Crystalline Metal Research Articles

Nanoporous Metal-Organic Framework Thin Films Prepared Directly from Gaseous Precursors by Atomic and Molecular Layer Deposition: Implications for Microelectronics.

Atomic/molecular layer deposition (ALD/MLD) allows for the direct gas-phase synthesis of crystalline metal-organic framework (MOF) thin films. Here, we show for the first time using krypton and methanol physisorption measurements that ALD/MLD-fabricated copper 1,4-benzenedicarboxylate (Cu-BDC) ultrathin films possess accessible porosity matching that of the corresponding bulk MOF.

Strong dependency of the tribological behavior of CuZr-based bulk metallic glasses on relative humidity in ambient air

Thanks to their outstanding mechanical properties, Bulk Metallic Glasses (BMGs) are new alternatives to traditional crystalline metals for mechanical and micromechanical applications including power transmission. However, the tribological properties of BMGs are still poorly understood, mostly because their amorphous nature induces counter intuitive responses to friction and wear. In the present study, four different BMGs (Cu47Zr46Al7, Zr46Cu45Al7Nb2, Zr60Cu28Al12, and Zr61Cu25Al12Ti2) underwent ball-on-disc friction tests against 100Cr6 steel balls (American Iron and Steel Institute (AISI) 52100) at different relative humidities (RHs) ranging from 20% to 80%. Controlling humidity enabled to observe a high repeatability of the friction and wear responses of the BMG. Interestingly, the friction coefficient decreased by a factor of 2 when the humidity was increased, and the wear rate of BMGs was particularly low thanks to a 3rd-body tribolayer that forms on the BMG surface, composed of oxidized wear particles originating from the ball. The morphology of this tribolayer is highly correlated to humidity. The study also identifies how the tribolayer is built up from the initial contact until the steady state is achieved.

Oxygen Vacancy-Rich Amorphous BiVO4 Nanoparticles for Colorimetric Sensing

Defects in crystalline nanozymes play a critical role in enhancing their performances and related catalytic events. However, creating a high concentration of active and robust defects in well-explored crystalline metal oxides to achieve high-performance single-enzymatic activity is challenging. Herein, amorphous BiVO4 beyond traditional crystalline nanozymes is prepared via a facile solution-processed coprecipitation method favorable to large-scale manufacturing to mimic enzymatic properties. As expected, the specially designed amorphous material without any post-treatments has sufficient and robust oxygen vacancies, which are highly active in converting oxygen to reactive radicals (O2–•). Simultaneously, the negatively charged surface has a high affinity for the substrate, facilitating charge transfer between materials and substrates and, in turn, providing higher catalytic efficiency compared to the crystalline counterparts. Most importantly, the sample can only mimic oxidase-like activity rather than the multienzyme-like activity generally observed in most reported crystalline metal oxides, which is a step forward in the development of nanozymes. This amorphous BiVO4-based system is also evaluated for the sensitive and selective detection of l-cysteine. The study provides insight into nanozyme development and highlights the great potential of amorphous materials in addition to amorphous BiVO4.

Metal-organic framework glass composites.

The melting phenomenon in metal-organic frameworks (MOFs) has been recognised as one of the fourth generation MOF paradigm behaviours. Molten MOFs have high processibility for producing mechanically robust glassy MOF macrostructures, and they also offer highly tunable interfacial characteristics when combined with other types of functional materials, such as crystalline MOFs, inorganic glass and metal halide perovskites. As a result, MOF glass composites have emerged as a family of functional materials with dynamic properties and hierarchical structural control. These nanocomposites allow for sophisticated materials science studies as well as the fabrication of next-generation separation, catalysis, optical, and biomedical devices. Here, we review the approaches for designing, fabricating, and characterising MOF glass composites. We determine the key application opportunities enabled by these composites and explore the remaining hurdles, such as improving thermal and chemical compatibility, regulating interfacial properties, and scalability.

