We discuss the design and performance of TEXES, the Texas Echelon Cross Echelle Spectrograph. TEXES is a mid-infrared (5-25 µm) spectrograph with several operating modes: high-resolution, cross-dispersed with a resolving power of R = λ/δλ ≈ 100,000, 0.5% spectral coverage, and a ∼ 1.5 × 8 ′′ slit; medium-resolution long-slit, with R ≈ 15,000, 0.5% coverage, and a ∼ 1.5×45 ′′ slit; low-resolution long-slit, with δλ ≈ .004 µm, 0.25 µm coverage, and a ∼ 1.5 × 45 ′′ slit; and source acquisition imaging with 0.33 ′′ pixels and a 25 × 25 ′′ field of view on a 3 m telescope. TEXES has been used at the McDonald Observatory 2.7m and the IRTF 3m telescopes, and has proven to be both sensitive and versatile.Subject headings: infrared: general -instrumentation: spectrographs -techniques: spectroscopic Observatory (ISO) short wavelength spectrometer with R = λ/δλ ≈ 2000. SIRTF, with R ≈ 600 and much better sensitivity than can be achieved from the ground, will continue this study. However, neither of these spacecraft spectrometers was optimized for studies of narrow gas-phase lines.Mid-infrared ionic lines have been studied in a number of sources by several ground-based instruments, as well as by ISO. These lines provide information similar to that obtained from visible wavelength forbidden and recombination lines, but can be studied in much more obscured sources. With widths ≈ 10 − 100 km s −1 (the latter in external galaxies), these lines are best studied by instruments with R ∼ 10 4 . Our previous instrument, Irshell (Lacy et al. 1989), was optimized for the study of these lines. ISO greatly expanded on the earlier ground-based work, as will SIRTF, although the lower resolution on the space-based mid-IR spectrometers is insufficient for detailed kinematic studies.Less work has been done on molecular lines in the mid-infrared. In molecular clouds these lines have widths of only a few km s −1 , requiring R ≥ 100,000 for optimal sensitivity and to obtain kinematic information in line profiles. Although a few instruments have achieved such high resolution in the mid-infrared (heterodyne spectrometers, e.g. Mumma et al. 1982, and Fourier transform spectrometers, e.g. Ridgway & Brault 1984), the sensitivity of these instruments was sufficient for the study of only a few of the brightest objects in the sky. Considerable work has been done with ISO (e.g. Lahuis & van Dishoeck 2000) concentrating on the many lines of molecular Q-branches. Using Irshell, with R ≈ 10,000, we observed interstellar C 2 H 2 and CH 4 , as well as several other molecules, but could not resolve the individual lines except in regions of shocks or rapid outflows. As a result, we were limited to measurements of equivalent widths of often saturated lines. From this experience we concluded that whereas space-based spectrometers will improve on our observations of solid-state and ionic lines, at least in cases where high spatial resolution is not required, a high spectral resolution and high sensitivity ground-based (or airborne) spectrograph was required to fur...

The photovoltaic conversion efficiency of perovskite solar cells based on organic-inorganic CHNHPbI has risen spectacularly from 3.8% to over 20% in just seven years, yet quite a few important fundamental issues have not been settled, and the role of spontaneous polarization remains poorly understood. While piezoresponse force microscopy (PFM) has been adopted to probe possible ferroelectricity in CHNHPbI, the reported data are often conflicting and inconclusive, due to the complexity in the apparent piezoresponse and its switching that may arise from ionic motions, electrostatic interactions, and other electromechanical mechanisms. Here, using a combination of microscopic and macroscopic measurements, we unambiguously establish the linear piezoelectricity of CHNHPbI arising from its spontaneous polarization, which can be switched by an electric field, though other electromechanical contributions such as ionic motions are also shown to exist. More importantly, we demonstrate strong interactions between polarization and light in technologically relevant CHNHPbI films with good conversion efficiencies, observing that the spontaneous polarization can also be switched by light illumination in the absence of an electric field. The light is shown to reduce the coercive voltage of CHNHPbI and shifts its nucleation bias, suggesting that the photo-induced switching is caused by ionic motions in combination with a photovoltaic field. This set of studies offer strong evidence on the interactions among photo-induced charges, polarization, and ions in perovskite CHNHPbI, and these fundamental observations lay the ground for answering the technologically important question regarding the effects of ferroelectricity on its photovoltaic conversion.

Stellar feedback from high-mass stars (e.g., Hii regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one sub-virial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM 1-12) detected by ALMA are at very different evolutionary stages, from starless core phase to UC Hii region phase.

Robust and reversible polar topological center domains were found in BiFeO3 nanodots, which are individually controllable.