Image of the Month

Image of the Month
Posted Date: May 1, 2017

Figure 3. Scanning tunneling microscopy images of Aβ1−16-Cu2+ (a,b) and Aβ1−16 (c,d). Imaging conditions: (a,b) 10 nm × 10 nm, Vsample = 0.55 V, Itunnel =10pA;(c)10nm×10nm,Vsample =0.25V,Itunnel =17pA;(d)10nm×10nm,Vsample =0.30V,Itunnel =14pA.

Abstract
β-Amyloid aggregates in the brain play critical roles in Alzheimer’s disease, a chronic neurodegenerative condition. Amyloid-associated metal ions, particularly zinc and copper ions, have been implicated in disease pathogenesis. Despite the importance of such ions, the binding sites on the β-amyloid peptide remain poorly understood. In this study, we use scanning tunneling microscopy, circular dichroism, and surface-enhanced Raman spectroscopy to probe the inter-actions between Cu2+ ions and a key β-amyloid peptide fragment, consisting of the first 16 amino acids, and define the copper−peptide binding site. We observe that in the presence of Cu2+, this peptide fragment forms β-sheets, not seen without the metal ion. By imaging with scanning tunneling microscopy, we are able to identify the binding site, which involves two histidine residues, His13 and His14. We conclude that the binding of copper to these residues creates an interstrand histidine brace, which enables the formation of β-sheets.

Reference:
Nano Letters 2016, 16, 6282-6289

Credits:
Diana Yugay,†,‡ Dominic P. Goronzy,†,‡ Lisa M. Kawakami, Shelley A. Claridge,‡,§,∥ Tze-Bin Song, ZhongboYan, Ya-HongXie,*,†,⊥ Jeŕom̂eGilles,*,∇ YangYang,*,†,⊥ and PaulS.Weiss*,†,‡,⊥

California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
§Department of Chemistry and Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
Department of Mathematics and Statistics, San Diego State University, San Diego, California 92182, United States

Microscope:
Agilent Pico SPM

Control System:
RHK R9

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Image of the Month
Posted Date: April 1, 2017

(c) STM image of a branch of a fractal. The sample bias is 0.5 V and the tunnel current is 0.2 nA. (d) Differential conductivity recorded at the environment of the fractal, red curve (region (i) of (c)), and on the fractal, blue curve (region (i) of (c)), and on the fractal, blue curve (region (ii) of (c)). The sample bias for both curves is 0.5 V and the tunnel current is 0.2 nA.

Abstract
The basic science responsible for the fascinating  shapes of ice crystals and snowflakes is still not understood. Insufficient knowledge of the interaction potentials and the lack of relevant experimental access to the growth process are to blame for this failure. Here, we study the growth of fractal nanostructures in a two-dimensional  (2D) system, intercalated between mica and graphene. Based on our scanning tunneling spectroscopy data, we provide compelling evidence that these fractals are 2D ice. They grow while they are in material contact with the atmosphere at 20 ºC and without significant thermal contact to the ambient. The growth is studied in situ, in real time and space at the nanoscale. We find that the growing 2D ice nanocrystals assume a fractal shape, which is conventionally attributed to Diffusion Limited Aggregation (DLA). However, DLA requires a low mass density mother phase, in contrast to the actual currently present high mass density mother phase. Latent heat effects and consequent transport of heat and molecules are found to be the key ingredients for understanding the evolution of the snow (ice) flakes. We conclude that not the local availability of water molecules (DLA), but rather them having the locally required orientation is the key factor for incorporation into the 2D ice nanocrystal. In combination with the transport of latent heat, we attribute the evolution of fractal 2D ice nanocrystals to local temperature dependent rotation limited aggregation. The ice growth occurs under extreme supersaturation, i.e., the conditions closely resemble the natural ones for the growth of complex 2D snow (ice) flakes and we consider our findings crucial for solving the “perennial” snow (ice) flake enigma. © 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4926467]

Reference:
Journal of Chemical Physics 143, 034702 (2015)

Credits:
Pantelis Bampoulis,1,2,a) Martin H. Siekman,1  E. Stefan Kooij,1 Detlef Lohse,2 Harold J. W. Zandvliet,1  and Bene Poelsema1

1Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
2Physics of Fluids and J. M. Burgers Centre for Fluid Mechanics, MESA+ Institute of Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands

Microscope:
RHK UHV3500 STM/AFM with Inverted Viewport

Control System:
RHK SPM1000

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Image of the Month
Posted Date: March 7, 2017
institution

