Ultrathin Nanolayers Research Articles

Atomic layer deposition of transition metal chalcogenide TaSx using Ta[N(CH3)2]3[NC(CH3)3] precursor and H2S plasma

As a transition metal chalcogenide, tantalum sulfide (TaSx) is of interest for semiconductor device applications, for example, as a diffusion barrier in Cu interconnects. For deposition of ultrathin nanolayers in such demanding 3D structures, a synthesis method with optimal control is required, and therefore, an atomic layer deposition (ALD) process for TaSx was developed. ALD using (tert)-butylimidotris(dimethylamido)tantalum (Ta[N(CH3)2]3[NC(CH3)3]) as the precursor and an H2S-based plasma as the coreactant results in linear growth of TaSx films as a function of the number of cycles for all temperatures in the range 150–400 °C with growth per cycle values between 1.17±0.03 Å and 0.87±0.08 Å. Saturation of the precursor and plasma dose times, established at 300 °C, was reached after 20 and 10 s, respectively. Variation of the table temperature or the plasma composition offers the possibility to tune the film properties. At 300 °C, amorphous TaS3 films were grown, while addition of H2 to the plasma led to polycrystalline TaS2 films. The difference in sulfur content in the films correlates to a change in resistivity, where the least resistive film had the lowest S content.

Architecting precise and ultrathin nanolayer interface on 4.5V LiCoO2 cathode to realize poly (ethylene oxide) cycling stability

The poly (ethylene oxide) (PEO) solid polymer electrolytes suffer from narrow electrochemical stability window and cannot match high voltage lithium cobalt oxide (LCO) cathode. Herein, an ultrathin Al2O3 nanolayer was uniformly deposited on the surface of LCO via powder atomic layer deposition (PALD) to realize poly (ethylene oxide) polymer electrolyte cycling stability. The PEO solid polymer electrolyte contains 20 % (w/w) lithium difluoro(oxalate)borate (LiDFOB) and 7.5 % (w/w) lithium titanium aluminum phosphate (LATP) with cellulose nonwoven as a support substrate. The electrolyte exhibitsionic conductivity of 1.2×10−4 S cm−1, an electrochemical stability window of 4.5 V (vs. Li+/Li) and lithium-ion transference number of 0.38. Al2O3@LCO/PEO-LiDFOB20%-LATP7.5%/Li cell at high cut-off 4.5 V delivered better initial discharge specific capacity of 178.5 mAh g−1 and achieved a capacity retention ratio of 81.6 % after 200 cycles under 0.1 C at 50 °C. Further analysis showed that Al2O3 layer served as stable a protective layer to suppress the generation of strong oxidative Co4+ and O– species and separate from the PEO solid polymer electrolyte, inhibiting the side reactions at the cathode-side interface. Therefore, architecting precise and ultrathin protective nanolayer interface on high voltage LCO cathode via PALD is conducive to cycling performance of solid polymer electrolyte.

Polyvinylpyrrolidone-assisted synthesis of ultrathin multi-nanolayered Cu2Nb34O87−x for advanced Li+ storage

The ultrathin multi-nanolayered structure with ultrathin monolayer thickness (<10 nm) and certain interlayer spacing can significantly shorten Li+ paths and alleviate the volume effect for Li+-storage materials. However, unlike layered materials such as MXene and MoS2, shear ReO3-type niobates have difficulty forming ultrathin multi-nanolayered structures due to their crystal structures, which still remains a challenge. Herein, by a polyvinylpyrrolidone (PVP)-assisted solvothermal method, we first synthesize ultrathin multi-nanolayered Cu2Nb34O87−x with oxygen vacancies composed of ultrathin nanolayers (2–10 nm in thickness) and interlayer spacing (1–5 nm). Oxygen vacancies can radically enhance the inherent electronic/ionic conductivity and Li+ diffusion coefficient of this material. The PVP-induced formation mechanism of this material is expounded in detail. The well-preserved ultrathin multi-nanolayered structure and excellent multi-electron electrochemical reversibility (Nb5+ ↔ Nb4+ ↔N b3+ and Cu2+ ↔ Cu+) of this material during cycling are fully verified. Based on an ultrathin multi-nanolayered structure and oxygen vacancies, this material as the anode of lithium-ion batteries is highly competitive among reported shear ReO3-type Cu-Nb-O anodes, displaying a high reversible capacity (315.3 mAh g−1 after 300 cycles at 1 C), durable cycling stability (85.7 % capacity retention after 1000 cycles at 10 C), and outstanding rate performance. Moreover, the application of this material to lithium-ion capacitors generates a large energy density (97.9 Wh kg−1 at 87.5 W kg−1) and a high power density (17,500 W kg−1 at 12.6 Wh kg−1), thus further indicating its fast faradaic pseudocapacitive behavior for practical applications. The results of this work indicate a breakthrough in synthesizing ultrathin multi-nanolayered shear ReO3-type niobates.

