Optical properties of high aspect ratio plasma etched silicon nanowires: fabrication-induced variability dramatically reduces reflectance

In this work we investigate both experimentally and theoretically the optical properties of aligned, perpendicular to the substrate, high aspect ratio (AR), plasma etched Si nanowires (SiNWs) with controlled variability. We focus on the role of imperfections in fabrication, which manifest themselves as dimensional variability of SiNW, lattice defects or positional randomization. SiNW arrays are fabricated by e-beam lithography (perfectly ordered array) or colloidal particle self-assembly (quasi-ordered array) followed by cryogenic Si plasma etching, which offers fast etch rate (up to 3 μ m min −1 ) combined with clean, smooth, and controllable sidewall profile, but induces some dimensional variability on the diameters of the SiNWs. Sub-200 nm diameter SiNWs having AR as high as 37:1 are demonstrated. The total reflectance of SiNWs is below 2% in a wide range of the optical spectrum. We experimentally demonstrate improved light absorption when moving from a perfectl...

A Smyrnakis, E Almpanis, V Constantoudis, N Papanikolaou and E Gogolides

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DNA stretching and optimization of nucleobase recognition in enzymatic nanopore sequencing

In nanopore sequencing, where single DNA strands are electrophoretically translocated through a nanopore and the resulting ionic signal is used to identify the four DNA bases, an enzyme has been used to ratchet the nucleic acid stepwise through the pore at a controlled speed. In this work, we investigated the ability of alpha-hemolysin nanopores to distinguish the four DNA bases under conditions that are compatible with the activity of DNA-handling enzymes. Our findings suggest that in immobilized strands, the applied potential exerts a force on DNA (∼10 pN at +160 mV) that increases the distance between nucleobases by about 2.2 Å V −1 . The four nucleobases can be resolved over wide ranges of applied potentials (from +60 to +220 mV in 1 m KCl) and ionic strengths (from 200 mM KCl to 1 M KCl at +160 mV) and nucleobase recognition can be improved when the ionic strength on the side of the DNA-handling enzyme is low, while the ionic strength on the opposite side is high.

David Stoddart, Lorenzo Franceschini, Andrew Heron, Hagan Bayley and Giovanni Maglia

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Synthesis and magnetic properties of Fe 3 C–C core–shell nanoparticles

Fe 3 C–C core–shell nanoparticles were fabricated on a large scale by metal-organic chemical vapor deposition at 700 °C with ferric acetylacetonate as the precursor. Analysis results of x-ray diffraction, transmission electron microscope and Raman spectroscope showed that the Fe 3 C cores with an average diameter of ∼35 nm were capsulated by the graphite-like C layers with the thickness of 2–5 nm. The comparative experiments revealed that considerable Fe 3 O 4 –Fe 3 C core–shell nanoparticles and C nanotubes were generated simultaneously at 600 and 800 °C, respectively. A formation mechanism was proposed for the as-synthesized core–shell nanostructures, based on the temperature-dependent catalytic activity of Fe 3 C nanoclusters and the coalescence process of Fe 3 C–C nanoclusters. The Fe 3 C–C core–shell nanoparticles exhibited a saturation magnetization of 23.6 emu g −1 and a coercivity of 550 Oe ...

Jun Liu, Bowen Yu, Qiankun Zhang, Lizhen Hou, Qiulai Huang, Chunrui Song, Shiliang Wang, Yueqin Wu, Yuehui He, Jin Zou and Han Huang

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Data analysis methods for solid-state nanopores

We describe a number of techniques for the analysis of solid-state nanopore ionic current traces and introduce a new package of Matlab analysis scripts with GUI front ends. We discuss methods for the detection of the local baseline and propose a new detection algorithm that bypasses some of the classical weaknesses of moving-average detection. Our new approach removes detected events and re-creates an ideal event-free baseline subsequently used to recalculate the local baseline. Iterative operation of this algorithm causes both the moving average of the baseline current and its standard deviation to converge to their correct values. We explain different approaches to selecting events and building event populations, and we show the value of keeping track of the changes in parameters, such as the event rate and the pore resistance, throughout the course of the experiment. Finally, we introduce a new technique for separating unfolded events and detecting current spikes present withi...

