Papers by Christoph Nebel
Proceedings of SPIE, Feb 29, 2016
We report on the design, fabrication and measurement of travelling-wave superconducting nanowire ... more We report on the design, fabrication and measurement of travelling-wave superconducting nanowire single-photon detectors (SNSPDs) integrated with polycrystalline diamond photonic circuits. We analyze their performance both in the near-infrared wavelength regime around 1600 nm and at 765 nm. Near-IR detection is important for compatibility with the telecommunication infrastructure, while operation in the visible wavelength range is relevant for compatibility with the emission line of silicon vacancy centers in diamond which can be used as efficient single-photon sources. Our detectors feature high critical currents (up to 31 µA) and high performance in terms of efficiency (up to 74% at 765 nm), noise-equivalent power (down to 4.4×10 -19 W/Hz 1/2 at 765 nm) and timing jitter (down to 23 ps).
Nanomaterials, Nov 17, 2016
Electrostatic self-assembly of diamond nanoparticles (DNPs) onto substrate surfaces (so-called na... more Electrostatic self-assembly of diamond nanoparticles (DNPs) onto substrate surfaces (so-called nanodiamond seeding) is a notable technique, enabling chemical vapor deposition (CVD) of nanocrystalline diamond thin films on non-diamond substrates. In this study, we examine this technique onto differently polarized (either Al-or N-polar) c-axis oriented sputtered aluminum nitride (AlN) film surfaces. This investigation shows that Al-polar films, as compared to N-polar ones, obtain DNPs with higher density and more homogeneously on their surfaces. The origin of these differences in density and homogeneity is discussed based on the hydrolysis behavior of AlN surfaces in aqueous suspensions.
Diamond and Related Materials, Apr 1, 2014
We demonstrate integrated optomechanical circuits with high mechanical quality factors prepared f... more We demonstrate integrated optomechanical circuits with high mechanical quality factors prepared from nanocrystalline diamond thin films. Using chemomechanical polishing, the RMS surface roughness of as grown polycrystalline diamond films is reduced below 3 nm to allow for the fabrication of high-quality nanophotonic circuits. By integrating free-standing nanomechanical resonators into integrated optical devices, efficient read-out of the thermomechanical motion of diamond resonators is achieved with on-chip Mach-Zehnder interferometers. Mechanical quality factors up to 28,800 are measured for four-fold clamped optomechanical resonators coupled to the evanescent near-field of nanophotonic waveguides. Our platform holds promise for large-scale integration of optomechanical circuits for on-chip metrology and sensing applications.
Applied Physics Letters, Dec 22, 2014
Diamond integrated photonic devices are promising candidates for emerging applications in nanopho... more Diamond integrated photonic devices are promising candidates for emerging applications in nanophotonics and quantum optics. Here we demonstrate active modulation of diamond nanophotonic circuits by exploiting mechanical degrees of freedom in free-standing diamond electro-optomechanical resonators. We obtain high quality factors up to 9600, allowing us to read out the driven nanomechanical response with integrated optical interferometers with high sensitivity. We are able to excite higher order mechanical modes up to 115 MHz and observe the nanomechanical response also under ambient conditions.
Physica Status Solidi A-applications and Materials Science, Nov 1, 2015
Diamond provides superior optical and mechanical material properties, making it a prime candidate... more Diamond provides superior optical and mechanical material properties, making it a prime candidate for the realization of integrated optomechanical circuits. Because diamond substrates have matured in size, efficient nanostructuring methods can be used to realize full-scale integrated devices. Here we review optical and mechanical resonators fabricated from polycrystalline as well as single crystalline diamond. We present relevant material properties with respect to implementing optomechanical devices and compare them with other material systems. We give an overview of diamond integrated optomechanical circuits and present the optical readout mechanism and the actuation via optical or electrostatic forces that have been implemented to date. By combining diamond nanophotonic circuits with superconducting nanowires single photons can be efficiently detected on such chips and we outline how future single photon optomechanical circuits can be realized on this platform.
Light-Science & Applications, Oct 9, 2015
Photonic quantum technologies hold promise to repeat the success of integrated nanophotonic circu... more Photonic quantum technologies hold promise to repeat the success of integrated nanophotonic circuits in non-classical applications. Using linear optical elements, quantum optical computations can be performed with integrated optical circuits and can therefore overcome the existing limitations in terms of scalability. In addition to passive optical devices for realizing photonic quantum gates, active elements, such as single-photon sources and single-photon detectors, are essential ingredients for future optical quantum circuits. Material systems that allow for the monolithic integration of all components are particularly attractive, including III-V semiconductors, silicon and diamond. Here, we demonstrate nanophotonic integrated circuits made from high-quality polycrystalline diamond thin films in combination with on-chip single-photon detectors. By using superconducting nanowires that are coupled evanescently to traveling waves, we achieve high detection efficiencies of up to 66% as well as low dark count rates and a timing resolution of 190 ps. Our devices are fully scalable and hold promise for functional diamond photonic quantum devices.