Encapsulation of N-containing compounds in a new hydrophilic Cd-based crystalline sponge via coordinative alignment method

The crystalline sponge method (CSM) is a technology which allows precise molecular determination of non-crystalline compounds, without the need to crystallise them independently, by soaking them in a crystalline metal–organic framework (MOF).

Исследование сжимаемости цианамидов металлов и влияния давления на их электронные свойства

Based on the density functional theory, the effect of pressure on the structure and electronic properties of crystalline metal cyanamides Zn(CN2) and NaSc(CN2)2 has been studied. The negative linear compressibility of Zn(CN2) was revealed and its correlation with microscopic changes in the atomic structure under pressure was established. It is shown that NaSc(CN2)2 has a low compressibility (0.2 TPa-1) in a direction close to that of cyanamide anions. Based on the quantum topological analysis of the electron density, interatomic interactions were studied and it was found that the Zn-N and Sc-N bonds have a partially covalent character. The band gaps of Zn(CN2) and NaSc(CN2)2 at pressures up to 1 GPa have been determined and found to correspond to the UV range of 224-271 nm.

Observation of enhanced nanoscale creep flow of crystalline metals enabled by controlling surface wettability

Understanding and controlling interface friction are central to many science and engineering applications. However, frictional sliding is closely related to adhesion, surface roughness, surface chemistry, mechanical deformation of contact solids, which poses the major challenge to experimental studying and theoretical modeling of friction. Here, by exploiting the recent developed thermomechanical nanomolding technique, we present a simple strategy to decouple the interplay between surface chemistry, plastic deformation, and interface friction by monitoring the nanoscale creep flow of metals in nanochannels. We show that superhydrophobic nanochannels outperforming hydrophilic nanochannels can be up to orders of magnitude in terms of creep flow rate. The comparative experimental study on pressure and temperature dependent nanomolding efficiency uncovers that the enhanced creep flow rate originates from diffusion-based deformation mechanism as well as the superhydrophobic surface induced boundary slip. Moreover, our results reveal that there exists a temperature-dependent critical pressure below which the traditional lubrication methods to reduce friction will break down. Our findings not only provide insights into the understanding of mechanical deformation and nanotribology, but also show a general and practical technique for studying the fundamental processes of frictional motion. Finally, we anticipate that the increased molding efficiency could facilitate the application of nanoimprinting/nanomolding.

Nanoscale deformation of crystalline metals: Experiments and simulations

In the present work, we performed experiments and molecular dynamic simulations to study the atomic physical process and deformation mechanism involved in nanoscale deformation of crystalline metals. By contact deforming bulk metals using hard molds with different cavity sizes at various temperatures and different stress levels, the flow of metals (e.g., Au and Ag) into nanocavities is quantified by the aspect ratio of molded micro-/nanorods, based on which the dependence of deformability on cavity size, temperature and stress is revealed. It is found that the critical forming pressure is determined by the entering barrier. Once the entering barrier can be overcome, quantified by the aspect ratio of metal nanorods, the molding efficiency increases with the cavity size decreasing. Moreover, three deformation modes are uncovered in the nanoscale plastic flow of metals and directly related with the atomic physical processes, i.e. atomic diffusion, dislocation nucleation, multiplication and movement. In the dislocation dominated temperature regime, a transition of deformation mode from burst growth to continuous growth is observed as the cavity size increases. When the mold cavity size is very small (100-101 nm), the metal atoms flowing in a mold cavity will arrange amorphously even at low temperature, which usually only occurs at high temperature for large cavity sizes. Therefore, reducing the size shows the same effect as increasing the temperature, making nanomolding easier.

Bifunctional Mesoporous MOx (M = Cr, Fe, Co, Ni, Ce) Oxygen Electrocatalysts for Platinum Group Metal‐Free Oxygen Pumps

A family of crystalline mesoporous metal oxides was synthesized via a soft-templated hydrothermal synthesis route and evaluated as electrocatalysts for oxygen evolution and reduction reactions. The mesoporous NiO was used to elaborate, for the first time, a symmetrical platinum group metal-free oxygen pump. More details can be found in article number 2200927, Zhixing Wu and co-workers.

