Sorry, this entry is only available in Brazilian Portuguese.
Author: Verónica Savignano
One assistant professor permanent position in the field of materials at the nanoscale.
Edital IF-13/2018 – (English Version)
The Institute of Physics, University of São Paulo, Brazil, invites highly-motivated candidates to apply for one assistant permanent position in the field of Materials at the Nanoscale.
For more details, including instructions regarding the application procedure, please contact Antonio Domingues dos Santos at adsantos@if.usp.br. The application deadline is September 12, 2018.
Application process
Applicants with a strong research record in Materials at the Nanoscale are encouraged to begin the application process early, by following the two-step process outlined below.
1) The first step in the application process is obtaining a certification of your Ph.D. from USP
2) The second step is the submission of your full application, with a CV and statement of research interests.
Step 1 (only needed for those with a Ph.D. diplomma obtained outside of Brazil)
E-mail the following documents to the address: cpgusp@if.usp.br, with copy to adsantos@if.usp.br, with the subject line: Pedido de equivalencia,
Ref. Concurso Materiais em Escala Nanometrica
Required documents:
(a) the filled, dated and signed form which can be found on this link.
(b) a scanned copy (PDF) of your passport or ID document
(c) a copy (PDF) of your Ph.D. thesis
(d) a copy (PDF) of your Ph.D. diploma
(e) a copy (PDF) of your graduate transcript*
[* If your Ph.D. institution does not require graduate courses, please attach a letter stating that.]
Step 2
After Step 1 has been completed, and you have received the certification by USP (or, alternatively, if you already have a diploma valid in Brazil), submit your full application by early August to the e-mail: adsantos@if.usp.br, with the subject line: INSCRICAO PARA CONCURSO DE MATERIAIS EM ESCALA NANOMETRICA.
[Se você for brasileiro(a), essa fase deve ser feita diretamente pelo site oficial dos concursos da USP.]
Required documents (all in PDF format):
(a) the Ph.D. certification (see Step 1 above)
(b) a research proposal or statement of research interests
(c) a document entitled Memorial, with a narrative about of your reasearch experience from graduate school on and a description of your research interests, followed by your CV (it must contain a complete list of your publications with appropriate referencing)
(d) this filled form.
[Letters of recommendation are not required at this point, but if you wish, you may send them to your local contact or to adsantos@if.usp.br (Head of DFMT).]
The two-stage examination will consist of the following exams:
1st stage (eliminative):
a written exam on one of the topics described in this link – weight 3.
2nd stage:
- i) Analysis and Public examination of the Curriculum Vitae (Memorial) – weight 4.
- ii) Teaching exam (public lecture on one of the topics described inthis link– weight 3.
Further information and relevant rules for the examination are available at this link.
If you have any question, please feel free to contact the Head of DFMT, Antonio Domingues dos Santos (adsantos@if.usp.br).
B-MRS Newsletter. Year 5, issue 7.
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From idea to innovation: The glass wire that connected the world (part 2).
And now we are back to the history of optical fibers. [See the first part of our story]
In the late 1950s, short optical fibers were already industrially produced and used in certain segments, especially in medicine to inspect the interior of the human body using endoscopes.
In telecommunications, the transmission of information through copper wires and radio waves was established and continued to advance. The first transatlantic copper wire cable was installed in 1956, and the first telecommunications satellite, which used radio waves, was launched two years later. However, the increasing use of the telephone and television was creating an urgent demand to increase the capacity to transmit information.
Telecommunication companies in Europe and the United States began to seek solutions in their research labs. Most of the research focused primarily on the use of microwaves and short-wave radio waves, but did not consider the waves of the so-called “optical region,” which is mainly made up of visible light. Yet it was in the waves of visible light where the greatest potential for communications could be found. To give you an idea, for example, these waves can carry tens of thousands of times more information than radio waves.
The emergence of the laser somewhat changed the story of optical telecommunications. Invented in 1960 at a research center of an aerospace company of the United States, the laser began to gain new and better versions throughout the decade. With its ability to emit light in the form of very narrow beams that are preserved over large distances, the laser could be a great partner to fiber optics.
