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Volume 4 Issue 5, May 2009

Force spectroscopy allows the measurement of reaction rates as a function of the restoring force in molecules that have been stretched or compressed, but it lacks the temporal and spatial resolution needed to study small functional groups. A molecular force probe that extends force spectroscopy to the size-scale of such reactions has now been reported by roman Boulatov and co-workers. This artist's impression shows how stiff stillbene molecules can be used to apply forces to a small functional group: the stiff stilbene molecule changes shape when it is exposed to certain wavelengths of light, and this changes the force experienced by the smaller molecule.

Image credit: Marina Bulan

Letter p302; News & Views p284; Editorial p271

Editorial

  • It may be thought that force is the province of physicists and structural engineers, but it is also important in many other areas of research.

    Editorial

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Commentary

  • It is important to consider the ethical aspects of nanotechnology, but it is equally important to ensure that these considerations do not end up as 'speculative ethics'.

    • Alfred Nordmann
    • Arie Rip
    Commentary
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Thesis

  • Nanomedicine and homeopathy both involve very small amounts of material, but that is where the similarity ends, as Chris Toumey explains.

    • Chris Toumey
    Thesis
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Research Highlights

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News & Views

  • An atomic force microscope has been used to create nanoscale field-effect transistors and other electronic devices at the interface between two different oxide materials.

    • Dave H. A. Blank
    • Guus Rijnders
    News & Views
  • A DNA-based device can act as a pH sensor inside living cells.

    • Yuji Ishitsuka
    • Taekjip Ha
    News & Views
  • Semiconductor nanowires need to be doped before they can be used for many applications, but this process is not well understood. A laser-based approach has now shed new light on the doping of nanowires.

    • Pavle V. Radovanovic
    News & Views
  • A rigid molecule that changes shape when exposed to light can be used to explore the influence of mechanical force on chemical reactions involving small functional groups.

    • Jeremy M. Lenhardt
    • Stephen L. Craig
    News & Views
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Letter

  • When a semiconductor is subjected to pressure, its mechanical and electrical properties change. Now, the observation of a previously undetected current spike during the nanoscale deformation of gallium arsenide calls for a significant revision of our understanding of nanoscale plasticity.

    • Roman Nowak
    • Dariusz Chrobak
    • Markus Pessa
    Letter
  • Metal–insulator–metal electrostatic nanocapacitors can be fabricated in anodic aluminum-oxide nanopores using atomic layer deposition. This approach gives a planar capacitance of up to 100 µF cm−2 — substantially higher than previously reported values for nanostructured electrostatic capacitors.

    • Parag Banerjee
    • Israel Perez
    • Gary W. Rubloff
    Letter
  • DNA base pairs are held together by hydrogen bonds. It has now been shown that a scanning tunnelling microscope can be used to measure the strength of hydrogen bonding in such base pairs. These results provide a basis for new types of electronic biosensors and chemosensors.

    • Shuai Chang
    • Jin He
    • Stuart Lindsay
    Letter
  • Force spectroscopy allows measurement of reaction rates as a function of the restoring force in molecules that have been stretched or compressed, but at present this approach lacks the temporal and spatial resolution to study systematically the reactivities of small functional groups. A molecular force probe — stiff stilbene — that extends force spectroscopy to the size scale of such reactions has now been reported.

    • Qing-Zheng Yang
    • Zhen Huang
    • Roman Boulatov
    Letter
  • Chemical forces on surfaces have a central role in catalysis, thin-film growth and tribology. Many applications require knowledge of the strength of these forces as a function of position in three dimensions, but until now such information has only been available from theory. An approach based on atomic force microscopy has now been used to experimentally obtain this data, imaging the three-dimensional surface force field of graphite.

    • Boris J. Albers
    • Todd C. Schwendemann
    • Udo D. Schwarz
    Letter
  • Silicon nanowires could be central components in electronic and thermoelectric devices, but understanding nanowire surface properties and dopant distribution will be essential for making reproducible high-performance devices. Present methods for determining these parameters are problematic. Now, by using capacitance-voltage analysis, the radial profile and interface state density of silicon-nanowire field-effect transistors have been measured.

    • Erik C. Garnett
    • Yu-Chih Tseng
    • Peidong Yang
    Letter
  • The first direct measurements of dopant concentrations in arbitrary regions of individual nanowires are reported. Decomposition rates of heterogeneous precursors cause a heavily doped shell to surround an underdoped core. A thermodynamic model relating liquid and solid compositions to dopant fluxes is also presented.

    • Daniel E. Perea
    • Eric R. Hemesath
    • Lincoln J. Lauhon
    Letter
  • Carbon nanotubes and graphene are potential components for nanoscale electronic devices, but power dissipation — a significant issue for high-density electronic circuits — is not fully understood in such materials. Researchers have now mapped the electrically excited phonon populations and the power dissipation pathways in a working carbon nanotube transistor.

    • Mathias Steiner
    • Marcus Freitag
    • Phaedon Avouris
    Letter
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Article

  • DNA nanomachines are synthetic DNA assemblies that switch between defined molecular conformations when stimulated by external triggers. So far, DNA devices have been limited to in vitro applications. A DNA nanomachine has now been constructed that can function as a pH sensor based on fluorescence resonance energy transfer (FRET) inside living cells.

    • Souvik Modi
    • Swetha M. G.
    • Yamuna Krishnan
    Article
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