On the transport of alkali ions through polymeric mold compounds and polyelectrolyte membranes.

The aim of this work is the attempt in understanding ion transport properties across structured materials such as polyelectrolyte multilayers (PEMs) and highly filled epoxy resins used as an encapsulant, i.e. mold compounds. The ion transport properties are studied by means of the technique of charge attachment induced transport (CAIT), which was recently developed and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The mold compounds studied in this work are of four types (MCP1, MCP2, MCP3, MCP4) with a composition of 80% - 88% of silica filler and the rest of raw materials such as epoxy resin, hardener and flame retardant. The samples are analyzed by means of the CAIT technique, leading to the evaluation of values of ionic conductivity and activation energy related to the process of transport of potassium ions. The ionic conductivity of the mold compounds is on the order of 10-12/10-13 S/cm, while activation energy values are in a range of 1.3 eV - 2.7 eV. For a better understanding of the potassium diffusion process into the mold compounds, the diffusion of potassium through MCP3 sample is investigated via a combination of CAIT method and an ex-situ ToF-SIMS analysis. The ToF-SIMS analysis reveals a depth diffusion profile of the potassium into the material. A mathematical theory is established in order to evaluate the diffusion coefficients for the transport of potassium. According to the numerical procedure, a good fit between experimental and theoretical data is achieved assuming the presence of two different transport pathways operative inside the material: diffusion along the boundaries of grains, i.e. zones of accumulation of the inorganic component of the mold compound and diffusion through the bulk. Diffusion coefficients of DB = 1.8 x 10-21 cm2s-1 and DBG = 5.4 x 10-20 cm2s-1 are found for bulk and grain boundary diffusion, respectively. The PEM films studied in this work are prepared from the layer-by-layer assembly of ionic p-sulfonato-calix[8]arene (calix8) and cationic poly(allylamine hydrochloride) (PAH) onto functionalized gold substrates. Samples with n = 1, 3, 6, 9, 12, 15, 20, 30 bilayers are analyzed by means of the CAIT technique. The data lend support to the conclusion that conductivity, as well as activation energy measurements for (PAH/calix8)n, cannot be acquired under the conditions of the CAIT method, due to the low resistivity shown from the specific PEMs analyzed. Studies on the transport of Li+, K+ and Rb+ through (PAH/calix8)30 are performed by means of CAIT and ToF-SIMS. For each ion beam (Li+, K+, Rb+) two kind of experiments are performed: (PAH/calix8)30 samples are bombarded with the three different alkali ions varying the time for the bombardment, i.e. 5 seconds in one case and 100 seconds in the other. The evaluation of the concentration profiles gives qualitative information regarding the transport properties, whereas numerical analysis of the lithium and rubidium concentration profiles for 5 seconds long bombardment provides quantitative information on the diffusion process. The numerical calculation reveals that the lithium and rubidium transport across the membrane results in a combination of two diffusion pathways accounting for diffusion of slow ions and fast ions. For the lithium case, a good fit is achieved using diffusion coefficients of Dslow,Li+ = 0.4 x 10-16 cm2/s and Dfast,Li+ = 1.2 x 10-15 cm2/s and assuming that 40% of the incoming ions enter the slow pathway, whereas the rest of the ions is transported via a fast pathway. For the rubidium case, the numerical calculation reveals that the fast diffusion pathway is predominant: only the 0.01% of the rubidium ions enter the slow pathway, whereas the rest is dominated from the faster one, with a Dfast,Rb+ = 7 x 10-15 (± 1.5 x 10-15) cm2/s. The study of ion transport of alkali ions Li+ and Rb+ across calixarenes-based PEMs leads thus to the conclusion that the presence of the calixarenes units may influence the type of transport. Lastly, studies of voltage offset measured on current-voltage curves in a typical CAIT experiment are presented. This study aims to give a better understanding of the process beyond the measured voltage offset. In order to do that, a basic CAIT experiment is performed, where a metal plate is bombarded with an ion beam from a potassium emitter of the composition KAlSi2O6 : Mo (1:9). The registered current–voltage curves show finite offsets in the order of 0.5 eV. In order to investigate the detection process of the specific KAlSi2O6 : Mo (1:9) emitter, values of ionic and electronic work function are evaluated. By means of a theoretical model, the recombination of K+ ions from Leucite KAlSi2O6 : Mo (1:9) onto the metal detector is traced to a combination of the ionic work function of the emitter material, the electronic work function of the emitter material and the recombination energy of the elemental potassium I.E.K

