The Kelvin Probe Force Microscope is a type of scanning probe instrument that is used to discern the different work functions of a sample. A sharp probe at the end of a cantilever is lowered onto a substrate where electrostatic forces, caused by the difference in work function cause the cantilever to oscillate at the modulated frequency. Using this instrument, high resolution images can be obtained, mapping the surface electronic characteristics. However, developments of this instrument have generally been limited to obtaining higher resolution images as well as reducing noise in the output, limiting the widespread appeal of this expensive instrument. There exist many applications where extremely cheap, low footprint and easy-to-use Kelvin Probe Force Microscopes would be beneficial. In order to cheaply produce this microscope in batch, a post-processed CMOS-MEMS device is utilized. The polysilicon resistors act as a strain gauge such that a conventional optical system will not have to be employed. The ability to use integrated bimorph actuators on chip allow for movement of the cantilever without the employment of large piezoelectric stages with creep effects. Embedded electronics can be fabricated with the CMOS process alongside the MEMS device, allowing full integration of an on board amplifier and read out system. In general, a large table top system can be minimized onto the size of a <1 mm2 area, a microcontroller and a computer. In this work, a Kelvin Probe Force Microscope is designed, fabricated and validated. A MEMS device was designed following similar characteristics of a generic cantilever beam. The stiffness, length, resonant frequency, and other tip characteristics can be mimicked with careful design. The resultant designs were fabricated using a CMOS-MEMS process. In order to obtain a sharper tip with modified characteristics, various methods were employed; such as gallium-aluminum alloy tip formation as well as electroless plating onto the tip of the device. Finally, the resultant device is tested against a sample. It was seen that the MEMS device followed similar characteristics of the conventional microscope itself, validating the equations that define the method. Bimorph actuators were tested to show movement, allowing the integration of the cantilever with the XYZ-stage. Work function changes are observed while scanning different materials. It is shown throughout the course of this thesis, that a true Kelvin Probe Force Microscope can be designed, fabricated and validated using CMOS-MEMS technology.

Many proteins are known to actively interact with biological, as well as inorganic and synthetic surfaces that are widely used in nano- and bio-technology as biosensing platforms and in tissue engineering. Amyloid fibrils are insoluble protein aggregates in beta-sheet conformation that are implicated in at least 20 diseases for which no cure is currently available. The molecular mechanism of fibril formation, as well as the mechanism of fibril clusters interacting with lipid membrane surfaces is currently unknown. The lipid membrane surface has a complex biochemical composition and is also electrostatically non-homogeneous. Currently, the experimental data available for amyloid fibril formation both on lipid and artificial surfaces is limited. The goal of our study is to investigate how the physical properties of the surfaces affect binding of amyloid peptides and affect the fibril formation. We seek to elucidate the effect of electrostatic interactions of amyloid peptides with surfaces using Atomic Force Microscopy (AFM) and Kelvin probe force microscopy (KPFM). We show using KPFM that electrostatic domains readily form within biological systems such as lung surfactant and lipid monolayers. We compared three different implementations of KPFM to demonstrate that frequency modulated (FM-) KPFM provides significant advantages over other modes. We also present a study of Amyloid beta (1-42) fibril formation on model surfaces, which are uniformly charged or possess periodicity of charges and hydrophobic functionality based on thiol self-assembly. Effect of membrane composition, surface charge, and presence of steroids will be discussed.

Current magnetic data storage technology is encountering certain fundamental limitations that present roadblocks to its scalability to areal densities of 1 Tbit/in^2 and beyond. Next generation magnetic storage technology is expected to use optical near field techniques to heat the magnetic film locally to write data bits. This requires experimental measurement of thermal conductivity of materials with sub--100 nm resolution. This is essential for the tailoring of the thin film stack to optimize the heat transfer of the process. This can be accomplished with a simple modification to a traditional atomic force microscopy (AFM) system. The modification requires the deposition of a thin metal film on the AFM cantilever thus creating a bimetallic cantilever. The curvature of a bimetallic cantilever is sensitive to temperature. Another modification is the use of a heating laser to raise the temperature of the cantilever so that when it scans across a sample with areas of varying thermal conductivity the bimetallic deformation of the heated cantilever is altered. The resulting system is sensitive to local variations in thermal conductivity with nanoscale resolution. Nanoscale thermal conductivity measurements can then be used to optimize the heat transfer properties of the materials used in a heat assisted magnetic recording system. AFM technology can also play a key role in the development of next generation solid-state chemical sensors. An AFM can be used to measure the workfunction of a material with near atomic resolution thus enabling the study of chemical reactions with high spatial resolution. Since chemical sensors typically use a chemical reaction at their front end to monitor the prescience of a gas, an AFM system can thus be used to understand and optimize the properties of the chemical reaction by monitoring the local workfunction. In this thesis, I explain the use of atomic force microscopy in measuring thermal and chemical properties of materials with applications towards the magnetic storage industry and chemical sensing.

