Ida Pavlichenko

Low-Cost Thermo-Optic Imaging Sensors: A Detection Principle Based on Tunable One-Dimensional Photonic Crystals

Infrared (IR) sensors employing optical readout represent a promising class of devices for the development of thermographic imagers. We demonstrate an infrared radiation detection principle based on thermally tunable one-dimensional (1D) photonic crystals acting as optical filters, integrated with organic and inorganic light emitting diodes (OLEDs and LEDs, respectively). The optical filters are composed of periodically assembled mesoporous TiO2 and SiO2 layers. Due to the thermal tunability of the transmission spectrum of the optical filter, the intensity of light passing through the filter is modulated by temperature. The tuned spectrum lies in the visible region and, therefore, can be directly detected by a visible-light photodetector. The thermal response of the luminance of the OLED-photonic crystal ensemble is 3.8 cd m(-2) K(-1). Furthermore, we demonstrate that the local temperature profile can be time and spatially resolved with a resolution of 530 by 530 pixel, thus enabling a potential application as an infrared imaging sensor featuring low power consumption and low fabrication costs.

Bringing one-dimensional photonic crystals to a new light: an electrophotonic platform for chemical mass transport visualisation and cell monitoring

Photonic sensor technologies represent an important milestone in monitoring complex physical, chemical and biological systems. We present an integrated chemo- and bio-photonic sensing scheme drawing on the integration of one-dimensional (1D) stimuli-responsive photonic crystals (PCs) with an electrophotonic visualisation platform. We demonstrate various modi operandi, including the real-time mapping of spatial concentration distribution of a chemical analyte and the in situ monitoring of adhesive cell cultures, enabled by the modular combination of stimuli-responsive 1D PCs with various light emitters and detectors.

Ultra-thin titanium oxide

We demonstrate the fabrication of ultra-thin titanium oxide films by plasma-induced surface oxidation. Ellipsometry measurements indicate an oxide thickness of about 2 nm. Electrical characterization was performed on microscale and nanoscale metal-insulator-metal tunneling diodes. Electrical fields up to 22 MV/cm were applied without destroying the titanium oxide films. The current-voltage-characteristic of the diodes are found to be asymmetric with respect to zero bias when employing electrodes with different work functions. The permittivity of the ultra-thin titanium oxide was determined to be less than 6, which is the smallest permittivity that has been reported for titanium oxide.

Tunable thermoresponsive TiO2/SiO2 Bragg stacks based on sol–gel fabrication methods

Thermoresponsive TiO2/SiO2 one-dimensional photonic crystals (Bragg stacks) fabricated via sol–gel processing methods represent a promising class of environmentally responsive nanostructures featuring optically encoded temperature and humidity detection. The thermo-optic response of the layer materials is amplified by their inherent porosity owing to adsorption/desorption of ambient humidity into the mesoporous multilayer structure. Based on a comprehensive analysis of the impact of layer thickness, refractive index and thermo-optic coefficient on the stop band position, and width of various Bragg stack architectures, design criteria for thermoresponsive Bragg stacks operating in the visible range of the optical spectrum are put forward. A large and well-defined thermo-optic signature is expected for material combinations featuring individually high thermo-optic coefficients with the same sign or allowing for large changes in the effective refractive indices due to water adsorption in the porous layers reinforcing the thermo-optic response, as observed in the TiO2/SiO2 couple. Important practical aspects of the performance of thermoresponsive Bragg stacks are addressed, including the hysteresis properties of TiO2/SiO2 Bragg stacks during multiple heating/cooling cycles, as well as response and recovery times (~2–4 s) of the multilayer system during external changes in ambient humidity.