Development and modelling of a versatile active micro-electrode array for high density in-vivo and in-vitro neural signal investigation

The electrophysiological observation of neurological cells has allowed much knowledge to be gathered regarding how living organisms are believed to acquire and process sensation. Although much has been learned about neurons in isolation, there is much more to be discovered in how these neurons communicate within large networks. The challenges of measuring neurological networks at the scale, density and chronic level of non invasiveness required to observe neurological processing and decision making are manifold, however methods have been suggested that have allowed small scale networks to be observed using arrays of micro-fabricated electrodes. These arrays transduce ionic perturbations local to the cell membrane in the extracellular fluid into small electrical signals within the metal that may be measured. A device was designed for optimal electrical matching to the electrode interface and maximal signal preservation of the received extracellular neural signals. Design parameters were developed from electrophysiological computer simulations and experimentally obtained empirical models of the electrode-electrolyte interface. From this information, a novel interface based signal filtering method was developed that enabled high density amplifier interface circuitry to be realised. A novel prototype monolithic active electrode was developed using CMOS microfabrication technology. The device uses the top metallization of a selected process to form the electrode substrate and compact amplification circuitry fabricated directly beneath the electrode to amplify and separate the neural signal from the baseline offsets and noise of the electrode interface. The signal is then buffered for high speed sampling and switched signal routing. Prototype 16 and 256 active electrode array with custom support circuitry is presented at the layout stage for a 20 μm diameter 100 μm pitch electrode array. Each device consumes 26.4 μW of power and contributes 4.509 μV (rms) of noise to the received signal over a controlled bandwidth of 10 Hz - 5 kHz. The research has provided a fundamental insight into the challenges of high density neural network observation, both in the passive and the active manner. The thesis concludes that power consumption is the fundamental limiting factor of high density integrated MEA circuitry; low power dissipation being crucial for the existence of the surface adhered cells under measurement. With transistor sizing, noise and signal slewing each being inversely proportional to the dc supply current and the large power requirements of desirable ancillary circuitry such as analogue-to-digital converters, a situation of compromise is approached that must be carefully considered for specific application design

A Study on the Nature of Anomalous Current Conduction in Gallium Nitride

Current leakage in GaN thin films limits reliable device fabrication. A variety of Ga and N rich MBE GaN thin films grown by Rf, NH3, and Rf+ NH3, are examined with electrical measurements on NiIAu Schottky diodes and CAFM. Current-voltage (IV) mechanisms will identify conduction mechanisms on diodes, and CAFM measurements will investigate the microstructure of conduction in GaN thin films. With CAFM, enhanced conduction has been shown to decorate some extended defects and surface features, while CAFM spectroscopy on a MODFET structure indicates a correlation between extended defects and field conduction behavior at room temperature. A remedy for poor conduction characteristics is presented in molten KOH etching, as evidenced by CAFM measurements, Schottky diodes, and MODFET\u27s. The aim of this study is to identify anomalous conduction mechanisms, the likely cause of anomalous conduction, and a method for improving the conduction characteristics. Keywords: 111-Nitride, 111-V, Gallium Nitride, GaN, Electrical Properties, Conduction, Conductivity, Mobility, Hall Measurements, Resistivity, Schottky Diode, Modulation Doped Field Effect Transistor (MODFET), Conductive Atomic Force Microscopy (AFM), Defects, Molten Potassium Hydroxide (KOH) etching, Silvaco, Atlas, and Illumination

Characterization of Nanoparticles Using Solid State Nanopores

Solid state nanopores are widely used in detection of highly charged biomolecules like DNA and proteins. In this study, we use a solid state nanopore based device to characterize spherical nanoparticles to estimate their size and electrical charge using the principle of resistive pulse technique. The principle of resistive pulse technique is the method of counting and sizing particles suspended in a fluid medium, which are electrophoretically driven through a channel and produce current blockage signals due to giving rise to a change in its initial current. This change in current is denoted as a current blockage or as a resistive pulse. The information from these current blockage signals in case of nanopore devices and spherical nanoparticles helps us to look at the properties of each individual nanoparticles such as size, electrical charge and electrophoretic mobility. In this thesis, two spherical nanoparticles of different sizes and different surface charge groups are used: Negatively charged 25 nm iron oxide nanoparticle with – COOH surface group and positively charged 53 nm polystyrene nanoparticle with – NH2 surface group. Nanopores used in these studies are about twice the nanoparticle size. These nanopores were fabricated by various fabrication techniques such as, Focused ion beam milling and ion beam sculpting method. The current blockage events produced by these two nanoparticles were measured as a function of applied voltage. The parameters extracted from the current blockage events, such as the current drop amplitudes and event duration are analyzed to estimate the size and electrical charge of the nanoparticles. Estimation of drift velocity of the nanoparticle and diffusion coefficient are also discussed. The estimated size is then compared to the nanoparticle size obtained from dynamic light scattering technique. Stable nanoparticles are widely used in biological and pharmacological studies and understanding the behavior of these nanoparticles in a nanopore environment would make a significant contribution to the studies at the nanoscale

