Diamond’s relatively low mass elemental mass, strong bonding and highly symmetric lattice provide a host of attractive and outstanding properties including large Raman scattering cross-section, high thermal conductivity, wide transparency range and lattice stability to name a few. Interest in exploiting these properties for optical devices has increased recently in parallel with improvements in the quality of synthetic material grown by chemical vapor deposition. Diamond lasers, which use the phenomenon of stimulated Raman scattering to provide optical gain, is one area in the emergent fields of diamond photonics and optical engineering that has excellent prospects for addressing important challenges in laser source development. In this paper, the recent progress in diamond Raman lasers others will be reviewed. The talk will highlight areas in which diamond holds promise for enhancing laser performance beyond that easily achieved by other means and for addressing important applications.

A major challenge in graphene-based devices is opening the energy band gap and doping. Molecular functionalization of graphene is one approach to modifying its electronic properties. Surface transfer doping by surface modification with appropriate molecular donors or acceptors represents a simple and effective method to non-destructively dope graphene. Surface transfer doping relies on charge separation at interfaces, and represents a valuable tool for the controlled and non-destructive doping of 2D materials, since traditional dopant implantation methods are not suitable. Molecular self-assembly of bimolecular systems on graphene is demonstrated, and represents a controlled method of surface engineering the properties of graphene. The doping of epitaxial graphene using oxide thin films is also presented. The hole doping effect of graphene modified by MoO3 thin film is confirmed by electrical transport measurements on prototype graphene devices.

Nitrogen-vacancy defects (NV) in the diamond lattice have been extensively studied in the past for several reasons. NV centers can act as single photon emitters in the visible range with absolute photo-stability. They have found applications in novel fields like quantum computation [1] and single spin magnetometry. In this context, it is of great interest to understand the effect of diamond surface termination and gain control over the charge state of NV centers in diamond.In ensemble experiments with shallow implanted defects we have shown that by changing the diamond surface termination from oxygen to hydrogen, the fluorescence of the negatively charged NV (NV^-) can be suppressed. This effect depends on the implantation energy and dose used for the creation of NV-centers in diamond by low-energy nitrogen implantation [2]. We attribute this behavior to the band bending which occurs at hydrogen-terminated diamond surfaces according to the transfer-doping model. A two-dimensional hole gas is formed at the diamond surface, converting the NV^- to either neutral (NV⁰) or even positively charged NV-centers (NV⁺). Recently, we have shown that electrostatic control of the charge state of single NV centers can be achieved by using H-terminated surface-conductive diamond devices and an electrolyte gate electrode. Similar to diamond solution-gated field effect transistors [3], the electrolytic gate electrode provides a precise control over the Fermi level position at the diamond surface. In areas of high nitrogen implantation density, this allows a reversible switching of NV centers from NV^- to NV⁰, whereas in areas of low implantation density single centers could be switched from NV⁰ into a state which shows now fluorescence, most likely NV⁺. We have performed self-consistent numerical simulations which can reproduce the surface band bending and the concurrent disappearance of the NV^--fluorescence for hydrogen-terminated diamond surfaces in contact with an electrolyte. Furthermore, we can simulate the control of the charge state with an external electrolytic gate for the charge transfer levels NV^0/- as well as NV^+/0.[1]P. Neumann et al., Nat. Phys. 6, 249 (2010)[2]M.V. Hauf et al., Phys. Rev. B 83, 081304 (2011)[3]M. Dankerl et al., Phys. Rev. Lett. 106, 196103 (2011)

Individual color centers in diamond have recently emerged as a promising solid-state platform for quantum communication and quantum information processing systems, as well as sensitive nanoscale magnetometry with optical read-out. Performance of these systems can be significantly improved by engineering optical properties of color centers using nanophotonic approaches. In this work we describe a high-flux, room temperature, source of single photons based on an individual Nitrogen-Vacancy (NV) center embedded in a top-down nanofabricated, single crystal diamond nanowires^{1, 2}, plasmonic nano-apertures³, and diamond-based optical cavities⁴ and waveguides. Using the nanowire geometry, for example, an order of magnitude brighter single photon source is realized, with an order of magnitude lower pump power, compared to an NV center in a bulk diamond1. By embedding diamond nanowires in metals³, it is possible to further increase photon flux by increasing photon production rate via Purcell effect. To that end, we demonstrated Purcell factors of ~6 in geometry that consists of diamond nanoposts embedded in silver. Finally, recently we demonstrated optical nanocavities and waveguides fabricated directly in thin diamond films⁵. Single-photon emission of NV centers embedded in diamond ring resonators, featuring quality factors on the order of 10,000, has been demonstrated. These devices could enable strong coupling between photons and NV centers. 1.T.M. Babinec, B.M. Hausmann, M. Khan, Y. Zhang, J. Maze, P.R. Hemmer, M. Lončar, Nature Nanotechnology, 5, 195 (2010) 2.B.J.M. Hausmann*, T.M. Babinec*, J.T. Choy*, J.S. Hodges, S. Hong, I. Bulu, A. Yacoby, M.D. Lukin, M. Lončar, New Journal of Physics, 13, 045004 (2011)3.I. Bulu, T.M. Babinec, B.M. Hausmann, J.T. Choy, M. Lončar, Optics Express, 19, 5268-5276 (2011)4.B. J. Hausmann, J. Choy, T. Babinec, Q. Quan, M. McCutcheon, P. Maletinsky, A. Yacoby, M. Loncar, CLEO/QuELS 2011, Baltimore, MD May 5, 2011

