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In this article, we discuss the synthesis of eight novel zirconium and hafnium complexes containing amidoxime ligands as potential precursors for atomic layer deposition (ALD). Two amidoximes, viz., (E)-N'-hydroxy-N,N-dimethylacetimidamide (mdaoH) and (Z)-N'-hydroxy-N,N-dimethylpivalimidamide (tdaoH), along with their Zr and Hf homoleptic complexes, Zr(mdao)4 (1), Hf(mdao)4 (2), Zr(tdao)4 (3), and Hf(tdao)4 (4) were prepared. We further synthesized heteroleptic compounds with different physical properties by introducing cyclopentadienyl (Cp) ligand, namely, CpZr(mdao)3 (5), CpHf(mdao)3 (6), CpZr(tdao)3 (7), and CpHf(tdao)3 (8). Thermogravimetric analysis was used for the assessment of the evaporation characteristics of complexes 1, 2, 5, and 6, and it revealed multistep weight losses with high residues. On the other hand, the thermogravimetric analysis curves of complexes 3, 4, 7, and 8 comprising tdao ligands revealed single-step weight losses with moderate residues. Single-crystal X-ray diffraction studies of complexes 1, 3, and 7 showed that all of the complexes have monomeric molecular structures. Complex 7 exhibited a low melting point (75 °C), good volatility, and high thermal stability compared with other complexes. Therefore, an atomic layer deposition process for the growth of ZrO2 was developed by using ZrCp(tdao)3 (7) as a novel precursor.
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This paper reports the synthesis of three novel titanium complexes containing amidoxime ligands as potential precursors for titanium nitride (TiN) thin films fabricated using atomic layer deposition (ALD). A series of ligands, viz., N'-methoxy-N-methylacetimidamide (mnnoH), N'-ethoxy-N-methylacetimidamide (ennoH), and N'-methoxy-N-methylbenzimidamide (pnnoH), were successfully synthesized and used to produce Ti(mnno)(NMe2)3 (4), Ti(enno)(NMe2)3 (5), and Ti(pnno)(NMe2)3 (6). Thermogravimetric analysis curves of complexes 4-6 revealed a single-step weight loss up to 200 °C. Pyrolysis occurred beyond 200 °C. Among the three new complexes, 5 was liquid at room temperature. Therefore, TiN was synthesized by ALD using Ti(enno)(NMe2)3 (5) as a novel precursor. A TiN thin film was deposited from the Ti(enno)(NMe2)3 (5) precursor and NH3 plasma, and self-limiting growth was achieved by varying the injection/purge duration. TiN thin film growths were observed with a growth per cycle (GPC) of 0.05-0.13 nm·cy-1 at deposition temperatures between 150 and 300 °C, while the measured resistivity was as low as 420 µΩ·cm. The high reactivity of the precursor promotes nucleation, resulting in TiN thin films with smooth, good step coverage and preferentially orientated microstructure.
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This paper describes the synthesis of eight novel zirconium and hafnium complexes containing N-alkoxy carboxamidate-type ligands, as potential precursors for metal oxides and atomic layer deposition (ALD) for HfO2. A series of ligands, viz., N-ethoxy-2,2-dimethylpropanamide (edpaH), N-ethoxy-2-methylpropanamide (empaH), and N-methoxy-2,2-dimethylpropanamide (mdpaH), were used to afford complexes Zr(edpa)4 (1), Hf(edpa)4 (2), Zr(empa)4 (3), Hf(empa)4 (4), Zr(mdpa)4 (5), Hf(mdpa)4 (6), ZrCp(edpa)3 (7), and HfCp(edpa)3 (8). Thermogravimetric analysis curves assessed for the evaporation characteristics of complexes 1-8 revealed single-step weight losses with low residues, except for the mdpa-containing complexes. Single-crystal X-ray diffraction studies of 1, 2, 5, and 6 revealed that all the complexes have monomeric molecular structures, with the central metal ion surrounded by eight oxygen atoms from the four bidentate alkoxyalkoxide ligands. Among the complexes prepared, 8 exhibited a low melting point (64 °C), good volatility (1 Torr at 112 °C), high thermal stability, and excellent endurance over 6 weeks at 120 °C. Therefore, an ALD process for the growth of HfO2 was developed using HfCp(edpa)3 (8) as a novel precursor. Furthermore, the HfO2 film exhibited a low capacitance equivalent oxide thickness of â¼1.5 nm, with Jg as low as â¼3 × 10-4 A/cm2 at Vg -1 V in a metal-insulator-semiconductor capacitor (Au/HfO2/p-Si).