However, the optical fiber was left out because of its enormous attenuation – a reduction in the intensity of the light signal between two points, which is measured in decibels lost per kilometer (dB/km). In fact, using the available optical fibers at that time, only 1% of the light injected into the fiber remained within it 20 meters ahead. Faced with this very low efficiency, other ways of guiding light began to be proposed and tested by some groups, while other researchers continued to invest efforts and resources into radio or microwave waveguides.
The few groups that opted for fiber optics or similar optical waveguides (thin films, for example) in the early 1960s were located at STL (research center of the British telecommunications company STC); at CSF (a strong French business group active in areas such as telecommunications, defense, materials and electronics); at the Bell Labs (US industrial research laboratory then connected to the AT&T telecommunications company), and at the Japanese university of Tohuku.
In the STL group, there was a man called Charles Kao, who would go on to win the Nobel Prize for Physics in 2009 in recognition of his work with fiber optics. Born in Shanghai, China, Kao attended high school at a British college in Hong Kong and moved to England to pursue university studies in electronics and communications, which he loved. He graduated in Electrical Engineering from the University of London in 1957, and soon began working for STC, until he received and accepted a proposal to do a business doctorate in the company’s research arm, STL. There he helped the researcher Antoni E. Karbowiak in his studies on various waveguides until Karbowiak left STL to take up a professorship. At that time, Kao dedicated himself to a project at STL which he believed in, the development of fibers composed of core and coating to be used in telecommunications as guides of visible light waves.
Kao then relied on the help of his colleague, the young engineer George Hockham, to develop his studies on fiber optics. Together they set out to understand the causes of light loss in the fiber to assess whether they could be eliminated or diminished, or whether, on the contrary, trying to lower the attenuation meant facing a losing battle. While Hockham studied the imperfections in the shape or size of the fibers, Kao concentrated on the characteristics of the material, in particular its structure and the impurities and defects. The results of their studies were published in June 1966 in the IEEE Proceedings [K.C. Kao and G.A. Hockham, “Dielectric-Fibre Surface Waveguides for optical frequencies”. Proc. IEE, 113, 1151 (1996)].
This paper can be considered a milestone in the history of fiber optics, since it is the first to report the causes of light loss in fiber optics and it has shown the way forward and the goal to be reached in order to achieve suitable for use in telecommunications.
Based on the characteristics of existing light emitters (laser) and detectors, Kao and his co-author argued that in order to use the fibers in optical telecommunications, it was necessary to lower their attenuation to 20 dB/km. The goal was very challenging, because in the fibers then available the light attenuated 20 dB… every 20 meters! At its best. However, by showing that the main causes of light loss in optical fibers were related to the presence of impurities in the material, which absorbed or scattered light and diverted it from its path, the paper pointed out a way to reduce the attenuation: the use of purest glasses.
The article concluded that cylindrical fibers composed of a core and a coating, both made of vitreous materials with slightly different refractive indices (higher in the nucleus), could be a much better means for transmitting information than those existing at the time, in addition to being inexpensive.
In these fibers, the information would travel encoded in light signals that would run through the core, while the coating would ensure that the light remained in the nucleus, even in the curves.
After that, Charles Kao continued to focus on fiber optics, investing his time not only in research but also in dissemination. In fact, he lectured on his studies and on the potential of fiber optics in several laboratories and companies around the world. In addition, STL released a press release highlighting the possibilities of fiber optics in the field of telecommunications, with little impact on the press.
In parallel, along with new collaborators, Kao performed a series of experiments with various glasses and other materials and showed, among other results, that in fused silica glass, the attenuation could reach only 5 dB/km. The result was encouraging, but turning that material made of pure silicon dioxide (SiO2) into an optical fiber was another story. Due to its purity, this glass could only be melted at very high temperatures, above 1,500 °C. In addition, after melting, its viscosity made it difficult to transform into any product. Finally, the refractive index of the fused silica was extremely low. Thus, using it to make the fiber core, if on the one hand it would be advantageous in terms of purity, on the other hand it would be very complicated, not only because of the difficulty of processing the material, but also because of the impossibility of finding a material with a lower refraction index for the coating.
At that time, some laboratories from companies in Germany, the United States, France, the United Kingdom and Japan decided to face the challenge of developing low-attenuation fiber optics. Faced with the difficulty of dealing with the fused silica, most of them gave up on this material and tried to make optical fibers with other glasses, removing the impurities. Other groups, on the other hand, gave up making low attenuation optical fibers upon hearing from glass experts who claimed that it would be impossible to remove the impurities that were so problematic.
