Highly strained graphene samples of varying thickness and comparison of their behaviour

Mechanically straining graphene opens the possibility to exploit new properties linked to the stressed lattice of this two-dimensional material. In particular, theoretical analyses have forecast that straining graphene by more than 10% is a requirement for many novel applications that have not yet been experimentally demonstrated. Recently, we reported having achieved 12.5% strain in a trilayer graphene sample (3LG) in a controlled, reversible and non-destructive way. In this paper, we explore our method by straining samples of varying thicknesses and comparing their behavior, where strains of 14% and 11% were achieved for monolayer and four-layer graphene (4LG), respectively. For the analysis, optical tracking and the correspondent Raman spectra were taken. While doing so, we observed slippage between two layers in a bilayer sample of which one layer was clamped on one side only. The obtained results when stretching different samples to extreme strains demonstrated the exception...

Héctor Hugo Pérez-Garza, Eric Walter Kievit, Grégory F Schneider and Urs Staufer

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High aspect ratio SiNW arrays with Ag nanoparticles decoration for strong SERS detection

Well-ordered silicon nanowires (SiNWs) are applied as surface-enhanced Raman scattering (SERS) substrates. Laser interference lithography is used to fabricate large-area periodic nanostructures. By controlling the reaction time of metal assisted chemical etching, various aspect ratios of SiNWs are generated. Ag nanoparticles are decorated on the substrates via redox reaction to allow a good coverage of Ag over the SiNWs. As the height of the SiNWs increases, the light scattering inside the structures is enhanced. The number of the probing molecules within the detection volume is increased as well. These factors contribute to stronger light–matter interaction and thus lead to higher SERS signal intensity. However, the light trapping effect is more significant for higher SiNWs, which prevents the detection of the SERS signals. An optimized aspect ratio ∼5:1 (1 μ m height and 200 nm width) for the SiNW array is found. The well-ordered SiNWs demonstrate better SERS signal inten...

J Yang, J B Li, Q H Gong, J H Teng and M H Hong

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Probing the spatial extension of light trapping-induced enhanced Raman scattering in high-density Si nanowire arrays

This paper reports an experimental investigation of surface-enhanced Raman scattering in high-density Si nanowire arrays obtained by electroless etching. A direct relationship between light trapping capabilities of Si nanowires and enhanced Raman scattering was demonstrated. Optimized arrays allowed for a remarkable increase of Raman sensitivity in comparison to reference planar samples. As a result, the detection limit of molecular probes under resonant excitation (e.g. methylene blue) can be extended by three orders of magnitude. In addition, continuous ultrathin films, that cannot be analyzed in conventional Raman experiments, are made detectable. In the case of anatase thin films, the detection limit of 5 nm was reached. Raman spectra of Si/TiO 2 core/shell heterostructures demonstrate that the enhanced field resulting from surface multiple scattering is characterized by a large spatial extension (about fifty nanometers), making these materials a potential alternati...

Nicolò Bontempi, Marco Salmistraro, Matteo Ferroni, Laura E Depero and Ivano Alessandri

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Raman scattering study of InAs nanowires under high pressure

The pressure-dependent phonon modes of InAs nanowires have been investigated by Raman spectroscopy under high pressure up to ∼58 GPa. X-ray diffraction measurements show that InAs nanowires at 21 GPa exhibit a phase transition from a wurtzite to an orthorhombic crystal structure, with a corresponding drastic change in the first-order Raman spectra. In the low-pressure regime, a linear increase in phonon frequencies is observed, whereas splitting between longitudinal and transversal optical phonon modes decreases as a function of applied pressure. The calculated mode Grüneisen parameters and Born’s transverse effective charge indicate that the wurtzite InAs nanowires exhibit a more covalent nature under compression.

Dipanwita Majumdar, Abhisek Basu, Goutam Dev Mukherjee, Daniele Ercolani, Lucia Sorba and Achintya Singha

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Fabrication of double-tubular carbon nanofibers using quadruple coaxial electrospinning

This work reports the fabrication of double-tubular (or tube-in-tube) carbon nanofibers (CNFs). Tetra-layered nanofibers were manufactured using coaxial electrospinning with a concentric quadruple cylindrical nozzle system. Subsequent heat treatment eroded the first and third layers and converted the second and fourth layers into the carbonized structure, resulting in double-tubular CNFs. The morphologies and microstructures of the two tubes in the CNFs were investigated, revealing that the outer layer possessed denser and higher quality carbon crystals due to the coaxial electrospinning mechanism. Nanoparticles were readily incorporated between the two tubes in the double-tubular CNFs, providing a method for developing new multi-functional one dimensional materials.