Figure 2 | Imaging silicon atoms with terahertz-driven scanning tunnelling microscopy (TD-STM). a. Topographic images of the Si(111)-(7 x 7) surface measured in constant-current mode with standard STM at Vd.c. = -0.5 V, ETHz,pk = 0 V cm-1, Id.c. = -20 pA b. and terahertz-driven STM (TD-STM) of the same region with Vd.c. = 0 V, ETHz,pk = -200 V cm-1ITHz,avg = -20 pA

Abstract
Ultrafast control of current on the atomic scale is essential for future innovations in nanoelectronics. Extremely localized transient electric fields on the nanoscale can be achieved by coupling picosecond duration terahertz pulses to metallic nanostructures. Here, we demonstrate terahertz scanning tunnelling microscopy (THz-STM) in ultrahigh vacuum as a new platform for exploring ultrafast non-equilibrium tunnelling dynamics with atomic precision. Extreme terahertz-pulse-driven tunnel currents up to 107 times larger than steady-state currents in conventional STM are used to image individual atoms on a silicon surface with 0.3 nm spacial resolution. At terahertz frequencies, the metallic-like Si(111)-(7 x 7) surface is unable to screen the electric field from the bulk, resulting in a terahertz tunnel conductance that is fundamentally different than that of the steady state. Ultrafast terahertz-induced band bending and non-equilibrium charging of surface states open new conduction pathways to the bulk, enabling extreme transient tunnel currents to flow between the tip and sample.

Public Reference:
NATURE PHYSICS: DOI: 10.1038/NPHYS4047

Credits:
Vedran Jelic1*, Krzysztof Iwaszczuk2, Peter H. Nguyen1, Christopher Rathje3, Graham J. Hornig1, Haille M. Sharum1, James R. Hoffman1, Mark R. Freeman1 and Frank A. Hegmann1*

1Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada. 2DTU Fotonik – Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark. 34th Physical Institute, University of Gottingen, 37077 Gottingen, Germany.
*e-mail: jelic@ualberta.ca;, hegmann@ualberta.ca

Microscope:
RHK UHV3500 STM/AFM with Inverted Viewport

Control System:
RHK SPM1000

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Image of the Month
Posted Date: February 8, 2017
institution

Figure 2 | Charge density wave (CDW) transition in MTBs. (a) STM images of a single MTB at low temperatures (120 K) exhibit three times the periodicity than the atomic corrugation imaged at room temperature. In (b) a larger scale low-T STM image and the corresponding cross-section along the indicated MTB is shown that measured the periodicity of the CDW as B1.0 nm. The schematic in (c) illustrates the relationship between CDW period and nesting vector q = 2kF. Also the opening of a band gap at kF is illustrated. Temperature dependent resistance measurements, shown in (d), indicate two CDW transitions. The transitions at 235 and 205 K correspond to incommensurate and commensurate CDW transitions, respectively. Depending on the applied bias voltage we also observe a drop in resistance below the CDW transition temperatures, which is attributed to CDW-sliding. The inset shows the control measurement on a bare MoS2 substrate and shows no transitions.

Material line defects are one-dimensional structures but the search and proof of electron behaviour consistent with the reduced dimension of such defects has been so far unsuccessful. Here we show using angle resolved photoemission spectroscopy that twin-grain boundaries in the layered semiconductor MoSe2 exhibit parabolic metallic bands. The one-dimensional nature is evident from a charge density wave transition, whose periodicity is given by kF/π, consistent with scanning tunnelling microscopy and angle resolved photoemission measurements. Most importantly, we provide evidence for spin- and charge-separation, the hallmark of one-dimensional quantum liquids. Our studies show that the spectral line splits into distinctive spinon and holon excitations whose dispersions exactly follow the energy-momentum dependence calculated by a Hubbard model with suitable finite-range interactions. Our results also imply that quantum wires and junctions can be isolated in line defects of other transition metal dichalcogenides, which may enable quantum transport measurements and devices.

Credits:
Yujing Ma1, Horacio Coy Diaz1, José Avila2,3, Chaoyu Chen2,3, Vijaysankar Kalappattil1, Raja Das1, Manh-Huong Phan1, Čadež4,5, Josè M.P. Carmelo4,5,6, Maria C. Asensio2,3 & Matthias Batzill1

1 Department of Physics, University of South Florida, Tampa, Florida 33620, USA. 2 Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin-BP 48, Gif sur Yvette Cedex 91192, France. 3 Universite ́ Paris-Saclay, L’Orme des Merisiers, Saint Aubin-BP 48, Gif sur Yvette Cedex 91192, France. 4 Beijing Computational Science Research Center, Beijing 100193, China. 5 Center of Physics of University of Minho and University of Porto, Oporto P-4169-007, Portugal. 6 Department of Physics, University of Minho, Campus Gualtar, Braga P-4710-057, Portugal.

Microscope:
PanScan Freedom UHV

Control System:
RHK R9 Control System

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