Size‐Induced Switching of Nanowire Growth Direction: a New Approach Toward Kinked Nanostructures

Exploring self‐assembled nanostructures with controllable architectures has been a central theme in nanoscience and nanotechnology because of the tantalizing perspective of directly integrating such bottom‐up nanostructures into functional devices. Here, the growth of kinked single‐crystal In₂O₃ nanostructures consisting of a nanocone base and a nanowire tip with an epitaxial and defect‐free transition is demonstrated for the first time. By tailoring the growth conditions, a reliable switching of the growth direction from [111] to [110] or [112] is observed when the Au catalyst nanoparticles at the apexes of the nanocones shrink below ≈100 nm. The natural formation of kinked nanoarchitectures at constant growth pressures is related to the size‐dependent free energy that changes for different orientations of the nanowires. The results suggest that the mechanism of forming such kinked nanocone–nanowire nanostructures in well‐controlled growth environment may be universal for a wide range of functional materials.     

Growth mechanism and properties of the well-aligned-carbon-coated Si nanocones by MPCVD

In order to clarify the possibility to form Si nanocones under the same gas sources (CH₄ and H₂) and deposition system (microwave plasma chemical vapor deposition (MPCVD)), a process were successfully developed to synthesize the well-aligned amorphous carbon-coated Si nanocones (a:C-SNCs), and their growth mechanism is proposed. This process includes depositing 10 nm Co-catalyst on Si wafer by physical vapor deposition (PVD) and then followed by H-plasma pretreatment to form Co nanoparticles. The pretreated specimens were then used to synthesize various nanostructures under a higher negative substrate bias. The deposited nanostructures and their compositions were characterized by SEM, HRTEM, ED, EDS and Raman spectroscopy. The results indicate that the most important parameters for forming a:C-SNCs include a lower CH₄ / H₂ ratio, a higher negative substrate bias and assistance of the carbon-soluble nano-sized catalysts, such as Co. Under a higher enough negative substrate bias (≥ 240 V), the etching rates of the catalyst particles and the substrate by the positive species are greater than the carbon deposition rate; a:C-SNCs can be formed. We propose that the cone shape of the nanostructures is essentially resulted from a progressive reduction in catalyst particle sizes under the conditions of higher etching rate than deposition rate on the catalyst surfaces, which may be partially due to a reduction in the Co melting temperature by the presence of carbon in the Co matrix. This mechanism is supported by the facts that a:C-SNCs find no catalysts or very small catalysts on the tips; the catalyst sizes show no significant reduction in sizes after the same a:C-SNCs deposition conditions except no presence of carbon; the diameter of the cone base has no significant differences in size as the original catalyst size after H-plasma pretreatment. Our mechanism gives the guideline to form the nanocone structures by MPCVD with same gas sources (CH₄ and H₂).     

0D/1D Heterojunction Implant with Electro-Mechanobiological Coupling Cues Promotes Osteogenesis

Mimicking the natural bone extracellular matrix containing intrinsic topography and electrical signals is an effective way to modulate bone regeneration. However, simultaneously coupling of the intrinsic mechanobiology and electrical cues of implant to modulate bone regeneration remains ignored. Here, the authors report in situ designation of titanium dioxide (TiO₂) nanocone/bismuth oxide (Bi₂O₃) nanodot heterojunctions on bone implant surface to electro-biomechanically trigger osseointegration at bone/implant interface. TiO₂ nanocone/Bi₂O₃ nanodot heterojunctions exhibit built-in electric field at the nanoscale interface and elastic modulus equivalent to that of bone tissue. The nano-heterojunctions significantly promoted the attachment, spreading, and osteogenic differentiation of bone marrow mesenchymal stem cells in vitro, and the osteogenesis in vivo. The authors also show that the effects of nano-heterojunctions on osteogenesis are mediated by yes-associated protein biomechanical signal pathway and intracellular enrichment induced Phosphatidylinositol 3-kinase signal pathway. Their findings highlight the coupling of topographical and electric parameters of biomaterials for modulating cell behaviors.     