Only one of these groups made different choices, the Corning company in the United States. Founded in 1851, the company always worked with glasses, but far from stagnating in the production of low value-added products, it led the development of many innovations, starting with the glass globe of Thomas Edison’s incandescent lamp. In the early 1930s, it was at Corning that the chemist Franklin Hyde created the flame hydrolysis method that enabled the manufacture and processing of fused silica. This method, instead of fusing silicon dioxide crystals, is based on a silicon-based liquid compound which when heated on top of a flame, generates a powder that can be deposited forming layers of silica.
In 1966, Corning commissioned physicist Robert Maurer to research and develop fiber optics of less than 20 dB km attenuation for use in optical communications. In 1968, two more scientists had joined Maurer in this project: Peter Schultz, PhD in Glass Science, and Donald Keck, PhD in Physics.
The trio firmly worked on ideas that were opposite to those that the other groups in the world were following. When choosing the material, Corning’s group opted to use the purest glass and added impurities when necessary, instead of removing impurities from less noble glass until it reached the desired attenuation. The Corning scientists then used pure fused silica to coat the optical fiber, which required a material with a lower refractive index, and silica with very small amounts of titanium in the core, in order to increase the refractive index only as necessary and to reduce purity as little as possible.
For the fiber manufacturing method, the Corning group also followed its own path, based on the method Hyde had developed more than thirty years ago. The trio made a tube of pure silica and deposited the doped silica into it. With this fiber, about four years after the start of the low attenuation fiber optic development project, the Corning group obtained the first attenuation measure of less than 20 dB / km. The first low attenuation optical fiber was developed!
In May 1970, the team filed two patents disclosing, respectively, the composition and manufacturing method of this fiber and, thereafter, began to disclose the results.
In 1971, Corning decided that the project could move from the research phase to the development phase, in which engineers worked to make the manufacturing process adequate to make the fiber stronger (the first fiber was more fragile than desirable) and to finalize the development with companies that were interested in buying the fiber. In the mean time, the research team continued to explore, with good results, new possibilities for better optical fibers. Subsequently, Maurer, Schultz, and Keck were forced to devote much of their time to litigation related to the fiber optic patents granted to Corning in 1972 and 1973.
In the early 1970s, fiber optics was not yet commercially available. In fact, it took more than 10 years for insertion of this technology in the market to take place. That part of the story, also interesting, will not be addressed here, but we can cite some landmarks. In 1975, in the United Kingdom, the first non-experimental optical fibers were installed. In 1976, Corning inaugurated its first industrial fiber optic plant. In 1983, in the United States, the first national fiber-optic telephone network was installed. In 1988, the first transatlantic fiber optic cable was installed.
Today, with billions of kilometers of fiber optics installed, telecommunications on planet Earth, mainly via the Internet, relies heavily on these fine glass or plastic wires. With regard to other technologies, fiber optics maintains first place in speed of data transmission, with immense amounts of information that can be transmitted in 1 second between distant points in the planet. With respect to the radio waves that prevailed in optical communications 60 years ago, this capacity increased by no less than a million times. All the effort of everyone involved in the history was worth it, wasn´t it?
To learn more
- Two revolutionary optical technologies. The Royal Swedish Academy of Sciences. https://www.nobelprize.org/nobel_prizes/physics/laureates/2009/advanced-physicsprize2009.pdf
- Making the first low-loss optical fibers. Peter C. Schultz. http://www.peterschultzconsulting.com/wp-content/uploads/2015/03/SchultzOPN2010Makinglowlossfiber.pdf
- Optical fiber spans 30 years. Dr Donald B. Keck. http://www.corning.com/media/worldwide/coc/documents/Fiber/Resource%20Center%20-%20General/r3461.pdf
- City of light. The story of fiber optics. Jeff Hecht. Oxford University Press (1999).
Featured paper: Clay Labyrinth in Hydrogel Matrix for Controlled Drug Release.
