Fivefold Twins Research Articles

Preparation and electrochemical properties of boron-doped polycrystalline diamond film with five-fold twin structure

In this study, boron-doped polycrystalline diamond (BDD) films were deposited on 6-inch silicon wafer by using microwave plasma chemical vapor deposition (MPCVD). Mixed gas containing hydrogen, methane, and diborane was used as precursor and the wafer temperatures were set at 750 °C, 850 °C and 950 °C, respectively. Five-fold twin structures were observed in the samples prepared at 850 °C and they promote the increase of surface roughness. Furthermore, these twin structures may lead to the increase of boron atoms at the surface, which was verified by first-principles calculation. BDD film that contains five-fold twin structures has higher Hall mobility, lower electrical resistivity and larger hole carrier concentrations at room temperature. Besides, reactive red X-3B (200 mg/L) was fully degraded by BDD electrodes at current density of 100 mA/cm2 within 40 min using NaCl as supporting electrolyte. Overall, BDD film electrodes prepared by appropriate methods contain a large quantity of five-fold twin structures surface have excellent electrochemical properties and thereby demonstrate potential as a promising waste water degradation material.

Size-dependent strain in fivefold twins of gold

Multiple twinned structures are common in low-dimensional materials. They are intrinsically strained due to the geometrical constraint imposed by the non-crystallographic fivefold symmetry. In this study, the strain distributions in sub-10 nm fivefold twins of gold have been analyzed by combining aberration-corrected transmission electron microscopy and first-principles calculations. Bending of atomic planes has been measured by both experiments and calculations, and its contribution to the filling of the angular gap was shown to be size-dependent.

New phase transition pattern of fivefold twins transformed into lamellar structure in Ti3Al alloy

A new phase transition pattern of fivefold twins into a lamellar structure leading to a second phase transition was found in Ti3Al alloy.

Twin Boundary and Fivefold Twins in Nickel Oxide

Twinning is a common phenomenon in crystal growth and mechanical deformation. It plays a key role in tuning the mechanical and transport properties of metals. In transition metal oxides, the twinning may give additional changes related to magnetism. Herein, the atomic configuration and the electronic structure of the twin boundaries (TBs) in rock‐salt‐type NiO are studied, combining aberration‐corrected transmission electron microscopy and first‐principles calculations. For NiO, the twinning occurs on the (111) plane, with oxygen atoms located at the TB and antiferromagnetic (AFM) coupling between the mirroring Ni atomic planes near the TB. The configuration gives the TB energy of 0.26 J m−2. Atomic and magnetic structures of fivefold twins in NiO are also investigated. In the structure of fivefold twins with the lowest energy, ferromagnetic coupling is formed in the AFM TBs due to the competing exchange interaction at the core of fivefold twins.

Designing ultrahard nanostructured diamond through internal defects and interface engineering at different length scales

Nanocrystalline diamonds (NCDs) are promising structural materials due to their extraordinary mechanical properties such as ultrahigh hardness and excellent toughness, however, a rational design rule in plasticity and fracture through controlling nanostructures at different length scales is far from being explored. By means of atomic simulations and plasticity theory in the present paper, we comprehensively explored the plastic deformation behaviors of a series of well-defined NCDs by varying amorphous interfacial layers (AILs) and internal defects, e.g., twin boundary, stacking fault, π-bonded interface, and fivefold twin. It was observed that the effect of internal defects on the mechanical response of NCD can be attributed to the competition between dislocation blocking process and interface sliding process. The introduction of AIL at grain boundary (GB) is found to provide an effective solution to decrease both dislocation nucleation and penetration at GBs. These findings provide not only a mechanistic insight into the unique strengthening and toughening in various NCDs, but a rational guidance in designing novel superhard carbon materials with superior performance by engineering internal defects and GB structures at different length scales.

Atomistic mechanisms of twin–twin interactions in Cu nanopillars

Twinning is an important mode of plastic deformation in metallic nanopillars. When twinning occurs on multiple systems, it is possible that twins belonging to different twin systems interact and forms a complex twin–twin junctions. Revealing the atomistic mechanisms of how twin–twin interactions lead to different twin junctions is crucial for our understanding of mechanical behaviour of materials. In this paper, we report the atomistic mechanisms responsible for the formation of two different twin–twin interactions/junctions in Cu nanopillars using atomistic simulations. One junction contains two twin boundaries along with one Σ9 boundary, while the other contains five twin boundaries (fivefold twin). These junctions were observed during the tensile deformation of [100] and [11¯0] Cu nanopillars, respectively.