Hydrogen terminated diamond is a very promising material for high energy photocatalytic reactions... more Hydrogen terminated diamond is a very promising material for high energy photocatalytic reactions1 owing to its large band gap(5.5 eV) and a unique capability of generating solvated electrons due t ...
Small, 2019
Scanning probe microscopy techniques providing information on conductivity, chemical fluxes, and ... more Scanning probe microscopy techniques providing information on conductivity, chemical fluxes, and interfacial reactivity synchronized with topographical information have gained importance within the last decades. Herein, a novel colloidal atomic force microscopy (AFM) probe is presented using a spherical boron‐doped diamond (BDD) electrode attached and electrically connected to a modified silicon nitride cantilever. These conductive spherical BDD–AFM probes allow for electrochemical force spectroscopy. The physical robustness of these bifunctional probes, and the excellent electrochemical properties of BDD renders this concept a unique multifunctional tool for a wide variety of scanning probe studies including conductive AFM, hybrid atomic force–scanning electrochemical microscopy, and tip‐integrated chem/bio sensing.
Analytical Methods, 2018
A non-destructive chemometric method to determine thickness and boron concentration of as-deposit... more A non-destructive chemometric method to determine thickness and boron concentration of as-deposited, thin, heavily doped diamond films by Raman microscopy.
Thin Solid Films, 2014
Nanocrystalline diamond-(NCD) and AlN-based ultrathin single layer and bilayer membranes are inve... more Nanocrystalline diamond-(NCD) and AlN-based ultrathin single layer and bilayer membranes are investigated towards their mechanical properties. It is shown that chemo-mechanical polishing and heavy boron doping of NCD thin films do not impact the elastic properties of NCD layers as revealed by negligible variations of the NCD Young's modulus (E). In addition, it is demonstrated that the combination of NCD elastic layer and AlN piezo-actuator is highly suitable for the fabrication of mechanically stable ultrathin membranes in comparison to AlN single layer membranes. The elastic parameters of NCD/AlN heterostructures are mainly determined by the outstanding high Young's modulus of NCD (E = 1019 ± 19 GPa). Such ultrathin unimorph membranes allow for fabrication of piezo-actuated AlN/NCD microlenses with tunable focus length.
MRS Proceedings, 1996
Transient grating (TG) experiments were performed to study carrier diffusion and recombination in... more Transient grating (TG) experiments were performed to study carrier diffusion and recombination in amorphous silicon films (a-Si:H) at high light intensities using 8 ns pulses from a frequency-doubled Nd:YAG laser. The ambipolar diffusion coefficients reached about 10−2cm2/s, which is 2 orders of magnitude larger than the steady-state value. Similar results were obtained in intrinsic, p-, and n-doped a-Si:H films, indicating that the diffusion coefficients in all cases reflect the near band edge mobility of the slower carriers, that is holes. In particular, the p-type sample shows an initially fast, then a slow grating efficiency decay, consistent with dispersive transport.
ABSTRACT In this work we report on membranes made of nanocrystalline diamond (NCD) and AlN for th... more ABSTRACT In this work we report on membranes made of nanocrystalline diamond (NCD) and AlN for the use in tunable micro-optics. For the growth of the AlN and NCD thin films, magnetron sputtering and chemical vapor deposition techniques have been used, respectively. A chemical-mechanical polishing process of NCD layers has been introduced, which is crucial for the growth of c-oriented, fiber textured AlN films. AlN layers deposited on as grown and polished nanocrystalline diamond along with free standing membranes have been compared by studying microstructure, surface morphology, piezoelectrical response as well as optical properties.
physica status solidi (a), 2002
Hydrogen surface conductivity has been a controversial subject since its discovery. Initial plasm... more Hydrogen surface conductivity has been a controversial subject since its discovery. Initial plasma treatments on single crystal diamond and polycrystalline diamond have lead to the widespread use of this material in active electronics. However, "Black" polycrystalline diamond, usually termed "Thermal Management Grade", shows carrier concentration and mobility values similar to both white polycrystalline diamond and single crystal material. Schottky contacts have also been fabricated and show promising characteristics. Black diamond can be grown considerably faster than white diamond and is hence much cheaper.
Journal of Micromechanics and Microengineering, 2013
ABSTRACT Micro electromechanical systems are a matter of intense research pursuing to replace sil... more ABSTRACT Micro electromechanical systems are a matter of intense research pursuing to replace silicon and III-V semiconductor-based components in prospective radio frequency communication devices. Due to their unique material properties, microstructures combining doped nano-crystalline diamond (NCD) and AlN thin films are promising for piezo-actuated microsystems in order to increase operating frequencies. In this work, single and doubly clamped unimorph NCD-on-AlN micro-resonators were fabricated and then characterized by laser vibrometry towards their flexural resonant frequencies in the range of 0.1-20 MHz to deduce their mechanical properties. Enhancements in the structural properties of an AlN piezo-actuator united with an advanced elasticity of nano-diamond electrode lead to superior mechanical parameters of the resulting unimorphs. These allow for the fabrication of flexural resonant microsystems with a potential to extend the operating frequencies well above 1 GHz.
