Materials Science and NanoEngineering Publications

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Area-selective atomic layer deposition on 2D monolayer lateral superlattices
(Springer Nature, 2024) Park, Jeongwon; Kwak, Seung Jae; Kang, Sumin; Oh, Saeyoung; Shin, Bongki; Noh, Gichang; Kim, Tae Soo; Kim, Changhwan; Park, Hyeonbin; Oh, Seung Hoon; Kang, Woojin; Hur, Namwook; Chai, Hyun-Jun; Kang, Minsoo; Kwon, Seongdae; Lee, Jaehyun; Lee, Yongjoon; Moon, Eoram; Shi, Chuqiao; Lou, Jun; Lee, Won Bo; Kwak, Joon Young; Yang, Heejun; Chung, Taek-Mo; Eom, Taeyong; Suh, Joonki; Han, Yimo; Jeong, Hu Young; Kim, YongJoo; Kang, Kibum
The advanced patterning process is the basis of integration technology to realize the development of next-generation high-speed, low-power consumption devices. Recently, area-selective atomic layer deposition (AS-ALD), which allows the direct deposition of target materials on the desired area using a deposition barrier, has emerged as an alternative patterning process. However, the AS-ALD process remains challenging to use for the improvement of patterning resolution and selectivity. In this study, we report a superlattice-based AS-ALD (SAS-ALD) process using a two-dimensional (2D) MoS2-MoSe2 lateral superlattice as a pre-defining template. We achieved a minimum half pitch size of a sub-10 nm scale for the resulting AS-ALD on the 2D superlattice template by controlling the duration time of chemical vapor deposition (CVD) precursors. SAS-ALD introduces a mechanism that enables selectivity through the adsorption and diffusion processes of ALD precursors, distinctly different from conventional AS-ALD method. This technique facilitates selective deposition even on small pattern sizes and is compatible with the use of highly reactive precursors like trimethyl aluminum. Moreover, it allows for the selective deposition of a variety of materials, including Al2O3, HfO2, Ru, Te, and Sb2Se3.
Switching the spin cycloid in BiFeO3 with an electric field
(Springer Nature, 2024) Meisenheimer, Peter; Moore, Guy; Zhou, Shiyu; Zhang, Hongrui; Huang, Xiaoxi; Husain, Sajid; Chen, Xianzhe; Martin, Lane W.; Persson, Kristin A.; Griffin, Sinéad; Caretta, Lucas; Stevenson, Paul; Ramesh, Ramamoorthy; Rice Advanced Materials Institute
Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.
Hydrogen Peroxide Electrosynthesis in a Strong Acidic Environment Using Cationic Surfactants
(American Chemical Society, 2024) Adler, Zachary; Zhang, Xiao; Feng, Guangxia; Shi, Yaping; Zhu, Peng; Xia, Yang; Shan, Xiaonan; Wang, Haotian
The two-electron oxygen reduction reaction (2e–-ORR) can be exploited for green production of hydrogen peroxide (H2O2), but it still suffers from low selectivity in an acidic electrolyte when using non-noble metal catalysts. Here, inspired by biology, we demonstrate a strategy that exploits the micellization of surfactant molecules to promote the H2O2 selectivity of a low-cost carbon black catalyst in strong acid electrolytes. The surfactants near the electrode surface increase the oxygen solubility and transportation, and they provide a shielding effect that displaces protons from the electric double layer (EDL). Compared with the case of a pure acidic electrolyte, we find that, when a small number of surfactant molecules were added to the acid, the H2O2 Faradaic efficiency (FE) was improved from 12% to 95% H2O2 under 200 mA cm–2, suggesting an 8-fold improvement. Our in situ surface enhanced Raman spectroscopy (SERS) and optical microscopy (OM) studies suggest that, while the added surfactant reduces the electrode’s hydrophobicity, its micelle formation could promote the O2 gas transport and its hydrophobic tail could displace local protons under applied negative potentials during catalysis, which are responsible for the improved H2O2 selectivity in strong acids.
