Invited Speakers

Jesse Maassen
Dalhousie University (Canada)

First-principles transport modeling of thermoelectrics: the unusual case of germanium telluride

A major challenge facing the world today involves exploiting clean, abundant energy sources, and reducing our overall consumption. A significant untapped energy source is waste heat, accounting for ~60% of the energy humans produce. Thermoelectrics can convert heat into useful electrical power, and hence have the potential to impact our energy future by recuperating this large unutilized source. The challenge is to increase the thermoelectric conversion efficiency for this technology to become widespread, which requires exploring and discovering new materials with enhanced electronic and thermal (phonon) transport properties. Advances in theoretical modeling now allow the thermoelectric characteristics of materials to be calculated fully predictively, and thus represents a powerful tool to be partnered with experimental efforts. In the first half of the presentation I will describe our simulation approach based on combining density functional theory (DFT) with the Boltzmann transport equation (BTE). DFT provides detailed material properties, including electron & phonon energies along with the electron-phonon scattering potential, which serve as input to rigorously compute the scattering and transport characteristics within the BTE framework, as a function of carrier concentration and temperature. In the second half of the talk, I will illustrate how this predictive framework can be used to develop design strategies, provide new insights into the scattering and transport physics, and explore promising materials. Specifically, I will present our recent findings on rhombohedral GeTe, a layered material predicted to have unusual anisotropic transport properties [1]. Interestingly, in GeTe the dominant transport directions for electrons and phonons are decoupled – the electrical and thermal conductivities are largest perpendicular and parallel to the atomic layers, respectively. This behavior leads to a three-fold increase in the thermoelectric figure-of-merit. The origin of this unusual feature is discussed, along with some initial work to find this same behavior in other similar material systems. This research is helping to advance thermoelectrics by providing new insights into the scattering/transport physics and identifying promising novel materials. [1] Askarpour and Maassen, “Unusual thermoelectric transport anisotropy in quasi-two-dimensional rhombohedral GeTe”, Phys. Rev. B 100, 075201 (2019).
Balla Diop Ngom
University Cheikh Anta Diop of Dakar (Senegal)

Vanadium dioxide/activated expanded graphite composite and carbon-vanadium oxynitride for high performance asymmetric supercapacitor

A Thermal decomposition process has been used to synthesise vanadium dioxide/activated expanded graphite (VO2/AEG) composite and carbon-vanadium Oxynitride (C-V2NO) porous web-like structures. The X ray diffraction analysis of the composite showed the diffraction peaks of the monoclinic VO2 and hexagonal AEG structure. C-V2NO sample were indexed to a cubic structure. The presence of a successful incorporation of disordered carbon into the main vanadium-based matrix was confirmed by the Raman spectroscopy analysis. The Bands of the VO2/AEG composite as well as of the C-V2NO materials exhibited vibration modes which are associated to vanadium dioxide with the distinct D, G, and D' peaks. An asymmetric supercapacitor (VO2/AEG//C-V2NO) was assembled using VO2/AEG composite as a positive electrode and C-V2NO as a negative electrode operating in 6 M KOH electrolyte. The VO2/AEG//C-V2NO showed a specific energy of 41.6 Wh kg-1 with a corresponding specific power of 904 W kg-1 at 1 A g-1 in a large operating voltage of 1.8 V. The asymmetric device displayed a capacity retention of 93% up to 10,000 cycles at 10 A g-1. In addition, the voltage holding of the device was maintained without any significant degradation up to 100 h.
Dominik Bresser
Karlsruhe Institute of Technology (Germany)

Alternative Lithium-Ion Storage Mechanisms of Nanostructured Transition Metal Oxides

The unique combination of exceptional energy and power density has made lithium-ion batteries the state-of-the-art electrochemical energy storage technology for small- and large-scale applications [1]–[3]. Nonetheless, further improvement is needed for realizing lightweight and small-sized batteries to achieve, for instance, in case of electric vehicles extended driving ranges without requiring tremendous additional load [3]. For this reason, alternatives to the classic intercalation chemistry are attracting great attention. With respect to the anode, these are so far mainly alloying [4] and conversion materials [5]–[7]. Both, however, suffer from intrinsic issues, including extensive volume variations and large voltage hystereses, as in particular in case of the former and the latter, respectively [4]–[7]. Recently, an additional class of anode materials has gained steadily increasing attention, combining these two lithium storage mechanisms in a single compound: conversion/alloying materials (CAMs) [8]. The key to the successful implementation of both mechanisms in one single compound is the incorporation of one element that can reversibly alloy with lithium, while the other one is reversibly reduced to the metallic state, accompanied by the (re )formation of, e.g., lithium oxide. Herein, a comprehensive overview on this material class will be provided, including an update on the reaction mechanism, the potential scale-up, and some first results on lithium-ion full-cells to outline their potential advantages and the remaining challenges. Moreover, the realization of a new reaction mechanism will be introduced that is based on an insertion-type mechanism, but greatly benefits of the findings for CAMs.
Yifan Chen
The University of Waikato (New Zealand)

