Panos G. Datskos

In this work, we describe the design, fabrication, and characterization of purely mechanical miniature resonating structures that exhibit gyroscopic performance comparable to that of more complex microelectromechanical systems. Compared to previous implementations of Coriolis vibratory gyroscopes, the present approach has the key advantage of using excitation and probing that do not require any on-chip electronics or electrical contacts near the resonating structure. More specifically, our design relies on differential optical readout, each channel of which is similar to the “optical lever” readout used in atomic force microscopy. The piezoelectrically actuated stage provides highly efficient excitation of millimeter-scale tuning fork structures that were fabricated using widely available high-throughput wafer-level silicon processing. In our experiments, reproducible responses to rotational rates as low as 1.8 × 10³° h⁻¹ were demonstrated using a benchtop prototype without any additional processing of the raw signal. The noise-equivalent rate, Ω_NER, derived from the Allan deviation plot, was found to be −1 for a time of 10³ s. Despite the relatively low Q factors (4) of the tuning fork structures operating under ambient pressure and temperature conditions, the measured performance was not limited by thermomechanical noise. In fact, the performance demonstrated in this proof-of-principle study is approximately four orders of magnitude away from the fundamental limit.

We report on a standoff spectroscopic technique for detecting chemical residues on surfaces. An infrared (IR) camera was used in combination with a wavelength tunable mid-IR quantum cascade laser to acquire multispectral image arrays of a surface with explosive residue. IR spectral signatures of residue of cyclotrimethylenetrinitramine (commonly known as RDX) were extracted in the wavelength range 7.9 to 9.7 $\mu \text{m}$ from the multispectral IR images. Detection of RDX was achieved for a lower surface concentration of $5~\mu \text{g}$ cm ⁻² and a higher surface concentration of $20~\mu \text{g}$ cm ⁻² at distances of 0.15 m and 1.5 m, respectively. We performed no background subtraction and the resulting IR spectra of RDX were compared with reference Fourier Transform IR Spectroscopy data that were acquired by placing 20 $\mu \text{g}$ of RDX on a ZnS window. We found that the detection of RDX can be made with negligible interfering contribution of reflected IR photons from the substrate surface.

Sensitive detection of harmful chemicals in industrial applications is pertinent to safety. In this work, we demonstrate the use of a sensitive silicon microcantilever (MC) system with a porous silicon oxide layer deposited on the active side of the MCs that have been mechanically manipulated to increase sensitivity. Included is the evaluation of porous silicon oxide present on different geometries of MCs and exposed to varying concentrations of hydrogen fluoride in humid air. Profilometry and the signal generated by the stress-induced porous silicon oxide (PSO) coating and bending of the MC were used as methods of evaluation.

Shape control of silica structures is demonstrated by localization of the reagents. A uniform dispersion of reagents provided straight silica rods, whereas localization of the reagents in the emulsion droplet periphery provided a new type of half-sphere/half-funnel structure. The effect of water concentration appeared to be related to the ease of diffusion of the silica precursor inside the emulsion droplet (i.e., the higher the water concentration, the lower the silica precursor diffusion).

Self-assembly of one-dimensional structures is attracting a great deal of interest because assembled structures can provide better properties compared to individual building blocks. In the present work, silica microrod self-assembly has been demonstrated by exploiting Pickering emulsion based strategy. Micron-sized silica rods were synthesized employing previously reported methods based on polyvinylpyrrolidone/pentanol emulsion droplets. Rods self-assembled to make structures in the range of ≈10–40 μm. Smooth rods assembled better than segmented rods. The assembled structures were bonded by weak van der Waals forces.

Metal monochalcogenide quantum dot nanocrystals of ZnS, CdS and SnS were prepared by anaerobic, metal-reducing bacteria using in situ capping by oleic acid or oleylamine. The capping agent preferentially adsorbs on the surface of the nanocrystal, suppressing the growth process in the early stages, thus leading to production of nanocrystals with a diameter of less than 5 nm.

The synthesis of complex and hybrid oxide microstructures is of fundamental interest and practical applications. However, the design and synthesis of such structures is a challenging task. A solution‐phase process to synthesize complex silica and silica–titania hybrid microstructures was developed by exploiting the emulsion‐droplet‐based step‐by‐step growth featuring shape control. The strategy is robust and can be extended to the preparation of complex hybrid structures consisting of two or more materials, with each having its own shape.