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Four new and five known sesquiterpenoids were isolated from the agarwood of Aquilaria malaccensis. Aquilanols A and B (1 and 2) have an unprecedented macrocyclic humulene structure with a bicyclic 7/10 ring system. Compound 2 was obtained as a scalemic mixture that was resolved by HPLC analysis using a chiral column. Their structures were deduced based on spectroscopic data analysis, and the absolute configurations were unambiguously determined by X-ray crystallographic data and ECD spectroscopic analysis. A putative biosynthetic pathway of these sesquiterpenoids is proposed.
Assuntos
Inibidores da Colinesterase/isolamento & purificação , Sesquiterpenos/isolamento & purificação , Thymelaeaceae/química , Madeira/química , Algoritmos , Inibidores da Colinesterase/química , Cromatografia Líquida de Alta Pressão , Cristalografia por Raios X , Enterococcus faecalis/efeitos dos fármacos , Escherichia coli/efeitos dos fármacos , Klebsiella pneumoniae/efeitos dos fármacos , Laos , Testes de Sensibilidade Microbiana , Conformação Molecular , Estrutura Molecular , Sesquiterpenos Monocíclicos , Ressonância Magnética Nuclear Biomolecular , Salmonella enterica/efeitos dos fármacos , Sesquiterpenos/química , Sesquiterpenos/metabolismo , Staphylococcus aureus/efeitos dos fármacos , EstereoisomerismoRESUMO
Memristor-integrated passive crossbar arrays (CAs) could potentially accelerate neural network (NN) computations, but studies on these devices are limited to software-based simulations owing to their poor reliability. Herein, we propose a self-rectifying memristor-based 1 kb CA as a hardware accelerator for NN computations. We conducted fully hardware-based single-layer NN classification tasks involving the Modified National Institute of Standards and Technology database using the developed passive CA, and achieved 100% classification accuracy for 1500 test sets. We also investigated the influences of the defect-tolerance capability of the CA, impact of the conductance range of the integrated memristors, and presence or absence of selection functionality in the integrated memristors on the image classification tasks. We offer valuable insights into the behavior and performance of CA devices under various conditions and provide evidence of the practicality of memristor-integrated passive CAs as hardware accelerators for NN applications.
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This study describes a modified atomic layer deposition (ALD) process for fabricating BiOxSey thin films, targeting their application as high-k dielectrics in semiconductor devices, especially for two-dimensional semiconductors. Using an intermediate-enhanced ALD technique for Bi2Se3 and a plasma-enhanced ALD process for Bi2O3, a method for the sequential deposition of Bi2SeO5 ternary films has been established. The thin film has been deposited on SiO2 and TiN substrates, exhibiting growth rates of 0.17 to 0.16 nm·cycle-1 without an incubation period, thanks to facile nucleation characteristics. The resulting film exhibited high flatness and reached 96% of its theoretical density, forming a uniform nanocrystalline structure. Electrical evaluations using metal-insulator-metal capacitors indicated the dielectric constant (â¼17.6) and electrical breakdown strength (2.6 MV·cm-1), demonstrating their potential as a dielectric layer.