Sulfur Vacancy Related Optical Transitions in Graded Alloys of MoxW1-xS2 Monolayers
(Wiley, 2024) Ghafariasl, Mahdi; Zhang, Tianyi; Ward, Zachary D.; Zhou, Da; Sanchez, David; Swaminathan, Venkataraman; Terrones, Humberto; Terrones, Mauricio; Abate, Yohannes
Engineering electronic bandgaps is crucial for applications in information technology, sensing, and renewable energy. Transition metal dichalcogenides (TMDCs) offer a versatile platform for bandgap modulation through alloying, doping, and heterostructure formation. Here, the synthesis of a 2D MoxW1-xS2 graded alloy is reported, featuring a Mo-rich center that transitions to W-rich edges, achieving a tunable bandgap of 1.85 to 1.95 eV when moving from the center to the edge of the flake. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy showed the presence of sulfur monovacancy, VS, whose concentration varied across the graded MoxW1-xS2 layer as a function of Mo content with the highest value in the Mo-rich center region. Optical spectroscopy measurements supported by ab initio calculations reveal a doublet electronic state of VS, which is split due to the spin-orbit interaction, with energy levels close to the conduction band or deep in the bandgap depending on whether the vacancy is surrounded by W atoms or Mo atoms. This unique electronic configuration of VS in the alloy gave rise to four spin-allowed optical transitions between the VS levels and the valence bands. The study demonstrates the potential of defect and optical engineering in 2D monolayers for advanced device applications.
Influence of size and crystallinity of nanohydroxyapatite (nHA) particles on the properties of Polylactic Acid/nHA nanocomposite scaffolds produced by 3D printing
(Elsevier, 2024) Rodovalho, Arthur João Reis Lima; Barbosa, Willams Teles; Vieira, Jaqueline Leite; Oliva, Caio Athayde de; Gonçalves, Ana Paula Bispo; Cardoso, Pollyana da Silva Melo; Modolon, Henrique Borba; Montedo, Oscar Rubem Klegues; Arcaro, Sabrina; Hodel, Katharine Valéria Saraiva; Soares, Milena Botelho Pereira; Ajayan, Pulickel M.; Barbosa, Josiane Dantas Viana
Polylactic acid (PLA) and hydroxyapatite (HA) composite scaffolds have been widely studied for applications in bone tissue engineering (BTE) due to their bioactive and biocompatible properties. However, there is a need for more knowledge about the influence of size and crystallinity of HA nanoparticles (nHA) on the properties of PLA/nHA nanocomposite scaffolds produced by 3D printing. In this study, 3D printing was used to produce PLA nanocomposite scaffolds incorporated with nHA filler with different particle sizes and crystallinities. Initially, the nanocomposites were prepared by casting for 3D printing of scaffolds, which were characterized by analysis of thermal, morphological, physical-chemical, mechanical, and biological properties in vitro. The results showed that the size and crystallinity of nHA particles mainly influenced the scaffolds' mechanical properties, degradation rate, and bioactivity. Incorporating nHA provided a gain in compressive strength compared to pure PLA, superior to natural cancellous bone, which varies between 2 and 12 MPa. The lower crystallinity, 39.46 %, promoted a higher rate of degradation and bioactivity in vitro due to its solubility in the simulated fluid. All nanocomposite scaffolds showed cell viability above 90 %. The scaffolds showed suitable properties for BTE applications.
Effect of fabrication processes on BaTiO3 capacitor properties
(AIP Publishing, 2024) Jiang, Yizhe; Tian, Zishen; Kavle, Pravin; Pan, Hao; Martin, Lane W.; Rice Advanced Materials Institute
There is an increasing desire to utilize complex functional electronic materials such as ferroelectrics in next-generation microelectronics. As new materials are considered or introduced in this capacity, an understanding of how we can process these materials into those devices must be developed. Here, the effect of different fabrication processes on the ferroelectric and related properties of prototypical metal oxide (SrRuO3)/ferroelectric (BaTiO3)/metal oxide (SrRuO3) heterostructures is explored. Two different types of etching processes are studied, namely, wet etching of the top SrRuO3 using a NaIO4 solution and dry etching using an Ar+-ion beam (i.e., ion milling). Polarization-electric-field hysteresis loops for capacitors produced using both methods are compared. For the ion-milling process, it is found that the Ar+ beam can introduce defects into the SrRuO3/BaTiO3/SrRuO3 devices and that the milling depth strongly influences the defect level and can induce a voltage imprint on the function. Realizing that such processing approaches may be necessary, work is performed to ameliorate the imprint of the hysteresis loops via ex situ “healing” of the process-induced defects by annealing the ferroelectric material in a barium-and-oxygen-rich environment via a chemical-vapor-deposition-style process. This work provides a pathway for the nanoscale fabrication of these candidate materials for next-generation memory and logic applications.
