Transverse spin relaxation time in organic molecules

We report a measurement of the ensemble-averaged transverse spin relaxation time (T∗2) in bulk and few molecules of the organic semiconductor tris-(8-hydroxyquinolinolato aluminum) or Alq3. This system exhibits two characteristic T∗2 times: the longer of which is temperature independent and the shorter is temperature dependent, indicating that the latter is most likely limited by spin-phonon interaction. Based on the measured data, we infer that the single-particle T2 time is probably long enough to meet Knill’s criterion for fault-tolerant quantum computing even at room temperature. Alq3 is also an optically active organic, and we propose a simple optical scheme for spin qubit readout. Moreover, we found that the temperature-dependent T∗2 time is considerably shorter in bulk Alq3powder than in few molecules confined in 1–2-nm-sized cavities. Because carriers in organic molecules are localized over individual molecules or atoms but the phonons are delocalized, we believe that this feature is caused by phonon bottleneck effect

Giant increase in the metal-enhanced fluorescence of organic molecules in nanoporous alumina templates and large molecule-specific red/blue shift of the fluorescence peak

The fluorescence of organic fluorophore molecules is enhanced when they are placed in contact with certain metals (Al, Ag, Cu, Au, etc.) whose surface plasmon waves couple into the radiative modes of the molecules and increase the radiative efficiency. Here, we report a hitherto unknown size dependence of this metal enhanced fluorescence (MEF) effect in the nanoscale. When the molecules are deposited in nanoporous anodic alumina films with exposed aluminum at the bottom of the pores, they form organic nanowires standing on aluminum nanoparticles whose plasmon waves have much larger amplitudes. This increases the MEF strongly, resulting in several orders of magnitude increase in the fluorescence intensity of the organic fluorophores. The increase in intensity shows an inverse super-linear dependence on nanowire diameter because the nanowires also act as plasmonic 'waveguides' that concentrate the plasmons and increase the coupling of the plasmons with the radiative modes of the molecules. Furthermore, if the nanoporous template housing the nanowires has built-in electric fields due to space charges, a strong molecule-specific red- or blue-shift is induced in the fluorescence peak owing to a renormalization of the dipole moment of the molecule. This can be exploited to detect minute amounts of target molecules in a mixture using their optical signature (fluorescence) despite the presence of confounding background signals. It can result in a unique new technology for bio- and chemical-sensing

Field Emission from Self-Assembled Arrays of Lanthanum Monosulfide Nanoprotrusions

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is 3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is, 1 eV, a field enhancement factor of 5.8 is extracted for the nanodome emitters from Fowler-Nordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements

Field Emission from Self-Assembled Arrays of Lanthanum Monosulfide Nanoprotrusions

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is ∼3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is, ∼1 eV, a field enhancement factor of ∼5.8 is extracted for the nanodome emitters from Fowler-Nordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements

Field Emission from Self-Assembled Arrays of Lanthanum Monosulfide Nanoprotrusions

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is ∼3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is, ∼1 eV, a field enhancement factor of ∼5.8 is extracted for the nanodome emitters from FowlerNordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements. The promise of producing extremely high current densities in near-vacuum with no external source (such as heater, primary electron-beam, or intense light source) has generated significant interest in robust, reproducible, and fieldemission-based cold cathodes Recently, we reported the first successful deposition of lanthanum monosulfide (LaS) thin films on Si substrates using pulsed laser deposition (PLD) The nanodomes are cone-shaped LaS structures with base diameter 2r ranging from 50 to 100 nm and height h ranging from 100 to 150 nm. They were found to grow on the boundaries separating regions of the anodic alumina film that have near perfect pore ordering. Their density is ∼10 9 /cm 2 , as extracted from the field emission-scanning electron micrographs (FE-SEM) and atomic force micrographs (AFM) such as those shown in The SAFEM technique was used to measure the FE current-voltage (I-V) characteristics at different surface locations. As the nanowires are buried inside the pores, they contribute very little, if any at all, to the net FE current. Moreover, FE measurements from the arrays of nanodomes and nanodots were possible because the regions joining adjacent nanodomes and nanodots are covered with a thin percolating network of LaS over the entire array. Its presence was confirmed by measuring a low resistance value of about 2 Ohms between two electrical contacts about 1 cm apart. For each location, a full set of I-V characteristics (total measured current versus applied voltage) for different values of d, the distance between the cathode surface and the probe ball, was measured. This set of measurements was then analyzed in order to extract the apparent current density αJ versus actual applied local field γF, where γ is the local geometrical field enhancement at the surface of the cathode In order to assess the FE properties from LaS nanoprotrusions, we have compared the FE from nanodome cathodes with that from planar thin film LaS cathodes. This comparative methodology was chosen because a precise quantitative estimation of γ from topographic measurements is still subject to controversy, except for a flat surface. These experimental measurements were performed for both LaS thin films of 100 nm thickness on Si wafers and LaS nanodomes on anodic alumina films. The analysis consisted of the following steps. (1) In order to restrict the analysis of the differences in the I-V data to the surface morphology of the cathodes, both SAFEM measurements were performed with the same probe ball-to-cathode distance d = 3.65 μm. Typical I-V characteristics are shown in (2) The total FE current versus applied voltage (I-V) characteristics were measured for different values of the probe-ball-to-cathode-surface distance d. From these data, the apparent current densities (α t f J and α nd J) as a a function of the applied local field were extracted ACKNOWLEDGMEN

Measurement and modelling of blast movement to reduce ore losses and dilution at Ahafo Gold Mine in Ghana

Blast induced rock mass displacement can have a significant impact on grade control. The mischaracterisation of the grade boundaries without proper understanding of blast movement can lead to significant financial losses in terms of ore losses and dilution. Ore dilution occurs when waste material is miscategorised as ore and sent for processing diluting the run of mine head grade and recovery. Ore losses take place when valuable mineral is miscategorised as waste and sent to the waste dumps. The geologists at Newmont Ahafo Mine have realised the impact of blast  movement on ore losses and dilution and have implemented a blast movement study to minimise blast induced ore losses and dilution. This paper describes the application of the latest measurements and modelling techniques in understanding the blast dynamics and develops site specific solutions to minimise blast induced dilution and ore losses. These solutions are validated at Newmont Ahafo open pit mine through systematic trials and subsequently incorporated into site standard operating procedures to sustain the benefits

Field Emission Properties of Multi-level Self Assembled Mesoscopic Structures on Nanoporous Templates

We report a new multi-modal self assembly technique in which a rich structural diversity of distinct moieties emerge when thin films of a wide variety of materials are deposited on nanoporous substrates using different techniques. We also report multi-level self assembly where one set of self assembled nanostructures seeds the self assembly of another set. The multi-modal self assembly has been observed using flexible alumina templates containing hexagonal arrays of cylindrical pores that are 50 nm wide and 500 nm in length and also on nanoporous Si templates. The latter were formed by anodization of thin film alumina templates deposited on platinum coated silicon substrates. The deposition parameters leading to the observation of each of the moieties will be discussed in detail and the field emission (FE) properties, measured by scanning anode field emission microscopy (SAFEM), will be reported.NRC publication: Ye