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Register a new userDetection of Individual Gas Molecules Absorbed on Graphene
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The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.
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Graphene is expected to complement todays Si-based information technology. In particular, magnetic molecules in contact with graphene constitute a tantalizing approach towards organic spin electronics because of the reduced conductivity mismatch at the interface. In such a system a bit is represented by a single molecular magnetic moment, which must be stabilized against thermal fluctuations. Here, we show in a combined experimental and theoretical study that the moments of paramagnetic Co-octaethylporphyrin (CoOEP) molecules on graphene can be aligned by a remarkable antiferromagnetic coupling to a Ni substrate underneath the graphene. This coupling is mediated via the pi electronic system of graphene, while no covalent bonds between the molecule and the substrate are established.
The most important bands for the evaluation of strain in graphene (the 2D and 2D prime modes) are investigated. It is shown that for Bernal-stacked bilayers, the two-phonon Raman features have three different components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The individual components of the 2D and 2D prime modes are disentangled. The reported results enable addressing the properties of individual graphene layers in isotopically labelled turbostratic and Bernalstacked graphene systems.
In this paper, we have done a comparative study of electronic and magnetic properties of iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) molecules physisorbed on monolayer of MoS$_2$ and graphene by using density functional theory. Various different types of physisorption sites have been considered for both surfaces. Our calculations reveal that the $M$Pc molecules prefer the S-top position on MoS$_2$. However, on graphene, FePc molecule prefers the bridge position while CoPc molecule prefers the top position. The $M$Pc molecules are physisorbed strongly on the MoS$_2$ surface than the graphene ($sim$ 2.5 eV higher physisorption energy). Analysis of magnetic properties indicates the presence of strong spin dipole moment opposite to the spin moment and hence a huge reduction of effective spin moment can be observed. Our calculations of magnetic anisotropy energies using both variational approach and $2^{nd}$ order perturbation approach indicate no significant changes after physisorption. In case of FePc, an out-of-plane easy axis and in case of CoPc, an in-plane easy axis can be seen. Calculations of work function indicate a reduction of MoS$_2$ work function $sim$ 1 eV due to physisorption of $M$Pc molecules while it does not change significantly in case of graphene.
Low-temperature spin-polarized scanning tunneling microscopy is employed to study spin transport across single Cobalt-Phathalocyanine molecules adsorbed on well characterized magnetic nanoleads. A spin-polarized electronic resonance is identified over the center of the molecule and exploited to spatially resolve stationary spin states. These states reflect two molecular spin orientations and, as established by density functional calculations, originate from a ferromagnetic molecule-lead superexchange interaction mediated by the organic ligands.
Formation, evolution, and vanishing of bubbles are common phenomena in our nature, which can be easily observed in boiling or falling waters, carbonated drinks, gas-forming electrochemical reactions, etc. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in liquid phase. Here we demonstrate, for the first time, that the nanobubbles in water encapsulated by graphene membrane can be visualized by in situ ultrahigh vacuum transmission electron microscopy (UHV-TEM), showing the critical radius of nanobubbles determining its unusual long-term stability as well as two distinct growth mechanisms of merging nanobubbles (Ostwald ripening and coalescing) depending on their relative sizes. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation. Our finding is expected to provide a deeper insight to understand unusual chemical, biological and environmental phenomena where nanoscale gas-state is involved.
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