Fall 2017

Discovery of a Mechanism for Dislocation Nucleation and Migration Driven by Surface Segregation

  • By Burcu Ozden
  • 6 December 2017

Judith C. Yang and her colleagues answered the question of how dislocations nucleate and migrate at heterointerfaces in dissimilar-material systems on their recently published article on Nature Materials. n this study, Judith Yang and her colleagues showed that atomic segregation acts as a source for generating dislocations for the first time. They have used Cu–Au alloy system for studying surface segregation. Real-time transmission electron microscopy (TEM) was used to both spatially and temporally resolve the transition of the coherent, dislocation free interface between a Cu3Au-segregated surface and a Cu(Au) crystal substrate into a semi-coherent structure through the nucleation and subsequent migration of misfit accommodating dislocations. They combined their experimental study with the teory by using density functional theory (DFT) and molecular dynamics (MD) simulations. They discovered a mechanism for dislocation nucleation and migration driven by surface segregation of solute atoms in a solid solution. Their results show that the surface-segregation-induced composition variations act as the source of strain/stress that drives the nucleation and migration of misfit dislocations, and demonstrate how the surface segregation phenomenon of an alloy constituent can be employed for developing atomistic insight into understanding the formation processes of misfit-accommodating dislocations.

Structure-Property Relationships in Nanostructured Materials: Aqueous Semiconductor Interfaces

Speaker(s): 
Mark S. Hybertsen
Dates: 
Friday, December 8, 2017 - 11:30am

Understanding structure-property relationships in fields as diverse as nanoscale electronic junctions, heterogeneous catalysis, electrochemistry and energy storage often starts by meeting the challenge of identifying key structure motifs. For the theorist this is followed by tackling the problem of calculating the relevant functional characteristics, also challenging, particularly for excited state properties. I will discuss the modern toolbox for these problems, including a brief outline of the basic physical ingredients of modern manybody perturbation theory which enables studies of excited state properties. I will then discuss its application in the context of the search to develop new materials for use in photocatalysis. In particular, I will discuss the search for key structural motifs at semiconductor-water interfaces and the connection to electrochemical energy level alignment. 

DSN-I Seminar "State of the Nanofab"

Speaker(s): 
Multiple Speakers
Dates: 
Wednesday, December 13, 2017 - 12:00pm to 1:30pm

As a premier multidisciplinary, open, and shared research lab, the Carnegie Mellon Nanofabrication Facility, or Nanofab, is a nanomanufacturing hub that plays a vital role in major research thrusts for the College and the University, namely in Information Technology, Internet of Things, Energy, and Life Sciences. The Nanofab serves a broad community at Carnegie Mellon and beyond, providing equipment, services, and process support for the invention, synthesis, and fabrication of new materials and devices in the areas of magnetics and spintronics, MEMS and NEMS, optics and photonics, functional oxides, 2-dimensional materials, bioelectronics, and much more. This talk will focus on the current state of the Nanofab as it relates to both research, equipment capabilities and user interface. In particular, we will highlight the transformative impact that the new Claire and John Bertucci Nanotechnology Laboratory will have for the CMU community and the region. The new facility will play a critical role in facilitating housing of cutting-edge nanomanufacturing equipment as well as creating new synergies and means for research collaboration across campus. We will discuss these new capabilities and some of the future initiatives we would like to purse to revolutionize nanoscale science and engineering within Carnegie Mellon and the region.

Interview with Dr. Pedram Roushan

Speaker(s): 
Pedram Roushan
Dates: 
Friday, December 1, 2017 - 10:00am to 11:00am

Pedram Roushan was born and raised in Iran. In 2001, he moved to the US as a religious refugee and attended Pitt, where he graduated summa cum laude in 2005. During his years at Pitt, he worked at the laboratories of X. L. Wu and W. Goldberg, focusing on the dynamics in 2D fluids. He received his PhD in 2011 from Princeton University, performing the first scanning tunneling microscopy on the surface of topological insulators in the lab of A. Yazdani. After three years of post-doctoral studies in the J. Martinis lab at the University of California, Santa Barbara, in 2014 he joined the Google quantum hardware lab aiming on making a quantum computer. The current focus of his research is on simulating condensed matter systems with engineered quantum platforms.

