Charge carrier trapping in diamond crystals containing well-defined concentrations of dislocations was investigated by several complementary techniques. Samples with dislocation densities ndis between <1 × 107 and ≈1 × 109 cm−2 were grown heteroepitaxially on Ir/YSZ/Si(001). In optical pump–probe experiments, ambipolar diffusion coefficients were determined from the decay of light-induced transient free carrier gratings. Modeling their variation with excitation density yielded trapping cross sections σ of 29 and 10 nm for the dislocations and a stress-field-induced reduction in exciton binding energies from 80 to 73 and 60 meV at ndis = 1 × 108 and 1 × 109 cm−2, respectively. The lifetime measured by induced absorption scaled proportional to 1/ndis with absolute values ranging from 0.1 to 10 ns. In the electrical measurements on two sets of detector slices, electron–hole pairs were excited by α-particles and transport was measured separately for electrons and holes. Both types of carriers showed fast transient current signals. The time constant of the additional slow component exclusively seen for holes was in agreement with the activation energy of boron acceptors. Their concentration of ≈0.5 ppb yielded σ = 1.77 × 10−13 cm2 for charged point traps. Schubweg and carrier lifetime due to deep trapping roughly reproduced the 1/ndis trend. For electrons at 3 V/μm, a value σ = 40 nm was deduced. Cross sections for holes were significantly smaller. Differences in hole trapping between the samples are attributed to charging of dislocations controlled by chemical impurities. Increase in lifetime at high voltages is explained by reduced capture cross sections for hot carriers.

We describe a method that allows an easy separation of a single crystal diamond layer grown by homoepitaxy in a chemical vapour deposition (CVD) process from the growth substrate. In a first step a thin SiO2 layer is deposited on top of the seed crystal. This layer is patterned by photolithography and reactive ion etching (RIE) to obtain a mask with open windows and covered areas. In an epitaxial lateral overgrowth (ELO) process diamond is grown homoepitaxially through the free window areas and laterally across the covered areas until the mask is completely covered by diamond. During cool down from deposition temperature tensile stress c., perpendicular to the growth surface is formed in the diamond bridges grown in the window areas. The absolute value of the stress depends on growth temperature, difference in coefficients of thermal expansion (CTE) between diamond and the specific mask material and finally on the fill factor (FF). The stress amplitude can reach more than +2 GPa and stress intensity factors in the range of typical fracture toughness values reported for single crystal diamond. Our experiments demonstrate that an immediate crack formation can be achieved which facilitates an easy separation between the CVD grown diamond layer and the seed crystal. The described concept develops its highest potential with increasing lateral dimensions of the seed wafers.

The development of CVD grown single-crystal Diamond-on-Iridium (DOD sensors for charged-particle detection in hadrons and nuclei physics research is reviewed. A variety of samples grown at the University of Augsburg has been investigated with alpha and beta sources in the laboratory, swift ions from the heavy-ion synchrotron SIS in Darmstadt, and relativistic protons from the COoler-SYnchrotron COSY in Julich. The results obtained by means of I-E(V) studies, transient-current techniques (TCT), alpha-spectroscopy, and heavy-ion time-of-flight (ToF) measurements are compared to those of commercially available \polycrystalline and homoepitaxial single crystal CVD diamond sensors of electronic grade quality. In many aspects, the performance of DOI sensors was found quite similar to that of homoepitaxial counters, and in any case far superior to that of polycrystalline detectors. Under single-carrier drift conditions, the CCE and energy resolution (delta E/E) for holes reached levels CCEh > 95% and delta E/E-h similar to 0.3%, respectively, which correspond to values of the Schubweg w(h,e) well above the detector thickness. In contrast, the CCEe for electrons was typically lower than similar to 40%, leading to appreciable reduction of the detection efficiency in the dual-carrier drift mode (CCE similar to 60%), which characterizes the experiments with swift heavy ions and high-energy particles. We measured transport parameters comparable to those of homoepitaxial devices: mu(h)(0) similar to 3080-1756 and mu(e)(0) similar to 2276-1150 cm(2)/Vs, v(sat)(h) similar to(1.7-1.4) *10(7) and v(sat)(e) similar to(1.5-1.0)* 10(7) cm/s, as well as intrinsic time resolutions sigma(i) similar to 15 ps. It is shown, that substantial improvements have been achieved in recent years, albeit reproducibility and the understanding of the reduced electron collection remain challenging issues. Prime novelty: Comprehensive electrical characterization of intrinsic single-crystal CVD Diamond-OnIridium sensors produced at the University of Augsburg and their classification into the range of commercial electronic grade polycrystalline and homoepitaxial diamond sensors supplied by Element Six.

