Germanium Nanosheets with Dirac Characteristics as a Saturable Absorber for Ultrafast Pulse Generation.

Bulk germanium as a group-IV photonic material has been widely studied due to its relatively large refractive index and broadband and low propagation loss from near-infrared to mid-infrared. Inspired by the research of graphene, the 2D counterpart of bulk germanium, germanene, has been discovered and the characteristics of Dirac electrons have been observed. However, the optical properties of germanene still remain elusive. In this work, several layers of germanene are prepared with Dirac electronic characteristics and its morphology, band structure, carrier dynamics, and nonlinear optical properties are systematically investigated. It is surprisingly found that germanene has a fast carrier-relaxation time comparable to that of graphene and a relatively large nonlinear absorption coefficient, which is an order of magnitude higher than that of graphene in the near-infrared wavelength range. Based on these findings, germanene is applied as a new saturable absorber to construct an ultrafast mode-locked laser, and sub-picosecond pulse generation in the telecommunication band is realized. The results suggest that germanene can be used as a new type of group-IV material for various nonlinear optics and photonic applications.

Catalyst-Free Growth of Two-Dimensional BCxN Materials on Dielectrics by Temperature-Dependent Plasma-Enhanced Chemical Vapor Deposition.

Traditional methods to prepare two-dimensional (2D) B-C-N ternary materials (BCxN), such as chemical vapor deposition (CVD), require sophisticated experimental conditions such as high temperature, delicate control of precursors, and postgrowth transfer from catalytic substrates, and the products are generally thick or bulky films without the atomically mixed phase of B-C-N, hampering practical applications of these materials. Here, for the first time, we develop a temperature-dependent plasma-enhanced chemical vapor deposition (PECVD) method to grow 2D BCxN materials directly on noncatalytic dielectrics at low temperature with high controllability. The C, N, and B compositions can be tuned by simply changing the growth temperature. Thus, the properties of the as-made materials including band gap and conductivity are modulated, which is hardly achieved by other methods. A 2D hybridized BC2N film with a mixed BC2N phase is produced, for the first time, with a band gap of about 2.3 eV. The growth temperature is 580-620 °C, much lower than that of traditional catalytic CVD for growing BCxN. The product has a p-type conducting property and can be directly applied in field-effect transistors and sensors without postgrowth transfer, showing great promise for this method in future applications.

Soft-templated mesoporous carbon-modified glassy carbon electrode for sensitive and selective detection of aristolochic acids.

In this study, ordered mesoporous carbon (OMC) was synthesized by applying a soft template method, and its mesoporous structure was characterized by scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption techniques. X-ray diffraction and Raman spectroscopic analyses were conducted to demonstrate the high graphitization and topological defects at the sample surface. An electrochemical sensor based on an OMC-modified glassy carbon electrode (OMC/GCE) was constructed to detect aristolochic acids (AAs) using cyclic voltammetry and linear sweep voltammetry. The dependence of the experimental parameters including solution pH, scan rate, and accumulation time were examined and optimized. Under the optimal conditions, the response of OMC/GCE was linear over wide concentration ranges of AAs (0.6-10 µM and 10-50 µM), with sensitivities of -1.77 and -0.31 µA/µM, respectively. The limit of detection was calculated to be 0.186 µM (at S/N = 3). Furthermore, the proposed OMC/GCE was applied to detect AAs in Asarum sieboldini and the content of AAs was calculated to be 8.9 µg/g with high accuracy and precision. In addition, the modified electrode also exhibited good selectivity, reproducibility, and stability. Therefore, the OMC/GCE can be used as a platform for the determination of AAs.

Double-shelled yolk-shell Si@C microspheres based electrochemical sensor for determination of cadmium and lead ions.