Byoung-Sun Lee, Ho-Sung Yang and Woong-Ryeol Yu

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Complex nonlinear dynamics in the limit of weak coupling of a system of microcantilevers connected by a geometrically nonlinear tunable nanomembrane

Intentional utilization of geometric nonlinearity in micro/nanomechanical resonators provides a breakthrough to overcome the narrow bandwidth limitation of linear dynamic systems. In past works, implementation of intentional geometric nonlinearity to an otherwise linear nano/micromechanical resonator has been successfully achieved by local modification of the system through nonlinear attachments of nanoscale size, such as nanotubes and nanowires. However, the conventional fabrication method involving manual integration of nanoscale components produced a low yield rate in these systems. In the present work, we employed a transfer-printing assembly technique to reliably integrate a silicon nanomembrane as a nonlinear coupling component onto a linear dynamic system with two discrete microcantilevers. The dynamics of the developed system was modeled analytically and investigated experimentally as the coupling strength was finely tuned via FIB post-processing. The transition from the ...

Bongwon Jeong, Hanna Cho, Hohyun Keum, Seok Kim, D Michael McFarland, Lawrence A Bergman, William P King and Alexander F Vakakis

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Fast and low-temperature sintering of silver complex using oximes as a potential reducing agent for solution-processible, highly conductive electrodes

Highly conductive, solution-processed silver thin-films were obtained at a low sintering temperature of 100 °C in a short sintering time of 10 min by introducing oximes as a potential reductant for silver complex. The thermal properties and reducibility of three kinds of oximes, acetone oxime, 2-butanone oxime, and one dimethylglyoxime, were investigated as a reducing agent, and we found that the thermal decomposition product of oximes (ketones) accelerated the conversion of silver complex into highly conductive silver at low sintering temperature in a short time. Using the acetone oxime, the silver thin-film exhibited the lowest surface resistance (0.91 Ω sq −1 ) compared to those sing other oximes. The silver thin-film also showed a high reflectance of 97.8%, which is comparable to evaporated silver films. We also demonstrated inkjet printed silver patterns with the oxime-added silver complex inks.

Ji Hoon Yoo, Dae Sang Han, Su Bin Park, Jangwoo Chae, Ji Man Kim and Jeonghun Kwak

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Scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms for heat transfer control at the nanoscale

We report on scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms that have been studied with the phonon Monte Carlo technique. It has been found that the reduction of the thermal conductivity scales with the nanostructure transmissivity, a property entirely determined by the modulation geometry, irrespectively of the material choice. Tuning of the thermal conductivity is possible by the nanostructure width-modulation without strict limitations for the modulation profile. In addition, a very significant constriction thermal resistance due to width-discontinuity has been identified, in analogy to the contact thermal resistance between two dissimilar materials. The constriction thermal resistance also scales with the modulated nanostructure transmissivity. Our conclusions are generic indicating that a wide range of materials can be used for the modulated nanostructures. Direct heat flow control can be provided by designing the nanostructure width-...

Xanthippi Zianni, Valentin Jean, Konstantinos Termentzidis and David Lacroix

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Biophysical and morphological effects of nanodiamond/nanoplatinum solution (DPV576) on metastatic murine breast cancer cells in vitro

Nanoparticles have recently gained increased attention as drug delivery systems for the treatment of cancer due to their minute size and unique chemical properties. However, very few studies have tested the biophysical changes associated with nanoparticles on metastatic cancer cells at the cellular and sub-cellular scales. Here, we investigated the mechanical and morphological properties of cancer cells by measuring the changes in cell Young’s Modulus using AFM, filopodial retraction (FR) by time lapse optical light microscopy imaging and filopodial disorganization by high resolution AFM imaging of cells upon treatment with nanoparticles. In the current study, nanomechanical changes in live murine metastatic breast cancer cells (4T1) post exposure to a nanodiamond/nanoplatinum mixture dispersed in aqueous solution (DPV576), were monitored. Results showed a decrease in Young’s modulus at two hours post treatment with DPV576 in a dose dependent manner. Partial FR at 20 min and comp...