Thickness-Dependent Terahertz Permittivity of Epitaxially Grown PbTe Thin Films
(MDPI, 2023) Kawahala, Nicolas M.; Matos, Daniel A.; Rappl, Paulo H. O.; Abramof, Eduardo; Baydin, Andrey; Kono, Junichiro; Hernandez, Felix G. G.; Smalley-Curl Institute
The exceptional thermoelectric properties of PbTe are believed to be associated with the incipient ferroelectricity of this material, which is caused by strong electron–phonon coupling that connects phononic and electronic dynamics. Here, we have used terahertz time-domain spectroscopy measurements to generate complex permittivity spectra for a set of epitaxially grown PbTe thin films with thicknesses between 100 nm and 500 nm at temperatures from 10 K to 300 K. Using a Drude–Lorentz model, we retrieved the physical parameters of both the phononic and electronic contributions to the THz permittivity. We observed a strong decrease, or softening, of the transverse optical phonon mode frequency with decreasing temperature, determining a thickness-independent negative ferroelectric-transition critical temperature, while we found a thickness-dependent anharmonic phonon decay lifetime. The electronic contribution to the permittivity was larger in thinner films, and both the carrier density and mobility increased with decreasing temperature in all films. Finally, we detected a thickness-dependent longitudinal optical phonon mode frequency, indicating the presence of plasmon–phonon coupling.
A scientific machine learning framework to understand flash graphene synthesis
(Royal Society of Chemistry, 2023) Sattari, Kianoosh; Eddy, Lucas; Beckham, Jacob L.; Wyss, Kevin M.; Byfield, Richard; Qian, Long; Tour, James M.; Lin, Jian; NanoCarbon Center; Welch Institute for Advanced Materials
Flash Joule heating (FJH) is a far-from-equilibrium (FFE) processing method for converting low-value carbon-based materials to flash graphene (FG). Despite its promises in scalability and performance, attempts to explore the reaction mechanism have been limited due to the complexities involved in the FFE process. Data-driven machine learning (ML) models effectively account for the complexities, but the model training requires a considerable amount of experimental data. To tackle this challenge, we constructed a scientific ML (SML) framework trained by using both direct processing variables and indirect, physics-informed variables to predict the FG yield. The indirect variables include current-derived features (final current, maximum current, and charge density) predicted from the proxy ML models and reaction temperatures simulated from multi-physics modeling. With the combined indirect features, the final ML model achieves an average R2 score of 0.81 ± 0.05 and an average RMSE of 12.1% ± 2.0% in predicting the FG yield, which is significantly higher than the model trained without them (R2 of 0.73 ± 0.05 and an RMSE of 14.3% ± 2.0%). Feature importance analysis validates the key roles of these indirect features in determining the reaction outcome. These results illustrate the promise of this SML to elucidate FFE material synthesis outcomes, thus paving a new avenue to processing other datasets from the materials systems involving the same or different FFE processes.
Hybrid method for full-field response estimation using sparse measurement data based on inverse analysis and static condensation
(Elsevier, 2022) Pal, Ashish; Meng, Wei; Nagarajaiah, Satish; Smalley-Curly Institute
In structural health monitoring, measuring the accurate and spatially dense response near critical locations of the structure can be advantageous to estimate damage to the structure. Due to several physical restrictions or limitations of the sensing method, it may not always be possible to generate reliable data at critical locations. In this study, a hybrid method is presented that makes use of the measured displacement data and finite element (FE) model of the structure to predict dense full-field response. The presented method can incorporate unknown boundary conditions and unknown body forces by applying correction/fictitious forces to match predicted and measured responses. Using static condensation followed by inverse analysis, these additional forces are found by setting up a least square problem. Due to the problem being ill-posed, L2-penalty is used to control the prediction error. Numerical simulation of a plate subjected to body force showed an accurate prediction of full-field response except for a few boundary locations. To handle this, the proposed method is used in conjunction with linear interpolation near boundary locations. The method is validated in a laboratory experiment for a plate with a notch having displacement measured using Digital Image Correlation (DIC). On comparing strains calculated using predicted displacements, FEM, and DIC, the predicted strains show better agreement with the FEM than DIC. This affirms that the proposed hybrid technique can be used at critical locations where DIC fails to provide reliable strain data.
