The evolution of the optical phonons in layered semiconductor alloys SnSe(1-x)Sx is studied as a function of the composition by using polarized Raman spectroscopy with six different excitation wavelengths (784.8, 632.8, 532, 514.5, 488, and 441.6 nm). The polarization dependences of the phonon modes are compared with transmission electron diffraction measurements to determine the crystallographic orientation of the samples. Some of the Raman modes show significant variation in their polarization behavior depending on the excitation wavelengths. It is established that the maximum intensity direction of the Ag 2 mode of SnSe(1-x)Sx (0x1) does not depend on the excitation wavelength and corresponds to the armchair direction. It is additionally found that the lower-frequency Raman modes of Ag 1 , Ag 2 and B3g 1 in the alloys show the typical one-mode behavior of optical phonons, whereas the higher-frequency modes of B3g 2 , Ag 3 and Ag 4 show two-mode behavior.

We report the temperature dependence of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of biaxial α-SnS in the spectral energy region from 0.74 to 6.42 eV and temperatures from 27 to 350 K using spectroscopic ellipsometry. Bulk SnS was grown by temperature gradient method. Dielectric response functions were obtained using multilayer calculations to remove artifacts due to surface roughness. We observe sharpening and blue-shifting of CPs with decreasing temperature. A strong exciton effect is detected only in the armchair direction at low temperature. New CPs are observed at low temperature that cannot be detected at room temperature. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that contains the Bose–Einstein statistical factor and the temperature coefficient for describing the electron–phonon interaction.

A perfect isotactic poly(methacrylic acid) (it‐PMAA) is synthesized and characterized by NMR spectroscopy. Surface pressure versus mean area per repeat unit (π−A) isotherms are recorded and compared with atactic poly(methacrylic acid) (at‐PMAA). it‐PMAA exhibits a π−A isotherm, indicating the formation of a stable Langmuir film. The isotherm has a characteristic pseudo‐plateau at π of ≈11–14 mN m−1 attributed to the creation of worm‐like entities confirmed by atomic force microscopy (AFM) in Langmuir–Blodgett (LB) films. These structures transform into spherical nanoparticles of ≈40 to 80 nm seen in LB films transferred at the end of the pseudo‐plateau of the isotherm. Grazing incidence wide‐angle X‐ray scattering (GI‐WAXS) shows a broad scattering signal (halo‐like) at a q position of ≈11.12 nm−1, revealing the amorphous nature of the nanoparticles. An ordered morphology, however, is observed in thin films prepared by precipitating it‐PMAA from dimethylformamide (DMF) solution under vigorous stirring and coating them on a solid support. Optical microscopy (OM), AFM, and GI‐WAXS reveal more details about the structure. Finally, various structural modifications of PMAAs are explained based on their tacticity and the subsequent hydrogen bonding effects between the carboxylic acid groups.

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We report the dielectric tensors on the cleavage plane of biaxial SnSxSe1-x alloys in the spectral energy region from 0.74 to 6.42 eV obtained by spectroscopic ellipsometry. Single-crystal SnSxSe1-x alloys were grown by the temperature-gradient method. Strongly anisotropic optical responses are observed along the different principal axes. An approximate solution yields the anisotropic dielectric functions along the zigzag (a-axis) and armchair (b-axis) directions. The critical point (CP) energies of SnSxSe1-x alloys are obtained by analyzing numerically calculated second derivatives, and their physical origins are identified by energy band structure. Blue shifts of the CPs are observed with increasing S composition. The fundamental bandgap for Se = 0.8 and 1 in the armchair axis arises from band-to-band transitions at the M0 minimum point instead of the M1 saddle point as in SnS. These optical data will be useful for designing optoelectronic devices based on SnSxSe1-x alloys.