Presentations

Hyperdoped and microstructured silicon for solar energy harvesting, at PIERS 2012 (Kuala Lumpur, Malaysia), Wednesday, March 28, 2012:
talk_1858.pdf
We have developed a unique technique to significantly change the optoelectronic properties of silicon through hyperdoping and texturing. By irradiating silicon with a train of amplified femtosecond laser pulses in the presence of a wide variety of dopant precursors, we can hyperdope silicon to > 1 at.% in a 300-nm thin layer. In addition, laser-induced semi-periodic surface textures have excellent anti-reflection and light-trapping properties. The technique is robust: it is effective on both crystalline and amorphous silicon and for both thin films and thick substrates. When the dopant is... Read more about Hyperdoped and microstructured silicon for solar energy harvesting
Fabricating nanostructured TiO₂ by femtosecond laser irradiating titanium, at PIERS 2012 (Kuala Lumpur, Malaysia), Wednesday, March 28, 2012:
talk_1859.pdf
many materials including titanium. Laser structuring of titanium surfaces has been investigated for a variety of applications, including biocompatibility and solar energy harvesting. We use femtosecond laser irradiation of titanium to create nanometer scale laser-induced periodic surface structures and study the influence of atmospheric composition on these surface structures. Altering the gas composition and pressure does not change the surface morphology, but it does impact the chemical composition of the surface. We demonstrate that irradiation of titanium in oxygen containing atmospheres... Read more about Fabricating nanostructured TiO₂ by femtosecond laser irradiating titanium
Applications of femtosecond lasers in materials processing, at Data Storage Institute, NUS (Singapore), Friday, March 30, 2012:
talk_1894.pdf
The intersection of materials research and ultrafast optical science is producing many valuable fundamental scientific results and applications, and the trend is expected to evolve as new and exciting discoveries are made. Femtosecond laser micromachining presents unique capabilities for three-dimensional, material-independent, sub-wavelength processing. At the same time the surface processing of materials permits the creation of novel materials that cannot (yet) be created under other conditions.
In this talk we will discuss how shining intense, ultrashort laser pulses on the surface of...
Read more about Applications of femtosecond lasers in materials processing
Femtosecond Laser Nanostructuring of Semiconductors and Metals, at 13th International Symposium on Laser Precision Microfabrication (LPM), The Catholic University of America (Washington, DC), Thursday, June 14, 2012:
talk_1949.pdf
We have developed a unique technique to change the optoelectronic properties of many materials through hyperdoping and texturing [1]. By irradiating materials, such as silicon and titanium dioxide, with a train of amplified femtosecond (fs) laser pulses in the presence of a wide variety of dopant precursors, we can introduce dopants above the solubility limit while producing surface structures that have excellent anti-reflection and light-trapping properties.
Femtosecond-laser texturing originates from the formation of laser induced period surface structures (LIPSS) and consists of semi...
Read more about Femtosecond Laser Nanostructuring of Semiconductors and Metals
Educating the Innovators of the 21st Century, at Strengthening Teaching and Learning in STEM Fields, LASPAU Harvard University (Cambridge, MA), Friday, June 22, 2012:
talk_1954.pdf
Can we teach innovation? Innovation requires whole-brain thinking — left-brain thinking for creativity and imagination, and right-brain thinking for planning and execution. Our current approach to education in science and technology, focuses on the transfer of information, developing mostly right-brain thinking by stressing copying and reproducing existing ideas rather than generating new ones. I will show how shifting the focus in lectures from delivering information to team work and creative thinking greatly improves the learning that takes place in the classroom and promotes independent... Read more about Educating the Innovators of the 21st Century
Memorization or understanding: are we teaching the right thing?, at China-US Advanced Forum on Physics Education, Tsing Hua University (Beijing, China), Monday, August 6, 2012:
talk_1963.pdf
Education is more than just transfer of information, yet that is what is mostly done in large introductory courses -- instructors present material (even though this material might be readily available in printed form) and for students the main purpose of lectures is to take down as many notes as they can. Few students have the ability, motivation, and discipline to synthesize all the information delivered to them. Yet synthesis is perhaps the most important -- and most elusive -- aspect of education. I will show how shifting the focus in lectures from delivering information to synthesizing... Read more about Memorization or understanding: are we teaching the right thing?
