Germanium nanowire microbolometer.

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in theµm range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K-1atT = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Verifying the band gap narrowing in tensile strained Ge nanowires by electrical means.

Group-IV based light sources are one of the missing links towards fully CMOS compatible photonic circuits. Combining both silicon process compatibility and a pseudo-direct band gap, germanium is one of the most viable candidates. To overcome the limitation of the indirect band gap and turning germanium in an efficient light emitting material, the application of strain has been proven as a promising approach. So far the experimental verification of strain induced bandgap modifications were based on optical measurements and restricted to moderate strain levels. In this work, we demonstrate a methodology enabling to apply tunable tensile strain to intrinsic germanium [Formula: see text] nanowires and simultaneously perform in situ optical as well as electrical characterization. Combining I/V measurements and µ-Raman spectroscopy at various strain levels, we determined a decrease of the resistivity by almost three orders of magnitude for strain levels of âˆ¼5%. Thereof, we calculated the strain induced band gap narrowing in remarkable accordance to recently published simulation results for moderate strain levels up to 3.6%. Deviations for ultrahigh strain values are discussed with respect to surface reconfiguration and reduced charge carrier scattering time.

Ge quantum wire memristor.

Despite being known of for decades, the actual realization of memory devices based on the memristive effect is progressing slowly, due to processing requirements and the need for exotic materials which are not compatible with today's complementary-metal-oxide-semiconductor (CMOS) technology. Here, we report an experimental study on a Ge quantum wire device featuring distinct signatures of memristive behavior favorable for integration in CMOS platform technology. Embedding the quasi-1D Ge quantum wire into an electrostatically modulated back-gated field-effect transistor, we demonstrate that individual current transport channels can be addressed directly by controlling the surface trap assisted electrostatic gating. The resulting quantization of the current represents the ultimate limit of memristors with practically zero off-state current and low footprint. In addition, the proposed device has the advantage of non-destructive successive reading cycles capability. Importantly, our findings provide a framework towards fully CMOS compatible ultra-scaled Ge based memristors.

Quasi One-Dimensional Metal-Semiconductor Heterostructures.

The band offsets occurring at the abrupt heterointerfaces of suitable material combinations offer a powerful design tool for high performance or even new kinds of devices. Because of a large variety of applications for metal-semiconductor heterostructures and the promise of low-dimensional systems to present exceptional device characteristics, nanowire heterostructures gained particular interest over the past decade. However, compared to those achieved by mature two-dimensional processing techniques, quasi one-dimensional (1D) heterostructures often suffer from low interface and crystalline quality. For the GaAs-Au system, we demonstrate exemplarily a new approach to generate epitaxial and single crystalline metal-semiconductor nanowire heterostructures with atomically sharp interfaces using standard semiconductor processing techniques. Spatially resolved Raman measurements exclude any significant strain at the lattice mismatched metal-semiconductor heterojunction. On the basis of experimental results and simulation work, a novel self-assembled mechanism is demonstrated which yields one-step reconfiguration of a semiconductor-metal core-shell nanowire to a quasi 1D axially stacked heterostructure via flash lamp annealing. Transmission electron microscopy imaging and electrical characterization confirm the high interface quality resulting in the lowest Schottky barrier for the GaAs-Au system reported to date. Without limiting the generality, this novel approach will open up new opportunities in the syntheses of other metal-semiconductor nanowire heterostructures and thus facilitate the research of high-quality interfaces in metal-semiconductor nanocontacts.

A computationally bio-inspired framework of brain activities based on cognitive processes for estimating the depth of anesthesia.