An atomic view of dealloying

Nanomaterials The dealloying of metals to create nanoporous materials with bicontinuous surfaces is often modeled as a surface dissolution and diffusion process, but many of the details lack experimental verification. Liu et al. used liquid-cell high-resolution scanning transmission electron microscopy to follow the nitric acid–driven dissolution of silver from gold-silver alloy (Au0.2Ag 0.8) nanospheres, nanocubes, and fivefold twin nanorods. Whereas the nanoparticles had more surface defects than the nanorods and began to dissolve immediately, the nanorods had an induction period in which surface dealloying created defects that then allowed bulk silver to dealloy. Dealloying led to large decreases in particle volumes that were attributed to the inward movement of exterior atoms, creating a denser, less porous outer shell. Nano Lett. 10.1021/acs.nanolett.9b05216 (2020).

Growth and morphology tuning of ordered nickel nanocones routed by one-step pulse electrodeposition

Metallic surface nano-array structures receive considerable interests for their versatile applications, and the cost-effective fabrication of such coatings is a constant pursuit. In this work, a one-step template-free pulse electrodeposition (PED) approach was utilized to fabricate a nickel plating of fine-crystal ordered nanocone. By adjusting the pulse current waveform, the mass transportation and nucleation on the cathode during the PED were manipulated so the fine morphology of the Ni nanocones can be readily tuned with nanometric uniformity. Detailed crystallographic analysis verified that a single nanocone grew along 〈1 1 0〉 direction based on a five-fold annular twinning structure. The conical geometry as well as the nanoscale fine structure endowed the PED-obtained Ni plating with superior physiochemical properties such as superhydrophobicity, light absorbency, as well as stable hydrogen evolution activity, proving PED to be a facile approach of engineering functional metallic surface at nanoscale.

Finding the fivefold path

Nanoparticles Crystals formed in nature or synthesized in a lab can have domains with different orientations that are called twins. Having five of these domains is relatively common, but how these fivefold twins form is still a mystery. Song et al. combined in situ transmission electron microscope observations with simulations to find two different pathways for forming fivefold twins in gold, platinum, and palladium nanoparticles. This combination provides a key insight into the twin-forming process, which might be exploited for developing nanoparticles suitable for a variety of applications. Science , this issue p. [40][1] [1]: /lookup/doi/10.1126/science.aax6511

Oriented attachment induces fivefold twins by forming and decomposing high-energy grain boundaries.

Natural and synthetic nanoparticles composed of fivefold twinned crystal domains have distinct properties. The formation mechanism of these fivefold twinned nanoparticles is poorly understood. We used in situ high-resolution transmission electron microscopy combined with molecular dynamics simulations to demonstrate that fivefold twinning occurs through repeated oriented attachment of ~3-nanometer gold, platinum, and palladium nanoparticles. We discovered two different mechanisms for forming fivefold twinned nanoparticles that are driven by the accumulation and elimination of strain. This was accompanied by decomposition of grain boundaries and the formation of a special class of twins with a net strain of zero. These observations allowed us to develop a quantitative picture of the twinning process. The mechanisms provide guidance for controlling twin structures and morphologies across a wide range of materials.

Strong strain hardening in ultrafast melt-quenched nanocrystalline Cu: The role of fivefold twins

Nanocrystalline and nanotwinned metals exhibit ultrahigh strength but suffer from low ductility due to the absence of the strain hardening effect. Here, we report sustained strong strain hardening up to 20% compressive strain in a melt-quenched nanocrystalline Cu structure, which contains numerous fivefold twins, stacking faults, and twin boundaries. Our molecular dynamics simulations reveal that the strong strain hardening results from the synergistic effect of constant nucleation and impedance of dislocations, restricted twin boundary migration, and abundant dislocation reactions in fivefold twin networks. Specifically, we find that fivefold twins both nucleate and impede dislocations, and the migration of fivefold twin boundary is restricted by the core of fivefold twins. Moreover, we observe a new migration mechanism, in which fivefold twin boundary migrates by two atomic planes directly, enabled by the gliding of two different Shockley partial dislocations in the opposite directions. Finally, dislocation transmission, which is adverse to strain hardening, occurs very scarcely in fivefold twins. This is caused by the large misfit strains in fivefold twins and abundant immobile dislocations generated by frequent dislocation reactions in fivefold twin networks. This work reveals the advantage of fivefold twins over nanotwins to overcome the strength-ductility trade-off.

