AVS 67 Session CA-Contributed On Demand: Chemical Analysis and Imaging at Interfaces Contributed On Demand Session

Energy Supply and Storage Systems play pivotal role in current and future scientific and technological activities, and batteries are still on top of the list. However, batteries are slow, since they involve sluggish chemical reactions. Electrical-Double Layer Capacitors, or Super-Capacitors have recently been proposed as alternative, since they involve movement of ions only through liquid/solid interfaces.¹ Transport of the ions also controlls performance of these devices and need to be investigated during their operation. XPS is one of the most informative surface analyses techniques, which can deliver chemical as well as electrical properties of systems, when used in-Operando (o-XPS). Unfortunately, the technique requires Ultra-High-Vacuum environment, not very suitable for volatile liquids like water, but there are also several non-volatile liquids, like ionic liquids, which are also excellent electrolytes for battery and super-capacitor applications. Emergence of Ionic Liquids with several promising properties, including their low volatility, has rekindled the use of XPS.² Our recent efforts have also concentrated on ionic-liquids and their interfaces under dc and ac bias, and extended to monitoring electrochemical reactions, as well.^3-5 The common theme in our studies is the use of the bias dependent shifts in the positions of the core-levels as reflection of the electrical potentials, recorded in a non-invasive and chemically resolved fashion. We use both the magnitude and the frequency dependence of such potentials to extract pertinent information related to static, as well as dynamic chemical and/or electrochemical properties of the materials and their interfaces, configured as devices,^6-7 with particular emphases on the ionic liquids’ certain chemical/physical parameters, like steric effects, ion size, diffusivity, etc.⁹ Examples using ionic liquids, liquid poly-ethylene-glycol (PEG) and salts, as well as their mixtures, as electrolytes, will be presented and discussed.

References

1. X. Wang et al., Nature Reviews Materials, 5 (2020)787-808.
2. K.R.J. Lovelock et al., Chemical Reviews 110 (2010), 5158-5190,
3. M. Camci et al., Phys. Chem. Chem. Phys. 8 (2016), 28434-28440.
4. M.T. Camci et al., ACS Omega 2, 478-486 (2017).
5. P. Aydogan-Gokturk et al., New J. Chem., 41 (2017), 10299-10304.
6. O. Salihoglu et al., Nano Letters 18 (2018), 4541-4548.
7. C.B. Uzundal et al. J. Phys. Chem. C 123 (2019), 13192-13200.
8. P. Aydogan-Gokturk and S. Suzer, J. Phys. Chem. C 125 (2021), 9453-9460.
9. M. V. Fedorov and A. A. Kornyshev, Chemical Reviews, 114 (2014), 2978-3036.

Effects of the electrical potential developments along a co-planar capacitor, having an ionic liquid as the electrolyte, have been examined by a combination of two powerful analyses techniques, X-Ray Photoelectron Spectroscopy and Secondary Electron Microcopy for investigating the polarization dependent spatio-temporal response of the system, while imposing the device to external DC or AC (Square-Wave) biasing. The applied potential screening manifest as binding energy shifts using XPS and intensity variations using SEM. The magnitude of the developed electrical potential can be extracted under both DC (t = ∞) and AC (fast 1 kHz and slow 10 mHz) bias using both techniques to yield similar time-constants. This similarity is surprising, considering the differences in the underlying principles of the detected signals of the two techniques, but brings out the power of a synergistic combination of the two techniques with complementary capabilities, XPS with a higher chemical specificity but a lower spatial resolution, SEM with a higher spatial resolution and faster data accumulation speed.

Water-lean solvents are considered a promising technology for carbon dioxide (CO₂) capture. Such solvent molecules include but not limited to N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA), 3-methoxy-N-(pyridine-2-ylemthyl)propan-1-amine (MPMPA), and 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (IPADM-2-BOL). To better apply these solvents for direct air capture of CO₂, it is necessary to understand the molecular structures, chemical compatibility with separation membranes, and CO₂ capture mechanisms. In this presentation, we will compare the three prominent water-lean solvents as CO₂ capture candidates.Non-CO₂ loaded and CO₂ loaded amine-based solvents were studied using static and in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS). Static SIMS is used to assure peak identification.We investigate the water-lean solvents using mass spectral imaging, namely time-of-flight secondary ion mass spectrometry (ToF-SIMS).Static SIMS was used to acquire high mass resolution reference spectra and support peak identification.In situ liquid SIMS imaging was performed to study liquid structural changes and select the optimal CO₂ capture solvent using the system for analysis at the liquid vacuum interface (SALVI) microreactor. Characteristic peaks indicative of 2-EEMPA were observed using in situ liquid SIMS, for example m/z^- 73 C₄H₉O^-, 86 C₄H₈NO^- in the negative mode and m/z⁺ 29 C₂H₅⁺ and 128 C₇H₁₄NO⁺ in the positive mode. The pseudo-molecular peaks, m/z^- 215 C₁₁H₂₃N₂O₂^- deprotonated 2-EEMPA in the negative mode and m/z⁺ 217 C₁₁H₂₅N₂O₂^- protonated-2-EEMPA in the positive mode, were also observed, showing the power of molecular detection of liquid ToF-SIMS. In addition, ion pair peaks were observed including m/z⁺ 261, 305, 349, and 393 corresponding to EEMPA··· nCO₂, n=1-3, respectively, in the positive mode and the product peak of m/z^- 61 CHO₃^- in the negative mode, all suggesting complex solvent structural changes as a result of CO₂ capture in the water-lean solvents. These new in situ observations, mass spectral analysis, and liquid structural simulation facilitate the selection of a suitable candidate in direct air capture for follow-on applications.

