Gas-mediated electron beam induced etching

University of Technology Sydney. Faculty of Science.Gas-mediated electron beam induced etching is a direct-write nanolithography technique. In this thesis, through experimental observation and numerical simulation, descriptions of reaction kinetics of electron beam induced etching were refined to include effects of residual contaminants, substrate material properties, and temperature dependence. Reaction kinetics of electron beam induced etching are of interest because they affect resolution, throughput, proximity effects, and topography of nanostructures and nanostructured devices fabricated by electron beam induced etching. A number of mechanisms proposed in the literature for electron beam induced removal of carbon were shown to be insignificant. These include atomic displacements caused by knock-on by low energy electrons, electron beam heating, sputtering by ionised gas molecules, and chemical etching driven by a number of gases that include N₂. The behaviour ascribed to these mechanisms was instead explained by chemical etching caused by electron beam induced dissociation of residual contaminants such as H₂O present in the vacuum systems that are typically used for EBIE. Reaction mechanisms in single crystal and ultra nano-crystalline diamond were shown to be dependent on substrate material properties. Single crystal diamond etch morphology is attributed to anisotropic etching along crystal planes, which varies with precursor composition. In contrast to single crystal diamond, etching of ultra nano-crystalline diamond was shown to proceed via an electron activated pathway. A refined electron beam induced etching model incorporating the role of electron induced damage in ultra nano-crystalline diamond yields higher order reaction kinetics, predicting a new reaction regime limited by the concentration of chemically active surface sites. A temperature dependent, cryogenic electron beam induced etching technique was implemented to increase the residence time of adsorbates on the surface. This technique efficiently increases the rate of electron beam induced etching, demonstrated using nitrogen trifluoride as the etch precursor for silicon. Cryogenic cooling broadens the range of precursors that can be used for electron beam induced etching, and enables high-resolution, deterministic etching of materials that are volatilised spontaneously by conventional etch precursors. Determining the reaction kinetics of electron beam induced etching enables new applications in nanoscale material modification. Methods for the fabrication of optically active, functional diamond structures from single crystal diamond and rapid Stardust particle extraction were demonstrated. Electron beam induced etching is ideal for these applications, where high-resolution, damage-free etching is required

Cryogenic electron beam induced chemical etching

© 2014 American Chemical Society. Cryogenic cooling is used to enable efficient, gas-mediated electron beam induced etching (EBIE) in cases where the etch rate is negligible at room and elevated substrate temperatures. The process is demonstrated using nitrogen trifluoride (NF3) as the etch precursor, and Si, SiO2, SiC, and Si3N4 as the materials volatilized by an electron beam. Cryogenic cooling broadens the range of precursors that can be used for EBIE, and enables high-resolution, deterministic etching of materials that are volatilized spontaneously by conventional etch precursors as demonstrated here by NF3 and XeF2 EBIE of silicon

Helicity at Photospheric and Chromospheric Heights

In the solar atmosphere the twist parameter $\alpha$ has the same sign as magnetic helicity. It has been observed using photospheric vector magnetograms that negative/positive helicity is dominant in the northern/southern hemisphere of the Sun. Chromospheric features show dextral/sinistral dominance in the northern/southern hemisphere and sigmoids observed in X-rays also have a dominant sense of reverse-S/forward-S in the northern/southern hemisphere. It is of interest whether individual features have one-to-one correspondence in terms of helicity at different atmospheric heights. We use UBF \Halpha images from the Dunn Solar Telescope (DST) and other \Halpha data from Udaipur Solar Observatory and Big Bear Solar Observatory. Near-simultaneous vector magnetograms from the DST are used to establish one-to-one correspondence of helicity at photospheric and chromospheric heights. We plan to extend this investigation with more data including coronal intensities.Comment: 5 pages, 1 figure, 1 table To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

Subtractive 3d printing of optically active diamond structures

Controlled fabrication of semiconductor nanostructures is an essential step in engineering of high performance photonic and optoelectronic devices. Diamond in particular has recently attracted considerable attention as a promising platform for quantum technologies, photonics and high resolution sensing applications. Here we demonstrate the fabrication of optically active, functional diamond structures using gas-mediated electron beam induced etching (EBIE). The technique achieves dry chemical etching at room temperature through the dissociation of surface-adsorbed H2O molecules by energetic electrons in a water vapor environment. Parallel processing is possible by electron flood exposure and the use of an etch mask, while high resolution, mask-free, iterative editing is demonstrated by direct write etching of inclined facets of diamond microparticles. The realized structures demonstrate the potential of EBIE for the fabrication of optically active structures in diamond