We investigate native nitrogen vacancy (NV) and silicon vacancy (SiV) color centers in a commercially available, heteroepitaxial, wafer-sized, mm thick, single-crystal diamond. We observe single, native NV centers with a density of roughly 1 NV per μm3 and moderate coherence time (T2 = 5 μs) embedded in an ensemble of SiV centers. Using low temperature luminescence of SiV centers as a probe, we prove the high crystalline quality of the diamond especially close to the growth surface, consistent with a reduced dislocation density. Using ion implantation and plasma etching, we verify the possibility to fabricate nanostructures with shallow color centers rendering our material promising for fabrication of nanoscale sensing devices. As this diamond is available in wafer-sizes up to 100 mm, it offers the opportunity to up-scale diamond-based device fabrication.

The contribution describes the state of the art in heteroepitaxial diamond growth on Ir/YSZ/Si. Technological details for this approach towards wafer-size single crystals are given. Special emphasis is put on crystal defects, specifically threading dislocations, including information on concentrations, strategies for further reduction and their influence on crystal properties.

A detailed mechanism for heteroepitaxial diamond nucleation under ion bombardment in a microwave plasma enhanced chemical vapour deposition setup on the single crystal surface of iridium is presented. The novel mechanism of Ion Bombardment Induced Buried Lateral Growth (IBI-BLG) is based on the ion bombardment induced formation and lateral spread of epitaxial diamond within a ~1 nm thick carbon layer. Starting from one single primary nucleation event the buried epitaxial island can expand laterally over distances of several microns. During this epitaxial lateral growth typically thousands of isolated secondary nuclei are generated continuously. The unique process is so far only observed on iridium surfaces. It is shown that a diamond single crystal with a diameter of ~90 mm and a weight of 155 carat can be grown from such a carbon film which initially consisted of 2 · 1013 individual grains.

Threading dislocations in heteroepitaxial diamond films deposited on Ir/YSZ/Si(001) substrates with an off-axis angle of 4° towards [100] have been studied by cross-section transmission electron microscopy using the weak-beam dark-field (WBDF) technique for Burgers vector identification and large-angle convergent beam electron diffraction (LACBED) in order to facilitate a precise crystallographic determination of the local growth surface. Close to the diamond/iridium interface the films contain a high density of dislocations of both 90° and 45° types. Within the first micron of film growth their density decreases drastically by annihilation or mutual interaction resulting in a preference for 45° type dislocations. Vicinal growth surfaces cause a tilt of the dislocation line vector away from the crystallographic [001] axis in the step-flow direction. Tilting is influenced by gas phase impurities. With 100ppm nitrogen in the feed gas, step bunching produces a structured surface consisting of an alternating sequence of terraces with reduced off-axis angle crystallographically close to (001) and risers with increased off angle. The dislocations with lines close to [001] during terrace growth abruptly tilt by more than 20° at the transition to riser growth. The appearance of several discrete tilt angles during nitrogen free growth without pronounced step bunching is attributed to the corresponding Burgers vectors which cause either effective climb for the lower angles or effective glide for the higher ones. The present observations are of high relevance for improved strategies towards a further dislocation density reduction and an efficient control of intrinsic stress formation.

We demonstrate the controlled preparation of heteroepitaxial diamond nano- and microstructures on silicon wafer based iridium films as hosts for single color centers. Our approach uses electron beam lithography followed by reactive ion etching to pattern the carbon layer formed by bias enhanced nucleation on the iridium surface. In the subsequent chemical vapor deposition process, the patterned areas evolve into regular arrays of (001) oriented diamond nano-islands with diameters of <500nm and a height of approx. 60 nm. In the islands, we identify single SiV color centers with narrow zero phonon lines down to 1 nm at room temperature.

