Performance of long-wave infrared band of microstructured heavily doped InAsSb on type II superlattice layer part 1: the photonic study.

This article deals with the optical study of nanostructured components which absorb light across the entire long-wave infrared (LWIR) spectral band. The components are made of type-II superlattice (T2SL) absorber and highly doped InAsSb, the latter being nanostructured to ensure multiple resonances. We studied two components: in the first one, the T2SL has a thickness of 1.6 µm, and in the second its thickness is 300 nm. The calculated absorption spectra were shown and the components revealed high absorption thanks to optical resonance and high angular acceptance. A fabrication process has been developed, and optical measurements have confirmed the reliability of the model.

A Series of 8 Illicit Fentanyl Intoxication Deaths in Infants and Toddlers.

ABSTRACT: We report 8 children younger than 2 years who died from acute illicit fentanyl intoxications in Connecticut between 2020 and 2022.The Connecticut Office of the Chief Medical Examiner (CT OCME) investigates all unexpected, violent, and suspicious deaths in Connecticut. The CT OCME's electronic database was searched for fentanyl deaths by age. All underwent autopsies and toxicology testing.The ages ranged from 28 days to 2 years (mean age, 12 months). The causes of death involved acute fentanyl intoxications with 1 having xylazine, 1 having para-fluorofentanyl, and 1 having cocaine and morphine. All the manners of death were certified as homicide. The postmortem fentanyl blood concentrations ranged from 0.40 to 46 ng/mL. Most of the children were found unresponsive after being put to sleep. Three were co-sleeping with adults (2 in bed; 1 on a recliner). There was a known history of parental/caregiver drug abuse in 7 of 8 of the fatalities.We summarize the key investigative, autopsy, and toxicological findings. As illicit fentanyl use increases, there is a potential for infant exposure and death. The investigation and certification of these deaths and the role of intentional administration versus inadvertent exposure due to caregiver neglect in the context of the certification of the manner of death are described.

Multiresonant Grating to Replace Transparent Conductive Oxide Electrode for Bias Selected Filtering of Infrared Photoresponse.

Optoelectronic devices rely on conductive layers as electrodes, but they usually introduce optical losses that are detrimental to the device performances. While the use of transparent conductive oxides is established in the visible region, these materials show high losses at longer wavelengths. Here, we demonstrate a photodiode based on a metallic grating acting as an electrode. The grating generates a multiresonant photonic structure over the diode stack and allows strong broadband absorption. The obtained device achieves the highest performances reported so far for a midwave infrared nanocrystal-based detector, with external quantum efficiency above 90%, detectivity of 7 × 1011 Jones at 80 K at 5 µm, and a sub-100 ns time response. Furthermore, we demonstrate that combining different gratings with a single diode stack can generate a bias reconfigurable response and develop new functionalities such as band rejection.

Mid-wave infrared sensitized InGaAs using intraband transition in doped colloidal II-VI nanocrystals.

Narrow bandgap nanocrystals (NCs) are now used as infrared light absorbers, making them competitors to epitaxially grown semiconductors. However, these two types of materials could benefit from one another. While bulk materials are more effective in transporting carriers and give a high degree of doping tunability, NCs offer a larger spectral tunability without lattice-matching constraints. Here, we investigate the potential of sensitizing InGaAs in the mid-wave infrared throughout the intraband transition of self-doped HgSe NCs. Our device geometry enables the design of a photodiode remaining mostly unreported for intraband-absorbing NCs. Finally, this strategy allows for more effective cooling and preserves the detectivity above 108 Jones up to 200 K, making it closer to cryo-free operation for mid-infrared NC-based sensors.

Lithium-Ion Glass Gating of HgTe Nanocrystal Film with Designed Light-Matter Coupling.

Nanocrystals' (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm-2 and can be operated over a broad range of temperatures (130-300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W-1 or an external quantum efficiency of 500%) over a broadband spectral range.

Helmholtz Resonator Applied to Nanocrystal-Based Infrared Sensing.

While the integration of nanocrystals as an active medium for optoelectronic devices progresses, light management strategies are becoming required. Over recent years, several photonic structures (plasmons, cavities, mirrors, etc.) have been coupled to nanocrystal films to shape the absorption spectrum, tune the directionality, and so on. Here, we explore a photonic equivalent of the acoustic Helmholtz resonator and propose a design that can easily be fabricated. This geometry combines a strong electromagnetic field magnification and a narrow channel width compatible with efficient charge conduction despite hopping conduction. At 80 K, the device reaches a responsivity above 1 A·W-1 and a detectivity above 1011 Jones (3 µm cutoff) while offering a significantly faster time-response than vertical geometry diodes.