Battery metal recycling by flash Joule heating
(AAAS, 2023) Chen, Weiyin; Chen, Jinhang; Bets, Ksenia V.; Salvatierra, Rodrigo V.; Wyss, Kevin M.; Gao, Guanhui; Choi, Chi Hun; Deng, Bing; Wang, Xin; Li, John Tianci; Kittrell, Carter; La, Nghi; Eddy, Lucas; Scotland, Phelecia; Cheng, Yi; Xu, Shichen; Li, Bowen; Tomson, Mason B.; Han, Yimo; Yakobson, Boris I.; Tour, James M.; Welch Institute for Advanced Materials; NanoCarbon Center; Applied Physics Program; Smalley-Curl Institute
The staggering accumulation of end-of-life lithium-ion batteries (LIBs) and the growing scarcity of battery metal sources have triggered an urgent call for an effective recycling strategy. However, it is challenging to reclaim these metals with both high efficiency and low environmental footprint. We use here a pulsed dc flash Joule heating (FJH) strategy that heats the black mass, the combined anode and cathode, to >2100 kelvin within seconds, leading to ~1000-fold increase in subsequent leaching kinetics. There are high recovery yields of all the battery metals, regardless of their chemistries, using even diluted acids like 0.01 M HCl, thereby lessening the secondary waste stream. The ultrafast high temperature achieves thermal decomposition of the passivated solid electrolyte interphase and valence state reduction of the hard-to-dissolve metal compounds while mitigating diffusional loss of volatile metals. Life cycle analysis versus present recycling methods shows that FJH significantly reduces the environmental footprint of spent LIB processing while turning it into an economically attractive process.
Engineering chirality at wafer scale with ordered carbon nanotube architectures
(Springer Nature, 2023) Doumani, Jacques; Lou, Minhan; Dewey, Oliver; Hong, Nina; Fan, Jichao; Baydin, Andrey; Zahn, Keshav; Yomogida, Yohei; Yanagi, Kazuhiro; Pasquali, Matteo; Saito, Riichiro; Kono, Junichiro; Gao, Weilu; Carbon Hub; Smalley-Curl Institute
Creating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm−1. Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm−1, corresponding to a g factor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.
Domain-dependent strain and stacking in two-dimensional van der Waals ferroelectrics
(Springer Nature, 2023) Shi, Chuqiao; Mao, Nannan; Zhang, Kena; Zhang, Tianyi; Chiu, Ming-Hui; Ashen, Kenna; Wang, Bo; Tang, Xiuyu; Guo, Galio; Lei, Shiming; Chen, Longqing; Cao, Ye; Qian, Xiaofeng; Kong, Jing; Han, Yimo
Van der Waals (vdW) ferroelectrics have attracted significant attention for their potential in next-generation nano-electronics. Two-dimensional (2D) group-IV monochalcogenides have emerged as a promising candidate due to their strong room temperature in-plane polarization down to a monolayer limit. However, their polarization is strongly coupled with the lattice strain and stacking orders, which impact their electronic properties. Here, we utilize four-dimensional scanning transmission electron microscopy (4D-STEM) to simultaneously probe the in-plane strain and out-of-plane stacking in vdW SnSe. Specifically, we observe large lattice strain up to 4% with a gradient across ~50 nm to compensate lattice mismatch at domain walls, mitigating defects initiation. Additionally, we discover the unusual ferroelectric-to-antiferroelectric domain walls stabilized by vdW force and may lead to anisotropic nonlinear optical responses. Our findings provide a comprehensive understanding of in-plane and out-of-plane structures affecting domain properties in vdW SnSe, laying the foundation for domain wall engineering in vdW ferroelectrics.
