Effect of flexible supports on the frequencies of nanobeams with tip mass and axial load for applications in atomic force microscopy (AFM)

Doctoral Degree. University of KwaZulu-Natal, Durban.This aim of this investigation is to describe the mechanical performance of a beam (probe) used in dynamic atomic force microscopy (dAFM) which can be utilized in scanning the topographical features of biological samples or "pliable" samples in general. These nanobeams can also be used to modify samples by using high frequency oscillating contact forces to remove material or shape nano structures. A nanobeam with arbitrary boundary conditions is studied to investigate different configurations and the effects of the relevant parameters on the natural frequencies. The nano structure is modelled using the Euler-Bernoulli theory and Eringen's theory of nonlocal continuum or first order stress-gradient theory is incorporated to simulate the dynamics of the system. This theory is effective at nanoscale because it considers the small-scale effects on the mechanical properties of the material. The theory of Nonlocal continuum is based on the assumption that the stress at a single point in the material is influenced by the strains at all the points in the material. This theory is widely applied to the vibration modelling of carbon nanotubes in several studies. The system is modelled as a beam with a torsional spring boundary condition that is rigidly restrained in the transverse direction at one end. The torsional boundary condition can be tuned, by changing the torsional spring stiffness, such that the compliance of the system matches that of the sample to prevent mechanical damage of both the probe tip and the sample. When the torsional spring stiffness is zero, the beam is pinned and when the stiffness is infinite, the beam is a cantilever. In the first case, a mass is attached to the tip and a linear transverse spring is attached to the nanobeam. The mass and spring model the probe tip and contact force, respectively. In the second case, at the free end is a transverse linear spring attached to the tip. The other end of the spring is attached to a mass, resulting in a single degree of freedom spring-mass system. When the linear spring constant is infinite, the free end behaves as a beam with a concentrated tip mass. When the mass is infinite, the boundary condition is that of a linear spring. When the tip mass is zero, the configuration is that of a torsionally restrained cantilever beam. When tip of the nanobeam vibrates, the system behaves like a hammer and chisel. The motion of the tip of the beam and tip mass can be investigated to observe the tip frequency response, force, acceleration, velocity and displacement. The combined frequencies of the beam and spring-mass systems contain information about the maximum displacement amplitude and therefore the sample penetration depth

A nano-tensile testing system for studying nanostructures inside an electron microscope:design, characterization and application

Mechanical properties of nanostructures could be remarkably different from their bulk counterparts owing to scale effects, which have attracted considerable research interest in recent years. However, nanomechanics studies are hindered by the difficulties of conducting well-instrumented mechanical testing. The objective of this thesis is to develop a novel tensile stage that can be used to probe mechanical properties of universal one-dimensional (1D) nanostructures, like nanowires and nanotubes, inside a scanning/transmission electron microscope (SEM/TEM). The main challenges of performing tensile tests at the nanoscale are: (1) specimen alignment and fixation on the tensile stage; (2) application and measurement of tensile force with nano-Newton resolution; (3) measurement of specimen elongation with nanometer resolution. Previous studies have shown that micro-electromechanical system (MEMS) technology combined with advanced microscopy (e.g. SEM and TEM) provides promising perspectives to address these challenges. Two types of nano-tensile stages, fabricated in a silicon on insulator (SOI) wafer, were developed in this thesis, which consisted of a comb-drive actuator and either a differential capacitive force sensor or a double clamped beam force sensor. The optimized comb-drive actuators could output an in-plane force of about 210 µN at a drive voltage of 120 V, and the force sensors achieved resolutions of better than 50 nN. Individual 1D nanostructures were placed on the MEMS device by in-situ nanomanipulations and fixed at their two ends via focused electron beam induced deposition (FEBID). A strategy of modifying device topography, e.g. in the form of trenches or pillars, was proposed to facilitate the specimen preparation by in-situ manipulation that could achieve a high yield of about 80%. The mechanical testing function of the developed micro devices was demonstrated by tensile tests on individual Co and Si nanowires (NWs) inside an SEM. The average apparent Young's modulus, tensile strength and fracture strain of the electrochemically deposited Co NWs were measured to be (75.3±14.6) GPa, (1.6±0.4) GPa and (2.2±0.6) %, respectively. The measured Young's modulus is significantly lower than that of Co in the bulk form (209 GPa), which is likely caused by structural defects (e.g. pores) and surface effects (e.g. surface contaminations and surface oxide layers). The phosphorous-doped SiNWs grown bottom up by the vapor-liquid-solid (VLS) technique showed an average Young's modulus of (170.0±2.4) GPa and a tensile strength larger than 8.3 GPa. This finding confirms that materials strength increases as their sizes scale down. The top down electroless chemically etched Si NWs show a tensile strength of 5.4 GPa. The developed MEMS devices and experimental techniques enable an alternative way of in-situ nanomechanical characterization based on electron microscopy. The design methodology and learning presented in this thesis would be useful to develop nano-tensile stages of other configurations with more advanced functions

