6 research outputs found
Optical probes of molecules as nano-mechanical switches
Abstract: Molecular electronics promises a new generation of ultralow-energy information technologies, based around functional molecular junctions. Here, we report optical probing that exploits a gold nanoparticle in a plasmonic nanocavity geometry used as one terminal of a well-defined molecular junction, deposited as a self-assembled molecular monolayer on flat gold. A conductive transparent cantilever electrically contacts individual nanoparticles while maintaining optical access to the molecular junction. Optical readout of molecular structure in the junction reveals ultralow-energy switching of ∼50 zJ, from a nano-electromechanical torsion spring at the single molecule level. Real-time Raman measurements show these electronic device characteristics are directly affected by this molecular torsion, which can be explained using a simple circuit model based on junction capacitances, confirmed by density functional theory calculations. This nanomechanical degree of freedom is normally invisible and ignored in electrical transport measurements but is vital to the design and exploitation of molecules as quantum-coherent electronic nanodevices
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Terahertz Raman Spectroscopy of Organic Molecules in Plasmonic Nanogaps
This thesis contributes to the extension of the technique of surface-enhanced Raman spectroscopy (SERS) from the infrared to the terahertz (THz) region of the electromagnetic spectrum. SERS was first discovered in 1977, and has since become a widespread, powerful analytical tool for chemistry and has led to the development of many other surface-enhanced spectroscopies. However, its exploration of THz-frequency modes of materials was limited to measurements using low-throughput and expensive equipment until 2012. Recent advances in laser and notch filter technology have made the THz region accessible to Raman spectroscopy, accelerating the publication of THz Raman studies on a wide array of bulk materials. While THz SERS measurements are likewise possible, progress has been much slower than for bulk Raman, impeded by characteristics of the spectra that make the analysis challenging.
Two predominant characteristics were observed of all the measured THz SERS spectra of several different sets of systems, varying analyte and nanostructure parameters, and of the few THz SERS spectra reported in literature: a continuum underlying molecular SERS peaks which rises super-exponentially at decreasing Raman Shifts on both sides of 0 cm-1 and broadening of molecular SERS peaks at decreasing Raman Shifts. These complicate the interpretation of THz SERS spectra. This thesis presents investigations of both. The result is an approach to analyzing SERS data. As an example, this is applied to early diagnosis of Alzheimer’s Disease (AD), the archetype of amyloid diseases. The polymerization of the peptide β-amyloid is considered to be central to the pathogenesis of AD. Because of the delocalized nature of THz-frequency molecular vibrations, THz SERS has the potential to directly distinguish different structures of the peptide.Cambridge Trus
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Research data supporting "Optical Probes of Molecules as Nano-Mechanical Switches"
One .zip folder, containing two subfolders ('main' and 'SI'). Data are organised following the structure and figures of main manuscript and Supplementary Information. Datafiles, and all columns and rows inside datafiles, are explicitly labelled according to the part of the Figure they represent. Darkfield spectra were collected confocally with a spot size of approximately 1µm using broadband white light illumination from a halogen bulb, with specta referenced using a white scattering standard. Raman spectra were collected using either a 633nm or 785nm laser, focussed on individual nanoparticles with a spot size of approximately 1µm and optical power 200µW. Electrical measurements were perfomed with a Source Measure Unit, set to output a voltage and measure a current, with fixed detection range and current compliance for each measurement. Minimal post-processing was applied to the presented data, with post-processing generally limited to subtraction of background dark counts of optical detectors (darkfield and Raman spectroscopy), normalisation of the signal to input illumination (darkfield spectroscopy), and subtraction of average baseline electronic noise (electrical measurements). Additional details on equipment, protocols and simulation data are provided in the main manuscript
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Optical probes of molecules as nano-mechanical switches
Abstract: Molecular electronics promises a new generation of ultralow-energy information technologies, based around functional molecular junctions. Here, we report optical probing that exploits a gold nanoparticle in a plasmonic nanocavity geometry used as one terminal of a well-defined molecular junction, deposited as a self-assembled molecular monolayer on flat gold. A conductive transparent cantilever electrically contacts individual nanoparticles while maintaining optical access to the molecular junction. Optical readout of molecular structure in the junction reveals ultralow-energy switching of ∼50 zJ, from a nano-electromechanical torsion spring at the single molecule level. Real-time Raman measurements show these electronic device characteristics are directly affected by this molecular torsion, which can be explained using a simple circuit model based on junction capacitances, confirmed by density functional theory calculations. This nanomechanical degree of freedom is normally invisible and ignored in electrical transport measurements but is vital to the design and exploitation of molecules as quantum-coherent electronic nanodevices