Accelerating multielectron reduction at CuxO nanograins interfaces with controlled local electric field
(Springer Nature, 2023) Guo, Weihua; Zhang, Siwei; Zhang, Junjie; Wu, Haoran; Ma, Yangbo; Song, Yun; Cheng, Le; Chang, Liang; Li, Geng; Liu, Yong; Wei, Guodan; Gan, Lin; Zhu, Minghui; Xi, Shibo; Wang, Xue; Yakobson, Boris I.; Tang, Ben Zhong; Ye, Ruquan
Regulating electron transport rate and ion concentrations in the local microenvironment of active site can overcome the slow kinetics and unfavorable thermodynamics of CO2 electroreduction. However, simultaneous optimization of both kinetics and thermodynamics is hindered by synthetic constraints and poor mechanistic understanding. Here we leverage laser-assisted manufacturing for synthesizing CuxO bipyramids with controlled tip angles and abundant nanograins, and elucidate the mechanism of the relationship between electron transport/ion concentrations and electrocatalytic performance. Potassium/OH− adsorption tests and finite element simulations corroborate the contributions from strong electric field at the sharp tip. In situ Fourier transform infrared spectrometry and differential electrochemical mass spectrometry unveil the dynamic evolution of critical *CO/*OCCOH intermediates and product profiles, complemented with theoretical calculations that elucidate the thermodynamic contributions from improved coupling at the Cu+/Cu2+ interfaces. Through modulating the electron transport and ion concentrations, we achieve high Faradaic efficiency of 81% at ~900 mA cm−2 for C2+ products via CO2RR. Similar enhancement is also observed for nitrate reduction reaction (NITRR), achieving 81.83 mg h−1 ammonia yield rate per milligram catalyst. Coupling the CO2RR and NITRR systems demonstrates the potential for valorizing flue gases and nitrate wastes, which suggests a practical approach for carbon-nitrogen cycling.
High-temperature electrothermal remediation of multi-pollutants in soil
(Springer Nature, 2023) Deng, Bing; Carter, Robert A.; Cheng, Yi; Liu, Yuan; Eddy, Lucas; Wyss, Kevin M.; Ucak-Astarlioglu, Mine G.; Luong, Duy Xuan; Gao, Xiaodong; JeBailey, Khalil; Kittrell, Carter; Xu, Shichen; Jana, Debadrita; Torres, Mark Albert; Braam, Janet; Tour, James M.; NanoCarbon Center and the Rice Advanced Materials Institute; Smalley-Curl Institute
Soil contamination is an environmental issue due to increasing anthropogenic activities. Existing processes for soil remediation suffer from long treatment time and lack generality because of different sources, occurrences, and properties of pollutants. Here, we report a high-temperature electrothermal process for rapid, water-free remediation of multiple pollutants in soil. The temperature of contaminated soil with carbon additives ramps up to 1000 to 3000 °C as needed within seconds via pulsed direct current input, enabling the vaporization of heavy metals like Cd, Hg, Pb, Co, Ni, and Cu, and graphitization of persistent organic pollutants like polycyclic aromatic hydrocarbons. The rapid treatment retains soil mineral constituents while increases infiltration rate and exchangeable nutrient supply, leading to soil fertilization and improved germination rates. We propose strategies for upscaling and field applications. Techno-economic analysis indicates the process holds the potential for being more energy-efficient and cost-effective compared to soil washing or thermal desorption.