Alia Ghoneum, Huanqi Zhu, JungReem Woo, Nikita Zabinyakov, Shivani Sharma and James K Gimzewski

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Easy incorporation of single-walled carbon nanotubes into two-dimensional MoS 2 for high-performance hydrogen evolution

The limited intrinsic conductivity of two-dimensional (2D) MoS 2 nanosheets compromises its high electrocatalytic performance. In this work, we develop a facile method of simply dispersing MoS 2 nanosheets into a water–isopropanol solution of high-conducting single-walled carbon nanotubes (SWCNTs) for preparation of MoS 2 /SWCNT composites. The SWCNTs in the hybrid system serve as effective electron transport channels among 2D MoS 2 nanosheets and facilitate charge transfer at the catalyst–electrolyte interface. We investigated the influence of SWCNTs ratios on the catalytic activities and obtained a high-performance hybrid catalyst with a low Tafel slope of 40.82 mV/decade and prominent electrochemical durability. The demonstration of our hybrid electrocatalytic system, with its scalable capacity for facile preparation, provides a new pathway to enhance HER activity.

Yu Cai, Xi Yang, Tao Liang, Lu Dai, Lin Ma, Guowei Huang, Weixiang Chen, Hongzheng Chen, Huanxing Su and Mingsheng Xu

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In - situ TEM imaging of the anisotropic etching of graphene by metal nanoparticles

Few-layer graphene was successfully tailored with smooth edges along crystallographic directions by Joule heating-driven tungsten nanoparticles inside a transmission electron microscope. The dynamic process was monitored in real time at the atomic resolution level. These high-resolution in-situ observations show that the neighboring graphene layers joined together to form closed edges, which is in contrast to the supposed open edges formed with hydrogen passivation. The tungsten nanoparticles transformed to W 2 C in the intermediate stage of etching and to WC after etching, suggesting that carbon dissolution helped the continuous action of the metal nanoparticles in the catalytic anisotropic etching reaction.

Jiake Wei, Zhi Xu, Hao Wang, Xuezeng Tian, Shize Yang, Lifen Wang, Wenlong Wang and Xuedong Bai

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Formation of nanogaps in InAs nanowires by selectively etching embedded InP segments

We present a method to fabricate nanometer scale gaps within InAs nanowires by selectively etching InAs/InP heterostructure nanowires. We used vapor–liquid–solid grown InAs nanowires with embedded InP segments of 10–60 nm length and developed an etching recipe to selectively remove the InP segment. A photo-assisted wet etching process in a mixture of acetic acid and hydrobromic acid gave high selectivity, with accurate removal of InP segments down to 20 nm, leaving the InAs wire largely unattacked, as verified using scanning electron and transmission electron microscopy. The obtained nanogaps in InAs wires have potential as semiconducting electrodes to investigate electronic transport in nanoscale objects. We demonstrate this functionality by dielectrophoretically trapping 30 nm diameter gold nanoparticles into the gap.

M I Schukfeh, K Storm, A Hansen, C Thelander, P Hinze, A Beyer, T Weimann, L Samuelson and M Tornow

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Making good of losses: generating heat with nanostructures

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Anna Demming

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Atomistic simulations of electric field effects on the Youngʼs modulus of metal nanowires

We present a computational, atomistic study of electric field effects on the Youngʼs modulus of metal nanowires. The simulations are electromechanically coupled, where the mechanical forces on the atoms are obtained from realistic embedded atom method potentials, and where the electrostatic forces on the atoms are obtained using a point dipole electrostatic model that is modified to account for the different polarizability and bonding environment of surface atoms. By considering three different nanowire axial orientations ( ##IMG## [http://ift.tt/1FC83b5] {$\langle 100\rangle $} , ##IMG## [http://ift.tt/1FC83b7] {$\langle 110\rangle $} and ##IMG## [http://ift.tt/1uEAgFC] {$\langle 111\rangle $} ) of varying cross sectional sizes and aspect ratios, we find that the Youngʼs modulus of...