Modifiering av ytliga, mekaniska och optiska egenskaper hos TEMPO oxiderad nanofibrillerad cellulosa med poly(vinyl acetat) och glyoxal

Nanofibrillated cellulose (NFC) has become a material of interest, since it has unique surface, mechanical and optical properties, in addition, it is natural, biodegradable and biocompatible. However, aforementioned physical properties are application specific and the usage of NFC is limited in challenging applications such as in liquid environments, therefore, NFC films are usually modified to obtain custom-made films. In this thesis, the goal was to study the effect of the crosslinking mechanism in surface, optical and mechanical properties. Properties were modified by adding poly(vinyl acetate) (PVA) or PVA and glyoxal to TEMPO oxidized NFC (TOCN). The water contact angle increased notably when adding 20 % PVA compared to pure TOCN, while other amounts of PVA did not change the contact angle significantly. The addition of both PVA and glyoxal reduced the contact angle. The surface roughness decreased considerably when modifying the TOCN with PVA or PVA and glyoxal. The tensile strength increased notably and Young’s modulus increased slightly by adding 20 % PVA compared to pure TOCN, while the other amounts of PVA added did not cause significant change. The addition of glyoxal to the PVA modified TOCN increased the Young’s modulus markedly, while the tensile strength first increased and then decreased as more glyoxal was added. The transparency increased notably after modifying the TOCN and the ISO brightness decreased. The light transmittance for the samples ranged from 85 % to 88 %. The light transmittance was increased in the PVA based films, while the addition of glyoxal did not change the light transmittance notably.Nanofibrillerad cellulosa (NFC) har blivit ett mycket intresseväckande material på grund av dess unika ytliga, mekaniska och optiska egenskaper, dessutom är det ett naturligt, biologiskt nedbrytbart och biokompatibelt material. De ovannämnda fysiska egenskaperna är applikationsspecifika och användningen av NFC är begränsad i utmanande applikationer, såsom i fuktiga miljöer. NFC filmer är oftast modifierade så att man kan få filmer med skräddarsydda egenskaper. I denna avhandling var målet att studera effekten av tvärbindningsegenskaperna i de ytliga, mekaniska och optiska egenskaperna. Egenskaperna modifierades genom att tillsätta polyvinylacetat (PVA) eller PVA och glyoxal i den TEMPO oxiderade NFC:n (TOCN). Vattenkontaktvinkeln ökade speciellt mycket då 20 % PVA tillsattes i TOCN, jämfört med gedigen TOCN, medan andra mängder av PVA inte förändrade kontaktvinkeln betydligt. Genom att tillsätta både PVA och glyoxal minskades kontaktvinkeln. Ytsträvheten minskades avsevärt vid modifiering av TOCN med PVA eller PVA och glyoxal. Draghållfastheten ökade markant och Youngs modul ökade en aning då 20 % PVA tillsattes i TOCN jämfört med gedigen TOCN, medan de andra mängderna tillsatt PVA inte orsakade någon signifikant förändring. Tillsatsen av glyoxal i den PVA modifierade TOCN:n ökade avsevärt Youngs modul, medan draghållfastheten först ökade och sedan minskade då mer glyoxal tillsattes. Genomskinligheten ökade speciellt mycket då TOCN:n modifierades och ISO ljusstyrkan minskade. Ljustransmittansen för provbitarna varierade från 85 % till 88 %. Ju mera PVA som tillsattes, desto mer ökade ljustransmittansen, medan tillsatsen av glyoxal inte förändrade ljustransmittansen särskilt mycket