A study on elastic properties of carbon nanocones based on a temperature-related quasi-continuum model

In the present paper, general analytical formulas for calculating the Young's modulus and Poisson's ratio of single-walled carbon nanocones (SWCNCs) at finite temperatures are derived based on the proposed temperature-related multiscale quasi-continuum (QC) model. To this end, a temperature-related higher-order Cauchy-Born (THCB) rule is employed to establish the hyper-elastic constitutive model of SWCNCs. With use of the proposed approach, the influences of the temperature, apex angle, rotation angle of cutting lines and top end radius on the Young's moduli and Poisson's ratios of SWCNCs are investigated systematically.     

Predicting mechanical properties of single-walled carbon nanocones using a higher-order gradient continuum computational framework

The higher-order gradient continuum theory is employed to study the structural parameters and elastic properties of single-walled carbon nanocones (SWCNCs), where the higher-order Cauchy–Born rule is used to link the deformation of the carbon atomic structure to that of the continuum level. Unlike single-walled carbon nanotubes (SWCNTs), mechanical properties of SWCNCs vary along its side edge’s direction, owing to the monotonically increasing radius. In the constitutive model, a representative cell in an initial graphite sheet is selected to study the mechanical property of this domain of SWCNCs. By minimizing the potential energy of the representative cell in the undeformed SWCNC, structural parameters and elastic properties of the domain are obtained. The varying chiralities seem to have a large impact on mechanical properties of SWCNCs. Five kinds of SWCNCs are chosen in our study to test the influence of the apex angle on mechanical properties. The computational results demonstrate that mechanical properties of SWCNCs trend to the constant of graphite sheet when the radius is extremely large but this trend becomes mild as the apex angle increases.     

金刚石薄膜为掩膜离子束室温溅射可控制备硅纳米圆锥阵列

以金刚石薄膜为掩膜,采用低能Ar+室温倾角溅射的方法制备密度和形貌可控的硅纳米圆锥阵列.扫描电子显微镜(SEM)结果表明,离子束溅射后得到的硅纳米圆锥密度与作为掩膜的金刚石薄膜颗粒密度相当;硅纳米圆锥的形貌与离子束入射角有密切关系,随着入射倾角由30°增大到75°;得到的硅纳米圆锥的锥角由73°减小到23°,其长径比从500 am/360 nm增大到2400nm/600nm.由于金刚石比硅材料的溅射速率更低,因此以金刚石薄膜为掩膜可以制备较大长径比的硅纳米圆锥阵列;随着入射角的增大,离子束溅射诱导的表面原子有效扩散系数减小和溅射速率增大是硅纳米圆锥的锥角减小、长径比增大的主要原因.     

Modal analysis of carbon nanotubes and nanocones using FEM

Modal analysis of single-walled carbon nanotubes (SWCNTs) and nanocones (SWCNCs) was performed using a finite element method (FEM) with ANSYS. The vibrational behaviors of fixed beam and cantilever SWCNTs with different section types of a circle and an ellipse were modeled using three-dimensional elastic beams of carbon bonds and point masses. Also, the vibrational behaviors of fixed beam and cantilever SWCNCs with different disclination angles of 120°, 180°, and 240° were modeled using the same method. The beam element natural frequencies were calculated by considering the mechanical characteristics of the covalent bonds between the carbon atoms in the hexagonal lattice. Each mass element of the carbon atoms was assigned as a point mass at the nodes of the FEM elements. The natural frequencies of zigzag and armchair SWCNTs and SWCNCs were also computed. There were some differences between the findings obtained in this study and the molecular structural mechanics data available in the literature. The natural frequencies of SWCNCs were estimated depending on the geometrical type and disclination angle with different boundary conditions. The natural frequencies of the SWCNCs with disclination angles of 120°, 180°, and 240° increased significantly at higher modes of vibration.     

Topological modeling of 1-Pentagon carbon nanocones – topological efficiency and magic sizes

In this article topological modeling techniques have been applied to the study of one pentagon carbon nanocones (apical angle 19°) to derive important results about preferred sizes and chemical reactivity. This theoretical model looks to the nanocone just like a 3-connected graph and considers the topological efficiency (or topological roundness) of such a system as the long-range topological potential whose local minima correspond to magic sizes of the nanocone with high probability of formation. This study moreover shows that topology alone can determine a migration of the stable regions of the nanocone along the nanocone itself, leaving in such a way the apical pentagon in a topologically reactive status. This study expands and systematizes previous works on the same subject.