Crystalline clusters in mW water: Stability, growth, and grain boundaries.

With numerical simulations of the mW model of water, we investigate the energetic stability of crystalline clusters both for Ice I (cubic and hexagonal ice) and for the metastable Ice 0 phase as a function of the cluster size. Under a large variety of forming conditions, we find that the most stable cluster changes as a function of size: at small sizes, the Ice 0 phase produces the most stable clusters, while at large sizes, there is a crossover to Ice I clusters. We further investigate the growth of crystalline clusters with the seeding technique and study the growth patterns of different crystalline clusters. While energetically stable at small sizes, the growth of metastable phases (cubic and Ice 0) is hindered by the formation of coherent grain boundaries. A fivefold symmetric twin boundary for cubic ice, and a newly discovered coherent grain boundary in Ice 0, promotes cross nucleation of cubic ice. Our work reveals that different local structures can compete with the stable phase in mW water and that the low energy cost of particular grain boundaries might play an important role in polymorph selection.

Formation and disintegration investigation of fivefold annealing twins in copper nanoparticles

Fivefold annealing twins (FAT) have been assumed to form by grain boundary migration according to the Ashby model. However, the mechanism of boundary migration lacks experimental support. Moreover, the FAT disintegration process has never been reported. In our experiment, the complete formation and disintegration process of FAT in copper nanoparticles was investigated by in-situ transmission electron microscopy with high temporal and spatial resolution. The results show that FAT formation and disintegration arises from the layer-by-layer migration of twin boundaries, induced by partial dislocation emission. This experimental observation is significant to the basic understanding of twinning mechanisms.

Near-ideal compressive strength of nanoporous silver composed of nanowires

Nanoporous materials exhibit promising applications in energy storage, catalysis, and sensing. They are typically synthesized by dealloying, a costly and environmentally detrimental technology, valid only within a narrow compositional range of alloys. Surmounting these disadvantages, we assembled nanoporous silver materials via bottom-up nanoscale joining of nanowires, a technique also suitable for other metals. Furthermore, the resulting nanoporous materials exhibit an unprecedented, near-ideal compressive yield strength (∼2.6 GPa). Such an ultra-high strength, however, does not belong to the nanoporous materials composed of nanowires with the minimum length in our samples, challenging the smaller-is-stronger tenet. According to molecular dynamics simulations, such a strength degradation as nanowires shorten is attributed to the internal compressive stress arising from the five-fold twins within nanowires. Such internal stress maximizes at the center and diminishes near free surfaces, making the center part harder to compress than that adjacent to the free surfaces. The volume fraction of the latter increases as the nanowire shortens, diminishing the overall Young's modulus. For nanowires having aspect ratios smaller than six, a reduced Young's modulus lowers the yield strength since the yield strain is independent of aspect ratios. However, if the aspect ratio exceeds six, compression induces bending, reducing both yield strength and yield strain. Overall, this work not only provides new physical insights on the structure-mechanical property relationship for nanoporous silver, but also paves a new way for bottom-up synthesizing nanoporous metals with ultra-high compressive strength efficiently, economically, and environmental-friendly.

Evolution of solidification defects in deformation of nano-polycrystalline aluminum

Formation of solidification defects and their evolution in uniaxial tensile deformation of solidified polycrystalline aluminum (Al) were investigated by molecular dynamics (MD) simulations. First, solidification process was simulated both isothermally and with different quench rates. At the initial stages of nucleation, coherent twin boundaries and/or fivefold twins formed depending on the quench rate or the undercooling temperature. The solidified polycrystalline Al consisted of randomly distributed grains, twin boundaries, and vacancies. Evolution of nanostructures and defects in uniaxial tensile deformation of solidified Al under different temperatures and strain rates were studied. Void formation at grain boundaries and detwinning of preexisting solidification twins and deformation twins were observed during the uniaxial deformation. It was also found that the temperature of deformation has a stronger effect than the applied strain rate on the strength of solidified samples. For solidified cases with grain sizes lower than 10 nm, the yield strength and Young’s modulus increased with increasing grain size, indicating an inverse Hall-Petch relationship. Similar to experimental data, MD simulations showed a higher yield strength for single crystal Al and a large plastic deformation for polycrystalline Al.