Xue Ben and Harold S Park

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Incident-angle dependent color tuning from a single plasmonic chip

We report on a broad color tuning effect covering the visible range from a single plasmonic chip. By simply tilting the orientation of the designed plasmonic chip within a certain range, the photon–plasmon coupling interactions between the incident light and the plasmonic nanostructures on the chip can be finely tuned, resulting in an angle-dependent continuous color filtering effect. The physical mechanism of the device is investigated through the full-wave calculations, which provide important guidance for the design and optimization of the proposed devices. The broad color tuning from the demonstrated single chip will potentially benefit visualization and display technologies, and is particularly useful for the construction of reflection-based spatial light modulators.

Guangyuan Si, Yanhui Zhao, Eunice Sok Ping Leong, Jiangtao Lv and Yan Jun Liu

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Core–shell photoanode developed by atomic layer deposition of Bi 2 O 3 on Si nanowires for enhanced photoelectrochemical water splitting

Core–shell nanowire (NW) arrays, which feature a vertically aligned n-type Si NW core and a p-type α -Bi 2 O 3 shell, are developed as a highly efficient photoanode that is suitable for water splitting. The morphology and structure of the heterostructure were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The deposition of Bi 2 O 3 nanolayers on the surface of the smooth Si NWs causes the surface of the NWs to become rough. The as-prepared core–shell NW photoelectrode has a relatively low reflectance in the visible light region, suggesting good light absorption. The core–shell NW arrays show greatly improved photoelectrochemical water-splitting performance. Photoelectrochemical stability for over 16 h under constant light illumination and fixed bias potential was...

Baicheng Weng, Fenghua Xu and Jianguang Xu

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Magnetic particle hyperthermia—a promising tumour therapy?

We present a critical review of the state of the art of magnetic particle hyperthermia (MPH) as a minimal invasive tumour therapy. Magnetic principles of heating mechanisms are discussed with respect to the optimum choice of nanoparticle properties. In particular, the relation between superparamagnetic and ferrimagnetic single domain nanoparticles is clarified in order to choose the appropriate particle size distribution and the role of particle mobility for the relaxation path is discussed. Knowledge of the effect of particle properties for achieving high specific heating power provides necessary guidelines for development of nanoparticles tailored for tumour therapy. Nanoscale heat transfer processes are discussed with respect to the achievable temperature increase in cancer cells. The need to realize a well-controlled temperature distribution in tumour tissue represents the most serious problem of MPH, at present. Visionary concepts of particle administration, in particular by...

Silvio Dutz and Rudolf Hergt

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Electrostatic actuated strain engineering in monolithically integrated VLS grown silicon nanowires

In this paper we demonstrate the fabrication and application of an electrostatic actuated tensile straining test (EATEST) device enabling strain engineering in individual suspended nanowires (NWs). Contrary to previously reported approaches, this special setup guarantees the application of pure uniaxial tensile strain with no shear component of the stress while e.g. simultaneously measuring the resistance change of the NW. To demonstrate the potential of this approach we investigated the piezoresistivity of about 3 μm long and 100 nm thick SiNWs but in the same way one can think about the application of such a device on other geometries, other materials beyond Si as well as the use of other characterization techniques beyond electrical measurements. Therefore single-crystal SiNWs were monolithically integrated in a comb drive actuated MEMS device based on a silicon-on-insulator (SOI) wafer using the vapor–liquid–solid (VLS) growth technique. Strain values were verified by a preci...

Stefan Wagesreither, Emmerich Bertagnolli, Shinya Kawase, Yoshitada Isono and Alois Lugstein

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Nanoscale arrangement of diblock copolymer micelles with Au nanorods

We fabricated a single-layered film consisting of spherical micelles of diblock copolymers and one-dimensional Au nanorods that were surface modified with the same polymer as the corona block of the copolymers. When the diameters of micelles were larger than the lengths of the nanorods, spherical micelles arranged in a hexagonal configuration surrounded by nanorods with their long axes perpendicular to the radial direction of the micelles. This arrangement provided selective organization of the Au nanorods and Ag nanoparticles which were selectively synthesized within the cores of the copolymer micelles. Thus, position-selective arrangement of Au nanorods and Ag nanoparticles was demonstrated at the nanometer scale such that a homogenous distribution of two different nanomaterials over a large area without aggregation was achieved.

Hwan Kim, Yirang Lim, Sehee Kim, Sung-Soo Kim and Byeong-Hyeok Sohn

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Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains

The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson’s ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isot...

Ting Hu, Yang Han and Jinming Dong

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