Deformation nanomechanics and dislocation quantification at the atomic scale in nanocrystalline magnesium

Classical molecular dynamics(MD)simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium(Mg)of varying grain size levels.The mean grain size of the sample is varied from 6.4 nm to 45 nm,with each sample containing about 43 million atoms in the modeling system.The deformation nanomechanics reveals two distinct deformation mechanisms.For larger grain-sized samples,dislocation dominated deformation is observed while,in smaller grain-sized samples,grain boundary-based mechanisms such as grain boundary sliding,grain boundary rotation are observed.The transition of normal and inverse Hall-Petch relation occurs at around lOnm.Dislocation density quantification shows that the dislocation density in the sample drastically reduces with decreasing grain size.Elastic modulus of nanocrystalline Mg with mean grain size above 20 nm remains comparable to that of the coarse-grained polycrystalline bulk,followed by a rapid reduction below that grain size.The present work reveals the nanomechanics of nanocrystalline Mg,facilitating the design and development of Mg-based nanostructured alloys with superior mechanical properties.

Nanomechanics of Fiber-like Nanomaterials

Property characterization of nanomaterials is challenged by the small size of the structure be-cause of the difficulties in manipulation Here we demonstrate a novel approach that allows a direct measurement of the mechanical properties of individual nanotube-like structures by in-situ transmission electron microscopy (TEM). The technique is powerful in a way that it can directly correlate the atomic-scale microstructure of the carbon nanotube with its physical properties, providing a one-to-one correspondence in structure-property characterization Applications of the technique will be demonstrated on mechanical properties, the electron field emission and the ballistic quantum conductance in individual nanotubes.

CURRENT TRENDS OF MICRO-AND NANOMECHANICS

Introduction Scaling down to the micro- and nanoscale is a strong current trend in the development of science and technology. ＇Small is energy efficient and cost effective＇ has long been for the motto of the semiconductor industry, including micro- and nanoelectronics, micro-electro-mechanical systems （MEMS） and nanoelectro-mechanical systems （NEMS）.

3D printed fiber-optic nanomechanical bioprobe

Ultrasensitive nanomechanical instruments,e.g.atomic force microscopy(AFM),can be used to perform delicate biomechanical measurements and reveal the complex mechanical environment of biological processes.However,these instruments are limited because of their size and complex feedback system.In this study,we demonstrate a miniature fiber optical nanomechanical probe(FONP)that can be used to detect the mechanical properties of single cells and in vivo tissue measurements.A FONP that can operate in air and in liquids was developed by programming a microcantilever probe on the end face of a single-mode fiber using femtosecond laser two-photon polymerization nanolithography.To realize stiffness matching of the FONP and sample,a strategy of customizing the microcantilever’s spring constant according to the sample was proposed based on structure-correlated mechanics.As a proof-of concept,three FONPs with spring constants varying from 0.421 N m^(−1)to 52.6 N m^(−1)by more than two orders of magnitude were prepared.The highest microforce sensitivity was 54.5 nmμN^(−1)and the detection limit was 2.1 nN.The Young’s modulus of heterogeneous soft materials,such as polydimethylsiloxane,muscle tissue of living mice,onion cells,and MCF-7 cells,were successfully measured,which validating the broad applicability of this method.Our strategy provides a universal protocol for directly programming fiber-optic AFMs.Moreover,this method has no special requirements for the size and shape of living biological samples,which is infeasible when using commercial AFMs.FONP has made substantial progress in realizing basic biological discoveries,which may create new biomedical applications that cannot be realized by current AFMs.

Small scale effects on buckling and postbuckling behaviors of axially loaded FGM nanoshells based on nonlocal strain gradient elasticity theory

By means of a comprehensive theory of elasticity, namely, a nonlocal strain gradient continuum theory, size-dependent nonlinear axial instability characteristics of cylindrical nanoshells made of functionally graded material(FGM) are examined. To take small scale effects into consideration in a more accurate way, a nonlocal stress field parameter and an internal length scale parameter are incorporated simultaneously into an exponential shear deformation shell theory. The variation of material properties associated with FGM nanoshells is supposed along the shell thickness, and it is modeled based on the Mori-Tanaka homogenization scheme. With a boundary layer theory of shell buckling and a perturbation-based solving process, the nonlocal strain gradient load-deflection and load-shortening stability paths are derived explicitly. It is observed that the strain gradient size effect causes to the increases of both the critical axial buckling load and the width of snap-through phenomenon related to the postbuckling regime, while the nonlocal size dependency leads to the decreases of them. Moreover, the influence of the nonlocal type of small scale effect on the axial instability characteristics of FGM nanoshells is more than that of the strain gradient one.

