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Versteegh M.A.M.,University Utrecht | Versteegh M.A.M.,Debye Institute for Nanomaterials Science | Dieks D.,University Utrecht
American Journal of Physics | Year: 2011

Identical classical particles are distinguishable. This distinguishability affects the number of ways W a macrostate can be realized on the microlevel, and from the relation S=k ln W leads to a nonextensive expression for the entropy. This result is usually considered incorrect because of its inconsistency with thermodynamics. It is sometimes concluded from this inconsistency that identical particles are fundamentally indistinguishable and that quantum mechanics is indispensable for making sense of this inconsistency. In contrast, we argue that the classical statistics of distinguishable particles and the resulting nonextensive entropy function are perfectly acceptable from both a theoretical and an experimental perspective. The inconsistency with thermodynamics can be removed by taking into account that the entropy concept in statistical mechanics is not completely identical to the thermodynamical one. We observe that even identical quantum particles are in some cases distinguishable, and conclude that quantum mechanics is irrelevant to the Gibbs paradox. © 2011 American Association of Physics Teachers. Source

News Article
Site: http://phys.org/physics-news/

Fig. Visualisation of disorder-confined light in a photonic crystal. The green membrane is a photonic crystal with a waveguide; the patterns on top of it indicate the light signal that is stored. Credit: Utrecht University Faculty of Science Researchers at the Debye Institute for Nanomaterials Science, together with colleagues from the University of Twente and Thales Research and Technology (France), have found a non-invasive technique to measure the intensity profile of light that is confined by disorder in nano-sized photonic devices. This method may eventually lead to faster optical communications, and faster processing in quantum information technologies. The researchers published their results in the leading optical journal Optics Express on 12 September 2016. Every nanostructure suffers from unavoidable disorder: a disturbance of its function caused by unavoidable irregularities in nanofabrication. Contrary to what the name might suggest, disorder in a nanostructure is not necessarily a disadvantage. Disorder can cause light to be tightly confined, and if its intensity profile is measured accurately, the confined light might be used to make components for quantum information technology and high speed optical communication. One bottleneck in high-speed optical communication is that light signals have to be converted to electronic signals at nodes to switch data to different destinations. This conversion can be avoided with the help of optical buffers that store light signals temporarily. Right now, these buffers are usually implemented with optical fibres that are several centimeters long, which can store light for a few nanoseconds. However, with smart use of disorder-induced confinement, nanophotonic circuits 100 times smaller – only one-tenth of a millimeter long – can store light for a similar time. Photonic crystal waveguides are nanophotonic structures in which light confinement by disorder widely occurs. In order to make use of the confined light, the first essential step is to identify where the light is confined and what its spatial profile is. Compared to the previous measuring methods, which perturb the structure, Jin Lian (Debye Institute) and his colleagues have developed a new non-invasive method to precisely identify the spatial and spectral information, using local heating. The researchers used a blue laser to slightly heat a small spot on the crystal. The response of the optical system reveals how much light is confined there. Explore further: Unavoidable disorder used to build nanolaser More information: Measurement of the profiles of disorder-induced localized resonances in photonic crystal waveguides by local tuning, arxiv.org/abs/1606.01197

Rabouw F.T.,Debye Institute for Nanomaterials Science | Lunnemann P.,FOM Institute for Atomic and Molecular Physics | Lunnemann P.,Technical University of Denmark | Van Dijk-Moes R.J.A.,Debye Institute for Nanomaterials Science | And 5 more authors.
Nano Letters | Year: 2013

Progress to reduce nonradiative Auger decay in colloidal nanocrystals has recently been made by growing thick shells. However, the physics of Auger suppression is not yet fully understood. Here, we examine the dynamics and spectral characteristics of single CdSe-dot-in-CdS-rod nanocrystals. These exhibit blinking due to charging/discharging, as well as trap-related blinking. We show that one-dimensional electron delocalization into the rod-shaped shell can be as effective as a thick spherical shell at reducing Auger recombination of the negative trion state. © 2013 American Chemical Society. Source

Lunnemann P.,FOM Institute for Atomic and Molecular Physics | Lunnemann P.,Technical University of Denmark | Rabouw F.T.,Debye Institute for Nanomaterials Science | Van Dijk-Moes R.J.A.,Debye Institute for Nanomaterials Science | And 3 more authors.
ACS Nano | Year: 2013

We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows an extraction of calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultrastable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87 ± 0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature, and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states. © 2013 American Chemical Society. Source

Wadman S.H.,Debye Institute for Nanomaterials Science | Kroon J.M.,Debye Institute for Nanomaterials Science | Bakker K.,Debye Institute for Nanomaterials Science | Havenith R.W.A.,University Utrecht | And 3 more authors.
Organometallics | Year: 2010

To investigate the viability of cyclometalation as a general tool in the design of new sensitizers for dye-sensitized solar cells, a series of (cyclometalated) ruthenium complexes was prepared. To this purpose we have prepared the carboxylate-functionalized 2,2′:6′,2′′- terpyridine (tpy)-based tridentate ligands 4′-ethoxycarbonyl-2,2′: 6′,2′′-terpyridine (EtO2C-N∧N ∧N, 5), methyl-3,5-di(2-pyridyl)benzoate (MeO2C-N ∧C(H)∧N, 6), 4-ethoxycarbonyl-6-phenyl-2,2′- bipyridine (EtO2C-C(H)∧N∧N, 7), and 4,4′-bis(methoxycarbonyl)-6-phenyl-2,2′-bipyridine ((EtO 2C)2-C(H)∧N∧N, 8), and the ruthenium complexes thereof, [Ru(EtO2C-tpy)(tpy)](PF 6)2, 1a, [Ru(MeO2C-N∧C ∧N)(tpy)](PF6), 2a, [Ru(EtO2C-C ∧N∧N)(tpy)](PF6), 3a, and [Ru((MeO 2C)2-C∧N∧N)(tpy)](PF 6)2, 4a. In this series, cyclometalation results in a red shift as well as in a broadening of the electronic absorption features and is accompanied by a cathodic shift in the RuII/RuIII redox process. The complexes are photostable in both the Ru(II) and the Ru(III) state. Deprotection of the esters and grafting onto TiO2 resulted in a small additional red shift of the absorption features. Incorporation of the free acids of the complexes into a standardized solar cell shows efficient sensitization for the complexes 3b and 4b, with the C,N,N′-bonding motif. The dicarboxylated complex 4b showed short circuit currents similar to those obtained for the benchmark compound N719. In contrast, for the free acid of 1a, with the N,N′,N′′-bonding motif, and for 2a, with the N,C,N′-bonding motif, low efficiencies were observed. To put these results into perspective, we have applied TD-DFT calculations. The optical assignments based on these calculations correlated well with the spectral changes observed during pKa determinations. The complexes with the C,N,N′-bonding motif possess an excited state associated with the cyclometalated ligand, allowing efficient charge injection, while the complex with the N,C,N′-bonding motif possesses a more isolated excited state located on the remote tpy ligand and, as a result, is not capable of efficient charge injection into the TiO2 conduction band. This shows that the covalent carbon-to-ruthenium bond can be utilized as a tool to shift the operational threshold of the individual sensitizer for dye-sensitized solar cells toward lower energy, as long as care is taken that the nature of the excited state is appropriate for electron injection. © 2010 American Chemical Society. Source

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