In order to enable further advances in microelectronics, new processes capable of precisely depositing films are required. This is especially true of processes meant for depositing two-dimensional (2D) transition metal dichalcogenides, such as MoS2, a material of particular interest due to its high potential mobility even at a thickness of a few atoms. In this work, we report industry-compatible processes for depositing crystalline MoS2 with a high degree of precision. We demonstrate the successful conversion of both MoOx and MoSx films deposited via thermal atomic layer deposition using bis(tert-butylimido)bis(dimethylamino)Mo(VI) and H2O or H2S, respectively, into crystalline MoS2 films after an anneal in H2S. The quality of the MoS2 films was assessed using Raman spectroscopy and photoluminescence (PL) response. We found that the intensity of the obtained PL spectra for MoSx:MoS2 films could be directly controlled as a function of cycle number, demonstrating a precise degree of process control. The physical characteristics of the crystalline MoS2 deposited using this process were further studied using industry-relevant structures, with the process demonstrating conformal MoS2 films deposited evenly throughout lateral trench structures with an aspect ratio of over 20:1. These results provide insight into methodologies for both precisely depositing and rapidly characterizing crystalline MoS2, which can accelerate the integration of 2D materials into leading edge microelectronics.

Atomic force microscopy (AFM) is widely used to characterize the nanoscale electrical, magnetic, mechanical, thermal, electrochemical, and electromechanical properties of materials and devices; however, it does not directly provide chemical identification. In contrast, infrared (IR) spectroscopy probes chemical bonds through their vibrational signatures but is traditionally limited to micron-scale spatial resolution by optical diffraction. Photothermal AFM-IR spectroscopy (AFM-IR) combines AFM and IR spectroscopy to enable nanoscale chemical characterization by measuring localized photothermal expansion following IR absorption. This article presents a protocol for heterodyne-detected tapping-mode photothermal AFM-IR and its application to semiconductor materials and devices. The protocol describes instrument preparation, probe selection and tuning, AFM topography imaging, IR laser alignment and optimization, acquisition of localized IR spectra, and chemical mapping of selected vibrational modes. Particular emphasis is placed on practical implementation of tapping-mode AFM-IR for semiconductor characterization and factors that influence data quality, including probe selection, resonance tuning, and IR beam alignment. Representative examples demonstrate the use of AFM-IR to distinguish material composition in patterned structures, evaluate deposited materials on semiconductor substrates, and identify residual photoresist contamination following processing. The protocol enables acquisition of co-localized topographical and chemical information with nanoscale spatial resolution and illustrates how AFM-IR can be applied to characterization challenges encountered in semiconductor research and manufacturing. To assist new users, a brief overview of AFM-IR development and a comparison of commonly used IR sources and imaging modes are also provided.

Preserving a contamination-free metal-semiconductor interface in β-Ga2O3 is critical to achieve consistently low resistance ( < 1 Ω-mm) ohmic contacts. Here, we report a scanning transmission electron microscopy study on the variation in Ti/Au ohmic contact quality to (010) β-Ga2O3 in a conventional lift-off vs a metal-first process. We observe a thin ∼1 nm carbon barrier between the Ti and Ga2O3 in a non-conductive contact fabricated by a conventional lift-off process, which we attribute to photoresist residue, not previously detected by x-ray photoelectron spectroscopy due to the thinness and patchy coverage of the carbon layer, as well as roughness of the Ga2O3 surface. This thin carbon barrier is confirmed by electron energy loss spectroscopy and atomic force microscopy-infrared spectroscopy. We believe that the presence of the thin and patchy carbon layer leads to the highly inconsistent contact behavior in previous reports on non-alloyed contacts. Adventitious carbon is also observed in a conductive ohmic contact metal-first processing on an as-grown sample. We find that a five minute active oxygen descum is sufficient to remove this carbon on as-grown samples, further improving the ohmic behavior and reducing the contact resistance Rc to 0.06 Ω-mm. We also show that an hour long UV-ozone treatment of the Ga2O3 surface can eliminate carbon residue from the lift-off processing, resulting in a low Rc of 0.05 Ω-mm.