Ultrathin nanolayer constituted by a natural polysaccharide achieves “egg-box” structured SnO2 nanoparticles toward efficient and stable perovskite solar cells

Notorious nonradiative recombination and retarded charge dynamics corrodes the performance of perovskite solar cells (PSCs). Accordingly, a natural polysaccharide sodium alginate (SA) is introduced into SnO2 colloid solution, developing “egg-box” structured SnO2 nanoparticles wrapped by ultrathin SA nanolayer to achieve a bottom-up holistic passivation strategy. The active oxygen-containing functional groups with lone pair electrons of SA can coordinate with uncoordinated Sn4+/Pb2+. Meanwhile, hydroxyl groups can form hydrogen bonds with I of perovskite. Additionally, Na+ can fill the cation vacancies in perovskite and electrostatically interacts with the halogen ions, hindering the formation of iodine Frenkel defects. Based on the synergistic effects of various functional groups, SA-modification can simultaneously inhibit the agglomeration of SnO2 nanoparticles, improve carrier dynamics, release tensile stress and promote crystallization of perovskite. Finally, the SA-optimized methylammonium-free (MA-free) device fabiricated entirely in ambient air achieves a champion efficiency up to 23.61%. The optimized devices without encapsulation exhibit better thermal and moisture stability, with the PCE retaining 80.2% of its initial efficiency after 1080 h of thermal aging at 60 °C and 91.1% of its initial efficiency after 1440 h at 25% relative humidity, respectively.

Titanium Nitride Modified Fiber Optic Interferometer for Refractive Index Sensitivity Enhancement.

As one of the most well-established biocompatible transition metal nitrides, titanium nitride (TiN) has been widely applied for fiber waveguide coupling device applications. This study proposes a TiN-modified fiber optic interferometer. Benefiting from the unique properties of TiN, including ultrathin nanolayer, high refractive index, and broad-spectrum optical absorption, the refractive index (RI) response of the interferometer is greatly enhanced, which is desired all the time in the field of biosensing. The experimental results show that the deposited TiN nanoparticles (NPs) can enhance the evanescent field excitation and modulate the effective RI difference of the interferometer, which eventually results in the RI response enhancement. Besides, after incorporating the TiN with different concentrations, the resonant wavelength and the RI responses of the interferometer are enhanced to varying degrees. Benefitting from this advantage, the sensing performances, including sensitivity and measurement range, can be flexibly adapted based on different detection requirements. Since RI response can effectively reflect the detection ability of biosensors, the proposed TiN-sensitized fiber optic interferometer can be potentially applied for high-sensitive biosensing applications.

In situ construction of cyano-modified g-C3N4 nanolayer-coated SrTiO3 nanotubes by gas-solid reaction for efficient photocatalytic solar fuel production

For the transformation of the global energy structure, photocatalyst-based artificial photosynthesis for solar-to-chemical energy conversion has been regarded as promising. Herein, we report the homogenous construction of cyano-modified g-C3N4 ultrathin nanolayers onto SrTiO3 nanotubes using a simple one-step gas–solid reaction, as well as their application to photocatalytic H2 evolution and CO2 reduction. The creation of one-dimensional core–shell nanostructures and type II heterojunctions broaden visible light absorption range and shorten charge transfer path. The electron-absorbing cyano introduced in situ without any auxiliary salts can not only provide an appropriate driving force for electron transport and extend the active site of photocatalytic reaction, but also alter the band gap to accomplish energy band alignment. Moreover, in-situ irradiation X-ray photoelectron spectroscopy (ISI-XPS) was used to confirm the dual active site system consisting of cyano and SrTiO3. This work aims to promote the development of the surface modification of core-shell nanostructured photocatalysts.