MOLECULAR TRANSPORT PROPERTIES THROUGH CARBON NANOTUBE MEMBRANES

Molecular transport through hollow cores of crystalline carbon nanotubes (CNTs) are of considerable interest from the fundamental and application point of view. This dissertation focuses on understanding molecular transport through a membrane platform consisting of open ended CNTs with ~ 7 nm core diameter and ~ 1010 CNTs/cm2 encapsulated in an inert polymer matrix. While ionic diffusion through the membrane is close to bulk diffusion expectations, gases and liquids were respectively observed to be transported ~ 10 times faster than Knudsen diffusion and ~ 10000-100000 times faster than hydrodynamic flow predictions. This phenomenon has been attributed to the non-interactive and frictionless graphitic interface. Functionalization of the CNT tips was observed to change selectivity and flux through the CNT membranes with analogy to gate-keeper functionality in biological membranes. An electro-chemical diazonium grafting chemistry was utilized for enhancing the functional density on the CNT membranes. A strategy to confine the reactions at the CNT tips by a fast flowing liquid column was also designed. Characterization using electrochemical impedance spectroscopy and dye assay indicated ~ 5-6 times increase in functional density. Electrochemical impedance spectroscopy experiments on CNT membrane/electrode functionalized with charged macro-molecules showed voltage-controlled conformational change. Similar chemistry has been applied for realizing voltage-gated transport channels with potential application in trans-dermal drug delivery. Electrically-facilitated transport ( a geometry in which an electric field gradient acts across the membrane) through the CNT and functionalized CNT membranes was observed to be electrosmotically controlled. Finally, a simulation framework based on continuum electrostatics and finite elements has been developed to further the understanding of transport through the CNT membranes

QUANTITATIVE PROBING OF VACANCIES AND IONS DYNAMICS IN ELECTROACTIVE OXIDE MATERIALS

Oxygen vacancy and ion dynamics in functional oxides are critical factors influencing electrical conductivity and electrochemical activity of oxides assemblies. The recent advancements in deposition and fabrication of oxide heterostructured films with atomic-level precision has led to discovery of intriguing physical properties and new artificial materials. While still under debate, researchers most often attribute these observed behaviors to unique oxygen vacancy distributions in the substrate near heterointerfaces. In electroactive oxides devices such as solid oxide cells (SOCs), oxygen vacancy and ion transport at the triple-phase boundary determines the performance of the device. This complex process motivates numerous remaining questions regarding the redox reaction and performance limitation mechanism, both of which are waiting to be addressed. Improving the fundamental understanding of the aforementioned local physical properties at size scales approaching the mesoscale and nanoscale requires local characterization of oxygen vacancy dynamics and electrochemical activity under operating conditions. A miniature environmental chamber capable of operating at temperature above 500 ℃ and various gas environment was developed and introduced into this in situ research. I first demonstrated this novel in situ SSPM method to explore the local ionic conductivity / activation energy of electrolyte material in SOC assemblies. These results are subsequently compared to macroscopic electrochemical impedance results and bulk literature values, thus supporting the validity of the approach. I subsequently extended the high temperature SSPM technique to probe the surface potential variation across a multilayer complex oxide heterostructure films deposited on Nb:doped SrTiO3 substrates. Through classic semiconductor energy band diagram model analysis, the surface potential profiles measured were converted to spatially defined (\u3c 100 nm) [VO.. ] profiles within STO. The results presented herein i) introduce the means to spatially resolve quantitative vacancy distributions across oxide films, and ii) pose the mechanism by which oxide thin film getters both enhance then deplete vacancies within the underlying substrate. Finally, I made use of the ~100 nm resolution feature of the SSPM technique to investigate charged surface adsorbate-oxygen vacancy interactions at the triple-phase boundary region in a CO2 environment, manifested as small perturbations of opposite sign in reference to the applied biases. Through fabricating 2D planar structured SOEC assemblies and varying the GdO1.5 dopant concentration in ceria electrode material, the correlation between the potential loss at the electrode | electrolyte interface and oxygen vacancy concentration in ceria electrode was established based on the measured potential loss at the interfacial region. And potential works involving in situ APXPS to provide chemical information and theoretical modeling to further enhance our understanding of the CO2 reduction reaction mechanisms on ceria based SOEC electrode were proposed. In summary, the works in this thesis demonstrate functional imaging of electroactive oxide heterointerfaces in dynamic environments combined with dopant analysis to yield quantitative defect distributions within oxide films. I also show to probe the local ionic conductivity of SOC electrolyte and charge distribution / potential loss near electrode | electrolyte interface. These results are theoretically interpreted as local activation energy for anionic oxygen transportation in electrolyte and oxygen vacancy / surface adsorbates interactions at triple-phase boundary. The developed in situ SSPM technique provides a new approach to access the fundamental information hiding behind the surface electrical response and questions it is potentially able to address will broadly impact the materials science, electrochemical, and solid-state physics communities