Electrochemistry Communications, 2012
ABSTRACT Boron doped diamond (BDD) is a promising electrode material for electrochemical biosenso... more ABSTRACT Boron doped diamond (BDD) is a promising electrode material for electrochemical biosensor applications due to its low bio-fouling, chemical stability, and large potential window. For the first time, BDD nanoelectrode arrays (NEA) were studied using Scanning Electrochemical Microscopy (SECM) measurements. Using the phase-operated shear force technique and feedback mode, it was possible to scan a platinum (Pt) nanode with an active radius of 167 nm over a diamond array at a constant distance of 45 nm and to detect the electrochemical activity of single BDD nanodes in the 100 nm range.
Diamond and Related Materials, 2004
... Thus, despite the uncertainty introduced by ambient conditions, both Kelvin probe experiments... more ... Thus, despite the uncertainty introduced by ambient conditions, both Kelvin probe experiments and theoretical calculations support the conclusion that the Fermi level ... Research Center in Tsukuba, Dr P. Bergonzo and E. Snidero from LIST(CEA) in Saclay, and Dr J. Ristein and ...
Diamond and Related Materials, 2002
Homoepitaxially grown CVD-diamond to which H S was added during the growth was analyzed by electr... more Homoepitaxially grown CVD-diamond to which H S was added during the growth was analyzed by electrical and optical 2 measurements in order to investigate the nature of sulfur as a dopant in diamond. Hall measurements were carried out at low and high temperatures. In the low temperature range (175-290 K), p-type conduction was found with an activation energy of 360 meV. On the other hand, at high temperatures (650-900 K), n-type conductivity was observed with a carrier activation energy of 1.55 eV. Using photoconductivity spectroscopy, four dominant ionization energies are detected at 371 meV, 479 meV, 1 eV and 2 eV. The first ionization energy is attributed to the non-intentional incorporation of boron impurities, in agreement with the measured p-type conductivity. The level at 479 meV has been identified as an acceptor state, and its origin is discussed. The origin of the level detected by Hall measurements at 1.55 eV and by photoconductivity at 2 eV is not yet clear, and it has been tentatively attributed to nitrogen impurities.
Elsevier eBooks, 2014
Surface electronic properties of undoped hydrogen terminated diamond covered with adsorbates or i... more Surface electronic properties of undoped hydrogen terminated diamond covered with adsorbates or in electrolyte solutions are summarized. The formation of a conductive layer at the surface of diamond is discussed based on Hall effect, conductivity, contact potential difference (CPM), scanning electron microscopy (SEM), and cyclic voltammetry data applied on homoepitaxially grown CVD diamond films with atomically smooth hydrogen terminated surfaces. Due to electron transfer from valence band states into empty states of the electrolyte ("transfer doping"), a highly conductive surface layer is generated. Holes propagate in the layer with mobilities up to 350 cm 2 /Vs. The sheet hole density is in the range 10 11 to 5x10 12 cm -2 , and dependents on pH of the electrolyte. Numerical solutions of the Schrödinger and Poisson equations reveal a 2D density of state (DOS) distribution. This has been utilized to manufacture ion-sensitive field effect transistors (ISFET). The drain source conductivity is pH dependent, with about 66 mV/pH. Application of potentials larger than the oxidation threshold of +0.7 V (pH 13) to +1.6 V (pH 1) gives rise to strong leakage currents and to partial surface oxidation.
Physical review, Jul 2, 2021
Microwave pulse sequences are the basis of coherent manipulation of the electronic spin ground st... more Microwave pulse sequences are the basis of coherent manipulation of the electronic spin ground state in nitrogen-vacancy (NV) centers. In this work we demonstrate stimulated Raman transitions (SRT) and stimulated Raman adiabatic passage (STIRAP), two ways to drive the dipole-forbidden transition between two spin sublevels in the electronic triplet ground state of the NV center. is is achieved by a multitone Raman microwave pulse which simultaneously drives two detuned transitions via a virtual level for SRT or via two adiabatic and partially overlapping resonant microwave pulses for STIRAP. We lay the theoretical framework of SRT and STIRAP dynamics and verify experimentally the theoretical predictions of population inversion by observing the dipole-forbidden transition in the ground state of a single NV center. A comparison of the two schemes showed a be er robustness and success of the spin swap for STIRAP as compared to SRT.
Frontiers in photonics, Nov 29, 2022
Spin systems in solid state materials are promising qubit candidates for quantum information in p... more Spin systems in solid state materials are promising qubit candidates for quantum information in particular as quantum memories or for quantum sensing. A major prerequisite here is the coherence of spin phase oscillations. In this work, we show a control sequence which, by applying RF pulses of variable detuning, allows to increase the visibility of spin phase oscillations. We experimentally demonstrate the scheme on single NV centers in diamond and analytically describe how the NV electron spin phase oscillations behave in the presence of classical noise models. We hereby introduce detuning as the enabling factor that modulates the filter function of the sequence, in order to achieve a visibility of the Ramsey fringes comparable to or longer than the Hahn-echo T 2 time and an improved sensitivity to DC magnetic fields in various experimental settings.
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Papers by Christoph Nebel