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The emergence of 2D materials has led to increased attention on correlating the structural, optical, and optoelectronic properties of atomically thin transition metal chalcogenides like MoS2. We demonstrate the tunability of the photoluminescence (PL) properties of bulk MoS2 via implantation of Nb ions. Raman spectroscopy is used to confirm the p-type doping. The PL intensity of MoS2 is drastically enhanced by the adsorption of p-type dopants. X-ray photoelectron spectroscopy (XPS) is used to study the change of MoS2 structure postimplantation. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defect sites of MoS2 created by Nb ion implantation may have promising applications in optoelectronic devices.

We compare the distribution of hafnia chemistries as a function of sun and planet position in an ion beam sputtering system. Hafnia film chemistries were investigated both without and with planetary rotation. In the former case, the film thickness, stoichiometries and entrapped argon varied drastically as a function of sun position, with one sun position exhibiting high entrapped argon content. With full planetary rotation used during deposition, the film stoichiometry is nearly ideal with 6% entrapped argon content. It is observed that the center of the planets is an exception, with a slightly metallic stoichiometry and high entrapped argon. Interestingly, all hafnia optical films produced in this study exhibit an inverse relationship between oxygen content and entrapped argon.

Joule-heated electrodes have been used to enhance electrochemical analysis. Due to such direct heating, a steep temperature gradient is created near the electrode surface. The heating device that provides the high-frequency AC (50 kHz or more) has to be calibrated, in order to apply the desired temperature during analysis. The applied temperature of the working electrode influences both its electrical resistance and the electrochemical potential of a redox couple. Open circuit potentiometric (OCP) measurements were performed automatically with screen-printed gold loop electrodes (Au-LE), while applying 50 kHz AC heating pulses of increasing intensity provided by a ThermaLab® AC generator. Potentiometric temperature calibrations were performed using 5 mM equimolar ferri/ferrocyanide in 0.1 M of potassium chloride at 20 °C bulk temperature. Potential differences produced during each heat pulse were used to automatically calculate the electrode temperature using the temperature coefficient of this redox couple (-1.6 mV/K). The electrode resistance values at each heating pulse were obtained by measuring the heating voltage and heating current. The automatic temperature calibration experiments with five Au-LEs were shown to be highly reproducible and precise, with an RSD for the temperature of 0.24% and 4% for resistance. The average margin error of OCP temperatures were ±0.66 K at a 95% confidence level. The temperature coefficient (α) of electrical resistivity of the screen-printed gold layers was found to be 0.0025 °C-1, which is 27% lower than the theoretical value for gold metal. These findings were confirmed by DC resistance measurements using a potentiostat. Comparing the OCP temperature with the resistivity method, the temperature difference was about 0.94 °C (2.8%). Both methods enable quick, reproducible and accurate temperature calibration for disposable Au-LE, which were also used for trace mercury detection in lake water samples

The development of on-chip nonlinear optical devices in silicon is of great importance to silicon photonics and silicon chip based quantum information processing technologies. With the aim for a viable solution to overcome the lack of second harmonic generation (SHG) in Si, which is fundamentally limited by its centrosymmetric lattice structure, our work investigates SHG behaviors from Si (100) crystals with silver nanostructures formed following deposition of an ultrathin silver film and subsequent annealing. This study is aided by additional techniques, including x-ray photoelectron spectroscopy for measuring surface band bending, secondary electron microscopy for monitoring surface morphology, and Raman scattering for assessing crystal stress. The resultant Ag nanostructures are found to strongly impact the second order nonlinear polarizations in the Si surface regions rather than the bulk. The SHG intensities are increased following the Ag deposition but reduced below the Si control levels after annealing at 600 and 700 °C, which may be due to charge transfer from Ag to SiO2/Si and/or passivation of interfacial defects. Interestingly, annealing at higher temperatures (800 and 900 °C) leads to the formation of Ag nano-shell structures embedded below the SiO2/Si interface, different from the as-deposited and low-temperature annealing cases with Ag nano-spheroid structures appearing on the surface, and concomitantly, the SHG intensities are recovered and even exceed the level for the as-deposited sample in the p-Si case. The enhanced SHG following high-temperature annealing, particularly at 800 °C, is attributed to a redshift of the localized plasmon resonance of these embedded Ag nano-shells relative to the surface-covered nano-spheroids that leads to localized surface plasmon resonance around the fundamental light wavelength. Other factors including electric-field-induced SHG and the effects of stress or oxide thickness can be ruled out. This work suggests a novel approach to enhance second-order optical nonlinearity in Si through the formation of embedded metal nanostructures.

