Martin Fischer

Single photon emission from silicon-vacancy colour centres in chemical vapour deposition nano-diamonds on iridium

We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on iridium via microwave plasma assisted CVD-growth. We perform spectroscopy of single silicon-vacancy (SiV)-centres produced during the growth of the nano-diamonds. The colour centres exhibit extraordinary narrow zero-phonon-lines down to 0.7 nm at room temperature. Single photon count rates up to 4.8 Mcps at saturation make these SiV-centres the brightest diamond based single photon sources to date. We measure for the first time the fine structure of a single SiV-centre thus confirming the atomic composition of the investigated colour centres.

One- and two-dimensional photonic crystal microcavities in single crystal diamond

Diamond is an attractive material for photonic quantum technologies because its colour centres have a number of outstanding properties, including bright single photon emission and long spin coherence times. To take advantage of these properties it is favourable to directly fabricate optical microcavities in high-quality diamond samples. Such microcavities could be used to control the photons emitted by the colour centres or to couple widely separated spins. Here, we present a method for the fabrication of one- and two-dimensional photonic crystal microcavities with quality factors of up to 700 in single crystal diamond. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy colour centres, and we measure an intensity enhancement factor of 2.8. The controlled coupling of colour centres to photonic crystal microcavities could pave the way to larger-scale photonic quantum devices based on single crystal diamond.

Supramolecular Assemblies Formed on an Epitaxial Graphene Superstructure

The seminal work of Novoselov et al. has stimulated great interest in the controllable growth of epitaxial graphene monolayers. While initial research was focussed on the use of SiC wafers, the promise of transition metals as substrates has also been demonstrated and both approaches are scalable to large-area production. 12] The growth of graphene on transition metals such as Ru, Rh and Ir leads to a moir!-like superstructure, 10,12,13] similar to that observed for BN monolayers. Here we show that such a superstructure can be used to control the organization of extended supramolecular nanostructures. The formation of two-dimensional supramolecular arrays has received increasing attention over recent years primarily due to potential applications in nanostructure fabrication as well as fundamental interest in self-assembly processes. Such studies can be highly dependent on the nature of the substrate used, and the interplay between surface and adsorbed supramolecular structure is a topic of significant conjecture. Until now metallic surfaces or highly oriented pyrolytic graphite (HOPG) have typically been the surfaces of choice for such studies. Our results demonstrate that graphene is compatible with, and can strongly influence molecular selfassembly. We have studied the adsorption of perylene tetracarboxylic diimide (PTCDI) and related derivatives on a graphene monolayer grown on a Rh(111) heteroepitaxial thin film (Figure 1). In particular, we show that a near-commensur-

Low-temperature investigations of single silicon vacancy colour centres in diamond

We study single silicon vacancy (SiV) centres in chemical vapour deposition (CVD) nanodiamonds on iridium as well as an ensemble of SiV centres in a high-quality, low-stress CVD diamond film by using temperature-dependent luminescence spectroscopy in the temperature range 5?295?K. We investigate in detail the temperature-dependent fine structure of the zero-phonon line (ZPL) of the SiV centres. The ZPL transition is affected by inhomogeneous as well as temperature-dependent homogeneous broadening and blue shifts by about 20?cm?1 upon cooling from room temperature to 5?K. We employ excitation power-dependent g(2) measurements to explore the temperature-dependent internal population dynamics of single SiV centres and infer mostly temperature-independent dynamics.

How Does Graphene Grow? Easy Access to Well‐Ordered Graphene Films

The selective formation of large-scale graphene layers on a Rh-YSZ-Si(111) multilayer substrate by a surface-induced chemical growth mechanism is investigated using low-energy electron diffraction, X-ray photoelectron spectroscopy, X-ray photoelectron diffraction, and scanning tunneling microscopy. It is shown that well-ordered graphene layers can be grown using simple and controllable procedures. In addition, temperature-dependent experiments provide insight into the details of the growth mechanisms. A comparison of different precursors shows that a mobile dicarbon species (e.g., C(2)H(2) or C(2)) acts as a common intermediate for graphene formation. These new approaches offer scalable methods for the large-scale production of high-quality graphene layers on silicon-based multilayer substrates.

Fluorescence and polarization spectroscopy of single silicon vacancy centers in heteroepitaxial nanodiamonds on iridium

We introduce an advanced material system for the production and spectroscopy of single silicon vacancy (SiV) color centers in diamond. We use microwave plasma chemical vapor deposition to synthesize heteroepitaxial nanodiamonds of approx. 160 nm in lateral size with a thickness of approx. 75 nm. These oriented nanoislands combine the enhanced fluorescence extraction from subwavelength sized nanodiamonds with defined crystal orientation. The investigated SiV centers display narrow zero-phonon-lines down to 0.7 nm in the wavelength range 730-750 nm. We investigate in detail the phonon-coupling and vibronic sidebands of single SiV centers, revealing significant inhomogeneous effects. Polarization measurements reveal polarized luminescence and preferential absorption of linearly polarized light.

Reduction of mosaic spread using iridium interlayers: A route to improved oxide heteroepitaxy on silicon

Using epitaxial SrTiO3 and yttria-stabilized zirconia (YSZ) buffer layers deposited on silicon as a starting point, epitaxial iridium layers were grown by electron-beam evaporation using a two-step growth process with an extremely low initial deposition rate. The iridium layers had in-plane (twist) and out-of-plane (tilt) full widths at half maximum as narrow as 0.08° and 0.15°, respectively, up to an order of magnitude narrower than the underlying SrTiO3 and YSZ layers. SrTiO3 and ZnO films grown on the iridium showed significantly narrower twist and tilt values than without the iridium interlayer, demonstrating a route to improved oxide heteroepitaxy on silicon.

The physical meaning of charge extraction by linearly increasing voltage transients from organic solar cells

Carrier mobility in organic solar cells is almost exclusively determined with the Charge Extraction by Linearly Increasing Voltage (CELIV) technique; indeed much of our understanding of the recombination and charge transport mechanisms in organic solar cells is based on CELIV measurements. However, since the conception of the CELIV method, our understanding of organic semiconductors has significantly advanced. In this work, we critically examine the CELIV methods ability to provide accurate material data in the light of recent advances in our understanding of trap states and their influence on mobility in organic semiconductors. We then apply this knowledge to understand the mechanisms responsible for degradation in organic solar cells.

Electronic transitions of single silicon vacancy centers in the near-infrared spectral region

Photoluminescence (PL) spectra of single silicon vacancy (SiV) centers in diamond frequently feature very narrow room temperature PL lines in the near-infrared (NIR) spectral region, mostly between 820 nm and 840 nm, in addition to the well known zero-phonon line (ZPL) at approximately 738 nm [E. Neu et al., Phys. Rev. B 84, 205211 (2011)]. We here exemplarily prove for a single SiV center that this NIR PL is due to an additional purely electronic transition (ZPL). For the NIR line at 822.7 nm, we find a room temperature linewidth of 1.4 nm (2.6 meV). The line saturates at similar excitation power as the ZPL. The ZPL and NIR line exhibit identical polarization properties. Cross-correlation measurements between the ZPL and the NIR line reveal anticorrelated emission and prove that the lines originate from a single SiV center, furthermore indicating a fast switching between the transitions (0.7 ns).

Multimode photoacoustic method for the evaluation of mechanical properties of heteroepitaxial diamond layers

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