Properties and Manipulation of Ionic Liquid-Solid Interfaces in Complex Oxide Materials

Ionic liquids are liquid salts that are bringing rapid changes to the field of solid electronic materials. The implementation of ionic liquids in conjunction with these solid materials produces interfacial effects, especially when a bias is applied across the ionic liquid, forming an electric double layer. Electric double layers in ionic liquids are unique in their formation and the interfacial charges that are orders of magnitude higher than conventional techniques they can impart, providing new techniques for device design and implementation. In chapter 1, the fundamentals of the solid state electronic and magnetic materials are introduced, along with ionic liquids, and their essential properties that make them appropriate for use with solid films. Chapter 2 discusses the geometric impacts that should be taken into consideration when designing electric double layer devices, determining that the gate area to device area ratio plays the greatest role. Chapter 3 explores the application of electric double layer interfacial effects on ferroelectric lead zirconate- titanate films. The demonstrated large area switching, coupled with the minimal changes to film quality, and use on low quality films make this ionic liquid-solid interface an exciting proposition for future study and applications. Chapter 4 uses the same electric double layer to interrogate the ability to produce stoichiometry induced crystallographic transformations in strontium cobaltite family of films. Chapter 5 evaluates an antiferromagnetic lanthanum-strontium manganite that shows an unprecedented anisotropic magnetoresistance. These materials are excellent candidates for future spin based devices. The work discussed in this dissertation demonstrates a wide range of possible applications that can be affected by the use of ionic liquid solid interfaces, while also showing diversity in the types of studies and measurements that can be conducted by ionic liquids. Combining the electrostatic and electrochemical capabilities of ionic liquids with complex oxide films, the manipulation oxide properties can lead to advances in future electronic and magnetic properties and applications