The complex optical index of PbS nanocrystal thin films and their use for short wave infrared sensor design.

As nanocrystals (NCs) gain maturity, they become central building blocks for optoelectronics in devices such as solar cells and, more recently, infrared focal plane arrays. Now that the proof of concept of these devices has been established, their optimization requires a deeper understanding of their electronic and optical features to engineer their optoelectronic properties accurately. Though PbS NCs have been extensively investigated, the complex optical index of PbS NC thin films remains mostly unknown. Some previous works have unveiled the optical index for this type of material optimized for solar cells (excitonic peak at 940 nm), but longer wavelengths remain scarce and surface chemistry effects, which are known to be of central importance for layer doping, are simply unexplored. Here, we conduct a systematic investigation of the complex optical index of PbS NC thin films using broadband spectrally resolved ellipsometry. The obtained results are then compared with simulations combining tight-binding (TB) modeling at the NC level and the Bruggeman model to expand the results to the film scale. While TB calculation gives the NC optical indices, we extract the key NC film parameters such as the NC volume fraction and ligand indices by fitting the Bruggeman formula to ellipsometry measurements. We also bring evidence that this joint modeling method can be conducted without the need for ellipsometry data while preserving the main feature of the experimental results. Finally, the unveiled optical indices are used to model the absorption of short-wave infrared diode stacks based on PbS NCs and are relevant for state-of-the-art devices. Our electromagnetic modeling shows that the absorption within the contact is now a major limitation of the current device operated at the telecom wavelength.

Bias Tunable Spectral Response of Nanocrystal Array in a Plasmonic Cavity.

Nanocrystals (NCs) have gained considerable attention for their broadly tunable absorption from the UV to the THz range. Nevertheless, their optical features suffer from a lack of tunability once integrated into optoelectronic devices. Here, we show that bias tunable aspectral response is obtained by coupling a HgTe NC array with a plasmonic resonator. Up to 15 meV blueshift can be achieved from a 3 µm absorbing wavelength structure under a 3 V bias voltage when the NC exciton is coupled with a mode of the resonator. We demonstrate that the blueshift arises from the interplay between hopping transport and inhomogeneous absorption due to the presence of the photonic structure. The observed tunable spectral response is qualitatively reproduced in simulation by introducing a bias-dependent diffusion length in the charge transport. This work expands the realm of existing NC-based devices and paves the way toward light modulators.

Infrared photoconduction at the diffusion length limit in HgTe nanocrystal arrays.

Narrow band gap nanocrystals offer an interesting platform for alternative design of low-cost infrared sensors. It has been demonstrated that transport in HgTe nanocrystal arrays occurs between strongly-coupled islands of nanocrystals in which charges are partly delocalized. This, combined with the scaling of the noise with the active volume of the film, make case for device size reduction. Here, with two steps of optical lithography we design a nanotrench which effective channel length corresponds to 5-10 nanocrystals, matching the carrier diffusion length. We demonstrate responsivity as high as 1 kA W-1, which is 105 times higher than for conventional µm-scale channel length. In this work the associated specific detectivity exceeds 1012 Jones for 2.5 µm peak detection under 1 V at 200 K and 1 kHz, while the time response is as short as 20 µs, making this performance the highest reported for HgTe NC-based extended short-wave infrared detection.

Three multispectral configurations of a snapshot kaleidoscope-based camera in long wavelength infrared spectral band.

In the field of spectral imaging, numerous instruments use scanning-based technologies. However, the temporal dimension of these systems, whether to scan the spectrum or scan the scene, can be an issue for some applications. This is particularly the case when trying to observe and identify rapid temporal variations in a fixed scene or detecting objects of interest when moving. In this case, it is suitable to observe the desired spectral information of the scene simultaneously, and so-called snapshot systems have been thus investigated. In this paper, we study the ability of a kaleidoscope-based multiview camera to acquire multispectral information in the long wavelength infrared. Several strategies and technologies will be compared to add the spectral function inside the different blocks of a kaleidoscope-based camera: the front lens, the kaleidoscope, or the reimaging lens. The studied camera uses an uncooled infrared detector and thus must deal with the issue of having a large aperture.

Impact of statewide safe sleep legislation on hospital practices and rates of sudden unexpected infant deaths.

