Fabrication of diamond nanostructures and investigation of the imbedded NV centers

Diamant ist ein Material mit vielen außerordentlichen Eigenschaften, die ihn zu einem äußerst vielversprechenden Kandidaten für Anwendungen in Wissen-schaft und Technik machen. In den letzten Jahren wurde Diamant häufig als einzigartige Plattform für neue Anwendungen beispielsweise in der Quanteninformationstechnologie (QIT) oder in der Magnetometrie im Nanometermaßstab eingesetzt, wobei einer der wichtigsten lumineszierenden Gitterdefekte im Diamantgitter eingesetzt wird. Dabei handelt es sich um die sogenannten Stickstoff/Fehlenstellen-Farbzentren (NV-Zentren), die im sichtbaren Bereich mit einer absoluten Photostabilität bei Raumtemperatur emittieren. In dieser Arbeit wurden NV-Zentren in Diamantnanokristalliten und –nanosäulen untersucht, die während des Wachstumsprozesses erzeugt wurden. Einzelne Diamantnanokristallite und nanokristalline Diamantschichten (NCD), aus denen Nanosäulen geätzt wurden, wurden mithilfe der Hot Filament Chemical Vapour Deposition (HFCVD) abgeschieden. Zu Vergleichszwecken wurden auch ultrananokristalline Diamantschichten (UNCD) mittels Mikrowellen-CVD (MWCVD) hergestellt. Die Filme wurden sorgfältig in Bezug auf ihre Morphologie, kristallinen Eigenschaften und Zusammensetzung untersucht. Um die Möglichkeit einer Integration dieser Diamantschichten mit temperaturempfindlichen Materialien wie III/V-Halbleitern, Metallen mit niedrigem Schmelzpunkt oder Polymeren zu untersuchen, wurde der Einfluss der Substrattemperatur ermittelt. Eindimensionale NCD- und UNCD-Diamantnanostrukturen wurden mithilfe der Elektronenstrahllithographie (EBL) und reaktivem Ionenätzen in einem induktiv gekoppelten O2-Plasma (ICP-RIE) hergestellt. Zur Vorbereitung wurden zunächst die Ätzraten in Abhängigkeit von den vier wichtigsten Parametern ermittelt. Weitere Erkenntnisse über die Ätzmechanismen wurden durch Ätzexperiment mit unstrukturierten NCD- und UNCD-Schichten erhalten Mittels der EBL konnten mithilfe von Gold-Ätzmasken Nanosäulen mit Durchmessern von 50 nm bis zu 1 μm hergestellt werden.Eine optische Charakterisierung der NCD- und UNCD-Nanosäulen erfolgte mithilfe von Fluorenzenz-Mapping und Photomumineszenz-Spektroskopie. Diese Messungen ergaben, dass in beiden Arten von Säulen NV-Zentren vorhanden sind. Allerdings wurden nur in NCD-Säulen die gewünschten NV--Zentren gefunden, in UNCD-Säulen hingegen nur NV0-Zentren.

Lithography-free micro- and nanostructuring based on conventional plasma etching

In now-a-days semiconductor and MEMS technologies the photolithography is the working horse for fabrication of functional devices. The conventional way (so called Top-Down approach) of microstructuring starts with photolithography, followed by patterning the structures using etching, especially dry etching. The requirements for smaller and hence faster devices lead to decrease of the feature size to the range of several nanometers. However, the production of devices in this scale range needs photolithography equipment, which must overcome the diffraction limit. Therefore, new photolithography techniques have been recently developed, but they are rather expensive and restricted to plane surfaces. Recently a new route has been presented - so-called Bottom-Up approach - where from a single atom or a molecule it is possible to obtain functional devices. This creates new field - Nanotechnology - where one speaks about structures with dimensions 1 - 100 nm, and which has the possibility to replace the conventional photolithography concerning its integral part - the self-assembly. However, this technique requires additional and special equipment and therefore is not yet widely applicable. This work presents a general scheme for the fabrication of silicon and silicon dioxide structures with lateral dimensions of less than 100 nm that avoids high-resolution photolithography processes. For the self-aligned formation of extremely small openings in silicon dioxide layers at in depth sharpened surface structures, the angle dependent etching rate distribution of silicon dioxide against plasma etching with a fluorocarbon gas (CHF3) was exploited. Subsequent anisotropic plasma etching of the silicon substrate material through the perforated silicon dioxide masking layer results in high aspect ratio trenches of approximately the same lateral dimensions. The latter can be reduced and precisely adjusted between 0 and 200 nm by thermal oxidation of the silicon structures owing to the volume expansion of silicon during the oxidation. On the basis of this a technology for the fabrication of SNOM calibration standards is presented. Additionally so-formed trenches were used as a template for CVD deposition of diamond resulting in high aspect ratio diamond knife. A lithography-free method for production of periodic and nonperiodic surface structures using the angular dependence of the etching rate is also presented. It combines the self-assembly of masking particles with the conventional plasma etching techniques known from microelectromechanical system technology. The method is generally applicable to bulk as well as layered materials. In this work, layers of glass spheres of different diameters were assembled on the sample surface forming a mask against plasma etching. Silicon surface structures with periodicity of 500 nm and feature dimensions of 20 nm were produced in this way. Thermal oxidation of the so structured silicon substrate offers the capability to vary the fill factor of the periodic structure owing to the volume expansion during oxidation but also to define silicon dioxide surface structures by selective plasma etching. Similar structures can be simply obtained by structuring silicon dioxide layers on silicon. The method offers a simple route for bridging the Nano- and Microtechnology and moreover, an uncomplicated way for photonic crystal fabrication.

Model Calculations and Implementation of Filters and Hybrid Green VCSELs based on Optical Thin Film Stacks

This work introduced the novel conception of complex coupled hybrid VCSELs for the first time. Alternating organic and inorganic layers in the lasers provide periodic variation of refractive index and optical gain, which enable single mode operation and low threshold of the VCSELs. Model calculations revealed great reduction of the lasing threshold with factors over 30, in comparison with the existing micro-cavity lasers. Tunable green VCSEL has been also designed, implemented and analyzed taking advantage of the broad photoluminescence spectra of the organics. Free standing optical thin films without compressive stress are technologically implemented. Multiple membrane stacks with air gap in between have been fabricated for the implementation of complex coupled VCSEL structures. Complex coupled hybrid VCSEL is a very promising approach to fill the gaps in the green spectral range of the semiconductor lasers.