Bio-inspired Self-regulated In-vivo Computation for Smart Cancer Detection

This paper highlights a novel knowledge-less bioinspired systemic targeting strategy (STS) for tumor homing in complex human vasculature. We propose that biological organisms at very small scale such as nanoparticles can perform deterministic tasks when they aggregate and migrate together. We aim to demonstrate through computational experiments that nanoparticles which can act as contrast agents, use tumor triggered bio-physical gradients collectively to move towards the tumor and deposit themselves on it to highlight the disease area hence increasing the diagnostic efficiency of different existing medical imaging techniques.
Viktoriia Babicheva
University of New Mexico (USA)

Transdimensional photonic lattices with multipole Mie-resonant nanoantennas

Planar optical elements with efficient light control at the nanoscale can be designed based on transdimensional photonic lattices that operate in the translational regime between two and three dimensions. Such transdimensional lattices include 3D-engineered nanoantennas supporting multipole Mie resonances and arranged in the 2D arrays to harness collective effects in the nanostructure. We analyze optical antennas made of van der Waals layered materials including highly conductive materials, the ones with high refractive index, and natural material with strong anisotropy and hyperbolic dispersion in the mid-infrared range. The antennas in the periodic array support multipole resonances including electric and magnetic dipoles and higher. The resonances are controlled by the size and shape of the nanoantennas as well as the period of the array. The antenna resonances allow for efficient control of light scattering, reflection, and propagation and can be utilized in metasurfaces and flat optical components.
Paul O'Brien
York University (Canada)

Novel Spectrally Selective Mirrors and Optical Cavities for Thermophotovoltaic Systems

Thermophotovoltaic systems convert radiant heat into electric power. Thermophotovoltiac systems have been developed for applications in co-generation systems, industrial waste-heat recovery, military devices, space exploration, and automobile exhaust systems. Recently, there has been increasing interest in the research community to explore thermophotovoltaic systems for their potential to convert concentrated solar radiation to electric power with high efficiencies. This initiative is supported by advances in thermophotovoltaic system components such as near-field emitters, spectrally selective filters, and novel optical cavities,that enable photon recycling with unprecedented performance. In this work the application of novel spectrally selective mirrors and prolate-shaped optical cavities as components of a thermophotovoltiac system are presented. These spectrally selective mirrors, designed in the form of one-dimensional photonic crystals, are highly transmissive to higher energy photons and reflect sub-band gap thermal radiation. The optical cavities can be designed to control the effective emissivity of a thermal emitter situated at their focal point. The integrated design of the spectrally selective mirrors and optical cavities in a thermophotovoltaic system allows for a high degree of photon recycling. This enables control of the operating temperature of the emitter and increased power conversion efficiencies. Thermophotovoltaic conversion efficiencies achieved using these novel components will be presented and the implications for different thermophotovoltaic applications will be discussed.
Jordi Arbiol
ICREA and ICN2 (Spain)

Nanowire networks at atomic scale: from growth mechanisms to local properties            

The lack of mirror symmetry in binary semiconductor compounds turns them into polar materials, where two opposite orientations of the same crystallographic direction are possible. Interestingly, their physical properties (e.g.: electronic or photonic) and morphological features (e.g.: shape, growth direction, etc.) also strongly depend on the polarity. It has been observed that nanoscale materials tend to grow with a specific polarity, which can eventually be reversed for very specific growth conditions. In addition, polar-directed growth affects the defect density and topology and might induce eventually the formation of undesirable polarity inversion domains in the nanostructure, which in turn will affect the photonic and electronic final device performance. Here, we present a detailed study on the polarity-driven growth mechanism at the nanoscale, highlighting suitable future possibilities of polarity engineering of semiconductor nanostructures from VLS vertical complex heterostructures to the newest selected area growth hybrid quantum networks. The present study has been extended over a wide range of semiconductor compounds, covering the most commonly synthesized III-V and II-VI nanowires and other free-standing nanostructures (tripods, tetrapods, belts and membranes). This systematic study allowed us to explore the parameters that may induce polarity-dependent and polarity-driven growth mechanisms, as well as the polarity related consequences on the physical properties of the nanostructures. The tools used to study the polar nanostructures at the atomic scale will be mainly based on aberration corrected scanning transmission electron microscopy and related spectroscopies. From the structural data obtain we will create 3D atomic models that will allow us to understand the growth mechanisms as well as be used as input data for the further electronic/photonic properties simulations.
Francois Perreault
Arizona State University (USA)