The nitrogen-vacancy (NV) center in diamond is an excellent qubit candidate due to its long spin coherence, optical addressability, and fast manipulation rates, along with the engineering flexibility of solid-state devices. Furthermore, the coherent coupling of the electronic spin of a single NV center to light [1] provides a pathway towards integrating NV centers into photonic networks as well as for on-demand generation of spin-photon entanglement. Such applications require the ability to tune the NV-center optical transitions to compensate for the natural variations in local strain caused by sample inhomogeneities that perturbs the electronic orbital states. Here we demonstrate a method to electrically tune individual NV-center orbital Hamiltonians into specific regimes via the DC Stark effect by applying voltages to lithographic gates [2]. The DC Stark shifts reveal a significantly enhanced electric field due to the photoionization of deep charge traps within the diamond. These reproducible fields are predominantly directed perpendicular to the diamond surface allowing for three-dimensional control of the local electric field vector with surface gates only. By harnessing this effect, we are able to tune the excited-state orbitals of individual NV centers to degeneracy, a requirement for several spin-photon entanglement schemes. We also demonstrate the ability to tune multiple NV centers to the same degenerate transition energy. This method should enable the coherent coupling of multiple NV-center spins to indistinguishable photons within a photonic network.[1] B. B. Buckley, G. D. Fuchs, L. C. Bassett, and D. D. Awschalom, Science 330, 1212 (2010).[2] L. C. Bassett, F. J. Heremans, C. G. Yale, B. B. Buckley, and D. D. Awschalom, submitted (2011), arXiv:1104.3878v1 [cond-mat.mes-hall].

The NV-defect in diamond has been discussed as an excellent candidate for quantum-information processing at room-temperature. While creating these defect-centers by ion implantation with sufficient spatial resolution to enable entanglement is within reach, the challenge of deterministic creation (conversion efficiency >50%) remains. Increasing the conversion efficiency through co-implantation was studied using different co-implant species and fluences at room temperature and 780 C[1]. Despite the significantly different damage profiles of H, He and C, which were used for the co-implantation, the conversion efficiency did not show a species dependence and displayed similar trends across all combinations of parameters. This strongly indicates the additional effects of charging and possibly defect clustering, by which NV centers are prevented from forming or are trapped into an optically inactive state. We present first experimental results and discuss a strategic approach for investigating this phenomenon.This work was supported by the Laboratory Directed Research and Development Programof the Lawrence Berkeley National Laboratory under US Department of Energy contract no.DE-AC02-05CH11231 and through the DARPA Quest program.References[1] J Schwartz, P Michaelides, C D Weis and T Schenkel, New J. Phys.13, 035022 (2011)

The nitrogen-vacancy (NV) color center is a promising candidate for quantum information processing. Individual NV spins are very robust objects that can be coherently manipulated at room temperature, and used for fast and precise magnetometry. The only drawback of this solid-state qubit is that it cannot be created deliberately with atomic precision due to the inherent limitations of ion implantation. Molecular spin qubits, like the fullerene-encapsulated nitrogen atom N@C60, can be purified chemically and then placed on a Si surface with atomic resolution. The challenge of this project is to use the difficult diamond surface instead and engineer a coherent coupling between N@C60 and a shallow NV center. This would enable truly scalable quantum information processing.We have already achieved the first atomic resolution-imaging of single-crystalline diamond using non-contact AFM [1]. Using nanodiamonds (<50 nm diameter) as a model source for shallow NV centers, we demonstrated that even these slightly less advantageous qubits can be used at room-temperature in a quantum algorithm [2] and for magnetometry [3]. First steps to engineering the desired coupling will also be reported.References:[1] M. Nimmrich et al., Phys. Rev.B 106 (2010) 040504. [2] F. Shi, W. Harneit et al., Phys. Rev. Lett. 105 (2010) 040504.[3] R.S. Schoenfeld and W. Harneit, Phys. Rev. Lett. 106 (2011) 030802.