In this work, we report double-shelled yolk-shell Si@C structure as a high-performance electrochemical sensing material for heavy metal ions. A SiO2-assisted polybenzoxazine (PB) coating strategy is used to synthesize highly monodispersed Si@C microspheres. After thermal carbonization of PB layers and selective removal of the SiO2 layers, Si@C microspheres were prepared. The resultant Si@C microspheres exhibit uniform spherical morphology and clearly double-shelled yolk-shell structures. The obtained Si@C microspheres are employed to prepare the chemically modified electrode for the sensitive determination of Cd(II) and Pb(II). By the method of anodic stripping voltammetry, the Si@C-based electrode shows a very wide linear dynamic range for target ions (e.g., 0.5-400 µg L-1 for Cd(II) and Pb(II)) and low limit of detections (e.g., 0.068 µg L-1 for Cd(II) and for 0.105 µg L-1 Pb(II)). The remarkable results, such as excellent resistance to interference ions, good repeatability, and reproducibility were also obtained. Furthermore, compared with those Cd(II) and Pb(II) sensors known in the literature, the analytical performance of Si@C-based electrode is better. Finally, when further used to determine Cd(II) and Pb(II) in tap water and lake water, the results of fabricated electrode successfully achieve good consistency with the data obtained from inductively coupled plasma-mass spectrometry (ICP-MS).

Flexible, Printable Soft-X-Ray Detectors Based on All-Inorganic Perovskite Quantum Dots.

Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low-cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft-X-ray-induced photocurrent is demonstrated in both rigid and flexible detectors based on all-inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft-X-ray beamline, high sensitivities of up to 1450 µC Gyair -1 cm-2 are achieved under an X-ray dose rate of 0.0172 mGyair s-1 with only 0.1 V bias voltage, which is about 70-fold more sensitive than conventional α-Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large-scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X-rays and for large-area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.

Flexible photodetectors based on reticulated SWNT/perovskite quantum dot heterostructures with ultrahigh durability.

Recently, single-walled carbon nanotube (SWNT) films have been regarded as a promising channel material for flexible photodetectors due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. However, the application of SWNTs in photonic devices is limited due to their weak light absorption and the absence of a gain mechanism. Here, we demonstrate a high-performance flexible photodetector that consists of a reticulated SWNT film covered with a thin film of CsPbI3 perovskite colloidal quantum dots. The unique hierarchical reticulated structure of the SWNTs provides such films with extremely high tensile strength and great extensibility, which can ensure the appropriate toughness for achieving flexible photodetectors. Meanwhile, the perovskite quantum dots enhance light absorption, thereby sensitizing the creation of free electrical carriers within the SWNTs. This hybrid photodetector exhibits an extended photonic response and gain compared with the original pure SWNT devices. In addition, the device exhibits good robustness against repetitive bending and stretching, suggesting its applicability as a large-area wearable flexible photodetector.

Synthesis of an iron-nitrogen co-doped ordered mesoporous carbon-silicon nanocomposite as an enhanced electrochemical sensor for sensitive and selective determination of chloramphenicol.

In this study, we developed a sensitive electrochemical sensor for the detection of chloramphenicol (CAP). An iron-nitrogen co-doped ordered mesoporous carbon-silicon nanocomposite (Si-Fe/NOMC) was prepared as follows. First, an SBA-15 surface was treated with an iron and nitrogen co-doped carbon framework obtained from the polymerization of ethylenediamine and carbon tetrachloride via the hard templating method. The mixture was then carbonized at a high temperature (900℃). Finally, the Si-Fe/NOMC modified electrode was fabricated, and employed as a high-performance electrochemical sensor to trace the CAP in drug samples using the large surface area of the hetero-atoms iron, nitrogen and silicon co-doped in the porous structure. Cyclic voltammetry and differential pulse voltammetry tests were determine to assess the efficiency of the sensor. Under optimized conditions, the sensor exhibited rapid current response for CAP in a phosphate buffer solution PBS with pH 7.5. The linear concentration of CAP ranged from 1 µM to 500 µM, with a limit of detection of 0.03 µM (S/N = 3). Furthermore, the electrochemical sensor was used to detect CAP in eye drop samples with satisfactory results.