Engineering topics

Bielinski, Ashley R.

Publications and source records attributed to Bielinski, Ashley R..

9 records

DOE OSTI2024

Revealing subterahertz atomic vibrations in quantum paraelectrics by surface-sensitive spintronic terahertz spectroscopy

Understanding surface collective dynamics in quantum materials is crucial for advancing quantum technologies. For example, surface phonon modes in quantum paraelectrics are thought to be essential in facilitating interfacial superconductivity. However, detecting these modes, especially below 1 terahertz, is challenging because of limited sampling volumes and the need for high spectroscopic resolution. Here, we report surface soft transverse optical (TO1) phonon dynamics in KTaO 3 and SrTiO 3 by surface-sensitive spintronic terahertz spectroscopy that can sense the collective modes only a few nanometers deep from the surface. In KTaO 3 , the TO1 mode softens and sharpens with decreasing temperature, leveling off at 0.7 terahertz. In contrast, this mode in SrTiO 3 broadens substantially below the quantum paraelectric crossover and coincides with the hardening of a sub–milli–electron volt phonon mode related to the antiferrodistortive transition. These observations that deviate from their bulk properties may have implications for interfacial superconductivity and ferroelectricity. The developed technique opens opportunities for sensing low-energy surface collective excitations.

Chu, Zhaodong↗

DOE OSTI2024

Low temperature atomic layer deposition of PbO 2 for electrochemical applications

A low temperature atomic layer deposition (ALD) process for PbO 2 was developed using bis(1-dimethylamino-2-methyl-2-propanolate)lead(II), Pb(DMAMP) 2 , and O 3 as the reactants, with a high growth rate of 2.6 Å/cycle. PbO 2 readily reduces under low oxygen partial pressures at moderate temperatures making it challenging to deposit ALD PbO 2 from Pb 2+ precursors. However, thin films deposited with this process showed small crystalline grains of α-PbO 2 and β-PbO 2 , without signs of reduced PbO x phases. The ALD PbO 2 thin films show the high electrical conductivity characteristic of bulk PbO 2 . In situ measurements of ALD PbO 2 film conductivity during growth suggest a reaction mechanism by which sub-surface oxygen mobility contributes to the growth of resistive PbO or PbO x during the Pb(DMAMP) 2 surface reaction step, which is only fully oxidized from Pb 2+ to Pb 4+ during the O 3 reaction step. These films were electrochemically reduced to PbSO 4 in H 2 SO 4 and then reoxidized to PbO 2 , demonstrating their suitability for use as an electrode material for fundamental battery research and other electrochemical applications.

atomic layer deposition↗

DOE OSTI2024

Tunable Growth of Layered Double Hydroxide Nanosheets through Hydrothermal Conversion of Atomic Layer Deposition Seed Layers

To enable the design and manufacturing of hierarchical nanomaterial architectures, there is a need for synthesis and processing methods that can enable tunable geometric control at the nanoscale while maintaining conformality on complex 3-D templates. Here, in this study, we explore the programmable control of vertically oriented Zn-Al layered double hydroxide (LDH) nanosheet arrays using atomic layer deposition (ALD) to deposit a seed layer of Al 2 O 3 , which is subsequently consumed and converted into the LDH phase under hydrothermal growth conditions. We demonstrate tunable control over the spacing and length of the nanosheets by varying the thickness of the initial ALD seed layer with subnanometer precision. This can be viewed as a nanoscale titration reaction, where Al acts as the limiting reagent during the hydrothermal synthesis of the nanosheets. Elemental mapping demonstrates the dynamic evolution of the resulting morphology, which is driven by surface diffusion and nucleation processes. The conformal nature of ALD allows for hierarchical growth of nanosheets on the surface of a variety of nonplanar substrate geometries, including microposts, paper fibers, and porous ceramic supports. This illustrates the power of ALD to enable bottom-up growth of 3-D nanoarchitectures with tunable geometries by controlling nucleation and growth in subsequent solution reactions.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Production of microchannel plates using nano-scale additive manufacturing

Microchannel plate (MCP) detectors have been the workhorse detector for many applications, including space borne ultra-violet imaging and spectrographic instruments. Recent advances in additive manufacturing (AM) have enabled fabrication of complex structures with nano-scale resolution facilitating the production of highly customizable MCPs. Using AM to produce MCPs potentially has many advantages over traditional fused glass substrates, including better material control (e.g., more robust glasses or ceramics), better control of microscopic features (e.g., unique pore geometries to improve performance), and better control of macroscopic features (e.g., printing precision curved surfaces for focal plane matching). Through a collaboration with industry, national laboratory, and university partners, small format microcapillary array substrates were produced using a standard polymer photoresin. In conclusion, these substrates were functionalized using atomic layer deposition and their performance was compared to current state-of-the-art Pb-glass and borosilicate-glass MCPs.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Resolving the Heat Generated from ZrO 2 Atomic Layer Deposition Surface Reactions