Aggressive scaling of semiconductor technology nodes has led to copper-based interconnects beginning to approach the maximum scaling limit of the material, beyond which unacceptably high increases in interconnect resistance due to electron scattering at grain boundaries and interfaces begins to cause degradation of device performance. New materials are required for interconnect applications beyond the 7 nm node to produce devices with acceptable signal delay and power consumption parameters. Topological semimetals are one family of materials that are of interest for the replacement of copper in interconnect applications due to the predicted favorable resistance scaling, which results from topologically protected surface states that suppress electron scattering and act as conduction pathways in nanoscale films. This decrease in interconnect resistance has the potential to improve the efficiency of integrated circuits through reduced RC delay and reduced energy consumption, which is under increased scrutiny due to increasing computing demands, such as generative artificial intelligence and cloud computing. In order to aid in the integration of these promising materials into production environments, scalable synthesis methods, such as atomic layer deposition (ALD), are needed. In addition to the development of deposition chemistries for these materials, insight into how processing conditions impact the performance of the resulting film are also of importance. Here, we report on a new thermal ALD deposition chemistry for molybdenum phosphide (MoP) using molybdenum(V) chloride (MoCl 5 ) and tris(dimethylamino)phosphine (TDMAP) at temperatures between 350 °C and 425 °C. In-situ and ex-situ characterization of the resulting films was performed using quartz crystal microbalance (QCM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and four-point probe measurements. QCM measurements demonstrated a linear mass increase of 164 ng/cycle at 375 °C. Film deposition was confirmed through XRD and XPS chemical state analysis. The resulting films were near stoichiometric as determined via XPS. AFM and SEM characterization revealed a polycrystalline morphology with nanoscale grain sizes. Four-point probe measurements of the as-deposited films indicated non-ideal electrical performance which was subsequently improved through post deposition annealing. Although more work is needed to improve electrical performance, this new ALD chemistry may provide a method for the deposition of MoP films at the dimensions required for next generation technology nodes.

Area-selective deposition (ASD) is an appealing bottom-up nanopatterning technique for semiconducting devices, but its capabilities are typically limited to growth and nongrowth surfaces with significantly different chemical properties. Moreover, few studies explore ASD on "multicolor" substrates containing more than two materials. Unlocking the full potential of ASD requires new methods compatible with chemically similar surfaces, such as SiO2 and SiN. It is shown that exposing nanoscale patterns of SiO2 and SiN to MoF6 at 200 °C passivates SiO2 but allows chemical vapor deposition of polypyrrole and atomic layer deposition of TiO2 on adjacent SiN. Moreover, using three-color substrates with exposed Si-H, SiO2, and SiN, transmission electron microscopy shows that one dose of MoF6 is sufficient to achieve > 9 nm of TiO2 ASD with S ≳ 0.926 on treated Si-H and SiN versus SiO2. A mechanism for MoF6-induced passivation is proposed, involving F transfer and removal of surface -OH groups. It is hypothesized that amine groups remaining on the SiN after MoF6 subsequently hydrolyze, allowing selective growth on the fluorinated SiN with limited deposition on fluorinated SiO2. These findings provide new insight for advanced ASD and other atomic scale processes.

