We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 - 100 nm display long spin coherence times, T2 > 100 \mus at d = 5 nm and T2 > 600 \mus at d \geq 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.Comment: 14 pages, 4 figures, 11 pages of additional supplementary materia

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Tracer diffusion coefficients D* of deuterated polystyrene of molecular weight M diffusing into polystyrene of molecular weight P are measured by means of an ion-beam analysis method. While for P > 200 000, these D* values are independent of P, consistent with a reptation mechanism (D* = D R ) for the diffusion of M chains, D* increases rapidly as P is decreased, in quantitative agreement with D* = D R +D C R, where Z>CR is the diffusion coefficient of the M chain by constraint release.PACS numbers: 66.10.Cb, 61.40.Km, 82.35. + t Diffusion of high polymer chains in an entangled melt has been successfully described by reptation, a process by which a given chain crawls along a primitive path defined by topological constraints due to the other chains in the melt. These constraints are assumed to remain fixed for the time it takes the chain to diffuse its length along the primitive path. 1,2 A reptating chain of molecular weight M (M chain) should have a center-of-mass diffusion coefficient D* at infinite dilution given by 3

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