Journal: Science Advances

Article Title: Opposite and reversible optical switching in soft-lattice halide perovskites using light and heat

doi: 10.1126/sciadv.aeb1442

Figure Lengend Snippet: ( A ) Measured change in transmission (∆ T = T final − T initial ) as a function of wavelength resulting from heating the halide perovskite to 80°C (red solid triangles) and illumination with above-gap light (blue solid squares). The transmission consistently reverts once the stimulus (light/heat) is removed (open red triangles and blue squares). Inset is a photograph of 1- and 2-mm-thick crystals showing transparency for wavelengths longer than 550 nm. ( B ) Measured x-ray diffraction (XRD) at room temperature and 80°C showing the crystalline lattice thermally expanding. On cooling back to 25°C, the lattice recovers its original equilibrium parameters. ( C ) Measured XRD under dark conditions at 25°C followed by an illuminated scan (using 532 nm) and another dark scan (showing structural lattice recovery). The (040) peak shifts to smaller 2θ values in both cases, indicating an increase in the lattice parameter. The second dark scan indicates recovery to the original lattice parameter. ( D ) Schematic of orthorhombic ( Pnma ) CsPbBr 3 lattice in the equilibrium state (left). With above-bandgap excitation, the lattice is distorted (bottom right) due to electron-phonon coupling through the elongation of the Pb-Br-Pb bond along the {0b0} direction, i.e., the long axis. In the case of heating, the lattice thermally expands in the {0b0} and shifts to a more ordered structure (top right). For all illuminated measurements: light source = 532 nm laser at 40 mW, 3 mm beam diameter for FTIR and 1 mm for XRD.

Article Snippet: This research used a Rigaku SmartLab thin-film x-ray diffractometer in the UC Davis Advanced Materials Characterization and Testing (AMCaT) Laboratory, acquired with funding from the National Science Foundation Major Research Instrumentation (MRI) Program under award number MRI-2216198.

Techniques: Transmission Assay

Journal: Nature Communications

Article Title: Protonation and deprotonation of edges in graphene oxide and MXenes as a driving force for actuation in responsive 2D membranes

doi: 10.1038/s41467-025-63800-9

Figure Lengend Snippet: a Surface charge density of GO and MXene flakes at different pH, calculated using potentiometric titration. b Schematic diagram of the pH-programmed self-assembly process, where uncharged protonated flakes (gray) deposit first, followed by charged deprotonated flakes (brown). c Thermal actuation performance of GO and MXene at 100 °C. The actuators prepared at different pH. d X-ray photoelectron spectroscopy (XPS) of O1s analysis of GO membranes. The O1s spectrum further supports these observations. At pH2, the relative atomic concentrations of the functional groups are as follows: -OH (2.37 at%), C-O (55.18 at%), C=O (42.45 at%). At pH6, the concentrations are -OH (16.45 at%), C-O (66.55 at%), 531.03 eV C = O (16.99 at%). At pH10, the concentrations are C=O (44.28 at%), C-O (53.47 at%) and -OH (2.25 at%). e XPS of O1s analysis of MXene membranes. At pH2, the relative atomic concentrations of the functional groups are as follows: C-Ti-OH (38.45 at%), C-Ti-O (39.65 at.%), Ti-O (21.90 at%). At pH 6, the concentrations are C-Ti-OH (35.85 at%), C-Ti-O (39.92 at%), Ti-O (24.23 at%). At pH 10, the concentrations are Ti-H 2 O (2.57 at%), C-Ti-OH (32.10 at%), C-Ti-O (41.18 at%), Ti-O (24.15 at%). f Differential FTIR spectra of GO and MXene membranes at various pH, highlighting the C=O band at 1600–1700 cm −1 . The set-up for in-situ FTIR experiments before and after infrared irradiation is shown in Supplementary Fig. . The spectra were obtained by subtracting the room-temperature data from those after 3 min of infrared light irradiation. After infrared irradiation, a decrease in C=O band intensity is observed. Additionally, pH-dependent peak shifts are evident: under acidic conditions (pH 2), the C=O peak exhibits a red shift compared to alkaline conditions (pH 10), indicating protonation of carbonyl groups. g Thermal actuating performance of pH-programmed GO and MXene multilayers with different pH. The pH 2 GO membrane remains thermally unresponsive, while the pH 6 membrane exhibits the largest curvature. The pH 10 membrane bends under heating, but with a smaller curvature compared to pH 6, reflecting reduced thermal asymmetry. Actuator dimensions: 4 ×20 mm. Source data are provided as a file.

Article Snippet: The XRD patterns were obtained by a thin-film X-ray diffractometer (TF-XRD, Bruker D8 Advance).

Techniques: Titration, Spectroscopy, Functional Assay, In Situ, Irradiation, Membrane