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The growth of atomic layer deposited (ALD) Al2O3 on planar ZnSe substrates is studied using in situ spectroscopic ellipsometry. An untreated ZnSe surface requires an incubation period of 27 cycles of ALD Al2O3 before film growth is observed. Pretreating the surface with an ultraviolet generated ozone lowers the incubation to 17 cycles, whereas a plasma-enhanced ALD Al2O3 process can further lower the incubation period to 13 cycles. The use of ozone or plasma-activated oxygen species on ZnSe is found to create ZnO and SeO2, which are responsible for converting ZnSe from a hydrophobic to a hydrophilic surface. The interfacial layer between Al2O3 and ZnSe is mapped using high-resolution transmission electron microscopy and scanning transmission electron microscopy/energy dispersive spectroscopy. SeO2 is volatile and leaves a zinc-rich interface, which is 4.3 nm thick for the ultraviolet generated ozone pretreated sample and 2.5 nm for the plasma-enhanced ALD process.

The development of compact and fieldable mid-infrared (mid-IR) spectroscopy devices represents a critical challenge for distributed sensing with applications from gas leak detection to environmental monitoring. Recent work has focused on mid-IR photonic integrated circuit (PIC) sensing platforms and waveguide-integrated mid-IR light sources and detectors based on semiconductors such as PbTe, black phosphorus and tellurene. However, material bandgaps and reliance on SiO₂substrates limit operation to wavelengthsλ ≲ 4 μm. Here we overcome these challenges with a chalcogenide glass-on-CaF₂PIC architecture incorporating split-gate photothermoelectric graphene photodetectors. Our design extends operation toλ = 5.2 μm with a Johnson noise-limited noise-equivalent power of 1.1 nW/Hz^1/2, no fall-off in photoresponse up tof = 1 MHz, and a predicted 3-dB bandwidth off_3dB > 1 GHz. This mid-IR PIC platform readily extends to longer wavelengths and opens the door to applications from distributed gas sensing and portable dual comb spectroscopy to weather-resilient free space optical communications.

Owing to their unique tunable optical properties, chalcogenide phase change materials are increasingly being investigated for optics and photonics applications. However, in situ characterization of their phase transition characteristics is a capability that remains inaccessible to many researchers. Herein, a multifunctional silicon microheater platform capable of in situ measurement of structural, kinetic, optical, and thermal properties of these materials is introduced. The platform can be fabricated leveraging industry‐standard silicon foundry manufacturing processes. This platform is fully open‐sourced, including complete hardware design and associated software codes.