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The multi-level hierarchical surfaces combining different characteristics of single modified surfaces such as expanded heat transfer area, nucleation site density and capillary wickability can further enhance the heat transfer performance. The pool boiling experiment of FC-72 with 35 K subcooling was conducted on the hybrid micro/nanostructure surface (NPF50-60) with nanoforest structure fabricated on the top and bottom of micro-pin-fins using the dry etching and plasma repolymerization techniques. As a comparison, experiments were also conducted on the smooth surface (S), the micro-pin-finned surface (PF50-60) and the nanoforest surface (NS). The novel phenomenon of bubble oscillation on heating surface was observed, which is considered as the result of interactions between evaporation and condensation effects. The predictions of bubble center position during oscillation from forces analysis agree well with the experimental results. In addition, the bubble jumping induced by coalescence was also observed. The results indicated that the three micro/nanostructure surfaces can significantly enhance the boiling heat transfer performance compared to the smooth surface. The lower wall superheat and greater heat transfer coefficient (HTC) with relatively large critical heat flux (CHF) were achieved on the hybrid micro/nanostructure surface for the larger cavity size of nanoforest structure. The wicking velocity of different surfaces obtained from the capillary wickability tests shows a good linear relationship with the CHF. It was concluded that the mechanism of CHF enhancement on micro/nanostructure surfaces is the liquid replenishment with capillary wickability to prevent the expansion of dry spots and maintain a higher critical heat flux.

Efficient optical absorbers are critical for photo-related applications, and have attracted significant interest in material science and physics for decades. In this work, a broadband absorber based on candle soot is presented with an average absorption of 98.6% in a waveband of 400 nm–1.5 μm, and of 75.1% in a wavelength range as broad as 1.5–25 μm. Such an absorber can be prepared simply by using flame deposition, which is patternable and can adopt flexible substrates. By introducing the absorber onto optical sensors, an improvement of device output by 133% is achievable. It is expected that the absorber could provide a new approach for use of photo-absorption materials in a wide range of optical systems.

We present graphene oxide (GO) nanosheets functionalized long period grating (LPG) for ultrasensitive hemoglobin sensing. The sensing mechanism relies on the measurement of LPG resonant intensity change induced by the adsorption of hemoglobin molecules onto GO, where GO as a bio-interface linkage provides the significant light-matter interaction between evanescent field and target molecules. The deposition technique based on chemical-bonding associated with physical-adsorption was developed to immobilize GO nanosheets on cylindrical fiber device. The surface morphology was characterized by scanning electron microscope, atomic force microscopy, and Raman spectroscopy. With relatively thicker GO coating, the refractive index (RI) sensitivity of GO-LPG was extremely enhanced and achieved −76.5 dB/RIU, −234.2 dB/RIU and +1580.5 dB/RIU for RI region of 1.33-1.38, 1.40-1.44 and 1.45-1.46, respectively. The GO-LPG was subsequently implemented as an optical biosensor to detect human hemoglobin giving a sensitivity of 1.9 dB/(mg/mL) and a detectable concentration of 0.05 mg/mL, which was far below the hemoglobin threshold value for anemia defined by World Health Organization. The proposed GO-LPG architecture can be further developed as an optical biosensing platform for anemia diagnostics and biomedical applications.

This work presents a novel type of surface-enhanced Raman scattering (SERS) devices based on nanocone forests. The nanocone forests are fabricated by using a plasma repolymerization technique, which is a simple and parallel approach that has high reproducibility in wafer-level fabrication. The nanocone forest-based SERS devices exhibit an averaged enhancement factor at the order of 3 × 106, meanwhile, the relative standard deviation of Raman intensity over large areas is around 7%. These experimental results demonstrate great potential of the nanocone forest-based SERS devices in wide applications.

Positioning analyte molecules at “hot spots” precisely for highly sensitive and reproducible surface-enhanced Raman scattering (SERS) analysis is a challenge. This work presents a SERS device based on three-dimensional (3D) nanohybrids of Au/Ag-nanocone forests with parahydrophobicity, which effectively target analyte molecules at “hot spots” through superhydrophobic concentration and nanocage confine to achieve molecular enrichment. The multilevel plasmon hybridization of the 3D nanohybrids utilizes hybridization of different plasmon modes of gold and silver nanostructures, which enhances electromagnetic fields and thus endows the device with high sensitivity. Such a device achieves a relative standard deviation of less than 9.3% and a detection limit of malachite green of 10−15 M. The device also exhibits high specificity when detecting malachite green in mixtures. Our novel strategy to construct extremely sensitive SERS substrates can be extended to various nanohybrids with parahydrophobicity for fungicide detection and food safety analysis.

A nanoforest of black silicon was prepared using a method combining aluminum-induced crystallization (AIC) and reactive-ion etching (RIE). During the AIC period, a rough layer, incorporating AlSix intermetallics, was formed. This layer acted as an etch mask for the RIE step. X-ray photoelectron spectroscopic (XPS) measurements were performed to further analyze the formation of black silicon. Compared to Si 3 N 4 and polysilicon, the black silicon exhibits a high degree of infrared absorption for wavelengths of about 3 to 5 μm and 8 to 14 μm, respectively. In addition, black platinum overlaid on the base of black silicon further improves the infrared absorption. This nanostructure forests of black silicon could be incorporated into the fabrication process for gas detectors, photovoltaic devices, and imaging applications to improve the infrared absorption characteristics.

Piezoresistive effect of semiconductor materials is often used in microsensors as a sensing principle. Resonant tunneling diodes (RTDs) have been proved to have negative differential resistance effect, and their current–voltage characteristics change as a function of stress, which can be generated by external mechanical loads, such as pressures, accelerations and so on. According to this, the Meso-piezoresistive effect of RTDs can be used for stress measurement. This paper discusses two double-barrier resonant tunneling effect based stress measurement methods, including an RTD-Wheatstone bridge based method originally proposed. According to the results from the RTD-Wheatstone bridge based experiment, the piezoresistive sensitivity of RTD is adjustable in a range of 3 orders. And the largest piezoresistive sensitivity of RTD is larger than that of common semiconductor materials, such as silicon and GaAs.