“Nature” Reveals:

Technion Researchers Succeed in Demonstrating for the First Time that Low-Speed Cracks in Brittle Single-Crystals (Such as Silicon Wafers) Are Unstable

 Up until now it was thought that low-speed cracks were stable: the discovery constituted a basis for international research

Researchers at the Technion’s Faculty of Materials Engineering have succeeded in demonstrating for the first time that cracks in brittle single-crystal materials (such as silicon wafers) are unstable (i.e., their surfaces are disturbed)  if the crack speed is low. Up until now, it was thought that low-speed fractures were stable (smooth). This finding constituted the basis for international research, with the participation of both materials scientists and physicists from Great Britain, Germany, the US, Italy and Israel. Their findings were published in the latest issue of the prestigious journal “Nature”, describing simulations of experimental results that were carried out using complex atomistic analysis.

Prof. Dov Sherman from the Technion’s Faculty of Materials Engineering, who developed the instruments that enabled the finding, investigates the mechanical behavior of materials, focusing on their fracture. “Up until now, a lot of work was done on isotropic materials, i.e. – materials that have the same properties in all directions (for example - glass). In these materials, a crack propagates at a right angle to the direction of the maximum stress, and therefore, we know the path a crack selects,” he explains. “In the last two decades, research has been carried out on the topic of how fracture propagates in brittle single crystal materials – i.e. materials that have a specific internal arrangement, such that every atom resides in a specific, known and long-term arrangement. Therefore, their characteristics are dependent on the direction of the crystal arrangement, for example – silicon wafers, in which the characteristics are different in each direction. In these materials, the direction and way in which the fracture propagates is dependent, first and foremost, on crystal structure but also on the way in which the material is stressed. In such a case, it is yet impossible to predict how the crack will propagate.”

In recent years, Prof. Sherman and his students at the Technion have been carrying out precise, controlled experiments from which they have been able to learn exactly how a crack initiate and propagate in brittle, single-crystal materials. In order to do this, they developed unique methods that assist them in understanding fracture behavior. As the research progressed, they realized that the path in which that a fracture chooses to propagate is highly dependent on external forces. “We developed methods for precise sample loading so that the experiment is free of disturbances caused by inaccurate loading,” he says. “Thus we see fracture behavior in the material that was never before observed in scientific research.”

“Up until now, it is known that low-speed cracks in isotropic materials are stable. That is – their surfaces are smooth and disturbances on the surface increase with the speed of the crack. We showed that the situation in single crystals is the opposite. The low-speed cracks are not stable and they have strong surface disturbances. It is actually fast cracks that are stable – i.e. have smooth surfaces.”

To date, most of the controlled experiments were carried using tensile stress only. Prof. Sherman and his students have reached a point where they are slowly loading a specimen at controlled and combined tensile and shear stresses. In light of this, it will be possible to predict the path in which the cracks in brittle single crystals will propagate, something that is not yet possible.

The research published in “Nature” constitutes a basis for studying the behavior of how fractures spread in brittle single crystals, materials which are used in advanced industries, and can lead subject to improve planning to prevention of the growth of fractures. In addition, it is possible to use this understanding of how fractures propagate for other practical needs.

Technion Spokesperson – Amos Levav 

2700 New Students Start Their Studies at the Technion

In total, 8706 students are studying for their bachelor’s degree in 18 faculties; the most popular – medicine, electrical engineering and computer science

This year, a new program is being launched – “A Good Start” – which will improve and enrich the first-year student experience

2700 new students (an increase of more than 100 students over last year) will begin studying at the Technion next week (November 9). Orientation day for new students, in which they will receive a guided orientation, will take place on November 6.

The most popular faculties are medicine, electrical engineering and computer science. The demand for electrical engineering and computer science went up also this year for the fifth year in a row. The admission cut off points for both faculties went up as well. Admission quotas have been full for some time and outstanding candidates have been deferred to the spring semester. Demand for the Faculty of Industrial Engineering and Management also has been increasing in recent years.

In the new academic year, the Technion will be launching a new program – “A Good Start” – aimed at improving, enriching and enhancing the first-year learning experience. The Technion’s Senior Executive Vice President, Prof. Paul Feigin, said that in the first stage, the program will focus on base courses in mathematics. In the program’s framework, the number of students in exercise groups will decrease to 30 to 37 per group, additional teaching strategies will be integrated and personal interaction and learning between the student and the teaching assistant will be improved, as well as among students. Enrichment workshops in these courses will be provided as well as assistance in homework preparation.

The Technion has placed special emphasis on recruiting and encouraging outstanding graduate degree students (master’s and doctoral). The Institute is offering them generous stipends and to those with families – convenient apartments in student housing. Presently, work has started on building a new graduate student village on the campus. More than 3,000 graduate students will be studying at the Technion this year and the intention is to increase this number.

The students will have at their disposal advanced sports facilities, including two swimming pools (one of which is Olympic size), a new workout room and more than 4,000 beds in the student dorms. This year, the Technion opened for the first time a social network on the Internet, which is at the disposal of and for use by new students. Through this network, they can meet one another and find students from the same towns in order to organize transportation to the campus or find roommates.

Technion spokesman, Amos Levav, 052-4524873