A universal strategy for large-scale and controlled fabrication of conductive mesoporous polymer monolayers

A bottom-up approach for constructing large-area ultrathin nanolayers with meso-architectures and simultaneously patterning them on the required substrates is still facinga significant challenge thus far. In this work, polydopamine tightly adheres to substrate surfaces, then adsorbs and assembles amphipathic micelles to form a closely arranged monolayer. This surface modification enables the oriented growth of different precursors to prepare functional monolayer coating of various mesoporous materials with regular arrays and ultrathin thickness, including polymers (polypyrrole (PPy) and polyaniline (PANi), etc.) and metal oxides (tin oxide (SnO2), etc.). Furthermore, this process allows for the direct integration of material construction and device fabrication in one step. The resultant single-layer mesoporous PPy-based gas sensor device achieves an excellent sensing response to ammonia (concentration as low as 200 ppb), with an extremely rapid response time (4 s) and recovery time (13 s). This work provides a general control on engineering mesoscale materials and effective integration of material growth, structural control, and device fabrication for potential applications.

A Precise BSA Protein Template Developed the C, N, S Co-Doped Fe3O4 Nanolayers as Anodes for Efficient Lithium-Ion Batteries

Protein has abundant and exquisite multidimensional structures and numerous functional groups that can bind metal ions. Taking protein as a template can effectively promote the synthesis of metal oxide nanomaterials and form multidimensional network structures, which has great prospects in preparing high-performance lithium-ion battery (LIB) anode. However, these templates only act as carbon skeletons to support electrode materials. The biodiversity of proteins in precise regulation is not fully realized, limiting the application potential of protein templates. In this work, we selected biomineralized protein BSA as the template for the electrode materials synthesis, successfully regulated the nanocrystal and microstructure, and obtained a high-quality anode material with nanonetwork and ultrathin nanolayer structure. The nanocrystals of synthesized anode materials showed good uniformity and monodispersity, achieved the heteroatom doping, such as N and S elements, and in situ carbon coating. The carbon nanolayer structure formed by BSA protein improved the capacitance and stability of electrode materials, revealing a good application value for the LIB anode. This research can give us a further understanding and expand the idea of protein templates in the preparation of high-performance energy storage nanomaterials.

Ultrathin MnO2-Coated FeOOH Catalyst for Indoor Formaldehyde Oxidation at Ambient Temperature: New Insight into Surface Reactive Oxygen Species and In-Field Testing in an Air Cleaner.

Herein, we tailored a series of ultrathin MnO2 nanolayers coated on the surface of commercial goethite (α-FeOOH) by a facile in situ chemical precipitation method. α-FeOOH inhibited the MnO2 crystal growth via the incorporation of K+ ions between MnO2 and α-FeOOH interfaces during the synthesis process. The hybrid design of MnO2 with an ultrathin nanolayer structure could reduce the electron transfer resistance and bring abundant oxygen vacancies, accelerating the activation of molecular O2 to generate more oxygen-free radical species and favoring the thermodynamic HCHO oxidation. The ROS quenching in gas/aqueous systems and DRIFTS results demonstrated that •O2- was responsible for HCHO oxidization, which assisted the preliminary intermediate dioxymethylene dehydrogenation into formate species. The 25%MnO2@FeOOH(25wt% of MnO2) catalyst was subsequently loaded into the filter substrates of a commercial air cleaner and tested in an indoor room with actual application conditions. As a result, the composite filter could eliminate different initial concentrations of HCHO (150-450 ppb) to the WHO guideline value (≈81 ppb) within 60 min. Furthermore, the 25%MnO2@FeOOH sample was also effective against the representative bacteria and mold in indoor air. This study provides new insight into the role of the chemisorbed ROS for HCHO oxidation at ambient temperature.

