Properties Of Mesoporous Silicon Research Articles

Investigation of mesoporous silicon thermal conductivity: Effect of nanographene insertion

In this study, the impact of nanographene incorporation on the thermal properties of mesoporous silicon (PSi) was evaluated using two complementary experimental methods: the temperature gradient (TG) and the photothermal radiometry (MPTR) methods. It is shown that the measured thermal conductivity of the mesoporous silicon (PSi) ranges from 0.10 to 0.68 W/m.K in the case of TG and from 0.37 to 3.02 W/m.K in MPTR and is strongly correlated to the electrochemical etching parameters. These values are much lower than that of crystalline silicon, estimated to be from 100 to 140 W/m.K, depending on the doping rate. They appear to be, however, in the order of magnitude range for the percolation models that also include the in-depth porosity and the crystallite mean radius. This set of experiments on the thermal conductivity was extended to investigate the effect of graphene incorporation in the PSi matrix (G-PSi) as it has seldom been reported in the literature. The results from both methods exhibit significantly higher values (1.7 ± 0.3 W/m.K for TG, and from 0.7 to 2.13 W/m.K for MPTR). This spread of the thermal conductivity values is attributed to the intrinsic working principle of the TG versus the MPTR method as highlighted in the last part of the present paper. Targeting the thermoelectric application of both matrices (PSi, G-PSi), the thermal conductivity remains sufficiently low for them to be considered as very promising materials, keeping in mind the enhancement of the power-factor attributed to the incorporation of graphene.

Moldless Printing of Silicone Lenses With Embedded Nanostructured Optical Filters.

Optical lenses are among the oldest technological innovations (3000 years ago) and they have enabled a multitude of applications in healthcare and in our daily lives. The primary function of optical lenses has changed little over time; they serve mainly as a light-collection (e.g. reflected, transmitted, diffracted) element, and the wavelength and/or intensity of the collected light is usually manipulated by coupling with various external optical filter elements or coatings. This generally results in losses associated with multiple interfacial reflections, and increases the complexity of design and construction. In this work we introduce a change in this paradigm, by integrating both light-shaping and image magnification into a single lens element using a moldless procedure that takes advantage of the physical and optical properties of mesoporous silicon (PSi) photonic crystal nanostructures. Casting of a liquid poly(dimethyl) siloxane (PDMS) pre-polymer solution onto a PSi film generates a droplet with contact angle that is readily controlled by the silicon nanostructure, and adhesion of the cured polymer to the PSi photonic crystal allows preparation of lightweight (10 mg) freestanding lenses (4.7 mm focal length) with an embedded optical component (e.g. optical rugate filter, resonant cavity, distributed Bragg reflector). Our fabrication process shows excellent reliability (yield 95%) and low cost and we expect our lens to have implications in a wide range of applications. As a proof-of-concept, using a single monolithic lens/filter element we demonstrate: fluorescence imaging of isolated human cancer cells with rejection of the blue excitation light, through a lens that is self-adhered to a commercial smartphone; shaping the emission spectrum of a white light emitting diode (LED) to tune the color from red through blue; and selection of a narrow wavelength band (bandwidth 5 nm) from a fluorescent molecular probe.

The effect of low doses of gamma radiation on the electrophysical properties of mesoporous silicon

The effect of low exposure doses (5–40 kR) of gamma radiation on the electrical properties of structures based on a mesoporous silicon (SiMP) layer is investigated. It is demonstrated that the conductivity of the SiMP layer increases, the Fermi level shifts, and the trap density changes in gamma-irradiated Al/SiMP/p-Si/Al structures. Long-term stable switched-state memory in the region of the I–V curve hysteresis is revealed. This effect is controlled by the irradiation dose.

Electrophysical properties of mesoporous silicon passivated by iron

The current-voltage and capacitance-voltage characteristics of structures based on mesoporous silicon, obtained by electroless etching with passivation by iron, (SiMP:Fe) are investigated. It is shown that the conductivity and barriers in Al-SiMP:Fe-p-Si-Al heterostructures ambiguously depend on the Fe concentration. Passivation by iron changes not only the conductivity of the SiMP:Fe layer but also the character of carrier transport at low frequencies. At an iron concentration of ∼1 at % tunneling transport through barriers becomes dominant in comparison with jumps over dangling bonds. Passivation of the SiMP layer by iron stabilizes the SiMP electrical properties (which is confirmed by the values of the trap concentrations estimated from the current-voltage characteristic) of structures subjected to long-term storage. This is likely to be related to the interaction between iron ions and the silicon surface with the formation of oxides.