[Paper: Highly Controlled Diffusion Drug Release from Ureasil–Poly(ethylene oxide)–Na+–Montmorillonite Hybrid Hydrogel Nanocomposites. ACS Appl. Mater. Interfaces, 2018, 10 (22), pp 19059–19068. DOI: 10.1021/acsami.8b04559]
Clay Labyrinth in Hydrogel Matrix for Controlled Drug Release
By combining a clay and a polymer gel at the nanoscale, a brazilian scientific team with members of the São Paulo State University (UNESP) and the University of Franca (UNIFRAN) developed a new material that can carry drugs and release them in a gradual and controlled manner.
The team tested in vitro – that is, in the laboratory, in containers that simulate the biological conditions – the performance of the material in the release of sodium diclofenac. This drug is an anti-inflammatory, given orally or by injection, widely used to relieve swelling and pain from, for example, arthritis, rheumatism, muscle injuries, surgeries or gout.
The material developed is a nanocomposite that includes polymeric hydrogel, clay and the drug. The hydrogel (gel that absorbs water amounts higher than normal without dissolving) is composed of an organic-inorganic hybrid material known as siloxane-polyether or ureasil. The clay is known as montmorillonite, and is present in the nanocomposite in the form of nanometric lamellae homogeneously dispersed in the hydrogel. The diclofenac sodium, which appears encapsulated within the nanocomposite, is incorporated into the material during its preparation, as if it were another “ingredient”.
The nanocomposite was obtained by the São Paulo team through the sol-gel process. This preparation method is based on a series of chemical reactions with the transformation of a “sol” (liquid with nanometric particles in suspension) into a gel (rigid three-dimensional network with interstices in which the liquid remains immobilized).
In this nanocomposite the main function of the hydrogel, which is hydrophilic, is absorbing water from the external environment and storing it in its interstices. In this aqueous environment, the drug molecules disperse due to the physical diffusion process until they cross the pores of the hydrogel and exit into the external environment, in this case the human body if the material were being used to release drugs into real patients.
The main novelty of the material is the use of clay, which is impermeable, to control how the drug is released. In fact, in the material developed by the São Paulo team, the nanometric clay lamellae acted as a physical barrier to the passage of the molecules of water and drug.
As shown in the image below, the lamella set formed a real labyrinth that slowed the movement of these molecules, determining a specific rhythm to water absorption and the release of diclofenac sodium.
“The main contribution of this work was to develop a barrier system based on an organic-inorganic hybrid material containing polymer-clay for the fine control of the diclofenac sodium release,” says Eduardo Ferreira Molina, corresponding author of an article on the subject, recently published in the journal ACS Applied Materials & Interfaces. Molina is currently a professor at the University of Franca (SP).
In the work reported in this journal, the authors prepared a series of samples of the nanocomposite using different proportions of montmorillonite clay, as well as samples of the clayless hydrogel. The scientists used different characterization techniques to analyze the structure of the nanocomposites and their phases (hydrogel and clay) and also to study water absorption and release of the drug in the material. The team was able thus to verify that the presence of the clay was essential to control the way the drug was released. By adjusting the clay percentage used in nanocomposite preparation, the researchers were able to prevent the early release of a large dose of sodium diclofenac (a common problem in drug delivery systems). They also succeeded in releasing it slowly and at a steady and predictable rate.
The results of this work may constitute a first step towards the use of this nanocomposite as a drug release system for prolonged treatments of arthritis, migraine, postoperative pain and etc. With a system like this, medication could be released gradually at the most appropriate doses and rates, keeping the ideal concentration of the drug in the bloodstream.
The work, which received funding from the Brazilian federal agencies CAPES and CNPq and the São Paulo State agency FAPESP, was carried out at the Chemistry Institute of UNESP, in the city of Araraquara, with the exception of small-angle X-ray scattering (SAXS) measurements, performed at the Brazilian Synchrotron Light Laboratory (LNLS), in the city of Campinas.
The research was developed between 2010 and 2014 in the doctorate in Chemistry of Celso Ricardo Nogueira Jesus, under the supervision of Professor Celso Valentim Santilli (UNESP) and Professor Sandra Helena Pulcinelli (UNESP). The idea, previously unpublished, of developing these nanocomposites to function as barriers to controlled drug release arose at the beginning of the doctoral research of Nogueira Jesus. The theme brought together themes developed in two other postgraduate works. On the one hand, Eduardo Molina’s doctoral research, guided by Professor Santilli, on siloxane-polyether for controlled release of drugs. In 2010, this work was in the final phase. And on the other hand, Márcia Hikosaka’s master’s work, guided by Professor Pulcinelli and completed a few years ago, on the preparation of nanocomposites with polymers and montmorillonite clay.