Abstract In situ pyroelectric calorimetry and spectroscopic ellipsometry were used to investigate surface reactions in atomic layer deposition (ALD) of zirconium oxide (ZrO 2 ). Calibrated and time‐resolved in situ ALD calorimetry provides new insights into the thermodynamics and kinetics of saturating surface reactions for tetrakis(dimethylamino)zirconium(IV) (TDMAZr) and water. The net ALD reaction heat ranged from 0.197 mJ cm −2 at 76 °C to 0.155 mJ cm −2 at 158 °C, corresponding to an average of 4.0 eV/Zr at all temperatures. A temperature dependence for reaction kinetics was not resolved over the range investigated. The temperature dependence of net reaction heat and distribution among metalorganic and oxygen source exposure is attributed to factors including growth rate, equilibrium surface hydroxylation, and the extent of the reaction. ZrO 2 ‐forming surface reactions were investigated computationally using DFT methods to better understand the influence of surface hydration on reaction thermodynamics.

Bielinski, Ashley R.↗

DOE OSTI2023

Resolving the Heat Generated from ZrO 2 Atomic Layer Deposition Surface Reactions

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Resolving the Heat of Trimethylaluminum and Water Atomic Layer Deposition Half-Reactions

We report that atomic layer deposition (ALD) is a surface synthesis technique that is characterized by self-limiting reactions between gas-phase precursors and a solid substrate. Although ALD processes have been demonstrated that span the periodic table, a greater understanding of the surface chemistry that affords ALD is necessary to enable greater precision, including area- and site-selective growth. We offer new insight into the thermodynamics and kinetics of the trimethylaluminum (TMA) and H 2 O ALD half-reactions with calibrated and time-resolved in situ pyroelectric calorimetry. The half-reactions produce 3.46 and 2.76 eV/Al heat, respectively, which is greater than the heat predicted by computational models based on crystalline Al 2 O 3 substrates and closely aligned with the heat predicted by standard heats of formation. The pyroelectric thin-film calorimeter offers submilisecond temporal resolution that uniquely and clearly resolves precursor delivery and reaction kinetics. Both half-reactions are observed to exhibit multiple kinetic rates, with average TMA half-reaction rates at least 2 orders of magnitude faster than the H 2 O half-reaction kinetics. Comparing the experimental heat with published computational literature and additional first-principles modeling highlights the need to refine our models and mechanistic understanding of even the most ubiquitous ALD reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Pyroelectric Heat Detection for Calibrated Measurement of Atomic Layer Deposition Reaction Heat

Atomic layer deposition (ALD) precursors and processes have been identified that enable the deposition of materials that span the periodic table. However, the detailed mechanisms, kinetics, thermodynamics, and complexities of even the most well-studied ALD half-reactions remain insufficiently resolved experimentally to test present computational hypotheses. In this work, a pyroelectric calorimeter is designed, implemented, calibrated, and electrically modeled to enable quantitative ALD reaction heat detection. The operation and response of three ALD calorimeter designs were evaluated for use as absolute ALD half-reaction heat detectors. The most effective design was calibrated in situ before being utilized to measure the heat generated by the reaction of trimethylaluminum with a hydroxylated alumina surface to produce 96 μJ/cm 2 over a reaction time of ~30 ms. With thermal and temporal resolutions down to 0.1 μJ/cm 2 and 50 ns, respectively, this sensitive and ultrafast probe is poised to improve our fundamental understanding of numerous ALD reaction mechanisms through quantitative comparison with first-principles computation predictions.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Tunable Atomic Layer Deposition into Ultra-High-Aspect-Ratio (>60000:1) Aerogel Monoliths Enabled by Transport Modeling

Atomic layer deposition (ALD) modification of ultra-high-aspect-ratio structures (>10,000:1) is a powerful platform with applications in catalysis, filtration, and energy conversion. However, the deposition of conformal and tunable ALD coatings at these aspect ratios remains challenging, resulting in empirical tradeoffs between precursor utilization and reaction time. Here, we demonstrate tunable control of the ALD infiltration depth into an aerogel monolith (AM) and develop a reaction-diffusion model to accurately describe the coating process. Specifically, we investigate the ALD exposure time and precursor dose needed to conformally coat a silica AM with pore sizes of ~20 nm, a monolith thickness of ~2.5 mm, and aspect ratios exceeding 60,000:1. We demonstrate complete infiltration into the AM, which is quantified by elemental mapping. A reaction-diffusion model is developed, which accounts for multiple doses and precursor depletion in the ALD chamber during an exposure step. The experimentally validated model enables the prediction and tuning of infiltration depth into a tortuous, high-aspect-ratio structure such as an AM, allowing for the synthesis of rationally designed material architectures. Additionally, the model allows for co-optimization of the total deposition time and percentage of unreacted precursor, which are important for the manufacturability and sustainability of ALD processing. Lastly, we demonstrate that ultra-thin ALD Al 2 O 3 coatings can be used to stabilize silica AMs against structural degradation under high-temperature annealing conditions (700-800 °C), by limiting changes in surface area and monolith volume. As a result, this improved high-temperature stability has implications for numerous aerogel applications, including catalysis and thermal insulation.

14 SOLAR ENERGY↗