A complete description of Szep's (2,p)- semifields

Abstract

Two sub-band conductivity of Si quantum well

We report on two sub-band transport in double gate SiO$_2$-Si-SiO$_2$ quantum well with 14 nm thick Si layer at 270 mK. At symmetric well potential the experimental sub-band spacing changes monotonically from 2.3 to 0.3 meV when the total density is adjusted by gate voltages between $\sim 0.7\times 10^{16}$ $-3.0\times 10^{16}$ m$^{-2}$. The conductivity is mapped in large gate bias window and it shows strong non-monotonic features. At symmetric well potential and high density these features are addressed to sub-band wave function delocalization in the quantization direction and to different disorder of the top and bottom interfaces of the Si well. Close to bi-layer/second sub-band threshold the non-monotonic behavior is interpreted to arise from scattering from localized band tail electrons.Comment: Presented at MSS12 conference July 10-15, 2005 Albuquerque, New Mexico, USA. Post-deadline paper, Poster PA2-293. Version 2: typos corrected, few clarifications added in the text, summary shortened, title removed from Ref.

Thermoelectric bolometers based on ultra-thin heavily doped single-crystal silicon membranes

We present ultra-thin silicon membrane thermocouple bolometers suitable for fast and sensitive detection of low levels of thermal power and infrared radiation at room temperature. The devices are based on 40 nm-thick strain tuned single crystalline silicon membranes shaped into heater/absorber area and narrow n- and p-doped beams, which operate as the thermocouple. The electro-thermal characterization of the devices reveal noise equivalent power of 13 pW/rtHz and thermal time constant of 2.5 ms. The high sensitivity of the devices is due to the high Seebeck coefficient of 0.39 mV/K and reduction of thermal conductivity of the Si beams from the bulk value. The bolometers operate in the Johnson-Nyquist noise limit of the thermocouple, and the performance improvement towards the operation close to the temperature fluctuation limit is discussed.Comment: 11 pages, 3 figure

¿Volverán los tiempos del cólera a Colombia?

“La epidemia de cólera morbo, cuyas primeras víctimas cayeron fulminadas en los charcos del mercado, había causado en once semanas la más grande mortandad de nuestra historia (...) En las dos primeras semanas del cólera, el cementerio fue desbordado y no quedó sitio disponible en las iglesias, a pesar de que habían pasado al osario común los restos carcomidos de nuestros próceres sin nombre (...) Desde que se proclamó el bando del cólera, en el alcázar de la guarnición local se disparó un cañonazo cada cuarto de hora, de día y de noche, de acuerdo con la superstición cívica de que la pólvora purificaba el ambiente (...) Cesó de pronto como había empezado y nunca se conoció el número de sus estragos...” “Así describió Gabriel García Márquez el brote de cólera asiático que azotó a Cartagena en en 1849 y que dio muerte a la cuarta parte de su población. Fue éste seguramente el primer episodio de cólera asiático en nuestro país” (1)

Nano-thermoelectric infrared bolometers

Infrared (IR) radiation detectors are used in numerous applications from thermal imaging to spectroscopic gas sensing. Obtaining high speed and sensitivity, low-power operation and cost-effectiveness with a single technology remains to be a challenge in the field of IR sensors. By combining nano-thermoelectric transduction and nanomembrane photonic absorbers, we demonstrate uncooled IR bolometer technology that is material-compatible with large-scale CMOS fabrication and provides fast and high sensitivity response to long-wavelength IR (LWIR) around 10 $\mu$m. The fast operation speed stems from the low heat capacity metal layer grid absorber connecting the sub-100 nm-thick n- and p-type Si nano-thermoelectric support beams, which convert the radiation induced temperature rise into voltage. The nano-thermoelectric transducer-support approach benefits from enhanced phonon surface scattering in the beams leading to reduction in thermal conductivity, which enhances the sensitivity. We demonstrate different size nano-thermoelectric bolometric photodetector pixels with LWIR responsitivities, specific detectivities and time constants in the ranges 179-2930 V/W, 0.15-3.1$\cdot10^{8}$ cmHz$^{1/2}$/W and 66-3600 $\mu$s, respectively. We benchmark the technology against different LWIR detector solutions and show how nano-thermoelectric detector technology can reach the fundamental sensitivity limits posed by phonon and photon thermal fluctuation noise.Comment: 20 pages, 4 figures, 1 tabl