The Annals of the Brazilian Academy of Sciences (AABC) in partnership with the Brazilian Materials Research Society (B-MRS) will launch the special volume “Materials Sciences for a Better Future”.
According to the editor, Frank Crespilho, professor at the São Carlos Institute of Chemistry (IQSC) at the University of São Paulo (USP) and a B-MRS member, this is a great opportunity to celebrate the success of Brazilian research in the area of Materials. Crespilho adds that the theme of the special event is in tune with the title of the memorial lecture that professor Fernando Galembeck will deliver at the XVII B-MRS Meeting, an event to be held at Praiamar Natal Hotel in Natal (Brazil), from September 16 to 20 of 2018. Furthermore, this special volume is part of the continuation of the centenary celebrations of the Academy.
SBPMat members and other researchers are invited to submit their full original works through the SciELO journal’s website, from August 9 to November 9, 2018, indicating in the submission and Cover Letter their participation in the special volume.
AABC publications have no cost to authors and can be accessed freely. The AABC have been engaged in the publication of special volumes, covering all areas of science. Recently, the journal has published articles for the special “Brazil: Frontiers of Chemical Sciences,” which can be freely accessed at: http://www.scielo.br/scielo.php?script=sci_issuetoc&pid=0001-376520180002&lng=en&nrm=iso.
B-MRS Newsletter. Year 5, issue 6.
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Featured paper: Aluminum flakes to produce carbon nanotubes.
[Paper: High-yield synthesis of bundles of double- and triple-walled carbono nanotubes on aluminum flakes. Thiago H.R. da Cunha, Sergio de Oliveira, Icaro L. Martins, Viviany Geraldo, Douglas Miquita, Sergio L.M. Ramos, Rodrigo G. Lacerda, Luiz O. Ladeira, Andre S. Ferlauto. Carbon 133(2018) 53-61.]
Aluminum flakes to produce carbon nanotubes
A team of scientists from institutions in Minas Gerais made a promising contribution to the production of carbon nanotubes. These hollow cylinders, whose carbon walls are only 1 atom thick, are already part of some products (batteries, automotive materials, water filters), but their industrial production is still incipient and needs solutions to lower costs and to increase efficiency, among other challenges.
The Brazilian researchers introduced a novelty in a stage of one of the most consolidated techniques for the mass production of nanotubes, chemical vapor deposition (CVD). As a result, the team was able to produce double- and triple-walled nanotube bundles (somewhat similar to two or three hollow cylinders, one inside the other). Thin, long and of high purity, the nanotubes had diameters of 3 to 8 nanometers, lengths up to 50 thousand times the diameter (from 150 to 300 micrometers) and 90% of carbon in their composition.
“The main contribution of this work is the presentation of a scalable and cost effective process for the synthesis of carbon nanotube bundles with large surface area (625 m2/g) and aspect ratio (50000:1),” says Thiago Henrique Rodrigues da Cunha, researcher of the Nanomaterials Technology Center (CTNano) of the Brazilian Federal University of Minas Gerais (UFGM) and corresponding author of this paper, which was recently published in the journal Carbon (impact factor 2017 = 7,082).
The method, in addition to generating good quality nanotubes, allows producing relatively large quantities of this material using relatively low amounts of raw materials. “Even using small systems, it is possible to obtain carbon nanotubes at a kilogram/day scale,” says the researcher. As the nanotubes obtained showed a very large ratio between surface area and mass (more than 625 square meters weighing only one gram), the production of nanotubes by this method could reach a few million square meters per day.
With the nanotubes obtained and a type of alcohol, the scientific team prepared a paste which was distributed over filter paper, forming a film that was separated from the paper when the paste dried. The black film was 40 micrometers thick and was flexible and foldable. Macroscopic aggregates of carbon nanotubes like this are commonly called buckypapers.