Fivefold annealing twin in nanocrystalline Au/Pd film

In this study, we report the experimental observation of five-fold annealing twin in the nanocrystalline Au/Pd thin film without external stress by annealing the film for 20 min at 473 K using atomic-resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging, and energy dispersive X-ray spectroscopy (EDS) employing Cs aberration-corrected electron microscopy. As per the knowledge of the authors, this is the first time that five-fold annealing twin has been observed for Au/Pd thin films. Furthermore, the spectroscopic elemental analysis shows the uniform distribution of palladium in the film, indicating no palladium grain boundary segregation. Strain analyses have been performed by geometric phase analysis (GPA) across the five-fold structures. GPA method shows the non-uniform strain distribution across the various segments of the five-fold structure.

Solidification dynamics and microstructure evolution in nanocrystalline cobalt

Solidification and microstructures of fast quenched cobalt (from 1950K to 600K) are studied using molecular dynamics simulations. Two types of microstructures, a nanocrystalline type consisting of multiple grains and a lamellar type are obtained. The lamellar type microstructure shows a dominant layering direction with fcc phases separated by stacking faults, coherent twin boundaries or hcp phases. The nanocrystalline type is dominant at fast quenching rates. Both microstructures are highly twinned. Twins can originate either from ab initio faults of several morphologies in the nuclei or from stacking accidents in 〈111〉 directions during growth. It is supported that fivefold twins form by a successive growth of the fcc subunits, but not by an equilateral layer-by-layer growth from a five-folded symmetric core that exists at the very beginning of nucleation. Annealing of the as-quenched samples above the phase transformation temperature leads to gradual growth of the fcc phase and local reversible fcc-hcp transformation facilitated by existing Shockley dislocations. Under uniaxial tensile loading, the nanocrystalline samples show an early initial yielding, followed by continuous work hardening, reaching an ultimate tensile strength of about 3000 MPa. The lamellar samples, in contrast, show a much more intermittent plastic flow. The strongest sample has a nanotwinned structure resembling TEM images of vapor deposited films of fcc metals. The ultimate tensile strength is over 5000 MPa, assisted by coherent twin boundaries serving as strong obstacles to dislocation motion.

Atomistic Mechanisms of Twin-Twin Interactions in Cu Nanopillars

Twinning is an important mode of plastic deformation in metallic nanowires. When twinning occurs on multiple systems, it is possible that twins belonging to different twin systems interact and forms a complex twin-twin junctions. However, limited attention has been paid to characterize the twin-twin interactions in nanowires. In this paper, we report two different twin-twin interactions/junctions, one containing two twin boundaries along with one ∑9 boundary and the other with five twin boundaries (five-fold twin), which are observed during the deformation of Cu nanowires. Further, we explain the detailed mechanisms responsible for the formation of such junctions using atomistic simulations.

Atomic scale analyses of {\bb Z}-module defects in an NiZr alloy.

Some specific structures of intermetallic alloys, like approximants of quasicrystals, have their unit cells and most of their atoms located on a periodic fraction of the nodes of a unique {\bb Z}-module [a set of the irrational projections of the nodes of a (N > 3-dimensional) lattice]. Those hidden internal symmetries generate possible new kinds of defects like coherent twins, translation defects and so-called module dislocations that have already been discussed elsewhere [Quiquandon et al. (2016). Acta Cryst. A72, 55-61; Sirindil et al. (2017). Acta Cryst. A73, 427-437]. Presented here are electron microscopy observations of the orthorhombic phase NiZr - and its low-temperature monoclinic variant - which reveal the existence of such defects based on the underlying {\bb Z}-module generated by the five vertices of the regular pentagon. New high-resolution electron microscopy (HREM) and scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) observations demonstrate the agreement between the geometrical description of the structure in five dimensions and the experimental observations of fivefold twins and translation defects.

Origin and evolution of a fivefold twin on the surface of a nickel alloy

At present, one thinks that fivefold twins (FTs) are formed from the multiple partial dislocations emitted from the grain boundaries. This results in that there are no reports on the deformation twinning of FTs from a single crystal. In this study, deformation twinning of an FT is performed from a single crystal, which is induced on the surface of an alloy under nanoindentation. The origin and evolution of an FT is elucidated on the surface of a nickel alloy. Incoherent twin boundaries (ITBs) play the most important role during the formation of an FT.