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As semiconductor scaling continues to reach sub-nanometer levels, two-dimensional (2D) semiconductors are emerging as a promising candidate for the post-silicon material. Among these alternatives, Bi2O2Se has risen as an exceptionally promising 2D semiconductor thanks to its excellent electrical properties, attributed to its appropriate bandgap and small effective mass. However, unlike other 2D materials, growth of large-scale Bi2O2Se films with precise layer control is still challenging due to its large surface energy caused by relatively strong interlayer electrostatic interactions. Here, we present the successful growth of a wafer-scale (â¼3 cm) Bi2O2Se film with precise thickness control down to the monolayer level on TiO2-terminated SrTiO3 using metal-organic chemical vapor deposition (MOCVD). Scanning transmission electron microscopy (STEM) analysis confirmed the formation of a [BiTiO4]1- interfacial structure, and density functional theory (DFT) calculations revealed that the formation of [BiTiO4]1- significantly reduced the interfacial energy between Bi2O2Se and SrTiO3, thereby promoting 2D growth. Additionally, spectral responsivity measurements of two-terminal devices confirmed a bandgap increase of up to 1.9 eV in monolayer Bi2O2Se, which is consistent with our DFT calculations. Finally, we demonstrated high-performance Bi2O2Se field-effect transistor (FET) arrays, exhibiting an excellent average electron mobility of 56.29 cm2/(V·s). This process is anticipated to enable wafer-scale applications of 2D Bi2O2Se and facilitate exploration of intriguing physical phenomena in confined 2D systems.
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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.
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Novel Sn precursors, Sn(tbip)2, Sn(tbtp)2, and Sn(tbta)2, were synthesized and characterized using various analytical techniques and density functional theory calculations. These precursors contained cyclic amine ligands derived from iminopyrrolidine. X-ray crystallography revealed the formation of monomeric SnL2 with distorted seesaw geometry. Thermogravimetric analysis demonstrated the exceptional volatility of all complexes. Sn(tbtp)2 showed the lowest residual weight of 2.7% at 265 °C. Sn3N4 thin films were successfully synthesized using Sn(tbtp)2 as the Sn precursor and NH3 plasma. The precursor exhibited ideal characteristics for atomic layer deposition, with a saturated growth per cycle value of 1.9 Å cy-1 and no need for incubation when the film was deposited at 150-225 °C. The indirect optical bandgap of the Sn3N4 film was approximately 1-1.2 eV, as determined through ultraviolet-visible spectroscopy. Therefore, this study suggests that the Sn3N4 thin films prepared using the newly synthesized Sn precursor are suitable for application in thin-film photovoltaic devices.
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This study describes the synthesis of 12 new germanium complexes containing ß-diketonate and/or N-alkoxy carboxamidate-type ligands as precursors for GeO2 through atomic layer deposition (ALD). A series of Ge(ß-diketonate)Cl complexes such as Ge(acac)Cl (1) and Ge(tmhd)Cl (2) were synthesized by using acetylacetone (acacH) and 2,2,6,6-tetramethyl-3,5-heptanedione (tmhdH). N-Alkoxy carboxamidate-type ligands such as N-methoxypropanamide (mpaH), N-methoxy-2,2-dimethylpropanamide (mdpaH), N-ethoxy-2-methylpropanamide (empaH), N-ethoxy-2,2-dimethylpropanamide (edpaH), and N-methoxybenzamide (mbaH) were used to afford further substituted complexes Ge(acac)(mpa) (3), Ge(acac)(mdpa) (4), Ge(acac)(empa) (5), Ge(acac)(edpa) (6), Ge(acac)(mba) (7), Ge(tmhd)(mpa) (8), Ge(tmhd)(mdpa) (9), Ge(tmhd)(empa) (10), Ge(tmhd)(edpa) (11), and Ge(tmhd)(mba) (12), respectively. Thermogravimetric analysis curves, which mostly exhibited single-step weight losses, were used to determine the evaporation properties of complexes 1-12. Interestingly, liquid complex 2 has no residue at 198 °C and therefore exhibits excellent vaporization properties and high volatility. Single-crystal X-ray diffraction studies of 1 and 7 demonstrated that the complexes had monomeric molecular structures with germanium chelated by the oxygen atoms of one or two bidentate ligands, respectively. An ALD process was developed for the growth of GeO2 using Ge(tmhd)Cl (2) as a new precursor and H2O2 as an oxidant. This study demonstrates the achievement of self-limiting growth of GeO2 films by varying the duration of injection/purge, with an observed ALD window at deposition temperatures ranging from 300 to 350 °C. The saturated growth per cycle of the GeO2 film was determined as 0.27 Å/cycle at a deposition temperature of 300 °C. The deposited films were observed to be amorphous consisting of GeO2.