Understanding the origin of laser damage-prone precursors in high index materials such as hafnia holds the key to the development of laser damage-resistant multilayer dielectric coated optics for high power and energy laser systems. In this study, we investigate the source of sub-stoichiometry, a potent laser damage precursor, in hafnia films produced by an ion beam sputtering (IBS) deposition method and the effect of such defects on the film performance upon ns ultraviolet (UV) laser (8 ns, 355 nm) exposure. Chemical analysis of data obtained via Rutherford backscattering spectroscopy (RBS) suggests that hafnia films deposited at two different planetary locations from the same deposition run exhibit anisotropic and location-dependent stoichiometries. While the oxygen-to-hafnium ratio is at the stoichiometric value of 2 for the hafnia film at the edge location, the ratio is significantly deviated and is 1.7 for that deposited at the planetary center. The sub-stoichiometric hafnia films display a much lower 1-on-1 damage onset at 1.6 ± 0.2 J/cm2 compared to 2.3 ± 0.2 J/cm2 in a stoichiometric film. The low damage performance films also have an over three times higher damage density at fluences above initiation. Coupled with Monte Carlo simulations, we reveal that sub-stoichiometry is primarily attributed to preferential removal of oxygen during film deposition by the bombardment of energetic reflected argon neutrals. The resulting oxygen deficiencies create the sub-bandgap states which facilitate the strong laser energy coupling and reduce the resistance to laser-induced damage in the hafnia single layer films.

Silicon Photonics is a disruptive technology that promises to revolutionize high performance computing by taking advantage of light in data transmission. Due to inefficient emission from Si, an outstanding quest has been the development of non-equilibrium group IV nanoscale alloy in achieving new functionalities, such as the formation of a direct bandgap elemental semiconductor. To address this challenge, we propose to use ion beam processing to fabricate Ge 1−x Sn x alloy nanowires in Ge wafers as a potential material structure for building Si-compatible light sources. Preliminary investigations of ion implantation of Sn into Ge crystals using Rutherford backscattering technique (RBS), their structural properties examined through scanning electron microscopy (SEM) and Sn distribution using energy-dispersive X-ray spectroscopy (EDX), crystallinity and Sn substitutionality using Raman spectroscopy is presented. This non-equilibrium induction of Sn in Ge, a bottom-up approach to formation of direct bandgap Ge 1−x Sn x nanowires opens up unlimited possibilities in group IV photonics.

We developed an ion beam based processing scheme to synthesize Ag nanoparticles embedded within Si. Such embedded Ag nanostructures are expected to significantly enhance second harmonic generation thus the Pockel's effect in Si owing to the electric dipoles possessed by Ag nanostructures and the strong electric field effects associated with surface plasmon excitation of Ag nanostructures. Preliminary work in this direction has revealed an interesting correlation between the enhancement of second harmonic generation and the Ag nanostructure size/shape. Such nanosystems are capable of enhancing second harmonic generation from Si for on-chip silicon modulator fabrication.

Hafnia is a high refractive index material used in the manufacturing of dielectric coatings for next generation lasers. The formation of defects during deposition is the major barrier to realizing high laser-damage resistant coatings for future high energy density laser applications. Understanding the precursors responsible for laser-induced damage in hafnia is therefore critical. In this work, we investigate the mechanism of laser-induced damage in 90-nm thick hafnia films produced by an oxygen assisted dual ion beam sputtering (IBS) process. Under pulsed, nanosecond ultraviolet laser exposure (355 nm, 8 ns), the laser-induced damage onset is found to be strongly dependent on the amount of argon and excessive oxygen entrapped in the nanobubbles within the hafnia films. The presence of nanobubbles is revealed and confirmed by small angle X-ray scattering and scanning/transmission electron microscopy coupled with high-angle annular dark-field. The damage onset is stable initially but decreases as the energy of oxygen goes beyond 100 eV. The damage initiation is ascribed to a laser-induced plasma generation within the nanobubbles through multiphoton ionization. The results reveal that nanobubbles formed in the IBS produced coatings are a potent precursor. Although nanobubbles are commonly present in IBS films, their negative impact on laser damage resistance of hafnia films has not been previously recognized. Our findings provide a fundamental basis for the development of potential mitigation strategies required for the realization of laser damage resistant hafnia films.

While hydrogen passivation has led to enhanced luminescence in many erbium doped materials, its effects on Er oxides/silicates compounds has rarely been demonstrated. Here we report effects of forming gas annealing on the luminescence properties in such Er compound materials. A broad band photoluminescence in the ultraviolet/visible range, likely arising from structural defects in the material, is significantly suppressed after forming gas annealing. Concurrently, the Er near-infrared luminescence intensity and its lifetime increase by about a factor of two and three, respectively. The samples are further characterized with Rutherford backscattering for composition information, optical absorption for optically excitable Er concentrations and extended x-ray absorption fine structures for Er local environments. We discuss the hydrogen passivation effects in the context of diffusion limited relaxation processes and suggest pathways to further improving near-infrared luminescence properties in Er compound materials.