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A highly sensitive NO2 gas sensor of p-type SnS operating at room temperature is developed using crosslinked SnS nanoplates self-formed only on SiO2 nanorods, without an additional patterning process.

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.

Ruthenium (Ru) thin films were grown via atomic layer deposition (ALD) using a novel Ru precursor with enhanced reactivity, namely Ru(η5-cycloheptadienyl)2 (Ru(chd)2) and O2. Self-limiting growth during the Ru ALD process was achieved by varying the Ru precursor and O2 feeding times. Metallic Ru films with a low resistivity (10–16 μΩ cm) grew at deposition temperatures between 200 and 300 °C, where the growth per cycle (GPC) during Ru ALD was 0.2 to 0.4 A cy−1 at 265 °C. The Ru incubation times were considerably shorter using the novel precursor (negligible on Pt and TiN, ∼22 cycles on SiO2) compared with those associated with Ru ALD using a high-valency Ru precursor and O2. The characteristics of the Ru film were influenced by the substrate. Specifically, the Pt substrate gave rise to an amorphous film, while crystalline films were grown on the TiN and SiO2 substrates, where a high RuOx content resulted on the SiO2 substrate.

Atomic layer deposition (ALD) is a technique based on the surface reaction of precursors; thus, it strongly depends on the surface states of the substrate. We demonstrate significant changes in the structural and electrical properties of SnO thin films via modification of substrate surface states. The surface of SiO2 exposed to the atmosphere is usually contaminated by organic compounds and lacks hydroxyl groups. The plasma treatment effectively formed numerous functional groups on SiO2, eventually resulting in significant differences in the growth characteristics and properties of ALD-grown SnO films. In the case of a plasma-treated SiO2 substrate, the SnO layer was fully crystallized at the SnO/SiO2 interface, and the (00l) planes of SnO were aligned parallel to the substrate. The numerous functional groups on the plasma-treated SiO2 promoted a complete reaction on the surface, which resulted in the formation of more stoichiometric SnO containing fewer impurities near the interface. The changes in the interfacial properties by the plasma treatment of SiO2 enhanced the field-effect mobility from 0.7 to 2.0 cm2 V−1 s−1 and reduced the hysteresis voltage. The findings may contribute to the realization of complementary oxide thin film devices in future electronics.

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 contaminations 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.

This paper introduces a new atomic layer deposition process for highly conformal, nanocrystalline-as-deposited GeTe–Sb2Te3 pseudobinary film growth at a deposition temperature of 130 °C. The proces...

Analysis of mycotoxins in functional and medicinal herbs is a challenge because herbs have complicated and diverse matrices from different parts of plants as well as different species. Here, we introduce a rapid and comprehensive liquid chromatography–tandem mass spectrometry method for the determination of multi-class mycotoxins (aflatoxin B1, B2, G1, G2, ochratoxin A, zearalenone, deoxynivalenol, fumonisin B1, B2, B3 and T-2 toxin) in twenty different species of herbs that are used for both food and medicinal purposes. Various sample preparation methods were compared and optimized to obtain satisfactory extraction of mycotoxins in different matrices. The extraction efficiency was found to vary from not only extraction methods but also matrix types, demonstrating the complexity of herbal matrix. On the basis of optimization results, immunoaffinity column was selected as an extraction method to cover all types of samples. QuEChERS was also employed as a supplementary method to support the immunoaffinity column method. The developed method was validated by assessing specificity, linearity, precision, recovery, limit of quantification and uncertainty, and applied in a hundred of real samples to monitor target mycotoxins. The monitoring results were further verified using accurate high resolution mass measurements by Orbitrap mass spectrometry. As far as we know, this is the first time the multi-class mycotoxins were determined in a broad range of functional and medicinal herb matrices, with high selectivity and sensitivity. In addition, the proposed method was proven to be more efficient and sensitive than other methods.

2-dimensional materials are highlighted in various electronic device applications due to their tunable and unique anisotropic physical characteristics induced by inherent low-dimensional nature. Herein, a 2-dimensional layered structure of SnS2 is rationally adopted as an oxygen reservoir layer in a typical transition metal oxide based resistive switching device. The resistive switching media of stacked SnS2/TiO2 and lamella-like SnS2·TiO2 show 100 and 250 times higher endurance characteristics than that of individual TiO2 based resistive switching device, respectively. Additionally, the characteristic of the operation voltage distribution for resistive switching also exhibits improved homogeneity in SnS2-incorporated devices. Through the various microscopic analyses, it is revealed that the SnS2 can store the mobile oxygen ions from TiO2 in its interlayer, which facilitates boosted resistive switching characteristics. The oxygen reservoir layer is a crucial prerequisite for a reliable resistive switching device, however, the choice of materials that can serve as an oxygen reservoir is limited depending on the specific resistive switching system being used. This study demonstrates the 2-dimensional materials can be an unprecedented candidate for oxygen reservoir layers in resistive switching devices.

A series of novel Nb(V) tBu-imido/N-alkoxy carboxamide complexes, NbCl2(NtBu)(pyridine)(edpa) (1), NbCl2(NtBu)(pyridine)(mdpa) (2), and Nb(NtBu)(mdpa)3 (3), were successfully synthesized by metathesis reaction between Nb(NtBu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = Nethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). These complexes could potentially serve as precursors for Nb-containing thin films. Compounds 1–3 were characterized by FT-IR and 1H and 13C NMR spectroscopies, elemental analysis, and thermogravimetric analysis (TGA). Single crystal X-ray diffraction analysis suggested that complex 3 has a distorted pentagonal bipyramidal geometry around the central Nb atom, with three bidentate mdpa ligands and one tBu imido group saturating the coordination. TGA analysis revealed that the thermal characteristics of 3 were superior to those of 1 and 2. All prepared complexes were able to be distilled or sublimed and expected potential precursors for the fabrication of thin films.

