its compounds partially crystallize from the melt during cooling and partially cold crystallize on reheating, with the amount of polymer crystallizing in each stage depending strongly on the cooling rate. Melting is usually shown in DSC scans as complex (double) peaks, which are influenced by the heating/reheating thermal cycles. The melting and cold crystallization temperatures, and the rates of phase change depend strongly on the cooling and heating rates and CB content. CB acts as a nucleating agent, promoting the melt and cold crystallization of PHB as well as increasing the number of spherulites, with a mild effect on the melting transition. Light microscopy images suggest that a secondary crystallization of PHB also occurs during storage at room temperature.

We report on a kerfless exfoliation approach to further reduce the costs of crystalline silicon photovoltaics making use of evaporated Al as a double functional layer. The Al serves as the stress inducing element to drive the exfoliation process and can be maintained as a rear contacting layer in the solar cell after exfoliation. The 50–70 µm thick exfoliated Si layers show effective minority carrier lifetimes around 180 µs with diffusion lengths of 10 times the layer thickness. We analyze the thermo-mechanical properties of the Al layer by x-ray diffraction analysis and investigate its influence on the exfoliation process. We evaluate the approach for the implementation into solar cell production by determining processing limits and estimating cost advantages of a possible solar cell design route. The Al–Si bilayers are mechanically stable under processing conditions and exhibit a moderate cost savings potential of 3–36% compared to other c-Si cell concepts.

The enhanced photoresponse of commercial TiO2 (C-TiO2) nanoparticles in quantum dot (QD) sensitized solar cells, when doped with neodymium (Nd), is explored for graphene oxide–copper sulphide (GO–CuS) composite material as counter electrode. The modification of C-TiO2 and the preparation of GO–CuS were done by solid state and sonication methods respectively. The same were characterized by spectroscopy, microscopy, and cyclic voltammetry techniques. Results clearly indicate an enhanced conversion efficiency of ∼1.6 times over the undoped C-TiO2. UV and reflectance spectroscopy reveal that the dopants/defects/oxygen vacancies create midbands causing favorable surface electron states which act as electron traps suppressing recombination and the same is later detrapped leading to an efficient electron transfer. The retention of anatase phase, increase in particle size and decrease in band gap energy to visible range together with high surface area imparted by the GO to CuS in counter electrode facilitate good light harvesting and rapid enhanced electron transfer to redox system on doping. These findings make Nd–TiO2 a good photoanode material and GO–CuS a good counter electrode in QD solar cells.

NiCr2O4/Cr2O3 system with ferrimagnetic spinel and antiferromagnetic transition metal oxide has been firstly synthesized by a chemical co-precipitation method. Magnetic measurements on this system also exhibit the exchange bias (EB) and training effect for the first time. EB effect with evident shift of coercive field and remnant magnetization can be detected at low temperature after field cooling from 350 K. The EB field can reach about 2037 Oe and the magnetization shift is as large as 0.129 emu/g at 10 K. Furthermore, EB effect recedes gradually with temperature increasing and disappears at about 70 K. In this process, EB field decreases with a linear dependence on the magnetization shift. This EB behavior is discussed according to the disordered regions existed at the interface between NiCr2O4 and Cr2O3. In addition, we have analyzed the training effect, which indicates the coexistence of two distinct forms of training mechanism during cycle procedure. One is concerned with an athermal impact resulting in the abrupt single cycle training and the other is gradual reduction of EB field during the subsequent cycles due to the conventional thermal activation mechanism.

Nominal compositions of In2Ti1−xTmxO5−δ, (0.0 ≤ x ≤ 0.2 and Tm = Fe3+ and Cr3+) were synthesized by ceramic route and characterized by relevant techniques. In2Ti1−xFexO5−δ samples were single phased isomorphic with In2TiO5 phase while Cr substitution has resulted in mixed phased compositions. Dynamic light scattering experiments showed the increase in proportion of smaller sized particles with the increase in extent of Fe substitution. Mössbauer spectra revealed that Fe exists in +3 oxidation state in substituted oxides. The band gap decreased from 3.2 (In2TiO5) to 2.1 eV (In2Ti0.8Fe0.2Ox−δ) and to 1.9 eV in case of Cr substitution (In2Ti0.8Cr0.2O5−δ) attributed to participation of Fe 3d/Cr 3d levels. Photocatalytic H2 generation was evaluated over the substituted oxides from water–methanol mixtures under UV–visible irradiation. The decreasing order of photocatalytic activity is as follows: 20% Fe (mol%) > 10% Fe > indium titanate ≈ 20% Cr > 10% Cr. The loading of Pt as cocatalyst on surface of most active photocatalyst, In2Ti0.8Fe0.2Ox−δ further enhanced the photocatlytic H2 yield.

