Group-IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. Future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group-IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV − ) center, conventional 1 arXiv:1910.14165v1 [cond-mat.mes-hall] 30 Oct 2019 site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV − centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.Keywords diamond color centers, tin-vacancy center, CVD growth, ion implantation Group-IV color centers in diamond have emerged as promising candidates for optically active, solid-state spin qubits. 1-4 These color centers are comprised of a split vacancy in the diamond lattice and an interstitial group-IV atom. The inversion symmetry of this structure provides group-IV color centers beneficial properties such as insensitivity to electric field fluctuations to first order and high Debye-Waller factors. 5 These color centers also possess long-lived electron spins that can be harnessed as quantum memories. 6-8 All of these characteristics make group-IV color centers well suited to interface optical photons in nanophotonic platforms for applications in quantum networks.An outstanding challenge in implementing these color centers in scalable applications is their generation. The two most common methods of group-IV color center generation are ion implantation and synthesis. Ion implantation facilitates site-controlled generation of color centers by using either a mask 9,10 or focused ion beam (FIB). 11,12 However, the quality of ion-implanted emitters is often degraded by the large amount of damage introduced during implantation. 4 Synthesis techniques such as high-pressure high-temperature (HPHT) growth and chemical vapor deposition (CVD) growth often yield higher quality, more stable emitters with lower inhomogeneous broadening than ion implantation. [13][14][15][16] Unfortunately, synthesis techniques do not enable site-controlled generation. A better color center generation method is severely lacking.

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Nucleation is a core scientific concept that describes the formation of new phases and materials. While classical nucleation theory is applied across wide-ranging fields, nucleation energy landscapes have never been directly measured at the atomic level, and experiments suggest that nucleation rates often greatly exceed the predictions of classical nucleation theory. Multistep nucleation via metastable states could explain unexpectedly rapid nucleation in many contexts, yet experimental energy landscapes supporting such mechanisms are scarce, particularly at nanoscale dimensions. In this work, we measured the nucleation energy landscape of diamond during chemical vapor deposition, using a series of diamondoid molecules as atomically defined protonuclei. We find that 26-carbon atom clusters, which do not contain a single bulk atom, are postcritical nuclei and measure the nucleation barrier to be more than four orders of magnitude smaller than prior bulk estimations. These data support both classical and nonclassical concepts for multistep nucleation and growth during the gas-phase synthesis of diamond and other semiconductors. More broadly, these measurements provide experimental evidence that agrees with recent conceptual proposals of multistep nucleation pathways with metastable molecular precursors in diverse processes, ranging from cloud formation to protein crystallization, and nanoparticle synthesis.