BACKGROUND: Sudden Unexpected Infant Death (SUID) is the leading cause of death in the post-neonatal period in the United States. In 2015, Connecticut (CT) passed legislation to reduce the number of SUIDs from hazardous sleep environments requiring birthing hospitals/centers provide anticipatory guidance on safe sleep to newborn caregivers before discharge. The objective of our study was to understand the barriers and facilitators for compliance with the safe sleep legislation by birthing hospitals and to determine the effect of this legislation on SUIDs associated with unsafe sleep environments. METHODS: We surveyed the directors and/or educators of the 27 birthing hospitals & one birthing center in CT, about the following: 1) methods of anticipatory guidance given to parents at newborn hospital discharge; 2) knowledge about the legislation; and 3) barriers and facilitators to complying with the law. We used a voluntary online, anonymous survey. In addition, we evaluated the proportion of SUID cases presented at the CT Child Fatality Review Panel as a result of unsafe sleep environments before (2011-2015) and after implementation of the legislation (2016-2018). Chi-Square and Fisher's exact tests were used to evaluate the proportion of deaths due to Positional Asphyxia/Accident occurring before and after legislation implementation. RESULTS: All 27 birthing hospitals and the one birthing center in CT responded to the request for the method of anticipatory guidance provided to caregivers. All hospitals reported providing anticipatory guidance; the birthing center did not provide any anticipatory guidance. The materials provided by 26/27 (96%) of hospitals was consistent with the American Academy of Pediatrics (AAP) Guidelines. There was no significant change in rates of SUID in CT before (58.86/100,000) and after (55.92/100,000) the passage of the legislation (p = 0.78). However, more infants died from positional asphyxia after (20, 27.0%) than before the enactment of the law (p < 0.01). CONCLUSIONS: Despite most CT hospitals providing caregivers with anticipatory guidance on safe sleep at newborn hospital discharge, SUIDs rates associated with positional asphyxia increased in CT after the passage of the legislation. The role of legislation for reducing the number of SUIDs from hazardous sleep environments should be reconsidered.

Pushing Absorption of Perovskite Nanocrystals into the Infrared.

To date, defect-tolerance electronic structure of lead halide perovskite nanocrystals is limited to an optical feature in the visible range. Here, we demonstrate that IR sensitization of formamidinium lead iodine (FAPI) nanocrystal array can be obtained by its doping with PbS nanocrystals. In this hybrid array, absorption comes from the PbS nanocrystals while transport is driven by the perovskite which reduces the dark current compared to pristine PbS. In addition, we fabricate a field-effect transistor using a high capacitance ionic glass made of hybrid FAPI/PbS nanocrystal arrays. We show that the hybrid material has an n-type nature with an electron mobility of 2 × 10-3 cm2 V-1 s-1. However, the dark current reduction is mostly balanced by a loss of absorption. To overcome this limitation, we couple the FAPI/PbS hybrid to a guided mode resonator that can enhance the infrared light absorption.

HgTe Nanocrystals for SWIR Detection and Their Integration up to the Focal Plane Array.

Infrared applications remain too often a niche market due to their prohibitive cost. Nanocrystals offer an interesting alternative to reach cost disruption especially in the short-wave infrared (SWIR, λ < 1.7 µm) where material maturity is now high. Two families of materials are candidate for SWIR photoconduction: lead and mercury chalcogenides. Lead sulfide typically benefits from all the development made for a wider band gap such as the one made for solar cells, while HgTe takes advantage of the development relative to mid-wave infrared detectors. Here, we make a fair comparison of the two material detection properties in the SWIR and discuss the material stability. At such wavelengths, studies have been mostly focused on PbS rather than on HgTe, therefore we focus in the last part of the discussion on the effect of surface chemistry on the electronic spectrum of HgTe nanocrystals. We unveil that tuning the capping ligands is a viable strategy to adjust the material from the p-type to ambipolar. Finally, HgTe nanocrystals are integrated into multipixel devices to quantize spatial homogeneity and onto read-out circuits to obtain a fast and sensitive infrared laser beam profile.

Infrared spectral filter based on all-semiconductor guided-mode resonance.

We present a theoretical and experimental study of guided-mode resonant (GMR) spectral filters made of III-V semiconductors and operating in the long-wave infrared (LWIR) wavelength range. In the scope of the colorization of infrared photodetectors, we used materials fully compatible with the epitaxial growth of Type 2 super lattice LWIR photodetectors: heavily n-doped InAsSb for the grating and GaSb for the waveguide of the GMR resonator.

Pixel-sized infrared filters for a multispectral focal plane array.

