L. Himics

Sp2 carbon defects in nanocrystalline diamond detected by Raman spectroscopy

The properties of nanocrystalline diamond (NCD) thin films are significantly affected by the defects found in the interfacial regions between the diamond crystallites (in the so called grain boundaries). Dominant sources of these defects are the sp2 hybridized carbon atoms that terminate the sp3 diamond lattice and interconnect the neighboring crystallites. The detailed evaluation of these structural units is of great importance for practical applications of NCD. Since sp2 hybridized C atoms have high Raman scattering cross-section, Raman spectroscopy could be a valuable method for the determination of bonding configuration of these defects. In this work near-infrared excited Raman spectroscopy and surface-enhanced Raman spectroscopy were used to investigate the sp2 structural units in grain boundaries of different NCD thin films.

Creation of deep blue light emitting nitrogen-vacancy center in nanosized diamond

This paper reports on the formation of complex defect centers related to the N3 center in nanosized diamond by employing plasma immersion and focused ion beam implantation methods. He+ ion implantation into nanosized diamond “layer” was performed with the aim of creating carbon atom vacancies in the diamond structure, followed by the introduction of molecular N2+ ion and heat treatment in vacuum at 750 °C to initiate vacancy diffusion. To decrease the sp2 carbon content of nanosized diamond formed during the implantation processes, a further heat treatment at 450 °C in flowing air atmosphere was used. The modification of the bonding properties after each step of defect creation was monitored by Raman scattering measurements. The fluorescence measurements of implanted and annealed nanosized diamond showed the appearance of an intensive and narrow emission band with fine structures at 2.98 eV, 2.83 eV, and 2.71 eV photon energies.

Nickel-Silicon Related Color Center Formed in Nanodiamond Grains under CVD Growth

Formation of optical centers in nanodiamond grains with narrow, near-infrared emission at room temperature is one of the most important challenges nowadays. Our aim was to form a metal-related color center through the CVD growth process of nanodiamond. Previously undocumented photoluminescence (PL) system with 865 nm zero-phonon line (ZPL) and 2 nm full width at half maximum (FWHM) was successfully created in nanodiamond grains. According to the detailed analysis of the spectral features of the ZPL and quasilocal modes of the vibronic sideband, a complex center containing Ni and Si atoms could be accounted for these PL features. The inclusion of Ni and Si impurity atoms in the complex optical center was strengthened by micro-Raman spectroscopy performed in the frequency range due to quasilocal vibrations of the vibronic sideband.

Influence of microwave plasma parameters on light emission from SiV color centers in nanocrystalline diamond films

Abstract Zero phonon line (ZPL) shape, position and integral intensity of SiV defect center in diamond is presented for nanocrystalline diamond (NCD) films grown at different conditions, NCD films of average grain sizes from ~50 nm up to ~180 nm have been deposited onto c-Si wafer at substrate temperature of 700 and 850oC from mixture with different CH4 and H2 ratios using MWCVD process. Light emission of SiV defect center and Raman scattering properties of NCD samples were measured on a Renishaw micro-Raman spectrometer with 488 nm excitation. Scanning electron microscopy images were used for monitoring surface morphology and for the analysis of the average grain sizes. Sample thickness was determined by in situ laser reflection interferometry. Characteristics of SiV ZPL are discussed in light of the morphology, bonding structure and average grain size of NCD films.

Experimental Study of Spectral Parameters of Silicon-Vacancy Centers in MWCVD Nanodiamond Films Important for Sensing Applications

Microwave enhanced chemical vapor deposition (MWCVD) was used to prepare nanodiamond (ND) films with different process parameters containing silicon-vacancy (SiV) centers. The effect of the local environment on the spectral parameters of SiV center’s zero phonon line emission, like peak position and full width at half maximum (FWHM), being important for many applications, have been studied in films having different morphological and structural properties. Relationships between the residual internal stress of the nanodiamond films and the emission parameters of the SiV centers were found and explained by shifting of the electronic levels of ground and excited states of individual SiV centers within the probed SiV ensembles due to the internal stress.

Preparation and Characterization of SERS Substrates of Different Morphology

Gold coated patterned silicon substrates of different morphology, pattern size and period were prepared by photolithography and subsequent etching. Their performance in surface enhanced Raman scattering (SERS) was tested using an organic model compound. The highest enhancement was obtained for an array of inverse pyramids, followed by inverse hemispheres and rounded-edge inverse pyramids. The SERS performance of the substrates was demonstrated with silicon-carbide nanoparticles.

Creation of Blue Light Emitting Color Centers in Nanosized Diamond for Different Applications

Plasma immersion ion implantation and focused ion beam treatment techniques were used to create nitrogen-related complex defect centers in detonation nanodiamond crystals. Helium implantation was used to produce vacancies in the crystal structure, which was followed by the introduction of nitrogen ions (with the same method). Heat treatment at 1,023 K was applied to initiate vacancy diffusion and formation of complex defect centers. The sp2 carbon content of the samples formed during the implantation and the high-temperature annealing was decreased by oxidation at 723 K in air. Changes in the bonding structure were monitored by Raman and infrared spectroscopic measurements after each step of the defect creation process. It was found that the photoluminescence of nanosized diamond changes remarkably as a consequence of different treatments and a new, narrow, intense emission band develops in the deep blue wavelength region. The N3 nitrogen-related complex defect center was considered as source of this fine structured emission band in the luminescence spectrum.

Determination of the Distribution of Inhaled Drugs in Human Airways by Raman Spectroscopy

A novel Raman spectroscopic method has been developed to study the distribution of inhaled drugs and other airborn substances in human airway replicas. A drug from a metered dose inhaler was introduced into a realistic human respiratory tract prepared by 3D printing from computer tomographic data recorded on humans, and the deposited material was collected on silicon substrates fixed to the hollow airway’s walls. The analysis of the covered area was performed by mapping the characteristic Raman peak intensity of the drug over the substrate surface; the amount was determined by integration of the total intensity measured at different points. The Raman mapping method was verified by comparison with optical microscopic images of the same surface area.