Dans un contexte normatif toujours plus sévère concernant les rejets automobiles polluants, la substitution des aciers par des alliages d’aluminium dans les structures des véhicules est en plein essor. Ce projet de thèse, qui s’inscrit dans un programme de développement de la société Constellium, cible plus précisément les alliages d’aluminium de la série 7xxx (Al-Zn-Mg) qui, malgré leurs propriétés mécaniques élevées, peuvent présenter une sensibilité à la corrosion sous contrainte (CSC) liée au phénomène de fragilisation par l’hydrogène (FPH). La compréhension des mécanismes mis en jeu dans ce type d’endommagement constitue donc une première étape vers une optimisation métallurgique en vue d’une industrialisation future de ces alliages dans le secteur automobile. La première partie de ces travaux est consacrée à l’étude de l’influence de l’état métallurgique de l’alliage 7046 sur son comportement en CSC et à l’identification des mécanismes de dégradation. Un lien direct a pu être mis en évidence entre l’abattement des propriétés mécaniques et les modes de rupture actifs et la quantité d’hydrogène dans l’alliage. Les deux modes d’endommagement observés, intergranulaire-fragile et transgranulaire-fragile, ont respectivement été attribués à un enrichissement en hydrogène aux joints de grains et au piégeage de l’hydrogène au niveau des précipités intragranulaires. Les interactions entre l’hydrogène et les précipités fins d’une part et les dislocations d’autre part, identifiés comme deux hétérogénéités microstructurales critiques vis-à-vis de la FPH, ont été étudiées à une échelle plus locale dans la seconde partie du travail de thèse. Les essais ont été réalisés sur des échantillons modèles, chargés en hydrogène en milieu H2SO4 sous polarisation cathodique et la profondeur de pénétration de l’hydrogène a été évaluée par SKPFM (Scanning Kelvin Probe Force Microscopy). L’ensemble des résultats obtenus met en évidence : 1/ un effet « barrière » des précipités fins et des dislocations sur la diffusion de l’hydrogène en relation avec un abattement des propriétés mécaniques moins important, 2/ un transport possible de l’hydrogène par les dislocations et 3/ l’efficacité du SKPFM pour déterminer précisément des coefficients de diffusion apparents de l’hydrogène. Ces résultats ouvrent ainsi de nouvelles pistes vers la compréhension des mécanismes de CSC dans les alliages Al-Zn-Mg. / Automotive industry is increasingly affected by standards requiring a major cut of polluting emissions, leading R&D policies to focus on replacing steel by aluminum alloys. This thesis project, initiated by the manufacturer Constellium, focuses on 7xxx (Al-Zn-Mg) aluminum alloys known to have high mechanical properties but also to be susceptible to stress corrosion cracking (SCC) partly attributed to hydrogen embrittlement (HE). Understanding the mechanisms involved would be a first step towards a metallurgical optimization and a future industrialization of these alloys. The first part focuses on the SCC behavior of the 7046 aluminum alloy, related to its microstructure, and the identification of degradation mechanisms involved. A hydrogen amount – loss of mechanical properties relationship was highlighted. The damage observed was explained by the presence of hydrogen in the grain boundaries and by a trapping effect of the intragranular hardening precipitates, limiting the hydrogen diffusion to the grain boundaries. Interactions between hydrogen and hardening precipitates and dislocations, both identified as critical microstructural heterogeneities for HE, are studied at a local scale in a second part. The hydrogen effect was characterized by penetration depth measurements made by SKPFM (Scanning Kelvin Probe Force Microscopy) on “model” samples cathodically charged in H2SO4. The whole results finally highlight: 1/ a “shielding” effect of fine precipitates and dislocations on hydrogen diffusivity related to a lower susceptibility to HE, 2/ hydrogen transport by dislocations and 3/ the efficiency of SKPFM to precisely measure effective diffusion coefficients of hydrogen. These results lead to new opportunities to understand SCC mechanisms in Al-Zn-Mg alloys.

Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.