Layered NaTMO 2 (TM = Ni, Fe, Mn) materials with the O3-type structure are attractive positive electrodes for sodium ion batteries because of their high theoretical capacity. Li doping in these materials offers substantial enhancements to their electrochemical properties by promoting the formation of intergrowth structures that intimately integrate the substituent phases. However, the influence of the specific Li content on the structural and electrochemical properties of the intergrowth materials requires investigation. Systematic variation of Li content in Na x Li y Ni 0.4 Fe 0.2 Mn 0.4 O 2 was conducted to identify the role of Li in modification of the intergrowth structure and electrochemical performance. Li contents of 0.15 and greater generate a layered/layered Na-O3/Li-O’3 intergrowth structure. 7 Li and 23 Na solid-state nuclear magnetic resonance and x-ray absorption spectroscopy identify that when the total solubility for alkali ions in the layered structure is exceeded, Li continues to form the Li-O’3 phase while the excess Na forms residual sodium compounds such as Na 2 O. The mechanically linked Na-O3/Li-O’3 structure at higher Li content is associated with improved capacity retention in the initial cycles because it suppresses the P3 to OP2 phase transition during charge. However, high Li content increases the rate of parasitic side reactions and reduces long-term cycling stability. These side reactions are connected to the instability of the cathode-electrolyte interphase but can be partially mitigated by atomic layer deposition (ALD) coating with alumina, which significantly enhances the capacity retention and Coulombic efficiency. Overall, we find that the layered/layered Na-O3/Li-O’3 intergrowth structure can provide structural stability and suppress undesired phase transformations but is overwhelmed by the increased reactivity of the surface if not protected by surface coating.

Atomic layer etching (ALE) has emerged as a pivotal technique in the precise fabrication of two-dimensional (2D) materials, particularly molybdenum disulfide (MoS 2 ), which holds promise in the semiconductor industry due to its high mobility in monolayer form. The ability to precisely etch amorphous and crystalline MoS 2 films provides a pathway for controlling thickness, which is critical to achieving desired electrical and optical properties. Previous studies used MoF 6 and H 2 O in thermal ALE of MoS 2 . Here, we report studies of alternate sources of fluorination and oxygenation and evaluate their impact on thermal ALE of MoS 2 . Oxygen sources include water and ozone, and fluorine sources include HF/Pyridine and MoF 6 . Etch rates, uniformity, and surface chemistry post ALE were characterized using spectroscopic ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. Results indicated at ALE of amorphous MoS 2 with HF with either H 2 O or O 3 showed no signs of etching at 200 ºC or 250 ºC. Whereas the combination of MoF 6 + O 3 at 250 ºC on amorphous MoS 2 films exhibited an etch rate of 1.6 Å/cycle and a mass loss of 44 ng/cm 2 . Further MoF 6 + O 3 etching at 200 ºC showed a mass loss of 19 ng/cm 2 , similar to prior reports using MoF 6 + H 2 O at 200 ºC. Surface morphology showed little change from etching, but surface oxygen concentration increased. This research further expands the capabilities for atomic layer processing of 2D materials.

Sections of a magnesium alloy, AZ31B, joined with tungsten inert gas (TIG) welding, were examined with scanning electrochemical microscopy (SECM) and scanning Kelvin probe force microscopy (SKPFM) to investigate corrosion mechanisms by correlating observed corrosion behavior with weld-affected microstructural variations. Insight into the changing nature of the galvanic couples between weld zones and at localized microgalvanic sites were investigated using SECM and SKPFM to map both electrochemically active regions and Volta potential differences across the weld-affected zones. The formation of an Al-Zn solidification network in the fusion zone (FZ) at and near the TIG weld epicenter differs from the outer heat-affected zone (HAZ), where intermetallic particles (IMPs) are the notable secondary phase from the magnesium matrix. These microstructures were mapped with SKPFM before and after brief exposure to a salt solution, revealing micro-galvanic couples as the main driving force to corrosion initiation and propagation within each zone. The IMPs and Al-Zn solidification network act as strong cathodes and govern the corrosion processes. The galvanic coupling and evolution of the intrinsic corrosion behavior between the weld zones is explained by monitoring the hydrogen evolution reaction (HER) with SECM over time. Anodically induced cathodic activation is confirmed for this welded material, as micro-galvanic couples between microstructural features are found to transition over time to broad electrochemically active areas within the weld-affected zones, resulting in polarity reversal as time of exposure proceeds.