Calin Plesa and Cees Dekker

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Patterning of light-extraction nanostructures on sapphire substrates using nanoimprint and ICP etching with different masking materials

Sapphire nanopatterning is the key solution to GaN light emitting diode (LED) light extraction. One challenge is to etch deep nanostructures with a vertical sidewall in sapphire. Here, we report a study of the effects of two masking materials (SiO 2 and Cr) and different etching recipes (the reaction gas ratio, the reaction pressure and the inductive power) in a chlorine-based (BCl 3 and Cl 2 ) inductively coupled plasma (ICP) etching of deep nanopillars in sapphire, and the etching process optimization. The masking materials were patterned by nanoimprinting. We have achieved high aspect ratio sapphire nanopillar arrays with a much steeper sidewall than the previous etching methods. We discover that the SiO 2 mask has much slower erosion rate than the Cr mask under the same etching condition, leading to the deep cylinder-shaped nanopillars (122 nm diameter, 200 nm pitch, 170 nm high, flat top, and a vertical sidewall of 80° angle), rather th...

Hao Chen, Qi Zhang and Stephen Y Chou

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Size-dependent optical absorption modulation of Si/Ge and Ge/Si core/shell nanowires with different cross-sectional geometries

We present an atomic-level and quantitative study of the absorption properties in Si/Ge and Ge/Si core/shell nanowires (CSNWs) along [110] direction with different cross-sectional geometries using the atomic bond relaxation method. We find that the strain existing in self-equilibrium state of CSNWs and associated with elastic energy originating from interface mismatch and surface relaxation affect the band shift and absorption properties. Compared to the CSNWs with tetragonal, hexagonal and circular shapes, the triangular CSNWs have the largest band gap shift at a fixed strain and the smallest absorption coefficient at a determinate incident light wavelength. The tunable absorption property, realized by controlling the size and geometry structure, could be helpful for nanoelectronic applications.

S Luo, W B Yu, Y He and G Ouyang

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Physical model for recognition tunneling

Recognition tunneling (RT) identifies target molecules trapped between tunneling electrodes functionalized with recognition molecules that serve as specific chemical linkages between the metal electrodes and the trapped target molecule. Possible applications include single molecule DNA and protein sequencing. This paper addresses several fundamental aspects of RT by multiscale theory, applying both all-atom and coarse-grained DNA models: (1) we show that the magnitude of the observed currents are consistent with the results of non-equilibrium Green’s function calculations carried out on a solvated all-atom model. (2) Brownian fluctuations in hydrogen bond-lengths lead to current spikes that are similar to what is observed experimentally. (3) The frequency characteristics of these fluctuations can be used to identify the trapped molecules with a machine-learning algorithm, giving a theoretical underpinning to this new method of identifying single molecule signals.

Predrag Krstić, Brian Ashcroft and Stuart Lindsay

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First-Principles Study of Dislocation Slips in Impurity-Doped Graphene

The Journal of Physical Chemistry C

DOI: 10.1021/jp512364p

Fanchao Meng, Bin Ouyang and Jun Song

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Charge-Transfer Emission of Mixed Organic Cocrystal Microtubes over the Whole Composition Range

Chemistry of Materials

DOI: 10.1021/cm5027249

Yan-Qiu Sun, Yi-Long Lei, Xu-Hui Sun, Shuit-Tong Lee and Liang-Sheng Liao

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Highly Scalable, Atomically Thin WSe2 Grown via Metal–Organic Chemical Vapor Deposition

