Towards practical applications of quantum emitters in boron nitride

We demonstrate quantum emission capabilities from boron nitride structures which are relevant for practical applications and can be seamlessly integrated into a variety of heterostructures and devices. First, the optical properties of polycrystalline BN films grown by metalorganic vapour-phase epitaxy are inspected. We observe that these specimens display an antibunching in the second-order correlation functions, if the broadband background luminescence is properly controlled. Furthermore, the feasibility to use flexible and transparent substrates to support hBN crystals that host quantum emitters is explored. We characterise hBN powders deposited onto polydimethylsiloxane films, which display quantum emission characteristics in ambient environmental conditions.

Pushing Raman spectroscopy over the edge: purported signatures of organic molecules in fossils are instrumental artefacts

Claims for the widespread preservation of fossilized biomolecules in many fossil animals have recently been reported in six studies, based on Raman microspectroscopy. Here, we show that the putative Raman signatures of organic compounds in these fossils are actually instrumental artefacts resulting from intense background luminescence. Raman spectroscopy relies upon the detection of photons scattered inelastically by matter as a result of its interaction with a laser beam. For many natural materials, this interaction also generates a luminescence signal that is often orders of magnitude more intense than the light produced by Raman scattering. Such luminescence, coupled with the transmission properties of the spectrometer, induced quasi-periodic ripples in the measured spectra that have been incorrectly interpreted as Raman signatures of organic molecules. Although several analytical strategies have been developed to overcome this common issue, Raman microspectroscopy as used in the studies questioned here cannot be used to identify fossil biomolecules.

Structural and Photoluminescence Studies of Er Implanted Lt-GaAs:Be

Characteristic 1.54 μm Era3+ emission has been observed from Er-implanted and annealed, low-temperature grown GaAs:Be samples. Cross-sectional transmission electron microscopy (TEM) studies reveal very little structural damage for elevated temperature implants up to an Er total fluence of 1.36 × 1014 Er/cm2. No Er emission was observed from any of the as-implanted samples, while post-implantation annealing optimized the Er emission intensity near 650°C. The Er-emission appears on top of a broad background luminescence peaking near 1500 nm. Significant enhancement of the optically active Er incorporation was achieved when the implantation was carried out at 300TC. The Er emission intensity was found to scale linearly with the Er implantation fluence for samples with an Er concentration up to ∼1019 Er/cm3. The sample with the highest Er concentration (∼1020 Er/cm3) began to show a sublinear dependence. The beginning of Er precipitation was observed after 750°C annealing, but it could even be observed after a 650°C annealing for the highest Er concentration sample. These precipitates are likely ErAs.

Attempts to Visualize Conformational Changes in a Single Protein Molecule During Function

The operation of protein molecular machines is essentially stochastic. One cannot predict exactly when an ion channel opens, or when a molecular motor makes a step. As such, working molecular machines cannot be synchronized with each other in a rigorous sense. To understand the mechanism of a protein machine, therefore, one has to watch conformational changes of individual molecules while they are at work. To this end, we have been trying to develop two approaches based on optical microscopy. One is to attach a small tag, a fluorescent probe, to an appropriate site on the protein molecule of interest. Polarization of the probe fluorescence, for example, will reveal the orientation of the fluorophore, and thus of the portion of the protein molecule to which the fluorophore is attached. A conformational change of the protein will be detected as the reorientation of the fluorophore. A prerequisite is the ability to image a single fluorophore in an aqueous environment, which we have achieved on an epifluorescence microscope by reducing its background luminescence by two orders of magnitude