Two-dimensional materials, including transition metal dichalcogenides (TMDs), have attracted attention for potential use in electronic, photonic, and optoelectronic applications. Molybdenum disulfide (MoS2) is a widely studied TMD that offers potential for improving speed and efficiency in scaled electronic devices. However, advancing MoS2 and other 2D materials into high volume device manufacturing requires scalable deposition and etching processes that are compatible with manufacturing constraints. Atomic layer deposition (ALD) and atomic layer etching (ALE) are scalable deposition processes that deposit and etch films at relatively low temperatures. Together, atomic layer deposition and atomic layer etching constitute complementary facets of atomic layer processing. Here, we report progress in combining thermal ALD and thermal ALE of MoS2 followed by annealing to produce crystalline few-layer films. Combining the two processes offers greater control over film uniformity and thickness. Using ALD at 200 degrees C with MoF6 and H2S followed by ALE at 200 degrees C with MoF6 and H2O and post-deposition annealing in H2S, we achieved few-layer MoS2 films as assessed by the separation of the characteristic Raman modes of MoS2. Using analysis of the Raman spectra for indirect assessment of defect concentrations allowed correlation of the annealing conditions to the quality of the MoS2 films for accelerated process development. These combined thermal processes and the promising results represent progress towards the integration of MoS2 films into device manufacturing.

Biosensing using aptamers has been a recent interest for their versatility in detecting many different analytes across a wide range of applications, including medical and environmental applications. In our last work, we introduced a customizable aptamer transducer (AT) that could successfully feed-forward many different output domains to target a variety of reporters and amplification reaction networks. In this paper, we explore the kinetic behavior and performance of novel ATs by modifying the aptamer complementary element (ACE) chosen based on a technique for exploring the ligand-binding landscape of duplexed aptamers. Using published data, we selected and constructed several modified ATs that contain ACEs with varying length, position of the start sites, and position of single mismatches, whose kinetic responses were tracked with a simple fluorescence reporter. A kinetic model for ATs was derived and used to extract the strand-displacement reaction constant k1 and the effective aptamer dissociation constant Kd,eff, allowing us to calculate a relative performance metric, k1/Kd,eff. Comparing our results with the predictions based on the literature data, we provide useful insight into the dynamics of the adenosine AT's duplexed aptamer domain and suggest a high-throughput approach for future ATs to be developed with improved sensitivity. The performance of our ATs showed a moderate correlation to those predicted by the ACE scan method. Here, we find that predicted performance based on our ACE selection method was moderately correlated to our AT's performance.

DNA strand displacement networks are a critical part of dynamic DNA nanotechnology and are proven primitives for implementing chemical reaction networks. Precise kinetic control of these networks is important for their use in a range of applications. Among the better understood and widely leveraged kinetic properties of these networks are toehold sequence, length, composition, and location. While steric hindrance has been recognized as an important factor in such systems, a clear understanding of its impact and role is lacking. Here, a systematic investigation of steric hindrance within a DNA toehold-mediated strand displacement network was performed through tracking kinetic reactions of reporter complexes with incremental concatenation of steric moieties near the toehold. Two subsets of steric moieties were tested with systematic variation of structures and reaction conditions to isolate sterics from electrostatics. Thermodynamic and coarse-grained computational modeling was performed to gain further insight into the impacts of steric hindrance. Steric factors yielded up to 3 orders of magnitude decrease in the reaction rate constant. This pronounced effect demonstrates that steric moieties can be a powerful tool for kinetic control in strand displacement networks while also being more broadly informative of DNA structural assembly in both DNA-based therapeutic and diagnostic applications that possess elements of steric hindrance through DNA functionalization with an assortment of chemistries.

