J.A. Silva

The silicon on dust substrate path to make solar cells directly from a gaseous feedstock

In this paper, we present a silicon on dust substrate (SDS) process, a new method for the growth of silicon ribbons. As a demonstration of the concept, we also present results on solar cells made of these new silicon ribbons. SDS ribbons were obtained directly from a gaseous feedstock by a fast CVD step using silane. The resulting self-supported intrinsic ribbons were microcrystalline and porous. To make these ribbon films suitable for photovoltaic applications, a novel recrystallization with an in situ doping step was developed. To this purpose, the ribbons were sprayed with boric acid and then recrystallized by float zone melting. Simple solar cells were prepared by employing: aluminium back contacts, Ti/Pd/Ag front grid contacts, with no anti-reflective coating, doping optimization, passivation or gettering. The 1-sun I–V characteristics of the cells were: Voc ∼ 530 mV and Jsc ∼ 24 mA cm −2 .T he minority carrier diffusion length obtained from a spectral response at long wavelengths gave values of Ln ∼ 70 μm. (Some figures in this article are in colour only in the electronic version)

First solar cells on silicon wafers doped using sprayed boric acid

A new method for boron bulk doping of silicon ribbons is developed. The method is based on the spraying of the ribbons with a boric acid solution and is particularly suited for silicon ribbons that require a zone-melting recrystallization step. To analyse the quality of the material thus obtained, multicrystalline silicon samples doped with this doping process were used as substrate for solar cells and compared with solar cells made on commercial multicrystalline silicon wafers. The values obtained for the diffusion length and the IV curve parameters show that the method of doping with the boric acid solution is suitable to produce p-doped silicon ribbons for solar cell applications.

The Portuguese Popularizer of Science Teodoro De Almeida: Agendas, Publics, and Bilingualism

The life of the Portuguese Oratoriali priest Teodoro de Almeida (1722-1 804) spanned most of the eighteenth century. His works marked the Portuguese Enlightenment. He was persecuted by the Marquis of Pombal, Minister for King Jose I, and had to endure a period of exile abroad, from 1768 to 1778, first in Spain and then in France. Returning to Portugal, he was co-founder, in 1779, with the Duke of Lafoes, and Abbot Correia da Serra, amongst others, of the Royal Academy of Sciences of Lisbon. He was an advocate and a popularizer of the Moderns - by opposition to the Aristotelian-Scholastic natural philosophy - and the ten-volume Recreasao filolofica, ou Dialogo sobre afilozofia natural, para instruccâo depessoas curiozas, que nao frequentarao as aulas (Philosophical recreation, or Dialogue on natural philosophy, for the instruction of curious people who could not attend classes), giving an account of natural phenomena and the advancements of experimental philosophy, was his masterpiece on the subject. Almeida was, geographically, a peripheral natural philosopher, whose ideas on natural philosophy were moulded by three features: the articulation of experimental philosophy with Enlightenment ideas about the use of reason and experiment; a theological understanding of nature merged with the idea of harmony between natural philosophy and religious orthodoxy; and a methodological eclecticism opposing arguments of authority.In this paper I will analyse the different agendas that can be found in Almeidas Philosophical recreation. I will also examine the different types of audience involved in Almeidas project - lay versus expert and real versus virtual - and show in what ways these dichotomies are effective in describing Almeidas audience. I will also argue for the bilingual nature of Almeidas work, in the sense used by Mario Biagioli in regard to Galileo. This will be done in the context of a discussion of the manifold nature of the popularization of knowledge taken to be an instance of the process of appropriation of modern natural philosophy in eighteenth-century Portugal.PATHS OF MODERNIZATION IN EIGHTEENTH-CENTURY PORTUGALDuring the eighteenth century, the proliferation of Academies for the discussion of historical, literary or scientific questions, the publication of books and periodicals of philosophical character, the creation of public lectures on experimental philosophy and the increasing number of booksellers all constituted marks of modernization. Opposed to Aristotelianism and Scholasticism, modernization was characterized by what Immanuel Kant called the public use of reason:This enlightenment requires nothing but freedom - and the most innocent of all that may be called freedom; freedom to make public use of ones reason in all matters.... By public use of ones reason I mean that use which aman, as scholar, makes of it before the reading public. I call private use that use which a man makes of his reason in a civic post that has been entrusted to him.1Traceable throughout eighteenth-century Portugal, the emergence of the public use of reason encompassed the engagement of three groups of contributors: the Ericeira Circle, the so called Europeanized intellectuals, and the Oratorians.2 These groups are used here as structuring units involved in the appropriation of natural philosophy. But one should have in mind that they are not distinct groups. For instance, some Oratorians were Europeanized intellectuals and belonged to the Ericeira Circle. On the other hand, individual contributions cannot be always subsumed under collective trends.During the first half of the eighteenth century new practices of cultural, social and economic nature were furthered amongst a circle of friends and proteges of the D. Francisco Xavier de Menezes, fourth Count of Ericeira. The Count of Ericiera was a member of the Roman Academy of Arcadia and a fellow of the Royal Society of London. He corresponded with learned Europeans such as Nicolas Boileau (whose Art poetique he translated into Portugese), Francesco Bianchini, Ludovico Muratori, and Pierre Bayle. …

Measurement of the dopant concentration in a semiconductor using the Seebeck effect

This paper describes a method for measuring the dopant concentration in a semiconductor using the Seebeck effect at a given point of a sample using a transient thermal gradient. The system was tested with high-purity metallic samples and several silicon samples with different concentrations of boron. The dopant concentrations of these samples obtained via the Seebeck coefficient were compared with those estimated from electric resistivity measurements using the standard four- point method. The results show that the method can be used for the local measurement of the doping level.