다조성계 플라즈몬 나노 구조의 화학 및 전기적 산란 신호 조절

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 화학부, 2022.2. 남좌민.Plasmon resonance, which is a coherent collective oscillation of conductive electrons in the presence of an external electromagnetic field, effectively enhances various optical processes by means of strong light-matter interactions. Especially, plasmonic nanomaterials scatter light with extraordinary efficiency and the increased far-field radiation intensity can be exploited for the advanced design of biosensors, colorimetric methods for naked-eye detection, and smart displays. However, the full potential of the scattering from plasmonic nanomaterials cannot be fully realized by single component-based nanostructures with monotonic and confined properties. On the contrary, multi-component-based systems exhibit diverse properties and opportunities owing to the synergistically combined physicochemical functions of individual components or new features arising from the integrated structures. In this thesis, I present a chemical and an electrical strategy to modulate scattering response of plasmonic multi-component nanostructures and optimal examples of which showing benefits from the multicomponent systems. Chapter 1 introduces plasmonic properties of multicomponent nanostructures and following advantages of enhanced and modulated plasmonic scattering on applications. In Chapter 2, I developed a highly specific, well-defined Cu polyhedral nanoshell (CuPN) overgrowth chemistry and introduced to enhance light-scattering signal of Au nanoparticle probes for bio-detection. The CuPNs are exclusively formed on the surface of Au nanoparticles in a controllable manner without any noticeable non-specific signal amplification. This newly developed polymer-mediated multicomponent core-shell formation chemistry was shown as a means of the development of the naked-eye-based highly sensitive and quantitative detections of DNA and viruses. Chapter 3 includes new-found anomalous electrochromic behaviors of Au nanocubes. Plasmon scattering of the nanocubes showed higher shift rate of resonance frequency at the highly negative potential range in reversible manner. This unexpected change beyond classical understandings was attributed to the material-specific quantum mechanical electronic structures of the plasmonic materials. The substantial role of quantum capacitance in plasmonic material, which can be derived from the density of states of the composing metals, was able to be verified for the first time by means of altering the surface element by forming Ag-Au core-shell nanocubes.플라즈몬 공명은 외부 전기장에 따른 전도성 전자들의 정합 진동이며, 물질과 빛의 강력한 상호작용을 통하여 다양한 광학적 과정을 효과적으로 증대한다. 특히 플라즈모닉 나노물질은 비범할 정도의 효율로 빛을 산란하며, 증가된 원거리장 방사 세기는 바이오센서, 육안 검출을 위한 비색분석, 스마트 디스플레이 등의 발전된 설계를 위해 활용할 수 있다. 그러나 단조롭고 제한된 특성을 보이는 단일 조성의 나노 구조만으로는 플라즈모닉 나노물질의 산란이 갖는 모든 잠재력을 충분히 발휘할 수 없다. 반면 다조성계 기반 체계에서는 개별 요소로부터 오는 물리 화학적 특성의 상승적 조합이나 결합된 구조로부터 오는 새로운 특성과 같은 다양한 성질과 가능성을 보일 수 있다. 이 논문에서는 플라즈모닉 다조성계 나노구조의 산란 신호를 조절하기 위한 화학적 및 전기적 전략과 다조성계 시스템의 이점을 보여주는 최적의 예를 제시한다. 제1 장에서는 다조성계 나노구조의 플라즈몬 특성과 이를 응용할 때 플라즈모닉 산란의 조절 및 증강으로부터 기대할 수 있는 장점을 소개한다. 제2 장에서는 매우 특이적이고 잘 정의된 구리 다면체 나노쉘(CuPN)의 과성장을 위한 화학적 접근법 개발을 소개한다. 새로운 과성장 법은 바이오 검지를 위해 사용되는 금 나노입자 프로브의 빛 산란에 적용하였다. CuPN은 금 나노입자 표면에서만 선택적이고 제어 가능하도록 형성되었으며 비 특이적 신호 증폭을 나타내지 않았다. 이렇게 새로 개발된 다조성계 코어-쉘을 형성하는 고분자 기반 화학적 합성법이 DNA와 바이러스의 정량 가능한 고감도 육안 검출법의 개발에 사용됨을 보였다. 제3 장은 금 나노 큐브의 색전현상에서 새롭게 발견한 비정상적 거동을 포함한다. 나노 큐브의 플라즈몬 산란은 높은 음전위 영역에서 더 높은 진동수 변화율을 보였다. 고전적인 이해를 벗어나는 이러한 예기치 않은 변화는 플라즈모닉 재료의 물질 특이적인 양자 역학적 전자 구조에 기인한다. 플라즈모닉 재료를 구성하는 금속의 상태 밀도로부터 유도될 수 있는 양자 정전용량의 상당한 역할은, 은-금 코어-쉘 나노 큐브를 형성하여 표면 원소를 바꾸는 방법을 통해 처음으로 증명할 수 있었다.Abstract i Self-Citations of the Prior Publications iv Chapter 1. Introduction: Plasmonic Scattering of Multicomponent Nanostructures 1 1.1. Light Scattering of Plasmonic Nanomaterials 2 1.2. Plasmonic Multicomponent Nanostructures 7 1.3. Plasmonic Scattering Modulation for Applications 14 Chapter 2. Polyhedral Cu Nanoshell Formation Chemistry for Bio-Detections 23 2.1. Introduction 24 2.2. Experimental Methods 28 2.3. Results and Discussion 40 2.4. Conclusion 66 Chapter 3. Unconventional Electrochromic Behaviors of Plasmonic Au and Au-Ag Core-Shell Nanocubes 71 3.1. Introduction 72 3.2. Experimental Methods 81 3.3. Results and Discussion 90 3.4. Conclusion 115 Bibliography 119 Abstract in Korean 126박