Two-dimensional (2D) layered materials offer unique properties that make them attractive for continued scaling in electronic and optoelectronic device applications. Successful integration of 2D materials into semiconductor manufacturing requires high-volume and high-precision processes for deposition and etching. Several promising large-scale deposition approaches have been reported for a range of 2D materials, but fewer studies have reported removal processes. Thermal atomic layer etching (ALE) is a scalable processing technique that offers precise control over isotropic material removal. In this work, we report a thermal ALE process for molybdenum disulfide (MoS2). We show that MoF6 can be used as a fluorination source, which, when combined with alternating exposures of H2O, etches both amorphous and crystalline MoS2 films deposited by atomic layer deposition. To characterize the ALE process and understand the etching reaction mechanism, in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR), and quadrupole mass spectrometry (QMS) experiments were performed. From temperature-dependent in situ QCM experiments, the mass change per cycle was -5.7 ng/cm2 at 150 °C and reached -270.6 ng/cm2 at 300 °C, nearly 50× greater. The temperature dependence followed Arrhenius behavior with an activation energy of 13 ± 1 kcal/mol. At 200 °C, QCM revealed a mass gain following exposure to MoF6 and a net mass loss after exposure to H2O. FTIR revealed the consumption of Mo-O species and formation of Mo-F and MoF x =O species following exposures of MoF6 and the reverse behavior following H2O exposures. QMS measurements, combined with thermodynamic calculations, supported the removal of Mo and S through the formation of volatile MoF2O2 and H2S byproducts. The proposed etching mechanism involves a two-stage oxidation of Mo through the ALE half-reactions. Etch rates of 0.5 Å/cycle for amorphous films and 0.2 Å/cycle for annealed films were measured by ex situ ellipsometry, X-ray reflectivity, and transmission electron microscopy. Precisely etching amorphous films and subsequently annealing them yielded crystalline, few-layer MoS2 thin films. This thermal MoS2 ALE process provides a new mechanism for fluorination-based ALE and offers a low-temperature approach for integrating amorphous and crystalline 2D MoS2 films into high-volume device manufacturing with tight thermal budgets.

Molybdenum disulfide (MoS 2 ) is one of several transition metal dichalcogenides consisting of a layer of transition atoms sandwiched between layers of chalcogens. Interest in MoS 2 has been driven by its 1.8 eV direct electronic band gap in monolayer form and its moderate electron mobility (10-100 cm 2 /Vs) even when only three atoms (~6.5 Å) thick. These properties offer potential for retaining or improving speed and efficiency in scaled electronic devices. Advancing MoS 2 and other 2D materials into high volume manufacturing of semiconductor devices requires scalable deposition and etching processes. The process of atomic layer deposition (ALD) has been used to deposit 2D materials and can deposit films at lower temperatures for back-end-of-line (BEOL) compatibility. However, ALD relies on covalent surface reactions. When these reactions occur at high density during film nucleation, the resulting film is typically amorphous or nanocrystalline and requires thermal annealing to form a more well-ordered layered crystal structure. A key challenge is to establish a low temperature ALD process that achieves a layered crystal structure with low defectivity. In terms of material removal, MoS 2 films have been etched by plasma-based atomic layer etching (ALE). ALE is analogous to ALD except that cyclic surface reactions promote volatility and lead to film removal rather than deposition. Together, atomic layer deposition and atomic layer etching constitute complementary facets of atomic layer processing and enable new pathways for nanomanufacturing. Here, we describe our recent progress in thermal ALD and thermal ALE of MoS 2 films. For ALD of MoS 2 , we use cycles of MoF 6 and H 2 S between 150-350 °C. Nucleation on metal oxide surfaces shows a strong temperature dependence, which is attributed in part due to the temperature dependence of surface hydroxyl groups. Density functional theory (DFT) calculations support the role of hydroxyls in promoting nucleation and reveal that MoF 6 dissociates on the surface rather than participating in a ligand exchange reaction. The dissociation reaction leads to the formation of a metal fluoride interface between the oxide surface and the MoS 2 film. Surface species following MoF 6 include MoOF 4 and MoO 3 , both of which convert to MoS 2 during the H 2 S pulse, which releases H 2 O and HF byproducts. Films deposited at 200 °C and below are amorphous but convert to a layered structure upon annealing in H 2 S. Deposition at 250 °C yields films with a layered crystal structure without post-deposition annealing. Thermal ALE of MoS 2 films deposited by ALD can be achieved using alternating exposures of MoF 6 and H 2 O. It was found that MoS 2 films are fluorinated by the MoF 6 and then oxygenated by H 2 O. Volatile byproducts are MoF 2 O 2 , H 2 S, and HF, which are primarily released during the H 2 O half-cycle. Thermal ALE of MoS 2 is temperature dependent and follows Arrhenius behavior. At 200 °C, the mass loss per cycle is 6 ng/cm 2 (~0.5 Å/cycle) and reaches 271 ng/cm 2 at 300 °C. Etch stop behavior was observed once the etched film approached the metal fluoride interface of the growth surface. Layered MoS 2 deposited by ALD with post-deposition annealing exhibited layer-by-layer etching at 0.2 Å/cycle at 250 °C. The ALD results provide key insights into the nucleation and growth of MoS 2 films using low temperature ALD. Further work is required to control basal plane orientation but achieving crystalline films well within BEOL thermal budgets is promising. The results from the ALE study provide insights into the etching reactions for MoS 2 . Combining the two processes offers greater control over MoS 2 films. Using ALD followed by ALE and post-deposition annealing, we achieved few-layer MoS 2 films. These combined thermal processes represent a pathway for integration of MoS 2 films into device manufacturing.