We present an all-diamond photonic platform on chip for single photon routing as well as broadband optical characterization. An all-diamond photonic network on chip requires coupling of a quantum emitter to a low-loss optical cavity that is efficiently coupled to a routing element such as a waveguide while offering scalability to obtain multi-coupling between resonators and routing elements preferably at room temperature for practical applications. Here, we combine room temperature operation with efficient routing of single photons from a Nitrogen-Vacancy (NV) defect center [1] that are emitted into the tightly confined mode of a high-finesse ring resonator and evanescently coupled to a waveguide [2]. The single photon flux is extracted efficiently via gratings. Our approach offers versatile scalability of elements. Room temperature routing of single photon flux opens up scenarios for photon entanglement created on chip and extracted in free space which opens up a new route towards quantum key distribution and perfectly secure quantum cryptography.We also present measurements demonstrating broadband operation of single diamond ring resonators on quartz substrate in a transmission tapered fiber set-up in the telecom regime as well as in a scanning confocal microscope in the VIS. Quality factors as high as 12000 were measured [3].

Diamond is a very attractive material for high power and high frequency electronic applications because of its exceptional physical properties. But diamond devices face one specific difficulty: at room temperature, because of the high ionisation energy of dopants, 0.38 eV for boron and 0.6 eV for phosphorus, free carrier density is very low at room temperature, and resistivity is consequently very high. Ionization energy can be reduced with an increase in the doping concentration, down to zero at the metal-insulator transition, but it also induces a detrimental decrease in the carrier mobility. The solution, proposed initially for silicon in the 80’s and then for diamond, is to fabricate a very thin heavily delta-doped layer in sandwich between two high purity diamond epilayers. The quantum confinement in this thin layer induces a delocalization of the free carriers out of the doped region, allowing holes to move into a high mobility diamond. If the doping level is high enough to reach the metal-insulator transition, ie 4e20 cm-3, then a high hole concentration is expected, even at room temperature. The first critical point is to get a quantum confinement strong enough to delocalize a significant part of the free carriers out of the delta layer. The second point is the ability to modulate the hole concentration with a top gate to build a field effect transistor.In order to get quantitative values regarding these two critical points, we simulated the delta structure solving the Schrödinger and Poisson equations consistently. From the quantum confinement of the hole wavefunctions and their occupancy ratio, the part of holes moving out of the delta layer was deduced, depending on the doping level and delta layer thickness. Then, the field effect control of the hole concentration was addressed. In particular, results show that the diamond breakdown field, even very high, limits the sheet carrier density in the structure, otherwise the field is not strong enough to deplete the channel and close the transistor. Detailed behaviour of the delta structure will be presented, and the transistor properties depending on device structure will be discussed.

Due to its superlative properties, such as a wide bandgap, high breakdown voltage, and high electron and hole mobilities, diamond is a potentially exceptional semiconductor for electronic applications, especially high-temperature and high-power devices. Doping issues continue to be a limitation in this field, and the realization of useful electronic devices requires high quality films with controlled and uniform dopant levels. Precision doping is of increasing concern, as delta, or nm scale, doping, has become an increasingly active area of research for enabling active diamond devices. In our previous work on characterization of boron-doped single crystal diamond (SCD), we have used temperature-dependent conductivity measurements to fit the activation energy, and investigated feedgas chemistries containing carbon dioxide for the control of doping for boron incorporation levels less than 10¹⁷ cm^-3 [1,2]. We have also compared infrared absorption techniques and SIMS measurements for the determination of incorporated boron, and have shown that infrared absorption spectroscopy is sensitive to surface defects on grown samples [1].This work expands upon our previous effort to grow and characterize high-quality diamond for electrical applications. Films are deposited on high pressure high temperature SCD substrates in a microwave plasma-assisted CVD reactor with feedgas mixtures including hydrogen, methane, diborane, and carbon dioxide. The effect of carbon dioxide in the feedgas mixture on the incorporated boron is further investigated, and results showing the resulting decrease in electrically active boron are presented. We investigated the dopant spatial variation and the role of defect formation on boron incorporation, using infrared and Raman spectroscopy, conductivity and Hall effect measurements, secondary ion mass spectroscopy (SIMS) and scanning electron microscopy (SEM). We present the results of our investigation of the spatial uniformity of the dopant profile in boron doped diamond both across the growth surface and versus depth into the film, as well the properties of the boron doped layers as a function of temperature. Results for boron concentration levels ranging from below 10¹⁷ cm^-3 to approximately 10²⁰ cm^-3 are reported. References[1] S.N. Demlow, M. Becker, and T. Grotjohn, Electrical Conduction Properties of Single Crystal, Boron-Doped Diamond Films, New Diamond and Nano Carbon Confernce (2011). [2] S.N. Demlow, T.A. Grotjohn, T. Hogan, M. Becker and J. Asmussen, Determination of Boron Concentration in Doped Diamond Films, MRS Proceedings (2011) 1282, mrsf10-1282-a05-15 doi:10.1557/opl.2011.444