This paper develops a computationally bio-inspired framework of brain activities based on concepts, such as sensory register (SR), encoding, emotion, short-term memory (STM), selective attention, working memory (WM), forgetting, long-term memory (LTM), sustained memory (SM), and response selection for estimating the depth of anesthesia (DOA) using electroencephalogram (EEG) signals. Different brain regions, such as the thalamus, cortex, neocortex, amygdala, striatum, basal ganglia, cerebellum, and hippocampus, are considered for developing a cognitive architecture and a computationally bio-inspired framework. A clinical study was managed on twenty-two patients corresponding to three anesthetic states, including awake state, moderate anesthesia, and general anesthesia. The proposed approach utilizes a multiple of dynamically reconfigurable neural networks with radial basis function (RBF) and its associated data processing mechanisms. The emotion effect in the model, dynamic RBFs in WM and LTMs, and adjusting the adaptive weights in the last layer are the main innovations of the proposed approach. In the proposed approach, various incoming information is entered into the model. The correct labeling process of EEG signals is performed by qualitative and quantitative analyses of peripheral parameters. Then, an SR is used to accumulate the pre-processed EEG segment for a period of 2.3 s. Feature extraction is performed in the encoding stage as a primary perception. The output of this stage can be transferred to STM and WM with a bottom-up involuntary attentional capture. LTM and SM are a fairly permanent reservoir for information which is passed from WM using a top-down voluntary attention mechanism. Finally, weighting factors in SM and LTMs outputs are determined and then response selection is used by winner-take-all (WTA) strategy. The results indicate that the proposed approach can classify in different anesthetic states with an average accuracy of 89.2%. Results also indicate that the combined use of the above elements can effectively decipher the cognitive process task. A final comparison between the obtained results and the previous method on the same database indicate the effectiveness of the proposed approach for estimating DOA.

Monolithic Axial and Radial Metal-Semiconductor Nanowire Heterostructures.

The electrical and optical properties of low-dimensional nanostructures depend critically on size and geometry and may differ distinctly from those of their bulk counterparts. In particular, ultrathin semiconducting layers as well as nanowires have already proven the feasibility to realize and study quantum size effects enabling novel ultrascaled devices. Further, plasmonic metal nanostructures attracted recently a lot of attention because of appealing near-field-mediated enhancement effects. Thus, combining metal and semiconducting constituents in quasi one-dimensional heterostructures will pave the way for ultrascaled systems and high-performance devices with exceptional electrical, optical, and plasmonic functionality. This Letter reports on the sophisticated fabrication and structural properties of axial and radial Al-Ge and Al-Si nanowire heterostructures, synthesized by a thermally induced exchange reaction of single-crystalline Ge-Si core-shell nanowires and Al pads. This enables a self-aligned metallic contact formation to Ge segments beyond lithographic limitations as well as ultrathin semiconducting layers wrapped around monocrystalline Al core nanowires. High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and µ-Raman measurements proved the composition and perfect crystallinity of these metal-semiconductor nanowire heterostructures. This exemplary selective replacement of Ge by Al represents a general approach for the elaboration of radial and axial metal-semiconductor heterostructures in various Ge-semiconductor heterostructures.

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires.

Metastable germanium-tin alloys are promising materials for optoelectronics and optics. Here we present the first electrical characterization of highly crystalline Ge0.81Sn0.19 nanowires grown in a solution-based process. The investigated Ge0.81Sn0.19 nanowires reveal ohmic behavior with resistivity of the nanowire material in the range of ∼1 × 10-4Ω m. The temperature-dependent resistivity measurements demonstrate the semiconducting behavior. Moreover, failure of devices upon heating to moderate temperatures initiating material degradation has been investigated to illustrate that characterization and device operation of these highly metastable materials have to be carefully conducted.

Oral health literacy and information sources among adults in Tehran, Iran.

OBJECTIVE: To assess oral health literacy level and oral health information of Iranian adults in Tehran, and to determine the factors related to oral health literacy. BASIC RESEARCH DESIGN: A cross-sectional population study. PARTICIPANTS: A random sample of 1,031 adults in Tehran, Iran. METHODS: Oral health literacy was measured using an oral health adult literacy questionnaire (OHL-AQ). Variation in use of information sources by socio-economic and demographic background was estimated by odds ratios. A multiple linear regression model served to determine predictor factors of OHL-AQ scores controlling for characteristics of the subjects and number of information sources. RESULTS: The mean OHL-AQ score was 10.5 (sd 3.0). Women (p < 0.001), younger (p < 0.001), and better educated participants (p < 0.001) had higher OHL-AQ scores. The most common sources of oral health information were dentists (52.6%), and TV/Radio (49.5%). According to the regression model, females (p = 0.001), high educational level (p < 0.001), and use of multiple information sources (two sources p = 0.01, three sources or more p = 0.002) were the main predictor factors of OHL-AQ scores. CONCLUSIONS: The average oral health literacy level of Iranian adults was low. Disseminating evidence-based oral health care information from multiple sources including TV/radio, dentists, and other health professionals in different settings should improve public oral health literacy.