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It is demonstrated that a Cu2S gap-type atomic switch, referred to as a Cu2S inorganic synapse, emulates the synaptic plasticity underlying the sensory, short-term, and long-term memory formations in the human brain. The change in conductance of the Cu2S inorganic synapse is considered analogous to the change in strength of a biological synaptic connection known as the synaptic plasticity. The plasticity of the Cu2S inorganic synapse is controlled depending on the interval, amplitude, and width of an input voltage pulse stimulation. Interestingly, the plasticity is influenced by the presence of air or moisture. Time-dependent scanning tunneling microscopy images of the Cu-protrusions grown in air and in vacuum provide clear evidence of the influence of air on their stability. Furthermore, the plasticity depends on temperature, such that a long-term memory is achieved much faster at elevated temperatures with shorter or fewer number of input pulses, indicating a close analogy with a biological synapse where elevated temperature increases the degree of synaptic transmission. The ability to control the plasticity of the Cu2S inorganic synapse justifies its potential as an advanced synthetic synapse with air/temperature sensibility for the development of artificial neural networks.

147 Resorcin[4]arene cavitands with four quinoxaline bridges are a family of macrocycles that adopt, at elevated temperature, a contracted, vase-type conformation, capable of guest inclusion, whereas at low temperature they switch to an expanded, kite-type conformation with a large flat surface. The present investigations lay the foundation for the use of such dynamic cavitands as miniaturized mechanical grippers for supramolecular construction at the single-molecule level. New vase–kite switching modes, stimulated by pH changes or stoichiometric metal-ion complexation, have been discovered and monitored by 1 H NMR and optical absorption spectroscopy. The solid-state geometries of the two states have been revealed by X-ray crystallography, and the kinetics and thermodynamics of the switching processes in solution as well as their solvent dependency has been investigated in great detail. Monolayers of the cavitand in the vase form have been studied by scanning tunneling microscopy at molecular resolution; conformational switching is also observed in Langmuir monolayers at the air/water interface. Synthetic protocols have been developed for preparation of partially and asymmetrically bridged resorcin[4]arene cavitands, which are also shown to undergo conformational switching. These synthetic advances pave the way to new, dynamic molecular receptors for steroids, tetrathiofulvalene-bridged grippers with the potential to undergo electrochemically induced conformational switching, and systems with greatly extended, rigid cavity walls functionalized at the termini by dipyrrometheneboron difluoride dyes. The latter cavitands are shown by fluorescence resonance energy transfer to undergo geometrically precisely defined motions between a contracted (≈7 A linear extension) and a strongly expanded (≈7 nm linear extension) state.

Coordinated group movement (swarming) is a key aspect of Myxococcus xanthus’ social behavior. Here we report observation of domain structures formed by multiple cells within large three-dimensional swarming groups grown on amorphous glass substrates, using the atomic force microscope (AFM). Novel analyses revealed that � 90% of the wild type swarms displayed some form of preferential cell alignment. In contrast, cells with mutations in the social and adventurous motility systems displayed a distinct lack of cell alignment. Video microscopy observations of domain features of in vivo swarming M. xanthus cells were also consistent with the AFM data. The results presented here reveal that unique domain formation within swarms of wild type cells is a biologically driven process requiring the social and adventurous motility systems and is not a statistical phenomenon or thermodynamic process arising from liquid crystal behavior. Cell Motil. Cytoskeleton 63:141–148, 2006. ' 2006 Wiley-Liss, Inc.

The C60 electromechanical amplifier is a working 3-terminal device based on the modulation of the tunnel-transport regime through a C60 molecule by a reversible deformation of its cage. We present the advantages of the planarization of this triode such as a surface extension lower than 0.05μm2 on the wafer and a large gain (Gd > 40). High-speed operation (bandwidth greater than 1 GHz) and low energy dissipation in the attojoules range are discussed together with the technological difficulties to fabricate such a planar molecular triode.