For continual scaling in microelectronics, new processes for precise high volume fabrication are required. Area-selective atomic layer deposition (ASALD) can provide an avenue for self-aligned material patterning and offers an approach to correct edge placement errors commonly found in top-down patterning processes. Two-dimensional transition metal dichalcogenides also offer great potential in scaled microelectronic devices due to their high mobilities and few-atom thickness. In this work, we report ASALD of MoS2 thin films by deposition with MoF6 and H2S precursor reactants. The inherent selectivity of the MoS2 atomic layer deposition (ALD) process is demonstrated by growth on common dielectric materials in contrast to thermal oxide/ nitride substrates. The selective deposition produced few layer MoS2 films on patterned growth regions as measured by Raman spectroscopy and time-of-flight secondary ion mass spectrometry. We additionally demonstrate that the selectivity can be enhanced by implementing atomic layer etching (ALE) steps at regular intervals during MoS2 growth. This area-selective ALD process provides an approach for integrating 2D films into next-generation devices by leveraging the inherent differences in surface chemistries and providing insight into the effectiveness of a supercycle ALD and ALE process.

Molybdenum disulfide (MoS 2 ) is one of several transition metal dichalcogenides consisting of a layer of transition atoms sandwiched between layers of chalcogens.[l] Interest in MoS 2 has been driven by the fact that it exhibits a 1.8 e V direct electronic band gap in monolayer form and retains a moderate electron mobility (>10 cm 2 /Vs) even when only ∽6.5 Å (three atoms) thick. [2] These properties offer potential for retaining or improving speed and efficiency in scaled electronic devices.

Nanoarchitectural control of matter is crucial for next-generation technologies. DNA origami templates are harnessed to accurately position single molecules; however, direct single molecule evidence is lacking regarding how well DNA origami can control the orientation of such molecules in three-dimensional space, as well as the factors affecting control. Here, we present two strategies for controlling the polar (θ) and in-plane azimuthal (ϕ) angular orientations of cyanine Cy5 single molecules tethered on rationally-designed DNA origami templates that are physically adsorbed (physisorbed) on glass substrates. By using dipolar imaging to evaluate Cy5′s orientation and super-resolution microscopy, the absolute spatial orientation of Cy5 is calculated relative to the DNA template. The sequence-dependent partial intercalation of Cy5 is discovered and supported theoretically using density functional theory and molecular dynamics simulations, and it is harnessed as our first strategy to achieve θ control for a full revolution with dispersion as small as ±4.5°. In our second strategy, ϕ control is achieved by mechanically stretching the Cy5 from its two tethers, being the dispersion ±10.3° for full stretching. These results can in principle be applied to any single molecule, expanding in this way the capabilities of DNA as a functional templating material for single-molecule orientation control. The experimental and modeling insights provided herein will help engineer similar self-assembling molecular systems based on polymers, such as RNA and proteins.

