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Two-dimensional (2D) indium selenide (InSe) has been widely studied for application in transistors and photodetectors, which benefit from its excellent optoelectronic properties. Among the three specific polytypes (γ -, ϵ - and β -phase) of InSe, only the crystal lattice of InSe in β -phase (β -InSe) belongs to a non-symmetry point group of |$D_{6h}^4$|⁠ , which indicates stronger anisotropic transport behavior and potential in the polarized photodetection of β -InSe-based optoelectronic devices. Therefore, we prepare the stable p-type 2D-layered β -InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β -InSe have been experimentally and theoretically proven, showing that the β -InSe-based device has a ratio of 3.76 for the maximum to minimum dark current at two orthogonal orientations and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β -InSe as a competitive candidate for filter-free polarization-sensitive photodetectors. [ABSTRACT FROM AUTHOR]

The pn junctions significantly affect the responsivity of photodetectors (PDs). However, the enhancement mechanism of the pn junction is still unclear. Herein, operando Raman spectroscopy was employed to study PDs with NiO/TiO2 pn junctions composed of p-NiO nanoparticles (NPs) and n-TiO2 nanotube arrays (TNAs). The results suggest that the built-in potential field of the NiO/TiO2 interface decreases the charge transfer resistance and changes the vibrational frequency of the phonon modes of TiO2, which is attributed to the electron–phonon coupling effect. Operando Raman spectroscopy is proved to be a powerful tool for manufacturing highly responsive PDs. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite as SERS substrate improves spectral signal-to-noise ratio by narrowing the FWHM of adsorbed molecular spectrum. [Display omitted] • The SERS profile of CH 3 NH 3 PbBr 3 substrate displays high similarity with the bulk Raman spectra, its FWHM is exceeding narrow. • The significantly increased SNR of the probe molecules indicates that the substrate helps to improve the quantitative analysis capability of the SERS technology and alleviate the background-related problems. • The CH 3 NH 3 PbBr 3 has the advantage of maintaining the conformation and orientation consistency of adsorbed molecules. • The CH 3 NH 3 PbBr 3 substrate possesses specific recognition ability that has the same enhancement effect for a series of pyridine-containing probe molecules. Spectra in surface-enhanced Raman scattering (SERS) are always accompanied by a continuous emission known as "background", which complicates the analysis with a poor signal-to-noise ratio (SNR), especially for qualitative and quantitative detection. Here, the SERS profile of the CH 3 NH 3 PbBr 3 substrate displays high similarity with the bulk Raman spectra, and its FWHM is exceeding narrow. The significantly increased SNR of the probe molecules indicates that the substrate helps to improve the quantitative analysis capability of the SERS technology and alleviate the background-related problems. For the CH 3 NH 3 PbBr 3 substrate, good linearity (R2 = 0.9591) in the range of 1.0 × 10-7 − 1.0 × 10-3 mol/L was obtained and the limit of detection (LOD) is 7.88 × 10-6 mol/L. The reason for this excellent performance is that the introduction of organic molecules splits the 3D CH 3 NH 3 PbBr 3 substrate to form a 2D perovskite that fixes the molecular orientation through chemical interactions. The CH 3 NH 3 PbBr 3 has the advantage of maintaining the conformation and orientation consistency of adsorbed molecules. Meanwhile, compared with the commonly used noble metal (Au, Ag) and semiconductor (ZnO, TiO 2) SERS substrates, the CH 3 NH 3 PbBr 3 substrate has obvious superiorities in both spectral peak intensity and peak shape. Furthermore, the CH 3 NH 3 PbBr 3 substrate possesses specific recognition ability that has the same enhancement effect for a series of pyridine-containing probe molecules. Finally, the enhancement mechanism is discussed according to the CT contribution. As a promising substrate for SERS technology, CH 3 NH 3 PbBr 3 will provide more possibilities for quantitative and multiplex detection in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three types of DNA nanogels were assembled by the branched DNA units. • SERS has been successfully exploited for the structural analysis of DNA nanogels. • The mechanism for enhancing the SERS signal of DNA gels has been suggested. The direct characterization of DNA nanogels at the atomic level is desirable and of great significance, however, has been challenging because of structural complexity and the larger size of nanogels. Herein, we demonstrated a simple, sensitive and reliable SERS (Surface-enhanced Raman spectroscopy)-based approach towards direct monitoring microstructures, such as three types of nanogels crosslinked by DNA G-quadruplex, i-motif and GC duplex. The achievement is attributed to the detection of featured Raman bands corresponding to the formation of Watson-Crick and Hoogsteen hydrogen bonds as well as C·C+ base pairs. Importantly, this work reveals that the silver nanoparticles attaching on the surface of nanogels can form local 'hotspots' and produce high-quality of Raman spectra under the assistance of iodide, aluminum ions and dichloromethane, therefore, shows great potential for wide applications in accurate characterization of various DNA nanostructures. [ABSTRACT FROM AUTHOR]

Some functional nanomaterials can be used as both nanozymes and SERS substrates, thus a variety of nanozyme-SERS systems have been constructed, which have been broadly applicable in many fields. In this review, we will systematically present the recent development of the fabrication, properties and applications of the nanozyme-SERS systems. First, the fundamentals of the nanozymes and SERS technique have been introduced. Then, the classification of nanozyme-SERS systems is demonstrated. To further illustrate the SERS enhancement and the catalytic mechanisms, the influence factors such as light excitation, the introduction of the reducing reagents and metal ions, environmental conditions on the properties of nanozyme-SERS systems have been discussed. In the following, their applications for sensing, disease diagnosis and therapy, food safety, immunoassay, and environmental monitoring are reviewed. Finally, the challenges and perspectives to construct new nanozyme-SERS systems for more practical applications are featured. [Display omitted] • Recent progress of the surface-enhanced Raman spectroscopy to monitor nanozyme reaction are reported. • The fundamental and typical materials for nanozyme-SERS systems are introduced. • The SERS enhancement and catalytic mechanisms with the influencing factors are discussed. • The applications for the sensing and environmental monitoring are reviewed. • The challenges and future research opportunities of this field are summarized. [ABSTRACT FROM AUTHOR]