Genesis of Metal Sulfides and Its Significance on Graphite Mineralization in the Huangyangshan Graphite Deposit, East Junggar, Xinjiang Province, China

The Huangyangshan super-large graphite deposit is located in the Qitai area of East Junggar in Xinjiang Province, China. This deposit is well known for its distinguishing properties, including the alkaline granite complex that hosts the graphite ore, the dominantly orbicular structure developed in the graphite ore, and the association of graphite with metal sulfides in the orbicular ore. This study aims to determine the genetic relationship between graphite and metal sulfides in order to better understand the graphite mineralization process of the Huangyangshan deposit. The methods applied in the study include X-ray micro-CT scanning and scanning electron microscopy (SEM) analyses of the orbicular graphite ore and in situ inductive laser ablation-coupled plasma mass spectrometry (LA-ICP-MS) trace element analyses of the pyrrhotite and chalcopyrite associated with the graphite. The analytical results show that the graphite ore is composed of crystalline graphite, K-feldspar, albite, quartz, biotite, amphibole, and metal sulfides. The metal sulfides in the orbicular ore include pyrite, pyrrhotite, pentlandite, and chalcopyrite. According to the color, crystalline shape, texture, and occurrence, pyrrhotite can be classified into four types (I, II, III, and IV), and chalcopyrite into two types (I and II), of which types I, II, and III pyrrhotite and type I chalcopyrite have a close genetic relationship with graphite. The granular types (I, II, and III) of pyrrhotite are enriched in Co, Ni, Se, Ge, and Te and are depleted in As, Sb, Ag, and Au; they also have a high value of Co/Ni, indicating that these types of pyrrhotite have a magmatic origin. Low values of Co/Ni suggest that type IV pyrrhotite has a hydrothermal origin. The similar contents of Co and Ni and the values of Co/Ni compared with the chalcopyrite from the magmatic Co–Ni sulfide deposits imply that type I chalcopyrite has a magmatic origin. In summary, the metal sulfides of the Huangyangshan deposit are genetically related to graphite mineralization and formed predominantly by magmatic processes.

Crystalline flower-like nickel cobaltite nanosheets coated with amorphous titanium nitride layer as binder-free electrodes for supercapacitor application

Fabrication of high-performance supercapacitors involves a three-step strategy - selection of suitable electrode material, optimized morphology, and efficient synthesis approach. For the first time, an integrated synthesis approach using the facile hydrothermal technique (for growing NiCo2O4 nanosheets) followed by vacuum cathodic arc deposition (for depositing thin TiN layers) is used to improve the electrochemical stability of pristine nickel cobaltite (NiCo2O4). The hierarchical flower-like NiCo2O4@TiN nanosheets grown on nickel foam as binder-free electrode shows a high specific capacity of 402.57 Cg−1 at 1 Ag−1, excellent rate capability of 82.8% when current density increases from 1 Ag−1 to 20 Ag−1, and cycling stability of 90% over 2000 charge-discharge cycles. The remarkable electrochemical performance of NiCo2O4@TiN-220/Ni signifies its ample potential for the fabrication of a supercapacitor device. A coin-cell symmetric supercapacitor (CR2032) is assembled using the NiCo2O4@TiN-220/Ni electrodes, which exhibits remarkable electrochemical performance, including a specific capacitance of 178 Fg−1, an energy density of 46.4 Wh kg−1 at a power density of 1363 W kg−1, and a capacitance retention of 129.4% after running 3500 cycles. The enhanced performance can be attributed to the porous morphology with core/shell flower-like nanosheet structure of NiCo2O4@TiN grown on nickel foam. The study also emphasizes a good tuning of crystalline metal oxide (NiCo2O4) with amorphous metal nitride (TiN) as high performing electrode for supercapacitor application.