“The buckypaper produced from these nanotubes exhibited great surface area and good electrical conductivity, which makes them particularly interesting in the manufacture of electrodes for batteries and supercapacitors,” says Thiago da Cunha, who adds that the CTNano team is already working to use the buckypapers in these energy storage devices. A patent on the process was deposited at the end of 2017. “Our intention is to introduce this technology to potential partners in order to convert it into a high value-added product,” reveals Cunha.
The secret of the process
The CVD nanotube production processes take place inside a tube furnace into which gas containing carbon and catalytic nanoparticles are inserted. Subjected to high temperatures, the gas decomposes, and the carbon atoms deposit on top and around the nanoparticles, forming tubes (the nanotubes). The nanoparticles can be prepared in the same furnace used for nanotube growth.
The secret of the method developed by the Minas Gerais team lies precisely in the preparation of the catalytic nanoparticles. In broad lines, it is a matter of preparing a powder containing iron (Fe) and cobalt (Co) on aluminum flakes (material that had never before been mentioned in the scientific literature as a support for the growth of nanoparticles). The mixture is then subjected to temperatures of 350 to 650 °C for 4 hours, in an atmosphere similar to the air we breathe. This process, known as calcination, produces nanoparticles of iron and/or cobalt oxides. Then, the catalyst nanoparticles, still on the aluminum flakes, are introduced into the CVD furnace, whose internal temperature is brought to 730 °C. The ethylene gas (C2H4) is then introduced, which supplies the carbon so that the nanotubes grow perpendicular to the aluminum flakes.
Scientists observed an interesting advantage of using this new medium. During the calcination, a thin layer of aluminum oxide is formed on the surface of the aluminum that encapsulates the nanoparticles and prevents them from agglomerating or spreading. In addition, in the next step of the process, the aluminum oxide acts as a matrix of the nanotubes, driving their growth in the form of aligned bundles.
To test whether the calcination temperature of the nanoparticles would influence their performance as catalysts, the CTNano team carried out some experiments. The conclusion was that calcination at temperatures of 500-550 °C produces more mixed oxide nanoparticles (containing both iron and cobalt, of the CoFe2O4 formula) and produces better results in the production of nanotubes, both quantitatively (yield) and qualitative (diameter of the nanotubes).
“Unlike other methods described in the literature, which generally display low yield and are dependent on relatively expensive techniques (evaporation, sputtering) for the preparation of the catalyst, we describe in this paper a simple method to produce a catalyst in powder form, which can be used for continuous production of few-walled nanotubes using the chemical vapor deposition technique (CVD),” summarizes Thiago da Cunha.
CTNnano
The work was funded by the Brazilian agencies Fapemig (Minas Gerais State Research Foundation) and CNPq, as well as Petrobras. The work was carried out at CTNano, except for the microscopy images, conducted at the UFMG Microscopy Center.
CTNano emerged in 2010 based on the motivation to develop products, processes and services using carbon nanotubes and graphene, in order to meet industrial demands in line with the training of qualified human resources. The research realized in CTNano has already originated 26 patents and contributed to the development of more than 200 researchers in the area. According to Thiago da Cunha, CTNano will inaugurate, in 2018, its own headquarters with an area of approximately 3,000 m², located in the Technology Park of Belo Horizonte (BH-TEC).
From idea to innovation: The glass wire that connected the world.
You’re probably reading this on some Internet-connected device, aren’t you? It doesn’t matter if you are using a smartphone that receives the information from an antenna, or if the data arrives to your computer, or to the electric post of your neighborhood, through copper wires or coaxial cables. At some point, your access to the web will depend on optical fibers, those transparent, glass or plastic wires, whose diameter is similar to that of human hair strands (from a few tens of microns to a few hundreds of microns).
Fiber-optic cables are large data highways that connect continents, countries, cities, and data centers to each other. Only in the sections closest to the user, the information travels through other types of routes, in slower traffic. According to data from Corning Incorporated there are more than 2 billion kilometers of optical fibers installed in the world, enough to circle the Earth by the equatorial line 50 thousand times!
If optical fibers are highways, light is the means of transport that transits through them, and the data are the passengers, which travel coded as optical signals. On these highways, the passengers can travel about 200,000 km (five laps over the Equatorial line) in 1 second.
