Crystalline structure of -MoO3. a. Sketch of the unit cell of -MoO3 and correspondence between the crystallographic directions [100], [001], [010] and the spatial coordinates x, y, z; the lattice constants are a = 0.396 nm, b = 1.385 nm and c = 0.369 nm. Blue/red spheres represent molybdenum/oxygen atoms. b. Optical image of an -MoO3 flake on top of AgCl. -MoO3 crystals typically appear to be rectangular owing to the anisotropic crystal structure. Labelled arrows indicate crystal directions. Scale bar: 200 m.

Contexts in source publication

Context 1

... exotic properties of PhPs in -MoO3 stem from their strong anisotropy, a consequence of the crystal structure, which is orthorhombic (Figure 1a). In it, layers formed by distorted -MoO6 octahedra are weakly bound by vdW forces and all three lattice constants (a, b and c) are different, as are the three principal values ε x (ω), ε y (ω) and ε z (ω) -corresponding to the [100], [001] and [010] crystal directions, [24] respectively-of the dielectric tensor ε ̂(ω): ...

Context 2

... in principle FTIR micro-spectroscopy can determine the optical properties of extremely small -down to 10 x 10 µm-flakes, in practice this limits the spectral range, accuracy and signal-to-noise ratio of spectra, in comparison to measurements on large films, due to the diffraction limit of light. As -MoO3 is a biaxial crystal with optic phonons that occur in the LWIR (λ > 9.9 µm), we acquired polarized FTIR reflection (Figure 2) and transmission (Supporting Information) spectra from the same relatively large area of an -MoO3 single flake (red square in Figure 1b), to ensure that good quality data were obtained across the full spectral range of interest, with the polarizer aligned along both in-plane principal axes (see Experimental Section for the detailed experimental procedure). The flake, with lateral dimensions of about 150 m by 650 m and a thickness of approximately 3 m, was exfoliated from bulk -MoO3 crystals and then transferred onto an AgCl substrate (Figure 1b), which is highly transparent across the entire spectral range of interest (see dielectric function in the Supporting Information). ...

Context 3

... -MoO3 is a biaxial crystal with optic phonons that occur in the LWIR (λ > 9.9 µm), we acquired polarized FTIR reflection (Figure 2) and transmission (Supporting Information) spectra from the same relatively large area of an -MoO3 single flake (red square in Figure 1b), to ensure that good quality data were obtained across the full spectral range of interest, with the polarizer aligned along both in-plane principal axes (see Experimental Section for the detailed experimental procedure). The flake, with lateral dimensions of about 150 m by 650 m and a thickness of approximately 3 m, was exfoliated from bulk -MoO3 crystals and then transferred onto an AgCl substrate (Figure 1b), which is highly transparent across the entire spectral range of interest (see dielectric function in the Supporting Information). ...

Context 4

... infrared dielectric function of AgCl was extracted using the methods described in the main text. In brief, a 2-mm-thick AgCl window is mounted in the bench of a Fourier transform infrared (FTIR) spectrometer, and unpolarized reflection and transmission data are taken using a room temperature pyroelectric DLaTGs detector into the far infrared ( Figure S1a). These data are fit using JA Wollams VASE software, using a phenomenological model with multiple , where An is the amplitude, Brn is the full width at half maximum (FWHM) of the gaussian, E is the frequency, En is the center frequency and P is the Cauchy principal value. ...

Context 5

... tabulated values for the fit are shown in Table S1. The dielectric function associated with this material is shown in Figure S1b, showing minimal dispersion in the region of interest for our experiments on α-MoO3 samples. Figure S1. ...

Context 6

... dielectric function associated with this material is shown in Figure S1b, showing minimal dispersion in the region of interest for our experiments on α-MoO3 samples. Figure S1. IR optical response (a) and fitted dielectric function (b) of AgCl. ...

Context 7

... exotic properties of PhPs in -MoO3 stem from their strong anisotropy, a consequence of the crystal structure, which is orthorhombic (Figure 1a). In it, layers formed by distorted -MoO6 octahedra are weakly bound by vdW forces and all three lattice constants (a, b and c) are different, as are the three principal values ε x (ω), ε y (ω) and ε z (ω) -corresponding to the [100], [001] and [010] crystal directions, [24] respectively-of the dielectric tensor ε ̂(ω): ...

Context 8

... in principle FTIR micro-spectroscopy can determine the optical properties of extremely small -down to 10 x 10 µm-flakes, in practice this limits the spectral range, accuracy and signal-to-noise ratio of spectra, in comparison to measurements on large films, due to the diffraction limit of light. As -MoO3 is a biaxial crystal with optic phonons that occur in the LWIR (λ > 9.9 µm), we acquired polarized FTIR reflection (Figure 2) and transmission (Supporting Information) spectra from the same relatively large area of an -MoO3 single flake (red square in Figure 1b), to ensure that good quality data were obtained across the full spectral range of interest, with the polarizer aligned along both in-plane principal axes (see Experimental Section for the detailed experimental procedure). The flake, with lateral dimensions of about 150 m by 650 m and a thickness of approximately 3 m, was exfoliated from bulk -MoO3 crystals and then transferred onto an AgCl substrate (Figure 1b), which is highly transparent across the entire spectral range of interest (see dielectric function in the Supporting Information). ...

Context 9

... -MoO3 is a biaxial crystal with optic phonons that occur in the LWIR (λ > 9.9 µm), we acquired polarized FTIR reflection (Figure 2) and transmission (Supporting Information) spectra from the same relatively large area of an -MoO3 single flake (red square in Figure 1b), to ensure that good quality data were obtained across the full spectral range of interest, with the polarizer aligned along both in-plane principal axes (see Experimental Section for the detailed experimental procedure). The flake, with lateral dimensions of about 150 m by 650 m and a thickness of approximately 3 m, was exfoliated from bulk -MoO3 crystals and then transferred onto an AgCl substrate (Figure 1b), which is highly transparent across the entire spectral range of interest (see dielectric function in the Supporting Information). ...

Context 10

... infrared dielectric function of AgCl was extracted using the methods described in the main text. In brief, a 2-mm-thick AgCl window is mounted in the bench of a Fourier transform infrared (FTIR) spectrometer, and unpolarized reflection and transmission data are taken using a room temperature pyroelectric DLaTGs detector into the far infrared ( Figure S1a). These data are fit using JA Wollams VASE software, using a phenomenological model with multiple , where An is the amplitude, Brn is the full width at half maximum (FWHM) of the gaussian, E is the frequency, En is the center frequency and P is the Cauchy principal value. ...

Context 11

... tabulated values for the fit are shown in Table S1. The dielectric function associated with this material is shown in Figure S1b, showing minimal dispersion in the region of interest for our experiments on α-MoO3 samples. Figure S1. ...

Context 12

... dielectric function associated with this material is shown in Figure S1b, showing minimal dispersion in the region of interest for our experiments on α-MoO3 samples. Figure S1. IR optical response (a) and fitted dielectric function (b) of AgCl. ...