La nanostructure et les propriétés électroniques de matériaux modèles pour le photovoltaïque organique, ont été étudiées en utilisant la Microscopie à Force Atomique en mode non contact sous ultra-vide (NC-AFM) et la Microscopie à sonde de Kelvin (KPFM). En utilisant le mode modulation d'amplitude (AM-KPFM), le potentiel de surface photo- généré dans des mélanges donneur-accepteur présentant une ségrégation de phase optimale a pu être visualisé à l'échelle du nanomètre. Afin de préciser la nature des forces mises en jeu dans le processus d'imagerie KPFM, des oligomères π-conjugués auto-assemblés ont ensuite été étudiés. Une transition entre régimes à longue et à courte portée a ainsi été mise en évidence en combinant l'imagerie en haute résolution aux mesures de spectroscopie en distance. Ces mesures ont également démontré que l'influence des forces électrostatiques à courte portée peut être minimisée en travaillant au seuil du contraste de dissipation. Enfin cette procédure a été utilisée, en combinaison avec les mesures de spectroscopie de photoélectrons UV, pour analyser la fonction de sortie locale d'électrodes transparentes à base de nanotubes de carbone fonctionnalisés. / In this thesis, noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) under ultrahigh vacuum have been applied to investigate the nanostructure and electronic surface properties of model materials for organic photovoltaics. First, it has been demonstrated that the surface photovoltage of nanoscale phase segregated donor-acceptor photovoltaic blends can be finely resolved at the nanometer scale by using amplitude modulation KPFM (AM-KPFM). Next, model self-assembled π-conjugated oligomers have been investigated, in order to obtain a deeper insight into the nature of the tip-surface forces involved in the KPFM imaging process. A crossover between long-range (LR) and short-range (SR) regimes has been evidenced by combining high resolution imaging with distance-spectroscopy measurements. It has also been shown that the influence of the SR electrostatic forces can be minimized by working at the onset of the damping contrast. Finally, using this procedure, the local work function of flexible transparent electrodes, comprised of functionalized carbon nanotubes by metallic nanoparticles, has been investigated, and compared to the averaged value deduced from ultraviolet photoelectron spectroscopy.

Orientador: Monica Alonso Cotta / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T21:43:56Z (GMT). No. of bitstreams: 1 NarvaezGonzalez_AngelaCarolina_M.pdf: 14145813 bytes, checksum: 31ac8f1ebde240684c9bbe88b9c9b7a7 (MD5) Previous issue date: 2008 / Resumo: As propriedades elétricas de nanofios (InAs, InP, InP-InAs-InP, InAsP) individuais e em junções foram estudadas implementando simultaneamente as técnicas Non Contact Atomic Force Microscopy NC-AFM (para aquisição da topografia) e Amplitude-sensitive Modulated Kelvin Probe Microscopy AM-KPFM (fornece medidas do Potencial de Superfície), permitindo correlacionar as propriedades elétricas com a estrutura da amostra. Em particular, o comportamento do Potencial de Superfície (PS) em função do diâmetro do nanofio foi investigado e utilizado na identificação do material que o compõe. Em uma primeira etapa, a técnica AM-KPFM foi caracterizada, principalmente em termos de resolução para análise de nano-objetos. Nossos resultados evidenciaram um fator de escala presente associado à eletrônica do equipamento, que somente permitiu realizar uma análise qualitativa dos dados adquiridos. Além disso, foi observada uma diminuição no contraste nas medidas elétricas quando o tamanho do objeto analisado diminui. Medidas em nanofios individuais de InP e InAs permitiram estabelecer que há uma queda no PS quando o diâmetro do fio diminui. Este comportamento é o resultado de duas contribuições: a perda no contraste (efeito de tamanho na medida) e o incremento local da função trabalho, que poderíamos associar ao aumento da proporção entre a carga superficial e a carga no interior do fio. Nas junções, há um aumento no PS na região da junção, indicando a formação de uma barreira de energia associada à acumulção de carga. Isto isola as junções do comportamento típico observado em nanofios individuais. Medidas em junções montadas em dispositivos poderiam complementar o estudo deste tipo de configurações. A caracterização do PS em função do diâmetro para os nanofios de InP e InAs permitiu a identificação do material (InAs ou InP) presente ao longo dos fios heteroestruturados de InP-InAs-InP, mostrando também a presença da nanopartícula de ouro usada como catalisador no crescimento. Os contrastes no PS ao longo do fio não se correlacionam diretamente às imagens de Microscopia Eletrônica de Transmissão, sugerindo que a interface elétrica é diferente da metalúrgica. Nos nanofios de InAsP, pelo contrário, os dados obtidos indicam a formação de uma liga ternária / Abstract: The electric properties of InAs, InP, InP-InAs-InP and InAsP nanowires (NWs) -assembled both individually and in junctions - were studied by simultaneous imple-mentation of Non Contact Atomic Force Microscopy NC-AFM (for topography) and Amplitude-sensitive Modulated Kelvin Probe Microscopy AM-KPFM (for Surface Potential distribution), obtaining spatially resolved electrical measurements of the sample structure. In particular, the SP vs NW diameter behavior was investigated and used to identify the material composing the nanowires. In a first approach, AM-KPFM was characterized mainly in terms of resolution for the analysis of the nano-objects. Our results suggest there is a scale factor on our measurements associated to the equipment electronics, that limited our discussion to a qualitative interpretation of the acquired data. Also, a contrast decrease on SP measurements was observed when the size of the object is reduced, comparatively to the tip. The experimental results on individual InAs and InP nanowires showed a SP saturation level (SPsat) below which SP drops with the NW diameter. This behavior came from at least two contributions: a loss of SP contrast due to object/tip size effects and a local increment on work function, that we associate to the larger surface/volume ratio close to the NW tip which makes the material more intrinsic. For NWs on junctions, a larger SP value is correlated to the regions where the junction is formed, possibly due to charge accumulation. Measurements of junctions assembled on devices could complement the study of this kind of structures. The SP vs diameter characterization of InAs and InP nanowires also allowed the identification of the material along the heterostructured InP-InAs-InP nanowire, showing the presence of the Au nanoparticle used to catalyze the growth. The SP image is not directly correlated with HR-TEM images, suggesting that electric and metallurgic interfaces are not the same. For InAsP nanowires, the acquired data indicate the formation of an homogeneous ternary alloy / Mestrado / Física da Matéria Condensada / Mestre em Física

