Abstract High-precision placement of rare-earth ions in scalable silicon-based nanostructured materials exhibiting high photoluminescence (PL) emission, photostable and polarized emission, and near-radiative-limited excited state lifetimes can serve as critical building blocks toward the practical implementation of devices in the emerging fields of nanophotonics and quantum photonics. Introduced herein are optical nanostructures composed of arrays of ultrathin silicon carbide (SiC) nanowires (NWs) that constitute scalable one-dimensional NW-based photonic crystal (NW-PC) structures. The latter are based on a novel, fab-friendly, nanofabrication process. The NW arrays are grown in a self-aligned manner through chemical vapor deposition. They exhibit a reduction in defect density as determined by low-temperature time-resolved PL measurements. Additionally, the NW-PC structures enable the positioning of erbium (Er 3+ ) ions with an accuracy of 10 nm, an improvement on the current state-of-the-art ion implantation processes, and allow strong coupling of Er 3+ ions in NW-PC. The NW-PC structure is pivotal in engineering the Er 3+ -induced 1540-nm emission, which is the telecommunication wavelength used in optical fibers. An approximately 60-fold increase in the room-temperature Er 3+ PL emission is observed in NW-PC compared to its thin-film analog in the linear pumping regime. Furthermore, 22 times increase in the Er 3+ PL intensity per number of exited Er ions in NW-PC was observed at saturation while using 20 times lower pumping power. The NW-PC structures demonstrate broadband and efficient excitation characteristics for Er 3+ , with an absorption cross-section (~2 × 10 −18 cm 2 ) two-order larger than typical benchmark values for direct absorption in rare-earth-doped quantum materials. Experimental and simulation results show that the Er 3+ PL is photostable at high pumping power and polarized in NW-PC and is modulated with NW-PC lattice periodicity. The observed characteristics from these technologically friendly nanophotonic structures provide a promising route to the development of scalable nanophotonics and formation of single-photon emitters in the telecom optical wavelength band.
more »
« less
Inorganic Semiconductor Quantum Dots as a Saturated Excitation (SAX) Probe for Sub‐Diffraction Imaging
The photoluminescence (PL) saturation of CdSe/ZnS core/shell inorganic semiconductor quantum dots (QDs) and its utility as a probe for saturated excitation (SAX) microscopy are reported. Under saturating excitation power densities, the PL signal was demodulated and recorded at harmonics of the fundamental frequency. For commercially available Qdot® 655 ITK™ QDs, the power density required to achieve saturation was dependent upon the local environment of the QDs. For QDs deposited and dried on a glass substrate, the excitation power density required for PL saturation was less than 1 kW/cm2. Compared to this, saturation of PL for QDs dispersed in water required an excitation power density greater than 200 kW/cm2. This observation is manifested as a limitation in the imaging of hydrated samples, as demonstrated for HeLa cells labelled with biotinylated‐phalloidin followed by labelling with streptavidin‐coated QDs. As saturation affects the obtained spatial resolution in several imaging formats, including confocal imaging, the provided data will aid in obtaining the optimal spatial resolution when using QD probes to image biological samples.
more » « less- Award ID(s):
- 1709099
- NSF-PAR ID:
- 10258381
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhotoChem
- Volume:
- 5
- Issue:
- 3
- ISSN:
- 2367-0932
- Page Range / eLocation ID:
- p. 253-259
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract This paper reports the first integration of laser‐etched polycrystalline diamond microchannels with template‐fabricated microporous copper for extreme convective boiling in a composite heat sink for power electronics and energy conversion. Diamond offers the highest thermal conductivity near room temperature, and enables aggressive heat spreading along triangular channel walls with 1:1 aspect ratio. Conformally coated porous copper with thickness 25 µm and 5 µm pore size optimizes fluid and heat transport for convective boiling within the diamond channels. Data reported here include 1280 W cm−2of heat removal from 0.7 cm2surface area with temperature rise beyond fluid saturation less than 21 K, corresponding to 6.3 × 105W m−2K−1. This heat sink has the potential to dissipate much larger localized heat loads with small temperature nonuniformity (5 kW cm−2over 200 µm × 200 µm with <3 K temperature difference). A microfluidic manifold assures uniform distribution of liquid over the heat sink surface with negligible pumping power requirements (e.g., <1.4 × 10−4of the thermal power dissipated). This breakthrough integration of functional materials and the resulting experimental data set a very high bar for microfluidic heat removal.