Nanomechanical behaviors of (110) and (111) CdZnTe crystals investigated by nanoindentation

The nanomechanical behaviors of （110） and （111 ） CdZnTe crystals were investigated by nanoindentation. It was found that the indenter tip was adhered by the removed materials in scanning testing area although the scanning force on the tested surface was very small （1000 nN）, which would affect the testing result of nanoindentation, so the indenter was clean before nanoindentation test. The experimemtal results showed that the hardness and Young＇s modulus decreased with the increase of indentation loads on the same plane. Because of the anisotropy of the CdZnTe crystal, the average hardness of （110） plane is 35% lower than that of （111） plane, and there are about 30% difference of the hardness along different crystallographic directions on the same plane. The hardness in 0° and 120° testing directions was the same due to the threefold symmetry of a Berkovich indenter. And the anisotropy affected the surface quality during machining of CdZnTe crystal.

Diamond semiconductor and elastic strain engineering

Diamond,as an ultra-wide bandgap semiconductor,has become a promising candidate for next-generation microelec-tronics and optoelectronics due to its numerous advantages over conventional semiconductors,including ultrahigh carrier mo-bility and thermal conductivity,low thermal expansion coefficient,and ultra-high breakdown voltage,etc.Despite these ex-traordinary properties,diamond also faces various challenges before being practically used in the semiconductor industry.This review begins with a brief summary of previous efforts to model and construct diamond-based high-voltage switching diodes,high-power/high-frequency field-effect transistors,MEMS/NEMS,and devices operating at high temperatures.Following that,we will discuss recent developments to address scalable diamond device applications,emphasizing the synthesis of large-area,high-quality CVD diamond films and difficulties in diamond doping.Lastly,we show potential solutions to modulate diamond’s electronic properties by the“elastic strain engineering”strategy,which sheds light on the future development of diamond-based electronics,photonics and quantum systems.

Compressive deformation of ultralong amyloid fibrils

Involved in various neurodegenerative diseases, amyloid fibrils and plaques feature a hierarchical structure, ranging from the atomistic to the micrometer scale.At the atomistic level,a dense and organized hydrogen bond network is resembled in a beta-sheet rich secondary structure, which drives a remarkable stiffness in the range of 10-20GPa,larger than many other biological nanofibrils, a result confirmed by both experiment and theory.However, the understanding of how these exceptional mechanical properties transfer from the atomistic to the nanoscale remains unknown.Here we report a multiscale analysis that, from the atomistic-level structure of a single fibril,extends to the mesoscale level,reaching size scales of hundreds of nanometers.We use parameters directly derived from full atomistic simulations of Aβ（1-40） amyloid fibrils to parameterize a mesoscopic coarse-grained model,which is used to reproduce the elastic properties of amyloid fibrils.We then apply our mesoscopic model in an analysis of the buckling behavior of amyloid fibrils with different lengths and report a comparison with predictions from continuum beam theory. An important implication of our results is a severe reduction of the effective modulus due to buckling,an effect that could be important to interpret experimental results of ultralong amyloid fibrils.Our model represents a powerful tool to mechanically characterize molecular structures on the order of hundreds of nanometers to micrometers on the basis of the underlying atomistic behavior.The work provides insight into structural and mechanical properties of amyloid fibrils and may enable further analysis of larger-scale assemblies such as amyloidogenic bundles or plaques as found in disease states.

NANO SCIENCE AND ENGINEERING IN SOLID MECHANICS

According to National Science Foundation （NSF） Director A. Bement, ‘Transformative research is... research driven by ideas that stand a reasonable chance of radically changing our understanding of an important existing scientific concept or leading to the creation of a new paradigm or field of science is also characterized by its challenge to current understanding or its pathway to new frontiers.＇ Nanotechnology is one of such frontiers. It is the creation of new materials, devices and systems at the molecular level--phenomena associated with atomic and molecular interactions strongly influence macroscopic material properties with significantly improved mechanical, optical, chemical, electrical... properties. Former NSF Director Rita Colwell in 2002 declared, ‘nanoscale technology will have an impact equal to the Industrial Revolution＇. The transcendent technologies include nanotechnology, microelectronics, information technology and biotechnology as well as the enabling and supporting mechanical and civil infrastructure systems and materials. These technologies are the primary drivers of the twenty first century and the new economy. Mechanics is an essential eleraent in all of the transcendent technologies. Research opportunities, education and challenges in mechanics, including experimental, numerical and analytical methods in nanomechanics, carbon nano-tubes, bio-inspired materials, fuel cells, as well as improved engineering and design of materials are presented and discussed in this paper.

