Cold-atom scanning probe microscopy

• M. Gierling,
• P. Schneeweiss,
• G. Visanescu,
• P. Federsel,
• M. Häffner,
• D. P. Kern,
• T. E. Judd,
• A. Günther
• & J. Fortágh

Nature Nanotechnology

 

(2011)

 

doi:10.1038/nnano.2011.80

Received

 

29 March 2011

 

Accepted

 

21 April 2011

 

Published online

 

29 May 2011

Scanning probe microscopes are widely used to study surfaces with atomic resolution in many areas of nanoscience. Ultracold atomic gases trapped in electromagnetic potentials can be used to study electromagnetic interactions between the atoms and nearby surfaces in chip-based systems. Here we demonstrate a new type of scanning probe microscope that combines these two areas of research by using an ultracold gas as the tip in a scanning probe microscope. This cold-atom scanning probe microscope offers a large scanning volume, an ultrasoft tip of well-defined shape and high purity, and sensitivity to electromagnetic forces (including dispersion forces near nanostructured surfaces). We use the cold-atom scanning probe microscope to non-destructively measure the position and height of carbon nanotube structures and individual free-standing nanotubes. Cooling the atoms in the gas to form a Bose–Einstein condensate increases the resolution of the device.

All-Optical High-Resolution Nanopatterning and 3D Suspending of Graphene

Rainer J. Sthr*, Roman Kolesov, Kangwei Xia, and Jrg Wrachtrup

ACS Nano, Article ASAP

DOI: 10.1021/nn201226f

Publication Date (Web): May 19, 2011

We introduce a laser-based technique capable of both imaging and patterning graphene with high spatial resolution. Both tasks are performed in situ using the same confocal microscope. Imaging graphene is based on the recombination of a laser-created electron–hole plasma yielding to a broadband up- and down-converted fluorescence. Patterning is due to burning graphene by local heating causing oxidation and conversion into CO₂. By shaping the laser beam profile using 1D phase-shifting plates and 2D vortex plates we can produce graphene dots below 100 nm in diameter and graphene nanoribbons down to 20 nm in width. Additionally, we demonstrate that this technique can also be applied to freely suspended graphene resulting in freely suspended graphene nanoribbons. We further present a way of freely hanging graphene vertically and imaging it in 3D. Taking advantage of having vertically hanging graphene for the first time, we measure the out-of-plane anisotropy of the upconversion fluorescence.

26 Tbit s−1 line-rate super-channel transmission utilizing all-optical fast Fourier transform processing

• D. Hillerkuss,
• R. Schmogrow,
• T. Schellinger,
• M. Jordan,
• M. Winter,
• G. Huber,
• T. Vallaitis,
• R. Bonk,
• P. Kleinow,
• F. Frey,
• M. Roeger,
• S. Koenig,
• A. Ludwig,
• A. Marculescu,
• J. Li,
• M. Hoh,
• M. Dreschmann,
• J. Meyer,
• S. Ben Ezra,
• N. Narkiss,
• B. Nebendahl,
• F. Parmigiani,
• P. Petropoulos,
• B. Resan,
• A. Oehler
• et al.

Nature Photonics

 

(2011)

 

doi:10.1038/nphoton.2011.74

Received

 

11 August 2010

 

Accepted

 

07 April 2011

 

Published online

 

22 May 2011

Optical transmission systems with terabit per second (Tbit s⁻¹) single-channel line rates no longer seem to be too far-fetched. New services such as cloud computing, three-dimensional high-definition television and virtual-reality applications require unprecedented optical channel bandwidths. These high-capacity optical channels, however, are fed from lower-bitrate signals. The question then is whether the lower-bitrate tributary information can viably, energy-efficiently and effortlessly be encoded to and extracted from terabit per second data streams. We demonstrate an optical fast Fourier transform scheme that provides the necessary computing power to encode lower-bitrate tributaries into 10.8 and 26.0 Tbit s⁻¹ line-rate orthogonal frequency-division multiplexing (OFDM) data streams and to decode them from fibre-transmitted OFDM data streams. Experiments show the feasibility and ease of handling terabit per second data with low energy consumption. To the best of our knowledge, this is the largest line rate ever encoded onto a single light source.