Hollow fiber membrane supported metal organic framework-based packed bed for gas/vapor adsorption

Crystalline metal–organic frameworks (MOFs) with high porosity have high sorption capacities for various gases. Their fragile and pulverulent characteristics have prompted significant efforts to prepare shaped bodies e.g., pellets, granules for use in adsorbers. A hollow fiber membrane-based strategy is adopted since hollow fiber membrane (HFM) modules are highly preferred for industrial separation processes due to very high surface area provided per unit device volume and their easy scalability. We report herein a solvothermal synthesis method whereby nanocrystals of the MOF, UiO-66-NH2, are synthesized directly inside submicron pores of hydrophilic hollow fiber membranes of Nylon 6 as well as in the bores of the HFMs. Nanocrystals of around 100 nm populate HFM pores. Cylindrical modules containing such HFMs and MOF nanocrystals and microcrystals in membrane pores, HFM bores and the extra capillary space were studied for adsorption of ammonia from a dilute gas stream. High values of ammonia breakthrough time were achieved. The corresponding behaviors of three MOF configurations namely, MOF in membrane pores, MOF in membrane pores and the HFM bores and MOF present in membrane pores, HFM bores and in extra capillary space were studied. The values of time/MOF weight achieved were very high. The MOFs synthesized were characterized by Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffractometer (PXRD), Brunauer-Emmett-Teller (BET) adsorption isotherms, surface area, and pore size distribution. High performance of HFM-supported MOF-based scalable devices for gas/vapor adsorption has been demonstrated with values of 20,000 min/g of MOF for trace ammonia breakthrough from humid ammonia feed gas stream employed. Other potential uses of such devices for adsorbing 2 to 3 gases and liquid phase adsorption have also been discussed.

Growth of single-crystalline MAPbI3 perovskite film by a modified space-confined inverse temperature crystallization method

Single crystalline (SC) metal halide perovskite absorber film can outperform its polycrystalline counterpart in power conversion efficiency and stability due to the absence of grain boundaries. However, SC perovskite film's direct growth on charge selective contact layer coated substrates for solar cell applications is not widely explored. In this study, SC methylammonium lead iodide (MAPbI3) perovskite film is directly grown on charge selective (electron and hole transport) contact layer coated substrates (TiO2 coated fluorine doped tin oxide (FTO) glass substrate and poly(triarylamine) (PTAA) coated indium tin oxide (ITO) glass substrate) by inverse temperature crystallization (ITC) method. The PTAA/ITO substrate's hydrophobic nature led to faster ion migration and controlled nucleation, resulting in large-sized SC MAPbI3 perovskite film. X-ray diffraction of the MAPbI3/PTAA/ITO showed SC nature with diffraction from (200) and (400) planes, indicating that the film is majorly (100) oriented. The MAPbI3 film grown on TiO2/FTO is found to be relatively small in size (< 1 mm), majorly oriented in the (110) plane with diffraction also from other planes indicating polycrystalline nature. Long-term stability studies over 1500 h show that SC MAPbI3 films show more endurance to ambient conditions than polycrystalline MAPbI3. The growth time of 50 h was reduced to 30 h by employing antisolvent-assisted ITC, resulting in ultra-stable circular shaped films suitable for photovoltaic applications.