In the synthesis of epitaxial heterostructures with appreciable lattice misfit, dislocations represent a crucial linear defect. Since device quality is typically deteriorated by their presence, minimizing the dislocation density by optimized growth strategies is a key challenge for R&D. This especially holds also for the system diamond‐on‐iridium with its difference in lattice constants of more than 7%. As a consequence of this misfit, the initial dislocation density is very high. In this review we discuss different aspects of dislocations in heteroepitaxial diamond growth. They vary from mutual interaction mechanisms for an efficient reduction in density, over interaction with surface structures, their crucial role in the formation of intrinsic stress, their presumable role in formation of highly anisotropic stress and also their role as sink for the segregation of boron dopants. Finally, it is pointed out that the dislocation mediated stress formation may be used intentionally to strengthen devices by formation of compressively stressed surface layers. The present article is focused on recent studies from the authors’ research group.

Threading dislocations in off‐axis grown heteroepitaxial diamond films have been visualized by preferential etching of the surface. The lateral distributions of the etch pits display characteristic inhomogeneities. Patterns with fourfold symmetry consisting of a cell structure with dislocation poor cores and dislocation rich walls aligned along [100] and [010] appear on (001) samples with off‐axis tilt toward [110]. These patterns which developed after extended growth to a thickness of 1.5 mm are mainly attributed to intrinsic anisotropies in the mutual interaction between neighboring dislocations via their stress fields. In contrast, growth on (001) surfaces with off‐axis direction toward [100] yielded patterns with twofold symmetry. Here, the etch pits are aligned exclusively along the [100] off‐axis direction which is attributed to the additional impact of the local surface inclination on the dislocations, resulting in an effective lateral movement during growth. Dislocation tilting in the local step‐flow direction away from the crystallographic [001] axis, which provides a reasonable mechanism explaining the lateral movement, is confirmed by transmission electron microscopy. Homoepitaxial growth experiments on (001) surfaces 8° off toward [100] reveal etch pit patterns around “V” shaped microstructures that suggest a similar interpretation in terms of an effective lateral movement of dislocations induced by high local surface inclination.

Epitaxial graphene is expected to be the only way to obtain large-area sheets of this two-dimensional material for applications on an industrial scale. So far, there are different recipes for epitaxial growth of graphene, using either intrinsic carbon, such as the selective desorption of silicon from a SiC surface, or extrinsic carbon, as via the chemical vapor deposition (CVD) of simple hydrocarbons on transition metal surfaces. In addition, even liquid precursor deposition (LPD) provides well-ordered graphene monolayers. It will be shown that graphene formation on transition metal surfaces by LPD synthesis is a very robust mechanism that even works if carbon is provided in a quite undefined way, namely by using a human fingerprint as a liquid precursor. Graphene growth from fingerprints provides well-ordered monolayers with the same quality as LPD grown graphene using ultrapure synthetic single precursors. The reliability of the self-assembly process of graphene growth on transition metals by LPD therefore offers a simple and extremely robust synthesis route for epitaxial graphene and may give access to production pathways for substrates for which the CVD method fails.

Colour centres in diamond have emerged as versatile tools for solid-state quantum technologies ranging from quantum information to metrology, where the nitrogen-vacancy centre is the most studied to date. Recently, this toolbox has expanded to include novel colour centres to realize more efficient spin-photon quantum interfaces. Of these, the silicon-vacancy centre stands out with highly desirable photonic properties. The challenge for utilizing this centre is to realize the hitherto elusive optical access to its electronic spin. Here we report spin-tagged resonance fluorescence from the negatively charged silicon-vacancy centre. Our measurements reveal a spin-state purity approaching unity in the excited state, highlighting the potential of the centre as an efficient spin-photon quantum interface.

The setup of an apparatus for chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) and its characterization on four-inch wafers in ultra high vacuum (UHV) environment is reported. It provides well-controlled preparation conditions, such as oxygen and argon plasma assisted cleaning and high temperature annealing. In situ characterization of a wafer is accomplished with target current spectroscopy. A piezo motor driven x-y stage allows measurements with a step size of 1 nm on the complete wafer. To benchmark the system performance, we investigated the growth of single layer h-BN on epitaxial Rh(111) thin films. A thorough analysis of the wafer was performed after cutting in atmosphere by low energy electron diffraction, scanning tunneling microscopy, and ultraviolet and X-ray photoelectron spectroscopies. The apparatus is located in a clean room environment and delivers high quality single layers of h-BN and thus grants access to large area UHV processed surfaces, which had been hitherto restricted to expensive, small area single crystal substrates. The facility is versatile enough for customization to other UHV-CVD processes, e.g., graphene on four-inch wafers.

