T. Merritt

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

High-quality epitaxial Ge layers for GaAs/Ge/GaAs heterostructures were grown in situ in an arsenic-free environment on (100) off-oriented GaAs substrates using two separate molecular beam epitaxy (MBE) chambers, connected via vacuum transfer chamber. The structural, morphological, and band offset properties of these heterostructures are investigated. Reflection high energy electron diffraction studies exhibited (2 × 2) Ge surface reconstruction after the growth at 450  °C and also revealed a smooth surface for the growth of GaAs on Ge. High-resolution triple crystal x-ray rocking curve demonstrated high-quality Ge epilayer as well as GaAs/Ge/(001)GaAs heterostructures by observing Pendellosung oscillations and that the Ge epilayer is pseudomorphic. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of ∼0.45 nm and room temperature photoluminescence spectroscopy exhibited direct bandgap emission at 1583 nm. Dynamic secondary ion mass spectrometry depth profiles of Ga, As,...

Upconverting nanocomposites dispersed in urea-containing acrylics

Lanthanide-doped upconverting nanoparticles (UCNPs) have the ability to convert low energy photons into high energy photons, making this material appealing for a variety of scientific pursuits, from solar energy conversion to bioimaging. A combination of polymers and nanocomposites increases the utility of these upconverting nanoparticles allowing nanoparticles to be added to any device compatible with polymer coatings. Here, trifluoroacetate salt decomposition enables Er/Yb doped NaYF4 upconverting nanoparticle synthesis. The subsequent deposition of a silica nanoshell yields polar silica-coated upconverting nanoparticles, enabling composite formation with polar urea-containing methacrylic polymers. Hydrogen bonding between urea groups in the polymer and the silica-coated nanoparticles allowed for dispersion of the upconverting nanoparticles to form upconverting composite films. These films exhibit desirable upconversion comparable to the nanoparticles dispersed in methanol. Urea-containing polymers are promising candidates for matrices in nanocomposites formed with polar silica nanoparticles due to favorable polymer–nanoparticle interactions. This architecture is superior to urea-methacrylate homopolymers, since the central low glass transition temperature block will provide critical ductility to the film, thus rendering the film to be durable for optical applications.

Photoluminescence lineshape and dynamics of localized excitonic transitions in InAsP epitaxial layers

The excitonic radiative transitions of InAsxP1−x (x = 0.13 and x = 0.40) alloy epitaxial layers were studied through magnetic field and temperature dependent photoluminescence and time-resolved photoluminescence spectroscopy. While the linewidth and lineshape of the exciton transition for x = 0.40 indicate the presence of alloy broadening due to random anion distribution and the existence of localized exciton states, those of x = 0.13 suggest that this type of compositional disorder is absent in x = 0.13. This localization is further supported by the behavior of the exciton transitions at low temperature and high magnetic fields. InAs0.4P0.6 exhibits anomalous “S-shaped” temperature dependence of the excition emission peak below 100 K as well as linewidth broadening at high magnetic fields due to the compression of the excitonic volume amid compositional fluctuations. Finally, photoluminescence decay patterns suggest that the excitons radiatively relax through two channels, a fast and a slow decay. While ...

Optoperforation of single, intact Arabidopsis cells for uptake of extracellular dye-conjugated dextran

A plant science research goal is to manipulate single cells in an intact organism in order to study their interactions with neighboring cells. Based on a technique previously demonstrated in isolated plant cells, mammalian cells and cyanobacteria, Arabidopsis epidermal cells were optoperforated to allow for uptake of external cascade blue-labeled dextrans. Adverse organelle responses were determined to be minimal and dye retention was demonstrated for at least 72 hours. This technique overcomes the physical challenges presented by the plant cell wall and demonstrates the feasibility of in situ optoperforation.

Carrier Dynamics in Parabolic InSb Based Multi Quantum Wells

We report on time resolved differential transmission experiments in InSb/AlxIn1‐xSb multi‐parabolic quantum wells in the mid‐infrared. The results of our numerical calculations, which included band non‐parabolicity and the digital composition of the parabolic wells, allowed us to identify and probe the possible interband transitions. Our results provide new information on the carrier relaxations in this material system.

Time Resolved Spectroscopy of MOVPE Grown Narrow Gap Ferromagnetic Semiconductors

We report on time resolved differential transmission experiments to provide insight into both the time scales and the nature of the microscopic interactions and carrier dynamics in MOVPE grown ferromagnetic InMnAs and InMnSb. Theoretical calculations of the electronic structure for InMnAs are performed using an 8 band k⋅p model which includes non‐parabolicity of the conduction bands; strong band‐mixing of the valence bands; as well as coupling of Mn impurities to the electrons and holes. Our preliminary theoretical results explain the sign change in the differential transmission signal as a function of probe wavelength.