In this paper, a new atomic layer deposition (ALD) process for depositing binary GeTe and ternary Ge–Sb–Te thin films is reported, where HGeCl3 and ((CH3)3Si)2Te were used as Ge and Te precursors, respectively. The precursors reacted together to form the films at a low substrate temperature of 50–100 °C, without involving any additional reactive process gas. HCl elimination from the Ge precursor to form the divalent Ge intermediate, GeCl2, is proposed to explain the formation of 1:1 composition stoichiometric GeTe films. The GeTe films are promising for use in phase change memory applications. Ternary Ge–Sb–Te films were deposited by combining the GeTe ALD process with a previously developed ALD process for Sb2Te3 films, where Sb(OC2H5)3 and ((CH3)3Si)2Te were employed respectively as the Sb and Te precursors. However, the composition of the ternary GeSbTe films deviated slightly from the desired GeTe–Sb2Te3 pseudobinary composition suggesting that a certain unwanted reaction was involved between the prev...

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 precisio...

In this report, a new method to deposit GeTe thin film by atomic layer deposition (ALD) is described. Ge(N(Si(CH3)3)2)2, in which Ge is in +2 oxidation state, and ((CH3)3Si)2Te were used as Ge and Te precursors, respectively. GeTe films were deposited at a low wafer temperature of 70–120 °C. To improve low reactivity of Ge(N(Si(CH3)3)2)2 toward ALD-type reaction with ((CH3)3Si)2Te, methanol vapor was coinjected with the Ge precursor and the Te precursor to form a reactive Ge intermediate having methoxy ligands and a Te intermediate having hydrogen ligands in the gas phase. This chemistry-specific ALD process deposited films various compositional GeTe alloys including the desired composition of Ge:Te = 1:1. Detailed mechanism study on the probable chemical reactions and film composition analysis revealed that the film growth could proceed via the formations of GeTe2, GeTe, and Ge2Te phases depending on the relative Ge-precursor concentration during the ALD process. The films showed feasibility for phase-ch...

The multilayered optical coating whose structure consists of optical cavity and multiple layers of ultrathin phase change material (PCM) film is presented. The color changing is enabled via transition between amorphous and crystalline phases of PCM, which is accompanied by high optical contrast. The phase transition of each PCM layer, separated by ultrathin oxide barrier, can be realized through various crystallization temperatures with respect to the different thickness of ultrathin (

An atomic layer deposition (ALD) process for SrTiO3 (STO) thin film growth was developed using a newly designed and synthesized heteroleptic Sr-precursor, {Sr(demamp)(tmhd)}2 (demampH = 1-{[2-(dimethylamino)ethyl](methyl)amino}-2-methylpropan-2-ol, tmhdH = 2,2,6,6-tetramethyl-3,5-heptanedione), which offered an intermediate reactivity toward oxygen between Sr(tmhd)2 and Sr(iPr3Cp)2. Because of the appropriate reactivity of {Sr(demamp)(tmhd)}2 toward oxygen, the abnormal initial growth behavior (due to interaction between the Sr-precursor and active oxygen contained in the underlying oxidized Ru layer) became negligible during the growth of the SrO and STO films on the Ru electrode, which allowed the growth of the SrO and STO films to be highly controllable with a moderate growth rate. Using Ti(CpMe5)(OMe)3 as the Ti-precursor and O3 as the oxygen source in the TiO2 ALD subcycle, the ALD process of the STO film revealed a growth rate of 0.05 nm/cycle and ∼85% of step coverage in terms of the thickness and ...

For phase change memories application, Ge–Sb–Te films were prepared by a stable and reliable atomic layer deposition (ALD) method. Ge(OC2H5)4, Sb(OC2H5)3, [(CH3)3Si]3Sb, and [(CH3)3Si]2Te were used to deposit various layers with compositions that can be described by combinations of GeTe2–Sb2Te layers including Ge2Sb2Te5 at a substrate temperature as low as 70 °C. A shift in composition of Sb–Te films from Sb2Te3 to Sb2Te composition was achieved by combining ligand exchange and substitution reaction between Sb in [(CH3)3Si]3Sb and Te in the Sb2Te3 layer. This surface-limited ALD process allowed highly conformal, smooth, and reproducible film growth over a contact hole structure, highlighting the feasibility of phase change memory applications.

The chemical interaction between the [(CH3)3Si]3Sb precursor and atomic layer deposited Sb2Te3 thin films was examined at temperatures ranging from 70 to 220 °C. The trimethylsilyl group [(CH3)3Si] displays greater affinity for Te than for Sb, and this drives replacement of Te in the film with Sb from the [(CH3)3Si]3Sb precursor, while eliminating volatile [(CH3)3Si]2Te, especially at elevated temperatures. The compositions of the resulting Sb–Te layers lie on the Sb2Te3–Sb tie line. The incorporation behavior of [(CH3)3Si]3Sb was explained in terms of a Lewis acid–base reaction. The exchange reactions occurred to relieve the unfavorable hard–soft Lewis acid–base pair between the trimethylsilyl group and Sb in [(CH3)3Si]3Sb. Such a reaction could be usefully adopted to control the chemical composition of ternary Ge–Sb–Te thin films.

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 (∼103) 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 (∼5 nm) Te-rich layer formed at the bottom electrode interface.

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.

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.

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&ndash, Mehl&ndash, Avrami kinetics model. The device with TiN BE shows a high Avrami coefficient (&gt, 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.

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 (∼10(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 (∼5 nm) Te-rich layer formed at the bottom electrode interface.