Towards increased efficiency in solar energy harvesting via intermediate states, at Gordon Research Conference on Defects in Semiconductors, University of New England (Biddeford, ME), Monday, August 13, 2012:
talk_1973.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Towards increased efficiency in solar energy harvesting via intermediate states
Serendipity and the quest for new materials, at 9th Science and Technology in Society Forum (Kyoto, Japan), Monday, October 8, 2012:
talk_2019.pdf
Throughout history, the development of new materials and serendipity have been tightly interwoven. I will illustrate the need for exploration and risk-taking with two anecdotes
Using seminar-based instruction to convey contemporary research to undergraduates, at Materials Research Society 2012 Fall Meeting (Boston, MA), Monday, November 26, 2012:
talk_1955.pdf
In the standard lecture-based approach to teaching, the focus is often on content and not on the development higher cognitive skills. The seminar method of teaching focuses on the development of such important skills, including independent research, reading, writing, presenting, debating and peer review. The method involves creating an environment for students where they can interact with each other on one or more themes under the guidance of an instructor. While the focus is on the development of skills, the students must master advanced content in order to participate in the course. I will... Read more about Using seminar-based instruction to convey contemporary research to undergraduates
Towards increased efficiency in solar energy harvesting via intermediate states, at SPIE Laser Material Processing for Solar Energy Devices II (San Diego, CA), Wednesday, August 28, 2013:
talk_2070.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Towards increased efficiency in solar energy harvesting via intermediate states
Towards increased efficiency in solar energy harvesting via intermediate states, at SPIE Laser Material Processing for Solar Energy Devices II (San Diego, CA), Wednesday, August 28, 2013:
talk_2070.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Towards increased efficiency in solar energy harvesting via intermediate states
Science outreach: too little, too late, at 10th Science and Technology in Society Forum (Kyoto, Japan), Monday, October 7, 2013:
talk_2128.pdf
The goal of science outreach should be continued fueling of the curiosity of the mind not the reawakening of it. In order to achieve that goal we need to re-think our approach to teaching and above all our approach to assessment in science.
Laser-processing of semiconductors for solar energy harvesting applications, at Laser World of Photonics conference (Mumbai, India), Tuesday, November 12, 2013:
talk_2173.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Laser-processing of semiconductors for solar energy harvesting applications
Black silicon and the quest for intermediate band semiconductors, at Laser-Based Micro and Nano Processing VIII, Photonics West 2014 (San Francisco, CA), Thursday, February 6, 2014:
talk_2198.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Black silicon and the quest for intermediate band semiconductors
Black silicon and the quest for intermediate band semiconductors, at Laser-Based Micro and Nano Processing VIII, Photonics West 2014 (San Francisco, CA), Thursday, February 6, 2014:
talk_2198.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Black silicon and the quest for intermediate band semiconductors
Flat space, deep learning, at GIREP-MPTL International Conference on Teaching/Learning Physics: Integrating Research into Practice, University of Palermo (Palermo, Italy), Tuesday, July 8, 2014:
talk_2258.pdf
The teaching of physics to engineering students has remained stagnant for close to a century. In this novel team-based, project-based approach, we break the mold by giving students ownership of their learning. This new course has no standard lectures or exams, yet students’ conceptual gains are significantly greater than those obtained in traditional courses. The course blends six best practices to deliver a learning experience that helps students develop important skills, including communication, estimation, problem solving, and team skills, in addition to a solid conceptual understanding... Read more about Flat space, deep learning
Assessment: The silent killer of learning, at Siam Physics Congress 2015 (Krabi, Thailand), Wednesday, May 20, 2015:
talk_2461.pdf
Why is it that stellar students sometimes fail in the workplace while dropouts succeed? One reason is that most, if not all, of our current assessment practices are inauthentic. Just as the lecture focuses on the delivery of information to students, so does assessment often focus on having students regurgitate that same information back to the instructor. Consequently, assessment fails to focus on the skills that are relevant in life in the 21st century. Assessment has been called the "hidden curriculum" as it is an important driver of students' study habits. Unless we rethink our approach to... Read more about Assessment: The silent killer of learning
Teaching Physics, Conservation Laws First, at Siam Physics Congress 2015 (Krabi, Thailand), Thursday, May 21, 2015:
talk_2485.pdf
The Principles and Practice of Physics is a groundbreaking new calculus-based introductory physics textbook that uses a unique organization and pedagogy to allow students to develop a true conceptual understanding of physics alongside the quantitative skills needed in the course. The book organizes introductory physics around the conservation principles and provides a unified contemporary view of introductory physics. In this talk we will discuss the unique architecture of the book, the conservation-laws-first approach, and results obtained with this book.
Stopping time, at International Year of Light Special Lecture at the 11th Conference on Lasers and Electro- Optics Pacific Rim (CLEO-PR 2015) (Busan, South Korea), Monday, August 24, 2015:
talk_2402.pdf
Time is of philosophical interest as well as the subject of mathematical and scientific research. Even though it is a concept familiar to most, the passage of time remains one of the greatest enigmas of the universe. The philosopher Augustine once said: "What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know." The concept time indeed cannot be explained in simple terms. Emotions, life, and death - all are related to our interpretation of the irreversible flow of time. After a discussion of the concept of time, we will review... Read more about Stopping time
On-chip zero index metamaterials, at Advanced Laser Applications Workshop, Korea Institue of Machinery and Materials (Daejeon, South Korea), Friday, August 28, 2015:
talk_2516.pdf
Impedance-matched metamaterials with zero refractive index can be achieved by exploiting a Dirac cone at the center of the Brillouin zone. We present an in-plane Dirac-cone metamaterial consisting of low-aspect-ratio silicon pillar arrays in an SU-8 matrix with top and bottom gold layers. Using an integrated nano-scale prism constructed of the proposed material, we demonstrate unambiguously a zero refractive index in the optical regime. This design serves as a novel on-chip platform in the optical regime to explore the exotic physics of Dirac-cone metamaterials and to implement applications... Read more about On-chip zero index metamaterials

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