RESUMEN
Graphene is ideally suited for optoelectronics. It offers absorption at telecom wavelengths, high-frequency operation and CMOS-compatibility. We show how high speed optoelectronic mixing can be achieved with high frequency (~20 GHz bandwidth) graphene field effect transistors (GFETs). These devices mix an electrical signal injected into the GFET gate and a modulated optical signal onto a single layer graphene (SLG) channel. The photodetection mechanism and the resulting photocurrent sign depend on the SLG Fermi level (EF). At low EF (<130 meV), a positive photocurrent is generated, while at large EF (>130 meV), a negative photobolometric current appears. This allows our devices to operate up to at least 67 GHz. Our results pave the way for GFETs optoelectronic mixers for mm-wave applications, such as telecommunications and radio/light detection and ranging (RADAR/LIDARs.).
RESUMEN
Hard disk drives (HDDs) are used as secondary storage in digital electronic devices owing to low cost and large data storage capacity. Due to the exponentially increasing amount of data, there is a need to increase areal storage densities beyond ~1 Tb/in2. This requires the thickness of carbon overcoats (COCs) to be <2 nm. However, friction, wear, corrosion, and thermal stability are critical concerns below 2 nm, limiting current technology, and restricting COC integration with heat assisted magnetic recording technology (HAMR). Here we show that graphene-based overcoats can overcome all these limitations, and achieve two-fold reduction in friction and provide better corrosion and wear resistance than state-of-the-art COCs, while withstanding HAMR conditions. Thus, we expect that graphene overcoats may enable the development of 4-10 Tb/in2 areal density HDDs when employing suitable recording technologies, such as HAMR and HAMR+bit patterned media.
RESUMEN
We investigate the optoelectronic properties of the semiconducting (6,5) species of single-walled carbon nanotubes by measuring ultrafast transient transmission changes with 20 fs time resolution. We demonstrate that photons with energy below the lowest exciton resonance efficiently lead to linear excitation of electronic states. This finding challenges the established picture of a vanishing optical absorption below the fundamental excitonic resonance. Our result points towards below-gap electronic states as an intrinsic property of semiconducting nanotubes.
RESUMEN
The influence of nanocrystallinity on the electronic and mechanical properties of metal nanoparticles is still poorly understood, due to the difficulty in synthesizing nanoparticles with a controlled internal structure. Here, we report on a new method for the selective synthesis of Au nanoparticles in either a single-domain or a polycrystalline phase maintaining the same chemical environment. We obtain quasi-spherical nanoparticles whose diameter is tunable from 6 to 13 nm with a resolution down to ≈0.5 nm and narrow size distribution (4-5%). The availability of such high-quality samples allows the study of the impact of the particle size and nanocrystallinity on a number of parameters, such as plasmon dephasing time, electron-phonon coupling, period and damping time of the radial breathing modes.
RESUMEN
The aim of this investigation was to learn how a stressful event, often very mild, can determine a relapse of psoriasis. The research was carried out with clinical interviews and with the administration of Rorschach Psychoreactive, MMPI and H-T-P tests to 80 in-patients. Our data revealed a high prevalence of psychic disorders: 71.2% of patients showed symptoms which allowed a precise psychiatric diagnosis based on DSM-III-R criteria. 35% had personality disorders, 17.5% were moody, 12.5% were anxious and 6.25% had a schizophrenic trait. The analysis of the stressful events enabled us to determine the presence of a specific event in 88.7% of cases. For the majority of patients, the stressful event was felt as very mild: 67.6% of patients reported the existence of a low-impact stressful event according to the DSM-III-R classification. The average evaluation of the stressful event for all patients, based on a five-stage rating (ranging from 2 'light' to 6 'catastrophic') was 2.56. In conclusion, the analysis of the psychic conditions of in-patients showed that the importance in inducing an acute episode of psoriasis is the meaning of a stressful event as experienced by the patient, i.e. the questioning of his own identity, rather than the intensity of the aforementioned stressful event. In this case, the disease appears to be an attempt to express a defensive somatic response to a possible identity crisis.