The first fiber “usable” in communications was produced in 1970 in the United States, more precisely at Corning Glass Works (now Corning Inc.), a company specializing in vitreous and ceramic materials. But the history of the development of fiber optic begins much earlier. Let’s describe the moments we believe are the most important in this story, carried out by many scientists of different nationalities. It should be noted that there were many patent litigations and that several of the researchers involved did not recognize the work of the previous ones.
Nineteenth Century: guiding light by sinuous paths
In the nineteenth century, some renowned scientists experimentally demonstrated that light could be driven by certain means (in this case, a jet of water) forcing it to follow a certain path, including following curves. There are records of demonstrations and publications carried out in scientific societies in Europe in the 1840s and 1850s by the Swiss Jean-Daniel Colladon (1841), the Frenchman Jacques Babinet (1842) and the Irishman John Tyndall (1854). The experiment, which is illustrated in the image below, shows that light, guided by water, was diverted from its rectilinear path to make a curved path.
But was the light, following the water “path” really describing a curved trajectory? Of course not. What these scientists were showing was light reflecting again and again in the water stream, describing a kind of zigzag due to the phenomenon known as total internal reflection. This is more or less as follows. When the flow of water begins to curve, the light, which travels in a straight line, ends up reaching the interface between water and air. Then it is reflected by the inner “wall” of the water stream and hits the opposite “wall” where it is reflected back. And so it continues its zigzag path into the water. The phenomenon occurs due to differences between the way water and air interacts with light (refractive indexes). For the phenomenon to happen, it is critical that light describes a greater angle to the so-called “critical angle” when reaching the interface between water and air. Obviously, the phenomenon can happen in various media, not just in the water-air system.
The nineteenth-century experiment resembles the one that appears at the beginning of this video (except, of course, for some updates implemented in the video, such as the use of lasers). See how beautiful it is:
Flexible glass fibers to explore the digestive tract
Apparently Jaques Babinet went a little further in exploring full internal reflection and demonstrated that a curved glass rod could also guide the light.
The idea was in all probability taken up again in the 1920s, when attempts were made to use flexible glass rod bundles to conduct light and be able to see otherwise inaccessible places, such as the interior of the digestive tract (medicine). Not that there were no instruments for this, for instance endoscopes, but they were rigid and therefore feared by the patients (rightly so!).
But is glass flexible? Yes, when it’s thin, it’s very flexible.
However, these fiber ancestors were not efficient; the phenomenon of full reflection was not full at all there, the light escaped through the “walls” and the fibers did not fulfill their role of illuminating the human body.
Fortunately, in the 1960s flexible glass fibers capable of guiding light were now ready for various applications, largely due to two scientific contributions. On the one hand, Indian Narinder Singh Kapany and his doctoral advisor Harold Hopkins, working at Imperial College London (England), overcame the technological challenge of making a glass fiber bundle that delivered a quality image. The bundle, which the authors called the fibroscope, had several hundred fibers of 75 cm in length. On the other hand, the Dutchman Abraham C.S. van Heel of the Technical University of Delft (The Netherlands) successfully demonstrated the idea of coating glass fibers with lower refractive index materials to achieve full (or close to) reflection. Both papers were published in the same issue of the journal Nature (volume 173, number 4392). Published January 2, 1954, the edition can be considered a milestone in the field of optical fibers. The articles made public important developments and demonstrations, and encouraged the development of products.
One such product was the flexible gastrointestinal endoscope (gastroscope), which began to materialize when Basil Hirschowitz, a South African surgeon and a gastroenterologist in London, read the cited papers from Nature. The surgeon was currently doing a research internship at the University of Michigan (USA) and recruited an under graduate Physics student, Lawrence Curtiss. Young Larry, apparently very capable, was heavily involved in the project, enough not to give up given the difficulties he encountered in trying to reproduce the processes reported in the articles and in trying to reduce the light losses of the fibers. In 1956, Curtiss made an important contribution to the development of fiber optics: he developed the first fiber with glass core and coating. In fact, he was able to carry out his idea of coating a fiber made of a certain glass with another glass of lower refractive index. To do this, he developed a simple manufacturing method: introduce a stick of the core glass into a tube of the other glass, heat it all together and pull out a fiber from the medium. The resulting fibers were extremely thin, about 5 microns. In 1957, the patent application for this optical fiber and the process was deposited, and in 1971 it was granted.