Piezoresistive Hybrid Nanocomposites for Strain and Damage Sensing: Experimental and Numerical Analysis

Carbon nanomaterials such as carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) demonstrate remarkable electrical and mechanical properties, which suggest promising structural and functional applications as fillers for polymer nanocomposites. The piezoresistive behavior of these nanocomposites makes them ideal for sensing applications. Besides, hybrid nanocomposites with multiple fillers like carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) are known to exhibit improved electrical and mechanical performance when compared to mono-filler composites. To comprehensively understand the mechanisms of electrical percolation, conductivity, and piezoresistivity in hybrid nanocomposites, the author develops a two-dimensional (2D) and a three-dimensional (3D) computational Monte Carlo percolation network models for hybrid nanocomposites with CNT and GNP fillers. In the experimental studies correlated to the computational models, the author fabricates the hybrid nanocomposites made of both fillers using resin infiltration techniques and show an improvement of their electromechanical performance when compared to CNT nanocomposites. Due to the limitations of the resin infiltration techniques, the author develops an inkjet printing procedure with a new water-based CNT ink to fabricated printed nanocomposites on both polyimide film (Kapton) and paper with high device-todevice reproducibility. The ink formulation, as well as the substrate surface treatment, have been optimized to obtain conductive and piezoresistive devices. The author shows the effectiveness of the printed devices as strain sensors and impact damage sensors respectively under mechanical strains and hypervelocity impact damages. Devices printed with the minimum number of ink deposited layers lead to the best sensing performance

DESIGN, COMPACT MODELING AND CHARACTERIZATION OF NANOSCALE DEVICES

Electronic device modeling is a crucial step in the advancement of modern nanotechnology and is gaining more and more interest. Nanoscale complementary metal oxide semiconductor (CMOS) transistors, being the backbone of the electronic industry, are pushed to below 10 nm dimensions using novel manufacturing techniques including extreme lithography. As their dimensions are pushed into such unprecedented limits, their behavior is still captured using models that are decades old. Among many other proposed nanoscale devices, silicon vacuum electron devices are regaining attention due to their presumed advantages in operating at very high power, high speed and under harsh environment, where CMOS cannot compete. Another type of devices that have the potential to complement CMOS transistors are nano-electromechanical systems (NEMS), with potential applications in filters, stable frequency sources, non-volatile memories and reconfigurable and neuromorphic electronics

The Study of Biomolecule-Substrate Interactions by Single Molecule Force Spectroscopy and Brownian Dynamics Simulations