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A new heteroleptic complex series of tin was synthesized by the salt metathesis reaction of SnX2 (X = Cl, Br, and I) with aminoalkoxide and various N-alkoxy-functionalized carboxamide ligands. The complexes, [ClSn(dmamp)]2 (1), [BrSn(dmamp)]2 (2), and [ISn(dmamp)]2 (3), were prepared from the salt metathesis reaction of SnX2 with one equivalent of dmamp; [Sn(dmamp)(empa)]2 (4), [Sn(dmamp)(mdpa)]2 (5), and [Sn(dmamp)(edpa)]2 (6) were prepared via the salt metathesis reaction using complex 2 with one equivalent of N-alkoxy-functionalized carboxamide ligand. Complexes 1-5 displayed dimeric molecular structures with tin metal centers interconnected by µ2-O bonding via the alkoxy oxygen atom. The molecular structures of complexes 1-5 showed distorted trigonal bipyramidal geometries with lone pair electrons in the equatorial position. Using complex 6 as a tin precursor, SnO x films were deposited by chemical solution deposition (CSD) and subsequent post-deposition annealing (PDA) at high temperatures. SnO and SnO2 films were selectively obtained under controlled PDA atmospheres of argon and oxygen, respectively. The SnO films featured a tetragonal romarchite structure with high crystallinity and a preferred growth orientation along the (101) plane. They also exhibited a lower transmittance of >52% at 400 nm due to an optical band gap of 2.9 eV. In contrast, the SnO2 films exhibited a tetragonal cassiterite crystal structure and an extremely high transmittance of >97% at 400 nm was observed with an optical band gap of 3.6 eV.
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A quantitative single-molecule tip-enhanced Raman spectroscopy (TERS) study at room temperature remained a challenge due to the rapid structural dynamics of molecules exposed to air. Here, we demonstrate the hyperspectral TERS imaging of single or a few brilliant cresyl blue (BCB) molecules at room temperature, along with quantitative spectral analyses. Robust chemical imaging is enabled by the freeze-frame approach using a thin Al2O3 capping layer, which suppresses spectral diffusions and inhibits chemical reactions and contamination in air. For the molecules resolved spatially in the TERS image, a clear Raman peak variation up to 7.5 cm-1 is observed, which cannot be found in molecular ensembles. From density functional theory-based quantitative analyses of the varied TERS peaks, we reveal the conformational heterogeneity at the single-molecule level. This work provides a facile way to investigate the single-molecule properties in interacting media, expanding the scope of single-molecule vibrational spectroscopy studies.
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A series of Ta(V) t Bu-imido/N-alkoxy carboxamide complexes, TaCl2(N t Bu)(pyridine)(edpa) (1), TaCl(N t Bu)(edpa)2 (2), Ta(N t Bu)(edpa)3 (3), TaCl2(N t Bu)(pyridine)(mdpa) (4), and Ta(N t Bu)(mdpa)3 (5), were successfully synthesized by metathesis reactions between Ta(N t Bu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = N-ethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). Furthermore, complexes 3 and 5 were simply transformed to new dimeric structures [Ta(µ2-O)(edpa)3]2 (6) and [Ta(µ2-O)(mdpa)3]2 (7) with the elimination of the N t Bu imido group by air exposure. Compounds 1-7 were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that complexes 3 and 5 have a distorted pentagonal bipyramidal geometry around the central Ta atom, with three monoanionic bidentate N-alkoxy carboxamide ligands and one t Bu imido ligand saturating the coordination of tantalum ions. TGA revealed that complexes 3 and 5 had superior thermal characteristics and stability. These complexes could potentially be applied as precursors for tantalum oxide thin films.
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The electrical switching behavior of the GeTe phase-changing material grown by atomic layer deposition is characterized for the phase change random access memory (PCRAM) application. Planar-type PCRAM devices are fabricated with a TiN or W bottom electrode (BE). The crystallization behavior is characterized by applying an electrical pulse train and analyzed by applying the Johnson-Mehl-Avrami kinetics model. The device with TiN BE shows a high Avrami coefficient (>4), meaning that continuous and multiple nucleations occur during crystallization (set switching). Meanwhile, the device with W BE shows a smaller Avrami coefficient (~3), representing retarded nucleation during the crystallization. In addition, larger voltage and power are necessary for crystallization in case of the device with W BE. It is believed that the thermal conductivity of the BE material affects the temperature distribution in the device, resulting in different crystallization kinetics and set switching behavior.