The need for automatic tools for the metrology of semiconductor structures is more and more pressing as processes become more challenging. In addition to these tools for metrology, it is important to be able to easily transfer the process knowledge from the laboratory to the production chain. Current solutions in the semiconductor industry, mainly propose manual tools and transition from Lab to Fab is tedious and clumsy which results in slow yield ramp-up.

During R&D stages, there is a wide variability in the shape and size of objects before achieving the maturity of the recipe. For this reason, we developed a unique metrology software platform that allows users to perform automatic analysis of complex images, coming from TEM or SEM microscopes. Automation during R&D cycles is becoming a reality thanks to state of the art machine learning and deep learning approaches to overcome current traditional algorithm limitations. This metrology platform provides tools that allow users to define their structures of interest and the associated measurements. Once the structures are defined, users can analyse their images automatically and access their measurements, even with the inherited variability of R&D.

The machine learning pipeline, we present two linked strategies. The first focuses on object detection. It requires the user to annotate a rectangular box around their objects. The shape and aspect are covering any type of semiconductors structures including fuzzy boundaries such as fins, slanted structures or pillars. For the second strategy, we propose an instance segmentation method to extract precise boundaries of the defined structures.

Then, for the implementation of the algorithms library, we propose different tools that enable the use of the algorithms in a fab environment. The first one is the API (Application Programming Interface) which allows the automatic analysis of images through the Manufacturing Execution System (MES). The API will provide a report for each analysis to feed Statistical Process Control (SPC) tools.

Realtime demo of the software platform will be shown on several applications such as 3D Memory, Logic, AR/VR materials. Finally, key performance indicators will be presented and discussed.

Corrosion is an expensive problem for materials degradation that involves reactions that occur at the gas/solid and liquid/solid interfaces. These complex reactions involve surface chemical and physical changes including ion adsorption, charge transfer, redox reactions, pitting, and film growth. Iron surfaces are the classic material that corrodes, in both gases and liquids, through spontaneous redox reactions. At the liquid/solid interface, iron is oxidized at the anode with oxygen and water reduced at the cathode. Complexity arises from the presence of ions, which catalyze the surface reaction, and gas adsorption, transforming the metal surface into oxides and minerals. Chloride ions initiate the corrosion by breaking down the oxide layer and pitting the surface. Inorganic scale is grown as a result of buildup on the surface. However, the role of cations is unknown in this surface reaction. Understanding these fundamental processes are critical to addressing materials infrastructure degradation, mineral cycling, and other natural processes on Earth and other planets. Minerals, soils, and atmospheric dust are composed of iron, whose surfaces undergo electrochemical and catalytic reactions in the water and mineral cycles. Our research is presented to investigate iron surface oxidation and corrosion at the gas/liquid/solid interface using a surface catalysis approach.

We developed a new method that uses polarized modulated infrared reflection absorption spectroscopy (PM-IRRAS) with a liquid meniscus on a surface to measure the initial stages of surface oxidation and corrosion at the air/liquid/solid interface. This technique allows for observing the reaction of gradual atmospheric O₂ and CO₂ adsorption to the electrolyte/iron interface. In this presentation, the role of cations in chloride electrolytes was investigated on the oxidation and corrosion of iron interfaces. Iron surfaces were exposed to mono- and di-cation chloride electrolytes. We show how our PM-IRRAS method is used to observe the kinetics of oxidation and resulting formation of minerals at the air/electrolyte/iron interface. These results are corroborated with ex situ XPS and ATR-FTIR spectroscopy to measure the chemical changes of the interface. The physical changes of the surfaces were measured using in situ liquid AFM measurements during corrosion at the electrolyte/iron interface and after oxidation from O₂ and CO₂ at the air/iron interface. The findings of our studies suggest that cation partitioning at the air/electrolyte/iron interface catalyze and influence the mineral film formation in contrast to iron in the electrolyte, with no gradual adsorption of O₂ and CO₂. These results demonstrate how our PM-IRRAS method can be used to track other intermediate stages at gas/solid and liquid/solid interfaces for understanding electrochemical, catalytic, and environmental processes.

