Raman and Photoluminescence Mapping of Gem Materials

Raman and photoluminescence (PL) mapping is a non-destructive method which allows gemologists and scientists to evaluate the spatial distributions of defects within a gem; it can also provide a method to quickly distinguish different species within a composite gem. This article provides a summary of this relatively new technology and its instrumentation. Additionally, we provide a compilation of new data for various applications on several gemstones. Spatial differences within diamonds can be explored using PL mapping, such as radiation stains observed on the rough surface of natural green diamonds. Raman mapping has proven useful in distinguishing between omphacite and jadeite within a composite of these two minerals, identifying various tourmaline species within a heterogeneous mixture, and determining the calcium carbonate polymorphs in pearls. Additionally, it has potential to be useful for country-of-origin determination in blue sapphires and micro-inclusion analysis. As new avenues of research are explored, more applications for gem materials will inevitably be discovered.

Voltage-Controlled Anodic Oxidation of Porous Fluorescent SiC for Effective Surface Passivation

This study investigated the fabrication of porous fluorescent SiC using a constant voltage-controlled anodic oxidation process. The application of a high, constant voltage resulted in a spatial distinction between the porous structures formed inside the fluorescent SiC substrates, due to the different etching rates at the terrace and the large step bunches. Large, dendritic porous structures were formed as the etching process continued and the porous layer thickened. Under the conditions of low hydrofluoric acid (HF) concentration, the uniformity of the dendritic porous structures through the entire porous layer was considerably improved compared with the conditions of high HF concentration. The resulting large uniform structure offered a sizable surface area, and promoted the penetration of atomic layer-deposited (ALD) Al2O3 films (ALD–Al2O3). The emission intensity in the porous fluorescent SiC was confirmed via photoluminescence (PL) measurements to be significantly improved by a factor of 128 after ALD passivation. With surface passivation, there was a clear blueshift in the emission wavelength, owing to the effective suppression of the non-radiative recombination rate in the porous structures. Furthermore, the spatial uniformity of emitted light was examined via PL mapping using three different excitation lasers, which resulted in the observation of uniform and distinctive emissions in the fluorescent SiC bulk and porous areas.

Optically Detected Magnetic Resonance Study of 3D Arrayed Silicon Vacancies in SiC pn Diodes

We demonstrated optically detected magnetic resonance (ODMR) measurements using three-dimensional (3D) arrayed silicon vacancies (VSis) in in-plane SiC pn diodes. Proton beam writing successfully created 3D arrayed VSis using different ion (proton) energies. The results of PL mapping analysis indicate that the features of luminescent spot such as size and depth can be estimated by a Monte Carlo simulation (SRIM). This suggests that diagnosis at any locations in SiC devices can be realized using VSi quantum sensors. Luminescent spots with different depth ranging 4-60 μm showed similar ODMR spectra including its contrast, which means that a similar sensor sensitivity is expected. The results suggest that 3D arrayed VSi can act as quantum sensor elements with uniform sensitivity in SiC devices.

Effective Photoluminescence Imaging of Bubbles in hBN-Encapsulated WSe2 Monolayer

Interfacial bubbles are unintentionally created during the transfer of atomically thin 2D layers, a required process in the fabrication of van der Waals heterostructures. By encapsulating a WSe2 monolayer in hBN, we study the differing photoluminescence (PL) properties of the structure resulting from bubble formation. Based on the differentiated absorption probabilities at the bubbles compared to the pristine areas, we demonstrate that the visibility of the bubbles in PL mapping is enhanced when the photoexcitation wavelength lies between the n = 1 and n = 2 resonances of the A-exciton. An appropriate choice of detection window, which includes localized exciton emission but excludes free exciton emission, further improves bubble imaging capability. The interfacial position dependence of the bubbles, whether they are located above or below the WSe2 monolayer, gives rise to measurable consequences in the PL shape.

A deconvoluted PL approach to probe the charge carrier dynamics of the grain interior and grain boundary of a perovskite film for perovskite solar cell applications

2D photoluminescence (PL) mapping revealed the blueshift of PL at grain boundaries while relatively very uniform but longer wavelengths were observed at grain interiors.

The Surface and Photoluminescence Properties of GaAs Passivated by Wet Chemical Method

The optical and chemical properties of gallium arsenide (GaAs) surfaces treated by ammonium sulfide ((NH4)2S) treatments were studied via low-temperature photoluminescence (PL). From the PL mapping and Atomic Force Microscope (AFM) results, the treatment process by (NH4)2S is quite effective to remove the oxide layer of GaAs.The PL intensity of (NH4)2S-passivated sample was higher than the untreated sample, and the homogeneity of passivated surface was much better. This strategy provides superior promising passivation method for III-V compound semiconductor material in high-speed and optoelectronic device applications.

Photoluminescence and Raman mapping characterization of WS2 monolayers prepared using top-down and bottom-up methods

Two kinds of tungsten disulfide (WS2) monolayers, respectively prepared using top-down and bottom-up approaches, were studied with Raman and photoluminescence (PL) mapping techniques.

VF Degradation of 4H-SiC PiN Diodes Using Low-BPD Wafers

In this paper, we found origin of VFdegradation of SiC bipolar devices other than a basal plane dislocation (BPD) in the SiC substrate. A VFdegradation of the 4H-SiC PiN diodes with low-BPD wafers was evaluated and its origins were discussed. Some diodes suffered VFdegradation, even though they were fabricated on BPD-free area. PL mapping, TEM image, and optical observation after KOH etching showed that there were Shockley stacking faults and combined etch-pits arrays, which were presumed to be caused by the device process.

Formation of Double Stacking Faults from Polishing Scratches on 4H-SiC (0001) Substrate

Epitaxial layers grown on mechanically lapped 4H-SiC (0001) substrates were analyzed by using scanning ion microscopy (SIM), photoluminescence (PL) mapping and transmission electron microscopy (TEM). Even in the use of substrates with standard nitrogen concentration of 1.3 × 1019 cm-3, double Shockley-type stacking faults were observed to be formed in the epitaxial layer from the interface between the epitaxial layer and the substrate without any external stresses. Surface damaged layer seems to cause the formation of not only 2SSFs but also threading edge dislocation (TED) half-loops during epitaxial growth.