Novel nano-enabled membrane systems for sustainable water treatment and desalination

Nanotechnology can bring innovative solutions to the current limitations of water treatment technologies. These technological advances are enabled by the unique functional features of nanoscale materials, such as their high surface area, reactivity, intrinsic biocidal activity, high conductivity, or photo-enabled properties. In this seminar, the use of nanotechnology in membrane-based desalination processes will be discussed, with an emphasis on how to enhance membrane-based desalination processes by providing low-fouling surfaces, cost-efficient surface cleaning, or by enabling low-energy off-grid desalination. Material selection and design will be discussed based on a safe-by-design framework, with specific examples on how to tailor graphene-based materials for enhanced performance and reduced potential risks. Then, we will address how nanotechnology can be used to enable sustainable and off-grid water treatment, using solar energy to mitigate energy costs or reactive surfaces for fouling control. The broader implications of these different applications will be discussed in relationship with the current need for decentralized water treatment solutions for increased water security.
Bo Cui
University of Waterloo (Canada)

Nanofabrication on non-flat irregular surfaces

One challenge in nanofabrication is to pattern on non-flat surfaces, which is desired in many fields such as MEMS, bio-sensors, electronic devices, and optical devices. This is because the usual film coating method spin-coating can form a uniform film only on flat surfaces. The most straightforward method to pattern onto irregular surfaces is by using focused ion beam (FIB) milling, or ion/electron beam induced deposition. However, compared to electron beam lithography (EBL), FIB is a very slow and costly process. Various methods have been previously developed for performing EBL on irregular surfaces. One example is ice lithography, where water or organic ice is formed on a cold (non-flat) surface and acts as e-beam resist [1,2]. Similarly, frozen CO2 can also be used as an electron beam resist[3]. A third type of resist is plasma polymerized hexane to form a negative tone hydrocarbon resist. Lastly, evaporated resist can be coated onto any surfaces, and evaporated sterol resist has been demonstrated to enable nanofabrication on optical fibers and laser diode facet [4]. In this talk, I will show our work on evaporated polystyrene and polymer mono-layer brush that can also be utilized as e-beam resist for nanofabrication on irregular surfaces. It was found that low molecular weight polystyrene can be thermally evaporated for film coating, before its decomposition. After coating on AFM cantilever and optical fiber that are examples of irregular surface, we carried out EBL and demonstrated a high resolution of 30 nm [5]. For polymer brush resist, first, PMMA (contains 1.6% methacrylic acid that has the carboxyl group needed for grafting) is chosen and is grafted on irregular surfaces by thermal treatment which induces a chemical reaction of the carboxyl group with the hydroxyl group on substrate. Subsequently, nanostructures are patterned by electron beam lithography on this monolayer resist grafted on a non-flat surface [6]. It is well known that PMMA becomes negative tone at very high exposure doses, however, solvent developer will not work for negative tone PMMA because the brush on unexposed area is chemically bonded to the substrate and thus cannot be dissolved. Nevertheless, we demonstrated negative tone behavior for PMMA brush using thermal development [7]. Finally, it is found that polystyrene mono-layer brush can also be employed as both negative and positive tone resist, developed using thermal annealing or HF acid etch of the underneath pattern transfer layer, to allow nanofabrication on AFM cantilever [8].
Thomas Webster
Northeastern University (USA)

Two Decades of Commercializing Nanomedicine: Real Products Helping Real People

Nanotechnology has begun to revolutionize medicine in a number of ways, from improving disease detection to greater treatments. However, a particular growing concern to our healthcare system is the emergence of antibiotic-resistant bacteria. In fact, the Centers for Disease Control has predicted more deaths from antibiotic-resistant bacteria than all cancers combined by 2050. This talk will summarize efforts to utilize nanotechnology in reducing bacteria and antibiotic-resistant bacteria. Taking cues from nature, nanotextured surfaces have been shown to reduce bacteria attachment and growth without the use of antibiotics. Moreover, nanoparticles have been synthesized to attach to bacteria membranes, penetrate biofilms, and increase reactive oxygen species to kill bacteria without drugs. Lastly, chemistries that self assemble into nanofibers that can penetrate bacteria membranes to kill them. This talk will also cover FDA approved nanomedicine products being used today in humans. Overall, nanotechnology is showing promise to reduce bacteria infections without using antibiotics.
Sara Mahshid
McGill University (Canada)

Nanosurface platforms based on 2D and 3D nanostructures for optical/electrical sensing

Diagnostics of pathogenic and genetic disease (such as cancer) at the point of need, in particular at early-stage, requires dynamic manipulation and concentration of a small number of target molecules at individual single-molecule level. We focus on engineering of new approaches in biomedical devices via synergistically combining nanostructured materials with fluidic sample delivery systems to enhance the sensitivity and selectivity of the detection. Nanostructured materials boost the sensor resolution and show higher biochemical sensitivity and selectivity by significant amplification of the detection sites. We investigate 1) fabrication of novel nanostructured platforms based on 3D materials such as gold and 2D materials such as graphene and molybdenum disulfide, 2) integration of nanostructures with fluid sample delivery and biological assays (based on DNA/antibody) and 3) implementation of the device for detection of small molecules, pathogenic disease, and cancer genomics. In this regard, we address fundamental questions including: optimal interface of nanostructures with fluidic devices; target isolation, preparation and concentration in fluidic devices. We have successfully implemented the nanosurface fluidic devices for rapid and quantitative detection of bacteria such as Escherichia coli (E.coli) and Methicillin-resistant Staphylococcus aureus (MRSA), electrochemical detection of small molecules such as Dopamine and optical detection of extracellular vesicles (EVs).
Keith Morton
National Research Council Canada (Canada)

Vivid Plasmonic Colours on Nanostructured Plastic Substrates

We make vividly coloured polymer substrates by coating very thin gold films onto nanoimprinted gratings. Gold coatings on linear gratings give rise to a number of polarization dependent plasmonic colour change effects while periodic arrays of nanostructures yield fully isotropic colour effects. Additionally we use a mix and match mold mastering process that combines nanostructures together with larger microstructures, wide-scale artwork and lettering to enable single-step imprints of multi-length scale features directly into the optically clear plastic substrates. Thin conformal coatings of sputtered gold films everywhere on the as-fabricated structures results in a both uniform and striking plasmonic response, even over 5 cm x 5cm and larger areas. Applications range from brand packaging and document security devices to surface plasmon resonance bio-sensing
Peter Grutter
McGill University (Canada)

Measuring dynamics with atomic force microscopy

What limits the time resolution in force sensing? Conventional wisdom states that mechanical frequencies set a limit – miniaturization down to the nanoscale with the associated higher mechanical frequencies are thus the proposed solution. This is correct only for single shot measurements; many interesting ultra-fast phenomena can be time resolved by using suitable pump-probe techniques that only need relatively ‘slow’ detectors. The idea to observe ultrafast events combined with nanometer spatial resolution is of great interest and has been a primary pursuit of multiple research groups [1-3]. I will discuss how time resolution substantially faster than the cantilever period can be achieved. Using electrical pump-probe techniques some applications of ultrafast AFM ranging from measuring ion mobility in battery cathodes or the non-equilibrium barriers determining mobility of oxygen vacancies in SrTiO3 will be presented [4]. Optical pump-probe allows for much faster time resolution [3]. I will discuss the AFM methods necessary to measure the 1ps photocarrier decay time on low-T grown GaAs with nc-AFM [3]. These methods can also be used to spatially resolve the nonlinear optical response in MoSe2 and lithium niobate to femtosecond laser pump and probe pulses. We can directly measure a sample response on a 100 fs scale with 10nm spatial resolution! Time resolution is only limited by the thermal noise of the AFM detector and thus practically by the properties (i.e. laser pulse length) of our current pump-probe excitation system. In fact, the pump-probe autocorrelation function detected by AFM shows a measurable signal difference for delay times between the pump and probe as small as 25as! This opens the exciting possibility of measuring the nonlinear optical sample response with atomic scale spatial resolution using force detection. Finally, I will demonstrate how molecular vibrations can directly be measured using AFM [5]. We experimentally observed quantized electron transfer events at a single molecule–metallic electrode interface. An electron transfer event is measured as a peak in the bias voltage dependences of the resonance frequency and damping of the AFM cantilever. As a function of the experimentally controllable cantilever-molecular coupling strength, these peaks develop substructures due to quantized nuclear state transitions mediated by the molecular electron-vibron coupling. This allows us to quantitatively extract the electron-nuclear coupling strength, quantized nuclear state transitions, and single-mode phonon-mode reorganization energy upon heterogeneous electron transfer from purely experimental data. By scanning the AFM across a sample, the dependence of these parameters on the local molecular environment can be determined. In the language of physics these results can be quantitatively modelled by the transport of electrons between electrodes, suppressed by the Frank-Condon effect due to strong electron-phonon coupling (= molecular reorganization). In the language of chemistry our experiments are equivalent to a single molecule redox reaction, albeit in a 'strange' chemical environment (4K, UHV, no solvent). These experiments and their interpretation thus directly bridge single molecular charge transport and chemical rate theory (i.e. Marcus Theory). The realization of these ultrafast AFM techniques open the door to understanding ultrafast electron dynamics on surfaces, such as the new territory of atomic scale dynamics of polarization or charge transfer events in organic systems.
Antonio Di Bartolomeo
University of Salerno (Italy)

Electrical transport in two-dimensional PdSe2 and MoS2 nanosheets

We investigate the effect of pressure and gas species on the electrical transport in nanosheets of palladium diselenide (PdSe2) and molybdenum disulfide (MoS2), used as the channel of back-gate field-effect transistors. Air pressure can control the carrier polarity in PdSe2 devices and the dominant n-type conduction in a high vacuum can reversibly transform in p-type transport at atmospheric pressure. Structural defects facilitate gas adsorption, which widens the hysteresis of the transfer characteristics. We show that the hysteresis has a monotonic dependence on the gas adsorption energy on MoS2. We investigate the effect of a low-energy electron beam and find that a low fluence of a few tens e-/nm2 can significantly change the transistor characteristics. Finally, we measure a field emission current from both PdSe2 and MoS2 nanoflakes. The first experimental observation of the gate modulation of the field emission current from a MoS2 monolayer is reported. Such a finding gives the proof-of-concept of a field-effect transistor based on field emission and opens the way to new applications of 2D materials in vacuum electronics.
Diego Ghezzi
EPFL (Switzerland)

POLYRETINA: an injectable, wide-field, and photovoltaic epi-retinal prosthesis

POLYRETINA is a retinal prosthesis designed to restore a large field of view in blind patients. All the steps performed by our research group to translate this research activity into a clinical device will be presented.
Ron Naaman
Weizmann Institute (Israel)

Chiral Molecules and the Electron’s Spin- A Venue for New Magnetic in Bio Systems

Spin based properties, applications and devices are commonly related to magnetic materials. However, we found that chiral organic molecules act as spin filters for photoelectrons transmission, in electron transfer and in electron transport. The new effect, termed Chiral Induced Spin Selectivity (CISS)], was found, amongst others, in bio-molecules and in bio-systems . It has interesting implications on electron transfer in biological systems. Recently we observed that charge polarization in chiral molecules is accompanied by spin polarization. This finding sheds new light on enantio-specific interactions between chiral molecules and on the role of the electron’s spin in bio-chemical processes.
Mark Hersam
Northwestern University (USA)

Emerging Neuromorphic Devices Based on Two-Dimensional Materials

The exponentially improving performance of conventional digital computers has slowed in recent years due to the speed and power consumption issues that are largely attributable to the von Neumann bottleneck (i.e., the need to transfer data between spatially separate processor and memory blocks). In contrast, neuromorphic (i.e., brain-like) computing aims to circumvent the limitations of von Neumann architectures by spatially co-locating processor and memory blocks or even combining logic and data storage functions within the same device. In addition to reducing power consumption in conventional computing, neuromorphic devices also provide efficient architectures for emerging applications such as image recognition, machine learning, and artificial intelligence [1]. With this motivation in mind, this talk will explore the opportunities for two-dimensional materials in neuromorphic devices. For example, by combining p-type black phosphorus with n-type transition metal dichalcogenides, gate-tunable diodes have been realized, which show anti-ambipolar transfer characteristics that are suitable for artificial neurons, competitive learning, and spiking circuits [2]. In addition, by exploiting field-driven defect motion mediated by grain boundaries in monolayer MoS2, gate-tunable memristive phenomena have been achieved, which enable hybrid memristor/transistor devices (i.e., "memtransistors") that concurrently provide logic and data storage functions [3]. The planar geometry of memtransistors further allows multiple contacts to the channel region that mimic the behavior of biological neurons such as heterosynaptic responses [4]. Overall, this work introduces new foundational circuit elements for neuromorphic computing in addition to providing alternative pathways for studying and utilizing the unique charge transport characteristics of two-dimensional materials [5].
Suzanne Smith
University of Pretoria (South Africa)

Printed functionality for point-of-need diagnostics in resource-limited settings

The work presented details micro and nano technologies for point-of-need health and environmental diagnostics in resource-limited settings, specifically in Southern Africa. The challenges faced in these settings have limited the effectiveness of point-of-need diagnostic solutions. By combining the growing fields of paper-based diagnostics and printed electronics, the extensive possibilities of printed functionality can be utilized to develop novel, low-cost solutions for improving the quality of life of those who need it most. Point-of-care diagnostic testing in resource-limited settings – including many of the clinics found across Southern Africa – remains a challenge. Current constraints, such as cost, infrastructure and trained staff have limited the effective implementation of diagnostics at the point-of-care. The primary technical challenges lie in the accurate readout and communication of results from clinics, hospitals and laboratories, and the maintenance of equipment [1]. In recent years, there has been a drive to develop low-cost, innovative point-of-care diagnostics to reach populations such as these where the burden of disease is greatest and resources are fewest. These developments have been guided by the WHO through formalization of the ASSURED criteria, to which these diagnostics should conform if they are to be successful in resource-limited settings. More recently, the REASSURED principles have been defined as an update to the ASSURED criteria to incorporate newer technologies and important factors, including Real-time connectivity, Ease of specimen collection, and Environmental friendliness [2]. Although these guidelines were developed specifically for disease diagnostics, a similar approach can be applied to point-of-need solutions for environmental diagnostics, which are of increasing importance in terms of water quality in resource-limited settings. For both health and environmental point-of-need diagnostics, paper-based solutions have developed rapidly in recent years [3]. Paper is well suited to meeting many of the REASSURED aspects, as it is low-cost, disposable and provides automated fluidic handling and visual readout (e.g. typical lateral flow test (LFT) formats, such as pregnancy tests). Although these devices can be effective, they are prone to user error and lack the accuracy and quantitative capabilities afforded by external instrumentation. At the same time, automated and sophisticated equipment can introduce a number of challenges in resource-limited settings, including the need for an electricity supply, regular maintenance and user training. Limited network and maintenance infrastructure, intermittent power, and issues with theft in resource-limited settings create challenges in the successful implementation of instrumented solutions. This highlights the need for various functional components to be integrated into low-cost, automated and maintenance-free or low-maintenance systems. By combining the emerging fields of printed electronics with paper-based diagnostics, unique and integrated printed functionality solutions can be realized, where components and systems are printed directly onto paper and other low-cost, flexible substrates. The aim is to develop intelligent systems that are packaged into low-cost and maintenance-free solutions, focusing on point-of-need health and environmental diagnostics, and with high impact in developing settings. A number of locally developed components and solutions have been developed towards this goal, including fully printed and hybrid printed solutions for fluidics, sensing, readout and wireless communication [4]. In addition, the long-term goal is to enable distributed manufacturing, utilizing cost-effective methods that could be deployed at various sites for local manufacturing in Southern Africa at the point-of-need. The scalability of these technologies using locally available processes has been initially explored towards the goal of distributed manufacturing for developing local solutions to solve local challenges. The presented work illustrates how multidisciplinary approaches need to be leveraged to develop novel and high impact solutions. South African-based research affords the opportunity to understand first-hand the challenges faced and the potential to make a difference where it matters most. Printed functionality provides a powerful platform on which to develop a multitude of solutions for different applications, with emphasis on developing continents such as Africa.
Omar Tantawi
Purdue University (USA)

Evolution of Smartphones Metal Content with its Fast-Improving Functionalities

Smartphones, one of the most common consumer electronic devices, are an essential part of daily activities in modern society. Smartphones provide faster communication, easier access to information and many other important services. However, with a compressed product life cycle and growing consumer demand, a significant number of smartphones reach End-of-Life (EoL) annually. At the same time, due to many special physical properties, rare earth, critical and other important metals are very important for the manufacturing of smartphones. Hence, from various economic, resources availability and environmental perspectives, it is crucial to understand how metal content of different smartphones generations change over time. To this end, a high production cell phone series, produced between 2010 and 2015 were considered in the scope of this study. The devices were disassembled, sorted into different components and size reduced. All smartphones components, except the batteries, were then digested using microwave assisted acid digestion (MWAD). Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) was applied to detect and quantify 64 elements. Preliminary results indicate that up to 43% of smartphones printed circuit boards by weight are important recyclable metals (3 rare earth, 17 critical, 3 platinum group and 10 other important metals). The high concentration and value of these reclaimable metals suggests that consumer electronics EoL management strategies should focus on recovering and recycling important metals, which eventually will also reduce the total environmental impact associated with these devices. Environmental impacts include freshwater consumption and emissions of climate changing gases.
John T.W. Yeow
University of Waterloo (Canada)

A Dual-Frequency Capacitive Micromachined Ultrasonic Transducer (CMUT) for Vapor Detection

This study reports a novel single-chip dual-frequency (10 MHz/14 MHz) CMUT sensor that exhibits promising capabilities of vapor detection and discrimination. The CMUT is fabricated by the nitride-to-oxide wafer bonding process. Graphene oxide nanosheets are used to functionalize the device and make it sensitive to water vapors. Characterization on the electrical impedance reveals that the two resonances of the device can be easily identified with a single frequency sweep. The sensing performance of the device is analyzed by monitoring its resonance shifts as the relative humidity changes. High sensitivity and decent repeatability have been achieved. More importantly, the sensor is able to generate two independent frequency responses due to its multi-resonance feature, showing great potential for discrimination of multiple chemical vapors.
Christine Demore
Sunnybrook Research Institute (Canada)

Bio-derived Gas Vesicle Nano Structures for Ultrasound Contrast Imaging

Gas vesicles, protein-shelled nanoparticles produced by Bacteria and Archea can be used as ultrasound contrast agents. Short circulation times because of rapid uptake of the gas vesicles by the reticuloendothelial system (part of the immune system) limits their use to measure blood perfusion in tumours for pre-clinical oncology studies, a common application for ultrasound contrast imaging. In this paper we investigate approaches to circumvent the uptake of the gas vesicles and allow the nano contrast agents to circulate longer within a tumour model. We observe and measure ultrasound contrast signal amplitude in a mouse hind limb tumour using the non-linear contrast mode on a 21 MHz microultrasound imaging system. With no disruption of the reticular endothelial system, the contrast enhancement on reperfusion is 14% of the peak enhancement signal. Disruption of the reticuloendothelial system with an injection of gadolinium, Intralipid or previous injection of gas vesicles improves the contrast signal on reperfusion to 32%, 56%, and 38%. Shielding the gas vesicles from the reticuloendothelial system by coating with polyethylene glycol chains increases the contrast signal on reperfusion to >45% of peak signal for 5 kDa and 10 kDa long chains. In conclusion, circumventing the reticularendothelial system improved recirculation of the gas vesicle contrast agents within tumours.
Jiming Bao
University of Houston (USA)

Photoacoustic laser streaming: principle and applications

Transforming a laser beam into a liquid flow has been a challenge both scientifically and technologically. We report the discovery of a new optofluidic principle and demonstrate the generation of steady-state water flow by a pulsed laser beam through a glass window. We first fill a glass cuvette with an aqueous solution of Au nanoparticles and a nanoparticle-decorated cavity is self-fabricated on the glass by nanoparticle-assisted laser etching. Then, a flow will emerge from the focused laser spot on the window. The principle of this light-driven flow is photoacoustic streaming by combing the photoacoustics effect of decorated gold nanoparticles and acoustic streaming. We fabricate the Au-implanted plasmonic quartz plate as the laser-driving micropump. The Au-implanted optical fiber is also prepared to control the liquid flow in three dimensions accurately. Various solvents and acoustic wave distribution are investigated in the photoacoustic streaming to reveal the relationship between the pulse laser, acoustic wave, solvents type, and liquid flow. The combination of microchannels and photoacoustic streaming can greatly promote its fundamental research and applications in biological and medical science, such as acoustic surgery and drug delivery.
Neha Tiwari
NIIT University (India)

Multi Layered Hybrid Quantum Dot LEDs:  A stride towards cleaner greener and safe lighting Solution for Display Devices

Solid State lighting technology is making huge strides in the lighting and display industries with their unparalleled energy efficiency , high throughput, high longevity and ecofriendly attributes. Though LEDs are inherently monochromatic in nature researchers have come up with the strategies to have white light emissions from them. These strategies can be broadly classified into three different routes which starts from blending tricolor phosphors and exciting them by UVLEDs or combing a yellow phosphor with blue light emitting diode or combing a UV excited single phase white light emitting phosphor. The proliferation of phosphor coated white light emitting diodes in day to day applications has raised a concern of Blue light Hazard. Blue Light Hazard is defined as the acute photochemical damage to the retina of eye owing to the staring at an intense light source. The intense radiation absorbed by the retina eventually leads to a series of photochemical reactions which can cause retinal inflammation, cell death or white lesions. Research conducted over last few decades in the medical academia has connected these phototoxic responses to short wavelength radiations in the range of 400-500 nm with a peak around 440 nm. This has started prompting speculation about safety of blue rich light sources used in general illumination specially in display applications. Researchers are now investigating Semiconducting nanostructures like Quantum Dots for the development of highly efficient and tunable light emitting devices for futuristic display applications. The major bottleneck in the commercial viability of these QLEDs for display applications is their reliance on the highly toxic and environmentally restricted Cd. As a result, efforts are now beginning to shift towards non Cd device structures. This paper summarizes a novel approach for design and fabrication of Cd free, hybrid, bright warm white Light Emitting Diodes using conducting polymers and Semiconducting nanoparticles. These devices utilize vertically aligned multi layer superstrate architecture of self – organized semiconducting nanoparticle layers and polymeric layers. These all solution processed hybrid devices revealed diode like rectifying behavior with a substantially low turn on voltage and broad band white light emission. The detailed study of the emission spectra of the as prepared electroluminescent devices also revealed that green spectral component has the major contribution which has imparted warmth to the white light emission. Moreover, since human eyes are highly sensitive to green color, the as prepared hybrid LEDs being green rich are capable of giving a sense of high brightness without actually increasing the brightness level of the display thus confirming a very promising candidature for futuristic flexible low power display applications.
Feng Xiong
University of Pittsburgh (USA)