On the truth of nanoscale for nanobeams based on nonlocal elastic stress field theory:equilibrium,governing equation and static deflection

This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams： （i） why does the presence of increasing nonlocal effects induce reduced nanostructural stiffness in many, but not consistently for all, cases of study, i.e., increasing static deflection, decreasing natural frequency and decreasing buckling load, although physical intuition according to the nonlocal elasticity field theory first established by Eringen tells otherwise？ （ii） the intriguing conclusion that nanoscale effects are missing in the solutions in many exemplary cases of study, e.g., bending deflection of a cantilever nanobeam with a point load at its tip; and （iii） the non-existence of additional higher-order boundary conditions for a higher-order governing differential equation. Applying the nonlocal elasticity field theory in nanomechanics and an exact variational principal approach, we derive the new equilibrium conditions, do- main governing differential equation and boundary conditions for bending of nanobeams. These equations and conditions involve essential higher-order differential terms which are opposite in sign with respect to the previously studies in the statics and dynamics of nonlocal nano-structures. The difference in higher-order terms results in reverse trends of nanoscale effects with respect to the conclusion of this paper. Effectively, this paper reports new equilibrium conditions, governing differential equation and boundary condi- tions and the true basic static responses for bending of nanobeams. It is also concluded that the widely accepted equilibrium conditions of nonlocal nanostructures are in fact not in equilibrium, but they can be made perfect should the nonlocal bending moment be replaced by an effective nonlocal bending moment. These conclusions are substantiated, in a general sense, by other approaches in nanostructural models such as strain gradient theory, modified couple stress models and experiments.

Molecular Dynamic Study of Pull-In Instability of Nano-Switches

Capacitive nano-switches have been of great interest as replacements for conventional semiconductor switches. Accurate determination of the pull-in voltage is critical in the design process. In the present investigation, pull-in instability of nano-switches made of two parallel plates subjected to electrostatic force is studied. For this purpose, two parallel rectangular nanoplates with opposite charges are modeled based on molecular dynamics (MD) technique. Different initial gaps between nanoplates and its effect on pull-in phenomena are studied in addition to taking different values of geometrical and physical parameters into account to evaluate pull-in voltages. Here molecular dynamic simulations as an atomic interaction approach are employed for modeling of nano-switches in order to study pull-in instability considering atomic interaction and surface tension. Boundary conditions and also the van der Waals force are considered as important parameters to investigate their effects on pull-in voltage values.

A doublet mechanics model for the ultrasound characterization of malignant tissues

Non invasive ultrasound-based imaging systems are being more commonly used in clinical bio-microscopy applications for both ex vivo and in vivo analysis of tissue pathological and physiological states. These modalities usually employ high-frequency ultrasound systems to overcome spatial resolution limits of conventional clinical diagnostic approaches. Biological tissues are non continuous, non homogeneous and exhibit a multiscale organization from the sub-cellular level (￡1 mm) to the organ level (31 cm). When the ultrasonic wavelength used to probe the tissues becomes comparable with the tissue's microstructure scale, the propagation and reflection of ultrasound waves cannot be fully interpreted employing classical models developed within the continuum assumption. In this study, we present a multiscale model for analyzing the mechanical response of a non-continuum double-layer system exposed to an ultrasound source. The model is developed within the framework of the Doublet Mechanics theory and can be applied to the non-invasive analysis of complex biological tissues.

NANOMECHANICAL PROPERTIES OF POLYANILINE AND AZO POLYELECTROLYTE MULTILAYER FILMS

Nanomechanical properties of mulfilayer films constructed of polyaniline （PAN/） and azobeneze-containing polyelectrolytes （PNACN and PPAPE） were studied by using nanoindentation method. The multilayer films were prepared by the electrostatic layer-by-layer self-assembly through alternately dipping in the polymer solutions. The multilayer films deposited onto the glass slides after proper dry were used for the nanomechanical property testing. The nanomechanical measurement indicated that the PANI/PNACN and PANI/PPAPE multilayers possessed the mean elastic modulus of 5.42 GPa and 4.35 GPa, and hardness of 0.26 GPa and 0.18 GPa, respectively. The nanoscratch properties of the PANI/PNACN and PANI/PPAPE multilayer films were also measured. The critical loads of PANUPNACN and PANI/PPAPE films were 103.52 mN and 100.59 mN. The degree of electrostatic cross-linking in the multilayers could be altered by exposing the films to aqueous solutions with different pH values. As a result, the modulus and hardness of the multilayer films were changed through the solvent treatment. Both modulus and hardness of the PANI/PNACN films obviously increased after dipping the multilayer films in solutions with pH iri a range from 9 to 11.

