Superhydrophobic aerogel

Silica aerogels are composed of silica network of 3-4 nm particles surrounded with 30-40 nm holes. As a result of the three dimensional network with holes, they have very low density and up to 99.8% air trapped inside. The structure of aerogels provides them many different properties such as high specific surface area (500-1200 m2/g), high porosity (80–99.8%), low density (∼0.003 g/cm3), high thermal insulation value (0.005 W/mK), ultra low dielectric constant (k = 1.0–2.0) and low index of refraction (∼1.05). Some of the application fields are solar energy panels, radiation detectors and radioactive particle production, laser experiments, microelectronics and filtration of water and exhaust gas.

In our group we are capable of producing monolithic and superhydrophobic silica aerogels. Aerogels are not actively used because of their brittleness and we aim to overcome this problem by proceeding some modifications during the synthesis of aerogels. (Read the rest of this entry)

Towards Tunable Metamaterials

Electromagnetic metamaterials are of great interest due to their unusual permittivity and permeabilities. Recently negative index materials operating at microwave and THz frequencies are using wire arrays to obtain negative electric permittivity and split ring resonators (SRRs) to negative magnetic permeability. However using standard fabrication methods it is not possible to either tune or alter refractive indices from negative to positive.

In this study fabrication techniques from microfluidics is used in tuning the refractive indices of metamaterials. By fabricating SRR shaped micro-channels inside a polymer, PDMS, and by injecting a conducting liquid into the microchannels we showed that it is possible to obtain negative permeability. We are working on the fabrication of a double negative material, that exhibits both negative permeability and tunable permittivity. (Read the rest of this entry)

UNAM researchers engineer laser fibers for medical operations

UNAM researchers created an infrared fiber that can be used in hospitals for laser surgery. The fibers deliver intense laser light inside the body where it can be used to remove malignant tissues with high precision.

The specialty fibers are designed and developed fully at UNAM, which has its own fiber tower custom built for the project. After the completion of the 3.5 meter high fiber tower in August last year, the researchers are now able to draw tens of meters of photonic band gap fibers from polymer-chalcogenide glass composites.

In distinction to the regular optical fibers, these new generation fibers guide electromagnetic radiation by a dielectric mirror structure embedded inside the hollow core. The mirror structure consists of micrometer sized alternating layer materials. Also, the hollow core of the fiber enables high power laser light transmission that would easily melt solid-core fibers. (Read the rest of this entry)

All-chalcogenide tunable infrared Filter

Dielectric mirrors are simple one dimensional photonic structures made using quarter wave stacks (QWS). It was recently shown that QWSs fabricated with high contrast index materials may possess full photonic band gaps (PBG) resulting in omnidirectional reflection. This opens up the possibility of making infrared mirror or filter design at desired wavelengths by piling suitable dielectric materials and controlling their layer thicknesses.

Here, we present an infrared filter fabricated by thermal evaporation using only chalcogenide glasses. Based on the optical characterization of infrared transparent chalcogenide glasses, an omnidirectional filter is designed and simulated using the transfer matrix method (TMM). Accordingly, stacks of As2S3 and GAST are vacuum evaporated on a tilted silicon substrate. The slanted geometry gives graded layer thickness along the substrate length, resulting in a position dependent omnidirectional photonic band gap whose center shifts from 1.5 µm to 4 µm along the substrate. (Read the rest of this entry)

Nanocalorimetry: Calorimetry of ultra-small materials

In chemistry and materials science, the thermodynamical properties of bulk materials, such as phase transition temperatures and enthalpies, are obtained by calorimetry, making it an indispensible metrology technique. However, conventional differential scanning calorimeters require large sample mass to acquire data with reasonable accuracy. It is also known that nano-scale particles and materials show distinctly different thermodynamical properties than their bulk counterparts due to surface and interfacial effects. These effects are negligible in the bulk material but they become dominant at small scales where the total fraction of atoms at the surface is significant. With the ever increasing nanotechnology research, it is therefore desirable to have a means of studying thermodynamical properties of small volume samples, ultimately a single nanoparticle. (Read the rest of this entry)

Lasing action from a micro-toroid

Micro-resonators with ultrahigh quality factors (Q-factor) became an important field of study as they find potential applications in numerous fields such as laser action, nonlinear optics, frequency metrology, telecommunications and cavity quantum electrodynamics. The superior optical confinement properties of such resonators make them excellent research tools. Micro-toroids are remarkable micro-resonators; they can simply be produced by CMOS compatible fabrication techniques, and due to their relatively smaller mode volume they have a high confined electromagnetic energy density.

Inducing laser action from a micro-cavity with an ultrahigh Q-factor is a critical step in developing more efficient lasers -both low threshold and no threshold. In this regard, we generated laser action from a silica micro-toroid covered with an active polymer yielding the lowest threshold obtained until now by free space excitation. (Read the rest of this entry)