Mechanical Properties of Low Dimensional Materials

Recent advances in low dimensional materials (LDMs) have paved the way for unprecedented technological advancements. The drive to reduce the dimensions of electronics has compelled researchers to devise newer techniques to not only synthesize novel materials, but also tailor their properties. Although micro and nanomaterials have shown phenomenal electronic properties, their mechanical robustness and a thorough understanding of their structure-property relationship are critical for their use in practical applications. However, the challenges in probing these mechanical properties dramatically increase as their dimensions shrink, rendering the commonly used techniques inadequate. This Dissertation focuses on developing techniques for accurate determination of elastic modulus of LDMs and their mechanical responses under tensile and shear stresses. Fibers with micron-sized diameters continuously undergo tensile and shear deformations through many phases of their processing and applications. Significant attention has been given to their tensile response and their structure-tensile properties relations are well understood, but the same cannot be said about their shear responses or the structure-shear properties. This is partly due to the lack of appropriate instruments that are capable of performing direct shear measurements. In an attempt to fill this void, this Dissertation describes the design of an inexpensive tabletop instrument, referred to as the twister, which can measure the shear modulus (G) and other longitudinal shear properties of micron-sized individual fibers. An automated system applies a pre-determined twist to the fiber sample and measures the resulting torque using a sensitive optical detector. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers. Two industrially important fibers, IM7 carbon fiber and Kevlar® 119, were found to have G = 17 and 2.4 GPa, respectively. In addition to measuring the shear properties directly on a single strand of fiber, the technique was automated to allow hysteresis, creep and fatigue studies. Zinc oxide (ZnO) semiconducting nanostructures are well known for their piezoelectric properties and are being integrated into several nanoelectro-mechanical (NEMS) devices. In spite of numerous studies on the mechanical response of ZnO nanostructures, there is not a consensus in its measured bending modulus (E). In this Dissertation, by employing an all-electrical Harmonic Detection of Resonance (HDR) technique on ZnO nanowhisker (NW) resonators, the underlying origin for electrically-induced mechanical oscillations in a ZnO NW was elucidated. Based on visual detection and electrical measurement of mechanical resonances under a scanning electron microscope (SEM), it was shown that the use of an electron beam as a resonance detection tool alters the intrinsic electrical character of the ZnO NW, and makes it difficult to identify the source of the charge necessary for the electrostatic actuation. A systematic study of the amplitude of electrically actuated as-grown and gold-coated ZnO NWs in the presence (absence) of an electron beam using an SEM (dark-field optical microscope) suggests that the oscillations seen in our ZnO NWs are due to intrinsic static charges. In experiments involving mechanical resonances of micro and nanostructured resonators, HDR is a tool for detecting transverse resonances and E of the cantilever material. To add to this HDR capability, a novel method of measuring the G using HDR is presented. We used a helically coiled carbon nanowire (HCNW) in singly-clamped cantilever configuration, and analyzed the complex (transverse and longitudinal) resonance behavior of the nonlinear geometry. Accordingly, a synergistic protocol was developed which (i) integrated analytical, numerical (i.e., finite element using COMSOL ®) and experimental (HDR) methods to obtain an empirically validated closed form expression for the G and resonance frequency of a singly-clamped HCNW, and (ii) provided an alternative for solving 12th order differential equations. A visual detection of resonances (using in situ SEM) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior, the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers

Plasmomechanical Systems: Principles and Applications

AbstractExtreme confinement of electromagnetic waves and mechanical displacement fields to nanometer dimensions through plasmonic nanostructures offers unprecedented opportunities for greatly enhanced interaction strength, increased bandwidth, lower power consumption, chip‐scale fabrication, and efficient actuation of mechanical systems at the nanoscale. Conversely, coupling mechanical oscillators to plasmonic nanostructures introduces mechanical degrees of freedom to otherwise static plasmonic structures thus giving rise to the generation of extremely large resonance shifts even for minor position changes. This nanoscale marriage of plasmonics and mechanics has led to the emergence of a new field of study called plasmomechanics that explores the fundamental principles underneath the coupling between light and plasmomechanical nanoresonators. In this review, both the fundamental concepts and applications of plasmomechanics as an emerging field of study are discussed. After an overview of the basic principles of plasmomechanics, the active tuning mechanisms of plasmonic nano‐mechanical systems are extensively analyzed. Moreover, the recent developments on the practical implications of plasmomechanic systems for such applications as biosensing and infrared detection are highlighted. Finally, an outlook on the implications of the plasmomechanical nanosystems for development of point‐of‐care diagnostic devices that can help early and rapid detection of fatal diseases are forwarded