-
more » « less
Abstract Photoinduced oxidation (doping) of conjugated polymers by complexation with oxygen can have a significant impact on electronic properties and performance in device environments. Nanofiber model forms of poly(3‐hexylthiophene) (P3HT) are investigated using single molecule spectroscopy that possess similar morphological qualities as their bulk thin film counterparts yet, heterogeneity is confined to the spatial dimensions of these particles. Specifically, P3HT nanofibers assembled in anisole solutions contain both aggregated and nonaggregated (amorphous) chains with distinct electronic properties. Excitation intensity dependent photoluminescence (PL) emission imaging is then used to expose differences in oxygen affinity and reactivity upon photoexcitation. Nanofiber regions with low PL yields tend to show faster PL intensity saturation that also degrade much faster following periods of high excitation intensity soaking. Conversely, other regions show gains in PL intensity and virtually no saturation. These PL “gainer” and “loser” behaviors are assigned as originating from amorphous and aggregated P3HT chains, respectively. The apparent propensity of aggregated chains to undergo latent oxygen doping indicates a greater affinity probably due to a larger extent of electronic delocalization in these structures. The results shed new light on degradation factors studied frequently at the bulk material level, which often lacks sufficient sensitivity to specific structural forms.
-
more » « less
Abstract While metal‐halide perovskite light‐emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, their slow operation speed and response time limit their application scope. Here, high‐speed PeLEDs driven by nanosecond electrical pulses with a rise time of 1.2 ns are reported with a maximum radiance of approximately 480 kW sr−1 m−2at 8.3 kA cm−2, and an external quantum efficiency (EQE) of 1% at approximately 10 kA cm−2, through improved device configuration designs and material considerations. Enabled by the fast operation of PeLEDs, the temporal response provides access to transient charge carrier dynamics under electrical excitation, revealing several new electroluminescence quenching pathways. Finally, integrated distributed feedback (DFB) gratings are explored, which facilitate more directional light emission with a maximum radiance of approximately 1200 kW sr−1 m−2at 8.5 kA cm−2, a more than two‐fold enhancement to forward radiation output.
-
more » « less
This paper addresses one of the key issues in the scientific community of Si photonics: thin-film quality and the light emission properties of band-engineered n+Germanium-on-Silicon (Ge-on-Si). Compared to the traditional delta doping approach, which was utilized in the first electrically-pumped Ge-on-Si lasers, we offer an n+Ge-on-Si thin film with better material quality and higher carrier injection efficiency grown by metal-organic chemical vapor deposition (MOCVD). The impacts of thermal cycle annealing and Si substrate offcut on the thin film quality were investigated, including surface roughness, strain, threading dislocation density, Si-Ge interdiffusion, and dopant diffusion. It was revealed that: 1) MOCVD overcomes the outdiffision issue of n-type dopants by having the dopant peaks at the bottom of the Ge films; 2) the characterization of the light emission properties of these MOCVD n+Ge-on-Si samples (1.0 × 1019cm−3doped) compared to delta-doped ultra-high vacuum chemical vapor deposition (UHVCVD) Ge, showing comparable photoluminescence (PL) spectral intensity at 1/4 of the doping level; 3) Detailed PL spectral analyses showed that population inversion from the direct gap transition has been achieved, and the injected electron density in the direct Γ valley is comparable to that of the delta-doped sample even though the n-type doping level is 75% less; and 4) Experimental evidences that Si-Ge interdiffusion has a much larger impact on PL intensity than threading dislocation density in the range of 108-109/cm3. These results indicate that MOCVD n+Ge is very promising to reduce the threshold of Ge gain media on Si notably.
