Scalable manufacturing of quantum light emitters in silicon under rapid thermal annealing.

Quantum light sources play a fundamental role in quantum technologies ranging from quantum networking to quantum sensing and computation. The development of these technologies requires scalable platforms, and the recent discovery of quantum light sources in silicon represents an exciting and promising prospect for scalability. The usual process for creating color centers in silicon involves carbon implantation into silicon, followed by rapid thermal annealing. However, the dependence of critical optical properties, such as the inhomogeneous broadening, the density, and the signal-to-background ratio, on centers implantation steps is poorly understood. We investigate the role of rapid thermal annealing on the dynamic of the formation of single color centers in silicon. We find that the density and the inhomogeneous broadening greatly depend on the annealing time. We attribute the observations to nanoscale thermal processes occurring around single centers and leading to local strain fluctuations. Our experimental observation is supported by theoretical modeling based on first principles calculations. The results indicate that annealing is currently the main step limiting the scalable manufacturing of color centers in silicon.

Macrophage blockade using nature-inspired ferrihydrite for enhanced nanoparticle delivery to tumor.

The rapid elimination of systemically administered drug nanocarriers by the mononuclear phagocyte system (MPS) compromises nanomedicine delivery efficacy. To mitigate this problem, an approach to block the MPS has been introduced and implemented by intravenous pre-administering blocker nanoparticles. The required large doses of blocker nanoparticles appeared to burden the MPS, raising toxicity concerns. To alleviate the toxicity issues in MPS blockade, we propose an intrinsically biocompatible blocker, ferrihydrite - a metabolite ubiquitous in a biological organism. Ferrihydrite particles were synthesized to mimic endogenous ferritin-bound iron. Ferrihydrite surface coating with carboxymethyl-dextran was found to improve MPS blockade dramatically with a 9-fold prolongation of magnetic nanoparticle circulation in the bloodstream and a 24-fold increase in the tumor targeted delivery. The administration of high doses of ferrihydrite caused low toxicity with a rapid recovery of toxicological parameters after 3 days. We believe that ferrihydrite particles coated with carboxymethyl-dextran represent superior blocking biomaterial with enviable biocompatibility.

A comparative Raman study between PrMnO 3, NdMnO 3, TbMnO 3 and DyMnO 3.

In this paper, we present a detailed Raman study of the non-multiferroic compounds PrMnO 3 and NdMnO 3 and the multiferroic compounds TbMnO 3 and DyMnO 3 as a function of temperature and magnetic field. All studied systems show anomalous phonon shifts close to the Néel transition T N . In PrMnO 3 and NdMnO 3, the frequency softenings are partly attributed to an orbital-spin-phonon coupling whereas in TbMnO 3 and DyMnO 3, the relatively weak frequency shifts are rather attributed to an expansion of the Mn-O bond lengths. On the other hand, the frequencies of TbMnO 3 phonons are shifted as a function of magnetic field, while those of PrMnO 3 remain unaffected. These frequency shifts are interpreted in terms of local oxygen rearrangements under magnetic field that could play an important role in the multiferroicity of TbMnO 3 and DyMnO 3.

Super-diffusion of excited carriers in semiconductors.

The ultrafast spatial and temporal dynamics of excited carriers are important to understanding the response of materials to laser pulses. Here we use scanning ultrafast electron microscopy to image the dynamics of electrons and holes in silicon after excitation with a short laser pulse. We find that the carriers exhibit a diffusive dynamics at times shorter than 200 ps, with a transient diffusivity up to 1,000 times higher than the room temperature value, D0≈30 cm2s-1. The diffusivity then decreases rapidly, reaching a value of D0 roughly 500 ps after the excitation pulse. We attribute the transient super-diffusive behaviour to the rapid expansion of the excited carrier gas, which equilibrates with the environment in 100-150 ps. Numerical solution of the diffusion equation, as well as ab initio calculations, support our interpretation. Our findings provide new insight into the ultrafast spatial dynamics of excited carriers in materials.

Quantitative Tissue Spectroscopy of Near Infrared Fluorescent Nanosensor Implants.

