We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double-Lorentzian noise spectrum consistent with a surface electronic spin bath in the low frequency regime, along with a faster noise source attributed to surface-modified phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks.Nanoscale magnetic imaging and magnetic resonance spectroscopy, recently demonstrated using nitrogenvacancy (NV) color centers in diamond [1][2][3][4], are capable of yielding unique insights into chemistry, biology and physical sciences. The sensitivity and resolution of these techniques relies heavily on the NV coherence properties, which empirically are much worse for shallow NV centers than those deep within bulk diamond [5]. An understanding of the origin of surface related noise enables optimal decoupling or surface passivation to be performed. It is critical not only for improving NV applications in quantum sensing [6,7], quantum information processing [8], and photonics [9], but is also an outstanding problem in many solid-state quantum systems (e.g. [10,11]). Furthermore, overcoming noise at the diamond interface is a significant obstacle to realizing hybrid quantum systems with NV centers [12,13], which are expected to play an important role in realistic devices.For NV centers in bulk diamond, noise sources limiting coherence times have been identified with internal nuclear and electronic spin baths, and interactions with phonons [14,15]. Although additional noise sources related to the diamond surface, and affecting shallow NVs, have been observed [16], their origin is not currently well understood. This phenomenon is general and has been observed at various semiconductor interfaces, resulting in the development of several theoretical models, which are still without significant experimental confirmation [17,18]. Here we use shallow implanted NV centers as nanoscale sensors to perform spectroscopy of the diamond surface. We use dynamical decoupling techniques together with measurements of longitudinal (T 1 ) relaxation under varying conditions (surface coating, magnetic field, temperature) in order to characterize the surface-induced noise. The strength and frequency dependence of fluctuations as a function of the NV distance from the surface are investigated with nanometer precision. We directly measure the noise spectrum experienced by shallow NV centers, revealing an unexpected double-Lorentzian structure which indicates contributions from two distinct noise sources. We find that the low frequency noise experienced by shallow NVs is consistent with electronic spin impurities on the surface [ Fig. 1(a)], w...

A sub-10 nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5 nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4 nm). An Si-ND array with an SiO(2) matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6 nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.

Si self-diffusion in the presence of end-of-range (EOR) defects is investigated using nat Si/ 28 Si isotope multilayers. The isotope multilayers were amorphized by Ge ion implantation, and then annealed at 800-950 C. The behavior of Si self-interstitials is investigated through the 30 Si selfdiffusion. The experimental 30 Si profiles show further enhancement of Si self-diffusion at the EOR defect region, in addition to the transient enhanced diffusion via excess Si self-interstitials by EOR defects. To explain this additional enhanced diffusion, we propose a model which takes into account enhanced diffusion by tensile strain originated from EOR defects. The calculation results based on this model have well reproduced the experimental 30 Si profiles. V

A uniform 10 nm diameter Ge two-dimensional (2D) nanodisk array structure was fabricated using iron oxide cores in a 2D closed-packed array of cage shaped proteins, ferritins, as an etching mask. Thin Ge layer on Si substrate was protected by a-Si capping layer and etched, which eliminated an uncontrollable factor of Ge native oxide. The density of Ge nanodisks was as high as 5.8 × 1011 cm−2, and the center-to-center distance was estimated to be 14 nm. It was demonstrated that a quantum confinement effect can be obtained with our fabricated Ge nanodisk array by controlling the nanodisk thickness. The obtained high density Ge nanodisk is promising for Ge/Si quantum dot intermediate band solar cells and other photonics devices.

No abstract