Vertical Engineering for Large Brillouin Gain in Unreleased Silicon-Based Waveguides

[EN] Strong acousto-optic interaction in high-index waveguides and cavities generally requires the releasing of the high-index core to avoid mechanical leakage into the underlying low-index substrate. This complicates fabrication, limits thermalization, reduces the mechanical robustness, and hinders large-area optomechanical devices on a single chip. Here, we overcome this limitation by employing vertical photonic-phononic engineering to drastically reduce mechanical leakage into the cladding by adding a pedestal with specific properties between the core and the cladding. We apply this concept to a silicon-based platform, due to the remarkable properties of silicon to enhance optomechanical interactions and the technological relevance of silicon devices in multiple applications. Specifically, the insertion of a thick silicon nitride layer between the silicon guiding core and the silica substrate contributes to reducing gigahertz-frequency phonon leakage while enabling large values of the Brillouin gain in an unreleased platform. We numerically obtain values of the Brillouin gain around 300 ( W m ) ¿ 1 for different configurations, which could be further increased by operation at cryogenic temperatures. These values should enable Brillouin-related phenomena in centimeter-scale waveguides or in more compact ring resonators. Our findings could pave the way toward large-area unreleased-cavity and waveguide optomechanics on silicon and other high-index photonic technologies.This work was supported by the European Commission (PHENOMEN Grant No. H2020-EU-713450), the Universitat Politecnica de Valencia (Grant No. PAID-01-169), the Ministerio de Ciencia, Innovacion y Universidades (Grants No. PGC2018-094490-B and No. PRX18/00126), and the Generalitat Valenciana (Grant No. PROMETEO/2019/123)Mercadé-Morales, L.; Korovin, AV.; Pennec, Y.; Ahopelto, J.; Djafari-Rouhani, B.; Martínez Abietar, AJ. (2021). Vertical Engineering for Large Brillouin Gain in Unreleased Silicon-Based Waveguides. Physical Review Applied. 15(3):1-9. https://doi.org/10.1103/PhysRevApplied.15.0340211915

Conformal Titanium Nitride in a Porous Silicon Matrix: a Nanomaterial for In-Chip Supercapacitors

Today's supercapacitor energy storages are typically discrete devices aimed for printed boards and power applications. The development of autonomous sensor networks and wearable electronics and the miniaturisation of mobile devices would benefit substantially from solutions in which the energy storage is integrated with the active device. Nanostructures based on porous silicon (PS) provide a route towards integration due to the very high inherent surface area to volume ratio and compatibility with microelectronics fabrication processes. Unfortunately, pristine PS has limited wettability and poor chemical stability in electrolytes and the high resistance of the PS matrix severely limits the power efficiency. In this work, we demonstrate that excellent wettability and electro-chemical properties in aqueous and organic electrolytes can be obtained by coating the PS matrix with an ultra-thin layer of titanium nitride by atomic layer deposition. Our approach leads to very high specific capacitance (15 F/cm$^3$), energy density (1.3 mWh/cm$^3$), power density (up to 214 W/cm$^3$) and excellent stability (more than 13,000 cycles). Furthermore, we show that the PS-TiN nanomaterial can be integrated inside a silicon chip monolithically by combining MEMS and nanofabrication techniques. This leads to realisation of in-chip supercapacitor, i.e., it opens a new way to exploit the otherwise inactive volume of a silicon chip to store energy