Implantable, near infrared (nIR) fluorescent nanosensors are advantageous for in vivo monitoring of biological analytes since they can be rendered selective for a particular target molecule while utilizing their unique optical properties and the nIR tissue transparency window for information transfer without an internal power source or telemetry. However, basic questions remain regarding the optimal encapsulation platform, geometrical properties, and concentration ranges required for high signal to noise ratio and effective detection through biological tissue. In this work, we systematically explore these variables quantitatively to optimize the performance of such optical nanosensors for biomedical applications. We investigate both alginate and polyethylene glycol (PEG) as model hydrogel systems, encapsulating d(GT)15 ssDNA-wrapped single-walled carbon nanotubes (SWNT) as model fluorescent nanoparticle sensors, responsive to riboflavin. Hydrogel sensors implanted 0.5 mm into thick tissue samples exhibit 50% reduction of initial fluorescence intensity, allowing an optical detection limit of 5.4 mm and 5.1 mm depth in tissue for alginate and PEG gels, respectively, at a SWNT concentration of 10 mg L(-1), and 785 nm laser excitation of 80 mW and 30 s exposure. These findings are supported with in vivo nIR fluorescent imaging of SWNT hydrogels implanted subcutaneously in mice. For the case of SWNT, we find that the alginate system is preferable in terms of emission intensity, sensor response, rheological properties, and shelf life.

Magnetoelectric effect and phase transitions in CuO in external magnetic fields.

Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of ≈ 50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions.

In vivo biosensing via tissue-localizable near-infrared-fluorescent single-walled carbon nanotubes.

Single-walled carbon nanotubes are particularly attractive for biomedical applications, because they exhibit a fluorescent signal in a spectral region where there is minimal interference from biological media. Although single-walled carbon nanotubes have been used as highly sensitive detectors for various compounds, their use as in vivo biomarkers requires the simultaneous optimization of various parameters, including biocompatibility, molecular recognition, high fluorescence quantum efficiency and signal transduction. Here we show that a polyethylene glycol ligated copolymer stabilizes near-infrared-fluorescent single-walled carbon nanotubes sensors in solution, enabling intravenous injection into mice and the selective detection of local nitric oxide concentration with a detection limit of 1 µM. The half-life for liver retention is 4 h, with sensors clearing the lungs within 2 h after injection, thus avoiding a dominant route of in vivo nanotoxicology. After localization within the liver, it is possible to follow the transient inflammation using nitric oxide as a marker and signalling molecule. To this end, we also report a spatial-spectral imaging algorithm to deconvolute fluorescence intensity and spatial information from measurements. Finally, we demonstrate that alginate-encapsulated single-walled carbon nanotubes can function as implantable inflammation sensors for nitric oxide detection, with no intrinsic immune reactivity or other adverse response for more than 400 days.

Visualizing the distribution of synapses from individual neurons in the mouse brain.

BACKGROUND: Proper function of the mammalian brain relies on the establishment of highly specific synaptic connections among billions of neurons. To understand how complex neural circuits function, it is crucial to precisely describe neuronal connectivity and the distributions of synapses to and from individual neurons. METHODS AND FINDINGS: In this study, we present a new genetic synaptic labeling method that relies on expression of a presynaptic marker, synaptophysin-GFP (Syp-GFP) in individual neurons in vivo. We assess the reliability of this method and use it to analyze the spatial patterning of synapses in developing and mature cerebellar granule cells (GCs). In immature GCs, Syp-GFP is distributed in both axonal and dendritic regions. Upon maturation, it becomes strongly enriched in axons. In mature GCs, we analyzed synapses along their ascending segments and parallel fibers. We observe no differences in presynaptic distribution between GCs born at different developmental time points and thus having varied depths of projections in the molecular layer. We found that the mean densities of synapses along the parallel fiber and the ascending segment above the Purkinje cell (PC) layer are statistically indistinguishable, and higher than previous estimates. Interestingly, presynaptic terminals were also found in the ascending segments of GCs below and within the PC layer, with the mean densities two-fold lower than that above the PC layer. The difference in the density of synapses in these parts of the ascending segment likely reflects the regional differences in postsynaptic target cells of GCs. CONCLUSIONS: The ability to visualize synapses of single neurons in vivo is valuable for studying synaptogenesis and synaptic plasticity within individual neurons as well as information flow in neural circuits.