The pressure gap is a well-known obstacle in the development of instrumentation and catalysis. We have developed a new instrument that can perform truly high-pressure X-ray photoelectron spectroscopy (XPS) measurements, up to and over 1 bar. With the new pressure regime opened, many reactions now become possible to study. We will present several ongoing projects, including CO oxidation, methanol synthesis, Haber-Bosch process, and Fischer–Tropsch catalysis. With the higher-pressure ranges that can now be reached, direct measurements of industrial systems can yield new levels of understanding at the atomic scale.

We report low- and high-frequency electrically detected magnetic resonance (EDMR) and near-zero field magnetoresistance (NZFMR) measurements observed through spin-dependent trap-assisted-tunneling on unpassivated Si/SiO₂ metal-insulator-semiconductor (MIS) capacitors containing silicon of natural isotopic abundance and silicon depleted of ²⁹Si. This study explores the effects that electron-nuclear hyperfine interactions from nearby magnetic nuclei have on both the EDMR and NZFMR spectra. Although our measurements involve monitoring the spin-dependence of the trap-assisted-tunneling current responsible for leakage across the oxide, the high-frequency EDMR spectra resemble that of a combination of P_b0 and P_b1 silicon dangling bonds sites at the Si/SiO₂ interface. Additionally, we observed a half-field response in our low-frequency EDMR spectrum with the removal of ²⁹Si nuclei, indicating a small spin-spin separation distance. Capacitance versus voltage measurements also indicate a high interface trap density. These results suggest that the EDMR response is dominated by interface traps. We also observe a substantial narrowing of the NZFMR response with the removal of ²⁹Si nuclei. Since superhyperfine interactions between silicon dangling bonds at the Si/SiO₂ interface should be a full order of magnitude stronger than such interactions involving silicon dangling bonds defects (E’ center) within the oxide. Thus, the NZFMR results also strongly suggest a response dominated by Si/SiO₂ interface traps. These results collectively suggest very strongly that the leakage currents which we observe involve tunneling from Si/SiO₂ P_b dangling bonds to defects within the oxide, presumably oxide dangling bonds, that is E’ centers. Our results offer fundamental insight into technologically important phenomena involving oxide leakage currents in metal-oxide-semiconductor devices such as stress induced leakage currents and time dependent dielectric breakdown.

Acknowledgements

This work was supported by the Defense Threat Reduction Agency (DTRA) under award number HDTRA1-18-0012. The content of the information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred.

This work was also partially supported by the Intel Global Supply Chain internship program.

The initial oxidation processes of metals and alloys are essential for a fundamental understanding of oxidation and play key roles in corrosion prediction, catalyst design, and oxide control. Instead of uniform oxide films, 3D oxide islands are observed in many metals and alloys during initial oxidation. However, the mechanisms for 3D oxide growth are still not clear, especially at the atomic scale. Using correlated in situ environmental transmission electron microscopy (ETEM), statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu2O nano-island growth on Cu is layer-by-layer along Cu₂O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. The mechanism for this unusual layer-by-layer growth is elucidated using correlated density functional theory calculations and statistically validated quantitative analysis. These results shed new light on the epitaxial oxide growth mechanism and provide a deeper understanding of the dynamic processes involved in initial oxidation, which will ultimately help to precisely predict, design, and control nanostructured oxide growth.

Reference

M. Li, M. T. Curnan, M. A. Gresh-Sill, S. D. House, W. A. Saidi, J. C. Yang, Unusual layer-by-layer growth of epitaxial oxide islands during Cu oxidation. Nat. Commun.12, 2781 (2021).

Acknowledgment

Funding support: NSF-DMR grants 1905647, 1410055, 1508417, 1410335.