ACS Nano

DOI: 10.1021/nn5073286

Sarah M. Eichfeld, Lorraine Hossain, Yu-Chuan Lin, Aleksander F. Piasecki, Benjamin Kupp, A. Glen Birdwell, Robert A. Burke, Ning Lu, Xin Peng, Jie Li, Angelica Azcatl, Stephen McDonnell, Robert M. Wallace, Moon J. Kim, Theresa S. Mayer, Joan M. Redwing and Joshua A. Robinson

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Atomically Precise Arrays of Fluorescent Silver Clusters: A Modular Approach for Metal Cluster Photonics on DNA Nanostructures

ACS Nano

DOI: 10.1021/nn506322q

Stacy M. Copp, Danielle E. Schultz, Steven Swasey and Elisabeth G. Gwinn

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Upconversion Luminescence Properties of NaYF4:Yb:Er Nanoparticles Codoped with Gd3+

The Journal of Physical Chemistry C

DOI: 10.1021/jp5103548

Dennis T. Klier and Michael U. Kumke

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White-Light Optimal Control of Photoinduced Processes

The Journal of Physical Chemistry C

DOI: 10.1021/jp510875a

Franz Hagemann, Falko Schwaneberg, Cristina Stanca-Kaposta and Ludger Wöste

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Effect of the Size and Position of Ion-Accessible Nanoholes on the Specific Capacitance of Single-Walled Carbon Nanohorns for Supercapacitor Applications

The Journal of Physical Chemistry C

DOI: 10.1021/jp510630e

Cheol-Min Yang, Yong-Jung Kim, Jin Miyawaki, Yoong Ahm Kim, Masako Yudasaka, Sumio Iijima and Katsumi Kaneko

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Effects of Chromophore Conjugation Length and Concentration on the Photostability of Indoline-Based Nonlinear Optical Chromophore/Polymer Films

The Journal of Physical Chemistry C

DOI: 10.1021/jp509293m

Yasar Kutuvantavida, Grant V. M. Williams, M. Delower H. Bhuiyan, Sebastiampillai G. Raymond and Andrew J. Kay

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Hydrothermal Continuous Flow Synthesis and Exfoliation of NiCo Layered Double Hydroxide Nanosheets for Enhanced Oxygen Evolution Catalysis

Nano Letters

DOI: 10.1021/nl504872s

Hanfeng Liang, Fei Meng, Miguel Cabán-Acevedo, Linsen Li, Audrey Forticaux, Lichen Xiu, Zhoucheng Wang and Song Jin

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Transitions from Near-Surface to Interior Redox upon Lithiation in Conversion Electrode Materials

Nano Letters

DOI: 10.1021/nl5049884

Kai He, Huolin L. Xin, Kejie Zhao, Xiqian Yu, Dennis Nordlund, Tsu-Chien Weng, Jing Li, Yi Jiang, Christopher A. Cadigan, Ryan M. Richards, Marca M. Doeff, Xiao-Qing Yang, Eric A. Stach, Ju Li, Feng Lin and Dong Su

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Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut

Nano Letters

DOI: 10.1021/nl5048779

Loredana Protesescu, Sergii Yakunin, Maryna I. Bodnarchuk, Franziska Krieg, Riccarda Caputo, Christopher H. Hendon, Ruo Xi Yang, Aron Walsh and Maksym V. Kovalenko

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Direct Observation of Ordered Configurations of Hydrogen Adatoms on Graphene

Nano Letters

DOI: 10.1021/nl503635x

Chenfang Lin, Yexin Feng, Yingdong Xiao, Michael Dürr, Xiangqian Huang, Xiaozhi Xu, Ruguang Zhao, Enge Wang, Xin-Zheng Li and Zonghai Hu

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Inhibition of the Enhancement of Infection of Human Immunodeficiency Virus by Semen-Derived Enhancer of Virus Infection Using Amyloid-Targeting Polymeric Nanoparticles

ACS Nano

DOI: 10.1021/nn5067254

Daniel A. Sheik, Lauren Brooks, Kristen Frantzen, Stephen Dewhurst and Jerry Yang

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