Electron beam induced etching of carbon

© 2015 AIP Publishing LLC. Nanopatterning of graphene and diamond by low energy (≤ 30keV) electrons has previously been attributed to mechanisms that include atomic displacements caused by knock-on, electron beam heating, sputtering by ionized gas molecules, and chemical etching driven by a number of gases that include N2. Here, we show that a number of these mechanisms are insignificant, and the nanopatterning process can instead be explained by etching caused by electron induced dissociation of residual H2O molecules. Our results have significant practical implications for gas-mediated electron beam nanopatterning techniques and help elucidate the underlying mechanisms

Dynamic surface site activation: A rate limiting process in electron beam induced etching

We report a new mechanism that limits the rate of electron beam induced etching (EBIE). Typically, the etch rate is assumed to scale directly with the precursor adsorbate dissociation rate. Here, we show that this is a special case, and that the rate can instead be limited by the concentration of active sites at the surface. Novel etch kinetics are expected if surface sites are activated during EBIE, and observed experimentally using the electron sensitive material ultra nanocrystalline diamond (UNCD). In practice, etch kinetics are of interest because they affect resolution, throughput, proximity effects, and the topography of nanostructures and nanostructured devices fabricated by EBIE. © 2013 American Chemical Society

Electron beam controlled restructuring of luminescence centers in polycrystalline diamond

Color centers in diamond are becoming prime candidates for applications in photonics and sensing. In this work we study the time evolution of cathodoluminescence (CL) emissions from color centers in a polycrystalline diamond film under electron irradiation. We demonstrate room-temperature activation of several luminescence centers through a thermal mechanism that is catalyzed by an electron beam. CL activation kinetics were measured in realtime and are discussed in the context of electron induced dehydrogenation of nitrogen-vacancy-hydrogen clusters and dislocation defects. Our results also show that (unintentional) electron beam induced chemical etching can take place during CL analysis of diamond. The etching is caused by residual H2O molecules present in high vacuum CL systems. © 2014 American Chemical Society

Study of narrowband single photon emitters in polycrystalline diamond films

© 2014 AIP Publishing LLC. Quantum information processing and integrated nanophotonics require robust generation of single photon emitters on demand. In this work, we demonstrate that diamond films grown on a silicon substrate by microwave plasma chemical vapor deposition can host bright, narrowband single photon emitters in the visible - near infra-red spectral range. The emitters possess fast lifetime (∼ several ns), absolute photostability, and exhibit full polarization at excitation and emission. Pulsed and continuous laser excitations confirm their quantum behaviour at room temperature, while low temperature spectroscopy is performed to investigate inhomogeneous broadening. Our results advance the knowledge of solid state single photon sources and open pathways for their practical implementation in quantum communication and quantum information processing

Localized chemical switching of the charge state of nitrogen-vacancy luminescence centers in diamond

We present a direct-write chemical technique for controlling the charge state of near-surface nitrogen vacancy centers (NVs) in diamond by surface fluorination. Fluorination of H-terminated diamond is realized by electron beam stimulated desorption of H2O in the presence of NF3 and verified with environmental photoyield spectroscopy (EPYS) and photoluminescence (PL) spectroscopy. PL spectra of shallow NVs in H- and F-terminated nanodiamonds show the expected dependence of the NV charge state on their energetic position with respect to the Fermi-level. EPYS reveals a corresponding difference between the ionization potential of H- and F-terminated diamond. The electron beam fluorination process is highly localized and can be used to fluorinate H-terminated diamond, and to increase the population of negatively charged NV centers. © 2014 AIP Publishing LLC

Sparticle Spectrum Constraints

The supersymmetric standard model with supergravity-inspired soft breaking terms predicts a rich pectrum of sparticles to be discovered at the SSC, LHC and NLC. Because there are more supersymmetric particles than unknown parameters, one can write down sum rules relating their masses. We discuss the pectrum of sparticles from this point of view. Some of the sum rules do not depend on the input parameters and can be used to test the consistency of the model, while others are useful in determining the input parameters of the theory. If supersymmetry is discovered but the sum rules turn out to be violated, it will be evidence of new physics beyond the minimal supersymmetric standard model with universal soft supersymmetry-breaking terms.Comment: 25 pages. NUB-3067-93TH, UFIFT-HEP-93-16, SSCL-Preprint-439, June 199