Oxide and hydroxide minerals are a class of inorganic materials commonly associated with metals and are used in a wide variety of applications ranging from pigments and environmental cleanup to battery cells and catalysts. This work presents initial characterization of synthetic crystals of goethite, hematite, and cryptomelane subjected to shock compression experiments using transmission electron microscopy (TEM) and confocal Raman spectroscopy (CRS). Given the high adsorption property of these minerals, doping with rare-earth elements has the potential to result in novel optical properties and applications.
Minimally invasive surgeries use small incisions through needles for operations to be conducted from outside the patient’s body. Therefore, an accurate map of the distribution of tissues in real-time is critical to ensure patient safety. In this work, we explore all optical sensing methods as simple, fast, and economic alternatives to commercial imaging modalities. Simulated tissues have been prepared using gelatin to conduct optical characterization experiments. Transmission and fluorescence spectra on homogenous and heterogenous gelatin with different concentrations would be reported, with a focus on developing an optoelectronic technique for mapping of tissue distribution. Finally, this technique would be validated through real-time needle insertion experiment into a gelatin sample to track the spectral data of the tissue environments. This work could help track biological tissues where the spectral data could help surgeons visualize the needle-tissue environments in real-time.
In this work, we report postmortem studies in shock compressed direct band-gap semiconductor crystals. Commercial III-V wafers were characterized before and after dynamically compressing them using a laser driven flyer plate system (LDFPS), developed and characterized in the recent years by the Dlott research group. LDFPS is an inverted shock microscope with high time and space resolutions, and is suitable for high-throughput shock compression experiments. The postmortem characterization in recovered samples via x-ray diffraction, photoluminescence, and Raman measurements showed evidence of permanent alterations in the crystal structures of the compressed materials. Considering the wide usage of semiconductor bulk substrates in the hi-tech industry, we note the significance of practical, pressure-induced band structure engineering pathways.
The mineral apatite and apatite-like compounds are a class of promising inorganic materials, reported to have a wide range of applications including, but not limited to, oxide fuel cells, phosphors, catalysis, and biomaterials. The mineral could be easily tuned via ionic substitutions for enhancement of various optoelectronic properties. In this study we report characterization of natural apatite crystals from different sources using optical spectroscopy, transmission electron microscopy, and X-ray diffraction. We also note roles of external factors such as high pressure and doping with rareearth elements on the optoelectronic properties of the mineral to explore alternate pathways for material synthesis and potential new applications.
Quantum dots (QD) embedded in polymer matrix are a powerful material system for novel optoelectronic applications. Apart from the typical advantages available from QD systems such as size dependent optical properties and narrow emissions, they can also be used as a future multiplexed sensing device. In this work, we report optical emission from a two-color QD-doped silica and polymer system through photoluminescence measurements. The QD-based thin films could be excited through single wavelength in the visible range, and emitted at two distinct peaks with controllable intensities depending on the ratio of QDs doped into the silica and polymer. The emission increase of the two peaks as a function of excitation intensity was analyzed and compared with more traditional QD films deposited on bulk semiconductor substrates.
Light emission from PbS quantum dots (QDs) is an intriguing topic from application perspectives, and even after myriad of articles, still has open questions. The paper highlights the optical characterization of PbS QDs deposited via solvent deposition on semi-insulating GaAs substrates. The QD thin films were characterized by two-photon excited photoluminescence (TPL) measurements, exciting the samples with increasing pulsed laser (1064 nm, 10 Hz, 26 ps) intensities. The work reveals alterations of the optical properties of GaAs when hetero-paired with PbS QDs, as demonstrated by the trend of the TPL peak increase, the energy where the TPL peak takes place, and the overall dynamics of the peak shift. We also report that the TPL intensity increase of PbS QDs shows the same trend as the single-photon excited emission, and observed photo-induced doping of the QDs, i.e., the dynamic Burstein-Moss blue shift. The work stresses the possibility to modify the optical properties of semiconductor hosts by means of heteropairing with QDs. Through this work, we further attempt to reconcile observations, which are much different from reported classical models in semiconductor heterostructures.
In this work we investigate carrier dynamics of narrow gap ferromagnetic alloys grown by MOVPE. We determine the intraband and interband relaxation times in these material systems where the samples are excited with photon energies above the band gap of InMnAs and InMnSb films. Our results are important for understanding the electronic states and the relaxation mechanisms in these ferromagnetic materials.
In light of the growing interest in spin-related phenomena and devices, there is now renewed interest in the
science and engineering of narrow gap semiconductors. In this work, time resolved spectroscopy of InSb-based parabolic
multi-quantum wells and narrow gap ferromagnetic alloys grown by MOVPE, have been pursued. In addition, in this
study, we report on CR experiments carried out on the ferromagnetic InMnAs film, on which clear resonance signals
have been successfully observed in high magnetic fields. Investigation of the electronic structure of III-Mn-V alloys by
techniques such as the cyclotron resonance can shed important light on the origin of ferromagnetism and the p-d
exchange interaction in III-Mn-V systems. Our results are important for understanding the electronic and magnetic states
in these material systems.
In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the
science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such
as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies
have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs
ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers
and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW
where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the
differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly
influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as
the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our
measured T1 is comparable to the reported measurements in MBE grown InMnAs and several time resolved
measurements on InAs.
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