Solution Atomic Layer Deposition of Smooth, Continuous, Crystalline Metal–Organic Framework Thin Films

For the first time, a procedure has been established for the growth of surface-anchored metal-organic framework (SURMOF) copper(II) benzene-1,4-dicarboxylate (Cu-BDC) thin films of thickness control with single molecule accuracy. For this, we exploit the novel method solution atomic layer deposition (sALD). The sALD growth rate has been determined at 4.5 Å per cycle. The compact and dense SURMOF films grown at room temperature by sALD possess a vastly superior film thickness uniformity than those deposited by conventional solution-based techniques, such as dipping and spraying while featuring clear crystallinity from 100 nm thickness. The highly controlled layer-by-layer growth mechanism of sALD proves crucial to prevent unwanted side reactions such as Ostwald ripening or detrimental island growth, ensuring continuous Cu-BDC film coverage. This successful demonstration of sALD-grown compact continuous Cu-BDC SURMOF films is a paradigm change and provides a key advancement enabling a multitude of applications that require continuous and ultrathin coatings while maintaining tight film thickness specifications, which were previously unattainable with conventional solution-based growth methods.

Chemo-mechanical model for degradation of oil paintings by amorphous and crystalline metal soaps

Metal soap formation is recognised as a critical degradation mechanism in historical oil paintings, which threatens the preservation of museum collections worldwide. Metal soaps form via a complex sequence of chemical reactions between metal ions released by the pigments and saturated fatty acids originating from the drying oil. The latest advances in chemistry research suggest that metal ions and saturated fatty acids may initially react by means of a reversible reaction, which leads to the formation of metal soaps in an amorphous state. Metal soaps may subsequently crystallise via an irreversible reaction into large aggregates that deform the paint layers, potentially triggering delamination, cracking, and ultimately flaking of the paint. This paper proposes a chemo-mechanical model to predict metal soap formation and the consequent mechanical damage in historical oil paintings. The chemical process is described in terms of a set of diffusion–reaction equations, which account for both the reversible reaction between free saturated fatty acids and metal ions forming amorphous metal soap, and the subsequent irreversible reaction to crystalline metal soap. The chemical model is two-way coupled with a mechanical model that effectively describes the cracking processes caused by metal soap formation and growth. The coupling is generated from the mechanical model by accounting for the development of a chemically-induced growth strain in the crystalline metal soap. In addition, the presence of cracks locally hampers the diffusion of chemical species, which is taken into account in the chemical model through a dependency of the diffusion parameter at the crack faces on the amount of mechanical damage generated. The spatial development of the crystalline metal soap phase is simulated by using a tailor-made scanning algorithm that identifies the reaction zone in which metal soap formation takes place. The proposed model is calibrated on experimental data presented in the literature. The model is subsequently applied to analyse two numerical examples that are representative of typical metal soap-related degradation processes observed in historical oil paintings, revealing that the growth process of crystalline metal soap, the deformation of the paint surface, and the consequent cracking and delamination patterns are predicted in a realistic fashion.

Deformation of Nanoglass under High-pressure Torsion

Metallic glasses are amorphous solids with metallic atomic bonds. Different from traditional crystalline metals, they have no long-range atomic order. Only short-range order on the scale of 0.5–1 nm can be detected. Because of the lack of a lattice dislocation slip system, as in crystalline alloys, metallic glasses exhibit some outstanding properties, such as high elastic strain, high hardness and high strength.

Bifunctional Mesoporous MOx (M = Cr, Fe, Co, Ni, Ce) Oxygen Electrocatalysts for Platinum Group Metal‐Free Oxygen Pumps

Bifunctional electrocatalysts with both accelerated oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) enable high‐power density electricity storage and decentralized extraction of pure oxygen from air for usage in health care. Herein, a hydrothermal synthesis employing the anionic surfactant sodium dodecyl sulfate as structure‐directing agent is developed to fabricate a family of crystalline mesoporous metal oxides (meso‐MO X , M = Cr, Fe, Co, Ni, Ce). The pore size and specific surface area depend on the metal used and they range from 3 to 6 nm and 60 to 200 m2 g−1, respectively. NiO and Co3O4 show a higher catalytic efficiency in alkaline media in comparison with the other oxides studied, and their activities are comparable with the values reported for platinum group metal (PGM)‐based electrocatalysts. This stems from lower voltage losses and by the presence of specific hydroxide adsorbates on the surface. Both ORR and OER driven on Co3O4 show the unified rate‐determining chemical step (|OO−|• ads + H2O ↔ |OOH|• ads + OH−, where are the species adsorbed on active sites). The bifunctional ORR/OER electrocatalysis obtained on mesoporous NiO is utilized for the first symmetrical PGM‐free oxygen pump fed by air and water only.

Non-Hookean large elastic deformation in bulk crystalline metals

Crystalline metals can have large theoretical elastic strain limits. However, a macroscopic block of conventional crystalline metals practically suffers a very limited elastic deformation of <0.5% with a linear stress–strain relationship obeying Hooke’s law. Here, we report on the experimental observation of a large tensile elastic deformation with an elastic strain of >4.3% in a Cu-based single crystalline alloy at its bulk scale at room temperature. The large macroscopic elastic strain that originates from the reversible lattice strain of a single phase is demonstrated by in situ microstructure and neutron diffraction observations. Furthermore, the elastic reversible deformation, which is nonhysteretic and quasilinear, is associated with a pronounced elastic softening phenomenon. The increase in the stress gives rise to a reduced Young’s modulus, unlike the traditional Hooke’s law behaviour. The experimental discovery of a non-Hookean large elastic deformation offers the potential for the development of bulk crystalline metals as high-performance mechanical springs or for new applications via “elastic strain engineering.”

Facile preparation of hexagonal WO3 nanopillars and its reduced graphene oxide nanocomposites for high-performance supercapacitor

One-dimensional (1D) nanostructures are extremely important due to better charge transport capabilities. The ability to anchor 1D semiconductor nanostructures on graphene may give advantages in electrochemical charge storage applications. In this study, the authors explored the synthesis, growth mechanism, and insertion-type pseudocapacitive properties of 1D hexagonal (h) phase-WO3 (h-WO3) nanopillars and h-WO3/rGO nanocomposite. The nanocomposite is composed of h-WO3 nanopillars uniformly grown on a reduced graphene oxide (rGO) matrix and the resulting h-WO3/rGO nanocomposite shows the hexagonal structure and, 3D networks gathered during a hydrothermal process. XRD confirms the phase purity and crystalline nature, SEM confirms the hexagonal bundled nanopillar morphology of h-WO3 and its graphene composites, and rGO offered crumpled two-dimensional sheet-like morphologies. HRTEM and SAED analysis confirmed the highly oriented growth of h-WO3 nanowire along the [001] zone axis. XPS analysis confirms the presence of tungsten in +6 and + 5 oxidation states, indicating the formation of the oxygen-deficient h-WO3-x structure. The electrochemical characterizations are performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and stability tests. From the CV measurements, the outperformed exceptional h-WO3 and h-WO3/rGO nanocomposites exhibit specific capacitance (Csp) of ∼545 Fg−1 and ∼926 Fg−1, respectively, at a 5 mVs−1 scan rate, and from GCD measurements Csp found to be ∼504 Fg−1 and ∼991 Fg−1, respectively at 0.1 Ag−1 current density. Supercapacitor capacitances with carbon and metal oxide electrodes are typically related to the accessible surface areas. However, this work indicates that proton insertion, a rare capacitive charge storage mechanism, may significantly increase the capacitance of metal oxides with a limited surface area but a particular structure. Nonetheless, using the proton insertion process, scientists have shown that the electrodes made from an assembly structure of h-WO3 nanopillars have enhanced charge storage performance. According to detailed investigations, the electrochemical behavior of h-WO3 is dominated by the proton insertion mechanism and is critical in achieving high capacitance by eliminating alternative mechanisms. This research work presents a novel method for attaining extraordinary charge storage contribution into the ordered tunnels in crystalline metal oxides due to efficient proton insertion, which is especially significant for the construction of high-performance electrochemical energy storage systems: batteries and supercapacitors.

Metal-Organic Frameworks and Their Composites for Environmental Applications.

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.