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The separated silicon-vacancy (SiV) photoluminescent diamond particles were synthesized on a silica optical fiber by hot filament chemical vapor deposition (HFCVD). The effects of the pre-treated method and chamber pressure on the microstructure and photoluminescence of the diamond particles were investigated. The results show that the diamond particles are homogeneously distributed on the surface of the optical fiber. With the chamber pressure increasing from 1.6 kPa to 3.5 kPa, the shape of the particles transforms from flake to circle, while the diamond particles cannot be deposited on the fiber with the pressure further increased to 4.5 kPa. The samples synthesized under 2.5 kPa chamber pressure are composed of diamond particles with size around 200–400 nm, exhibiting stronger SiV photoluminescence with the width of around 6 nm.
Single photon source is critical for quantum information processing and quantum communication.[1] The ideal single photon source generates exactly one photon at a time and all photons are identical. As a result, if any two photons were sent through separated arms of a beam-splitter, they can produce full interference. For the application in quantum communication, the most widely used single photon source is generated with nonlinear optics or emitted by two-level systems such as quantum dot and color centers in diamond. The nonlinear optics is not a “real” single photon source which follows the Poisson distribution.[2] The quantum dot such as InAs quantum dot only works well under 10 K.[3] Color centers in diamond such as nitrogen vacancy (NV) center,[4,5] nickel-nitrogen (NE8) center,[6] Cr-related center,[7] and silicon vacancy (SiV) center[8–10] are highly photostable at room temperature.
The single photon source is generally obtained by coupling single photons into optical fibers, which is compatible with the current fiber communication network. There are various methods to achieve this integration of a single photon source with an optical fiber. Schroder et al.[11] picked the NV center containing diamond particles onto the optical fiber through the atomic force microscope (AFM) cantilever tip. Ruan et al.[12] directly doped the NV diamonds into the tellurite glass, which had a potentially high collection efficiency but increased the risk of damaging the color centers. Rabeau et al.[13] directly deposited NV diamond particles on the fiber endface and achieved fluorescence waveguiding. Besides that, scientists[14,15] also integrated the CdSe colloidal quantum dots with a microfiber and achieved a single photon waveguide.
The SiV center in diamond exhibits many extraordinary photon properties, such as high degree of photons polarization and short life time.[16] Recent work indicated that the single SiV center exhibited very high fluorescence counts, suggesting that it could be an efficient photon source for quantum communication application.[17] Kunuku et al.[18] prepared ultrananocrystalline diamond particles with the size of about
In this paper, we prepare individual diamond particles on the surface of the fibers and investigate the impact of the deposition conditions on the photoluminescence and microstructural properties of the diamond particles. Seeding is a key parameter[19,20] that can strongly affect the diamond CVD growth process on various substrates.[20,21] The dip-coating[22] by low concentration nanodiamond suspension is used to coat individual diamond nanoparticles onto the fiber surface. The effects of different seeding time on the structural and photoluminescent properties of the diamond particles are discussed. In addition, the chamber pressure is found to be another important parameter for the growth of the diamond particles and fabrication of SiV center, while there are few reports about the related studies.
In this paper, the effects of the pre-treatment method and chamber pressure on the diamond quality and SiV photoluminescent property are well studied. The results show that a chamber pressure of 2.5 kPa is superior for the growth of SiV photoluminescent diamond particles with size around 200–400 nm, exhibiting stronger SiV photoluminescence with the width of around 6 nm.
The standard silica single mode optical fiber with the polymer protection etched away in nitric acid was selected in the experiments. The fiber was 2-cm-long with a diameter about
The diamond particles were synthesized using a hot filament chemical vapor deposition (HFCVD) system. The filament power was kept at 1.7 kW, the relative concentration ratio of components in the gas mixture was acetone: hydrogen = 1:5. The pressure of the gas mixture in the reaction chamber was set as 1.6 kPa, 2.5 kPa, 3.5 kPa, and 4.5 kPa, respectively. The deposition time was fixed to 20 min according to our previous study. The efficient creation of SiV centers is attributed to the plasma etching of the fiber substrate.
Scanning electron microscopy (SEM) (TESCAN VAGA3) measurements were performed to investigate the morphology of the diamond particles on the fiber surface. Their microstructure and composition were examined by visible Raman spectroscopy. The presence of the SiV photoluminescence (PL) on the diamond endface was confirmed using PL spectroscopy. Raman and PL spectra of the diamond particles were collected on the deposition side using a Raman/PL spectrometer (HORIBA HR800) with 514 nm excitation laser.
Figure
Figure
The corresponding visible Raman spectra were collected to analyze the composition of the samples at room temperature and fitted with six Gaussian peaks, as shown in Fig.
Comparing the PL and Raman spectra of samples 1.6T5 and 1.6T15, we find that these samples have a strong diamond peak, but weak SiV ZPL. The Raman spectra indicate that the samples synthesized under 1.6 kPa mainly consist of TPA, graphite, and diamond, thus forming a flake-shape structure, as shown in the SEM morphology. The high content of TPA, which is related to hydrogen in amorphous carbon GBs, quenches the SiV luminescence.[9] Besides that, the existence of graphite has a major influence on the photoluminescence. For the NV center in diamond, it was proved that there exists an energy transfer from the NV center to the graphene monolayer, which results in weaker fluorescence.[30] Here, the graphite contents of samples 1.6T5 and 1.6T15 are 13.5% and 4.1%, which significantly decrease the photoluminescence intensity of SiV.
To decrease the contents of the amorphous carbon and TPA in the particles, we increased the chamber pressure to 2.5 kPa. Figure
Figure
Figure
The above results show that under 2.5 kPa, the particles have higher diamond content and stronger SiV PL intensity. The effects of the chamber pressure on the diamond deposition and SiV fabrication can be attributed to two factors. First, the concentration of hydrogen active groups increases with increased pressure.[31,32] The lifetime of the hydrogen active groups is much longer than that of the CH3 active group, and the CH3 active group is sensitive to the chamber pressure.[33] Second, the concentration of hydrogen atoms is reduced with reduced pressure.[34] Therefore, the ratio of CH3 groups to H groups on the substrate increases with the decreased chamber pressure. In addition, the SEM graphs in Figs.
Comparing the PL spectra and the corresponding Raman spectra in Fig.
To further investigate the effects of the pressure on the microstructure and SiV PL, we synthesized diamond particles on an optical fiber with the chamber pressure increased to 3.5 kPa and 4.5 kPa, respectively. Figure
Figure
Our results show that it is difficult to prepare diamond particles on the optical fiber with a single SiV center in our present study. By further adjusting the experiment parameters, like the controlled doping of silicon during diamond deposition, few SiV color centers in diamond will be obtained. Our results supply a crucial step toward the integration of optical fiber and SiV centered diamond particles.
By adjusting the deposition parameters in the CVD process, we synthesize the SiV photoluminescent diamond particles on the fiber surface. The effects of the chamber pressure on the microstructural and photoluminescent properties of the diamond particles are investigated. The results show that the samples synthesized under 2.5 kPa exhibit better SiV photoluminescent property. The particles with size around 200–400 nm are uniformly distributed on the fiber surface. With the chamber pressure increased to 3.5 kPa, the diamond quality becomes worse and non-diamond phase contents increase, weakening the SiV photoluminescent intensity. In the case of 4.5 kPa, the contents of diamond continuously decrease with increased TPA and graphite, so that the synthesized particles exhibit no SiV photoluminescence.
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