Experimental observations have shown that carbon nanotubes (CNTs)/Al nanocomposites with high level ordered nanolaminates exhibit greatly improved plasticity. The increased plasticity is mainly attributed to enhanced dislocation storage capability and two-dimensional alignment of the reinforcement. Here a theoretical model is proposed with interactions between aligned CNTs and grain boundary dislocations emitted from a crack tip taken into consideration to investigate crack blunting and fracture toughness in nanocrytalline metal matrix composites (MMCs). The critical shear stress for emission of first dislocation from intersections between a long, flat crack and aligned CNTs is quantitatively characterized. The final equilibrium positions and maximum numbers of emitted dislocations for different orientation angles and microstructures of aligned reinforcement are evaluated. In addition, the dependence of enhanced fracture toughness on effective gliding distance of emitted dislocations is also determined. The results show that the existence of aligned CNTs can lead to an increase of critical crack intensity factor by 77% than that in dislocation free case under certain conditions. The model may provide a basis understanding of ductility in aligned CNTs-reinforced nanocrystalline MMCs on respective of emission and motion of dislocations.

The forming limit strains (FLSs) of zircaloy-4 sheets are studied. After having obtained the true stress–strain curve of zircaloy-4 using the weighted-average method, limit dome height (LDH) tests are performed to establish experimental FLSs. We summarize related theoretical forming limit curves (FLC) and discuss their limitations. Two finite element (FE) models are established for determining FLSs; an LDH test FE model for the negative minor strain sector, and a biaxial tensile FE model for the positive minor strain sector. The numerical FLSs are found to agree well with experimental data. Since the numerical FLC gives the strain at the onset of local thinning (whereas the experimental FLC provides the strain between local necking and ductile fracture), resulting FE FLS values are slightly lower than the experimental ones so that results can be regarded as conservative. Our FE approach substitutes the expensive and time-demanding experimental LDH tests.

This article addresses the metallurgical and mechanical properties of Nd:YAG laser welded Inconel 625 and duplex stainless steel SAF 2205. Keyhole plasma mode laser welding was adopted to obtain the joints. Microstructure studies showed slight grain coarsening at the heat affected zone of Inconel 625. Line mapping and elemental mapping analysis were carried out at the weld interface and in the fusion zone to examine the elemental migration as well as the composition of the phases present in these regions. The fusion zone microstructure showed the presence of Nb, Mo rich Laves phase segregated at the interdendritic arms. Tensile studies corroborated that an average joint strength of 820 MPa has been displayed by these weldments, which was almost equal to one of the parent metals, SAF 2205. It is evident from the charpy v-notch studies that the impact toughness of these laser weldments was found to be 10 J and this low toughness could be reasoned out to the formation of Mo rich phases. The structure–property relationships of these weldments have been addressed in detail and the outcomes of the study will be highly useful for marine and geothermal applications.

Cr is one of common alloying elements that improve the oxidation resistance of Cu. Its content and distribution are the two important factors that influence the oxidation resistance of alloys. In this paper, the cluster structure model of stable solid solutions was used for designing Cu–Cu12–[Crx/(12+x)Ni12/(12+x)]5 (x = 1, 2, 4, 6 or 8) alloys. The insoluble antioxidative Cr was uniformly distributed in the Cu matrix with the help of Ni element. The solid solution and precipitation of alloys were effectively controlled by changing the Cr/Ni ratio, and the effects of the distribution of alloying elements on the oxidation resistance of Cu alloy were discussed. The studies on isothermal oxidation at 850 °C show that element Cr of the Cu–Ni–Cr alloys designed using cluster model can be dispersed in the Cu matrix, and a continuous protective Cr-rich oxide layer can be formed when the Cr content dispersed in the alloys reaches 9.26 at% during isothermal oxidation. 1/2 of Cr in the Cu–Ni–Cr alloys is replaced by Fe, forming Cu–Ni–(Cr + Fe) alloys; oxide precipitates exhibit a columnar structure revealing the orientation of growth perpendicular to the matrix, thereby forming a lot of O diffusion channels and resulting in a sharp decline in its oxidation resistance. Therefore, the growth morphology of the oxide precipitates may significantly affect the oxidation resistance.

The solidification of undercooled Ni–3.3 wt% B alloy was studied by high-speed video analysis and microstructural analysis. For moderate initial undercooling (ΔTp = 75 K), the solidification interface for primary phase transformation manifests a shape of a planar dendrite, and possesses an constant growth velocity, for eutectic transformation whereas the interface presents multi-dendrite shape and spasmodic growth, so that a constant velocity cannot describe the interface exactly. These differences suggest that primary phase solidification is controlled by far-distance diffusion while eutectic solidification by short-distance diffusion. For large initial undercooling (ΔTp = 262 K), a kinds of large “white dendrites”, which is in fact composed of multiple phases, were found in the microstructure, from inside to outside of which, the eutectic phase changes from dot phases (anomalous structure) to irregular eutectic and then to regular eutectic, indicating that the center of “white dendrites” may be the nucleation zone of eutectic reaction.

