Probing subwavelength in-plane anisotropy with antenna-assisted infrared nano-spectroscopy

Infrared nano-spectroscopy based on scattering-type scanning near-field optical microscopy (s-SNOM) is commonly employed to probe the vibrational fingerprints of materials at the nanometer length scale. However, due to the elongated and axisymmetric tip shank, s-SNOM is less sensitive to the in-plane sample anisotropy in general. In this article, we report an easy-to-implement method to probe the in-plane dielectric responses of materials with the assistance of a metallic disk micro-antenna. As a proof-of-concept demonstration, we investigate here the in-plane phonon responses of two prototypical samples, i.e. in (100) sapphire and x-cut lithium niobate (LiNbO3). In particular, the sapphire in-plane vibrations between 350 cm−1 to 800 cm−1 that correspond to LO phonon modes along the crystal b- and c-axis are determined with a spatial resolution of < λ/10, without needing any fitting parameters. In LiNbO3, we identify the in-plane orientation of its optical axis via the phonon modes, demonstrating that our method can be applied without prior knowledge of the crystal orientation. Our method can be elegantly adapted to retrieve the in-plane anisotropic response of a broad range of materials, i.e. subwavelength microcrystals, van-der-Waals materials, or topological insulators.

High-resolution characterization of the forbidden Si 200 and Si 222 reflections

The occurrence of the basis-forbidden Si 200 and Si 222 reflections in specular X-ray diffraction ω–2Θ scans is investigated in detail as a function of the in-plane sample orientation Φ. This is done for two different diffractometer types with low and high angular divergence perpendicular to the diffraction plane. It is shown that the reflections appear for well defined conditions as a result of multiple diffraction, and not only do the obtained peaks vary in intensity but additional features like shoulders or even subpeaks may occur within a 2Θ range of about ±2.5°. This has important consequences for the detection and verification of layer peaks in the corresponding angular range.

SOLUTION FOR THE PHOTOACOUSTIC WAVE EQUATION WITH A SINGLE SPATIAL DEGREE OF FREEDOM, BEER'S LAW ABSORPTION OF RADIATION AND MECHANICAL BARRIERS

A photoacoustic model with one degree of freedom in the spatial coordinates for a plane sample is studied. The model proposed considers a sample with Beer's law absorption immersed in a fluid with different acoustical impedance. An analytical solution for this problem is given. It is shown that the generated PA wave is composed of a pressure peak followed by a reflected and inverted pulse with diminished magnitude. It is also remarked that the form described for the pulse has a periodicity related to the sample's width and attenuated by the reflection coefficient. It is noted that, due to this attenuation, information about the sample's width is more easily detected at the irradiation side. Border cases are taken for equal impedances and infinite sample width.

The Polluted Characters of Cr, Toluene and Dimethylbenzene in Contaminated Soil of Dongsheng Chemical Plant in Suzhou

We sampled total of 74 polluted soil samples in the polluted field, and set up 5 surface water inspect spots by means of setting plane sample points and deep well sampling according to the original produce layout and pollution situation of Dongsheng chemical plant. At the same time, we set 4 soil sampling points outside the polluted field, 6 inspect positions of surface water, and 4 atmospheres inspect stations. The total quantity and the concentration of active form of heavy metals elements in the soil samples were analyzed by atomic absorption spectra; and the volatility organic matters in the soil are measured using gas chromatography-mass spectrograph jointed measurement. The results show that the polluted concentration of Cr in sub-surface layer of the field is highest, and the largest concentrations of the total quantity of Cr, Cr6+, toluene and dimethylbenzene are 13900, 4840, 258 and 33.6 mg•kg-1, respectively. The datum show that the soil in the field is heavily polluted by toluene, dimethylbenzene, total Cr, and Cr6+, and some soil is characteristic of strong acid or strong alkali, and surface water inner the field exists heavy Cr6+ pollution.

The Polluted Statu in Contaminated Soil of Suzhou Chemical Plant

We sampled total of 74 polluted soil samples in the polluted field by means of setting 37 plane sample points and digged sampling caves according to the original producing layout and pollution situation of Suzhou chemical plant. The total quantity and the concentration of active form of heavy metal elements in the soil samples were analyzed by atomic absorption spectra; and the volatility organics in the soil are measured using jointed gas chromatography-mass spectrograph measurement. The results show that the polluted area is over 30%. The main pollutants are carbon tetrachloride, methylene chloride, aromatic compounds in the north part of the field, and toluene, P-dichlorobenzene, and petroleum hydrocarbons in the south part. The main pollutants underground 2-3 m are petroleum-derived hydrocarbons, volatile halogenated hydrocarbons, and aromatic compounds.

Photocurrent measurements of MgxZn1-xO epitaxial layers of different x

The MgxZn1-xO alloy in wurtzite structure can be grown with Mg contents x up to 0.4. The band gap of the alloy increases with x. Furthermore, ZnO/MgxZn1-xO quantum well structures are of type I and thus are of interest for the active region of opto-electronic devices.We report on in-plane photocurrent measurements of MgxZn1-xO epitaxial layers with x up to about 0.4 in the temperature range from 80 K to 300 K. Epitaxial films are either grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates with a thin MgZnO buffer layer and by chemical vapor deposition on a-plane ZnO substrates. We map the evolution of the band gap transitions as a function of the Mg composition at different temperatures for the c-plane samples and as a function of polarization of the incoming light for an a-plane sample. The contributions of A, B and C interband transitions to the band gap signals are analysed and discussed.

Defect Structures of B12As2 Epilayers Grown on c-plane and a-plane 6H-SiC Substrates

B12As2 epitaxial layers grown on (0001) 6H-SiC and (1120) 6H-SiC substrates have been studied using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and synchrotron white beam x-ray topography (SWBXT) and investigated with the aid of crystal visualization software. SWBXT showed that B12As2 adopted [111] growth orientation, parallel to [0001]SiC, on c-plane 6H-SiC and adopted [101] growth orientation, parallel to [1120]SiC, on a-plane 6H-SiC. However, SWBXT also revealed the twins in both sets of the B12As2 films, consistent with the SEM observation of the surface morphology. Cross-sectional HRTEM also confirmed the presence of twins in both cases and also revealed the existence of an intermediate layer between the c-plane 6H-SiC and the B12As2 film. By correlating the HRTEM observation and crystal visualization, the atomic configurations across the twin boundaries in both samples as well as those in the intermediate layer in the c-plane sample were proposed.