Multiple processes related to semiconductor microfabrication, aerospace industries, environmental remediation, and biomedical technology rely on plasma processing. Therefore, there exists a great need for in situ nanoscale imaging of surfaces under the plasma environment. This, however, is a challenging task for commonly used electron beam or scanning probe-based microscopies due to pressure gaps, signal interferences, strong spatial potential gradients and, etc [1]. Recently, we proposed a microflow discharge reactor equipped with a few-10s nm-thick SiN membrane as a tool to image surfaces with near-field scanning-probe-based microwave microscope immediately (a few seconds) after plasma processing with a sub-100 nm spatial resolution [2]. These SiN membranes are also largely transparent to a few keV electrons and isolate high vacuum SEM column from plasma environment around the sample, and thus enables real-time SEM imaging of a surface of interest under plasma conditions. In this communication, using CVD graphene as a model system, we report on true operando SEM imaging of the plasma-assisted etching process. In particular, signal strength, frame rate, spatial resolution, probing depth, and beam-induced effects were evaluated. We observe that graphene degrades significantly after a few seconds of ca. 200 mW oxygen plasma treatment. Under optimal conditions, a spatial resolution below 10 nm and a frame rate on the order of 1 Hz can be achieved. We also found that the contrast formation in SEM is due to the local difference in the electron emission yields of the sample and the supporting SiN membrane and it can be affected by the presence of static charges in the SiN membrane. The plasma etching of the graphene often results in the formation of highly conductive filamentary structures - a phenomenon that requires further studies.

References

[1] K. Tai, T. Houlahan Jr, J. Eden, and S. Dillon, "Integration of microplasma with transmission electron microscopy: Real-time observation of gold sputtering and island formation," Scientific reports, vol. 3, pp. 1325, 2013.

[2] A. Tselev, J. Fagan, and A. Kolmakov, "In-situ near-field probe microscopy of plasma processing," Applied Physics Letters, vol. 113, no. 26, p. 263101, 2018.

Label-free methods of spectroscopy and microscopy of live cells offer the capability to examine the cellular functions and structure in-vivo thus providing valuable insight into biomolecular components of cells [1]. However, live cells require aqueous media to be in equilibrium with interstitial fluid to survive. This requirement is inherently incompatible with the vacuum-based analytical techniques that use soft x-rays and electrons and impedes electron or soft x-ray imaging and spectroscopic studies under physiological conditions. The recent development of ultrathin molecularly impermeable X-ray (electron) transparent membranes, i.e. graphene, makes it possible to isolate the hydrated sample environment from UHV conditions and thus apply powerful spectromicroscopy tools that previously have been only used with vacuum compatible samples [2]. This approach can now be extended to (bio-) medical samples and interfaces.

Herein we report the design and fabrication of graphene encapsulated liquid cell platform for in-vivo studies of hydrated biological samples with a photon (Vis, IR, and soft X-rays) and electron-based spectromicroscopies that operate both under ambient condition and high vacuum environment. The platform consists of an array of microfabricated 50 nm thick SiN windows allowing for combinatorial batch samples analysis both in transmission and reflection signal acquisition geometry. The samples are immobilized on top of the SiN windows and wet-encapsulated conformally with graphene. The encapsulation allows the sample to be isolated from the ambient and yet have its nutrition media preserved and sufficient to be studied with conventional analytical techniques [3]. This approach minimizes the volume of liquid retained along the optical axis, reducing the parasitic absorption and scattering while still providing cells with nutrients via peripheral cites [4]. Combining the sample immobilization with an onboard biocompatible hydrogel feeding media allows for extended cellular lifetimes during the measurement. Preliminary results on the viability of graphene encapsulation for biological samples were conducted with fluorescence optical, fluorescence, SEM, and synchrotron radiation bases XRF and FTIR spectromicroscopies.

References:

1. C. W. Freudiger et al, Science, 322 (2008) p. 1857-1861.

1. A. Kolmakov et al, Nature Nanotechnology 6 (2011) p. 651.

1. A. Yulaev et al, Advanced Materials Interfaces, 4, (2016) p.1600734

Many surface-sensitive techniques have been improved recently to narrow the gap between measuring environmental conditions from vacuum to practical gas and liquid environments. To extend the pressure range and to enable measurements of the liquid phase, thin film membranes acting as windows in environmental cells have been fabricated. Herein, we present a new generation of ultrathin (2-3nm) free-standing oxide membranes made with oxide films (Al₂O₃, TiO₂, etc.). The films, synthesized using Plasma Enhanced Atomic Layer Deposition (PE-ALD), are mechanically robust and transparent to electrons and photons. Their applicability for various environmental spectroscopies, such as X-ray Photoelectron Spectroscopy (XPS, 1bar) and Fourier Transform Infrared Nanospectroscopy (nano-FTIR, solid-liquid interface) is demonstrated. The remarkable properties of such ultra-thin oxide membranes open up broad opportunities for atomic/molecular level studies of interfacial phenomena (corrosion, catalysis, electrochemical reactions, energy storage, geochemistry, and biology) in a broad range of environmental conditions.