Surface-enhanced Raman scattering on nanodiamond-derived carbon onions

Annealing nanodiamonds(ND) at high temperatures up to 1700 ℃ is a common method to synthesize carbon onions. The transformation from NDs to carbon onions is particularly interesting because of carbon onions' potential in the field of tribology and their application in ultra-charge/discharge devices. In this paper, a novel surface-enhanced Raman scattering technique that involves coating the sample with nanoscopic gold particles is proposed to characterize the NDs after different annealing treatments. Conventional Raman and surfaceenhanced Raman spectra were obtained, and the changes of peak parameters as the function of annealing temperature were evaluated. It was found that the widths of the D and the G peaks decreased with increasing annealing temperature, reflecting an improved order in the sp^2-hybridized carbon during the transformation from NDs to carbon onions. After annealing at 1700 ℃, the sp^2?carbon was highly ordered, indicating desirable electrical conductivity and lubricity. With increasing annealing temperature, the D peak showed a blue shift of almost30 cm^(-1), while the G peak merely shifted by 5 cm^(-1). For annealing temperatures above 1100 ℃, an increase of intensity ratio ID/IGwas observed. Compared to the uncoated area, red shifts of 0.5-2 cm^(-1) and of 5-9 cm^(-1) for the G and D peaks, respectively, were detected for the gold-coated area, which was due to the coupling of the plasmons and the phonons of the samples.

Silicon Vacancy Color Centers in 6H-SiC Fabricated by Femtosecond Laser Direct Writing

As a single photon source,silicon vacancy(V_(Si))centers in wide bandgap semiconductor silicon carbide(SiC)are expected to be used in quantum technology as spin qubits to participate in quantum sensing and quantum computing.Simultaneously,the new direct femtosecond(fs)laser writing technology has been successfully applied to preparing V_(Si)s in SiC.In this study,6H-SiC,which has been less studied,was used as the processed material.V_(Si) center arrays were formed on the 6H-SiC surface using a 1030-nm-wavelength fs pulsed laser.The surface was characterized by white light microscopy,atomic force microscopy,and confocal photoluminescence(PL)/Raman spectrometry.The effect of fs laser energy,vector polarization,pulse number,and repetition rate on 6H-SiC V_(Si) defect preparation was analyzed by measuring the V_(Si) PL signal at 785-nm laser excitation.The results show that fs laser energy and pulse number greatly influence the preparation of the color center,which plays a key role in optimizing the yield of V_(Si)s prepared by fs laser nanomachining.