Dans un contexte normatif toujours plus sévère concernant les rejets automobiles polluants, la substitution des aciers par des alliages d’aluminium dans les structures des véhicules est en plein essor. Ce projet de thèse, qui s’inscrit dans un programme de développement de la société Constellium, cible plus précisément les alliages d’aluminium de la série 7xxx (Al-Zn-Mg) qui, malgré leurs propriétés mécaniques élevées, peuvent présenter une sensibilité à la corrosion sous contrainte (CSC) liée au phénomène de fragilisation par l’hydrogène (FPH). La compréhension des mécanismes mis en jeu dans ce type d’endommagement constitue donc une première étape vers une optimisation métallurgique en vue d’une industrialisation future de ces alliages dans le secteur automobile. La première partie de ces travaux est consacrée à l’étude de l’influence de l’état métallurgique de l’alliage 7046 sur son comportement en CSC et à l’identification des mécanismes de dégradation. Un lien direct a pu être mis en évidence entre l’abattement des propriétés mécaniques et les modes de rupture actifs et la quantité d’hydrogène dans l’alliage. Les deux modes d’endommagement observés, intergranulaire-fragile et transgranulaire-fragile, ont respectivement été attribués à un enrichissement en hydrogène aux joints de grains et au piégeage de l’hydrogène au niveau des précipités intragranulaires. Les interactions entre l’hydrogène et les précipités fins d’une part et les dislocations d’autre part, identifiés comme deux hétérogénéités microstructurales critiques vis-à-vis de la FPH, ont été étudiées à une échelle plus locale dans la seconde partie du travail de thèse. Les essais ont été réalisés sur des échantillons modèles, chargés en hydrogène en milieu H2SO4 sous polarisation cathodique et la profondeur de pénétration de l’hydrogène a été évaluée par SKPFM (Scanning Kelvin Probe Force Microscopy). L’ensemble des résultats obtenus met en évidence : 1/ un effet « barrière » des précipités fins et des dislocations sur la diffusion de l’hydrogène en relation avec un abattement des propriétés mécaniques moins important, 2/ un transport possible de l’hydrogène par les dislocations et 3/ l’efficacité du SKPFM pour déterminer précisément des coefficients de diffusion apparents de l’hydrogène. Ces résultats ouvrent ainsi de nouvelles pistes vers la compréhension des mécanismes de CSC dans les alliages Al-Zn-Mg.

This thesis deals with the use of Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) in solar cells production. Both techniques measure surface properties using interactions between surface and tip that progressively scans entire surface of the sample. Atomic force microscopy allows three dimensional imaging of surface structure. Kelvin probe force microscopy is used to measure the contact potential difference on the sample surface. There are described experimental measurements of monocrystalline and multicrystalline substrates after various etching processes using AFM. By using KPFM the contact potential difference was measured on dielectric layers PSG, SiOX, SiNX and Al2O3 and on selective emitter structures. All experiments described in this work were carried out at the Solartec Ltd. workplace and they completely correspond with the actual technology of crystalline solar cells production.

Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.