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A simple and rapid method for the simultaneous determination of 11 mycotoxins - aflatoxins B1, B2, G1 and G2; fumonisins B1, B2 and B3; ochratoxin A; zearalenone; deoxynivalenol; and T-2 toxin - in edible oils was established using liquid chromatography tandem mass spectrometry (LC-MS/MS). In this study, QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe), QuEChERS with dispersive liquid-liquid microextraction, and solvent extraction were examined for sample preparation. Among these methods, solvent extraction with a mixture of formic acid/acetonitrile (5/95, v/v) successfully extracted all target mycotoxins. Subsequently, a defatting process using n-hexane was employed to remove the fats present in the edible oil samples. Mass spectrometry was carried out using electrospray ionisation in polarity switching mode with multiple reaction monitoring. The developed LC-MS/MS method was validated by assessing the specificity, linearity, recovery, limit of quantification (LOQ), accuracy and precision with reference to Commission Regulation (EC) 401/2006. Mycotoxin recoveries of 51.6-82.8% were achieved in addition to LOQs ranging from 0.025 ng/g to 1 ng/g. The edible oils proved to be relatively uncomplicated matrices and the developed method was applied to 9 edible oil samples, including soybean oil, corn oil and rice bran oil, to evaluate potential mycotoxin contamination. The levels of detection were significantly lower than the international regulatory standards. Therefore, we expect that our developed method, based on simple, two-step sample preparation process, will be suitable for the large-scale screening of mycotoxin contamination in edible oils.
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Microextração em Fase Líquida , Micotoxinas/análise , Óleos de Plantas/química , Plantas Comestíveis/química , Solventes/química , Espectrometria de Massas em Tandem , Cromatografia LíquidaRESUMO
Direct analysis of melamine using reverse phase chromatography is a challenge because this compound's small size and strong polar nature leads to abnormal peak symmetry as well as poor retention. Here, we introduce a simple and reliable reverse phase liquid chromatographic method using sodium hexafluorophosphate to modify an acidic aqueous eluent, resulting in improved chromatographic behaviors of melamine in complex food matrices. Variables affecting the retention mechanism, including chaotrope type, concentration and stationary phase, were investigated. Under optimum conditions, melamine retention, separation efficiency, peak shape and reproducibility were significantly improved as compared to other methods that use ionic liquids or a micellar mobile phase. No interference affected melamine detection when infant formula was applied as the food matrix. Analytical reliability was demonstrated through estimation of validation parameters such as specificity, linearity, precision, accuracy and recovery. This method is suitable for routine analysis of melamine in infant formula. More noteworthy, this is the first time that an organic solvent-free mobile phase using chaotropic salt, meeting the concept of green chemistry, has been proposed.
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Cromatografia de Fase Reversa , Fórmulas Infantis/química , Triazinas/análise , Cromatografia Líquida de Alta Pressão , Análise de Alimentos , Química Verde , Humanos , Lactente , Líquidos Iônicos/química , Micelas , Reprodutibilidade dos Testes , Solventes/químicaRESUMO
The mechanism of bipolar resistive switching (BRS) of amorphous Ge2Sb2Te5 (GST) thin films sandwiched between inert electrodes (Ti and Pt) was examined. Typical bipolar resistive switching behavior with a high resistance ratio (â¼10(3)) and reliable switching characteristics was achieved. High-resolution transmission electron microscopy revealed the presence of a conductive Te-filament bridging between the top and bottom electrodes through an amorphous GST matrix. The conduction mechanism analysis showed that the low-resistance state was semiconducting and dominated by band transport, whereas Poole-Frenkel conduction governed the carrier transport in the high-resistance state. Thus, the BRS behavior can be attributed to the formation and rupture of the semiconducting conductive Te bridge through the migration of the Te ions in the amorphous GST matrix under a high electric field. The Te ions are provided by the thin (â¼5 nm) Te-rich layer formed at the bottom electrode interface.