25 May - Surface modification of nanocrystalline anatase with CTAB in the acidic condition and its effects on photocatalytic activity and preferential growth of TiO2

Today Lijie will present the following paper:


Surface modification of nanocrystalline anatase with CTAB in the acidic condition and its effects on photocatalytic activity and preferential growth of TiO2

Yichun Qu, Wenxin Wang, Liqiang Jing ∗, Shu Song, Xin Shi, Lianpeng Xue, Honggang Fu∗


Applied Surface Science 257 (2010) 151–156


The nanocrystalline anatase TiO2, which was synthesized by a sol–hydrothermal process in advance, has successfully modified with cetyltrimethylammonium bromide (CTAB) in the acidic condition as well as in the basic condition. On the basis of the measurements of infrared spectrum and X-ray photoelectron spectroscopy of the resulting TiO2, together with the phase-transfer experiments, it is suggested that the modification  mechanism in the acidic condition is closely related to Br−. Interestingly, compared with un-modified TiO2, the modified TiO2 exhibits high photocatalytic activity for degrading Rhodamine B (RhB) solution, especially for that modified in the acid. The enhanced photocatalytic activity of modified TiO2 in the acid is attributed to the role that the Br− can easily capture photo-induced holes and then form active Br, consequently effectively inducing photocatalytic oxidation reactions, based on the surface photovoltage responses of the resulting TiO2. After that, a one-pot sol–hydrothermal route at the temperature as low as 80 ◦C is developed to directly synthesize CTAB-modified nanocrystalline TiO2 with a little preferred growth along 001 direction, which can be easily dispersed in the organic system and possess good photocatalytic performance. This work provides a feasible strategy to further improve the photocatalytic performance of nanocrystalline anatase and to synthesize TiO2 nanocrystals with preferential growth.

See you in HARR254 at 17:00!

Diet Coke and Mentos: What is really behind this physical reaction?

Tonya Shea Coffey

Department of Physics and Astronomy, Appalachian State University, Boone, North Carolina 28608 

American Journal of Physics -- June 2008 -- Volume 76, Issue 6, pp. 551

The Diet Coke and Mentos reaction is a fun demonstration in chemistry and physics classes of many important concepts in thermodynamics, fluid dynamics, surface science, and the physics of explosions. The reaction has been performed numerous times on television and the Internet, but has not been systematically studied. We report on an experimental study of the Diet Coke and Mentos reaction, and consider many aspects of the reaction, including the ingredients in the candy and soda, the roughness of the candy, the temperature of the soda, and the duration of the reaction.

Carbon-Based Supercapacitors Produced by Activation of Graphene

1. Yanwu Zhu¹, 
2. Shanthi Murali¹, 
3. Meryl D. Stoller¹, 
4. K. J. Ganesh¹, 
5. Weiwei Cai¹ , 
6. Paulo J. Ferreira¹, 
7. Adam Pirkle²,
8. Robert M. Wallace² , 
9. Katie A. Cychosz³, 
10. Matthias Thommes³, 
11. Dong Su⁴, 
12. Eric A. Stach⁴, and 
13. Rodney S. Ruoff¹,*#

1. 
   

Science DOI: 10.1126/science.1200770

• Received for publication 22 November 2010.
• Accepted for publication 2 May 2011.

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high surface area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a BET surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low O and H content. This sp²-bonded carbon has a continuous three-dimensional network of highly curved, atom thick walls that form primarily 0.6- to 5-nm-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

Noncontact Sub-10 nm Temperature Measurement in Near-Field Laser Heating

Yanan Yue, Xiangwen Chen, and Xinwei Wang*

Department of Mechanical Engineering, Iowa State University, 2025 Black Engineering Building, Ames, Iowa 50011-2161, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn2011442

Publication Date (Web): May 10, 2011

An extremely focused optical field down to sub-10 nm in an apertureless near-field scanning optical microscope has been used widely in surface nanostructuring and structure characterization. The involved sub-10 nm near-field heating has not been characterized quantitatively due to the extremely small heating region. In this work, we present the first noncontact thermal probing of silicon under nanotip focused laser heating at a sub-10 nm scale. A more than 200 °C temperature rise is observed under an incident laser of 1.2 × 10⁷W/m², while the laser polarization is well aligned with the tip axis. To explore the mechanism of heating and thermal transport at sub-10 nm scale, a simulation is conducted on the enhanced optical field by the AFM tip. The high intensity of the optical field generated in this region results in nonlinear photon absorption. The optical field intensity under low polarization angles (10¹⁴ W/m² within 1 nm region for 15° and 30°) exceeds the threshold for avalanche breakdown in silicon. The measured high-temperature rise is a combined effect of the low thermal conductivity due to ballistic thermal transport and the nonlinear photon absorption in the enhanced optical field. Quantitative analysis reveals that under the experimental conditions the temperature rise can be about 235 and 105 °C for 15° and 30° laser polarization angles, agreeing well with the measurement result. Evaluation of the thermal resistances of the tip–substrate system concludes that little heat in the substrate can be transferred to the tip because of the very large thermal contact resistance between them.