Piezotronic devices and integrated systems

Novel technology which can provide new solutions and enable augmented capabilities to CMOS based technology is highly desired. Piezotronic nanodevices and integrated systems exhibit potential in achieving these application goals. By combining laser interference lithography and low temperature hydrothermal method, an effective approach for ordered growth of vertically aligned ZnO NWs array with high-throughput and low-cost at wafer-scale has been developed, without using catalyst and with a superior control over orientation, location/density and morphology of as-synthesized ZnO NWs. Beyond the materials synthesis, by utilizing the gating effect produced by the piezopotential in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) and universal logic operations such as NAND, NOR, XOR gates have been demonstrated for performing piezotronic logic operations for the first time. In addition, the first piezoelectrically-modulated resistive switching device based on piezotronic ZnO NWs has also been presented, through which the write/read access of the memory cell is programmed via electromechanical modulation and the logic levels of the strain applied on the memory cell can be recorded and read out for the first time. Furthermore, the first and by far the largest 3D array integration of vertical NW piezotronic transistors circuitry as active pixel-addressable pressure-sensor matrix for tactile imaging has been demonstrated, paving innovative routes towards industrial-scale integration of NW piezotronic devices for sensing, micro/nano-systems and human-electronics interfacing. The presented concepts and results in this thesis exhibit the potential for implementing novel nanoelectromechanical devices and integrating with MEMS/NEMS technology to achieve augmented functionalities to state-of-the-art CMOS technology such as active interfacing between machines and human/ambient as well as micro/nano-systems capable of intelligent and self-sufficient multi-dimensional operations.Ph.D

Agenda: Second International Workshop on Thin Films for Electronics, Electro-Optics, Energy and Sensors (TFE3S)

University of Dayton’s Center of Excellence for Thin Film Research and Surface Engineering (CETRASE) is delighted to organize its second international workshop at the University of Dayton’s Research Institute (UDRI) campus in Dayton, Ohio, USA. The purpose of the new workshop is to exchange technical knowledge and boost technical and educational collaboration activities within the thin film research community through our CETRASE and the UDRI

Mechanical Stiffness and Dissipation in Ultrananocrystalline Diamond Films

Tetragonal sp3-bonded diamond has the highest known atomic density. The nature of the bond and its high density enable diamond to have superior physical properties such as the highest Young’s modulus and acoustic velocity of all materials, and excellent tribological properties. Recently, conformal thin diamond films have been grown at CMOS-compatible temperatures in the form known as ultrananocrystalline diamond (UNCD). These make diamond promising for high frequency micro/nanomechanical devices. We have measured the Young’s modulus (E), Poisson’s ratio and the quality factors (Q) for microfabricated overhanging ledges and fixed-free beams composed of UNCD films grown at lower temperatures. The overhanging ledges exhibited periodic undulations due to residual stress. This was used to determine a biaxial modulus of 838 ± 2 GPa. Resonant excitation and ring down measurements of the cantilevers were conducted under ultra high vacuum (UHV) conditions on a customized atomic force microscope to determine E and Q. At room temperature we found E = 790 ± 30 GPa, which is ~20 % lower than the theoretically predicted value of polycrystalline diamond, an effect attributable to the high density of grain boundaries in UNCD. From these measurements, Poisson’s ratio for UNCD is estimated for the first time to be 0.057±0.038. We also measured the temperature dependence of E and Q in these cantilever beams from 60 K to 450 K. Mechanical stiffness of these cantilevers increased linearly with the reduction in temperature until ∼160 K where it then saturates. Reduction in the modulus of the film with temperature is slightly higher than that of single crystal diamond(averaged over all directions). We measured extremely low temperature coefficient of resonant frequency and results are promising for applications in MEMS and NEMS wireless devices and biosensors. The room temperature Q varied from 5000 to 16000 and showed a moderate increase as the cantilevers were cooled below room temperature followed by a characteristic low temperature plateau. Overall, results show that grain boundaries of UNCD films play a key role in determining its thermomechanical stability and mechanical dissipation. These results are extremely useful in understanding and controlling the dissipation in nanocrystalline materials