Typical size of the chemical vapor deposition (CVD) homoepitaxially grown diamond material (also known as the single crystal SC) is limited to some 5 x 5 mm due to the availability of growth substrates made from the highpressure high-temperature (HPHT) diamond. Presently, the only material readily available for the production of diamond detectors with larger area (∼10 cm) is polycrystalline (PC) film grown on silicon wafers with electronic characteristics far inferior in comparison to SC material. In order to produce a large-surface high-quality material for diamond detectors different techniques for heteroepitaxial growing of diamond films are being investigated and developed at the University of Augsburg. By using yttriumstabilized zirconium oxide (YSZ) buffer layer to produce iridium terminated substrate on silicon wafers [1] one can grow diamond films (also know as the diamond on iridium DoI) that are far more homogeneous than PC, however, still burdened with defects. In last few years a remarkable improvement in lowering of the level of impurities and defects was achieved so that the presently produced samples while still not comparable to SC material are far superior to any PC material. Most significant structural defect arising in heteroepitaxial growth are dislocations.In a recent study [2] in which the density of threading dislocations was determined by few methods over a large sample thickness, an inverse growth depth behaviour was found. While this at least in principle confirms that films with very low density of dislocations can be grown, presently procedure would not be economically effective therefore different growing techniques e.g. epitaxial lateral overgrowth are being developed. In order to assess the quality i.e. electronic characteristics of new DoI samples a typical measurement of the charge collection efficiency (CCE) is performed by using the transient current technique (TCT). Alpha particles (Am) are used to test the sample with different polarizations and drift fields so that the properties for both types of charge carriers can be evaluated. In Fig. 1 the set of measurements with a recent DoI sample of 190 μm thickness at different drift fields is presented showing the saturation at values above 0.8 V/μm. While the overall triangular shape of wave forms indicate the presence of the charge recombination defects, additional flat-top slope is related to losses due to the charge carrier trapping within the sample. For this sample we have measured an average CCE of about 60% for holes, which is below the level of the best samples ∗This work was supported in part by HadronPhysics3 (grant agreement No 283286 under the EU FP7.) † m.kis@gsi.de Figure 1: Pulse-shapes (waveforms) obtained for the drift of holes across the sample. The CCE is determined by waveform integration. Each waveform is an average from 1000 recorded events.

Deterministic coupling of single solid-state emitters to nanocavities is the key for integrated quantum information devices. We here fabricate a photonic crystal cavity around a preselected single silicon-vacancy color center in diamond and demonstrate modification of the emitters internal population dynamics and radiative quantum efficiency. The controlled, room-temperature cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon transition by a factor of 19, coming along with a 2.5-fold reduction of the emitter's lifetime.

The topographic surface features that develop during chemical vapour deposition of heteroepitaxial diamond on off‐axis Ir/YSZ/Si(001) and their implications on the incorporation and modification of 0D and 1D defects have been studied. After growth with nitrogen in the gas phase, the surface has split into alternating stripes of opposite inclination. The terrace regions are tilted towards the crystallographic [001] axis, while the risers are tilted in the opposite direction. AFM measurements on the macroscopic terraces reveal a microscopic substructure consisting of terraces and risers on a smaller length scale. Cross‐section SEM images display inclined dark and bright striations. In photoluminescence maps, the stripes ending at risers show a higher NV and SiV emission intensity thus indicating a stronger defect incorporation of colour centres. Relative growth rates on terrace and riser areas have been evaluated. In high resolution Raman measurements, the cross‐section maps display bands of high line width embedded in a background of lower line width. Conversion of these data into dislocation density maps reveals local variations by one order of magnitude. The tilt angle of the threading dislocation bundles is attributed to an interaction induced by the lateral step flow on the off‐axis growth surface.Scheme of the investigated diamond samples.

We report on the performance of the first diamond neutron monochromator built at the ILL. It has been designed for the hot neutron diffractometer D9 with the aim of improving significantly the instrument performance in particular for short wavelengths in the 0.3-0.9 Å wavelength range. Diamond crystal plates with dimensions of 1.5 x 1.5 x 0.18 cm3 an average mosaic spread of 0.15° have been synthesized at the University of Augsburg. They exhibited excellent neutron diffraction properties when examined on a neutron double-crystal test setup. Sufficiently thick diamond elements with a controlled mosaic spread of 0.25° have been obtained by stacking several of these crystals. First tests runs carried out at the ILL confirmed the predicted high reflectivity of the diamond stacks. The diamond prototype monochromator uses the (220) reflection in transmission geometry replacing the Cu (220) monochromator on D9 that has the same d-spacing. The final performance studies on D9 showed that the diamond device did not perform better than the original copper crystal. This unexpected result could be explained by significant optical aberrations caused by non- uniformities of both the angular and spatial mosaic distribution in the individual diamond crystals, as revealed by a detailed characterisation study using high-energy X-ray diffraction.