Vacancy-mediated anomalous phononic and electronic transport in defective half-Heusler ZrNiBi
(Springer Nature, 2023) Ren, Wuyang; Xue, Wenhua; Guo, Shuping; He, Ran; Deng, Liangzi; Song, Shaowei; Sotnikov, Andrei; Nielsch, Kornelius; van den Brink, Jeroen; Gao, Guanhui; Chen, Shuo; Han, Yimo; Wu, Jiang; Chu, Ching-Wu; Wang, Zhiming; Wang, Yumei; Ren, Zhifeng
Studies of vacancy-mediated anomalous transport properties have flourished in diverse fields since these properties endow solid materials with fascinating photoelectric, ferroelectric, and spin-electric behaviors. Although phononic and electronic transport underpin the physical origin of thermoelectrics, vacancy has only played a stereotyped role as a scattering center. Here we reveal the multifunctionality of vacancy in tailoring the transport properties of an emerging thermoelectric material, defective n-type ZrNiBi. The phonon kinetic process is mediated in both propagating velocity and relaxation time: vacancy-induced local soft bonds lower the phonon velocity while acoustic-optical phonon coupling, anisotropic vibrations, and point-defect scattering induced by vacancy shorten the relaxation time. Consequently, defective ZrNiBi exhibits the lowest lattice thermal conductivity among the half-Heusler family. In addition, a vacancy-induced flat band features prominently in its electronic band structure, which is not only desirable for electron-sufficient thermoelectric materials but also interesting for driving other novel physical phenomena. Finally, better thermoelectric performance is established in a ZrNiBi-based compound. Our findings not only demonstrate a promising thermoelectric material but also promote the fascinating vacancy-mediated anomalous transport properties for multidisciplinary explorations.
Observation of colossal terahertz magnetoresistance and magnetocapacitance in a perovskite manganite
(Optica Publishing Group, 2023) Tay, Fuyang; Chaudhary, Swati; He, Jiaming; Peraca, Nicolas Marquez; Baydin, Andrey; Fiete, Gregory A.; Zhou, Jianshi; Kono, Junichiro; Smalley-Curl Institute
Terahertz (THz) magnetoresistance effects have been extensively investigated and have shown promising results for applications in magnetic modulations of the amplitude of THz waves. However, THz magnetocapacitance in dielectric systems, which is essential for phase modulations of THz radiation, remains largely unexplored. Here, we study the THz response of a bulk single crystal of L a 0.875 S r 0.125 M n O 3 at around its Curie temperature, observing significant magnetic-field-induced changes in the THz resistance and capacitance extracted from the optical conductivity. We discuss possible mechanisms for the observed coexistence of colossal THz magnetoresistance and magnetocapacitance in a perovskite manganite that is not multiferroic. This work enhances our understanding of colossal magnetoresistance in a complex system with THz spectroscopy and demonstrates potential use of perovskite manganites in THz technology.
Creating a near-perfect circularly polarized terahertz beam through the nonreciprocity of a magnetoplasma
(Optica Publishing Group, 2023) Ju, Xuewei; Hu, Zhiqiang; Zhu, Guofeng; Huang, Feng; Chen, Yanqing; Guo, Cuixia; Belyanin, Alexey; Kono, Junichiro; Wang, Xiangfeng
Compared to other parts of the electromagnetic spectrum, the terahertz frequency range lacks efficient polarization manipulation techniques, which is impeding the proliferation of terahertz technology. In this work, we demonstrate a tunable and broadband linear-to-circular polarization converter based on an InSb plate containing a free-carrier magnetoplasma. In a wide spectral region (∼ 0.45 THz), the magnetoplasma selectively absorbs one circularly polarized mode due to electron cyclotron resonance and also reflects it at the edges of the absorption band. Both effects are nonreciprocal and contribute to form a near-zero transmission band with a high isolation of –36 dB, resulting in the output of a near-perfect circularly polarized terahertz wave for an incident linearly polarized beam. The near-zero transmission band is tunable with magnetic field to cover a wide frequency range from 0.3 to 4.8 THz.
Magnetic Nanoparticles with Fe-N and Fe-C Cores and Carbon Shells Synthesized at High Pressures
(MDPI, 2023) Bagramov, Rustem H.; Filonenko, Vladimir P.; Zibrov, Igor P.; Skryleva, Elena A.; Kulnitskiy, Boris A.; Blank, Vladimir D.; Khabashesku, Valery N.