The interfacial reactions in Cu/Sn–52In/Cu interconnects during solid–solid (S–S) and liquid–solid (L–S) electromigration (EM) under a current density of 2.0 × 104 A/cm2 at 90 and 150 °C have been in situ studied using synchrotron radiation real-time imaging technology. The In atoms directionally migrate toward the cathode due to the back-stress induced by the preferential migration of the Sn atoms over the In atoms toward the anode during the S–S EM, resulting in the segregation of the Sn and In atoms at the anode and cathode, respectively. During the L–S EM, however, the In atoms directionally migrate toward the anode due to the negative effective charge number (Z*) of In rather than the back-stress. The polarity effect, i.e., the intermetallic compounds growing continuously at the anode while becoming thinner at the cathode, is more significant during the L–S EM than the S–S EM. Furthermore, the consumption rate of the cathode Cu during the L–S EM is three orders of magnitude higher than that in the case of the S–S EM because of the significantly higher EM-induced atomic flux in the liquid solder. The migrations of the Sn, In, and Cu atoms are discussed in terms of diffusion flux.

The influence of cooling rates on the solidification and microstructure of rapidly solidified quasicrystal alloys with a nominal compositions of Mg57Zn37Y6 (at.%) prepared by melt spinning method was investigated. The microstructure, phase constitution, phase transition, and phase structure of the alloys were examined by means of scanning electron microscopy, x-ray diffraction, energy dispersive spectrometer, differential scanning calorimetry, and transmission electron microscopy. The results show that rapid solidification refines and homogenizes the microstructure of Mg57Zn37Y6 alloys, compared to the conventionally-cast master alloy. With the increasing cooling rate of rapid solidification, the thickness of the ribbon decreases greatly and a larger amount of I-phase can be formed. α-Mg, MgZn, and icosahedral phases are found in the as-cast alloy, but the MgZn phase is absent from rapidly solidified alloys. The I-phase in both as-cast and rapidly solidified alloys can precipitate directly from the melt during the solidification process. A higher cooling rate can lead to a large degree of supercooling, resulting in a decreased phase transition temperature and a large number of icosahedral short-range orders (ISROs). ISROs can act as templates in liquid and promote the nucleation of I-phase.

Two kinds of heavy-alloying β-type TiAl-based alloys Ti44Al6Nb1.0Cr2.0V (A1) and Ti44Al6Nb1.0Cr2.0V0.15Y0.1B (A2) are newly designed. They are prepared by vacuum consumable melting (VCM) and cold crucible directional solidification (CCDS). Via the theoretical analysis and tentative experiment, five alternative heat treatment (HT) schedules are proposed and studied that the corresponding microstructure and room temperature (RT) tensile property are investigated, and finally the optimized HT schedules are acquired. After HT5 (heat preservation in β phase region and at 1290 °C, and then ladder cooling), A2 alloy cast by VCM exhibits a better tensile property with average elongation of 1.20%. For the two CCDS ingots, after HT3 (mainly annealing at 1280 °C), B2 phase and (B2 + γ) blocky morphology are reduced, the columnar grains and small angle lamellas are reserved, and the tensile property also has a moderate improvement.

The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in situ using clamped micro-beam bend tests inside a scanning electron microscope (SEM). Clamped beam bending is a fairly well established micro-scale fracture test geometry that has been previously used in determination of fracture toughness of Si and PtNiAl bond coats. The increasing amount of Pt in the bond coat matrix was accompanied by several other microstructural changes such as an increase in the volume fraction of α-Cr precipitate particles in the coating as well as a marginal decrease in the grain size of the matrix. In addition, Pt alters the defect chemistry of the B2-NiAl structure, directly affecting its elastic properties. A strong correlation was found between the fracture toughness and the initial Pt layer thickness associated with the bond coat. As the Pt layer thickness was increased from 0 to 5 µm, resulting in increasing Pt concentration from 0 to 14.2 at.% in the B2-NiAl matrix and changing α-Cr precipitate fraction, the initiation fracture toughness (KIC) was seen to rise from 6.4 to 8.5 MPa·m1/2. R-curve behavior was observed in these coatings, with KIC doubling for a crack propagation length of 2.5 µm. The reasons for the toughening are analyzed to be a combination of material's microstructure (crack kinking and bridging due to the precipitates) as well as size effects, as the crack approaches closer to the free surface in a micro-scale sample.

The mechanical properties and internal friction (damping capacity) of Mg–Zn–Y alloys with a long-period stacking ordered (LPSO) structure at different Y/Zn atomic ratios (2/1, 3/2 or 4/3) in cast and extrusion were investigated. It was found that the as-cast Mg–Zn–Y alloys with different Y/Zn atomic ratios possess a single LPSO phase with the same stable 18R-type structure. Among the three alloys, the alloy with 3/2 atomic ratio yields the highest damping capacity in low- and high-strain amplitude stages. Two damping peaks particularly P1 and P2 are detected in the Mg–Zn–Y alloy with 3/2 atomic ratio at approximately 108 and 220 °C, respectively. These results may be attributed to few solute atoms in Mg matrix and grain boundaries. In addition, the studied alloy with 3/2 atomic ratio exhibits excellent comprehensive properties in as-cast and as-extruded states; this alloy yields an ultimate tensile strength of 346 MPa and maintains a certain damping capacity (Q−1 > 0.01) in extrusion.