Structure and Light Emission in Germanium Nanoparticles

PhDIn this study, advanced techniques in the synthesis of germanium nanoparticles have been investigated. Based on physical and chemical production methods, including stain etching, liquid-phase pulsed laser ablation, sol-gel synthesis and two benchtop colloidal synthesis techniques, germanium nanoparticles with various surface terminations were formed. Out of those, colloidal synthesis by benchtop chemistry (named CS1) were found to be the most promising synthesis route in terms of yield and stability of the as-prepared Ge qdots and its luminescence with almost no oxides present. For the characterisation of Ge nanoparticles, Raman spectroscopy, Photoluminescence (PL) spectroscopy, Transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX) and selective area electron diffraction (SAED) techniques were utilised before conducting X-ray absorption spectroscopy (XAS) measurements. The structure and morphology of Ge quantum dots formed using colloidal synthesis routes were found to fit best to the model of a nanocrystalline core surrounded by disordered Ge layers. Optically-detected X-ray absorption studies have enabled us to establish a direct link between nanoparticles structure and the source of the luminescence. The most important outcome of this study is that it provides a direct experimental route linking synthesis conditions and properties of nanosized Ge quantum dots. Furthermore, using annealing, we can control surface termination even further, as well as change particle size and possibly produce metastable phases.School of Physics and Astronomy, Queen Mary University of Londo

Spectroscopic super-resolution fluorescence cell imaging using ultra-small Ge quantum dots

QMUL/CSC scholarship (2011611045); BBSRC grant (BB/J001473/1)

Low-Temperature Synthesis of Silicon Oxynitride-Doped Si for Tunable Bragg Gratings Homogeneously Deposited on Si, SiO2, and Borosilicate Substrates and the tip of SM and PM Optical Fibers

Optical tunability and repeatability are essential in fabricating optoelectronic devices from waveguides to Bragg gratings (BGs) for high-energy, high-power, mode-locking, and sensing applications. For this purpose, a controlled adjustment in the optical properties, including the refractive index of the deposited nanolayers, becomes critical. This study reveals that silicon oxynitride (SiON) doping into silicon (Si) offers a new way for the preparation of novel Si-based devices with an emphasis on the BGs for filtering a particular portion of an electromagnetic spectrum, including the wavelengths of 800, 976, 1550, and 1840 nm. Control on the incident angle dependence of the BGs was demonstrated at Watt-level for the wavelength of 976 nm. Amorphous SiON-doped Si layers on alternating SiO2 can be synthesized on bulk substrates and different optical fibers at relatively low temperatures with wide and narrow bandwidths. The high reflectivity of the novel Si-based BGs reveals over −22 dB reflection using typical optical fibers, including standardsingle-mode fibers and high-birefringent polarization-maintaining (PM) fibers. The polarized transmission measurement over the BG on the PMfiber shows the BGs do not deteriorate the PM properties, strongly yielding a beat length of 1.68 mm and birefringence of 9.2 × 10−4 at the telecom C band

Phase-Shifted Bragg-Grating Consisting of Silicon Oxynitride Doped Silicon and Silica Alternating Layers Lab-on-Fiber for Biosensors with Ultrahigh Sensitivity and Ultralow Detection Limit

Fabry-Perot (FP) optical fiber sensors are reported to be highly sensitive for detecting various physical, chemical, and biological objects. In this study, an FP-based Phase Shifted Bragg-Grating Lab-on-Fiber (PSBG-LOF) is presented to determine ultralow glucose concentrations in liquids by using a novel PSBG at the end facet of a single-mode fiber (SMF). The proposed LOF consists of an intermediate silica layer sandwiched between two identical PSBGs formed by 4.5 pairs of siliconoxynitrite (SiON) doped silicon (Si), which are newly synthesized silica (SiO2) thin films, all deposited by the plasma enhanced chemical vapor deposition (PECVD) method. The SiON-doped Si molecule group was used for the first time as PSBG structures and LOF of the glucose in liquids. Our findings with the proposed sensors revealed that the sensitivity value was 14904 nm/RIU (4.3 pm/ppm and 4.29 nm/(mg/ml)) and the detection limit was calculated as 1.98 × 10−6 RIU. In addition, the proposed sensor is insensitive to temperature changes in the range of 25°C-45°C. The results are very promising for the in-vivo biosensing applications comprising temperature unresponsive LOF

Spectroscopic super-resolution fluorescence cell imaging using ultra-small Ge quantum dots

We demonstrate a spectroscopic imaging based super-resolution approach by separating the overlapping diffraction spots into several detectors during a single scanning period and taking advantage of the size-dependent emission wavelength in nanoparticles. This approach has been tested using off-the-shelf quantum dots (Invitrogen Qdot) and inhouse novel ultra-small (â¼3 nm) Ge QDs. Furthermore, we developed a method-specific Gaussian fitting and maximum likelihood estimation based on a Matlab algorithm for fast QD localisation. This methodology results in a three-fold improvement in the number of localised QDs compared to non-spectroscopic images. With the addition of advanced ultra-small Ge probes, the number can be improved even further, giving at least 1.5 times improvement when compared to Qdots. Using a standard scanning confocal microscope we achieved a data acquisition rate of 200 ms per image frame. This is an improvement on single molecule localisation super-resolution microscopy where repeated image capture limits the imaging speed, and the size of fluorescence probes limits the possible theoretical localisation resolution. We show that our spectral deconvolution approach has a potential to deliver data acquisition rates on the ms scale thus providing super-resolution in live systems. © 2017, OSA - The Optical Society. All rights reserved

Structural, Optical, Electrical and Electrocatalytic Activity Properties Of Luminescent Organic Carbon Quantum Dots

Bolat, Atilla (Arel Author), Yıldırım, Osman (Arel Author)Carbon is an essential element in human life and recently becoming technologically prominent due to the emerging field of "Carbononics". We demonstrate organic carbon quantum dots (qdots) containing nitrile bonded (C N bond) d-glucose-like traces in various sizes obtained from wheat flour to be promising for imaging applications and to possess a relaxor ferroelectric property and an enhanced electrocatalytic activity that could reduce the cost of energy devices and simple to scale up for the commercialization. The secondary electron microscopy (SEM) imaging shows that the particle size of carbon qdots can be controlled via the sonication exposure time. Elemental analysis and vibrational spectroscopy results show that carbon qdots are sensitive to N-2 gas in the atmosphere and could weaken its "carbogenic" property by making a stable C N bond at ambient atmosphere. Rietveld analysis and HR-TEM studies demonstrate that the structure of the C qdots was found to fit best with an acentric primitive orthorhombic lattice. The laser scanning confocal microscopy (LSCM) images show enhancement of the light emission when reducing the size and characteristic excitation wavelength-dependent light emission of C qdots. The photoluminescence and UV-Vis absorption spectroscopy techniques show surface dominant emission and absorption upon the nitrile bonding

Pressure-induced amorphization and a new high density amorphous metallic phase in matrix-free Ge nanoparticles

Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge