Surgical Instruments based on flexible micro-electronics

This dissertation explores strategies to create micro-scale tools with integrated electronic and mechanical functionalities. Recently developed approaches to control the shape of flexible micro-structures are employed to fabricate micro-electronic instruments that embed components for sensing and actuation, aiming to expand the toolkit of minimally invasive surgery. This thesis proposes two distinct types of devices that might expand the boundaries of modern surgical interventions and enable new bio-medical applications. First, an electronically integrated micro-catheter is developed. Electronic components for sensing and actuation are embedded into the catheter wall through an alternative fabrication paradigm that takes advantage of a self-rolling polymeric thin-film system. With a diameter of only 0.1 mm, the catheter is capable of delivering fluids in a highly targeted fashion, comprises actuated opposing digits for the efficient manipulation of microscopic objects, and a magnetic sensor for navigation. Employing a specially conceived approach for position tracking, navigation with a high resolution below 0.1 mm is achieved. The fundamental functionalities and mechanical properties of this instrument are evaluated in artificial model environments and ex vivo tissues. The second development explores reshapeable micro-electronic devices. These systems integrate conductive polymer actuators and strain or magnetic sensors to adjust their shape through feedback-driven closed loop control and mechanically interact with their environment. Due to their inherent flexibility and integrated sensory capabilities, these devices are well suited to interface with and manipulate sensitive biological tissues, as demonstrated with an ex vivo nerve bundle, and may facilitate new interventions in neural surgery.:List of Abbreviations 1 Introduction 1.1 Motivation 1.2 Objectives and structure of this dissertation 2 Background 2.1 Tools for minimally invasive surgery 2.1.1 Catheters 2.1.2 Tools for robotic micro-surgery 2.1.3 Flexible electronics for smart surgical tools 2.2 Platforms for shapeable electronics 2.2.1 Shapeable polymer composites 2.2.2 Shapeable electronics 2.2.3 Soft actuators and manipulators 2.3 Sensors for position and shape feedback 2.3.1 Magnetic sensors for position and orientation measurements 2.3.2 Strain gauge sensors 3 Materials and Methods 3.1 Materials for shapeable electronics 3.1.1 Metal-organic sacrificial layer 3.1.2 Polyimide as reinforcing material 3.1.3 Swelling hydrogel for self assembly 3.1.4 Polypyrrole for flexible micro actuators 3.2 Device fabrication techniques 3.2.1 Photolithography 3.2.2 Electron beam deposition 3.2.3 Sputter deposition 3.2.4 Atomic layer deposition 3.2.5 Electro-polymerization of polypyrrole 3.3 Device characterization techniques 3.3.1 Kerr magnetometry 3.3.2 Electro-magnetic characterization of sensors 3.3.3 Electro-chemical analysis of polypyrrole 3.3.4 Preparation of model environments and materials 3.4 Sensor signal evaluation and processing 3.4.1 Signal processing 3.4.2 Cross correlation for phase analysis 3.4.3 PID feedback control 4 Electronically Integrated Self Assembled Micro Catheters 4.1 Design and Fabrication 4.1.1 Fabrication and self assembly 4.1.2 Features and design considerations 4.1.3 Electronic and fluidic connections 4.2 Integrated features and functionalities 4.2.1 Fluidic transport 4.2.2 Bending stability 4.2.3 Actuated micro manipulator 4.3 Magnetic position tracking 4.3.1 Integrated magnetic sensor 4.3.2 Position control with sensor feedback 4.3.3 Introduction of magnetic phase encoded tracking 4.3.4 Experimental realization 4.3.5 Simultaneous magnetic and ultrasound tracking 4.3.6 Discussion, limitations, and perspectives 5 Reshapeable Micro Electronic Devices 5.1 Design and fabrication 5.1.1 Estimation of optimal fabrication parameters 5.1.2 Device Fabrication 5.1.3 Control electronics and software 5.2 Performance of Actuators 5.2.1 Blocking force, speed, and durability 5.2.2 Curvature 5.3 Orientation control with magnetic sensors 5.3.1 Magnetic sensors on actuated device 5.3.2 Reference magnetic field 5.3.3 Feedback control 5.4 Shape control with integrated strain sensors 5.4.1 Strain gauge curvature sensors 5.4.2 Feedback control 5.4.3 Obstacle detection 5.5 Heterogenous integration with active electronics 5.5.1 Fabrication and properties of active matrices 5.5.2 Fabrication and operation of PPy actuators 5.5.3 Site selective actuation 6 Discussion and Outlook 6.1 Integrated self assembled catheters 6.1.1 Outlook 6.2 Reshapeable micro electronic devices 6.2.1 Outlook 7 Conclusion Appendix A1 Processing parameters for polymer stack layers A2 Derivation of magnetic phase profile in 3D Bibliography List of Figures and Tables Acknowledgements Theses List of Publication

Optymalizacja procesów transferu energii i transferu elektronowego w biofotowoltaicznych nanourządzeniach zawierających fotosystem I oraz cytochrom c553 z ekstremofilnego krasnorostu Cyanidioschyzon merolae

One of the biggest challenges of modern-day solar technologies is to develop carbon-neutral, efficient and sustainable systems for solar energy conversion into electricity and fuel. Over the last two decades there has been a growing impact of ‘green’ solar conversion technologies based on the natural solar energy converters, such as the robust extremophilic photosystem I (PSI) and its associated protein cofactors. The main bottleneck of the currently available biophotovoltaic and solar-to-fuel technologies is the low power conversion efficiency of the available devices due to wasteful charge recombination reactions at the interfaces between the working modules, as well as instability of the organic and inorganic components. This thesis describes the development of three novel approaches to improve energy and electron transfer in PSI-based biophotoelectrodes and plasmonic nanostructures: (1) construction of all-solid-state mediatorless biophotovoltaic devices incorporating p-doped silicon substrate, extremophilic robust PSI complex and its associated light harvesting antenna (PSI-LHCI) in conjunction with its natural electron donor cytochrome c553 (cyt c553) from a red microalga Cyanidioschyzon merolae and (2), biofunctionalization of the silver nanowires (AgNWs) with a highly organised architecture of the cyt c553/PSI-LHCI assembly for the significant improvement of absorption cross-section of the C. merolae PSI-LHCI complex due to plasmonic interactions between the distinct subpool of chlorophylls (Chls) and AgNWs nanoconstructs. The third (3) approach was based on development of the photo-driven in vitro hydrogen production system following hybridisation of the robust extremophilic PSI-LHCI complex with the novel and established proton reducing catalysts (PRC). The last approach has led to generation of molecular hydrogen with TOF of 521 mol H2 (mol PSI)-1 min-1 and 729 mol H2 (mol PSI)-1 min-1 for the hybrid systems of PSI-LHCI with cobaloxime and the DuBois-type mononuclear nickel proton reduction catalysts, respectively. The TOF values for biophotocatalytic H2 production obtained in this study were 3-fold and 16.6-fold higher than those published for cyanobacterial PSI/PRC hybrid systems employing cobaloxime and a similar Ni mononuclear PRC, respectively. Construction of all-solid-state mediatorless PSI-based nanodevices was facilitated by biopassivation of the p-doped Si substrate with His6-tagged cyt c553, as evidenced by significant lowering of the inherent dark saturation current (J0), a well-known semiconductor surface recombination parameter. Five distinct variants of cyt c553 were obtained by genetically engineering the specific linker peptides of 0-19 amino acids in length between the cyt c553 holoprotein and a C-terminal His6-tag, the latter being the affinity ‘anchor’ used for specific immobilisation of this protein on the semiconductor surface. The calculated 2D Gibbs free energy maps for all the five cyt c553 variants and the protein lacking any peptide linker showed a much higher number of thermodynamically feasible conformations for the cyt c variants containing longer linker peptides upon their specific immobilisation on the Si surface. The bioinformatic calculations were verified by constructing the respective cyt c553/Si bioelectrodes and measuring their dark current-voltage (J-V) characteristics to determine the degree of p-doped Si surface passivation, measured by minimisation of the J0 recombination parameter. The combined bioinformatic and J-V analyses indicated that the cyt c553 variants with longer linker peptides, up to 19AA in length, allowed for more structural flexibility of immobilised cyt c553 in terms of both, orientation and distance of the haem group with respect to the Si surface, resulting in efficient biopassivation of this semiconductor substrate. This molecular approach has allowed for the developing of an alternative, cheap and facile route for significant reduction of the inherent minority charge recombination at the p-doped Si surface. To improve direct electron transfer within all-solid state PSI-based nanodevices, the specific His6-tagged cyt c553 variants, generated in this study, were attached to the Ni-NTA-functionalised p-doped Si surface prior to incorporation of the PSI-LHCI photoactive layer. Such nanoarchitecture resulted in an open-circuit potential increment of 333 μV for the specific PSI-LHCI/cyt c553/Si nanodevice compared to the control device devoid of cyt c553. Moreover, the all-solid state mediatorless PSI-LHCI-based devices produced photocurrents in the range of 104-234 μA/cm2 when a bias of -0.25 V was applied, demonstrating one of the highest photocurrents for this type of solid-state devices reported to date. The power conversion efficiency of the PSI-LHCI/p-doped Si devices was 20-fold higher when 19AA variant of cyt c553 was incorporated as the biological conductive interface between the PSI-LHCI photoactive module and the substrate, demonstrating the significant role of this cyt variant for improving direct electron transfer within the PSI-based all-solid-state mediatorless biophotovoltaic device. In a complementary line of research, it was demonstrated that the highly controlled assembly of C. merolae PSI-LHCI complex on plasmon-generating AgNWs substantially improved the optical functionality of such a novel biohybrid nanostructure. By comparing fluorescence intensities measured for PSI-LHCI complex randomly oriented on AgNWs and the results obtained for the PSI-LHCI/cyt c553 bioconjugate with AgNWs it was concluded that the specific binding of PSI-LHCI complex with the defined uniform orientation yields selective excitation of a pool of Chls that are otherwise almost non-absorbing. This is remarkable, as this work shows for the first time that plasmonic excitations in metallic nanostructures not only can be used to enhance native absorption of photosynthetic pigments, but also, by employing cyt c553 as the conjugation cofactor, to activate the specific Chl pools as the absorbing sites, only when the uniform and well-defined orientation of PSI-LHCI complex with respect to plasmonic nanostructures is achieved. This innovative approach paves the way for the next generation solar energy-converting technologies to outperform the reported-to-date biohybrid devices with respect to power conversion efficiency.Jednym z głównych wyzwań technologicznych jest opracowanie wydajnych i odnawialnych systemów konwersji energii słonecznej w elektryczność i paliwo, stosując zerowy bilans emisji związków węgla. W ciągu ostatnich dwóch dekad nastąpił znaczący postęp w zastosowaniu “zielonych” technologii biofotowoltaicznych, opartych na naturalnych białkach absorbujących energię słoneczną, takich jak fotosystem I (PSI) wraz ze związanymi z nim kompleksami antenowymi i kofaktorami transportu elektronowego. Głównym ograniczeniem obecnych urządzeń fotowoltaicznych jest ich niska wydajność kwantowa, związana z procesami rekombinacji ładunku w interfejsach pomiędzy modułami tych urządzeń, jak również ograniczona stabilność zastosowanych jak dotąd biologicznych i syntetycznych komponentów. W ramach niniejszej rozprawy doktorskiej opracowano nowatorską technologię, polegającą na zastosowaniu wysokostabilnego PSI oraz naturalnego donora elektronów dla tego kompleksu, cytochromu c553 (cyt c553), wyizolowanych z ekstremofilnego krasnorostu Cyanidioschyzon merolae, do konstrukcji trzech typów nanourządzeń biofotowoltaicznych: (1), biofotoogniw w stałej konfiguracji (ang., all-solid-state), zawierających domieszkowany pozytywnie półprzewodnikowy substrat krzemowy (ang., p-doped Si, p-Si) wraz z warstwami fotoaktywnego kompleksu PSI i cyt c553; (2), plazmonowych srebrnych bionanodrutów (AgNWs), funkcjonalizowanych wysokouporządkowaną nanoarchitekturą monowarstw PSI i cyt c553, oraz (3), systemu fotokatalitycznej produkcji wodoru cząsteczkowego in vitro z zastosowaniem kompleksów hybrydowych PSI wraz z syntetycznymi katalizatorami redukcji protonów (ang., proton reducing catalysts, PRC). W przypadku ostatniego z powyższych systemów, optymalizacja biofotokatalitycznej produkcji wodoru cząsteczkowego z zastosowaniem systemów hybrydowych z PSI i PRC, opartych na kobaloksymie i niklowym katalizatorze mononuklearnym typu DuBois, precypitowanych na powierzchni PSI w roztworze wodnym, pozwoliła na osiągnięcie aktywności wydzielania wodoru odpowiednio, 521 moli H2 (mol PSI)-1 min-1 oraz 729 moli H2 (mol PSI)-1 min-1, przewyższając tym samym 3-17-krotnie aktywność wydzielania wodoru w podobnych systemach biohybrydowych i warunkach pomiarowych. Poraz pierwszy zastosowano cyt c553 z C-terminalną metką His6 do biopasywacji półprzewodnikowego substratu p-Si, mierzonej minimalizacją parametru rekombinacji powierzchniowej J0. Poprzez inżynierię genetyczną sklonowano i wyrażono w E. coli 5 różnych wariantów cyt c553, z których 4 zawierały w swej strukturze sekwencje peptydowe o długości 5-19 aminokwasów (AA), aby zbadać ich wpływ na procesy rekombinacji ładunku w obrębie elektrody krzemowej. Peptydy te zostały wstawione pomiędzy holobiałkiem a metką His6, którą zastosowano do unieruchomienia każdego z wariantów cyt c553 na powierzchni elektrody. Obliczenie energii swobodnej Gibbsa pozwoliło na utworzenie konformacyjnych map 2D dla każdego z wariantów, w których pokazano, iż warianty z semi-helikalnym peptydem 19AA przyjmują znacząco większą liczbę termodynamicznie możliwych konformacji na powierzchni elektrody pod względem odległości i kąta nachylenia grupy hemowej w stosunku do powierzchni elektrody. Bioinformatyczna analiza została potwierdzona poprzez ciemniową charakterystykę prądowo-napięciową (J-V) utworzonych odpowiednio bioelektrod krzemowo-cytochromowych. Stwierdzono, że warianty cyt c553 z dłuższymi peptydami pomiędzy metką His6 a holobiałkiem efektywnie minimalizują prądy ciemniowe krzemowego substratu, najprawdopodobniej dzięki istnieniu większej ilości termodynamicznie zoptymalizowanych konformacji cytochromu, pozwalających na minimalizację rekombinacji ładunku powierzchniowego substratu. Funkcjonalizacja elektrody p-Si wariantem cyt c553, charakteryzującym się największym stopniem swobody orientacji grupy hemowej w stosunku powierzchni elektrody krzemowej, pozwoliła na efektywną biopasywację tego półprzewodnikowego substratu poprzez minimalizację parametru J0, co z kolei pozwoliło na zwiększenie parametru Voc o 333 μV w biofotoogniwach typu PSI/cyt c553/p-Si, w porównaniu do kontroli zawierającej jedynie PSI/p-Si. Uzyskano fotoprądy w stałych biofotoogniwach PSI/p-Si w zakresie 104-234 μA cm-2 (przy nadpotencjale -0.25 V), co należy do jednych z najwyższych wartości fotoprądów wygenerowanych przez stałe biofotoogniwa z PSI, w podobnych warunkach pomiarowych. Jednocześnie wydajność konwersji energii słonecznej w fotoogniwach typu PSI-LHCI/cyt c553/p-Si była 20-krotnie wyższa, w obecności wariantu cyt c553 19AA, zastosowanego w tych urządzeniech jako biologiczna warstwa biopasywacji substratu krzemowego oraz warstwa kondukcyjna pomiędzy substratem a PSI. Tym samym wykazano, że ów wariant może być zastosowany w urządzeniach biofotowoltaicznych do zwiększenia transferu elektronowego pomiędzy substratem a PSI. W równoległym i komplementarnym kierunku badań, zastosowanie równomiernej i specyficznie ukierunkowanej nanoarchitektury fotoaktywnej warstwy PSI na plazmonowych nanostrukturach metalicznych AgNWs, sfunkcjonalizowanych uprzednio cyt c553, pozwoliło na znaczące zwiększenie efektywnej absorpcji PSI, w zakresie spektralnym, w którym PSI jest nieaktywny in vivo, poprzez aktywację specyficznej puli tzw. czerwonych cząsteczek chlorofilu w obrębie fluoroforów PSI. Tym samym pokazano, że oddziaływania plazmonowe mogą być efektywnie zastosowane nie tylko do zwiększenia całkowitej absorpcji fotoaktywnych kompleksów białkowych, ale również do aktywacji spektralnej specyficznych pigmentów, wyłącznie w obrębie wysokouporządkowanej i zorientowanej nanoarchitektury tych fotokompleksów na nanokonstruktach plazmonowych. Powyższe nowatorskie podejście badawcze może być w przyszłości zastosowane do konstrukcji nowej generacji urządzeń biofotowoltaicznych o zwiększonej wydajności konwersji energii słonecznej

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)

Growth and application of wafer-scale hexagonal boron nitride

Hexagonal boron nitride (hBN) is a 2D material that has attracted considerable attention in recent years. As a layered material and a wide bandgap semiconductor, hBN has been used in different applications, ranging from deep UV emitters to gate dielectric in field effect devices based on 2D materials. hBN has also been used as a substrate for growing III-V semiconductors via van der Waals epitaxy, for the development of flexible optoelectronic devices. More recently, single photon emission (SPE) from defects in hBN have generated new interests in this material for quantum computing related applications. For many of the applications, hBN is obtained through facile exfoliation of atomically thin flakes, from commercially available bulk crystals. The lateral dimensions of flakes is less than a few tens of um. This severely limits scale-up and large-area applications of hBN. Therefore, this thesis explores wafer-scale growth of hBN, using metal organic vapour phase epitaxy (MOVPE). In this study, hBN was deposited over commercially available 2" sapphire substrates. Triethylboron (TEB) and ammonia were used as B and N growth precursors, respectively. Due to severe parasitic reactions between the precursors, a flow-modulation scheme for precursor injection was adopted. A comprehensive characterization of the deposited films was undertaken using different experimental techniques. hBN films deposited on sapphire had a wrinkled surface morphology, which was studied using AFM. TEM was used to evaluate the orientation of the induvial hBN crystal planes with respect to the substrate. Raman spectroscopy provided a quick and nondestructive method for confirming hBN deposition and analyzing residual strain in the deposited films. With the help of XPS, carbon was identified as the dominant impurity. The optical properties of MOVPE-hBN were studied using photo/cathodo-luminescence spectroscopies. Due to high carbon incorporation, no bandedge luminescence was recorded from MOVPE-hBN. Instead, the emission spectra was dominated by impurity related sub-bandgap luminescence between 300-350 nm, and between 570-750 nm (rPL), with a strong dependence on TEB flux and carbon incorporation. SPEs were reported for the first time from MOVPE-grown hBN films. SPEs were only observed in those hBN films, which had the lowest carbon doping and negligible rPL. Many of the SPEs found in MOVPE-hBN were photo-stable, had a narrow spectral distribution of the emission wavelength and emitter lifetimes of the order of few nanoseconds, consistent with previous reports. hBN films grown on sapphire were transferred onto substrates containing silver and gold nanoparticles (NPs). Being atomically thin and flexible, hBN was able to effectively wrap around Ag nanoparticles to form an impermeable barrier, which was found to be effective in preventing oxidation of Ag NPs even at elevated temperatures. Consequently, the plasmonic activity of the hBN covered Ag NPs remained preserved and was demonstrated through surface enhanced Raman spectroscopy. In a different study, AlN was grown on wafer-scale hBN (and on sapphire for comparison) using MOVPE, under different conditions. Detailed structural and morphological analysis of the AlN films were also undertaken. Using a modified, multi-step high temperature growth process, planar AlN films, with improved crystallinity were grown on hBN. The AlN films easily delaminated from the sapphire, due to underlying hBN and showed a relaxation in compressive strain. Overall, this work provides valuable insights into wafer-scale growth of hBN using MOVPE. The crystallinity, morphology and luminescent properties of MOVPE-hBN films were studied in detail and found to be critically effected by the choice of growth parameters. The versatility of large-area hBN films has also been showcased. Different applications of the MOVPE-hBN films, ranging from passivation of Ag NPs, to SPEs and van der Waals epitaxy of AlN films were demonstrated

