You are invited to attend a lecture

By

Eliezer Halpern

(Ph.D. student under the supervision of Prof. Yossi Rosenwaks)

School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel

Nanoscale-Electronic Characterization of InAs

Semiconductor nanowires (NWs) are one of the most promising building blocks for miniaturization, as well as a wealth of opportunities for pursuing nanoscale science, in particular mesoscopic physics, as well as a vast number of technological applications. Understanding their surface properties is crucial in developing both new electronic devices, as well as providing insight for future fundamental research. In this work we have studied InAs NWs, and investigated two main phenomena - surface states and quantum confinement. The former has a large effect on the performance of both electronic and optoelectronic devices. At present, determination of the surface state density is achieved via measurements of the capacitance and/or drain current, in a nanowire field-effect transistor, and fitting it to simulation. These methods rely on certain assumptions, which strongly affect the extracted density of states. In this work, we demonstrate direct measurement of the surface state density and energy distribution in individual nanowires, in the range of 10¹²-10¹³ cm^-2eV^-1. The measurement was done using Kelvin Probe Force Microscopy (KPFM), which is a highly sensitive method for detecting nm-scale work function variations. In the second part of the work, we have shown energy sub-bands formed due to quantum confinement; this observation was carried at room temperature, again using the KPFM. The extracted density of states and quantum confinement in nanowires is of importance in understanding the electronic overall performance of InAs nanowires in part, and of all semiconducting nanowires as a whole.

Monday, May 25, 2015, at 15:00

Room 146, Electronic Labs building

Information Spread in the 21^st Century

Alon Sela – PhD student

Abstract

The following work presents a theoretical framework to describe the dynamics of information spread in the 21^st century, followed by applicable methods.

The work starts by comparing the spread of messages by ‘word-of-mouth’ (WOM) vs. the spread through websites and search engines (WEB). It relays on observations that search engines grade webpages by PageRank-related algorithms, an approach that seems to be biased towards spreading messages that are globally popular vs. less popular ones. At the other hand, ‘word-of-mouth’ spread is less biased by global popularity trends, since each member is mainly exposed to its local social circle. As a consequence of these claims, it is reasonable to assume that i) the initial spread of new and less popular messages through WOM schemes are faster than such spread by WEB schemes; and  ii) that the contents’ diversity of messages is lower when solely relying on WEB spreading schemes.

Simulations of the two spreading models as well as empirical studies with human subjects support these two claims, and reveal that messages’ spreading by WOM is faster and enables a higher contents’ diversity.

Following these results, the work continues and presents two applicable tools: i) the "Scheduling Seeding" algorithm; a novel approach to message spread which is improve the spread by approximately 25%, and (ii) a method that successfully predicted hot trends, with 21/23 correct predictions, by searching "Viral Footprints" in time series of terms searched in Google.

This work was performed under the supervision of Irad Ben-Gal.

ההרצאה תתקיים ביום שלישי 26.5.15, בשעה 14:00, בחדר 206, בנין וולפסון הנדסה, הפקולטה להנדסה, אוניברסיטת תל-אביב.