The same year the fiber patent was deposited, Hirschowitz began testing and disseminating the fiber optic endoscope with glass core and coating. The flexible endoscope subsequently made a number of significant advances in medicine, such as minimally invasive surgeries such as laparoscopy.
However, in the 1950s, no applications were found or any attempts to apply optical fiber in the communications of the time (telephony, radio, television). However, data transmission through copper wires was not meeting the demands. In 1956, the first transatlantic telephone cable was installed, which actually worked. Nevertheless, it allowed only 36 simultaneous calls…
On the other hand, the laser had just been invented, opening possibilities for transporting information (including voice) encoded in light. This, however, required a medium that would guide the light through the desired routes.
For us, in 2018, it is obvious that this medium is the optical fiber, but fifty years ago it was discarded by many researchers. Why? Because of the strong attenuation (loss of light along the way) the fibers presented at that time. The amount could be negligible for an endoscope of less than a meter, but it was extremely significant in a cable of thousands of kilometers.
New work needed to be developed. New researchers would emerge. Who, when, where and how? We will tell you soon.
Interested? Our reading tip: Hecht, “City of light. The story of fiber optics”, Oxford University Press (1999).
Brief interviews with scientists: Bernhard Keimer (Max Planck Institute for Solid State Research, Germany).
Superconductivity and giant magnetoresistance are examples of phenomena that can occur in some materials or systems driven by the so-called electronic correlation, in which the behavior of an electron is strongly influenced by the behavior of other electrons of the same system.
At one of the Max Plank Institutes, located in Stuttgart, Germany, a group of researchers led by Professor Bernhard Keimer works hard to understand and control the behavior of correlated electrons. For this, the team produces heterostructures (structures composed of several materials with differentiated characteristics) of metallic oxides, and characterizes them using a series of experimental techniques, mainly of spectroscopy.
Professor Keimer will be at the XVII B-MRS Meeting in September talking about this research program in the lecture “Spectroscopy of collective excitations in oxide heterostructures”. In his plenary talk, Keimer will present methods and results, including some possibilities of controlling correlated-electrons phenomena.
Bernhard Keimer has been director of the Max Planck Institute for Solid State Research as well as honorary professor at the University of Stuttgart since 1998. From 1992 to 1998, he was Professor of Physics at Princeton University. He graduated in Physics from the Technical University of Munich in 1985 and, in 1991, obtained his PhD in Physics from the Massachusetts Institute of Technology (MIT), where he remained for one year as a postdoc. According to Google Scholar, Keimer has an H index of 86 and his scientific production has more than 24,500 citations.
See our mini interview with this German scientist.
B-MRS Newsletter: – One of the goals of the research you perform with your team at the Max Plank Institute is to control the behavior of strongly correlated electrons, right? In your opinion, what could be the most promising applications emerging from this control? Comment shortly, please.
Bernhard Keimer: – Quantum correlations between electrons generate a large variety of electronic ordering phenomena with vastly different macroscopic properties. Understanding and controlling the collective behavior of electrons in “quantum materials” is a grand intellectual challenge for fundamental research. In the long term, research on quantum materials might enable the design of a new generation of devices based on electrons flow with minimal – or even zero – dissipation.
B-MRS Newsletter: – We want to know more about your work. Please choose a paper of your own (your favorite one) related to the subject of the plenary lecture and briefly describe it, as well as share the reference.
Bernhard Keimer: – As a general introduction to the physics of quantum materials, I recommend a recent review article (B. Keimer & J.E. Moore, Nature Physics 13, 1045 (2017)) A particularly fascinating topic is high-temperature superconductivity. My group uses heterostructures and superlattices to investigate novel collective phenomena emerging at the interface between high-temperature superconductors and other quantum materials. As an example, the figure below shows a kaleidoscope of quantum phases in a 50 nm thin layer of a copper oxide superconductor sandwiched between two layers of an oxide ferromagnet (A. Frano et al., Nature Materials 15, 831 (2016)). My group is developing spectroscopic methods that allow visualization of these phases in a depth-resolved manner.
For more information on this speaker and the plenary talk he will deliver at the XVII B-MRS Meeting, click on the speaker’s photo and the title of the speech here https://www.sbpmat.org.br/17encontro/home/