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Ground and excited state electron transfer dynamics

The focus of this work is the investigation of the factors controlling electron transfer in molecular electronic systems, in particular those affecting electron transfer to and from electronically excited states. To achieve this, a number of mono- and trimetallic osmium and ruthenium complexes were synthesised and characterised. Monolayers of an osmium polypyridyl complex bound to a platinum microelectrode via a ¿rara-l,2-bis-(4-pyridyl)ethylene bridge were formed to probe ground state electron transfer dynamics. This is compared to the rate of photoinduced oxidative electron transfer quenching which occurs in a trimetallic osmium complex where the metal centres are linked by the same bridging ligand. The rate constant for this quenching is 1.3 xlO8 s '1, compared to 2 x 106 s '1 for the ground state process with the same driving force. These investigations show that the strength of coupling across the bpe ligand is higher when it links two metal centres as opposed to when it bridges a metal centre and an electrode. Extensive experiments were carried out to quantify the effect of laser pulses on an unmodified electrode surface. Laser activation improves the heterogeneous kinetics of a solution phase redox probe by removing polishing debris and other adsorbed impurities. Laser-induced current transients observed following a single laser pulse are due to a rapid (jas) restructuring of the double-layer followed by a slow (ms) thermal decay within the metal electrode. A mathematical model has yielded values of the thermal diffusion coefficient as a function of applied potential. To investigate excited state heterogeneous electron transfer, monolayers of a ruthenium polypyridyl complex containing the bridging ligand, 2,2':4,4":4',4"- Quarterpyridyl are used. Using Rehm-Weller calculations, the excited state redox potentials occur a t -0.71 and +1.05 V for oxidation and reduction respectively. Laser excitation of these monolayers in conjunction with high-speed cyclic voltammetry was utilised to attempt to directly measure the excited state redox potentials of this complex. This experiment has not been entirely successful and suggestions for improvements to the experiment are discussed

Electronic Nanodevices

The start of high-volume production of field-effect transistors with a feature size below 100 nm at the end of the 20th century signaled the transition from microelectronics to nanoelectronics. Since then, downscaling in the semiconductor industry has continued until the recent development of sub-10 nm technologies. The new phenomena and issues as well as the technological challenges of the fabrication and manipulation at the nanoscale have spurred an intense theoretical and experimental research activity. New device structures, operating principles, materials, and measurement techniques have emerged, and new approaches to electronic transport and device modeling have become necessary. Examples are the introduction of vertical MOSFETs in addition to the planar ones to enable the multi-gate approach as well as the development of new tunneling, high-electron mobility, and single-electron devices. The search for new materials such as nanowires, nanotubes, and 2D materials for the transistor channel, dielectrics, and interconnects has been part of the process. New electronic devices, often consisting of nanoscale heterojunctions, have been developed for light emission, transmission, and detection in optoelectronic and photonic systems, as well for new chemical, biological, and environmental sensors. This Special Issue focuses on the design, fabrication, modeling, and demonstration of nanodevices for electronic, optoelectronic, and sensing applications