Nanoparticles of iron carbides and nitrides enclosed in graphite shells were obtained at 2 ÷ 8 GPa pressures and temperatures of around 800 °C from ferrocene and ferrocene–melamine mixture. The average core–shell particle size was below 60 nm. The graphite-like shells over the iron nitride cores were built of concentric graphene layers packed in a rhombohedral shape. It was found that at a pressure of 4 GPa and temperature of 800 °C, the stability of the nanoscale phases increases in a Fe7C3 > Fe3C > Fe3N1+x sequence and at 8 GPa in a Fe3C > Fe7C3 > Fe3N1+x sequence. At pressures of 2 ÷ 8 GPa and temperatures up to 1600 °C, iron nitride Fe3N1+x is more stable than iron carbides. At 8 GPa and 1600 °C, the average particle size of iron nitride increased to 0.5 ÷ 1 μm, while simultaneously formed free carbon particles had the shape of graphite discs with a size of 1 ÷ 2 μm. Structural refinement of the iron nitride using the Rietveld method gave the best result for the space group P6322. The refined composition of the samples obtained from a mixture of ferrocene and melamine at 8 GPa/800 °C corresponded to Fe3N1.208, and at 8 GPa/1650 °C to Fe3N1.259. The iron nitride core–shell nanoparticles exhibited magnetic behavior. Specific magnetization at 7.5 kOe of pure Fe3N1.208 was estimated to be 70 emu/g. Compared to other methods, the high-pressure method allows easy synthesis of the iron nitride cores inside pure carbon shells and control of the particle size. And in general, pressure is a good tool for modifying the phase and chemical composition of the iron-containing cores.
Niobium Oxide Photocatalytically Oxidizes Ammonia in Water at Ambient Conditions
(SciELO, 2024) Elias, Welman; Clark, Chelsea; Heck, Kimberly; Arredondo, Jacob; Wang, Bo; Toro, Andras; Kürtib, László; Wong, Michael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
Ammonia contamination in water is a significant environmental issue since it is toxic and leads to eutrophication. Photocatalysis has been investigated as a strategy for ammonia degradation but can potentially form toxic nitrite (NO2–) and nitrate (NO3–) byproducts. This work reports on the ability of niobium oxide (Nb2O5) to photocatalytically oxidize aqueous-phase ammonia (NH3). Whereas as-synthesized Nb2O5 showed little catalytic activity (< 1% NH3 conversion after 6 h of UV-C irradiation, at room temperature and atmospheric pressure, and under O2 headspace), Nb2O5 treated in basic solution (OH-Nb2O5) was able to photocatalytically degrade NH3 at ca. 9% conversion after six hours, with ca. 70% selectivity to the desired N2, with a first-order rate constant of ca. 12 times higher than the as synthesize catalyst (1.6 × 10–3 min–1 vs. 2.0 × 10–2 min–1). Raman spectroscopic analysis indicated the presence of terminal Nb=O species after base treatment of Nb2O5, implicating them as catalytically active sites. These results underscore how a simple structural modification can significantly affect photocatalytic activity for aqueous ammonia oxidation.
Atomically precise nanoclusters predominantly seed gold nanoparticle syntheses
(Springer Nature, 2023) Qiao, Liang; Pollard, Nia; Senanayake, Ravithree D.; Yang, Zhi; Kim, Minjung; Ali, Arzeena S.; Hoang, Minh Tam; Yao, Nan; Han, Yimo; Hernandez, Rigoberto; Clayborne, Andre Z.; Jones, Matthew R.
Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures. However, the size, structure, and chemical properties of the seeds remain poorly understood, which partially explains the lack of mechanistic understanding of many particle growth reactions. Here, we identify the majority component in the seed solution as an atomically precise gold nanocluster, consisting of a 32-atom Au core with 8 halide ligands and 12 neutral ligands constituting a bound ion pair between a halide and the cationic surfactant: Au32X8[AQA+•X-]12 (X = Cl, Br; AQA = alkyl quaternary ammonium). Ligand exchange is dynamic and versatile, occurring on the order of minutes and allowing for the formation of 48 distinct Au32 clusters with AQAX (alkyl quaternary ammonium halide) ligands. Anisotropic nanoparticle syntheses seeded with solutions enriched in Au32X8[AQA+•X-]12 show narrower size distributions and fewer impurity particle shapes, indicating the importance of this cluster as a precursor to the growth of well-defined nanostructures.

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