A comparative study of uniaxial pressure effects in intraband AlGaAs/GaAs and interband InAs/AlSb/GaSb resonant tunneling diodes

We report on the effects of uniaxial pressure on (001)-oriented AlGaAs/GaAs and InAs/AlSb/GaSb double barrier resonant tunneling diodes (RTDs). The current–voltage characteristics of the AlGaAs/GaAs RTDs shift asymmetrically due to stress-induced piezoelectric fields in the barriers and well structures. Although all the materials involved are piezoelectric, the interband InAs/AlSb/GaSb resonant tunneling device surprisingly shows, in contrast to the AlGaAs/GaAs one, a symmetrical behavior for the same orientation [110] of the applied pressure. We explain the observed differences considering the different tunneling paths involved in the conduction mechanism of the two heterostructure device types as well as their pressure dependencies. ©1998 American Institute of Physics.published_or_final_versio

El Arte, un espectador de la Guerra. Del dolor de los cuerpos femeninos a la profanación del Ser

El arte en algunas de sus obras más importantes, ha sido observador declarante de la historia y la continuidad de un cierto proceso de “naturalización” por la que el cuerpo femenino ha sido botín de guerra. Las autorías que ilustran a través del tiempo “el rapto”, y en alguna medida la justificación de robo, sometimiento y sacrificio de mujeres a causa de su belleza como recompensa de guerra, revelan un problema vigente y crítico sobre nuestra contemporaneidad, el secuestro del cuerpo por sobre la anulación del ser femenino. Importantes obras de arte que registran de forma bella y acrítica, sucesos de la mitología tales como el rapto de Europa, el secuestro de Perséfone, las Sabinas, el sacrificio de Ifigenia, por mencionar algunas, fundamentan las bases de una maquillada “justificación” de la violencia sexual y la esclavitud femenina, que en la historia del mundo, casos como el de Boc Dong Kim y las “mujeres de solaz” o “mujeres de confort” de Corea, China, Filipinas, Malayas, entre otras (Segunda Guerra Mundial), y el caso de las mujeres de Sepur Zarco en Guatemala (1980-1983), son ejemplos de un doble crimen de guerra. Se anula al Sujeto femenino por la instrumentalización de su corporalidad. La belleza como mandato social y asignación de género es un enemigo profanador de la constitución ontológica del ser femenino. La mujer como cuerpo y el cuerpo que le es despojado. En tanto, el arte ha sido un testigo pasivo y quizá, en su indolencia, legitimador.In some of its most important works, Art has been an outspoken observer of history and of the continuity of a certain process of “naturalization” by which the female body has become spoils of war. The artists that throughout history illustrate the “rapture,” and, to some extent, the justification of the theft, subjugation, and sacrifice of women as spoils of war because of their beauty, reveal a prevailing and critical problem of our times: the kidnapping of the body through the abolition of the female Self. Important works of art register, both beautifully and uncritically, mythological events such as the abduction of Europe, the kidnapping of Persephone, the rape of the Sabine women, the sacrifice of Iphigenia, to mention a few examples. Thus, they become the foundation of an embellished “justification” of sexual violence and female slavery –as in world history cases like Bok-dong Kim and the comfort women in Korea during World War II, or that of Guatemala’s Sepur Zarco women (1980-1983) – which are examples of a double war crime. The female Self if obliterated through the instrumentalization of her corporality. Beauty as socially-demanded and gender-assigned is a defiling enemy of the ontological act of being female, and it creates the image of woman as body and as the body that is taken away. Meanwhile, art has been a passive and, in its indolence, maybe even a legitimizing witness of this process.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Artes y Letras::Instituto de Investigaciones en Arte (IIArte

Indium tin oxide as a semiconductor material in efficient p-type dye-sensitized solar cells

Indium tin oxide (ITO) is a well-known n-type degenerate semiconductor with a wide variety of electronic and optoelectronic applications. Herein ITO is utilized as a photocathode material in p-type dye-sensitized solar cells in place of the commonly applied and highly colored nickel oxide (NiO) semiconductor. The application of mesoporous ITO photocathodes, [Fe(acac)3] 0/ - as a redox mediator and a new organic dye afforded an impressive energy conversion efficiency of 1.96 ± 0.12%. Comparative transient absorption spectroscopic studies indicated that the recombination rate at the ITO-electrolyte interface is two orders of magnitude faster than that of NiO. Analysis of the operation mechanism of the ITO-based devices with ultraviolet photon spectroscopy and photoelectron spectroscopy in air showed that ITO exhibits a significant local density of states arising below - 4.8 eV, which enables electron transfer to occur from the ITO to the excited dye, thus giving rise to the sustained photocathodic current

The Use of Metal Oxide Semiconductors for THz Spectroscopy of Biological Applications

Terahertz (THz) waves refer to the electromagnetic radiation in the frequency range from 0.1 to 10 THz, which corresponds to the wavelengths from 3 mm to 30 µm, respectively. This spectral region, called also as ``T-gap'', is important for many practical applications, including THz imaging, chemical and biological sensing, high-speed telecommunication, security and medical applications. THz waves have low photon energies (~4.1 meV for 1 THz), which is about 1 million times weaker than the energy of X-ray photons. They do neither ignite any explosive materials at typical power levels nor cause any harmful ionization in biological tissues. The terahertz radiation is strongly attenuated by water and is very sensitive to water content. Unique THz absorption spectra caused by intermolecular vibrations in this spectral region have been found in different biological materials and tissues. Thus, Terahertz spectroscopy provides a powerful tool for characterization of a great many bio molecules and tissues. All these applications require relatively high power terahertz sources with milliwatt-level output power, which could operate at room temperature. Despite great progress, made in the last few years of design, fabrication and demonstration, THz devices based on GaAs/AlGaAs materials, there are some limits of bandgap engineering due to the relatively low (0.72 eV for GaAs/AlAs) conduction band offset, and most terahertz sources with one milliwatt-power like quantum cascade lasers (QCLs) require cryogenic cooling down to less than 200 K. To overcome the issue the new material systems such as metal oxide materials are considered as promising for room-temperature THz sources. The interest in terahertz imaging and spectroscopy of biologically related applications is increasing more and more within the last few years. This paper provides a review and current status of using metal oxide materials for THz spectroscopy, and recent advances in terahertz spectroscopy techniques in biological and medical applications