The Boston University Photonics Center annual report 2012-2013

This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2012-2013 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.This report summarizes activities of the Boston University Photonics Center during the period July 2012 through June 2013. These activities span the Center’s complementary missions in education, research, technology development, and commercialization. The Photonics Center continues to grow as an international leader in photonics research, while executing the Center’s strategic plan and serving as a university-wide resource for several affiliate Centers. For more information about the strategic plan, read the Photonics Center Strategic Plan section on page 10. In research, Photonics Center faculty published nearly 150 journal papers spanning the field of photonics. A number of awards for outstanding achievement in education and research were presented to Photonics Center faculty members, including a Peter Paul Professorship for Professor Xue Han, an NSF Career Award for Professor Ajay Joshi, and the 2012 Innovator of the Year Award from Boston University for Professor Theodore Moustakas. New external grant funding for the 2012- 2013 fiscal year totaled over $21.8M. For more information on our research activities, read the Research section on page 24. In technology development, the Photonics Center has turned a chapter, by completing the transition from a focus on Defense/ Security applications to a focus on the healthcare market sector. The commercial sector is expected to energize the technology development efforts for the foreseeable future, but the roots in defense/security are still important and the Center will continue to pursue new research grants in this area. For more information on our technology development program and on specific projects, read the Technology Development section on page 45. In education, 20 Photonics Center graduate students received Ph.D. diplomas. Photonics Center faculty taught 32 photonics courses. The Center supported a Research Experiences for Teachers (RET) site in Biophotonic Sensors and Systems for 10 middle school and high school teachers. The Photonics Center sponsored the Herbert J. Berman “Future of Light” Prize at the University’s Scholars Day. For more on our education programs, read the Education section on page 54. In commercialization, Boston University’s Business Innovation Center (BIC) currently hosts seven technology start-up companies. There is a healthy turnover in the Innovation Center space with a total of 19 companies residing at BIC over the past year. The mix of companies includes: life sciences, biotechnology, medical devices, photonics, and clean energy; and nine of the 19 companies originated from within BU. All the BIC tenants are engaged in the commercialization of new technologies of importance to society and all are active in the BU community in terms of offering internships, employment opportunities or research collaborations. For more information about Business Innovation Center activities, read the Business Innovation Center chapter in the Facilities and Equipment section on page 66

The Boston University Photonics Center annual report 2011-2012

This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2011-2012 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.This report summarizes activities of the Boston University Photonics Center during the period July 2011 through June 2012. These activities span the Center’s complementary missions in education, research, technology development, and commercialization. In 2010, the Photonics Center unveiled a five-year strategic plan as part of the University’s comprehensive review of centers and institutes. The Photonics Center continues to show progress on the Photonics Center strategic plan and is growing the Center’s position as an international leader in photonics research. For more information about the strategic plan, read the Photonics Center Strategic Plan section on page 11. In research, Photonics Center faculty published more than 100 journal papers spanning the field of photonics. A number of awards for outstanding achievement in education and research were presented to Photonics Center faculty members, including a Presidential Early Career Award for Scientists and Engineers (PECASE) for Professor Altug, the Boston University Peter Paul Professorship for Professor Han, and a Dean’s Catalyst Award for Professor Joshi. New external grant funding for the 2011-2012 fiscal year totaled $15.8M. For more information on our research activities, read the Research section on page 26. In technology development, the close of FY11 marked the end of the Photonics Center’s decade-long collaboration pipeline technology development with the Army Research Laboratory (ARL). The successful outcomes of that unique partnership include a compelling series of photonics technology prototypes aimed at force protection. Our direct collaboration with Army end users has enabled transformative advanced in sniper detection of bioterror agents, and nuclear threat detection. In the past year, the Photonics Center has expanded the scope of its unique photonic technology development program to include applications in the commercial healthcare sector. For more information on our technology development program and on specific projects, read the Technology Development section on page 52. In education, 17 Photonics Center graduate students received Ph.D. diplomas. Photonics Center faculty taught 29 photonics courses. The Center supported a Research Experiences for Teachers (RET) site in Biophotonic Sensors and Systems for 10 middle school and high school teachers. The Photonics Center sponsored the Herbert J. Berman “Future of Light” Prize at the University’s Science and Engineering Day. Professor Goldberg’s Boston Urban Fellows Project started its seventh year. For more on our education programs, read the Education section on page 64. In commercialization, the Business Innovation Center continues to operate at capacity. Its tenants include 11 technology companies with a majority having core business interests primarily in photonics and life sciences. It houses several companies founded by current and former BU faculty and students and provides students with an opportunity to assist, observe, and learn from start-up companies. For more information about Business Innovation Center activities, read the Business Innovation Center chapter in the Facilities and Equipment section on page 78