We present a theoretical study of guided-mode-resonance filters made of two sub-wavelength metallic gratings and a dielectric waveguide, with lateral geometries compatible with the size of infrared focal plane array pixels. Contrary to most of the studies described in the literature, we consider here a focused beam on finite-sized filters, and we investigate the optical properties of a mosaic of 30 µm-long filters. We demonstrate the spectral filtering ability and low crosstalk of such components. We also study the impact of an oblique beam onto a filtering mosaic. We finally discuss the opportunities offered by these results for a new generation of multispectral infrared cameras, and we give an example of a simple architecture.

Field extension inside guided-mode-resonance filters under a focused beam.

We present a theoretical study of the mid-infrared guided mode resonance spectral filters made of two subwavelength metallic gratings and a dielectric waveguide under a focused beam with a finite spot size. This Letter shows that, at the resonant wavelength, the lateral extension of the electromagnetic field in the waveguide is close to the width of the beam. We compare the performance of filters using gratings with a one-slit pattern and gratings with a two-slit pattern, and we show that the latter gratings (biatom gratings) provide a higher transmission and a better limitation of field extension, due to an improved angular acceptance. These results open new perspectives for pixel-sized infrared filters.

Infrared spectroscopy of molecules with nanorod arrays: a numerical study.

Nanorod arrays with diameters much smaller than the wavelength exhibit sharp resonances with strong electric-field enhancement and angular dependence. They are investigated for enhanced infrared spectroscopy of molecular bonds. The molecule 3-cyanopropyldimethylchlorosilane (CS) is taken as a reference, and its complex permittivity is determined experimentally in the 3-5 µm wavelength range. When grafted on silicon nitride nanorods, we show numerically that its weak absorption bands due to chemical bond vibrations can be enhanced by several orders of magnitude compared with unstructured thin film. We propose a figure of merit (FoM) to assess the performance of this spectroscopic scheme, and we study the impact of the nanorod cross section on the FoM.

An Underestimation of Heroin Deaths Due to the Use of "Acute Opiate Intoxication" on Death Certificates.

INTRODUCTION: Deaths due to drug intoxications in the United States have increased. Public health agencies track the specific intoxicants using death certificate data in order to develop and focus prevention strategies. Criteria used to decide what deaths need toxicological investigation and how these deaths are certified will affect this data. METHODS: We retrospectively reviewed the investigative, autopsy, and toxicology reports of 118 fatal intoxications that were certified as "acute opiate intoxication." RESULTS: Of the 113 decedents in whom morphine was detected, 84 were determined to involve heroin. For 61 of 84 heroin deaths, the heroin diagnosis was based upon the detection of diacetylmorphine, 6-acetylmorphine, and/or a lower blood codeine to morphine concentration. For 23 of 84 deaths, the determination was based upon morphine detection and illicit substances and/or paraphernalia at the scene. Of the 61 of 84 heroin deaths diagnosed by direct toxicology results, 33 of the 61 (54%) did not have illicit substances or paraphernalia at the scene. Toxicology identified 33 of 84 (39%) heroin fatalities that would not have been distinguished from morphine intoxication by the scene investigation. CONCLUSIONS: The majority of deaths due to opioids can be further classified based upon the toxicological analysis and scene investigation. As heroin deaths may have no illicit substances/paraphernalia at the scene, investigators should not solely base their decision to perform an autopsy/toxicology on the scene absence of illicit drugs/paraphernalia. In our study sample, if toxicology testing were to be only performed when illicit substances/paraphernalia were found at the scene, a high portion of heroin deaths (39%) would have been missed.

Extraordinary optical extinctions through dual metallic gratings.

We report on multiple extraordinary optical extinction (EOE) phenomena achieved through encapsulated dual metallic gratings. They are evidenced in TM polarization by angularly and spectrally resolved transmission measurements in the mid-infrared wavelength range. We show that EOE can be achieved on both sides of the extraordinary optical transmission (EOT) resonance, leading to pass-band filters with an improved rejection rate.

Metal-dielectric bi-atomic structure for angular-tolerant spectral filtering.

We theoretically study metal-dielectric structures made of bi-atomic metallic gratings coupled to a guided-mode dielectric resonator. The bi-atomic pattern grating allows tailoring of the Fourier spectrum of the inverse grating permittivity in order to adapt the frequency gap and obtain a flat dispersion band over a wide angular range. A significant enhancement (two-fold) of the angular tolerance as compared to a simply periodic structure is obtained.