The development of dislocation density and micro-strain in heteroepitaxial diamond films on iridium was measured over more than two decades of thickness up to d ≈ 1 mm. Simple mathematical scaling laws were derived for the decrease of dislocation density with increasing film thickness and for its correlation with micro-strain. The Raman line width as a measure of micro-strain showed a huge decrease to 1.86 cm−1, close to the value of perfect single crystals. The charge collection properties of particle detectors built from this material yield efficiencies higher than 90% in the hole-drift mode, approaching the performance of homoepitaxial films.

Summary form only given. Deterministic coupling of a single emitter to a photonic crystal cavity is an important step towards the realization of integrated solid-state devices for quantum photonics. As single emitters, color centers in diamond, e.g. the Nitrogen-Vacancy (NV) center or the Silicon-Vacancy (SiV) center have attracted significant interest due to their extraordinary properties like long spin-coherence times or narrowband and bright single photon emission, respectively. For the realization of recent proposals like cavity-enhanced spin measurements or cavity-enhanced single photon sources, it is necessary to couple single color centers to a cavity with small mode volume and high quality factor. Photonic crystal cavities directly fabricated within a monocrystalline diamond membrane are well suited for this task, as they offer tiny mode volumes for efficient emitter-cavity coupling as well as scalable architectures for integrated photonic devices.In order to achieve controlled coupling of a color center to a photonic crystal cavity, several challenges have to be tackled, e.g. exact emitter positioning and alignment of its dipole moment with the cavity electric field as well as the ability for cavity tuning. For deterministic emitter-cavity positioning, two different routes can be pursued: In the first approach, a single emitter is localized within the diamond, its dipole orientation is determined and the cavity is subsequently structured around it. In the second approach, the cavity is fabricated first and a single color center is created within the cavity, e.g. via ion implantion or creation of vacancies. Here we present strategies to realize both methods for deterministic emitter-cavity coupling. For the first approach, we use a monocrystalline diamond film containing single SiV centers. Figure 1a) shows a fluorescence scan of a single SiV center with position markers next to it. The position markers are subsequently used to structure a photonic crystal cavity around the color center using focused ion beam milling [1]. Figures 1b) and c) show SEMimages before and after the cavity fabrication. The photonic crystal lattice constant a ≈ 283nm is chosen such that the cavity modes are red shifted with respect to the SiV emission lines. Using an oxidation tuning method, the cavity modes are tuned into resonance with the zero-phonon line at 740nm of a single SiV center (see Fig. 1d)). On resonance, we measure an intensity enhancement by a factor of 3.8 compared to the off-resonant case.

Graphene is seen as potential successor to silicon [1,2] due to its high charge carrier mobility, which could facilitate ultra high speed electronic devices. Chemical vapour deposition (CVD) synthesis of graphene on single crystal metal surfaces [3] represents a widely used approach, which offers scalable methods for the large-scale production of high-quality graphene layer but it is severely limited by the high cost. The scalable approach of graphene formation reported here provides an important route to the low cost mass production of epitaxial graphene on silicon-based multilayer substrates, which are already available in 4-inch wafers [4]. We have investigated the selective formation of graphene on single crystal Ir(111) films, grown heteroepitaxially on Si(111) wafers with yttria stabilized zirconia (YSZ) buffer layers, using several hydrocarbons and substrate temperatures during CVD synthesis. This surface-induced chemical growth mechanism has been investigated using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorpion fine structure (NEXAFS), and angle-resolved photoemission spectroscopy (ARPES), showing that monolayer graphene grown on Ir(111) films on YSZ/Si(111) is comparable in surface quality to graphene/Ir(111) bulk single crystals and it represents a good way for an up-scalable and low cost synthesis of graphene. Using higher CVD temperatures, ARPES clearly shows double bands characteristic of bilayer graphene formation.