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We have used an isothermal microcalorimetric method to study photoinduced effects in porous silicon (PS). In the photo-oxidation investigations using constant wavelength, sharp threshold behavior with threshold energies 3.9 eV for n-PS and 4.7 eV for p+-PS were observed. The two discussed origins for the different threshold energies are based either on the energy gap transitions and enhanced electron transfer from the conduction band to the electron-affinity level of oxygen molecules, or the Si–O bond energy. Also nonlinear dependence on the irradiation intensity was found. Surprisingly, high exothermic signals were observed in measurements made under an inert perfusion. It is proposed that this is associated with relaxation of PS structure, which seems to be more efficiently induced by illumination than thermal treatment.

The oxidation behavior of porous silicon (PS) has been found to be related to illumination during etching. The autocatalytic oxidation behavior at room temperature arises from the unrelaxed surface induced by the preparation under illumination and can be removed using thermal treatment in a nitrogen atmosphere. The effect is absent in the case of degenerate PS and smaller in p type than in n-type PS. The correlation between the oxidation behavior and the microstructural dimensions is also discussed.

We have studied the thermal oxidation of free-standing porous silicon films from room temperature to 730 °C with a differential scanning calorimeter and a thermogravimeter. We have observed three different thermal oxidation processes for the porous silicon. The change of enthalpy (ΔH) and activation energy (Ea) for the first reaction has been calculated. The oxidation of a fresh sample has been compared with those of aged samples, which were stored in dry relative humidity (RH 0%), humid (RH 100%) and normal (RH 25%–35%) laboratory air atmospheres. We also used Fourier transform infrared spectroscopy to clarify the bonds for each process.

In this work, the feasibility of porous silicon particles for producing printed humidity sensors is examined. A proof of concept is provided by producing fully functional humidity sensors on a glass substrate by drop casting a particle solution on top of inkjet printed silver electrodes. Sensor sensitivity towards changes in relative humidity is examined. The results show that the sensors provide good sensitivity and reproducible results throughout the entire relative humidity range. In addition, negligibly small hysteresis accompanied by relatively fast response and recovery times is also demonstrated.

Color control of the white photoluminescence(PL) from carbon-incorporated silicon oxide is demonstrated. The carbon-incorporated silicon oxide was fabricated by carbonization of porous silicon in acetylene flow (at 650 and 850 °C) followed by wet oxidation (at 650 and 800 °C). It was shown that PL color can be controlled in the range of blue-white and yellow-white by selecting the porosity of starting porous silicon as well as the carbonization and oxidation temperatures. Low-temperature oxidation resulted in bluish light emission in lower porosity series, while high-temperature oxidation promoted yellow-white light emission. The maximal integral intensity of PL was observed after oxidation at 800 °C. It was shown that white PL from carbon-incorporated silicon oxide has blue and yellow-white PL bands originating from different light-emitting centers. The origin of blue PL is attributed to defects in silicon dioxide. Some trap levels at the interface of the carbon clusters and silicon oxide are suggested to be the origin of the yellow-white light emission.

Nanostructured porous silicon (PS) optical filters have been proposed for their use in biological and chemical sensing applications. PS, however, presents a reactive surface that must be adequately passivated in order to achieve the required chemical stability mandatory for sensing applications. In the present work, thermal carbonization (TC) by acetylene decomposition is shown to provide effective passivation of a PS internal surface. Thermally carbonized PS optical filters are stable even in strong oxidizing environments such as absolute ethanol. Moreover, it is shown that the TC process, as opposed to more commonly used oxidation treatments, has only minor effects on the optical properties of PS. Thus, the optical performance of PS interference filters is preserved after the carbonization process. In addition, the hydrophilicity of the PS device surface can be adjusted by setting the appropriate TC process temperature. These results show that it is possible to produce low-cost, reusable, chemically sta...

Three different thermal carbonization processes of porous silicon (PS) surface by acetylene occurring between 400 and 950 °C were observed by in situ measurements. The peak temperature of oxidation shifts from 300 to 600 °C and the activation energy from 130 to 500 kJ/mole in the samples treated at 900 °C compared to untreated PS. Using Fourier transform infrared spectroscopy (FTIR), the bonding configurations associated with the temperature dependent processes were found. In the samples treated at or below 600 °C, traces of C–Hx bonds were clearly seen, but above 600 °C the FTIR spectra started resemble those of the SiC. The graphitization process was found to take place on the surface of PS samples treated above 800 °C. By changing the time between the C2H2 flush and thermal treatment, the graphitization can be controlled and even avoided. The weight increase was observed to be nearly proportional to the reduction of the surface area while the decrease in the surface area due to the thermal carbonizatio...