The pronounced variation of the intensity of photons emitted from the tunneling gap of an STM with respect to the applied bias voltage V t is studied experimentally using simultaneous measurements of tunneling characteristics and photon emission. We show that the structure in isochromat photon spectra are determined by the following: bias-dependent changes in tunneling characteristics, density of initial and final states, and modifications of tip-induced plasmon modes. It is demonstrated that isochromat spectra provide a conclusive test for the inelastic tunneling mechanism. Coupling between tunneling electrons and tip-induced plasmon modes which gives rise to the intense photon emission observed is discussed within this model

Miniaturized molecular grippers for supramolecular construction are described by Francois Diederich and co-workers on p. 147. These grippers are based on resorcin[4]arene cavitands with four quinoxaline bridges; these macrocycles can be switched between a closed (left) and open (right) configuration via temperature changes, pH changes, or stoichiometric metal-ion complexation. The background is a scanning tunneling microscopy image of a self-assembled monolayer of the closed cavitands. Individual gripper “fingers” are seen as lighter spots, four per gripper, which in turn pack into a well-ordered array. Resorcin[4]arene cavitands with four quinoxaline bridges are a family of macrocycles that adopt, at elevated temperature, a contracted, vase-type conformation, capable of guest inclusion, whereas at low temperature they switch to an expanded, kite-type conformation with a large flat surface. The present investigations lay the foundation for the use of such dynamic cavitands as miniaturized mechanical grippers for supramolecular construction at the single-molecule level. New vase–kite switching modes, stimulated by pH changes or stoichiometric metal-ion complexation, have been discovered and monitored by 1H NMR and optical absorption spectroscopy. The solid-state geometries of the two states have been revealed by X-ray crystallography, and the kinetics and thermodynamics of the switching processes in solution as well as their solvent dependency has been investigated in great detail. Monolayers of the cavitand in the vase form have been studied by scanning tunneling microscopy at molecular resolution; conformational switching is also observed in Langmuir monolayers at the air/water interface. Synthetic protocols have been developed for preparation of partially and asymmetrically bridged resorcin[4]arene cavitands, which are also shown to undergo conformational switching. These synthetic advances pave the way to new, dynamic molecular receptors for steroids, tetrathiofulvalene-bridged grippers with the potential to undergo electrochemically induced conformational switching, and systems with greatly extended, rigid cavity walls functionalized at the termini by dipyrrometheneboron difluoride dyes. The latter cavitands are shown by fluorescence resonance energy transfer to undergo geometrically precisely defined motions between a contracted (≈ 7 A linear extension) and a strongly expanded (≈ 7 nm linear extension) state.

Many methods of reproducing nuclear fusion — the process that powers the Sun — at the table-top scale have been tried, but failed to convince. Remember ‘cold fusion’? More recently, fusion linked to sonoluminescence is still controversial. Now comes a claim from the labs of the University of California at Los Angeles of unequivocal evidence of nuclear fusion in a simple room-temperature experiment. They report that gently heating a pyroelectric crystal — material that becomes charged when heated — causes ionization of a surrounding deuterium gas. The ions bombard a deuterated solid target with such energy that a large neutron signal is detected, a hallmark of deuterium fusion. Though not a viable power source, ‘crystal fusion’ may find application as a generator of neutrons for imaging technology. While progress in fusion research continues with magnetic1 and inertial2 confinement, alternative approaches—such as Coulomb explosions of deuterium clusters3 and ultrafast laser–plasma interactions4—also provide insight into basic processes and technological applications. However, attempts to produce fusion in a room temperature solid-state setting, including ‘cold’ fusion5 and ‘bubble’ fusion6, have met with deep scepticism7. Here we report that gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (> 100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons from the reaction D + D → 3He (820 keV) + n (2.45 MeV) within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. As further evidence for this fusion reaction, we use a novel time-of-flight technique to demonstrate the delayed coincidence between the outgoing α-particle and the neutron. Although the reported fusion is not useful in the power-producing sense, we anticipate that the system will find application as a simple palm-sized neutron generator.

SUMMARY We have measured field-emission resonances (FER) to much higher quantum states than previously observed enabling fine structure in the resonance amplitudes to be investigated. We show that this electron wave interference effect carries additional information in the resonance amplitudes and energies and is sensitive to lateral tip position in a scanning tunnelling microscope experiment. We propose a new method of data analysis that can distinguish between some of the possible origins of the fine structure.

SUMMARY We have detected the light emitted from an STM at both ultraviolet (9·5 eV) and optical (1–4 eV) energies. We show that this light contains spectroscopic information on the sample surface comparable to conventional inverse photoelectric spectroscopy, but with nearly atomic spatial resolution. At optical energies we found sufficiently high intensities to allow spatial imaging of the emission probability. We propose that the high quantum efficiency is due to resonance phenomena, and present fluorescence spectra of the emitted light that support this view. We believe that atomic resolution inverse photoemission microscopy and spectroscopy will provide an important new dimension to surface studies.