Electrochemical Dynamic Synapses with Programmable Spatio-Temporal Dynamics

Neuromorphic computing has recently garnered significant research interest due to its potential to significantly improve the computing performance at a much better energy efficiency. However, it has been difficult to mimic the biological neural network with existing CMOS electronics due to its digital nature and the lack of temporal dynamics. In this work, we report an electrochemical dynamic synapse based on two-dimensional (2D) materials. The synaptic weight (channel conductance) of these dynamic synapses can be tuned via both the long-term doping effect from electrochemical intercalation and the short-term doping effect from ionic gating – demonstrating programmable spatio-temporal dynamics, which is essential for implementing spiking neural networks (SNNs). These 2D synapses also demonstrate other promising traits such as high-precision (~250 states) switching, low programming power (~500 fJ per switching), and good scalability. This work can lead to low-power hardware implementation of SNNs.
Chang-Ki Baek

Highly Sensitive Silicon-Based Electrochemical Sensor for On-Site Fluoride Ion Monitoring

Polycrystalline (poly) lanthanum fluoride (LaF3) Electrolyte-Insulator-Semiconductor (EIS) sensor, as one of silicon based electrochemical sensors, could be well suitable for promising on-site fluoride ion (F-) sensor platforms due to small size, fast response and simple fabrication method. The key to successful implementation is to optimize poly LaF3 film and measurement environments. Substrate temperature effects of thermal evaporation on the structural and sensing characteristics of poly LaF3 EIS sensor are investigated at 25 ℃, 150 ℃, 300 ℃ and 500 ℃. Sensors fabricated at 500 ℃ show excellent sensing performances such as high sensitivity (47.9 mV/pF) and low limit of detection (3.02 ppb) due to enhanced structural properties. In addition, the 100-times diluted total ionic strength adjustment buffer solution (TISAB) provides better measurement conditions for higher sensitivity (50.2 mV/pF), lower limit of detection (1.4 ppb), smaller hysteresis voltage (0.9 mV) and lower drift rate (0.60 mV/hr). As a result, when compared to commercial fluoride ion selective electrode, the poly LaF3 EIS sensors with 100-times diluted TISAB show a smaller difference (6.1 %) in F- analysis of tap water.
Yang Zhao
University of Illinois Urbana Champaign, USA

Nanoscopic imaging of molecular conformation under physiological conditions

Many biological processes are associated with conformational changes of macromolecules such as enzymes, proteins, and DNAs. Currently, these dynamic processes can be observed indirectly through techniques such as optical tweezers, förster resonance energy transfer (FRET), and optical beacon or directly with ultra-high frequency atomic force microscopy (AFM). While the last example points to the promises using AFM to directly visualize the molecules of interest, it only limits to certain processes where the speed is slower or comparable with the mechanical scanning of AFM. In this talk, I will discuss a new approach to visualize the conformational changes of biomolecules in situ. We constructed the technique based on the force exerted by polarized light on biomolecules. To enhance the light-molecular interactions, we created a plasmonic cavity formed between the plasmonic AFM tip and a plasmonic nano-aperture. We have shown that the plasmonic nano-aperture can exert differential optical forces down to piconewton ranges on chiral nanostructures when illuminated with circularly polarized light of opposite handedness. Here, instead of a nano-structured AFM tip, we functionalize DNA molecules on the plasmonic AFM tip with a controlled density. We investigate both single-strand and double-strand DNAs at 20-base pair length with various densities. We are able to measure the difference in optical forces with a sensitivity of ~2.1pN/100uW/um2. This sensitivity is associated with the optical forces exerted on single-strand and double-strand DNA molecules embedded between the plasmonic cavity. In addition, by introducing a denaturing agent to the solution, we observed in-situ dynamic conformational changes of the double-strand DNA molecules, directly measured with the optical force microscopy technique.