1,720,984 research outputs found
Fabrication of Silicon Nanowire Forests for Thermoelectric Applications by Metal-Assisted Chemical Etching
Full text linkSilicon nanowires, whose thermal conductivity is strongly reduced with respect to that of the bulk silicon, are very promising for high-efficient thermoelectric conversion. This work focuses on the development of a technique for the fabrication of thermoelectric generators which are based on vertical silicon nanowire forests, achieved through a metal-assisted chemical etch. As heavily doped nanowires are essential in thermoelectric applications, this chemical process has been applied both on lightly and on highly doped (> 1019 cm−3) silicon substrates. A comparison of the results shows that the etch behaves in a completely distinct way when applied to the differently doped substrates. The results of this comparison and a preliminary insight into the diverse behavior occurred are reported. The different initial nucleation of silver, which determines the hole injection, essential to the etching of silicon, seems to be the key point of this different behavior
Reliable Fabrication of Metal Contacts on Silicon Nanowire Forests
Full text linkWe present a technique for the fabrication of an electrical (and thermal) contact on the top ends of a large number of vertical silicon nanowires, which are fabricated perpendicularly to a silicon wafer (silicon nanowire forest). The technique is based on electrochemical deposition of copper and has been developed on silicon nanowire forests, fabricated by metal assisted chemical etching. We demonstrate that copper grows selectively only on the top end of the silicon nanowires, forming a layer onto the top of the forest. The presence of a predeposited metal seed is fundamental for the selective growth, meanwhile the process is very strong with respect to other parameters, such as concentration of the electrolytic solution and current density, used during the metal deposition. Typical I-V characteristics of top-to-bottom conduction through silicon nanowire forests with different n-doping are shown and discussed
Nanostructured silicon for thermoelectric applications
No full text26.1 Introduction 569
26.1.1 Thermoelectricity Fundamentals 569
26.1.2 Efficiency of a Thermoelectric Generator 571
26.1.3 Why Nanostructured Silicon for Thermoelectricity? 573
26.2 Lithographic processes for Si-Nanostructured Thermoelectric Generators 576
26.3 Nanowire Forests for Silicon-Based Thermoelectric Generators 581
26.4 Final Considerations 584
Reference
Nanostructured Silicon for High-Efficient and Cost-Effective Heat Recovery Through Thermoelectric Conversion
No full textNanostructuring is very effective in enhancing the thermal to electrical energy conversion efficiency of most materials, including in particular silicon which presents a perfect tradeoff between technical potentialities and environmental/political/social issues. Heat sources, that nowadays are exploited only in a small fraction, could become key players in energy production thanks to thermoelectric device based on nanostructured silicon. Successful strategies, including on-chip devices for micro-harvesting and cost-effective large-area vertical nanowire forests for macro-harvesting will be presented. An estimation of the efficiency will be reported, highlighting the competitiveness of these devices with respect to conventional techniques
Large increase of the thermoelectric power factor in multi-barrier nanodevices
No full textImproving the power factor (PF) of thermoelectric materials, crucial for enhancing the power output of thermoelectric generators, is challenging due to the adverse interdependence of the Seebeck coefficient and the electrical conductivity on carrier density. We introduce a novel strategy employing energy filtering via built-in potential barriers to alleviate this dependency, significantly enhancing the PF. Utilizing electron-beam lithography, we developed a Si-based nanodevice featuring a multiple well/barrier design. Measurements yielded a PF of 11 mW m−1 K−2, more than doubling the optimal PF achievable in bulk silicon. Experimental findings align well with theoretical models, affirming the efficacy of the approach. Leveraging established silicon technologies in device fabrication unveils pathways for on-chip micro-energy harvesters and localized Peltier coolers. Moreover, the results validate a material-agnostic energy filtering model, guiding the creation of PF-enhanced devices across various thermoelectric materials
Thermal Conductivity Reduction in Rough Silicon Nanomembranes
Full text linkNanostructured silicon is a promising material for thermoelectric conversion because the thermal conductivity in silicon nanostructures can be strongly reduced with respect to that of bulk materials. We present thermal conductivity measurements, performed with the 3ω technique, of suspended monocrystalline silicon thin films (nanomembranes or nanoribbons) with smooth and rough surfaces. We find evidence for a significant effect of surface roughness on phonon propagation: the measured thermal conductivity for the rough structures is well below that predicted by theoretical models which take into account diffusive scattering on the nanostructure walls. Conversely, the electrical conductivity appears to be substantially unaffected by surface roughness: the measured resistance of smooth and rough nanostructures is comparable, if we take into account the geometrical factors. Nanomembranes are more easily integrable in large area devices with respect to nanowires and are mechanically stronger and able to handle much larger electrical currents, thus enabling the fabrication of thermoelectric devices that can supply higher power levels with respect to existing solutions. © 2002-2012 IEEE
Fabrication techniques for thermoelectric devices based on nanostructured silicon
No full textWe discuss processes for the fabrication of devices for thermoelectric generation, based on silicon nanostructures. The main issue that we address is the design and development of fabrication processes for devices exploiting a large number of interconnected nanostructures. Such devices are characterized by good mechanical strength and at the same time they can handle large currents and deliver high power. First, techniques based on lithography and conventional CMOS processing are presented. These techniques allow the fabrication of suspended silicon masses, connected with the silicon substrate through nanomembranes. Then, a low-cost process for the fabrication of forests of long silicon nanowires is presented. Finally, a technique for the fabrication of a contact at the top of this silicon nanowire forest is reported and discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