To enable greater control over thermal atomic layer deposition (ALD) of molybdenum disulfide (MoS2), here we report studies of the reactions of molybdenum hexafluoride (MoF6) and hydrogen sulfide (H2S) with metal oxide substrates from nucleation to few-layer films. In situ quartz crystal microbalance experiments performed at 150, 200, and 250 °C revealed temperature-dependent nucleation behavior of the MoF6 precursor, which is attributed to variations in surface hydroxyl concentration with temperature. In situ Fourier transform infrared spectroscopy coupled with ex situ x-ray photoelectron spectroscopy (XPS) indicated the presence of molybdenum oxide and molybdenum oxyfluoride species during nucleation. Density functional theory calculations additionally support the formation of these species as well as predicted metal oxide to fluoride conversion. Residual gas analysis revealed reaction by-products, and the combined experimental and computational results provided insights into proposed nucleation surface reactions. With additional ALD cycles, Fourier transform infrared spectroscopy indicated steady film growth after ∼13 cycles at 200 °C. XPS revealed that higher deposition temperatures resulted in a higher fraction of MoS2 within the films. Deposition temperature was found to play an important role in film morphology with amorphous films obtained at 200 °C and below, while layered films with vertical platelets were observed at 250 °C. These results provide an improved understanding of MoS2 nucleation, which can guide surface preparation for the deposition of few-layer films and advance MoS2 toward integration into device manufacturing.

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin probe, both of which measure the Volta potential difference (VPD) between an oscillating probe tip and a sample surface by applying a nulling voltage equal in magnitude but opposite in sign to the tip-sample potential difference. By scanning a conductive KPFM probe over a sample surface, nanoscale variations in surface topography and potential can be mapped, identifying likely anodic and cathodic regions, as well as quantifying the inherent material driving force for galvanic corrosion. Subsequent co-localization of KPFM Volta potential maps with advanced scanning electron microscopy (SEM) techniques, including back scattered electron (BSE) images, energy dispersive spectroscopy (EDS) elemental composition maps, and electron backscattered diffraction (EBSD) inverse pole figures can provide further insight into structure-property-performance relationships. Here, the results of several studies co-localizing KPFM with SEM on a wide variety of alloys of technological interest are presented, demonstrating the utility of combining these techniques at the nanoscale to elucidate corrosion initiation and propagation. Important points to consider and potential pitfalls to avoid in such investigations are also highlighted: in particular, probe calibration and the potential confounding effects on the measured VPDs of the testing environment and sample surface, including ambient humidity (i.e., adsorbed water), surface reactions/oxidation, and polishing debris or other contaminants. Additionally, an example is provided of co-localizing a third technique, scanning confocal Raman microscopy, to demonstrate the general applicability and utility of the co-localization method to provide further structural insight beyond that afforded by electron microscopy-based techniques.

The developments of two major components of a three terminal dual wavelength LED for excitation of multiple phosphors are described. Such a configuration will be novel Broadband Spectrally Dynamic Light Emitting Diode (BSDLED). First, work towards a functional tunnel junction in the GaN system is discussed. The developments of p+ and n+ GaN layers are specifically discussed in relation to their use in a buried current spreading contact layer. Second, the analysis of several phosphors and their application in a spectrally dynamic source is explored. The response to multiple wavelengths of the phosphors is analyzed to create a light source that can be tuned in “real time” to a wide range of correlated color temperatures.