Cathodoluminescence of defects in diamond films and particles grown by hot-filament chemical-vapor deposition

Colloidal Nanoribbons: From Infrared to Visible

Using the cation-exchange method, colloidal PbS nanoribbons are converted completely into CdS nanoribbons. This process expands the emission spectrum of the nanoribbons from infrared to visible. The morphology of nanoribbons remains the same after cation exchange, but the crystal structure changes from rock salt to zincblende. CdS nanoribbons exhibit blue band-edge photoluminescence under ultraviolet-light excitation. Cathodoluminescence spectroscopy of the CdS nanoribbons shows multicolor (blue, green, and red) emissions. Further time-resolved photoluminescence spectroscopy studies show that the lifetime of the midgap states is more than 2 orders of magnitude longer than that of the band-edge states.

Electron-Induced State Conversion in Diamond NV Centers Measured with Pump-Probe Cathodoluminescence Spectroscopy

Nitrogen-vacancy (NV) centers in diamond are reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers, NV⁰ and NV^-, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, an understanding of the dynamics between the different states still remains challenging. Here, conversion from NV^- to NV⁰ due to electron-induced carrier generation is shown. Ultrafast pump-probe cathodoluminescence spectroscopy is presented for the first time, with electron pulses as pump and laser pulses as probe, to prepare and read out the NV states. The experimental data are explained with a model considering carrier dynamics (0.8 ns), NV⁰ spontaneous emission (20 ns), and NV⁰ → NV^- back transfer (500 ms). The results provide new insights into the NV^- → NV⁰ conversion dynamics and into the use of pump-probe cathodoluminescence as a nanoscale NV characterization tool.

Cathodoluminescence in the scanning transmission electron microscope

Cathodoluminescence (CL) is a powerful tool for the investigation of optical properties of materials. In recent years, its combination with scanning transmission electron microscopy (STEM) has demonstrated great success in unveiling new physics in the field of plasmonics and quantum emitters. Most of these results were not imaginable even twenty years ago, due to conceptual and technical limitations. The purpose of this review is to present the recent advances that broke these limitations, and the new possibilities offered by the modern STEM-CL technique. We first introduce the different STEM-CL operating modes and the technical specificities in STEM-CL instrumentation. Two main classes of optical excitations, namely the coherent one (typically plasmons) and the incoherent one (typically light emission from quantum emitters) are investigated with STEM-CL. For these two main classes, we describe both the physics of light production under electron beam irradiation and the physical basis for interpreting STEM-CL experiments. We then compare STEM-CL with its better known sister techniques: scanning electron microscope CL, photoluminescence, and electron energy-loss spectroscopy. We finish by comprehensively reviewing recent STEM-CL applications.

Electron beam controlled restructuring of luminescence centers in polycrystalline diamond

Color centers in diamond are becoming prime candidates for applications in photonics and sensing. In this work we study the time evolution of cathodoluminescence (CL) emissions from color centers in a polycrystalline diamond film under electron irradiation. We demonstrate room-temperature activation of several luminescence centers through a thermal mechanism that is catalyzed by an electron beam. CL activation kinetics were measured in realtime and are discussed in the context of electron induced dehydrogenation of nitrogen-vacancy-hydrogen clusters and dislocation defects. Our results also show that (unintentional) electron beam induced chemical etching can take place during CL analysis of diamond. The etching is caused by residual H2O molecules present in high vacuum CL systems.

Cathodoluminescence microscopy and spectroscopy of micro- and nanodiamonds: an implication for laboratory astrophysics

Color centers in selected micro- and nanodiamond samples were investigated by cathodoluminescence (CL) microscopy and spectroscopy at 298 K [room temperature (RT)] and 77 K [liquid-nitrogen temperature (LNT)] to assess the value of the technique for astrophysics. Nanodiamonds from meteorites were compared with synthetic diamonds made with different processes involving distinct synthesis mechanisms (chemical vapor deposition, static high pressure high temperature, detonation). A CL emission peak centered at around 540 nm at 77 K was observed in almost all of the selected diamond samples and is assigned to the dislocation defect with nitrogen atoms. Additional peaks were identified at 387 and 452 nm, which are related to the vacancy defect. In general, peak intensity at LNT at the samples was increased in comparison to RT. The results indicate a clear temperature-dependence of the spectroscopic properties of diamond. This suggests the method is a useful tool in laboratory astrophysics.

Effect of Doping with Nitrogen and Boron on Cathodoluminescence of CVD-Diamond

We have investigated cathodoluminescence (CL) of nitrogen- and boron-doped CVD diamonds compared with type Ib and undoped CVD diamonds. The CL spectrum of nitrogen-doped CVD diamond shows some luminescent centers, which are not observed in undoped one. Especially 2.15 eV (575 nm) and 1.67 eV (GRl) centers are prominent. CVD diamond doped with both nitrogen and boron shows a similar CL spectrum to boron-doped CVD diamond at lower concentration of nitrogen, and shows a spectrum composed of the centers obtained by nitrogen-doping and by boron-doping at higher concentration of nitrogen. Highenergy electron irradiation to nitrogen-doped CVD diamond produces an intense luminescent center having a zero-phonon line at 3.19 eV, and the following annealing make the emission of 2.15 eV center much more intense.

Photoluminescence Spectroscopy of Diamond Films

Photoluminescence spectroscopy has been used to characterize polycrystalline diamond films prepared by filament assisted chemical deposition and by combustion (in an oxygenacetylene flame) techniques. The luminescence spectra of the chemical vapor deposited films are dominated by a defect band possibly associated with a neutral vacancy with a strong zero phonon line at 1.68 eV and weak phonon replicas at lower energies. The combustion films exhibit two additional luminescence bands with zero phonon lines at 1.95 and 2.16 eV. The 1.95 eV band has been tentatively assigned to a nitrogen-vacancy pair. We have also observed a strong dependence of the PL spectra radially across a given combustion film and associated this with details of the flame chemistry.