Browsing by Autor "Ruy S. Bonilla"

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    A study of surfaces using a scanning tunneling microscope (STM)
    (National University of Colombia, 2009) Alba Ávila; Ruy S. Bonilla
    Sweeping/scanning microscopes have become an experimental scientist's hands and eyes in this century; they have become a powerful and necessary tool for nanoscale characterisation in education and research laboratories all around the world. This article presents the modifications made in the mechanical (isolation or designing an antivibration system) and electrical (piezoelectric and scanning system characterisation) implementation of a scanning tunnelling microscope (STM), thereby allowing nanoscale surfaces to be visualised and modified. A methodology for visualising and characterising surfaces using the aforementioned instrument is described, bidimensional quantification of up to 1,300 nm2, with ~15 nm resolution being reached. This experimental methodology took critical parameters for tunnelling current stability into account, such as scanning speed and microscope tip geometry and dimensions. This microscope's versatility allowed defects in highly oriented pyrolytic graphite (HOPG) samples to be modified and visualised by applying a voltage between the tip and the sample. The concepts of topography scanning and lithography can be easily understood by using the instrument implemented here.
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    Estudio de superficies usando un microscopio de efecto túnel (STM)
    (2009) Alba Ávila; Ruy S. Bonilla
    Los microscopios de barrido se han convertido en las manos y los “ojos” de experimentadores de nuestro siglo, son herramien- tas necesarias en los laboratorios de educación e investigación para la caracterización a nanoescalas. El presente artículo pre- senta las modificaciones en la implementación electrónica (caracterización de los piezoeléctricos y sistema de barrido) y mecáni- ca (diseño de un sistema de antivibración) de un microscopio de barrido de efecto túnel que han permitido visualización y modi- ficación de superficies a nanoescala. Se describe una metodología para la correcta visualización y caracterización de superficies usando el instrumento implementado, alcanzando la cuantificación bidimensional de características de hasta 1300nm2, con re- solución ~15nm. Esta metodología, determinada experimentalmente, tiene en cuenta parámetros críticos para la estabilización de la corriente túnel, como lo son la velocidad de barrido y las geometrías y dimensiones de las agujas del microscopio. La ver- satilidad del microscopio permite modificar y visualizar los defectos introducidos en muestras de HOPG al aplicar voltajes entre la punta del microscopio y la muestra. Los resultados aquí descritos permiten presentar fácilmente los conceptos de barrido to- pográfico y litografía.
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    LOCAL ANODIC OXIDATION ON SILICON (100) SUBSTRATES USING ATOMIC FORCE MICROSCOPY
    (2012) Alba Ávila; Ruy S. Bonilla
    A characterization of local anodic oxidation using scanning probe microscopy is performed on a (100) silicon substrate. The formation of patterns varies as a function of voltage, humidity, and scanning speed. A set of experiments is presented to analyze the voltage and scanning speed dependence under stable environmental conditions (50.5% relative humidity, 22 °C, and 767 mmHg). A finer control of the dimensions of the local oxidation patterns is attained at low voltages and low scanning speeds. Oxide ridges are observed at high voltages independently of the writing speed. Their presence sets up an upper limit for the oxide pattern formation