Carbon soot (CS) has the advantages of cost-effectiveness and production scalability over other carbons (i.e., graphene, CNTs) in their synthesis. However, little research has been conducted to explore the potential applications of CS. In this study, we demonstrated that a common daily waste-CS-can be used for developing a cost-effective absorbent (CS-sponge) to remove oil contaminants from water. The CS was synthesized by an ethylene-oxygen combustion flame. The CS-sponge was prepared via a dip-coating method. Without further surface modification and pretreatments, the CS-sponge demonstrates high absorption capacities (up to 80 times its own weight) for a broad spectrum of oils and organic solvents with a recyclability of more than 10 times. These research results show evidence that the CS-sponge is promising in environmental remediation for large-scale, low-cost removal of oils from water.

In this paper, we present a rigorous coupled-wave analysis (RCWA) of absorption enhancement in all-silicon (Si) photodiodes with integrated hole arrays of different shapes and dimensions. The RCWA method is used to analyze the light propagation and trapping in the photodiodes on both Si-on-insulator (SOI) and bulk Si substrates for the datacom wavelength at about 850 nm. Our calculation and measurement results show that funnel-shaped holes with tapered sidewalls lead to low back-reflection. A beam of light undergoes a deflection subsequent to the diffraction in the hole array and generates laterally propagating waves. SOI substrates with oxide layers play an important role in reducing the transmission loss, especially for deflected light with higher-order diffraction from the hole array. Owing to laterally propagating modes and back-reflection on the SiO2 film, light is more confined in the thin Si layer on the SOI substrates compared to that on the bulk Si substrates. Experimental results based on fabricated devices support the predictions of the RCWA. Devices are designed with a 2-μm-thick intrinsic layer, which ensures ultrafast impulse response (full-width at half-maximum) of 30 ps. Measurements for integrated photodiodes with funnel-shaped holes indicate an enhanced external quantum efficiency of more than 55% on the SOI substrates. This represents more than 500% improvement compared to photodiodes without integrated phototrapping nanoholes.

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Attempts on the selective promotion of gallium nitride (GaN) growth were investigated by deploying laserassisted vibrational excitation of reactant molecules, which deposits energy selectively into specific molecules and activate the molecules towards the selected reaction pathways. Laser-assisted metal organic chemical vapor deposition (LMOCVD) of GaN was studied using a wavelength-tunable CO 2 laser. The NH-wagging modes (υ 2) of ammonia (NH 3) precursor molecules are strongly infrared active and perfectly match the emission line of the CO 2 laser at 9.219, 10.350, and 10.719 µm. On-and off-resonance excitations of molecules were performed via tuning the incident laser wavelengths at on-resonant wavelength 9.219 µm and off-resonant wavelength of 9.201 µm. The on-resonant vibrational excitation allowed a largest fraction of the absorbed laser energy coupled directly into NH 3 molecules whereas energy coupling under off-resonant excitations is less efficient in energy coupling and influencing the GaN growth process. The GaN deposition rate was enhanced by a factor of 2.6 accompanied with an improvement of crystalline quality under the on-resonant excitation. Optical emission spectroscopic (OES) studies confirmed that the on-resonant vibrational excitation effectively promotes the dissociation of NH 3 molecules and creates N-containing species favoring the GaN growth. This study indicates that the resonant vibrational excitation is an efficient route coupling energy into the reactant molecules to surmount the chemical reaction barrier and steering the growth process.