From Quantum Mechanics to Force Fields

  • By Burcu Ozden
  • 22 November 2017

Ken Jordan and his colleague are invited to write a special topic issue in the journal of chemical physics (JCP). This work is dedicated to the ongoing efforts of the theoretical chemistry community to develop a new generation of accurate force fields based on data from high-level electronic structure calculations and to develop faster electronic structure methods for testing and designing force fields as well as for carrying out simulations. 

What molecular properties give rise to a strong piezoelectric response?

  • By Burcu Ozden
  • 22 November 2017

In this study Geoffrey R. Hutchison and his colleagues tried to answer the question of " What molecular properties give rise to a strong piezoelectric response?"  To do so, they systematically probe the interplay among peptide chemical structure, folding propensity, and piezoelectric properties, uncovering in the process new insights into the origin of peptide electromechanical response. They have designed variety of peptides and peptoids and test the effect of molecular properties on piezoelectric response via serious measurements including ircular dichroism (CD), Polarization-modulated infrared reflection−absorption spectroscopy (PM-IRRAS), tomic force microscopy (AFM), piezo-force microscopy (PFM), and X-ray photoelectron spectroscopy (XPS) measurements. They showed backbone rigidity is an important determinant in peptide electromechanical responsiveness. 

New Era in Thermal Scanning Probe Lithography

  • By Burcu Ozden
  • 15 November 2017

Tevis Jacobs and his collaborators from IBM and SwissLitho were achieved sub-10 nanometer feature size in Silicon using thermal scanning probe lithography. In this work, they  the t-SPL parameters that influence high-resolution patterning on the transfer stack and demonstrate that sub-15 nm half-pitch resolution patterning and transfer by t-SPL are feasible. They found that the resolution in t-SPL is limited by the extent of the plastic zone in thermo-mechanical indentation on the pattern transfer stack because, at temperatures approaching the resist’s decomposition temperature, the line shape widens, reducing the achievable resolution. They achieved reliable transfer of patterned dense lines down to 14 nm half-pitch and in the best case 11 nm half-pitch. Furthermore, evidently they showed that an enhanced resolution below 10 nm half-pitch might be possible on a mechanically different transfer stack.

NASA Workshop on Quantum Computing for Aeroscience and Engineering

  • By Leena Aggarwal
  • 15 November 2017

November 7-8, 2017, physics students and scientist from diffrent places were arrived at the NASA Langley research center for attending Quantum Computing workshop.

The objective of this workshop was to bring together experts on quantum information science and computation to understand the latest developments and current challenges in algorithms, hardware, and technology transition to engineering applications. The aims of workshop was to accelerate technology transition towards outstanding engineering problems that were expected to be achievable using quantum computations in the coming decade. The workshop’s goals were included developing a roadmap for success towards solution strategies for engineering applications. The interested stakeholders were presented or taken part in discussion on challenges to transition the current state-of-the-art to large scale engineering and data science related problems. 

 

Discussions were focused on the following four areas:

  • Quantum algorithms
  • Quantum computing hardware
  • Manufacturing and control of quantum systems
  • Engineering applications

Atomic Layer Semiconductor 2D Nanoelectromechanical Systems (NEMS)

Speaker(s): 
Philip Feng
Dates: 
Tuesday, December 12, 2017 - 3:00pm

Atomically thin semiconducting crystals derived from new classes of layered materials have rapidly emerged to enable two-dimensional (2D) nanostructures with unusual electronic, optical, mechanical, and thermal properties.  While graphene has been the forerunner and hallmark of 2D crystals, newly emerged 2D semiconductors offer intriguing, beyond-graphene, attributes.  The sizable and tunable bandgaps of compound and single-element 2D semiconductors offer attractive perspectives for strong multiphysics coupling and efficient transduction across various signal domains.  ...

2D Materials - A New Platform for Strong Light-Matter Interactions

Speaker(s): 
Ajit Srivastava
Dates: 
Thursday, November 16, 2017 - 4:30pm

A recent addition to low-dimensional materials are monolayer transition metal dichalcogenides (TMDs), such as WSe2, with an atomically thin, honeycomb lattice and optical band gaps. In addition to spin, charge carriers in TMDs exhibit a “valley” degree of freedom, which can be optically addressed using circularly polarized light, opening up exciting possibilities for “valleytronics". Another curious aspect of TMDs lies in the non-trivial geometry of their band structure which gives rise to equal but opposite Berry curvature, an effective magnetic field in the momentum...

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