Controllably Coupling Superconducting Charge and Flux Qubits by Using Nanomechanical Resonator

We propose an effective mechanism to couple superconducting charge and flux qubits by using a quantized nanomechanical resonator. The coupling between the charge and flux qubits can be controlled by the external flux of the charge qubit. Under the strong coupling limR, an iSWAP gate can be generated by this scheme. The experimental feasibility in our scheme is also presented.

Mechanical-force-promoted peptide assembly: a general method

A general method was developed for promoting peptide assembly and protein polymerization to form nanoscale patterns on various surfaces with an atomic force microscope(AFM) operated in a liquid. By scanning solid surfaces with an AFM tip, we showed that peptide monomers assemble at a higher rate in the tip-scanned area compared to other regions. The promotion is attributed to the mechanical force applied by the scanning tip. This kind of mechanical-force-promoted assembly was also observed with different peptides on various substrates. The force promoting peptide assembly provides a simple and practical solution for preparing and building peptide and protein architectures for future nanodevices.

Generating Squeezed States of Nanomechanical Resonator via a Flux Qubit in a Hybrid System

We propose a scheme for generating squeezed states based on a superconducting hybrid system. Our system consists of a nanomeehanical resonator, a superconducting flux qubit, and a superconducting transmission line resonator. Using our proposal, one can easily generate the squeezed states of the nanomechanical resonator. In our scheme, the nonlinear interaction between the nanomechanical resonator and the superconducting transmission line resonator can be implemented by the flux qubit as ＇nonlinear media＇ with a tunable Josephson energy. The realization of the nonlinearity does not need any operations on the flux qubit and just needs to adiabatically keep it at the ground state, which can greatly decrease the effect of the decoherenee of the flux qubit on the squeezed ef^ciency.

Nanomechanical Properties of Amyloid Fibrils Formed in a Water Nanofilm on Mica Surface

The assessment of nanomechanical properties of a single amyloid fibril in a confined space provides important information for understanding the role of fibrils in a cell microenvironment. In this study, the structure and nanomechanical properties of different fibrils formed in water nanofilms on mica surface are carefully investigated by using the new atomic force microscopy imaging mode-peak force quantitative nanomechanics （PF-QNM）. We find that two types of fibrils with different morphologies are formed in water nanofilm on mica. The compression elasticities of these two types of fibrils are 3.9±0.9 and 2.5±0.6 GPa, respectively. The remarkable difference is possibly due to the structural discrepancy in two types of fibrils.

Influence of nanomechanical force on the electronic structure of InAs/GaAs quantum dots

We show nanomechanical force is useful to dynamically control the optical response of self-assembled quantum dots, giving a method to shift electron and heavy hole levels, interval of electron and heavy hole energy levels, and the emission wavelength of quantum dots （QDs）. The strain, the electron energy levels, and heavy hole energy levels of InAs/GaAs（001） quantum dots with vertical nanomechanical force are investigated. Both the lattice mismatch and nanomechanical force are considered at the same time. The results show that the hydrostatic and the biaxial strains inside the QDs subjected to nanomechanical force vary with nanomechanical force. That gives the control for tailoring band gaps and optical response. Moreover, due to strain-modified energy, the band edge is also influenced by nanomechanical force. The nanomechanical force is shown to influence the band edge. As is well known, the band offset affects the electronic structure, which shows that the nanomechanical force is proven to be useful to tailor the emission wavelength of QDs. Our research helps to better understand how the nanomechanical force can be used to dynamically control the optics of quantum dots.

Nanomechanical Properties of Molecular Deposition Film

Two nanomechanical properties of the moleculor deposition （ MD ） film deposited on the Au substrate were studied. The first is its nanotribological property investigated by an atomic force microscope, which indicates that the deposition of the MD film could reduce the frictional force. The second is its nanoindent property studied by a nano-indenter. The results show that, after the MD film is deposited on the Au substrate , the elastic modulus, hardness and load decreased all, moreover, the elastic deformation increased and the plastic deformation decreased, which indicates that the MD film can improve the nanomechanical properties of the Au substrate.

Bell States and Two-Qubit Logic Gate with Superconducting Charge Qubits Coupling to a Nanomechanical Resonator

We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the twocharge qubits by choosing carefully the interaction time.