Heterostructured WO3/TiO2 photonic crystal films in the form of three-dimensional macroporous inverse opals were developed by single-step, three-phase co-assembly of colloidal templates with water soluble precursors enabling simultaneous growth of both metal oxides into a firmly interconnected periodic pore framework whose skeletal walls consisted of uniformly distributed nanoscale type II WO3-TiO2 heterojunctions. A marked size- and composition-dependence of the binary WO3/TiO2 inverse opal properties was evidenced by controlling the W/Ti molar ratio and macropore diameter that allowed Fermi level and photonic band gap engineering according to optical and photoelectron spectroscopies supplemented by electrochemical measurements. Compositional tuning along with the reduction of WO3 nanocrystallite size and the concomitant W5+ defect growth with increasing TiO2 phase content were explored for the optimization of photocurrent generation by WO3/TiO2 inverse opal photoanodes combining reduced charge carrier recombination and optimal slow light trapping. One step co-assembly of mixed metal oxides is concluded as a promising route for the development of heterostructured inverse opal networks with tailored electronic properties and improved solar light harvesting for photo-induced applications.

This study presents experimental evidence of field emission in MEMS capacitive switches. Devices with dielectric layers of silicon nitride of different thicknesses between 50 and 200 nm were investigated by current-voltage (I-V) measurements. These measurements were performed at room temperature and under a controlled atmosphere pressure of 3 × 10−2 mbar at bias levels below breakdown and corresponding electric fields encountered in MEMS capacitive switches during pull-in (1-2 × 106 V/cm). Field emission although was not always clearly observed, it occurred in all devices and clearly manifested at electric fields larger than 106 V/cm.

Metal-Insulator-Semiconductor micro-capacitors for on-chip energy storage were fabricated and characterized. The capacitors were based on Si nanowires fabricated by Metal Assisted Chemical Etching. 1.2μm long nanowires with 100nm average diameter were created leading to an effective area increase of 6.28, as compared to a flat surface. Nanowires were chemically treated to reduce surface roughness and electronic states and were coated by a HfO2 layer, deposited by Atomic Layer Deposition, to act as the dielectric. Al and Cu were deposited as two possible top metal electrodes. The use of Al as the top electrode was shown to create a parasitic interface oxide between the metal and the dielectric, reducing the measured capacitance. The use of Cu was shown to significantly reduce this problem, leading to more efficient devices. Capacitors with 5.4μF/cm2 capacitance and 8.9x10-7A/cm2 leakage current at -2.5V were demonstrated along with a cutoff frequency of 104Hz. These values make the demonstrated capacitors very attractive for on-chip energy storage applications.

The impact of ambient on the field emission and the resulting breakdown induced damage of rigid MEMS capacitive structure are investigated. The effect of asperities burning due to Joule heating and the resulting explosive breakdown are presented. The breakdown gives rise to almost mirror craters formation on the cathode and anode electrodes. A linear relation between crater diameter and the breakdown current is found when breakdown occurs in vacuum. In ambient atmosphere the breakdown leads to large amplitude current oscillations and the formation of extended damage on both electrodes.

Αn isotype heterojunction n+-ZnO/n-Si photodetector is developed, demonstrating wavelength-selective or broadband operation, depending on the applied bias voltage. Additionally, at self-powered (zero bias) operation, it distinguishes between UV, visible, and near IR (NIR) photons by polarity control of the photocurrent. The photodetector is developed by atomic layer deposition (ALD) of ZnO on n-Si, followed by electric contact deposition and annealing. Photoluminescence measurements reveal high optical quality and improved crystallinity of annealed ZnO on silicon. Photocurrent measurements as a function of illumination wavelength and bias voltage show small negative values in the UV–visible spectral range at zero and positive bias voltage and high positive values in the NIR spectral range. For these measurements, we consider the electric contact to ZnO as the anode and the electric contact to silicon as the cathode. At negative bias voltage, the device shows broadband operation with high photocurrent values across the UV–vis-NIR.