Hybrids of biomolecules and nanomaterials have been identified as promising candidates in the development of novel therapeutics and electronic devices. Single stranded DNA (ssDNA)-bound Single-walled carbon nanotubes (SWCNTs) are of particular interest as they may be the key to solving the challenges that face the carbon nanotube separation technology and because of their potential application in bio-nanomedicine. The ability of ssDNA to form a stable hybrid with CNTs has been attributed to the structure and amphiphilic nature of this macromolecule, enabling the dispersion, sorting and patterned placement of nanotubes. Considering the significant role of ssDNA-CNTs in future technologies and the potential toxicity of such nanomaterials in biological systems, it is essential to gain a quantitative and fundamental understanding on the interactions that allow, weaken or prevent the formation of these hybrids. In this dissertation, we use both experimental and theoretical methods to systematically investigate the major characteristics of these interactions.The free energy of binding of ssDNA homopolymers to solvated carbon nanotubes is one of the key characteristics that determine the stability of such dispersions. We used single molecule force spectroscopy (SMFS), first on graphite and next on single walled carbon nanotubes, to probe and directly quantify the binding strength of ssDNA homopolymer oligomers to these substrates. The force resisting removal of DNA molecules from these surfaces shows characteristic steady-state force plateaus which were distinguishable for each DNA sequence. The free energy of binding per nucleotide for these oligomers on graphite were ranked as T \u3e= A \u3e G \u3e= C (11.3 ± 0.8 kT, 9.9 ± 0.4 kT, 8.3 ± 0.2 kT, and 7.5 ± 0.8 kT, respectively). On SWCNTs, these interactions decreased in the following order: A \u3e G \u3e T \u3e C, and their magnitude was much larger than on graphite (38.1 ± 0.2; 33.9 ± 0.1; 23.3 ± 0.1; 17.1 ± 0.1 kT, respectively).In addition to the binding strength of ssDNA nucleotide to surfaces, it is equally as important to understand the dynamics of these interactions. The force response of a simple chain-like polymeric molecule (representative of single stranded DNA) was studied using Brownian dynamics to shed light on these dynamics and the features that may be masked in SMFS experiments. Through simulations at slow peeling rates, our Brownian dynamics model confirmed the predictions of an equilibrium statistical thermodynamic model. Faster removal rates resulted in deviations from equilibrium which were dominated by a combination of Stokes (viscous) drag and a finite desorption rate of the monomeric units. Furthermore, the force probe\u27s thermal fluctuations were shown to be affected by the spring constant of the contact mode AFM cantilever Consequently, this effect provided evidence on the source of disappearance for certain key features such as force spikes, associated with the desorption of individual links and predicted by the statistical thermodynamic model under displacement control, from SMFS experiments. In studying the elastic response of a freely jointed chain stretched in 2D and 3D, we obtained analytical expressions for two modes of stretching: i) when force is applied only to one end of the chain, and ii) when the applied force is distributed uniformly throughout the chain. By comparing, we confirmed that these expressions correctly predict the results obtained from our Brownian dynamics simulations as well as experimental results from the literature

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

Proceeding Of Mechanical Engineering Research Day 2016 (MERD’16)

This Open Access e-Proceeding contains a compilation of 105 selected papers from the Mechanical Engineering Research Day 2016 (MERD’16) event, which is held in Kampus Teknologi, Universiti Teknikal Malaysia Melaka (UTeM) - Melaka, Malaysia, on 31 March 2016. The theme chosen for this event is ‘IDEA. INSPIRE. INNOVATE’. It was gratifying to all of us when the response for MERD’16 is overwhelming as the technical committees received more than 200 submissions from various areas of mechanical engineering. After a peer-review process, the editors have accepted 105 papers for the e-proceeding that cover 7 main themes. This open access e-Proceeding can be viewed or downloaded at www3.utem.edu.my/care/proceedings. We hope that these proceeding will serve as a valuable reference for researchers. With the large number of submissions from the researchers in other faculties, the event has achieved its main objective which is to bring together educators, researchers and practitioners to share their findings and perhaps sustaining the research culture in the university. The topics of MERD’16 are based on a combination of fundamental researches, advanced research methodologies and application technologies. As the editor-in-chief, we would like to express our gratitude to the editorial board and fellow review members for their tireless effort in compiling and reviewing the selected papers for this proceeding. We would also like to extend our great appreciation to the members of the Publication Committee and Secretariat for their excellent cooperation in preparing the proceeding of MERD’16

Micro electro-mechanical system design, fabrication and application for atomic force microscopy probe elasticity characterisation

The work in this thesis is focused on characterising elastic behaviour of micro-cantilever probes found at the core of Atomic Force Microscopy (AFM) tools. It is an essential property to AFM force measurements, since interpretation of the cantilever deflection is directly related to the measure of the tip-sample force via its elastic conduct. It was demonstrated that the conventional micro-cantilevers can be well characterised using analytical and FE methods, together with the ready developed tools and experimental techniques, which formed the insights for the design practices used in further and more complex structure development efforts. However, this project’s emphasis was placed on assessment of non-traditional AFM cantilever structures that are not supported by the said methods, and hence necessitated in the conceptualisation and development of a dedicated micro electro-mechanical system (MEMS) solution. The sensitive force and elasticity measurement device, based on metal film resistive strain sensing, was realised using semiconductor and MEMS fabrication approaches in the James Watt Nanofabrication Centre, allowing the desired performance to be achieved with an in-house process optimisation. The functional MEMS tool paired with bespoke instrumentation was then employed to characterise a range of commercial cantilevers as well as non-standard probes consisting of complex composition multi-structures and non-linear elasticity, providing novel insights into their elastic character