Zn Dopants Synergistic Oxygen Vacancy Boosts Ultrathin CoO Layer for CO2 Photoreduction

AbstractPhotoreduction of CO2 without photosensitizers and scavengers runs into the development bottleneck for lack of excellent photocatalysts and ambiguous reduction mechanism. Herein, an ultrathin CoO layer containing Zn‐dopants and O‐vacancies (Vo‐Zn‐CoO) is designed as an archetype to explore the influence mechanism of Zn on O‐vacancies in ultrathin nanolayer for CO2 photoreduction. DFT calculations illustrate that Zn‐dopants not only reduce formation barriers of *COOH and *CO intermediates, but also form π‐back‐bonding with *CO stimulating CH4 evolution. Finally, Vo‐Zn‐CoO layer significantly enhances CO2 photoreduction efficiency and CH4 selectivity with 26.8 µmol g−1 h−1 (63.8%) compared to 7.2 µmol g−1 h−1 (23.6%) for CoO layer with O‐vacancies. Moreover, the synergistic effect of Zn and O‐vacancies benefits the stability of O‐vacancies in photocatalysts, achieving durable photocatalytic performance of Vo‐Zn‐CoO layer. This work manifests that the strategy of metal atoms synergistic O‐vacancies is effective to optimize CO2 photocatalytic efficiency, selectivity, and stability of photocatalyst with O‐vacancies.

Influence of Bias Potential Magnitude on Structural Engineering of ZrN-Based Vacuum-Arc Coatings

The creation of the scientific foundations for the structural engineering of ultrathin nanolayers in multilayer nanocomposites is the basis of modern technologies for the formation of materials with unique functional properties. It is shown that an increase in the negative bias potential (from -70 to -220 V) during the formation of vacuum-arc nanocomposites based on ZrN makes it possible not only to control the preferred orientation of crystallites and substructural characteristics but also changes the conditions for conjugation of crystal lattices in ultrafine (about 8 nm) nanolayers.

Nanostabilization of tetragonal distorted FeCo variants in ultra-thin FeCo/TiN multilayer films

Composites of ultra-thin nanolayers of FeCo/TiN with individual layer thickness of a few unit cells offer stability at elevated temperatures and exhibit defined magnetic properties which can be tuned by variying the layers thickness making them interesting candiates as components for magnetoelectric (ME) sensors. Initial studies describing the nanostructure of such thin films, however, left uncertainty about their exact crystal structure. With aberration-corrected microscopes the characterization of the local structure down to the atomic scale is possible to address the real structure with high precision. Here, by means of atomic resolution TEM imaging together with X-ray diffraction analysis, we were able to describe the nanostructure to be composed of individual layers of FeCo and TiN forming a superlattice with a defined cube-on-cube orientation relationship. The simulation of electron diffraction pattern featuring superlattice reflections on basis of structural modeling together with geometric phase analysis verified a defined orientation relationship resolving in the nanostabilization of a tetragonal distorted FeCo unit cell with c/a < 1.

Importance of Robust and Reliable Nanochannel Sealing for Enhancing Drug Delivery Efficacy of Hollow Mesoporous Nanocontainer.

Hollow mesoporous silica nanoparticles (HMSNPs) have been widely explored in the biomedical field as drug delivery nanocarriers by virtue of their large hollow cavity. However, the connectivity between the internal cavity and the outside environment by numerous nanochannels on the mesoporous shell allows for possible drug leakage, leading to nonsufficient drug loading due to unreliable capping of the nanopores. In addition, the issue of ensuring effective utilization of the hollow cavity for achieving high drug loading capacity of HMSNPs is seldom addressed. Thus, in this work, HMSNPs with the diameter of about 400 nm were prepared and completely encapsulated by growing an ultrathin nanolayer of aluminum oxide (Al2O3) of about 20 nm on the surface of the mesoporous shell with template-assisted sol-gel chemistry. The robust sealing layer of Al2O3 can ensure "zero release" of the delivery system under neutral conditions, which is crucial for achieving high drug loading capacity by physical encapsulation of cargo molecules within the hollow cavity. The Al2O3-coated HMSNP (denoted as HMSNP Al2O3 can improve the drug loading capacity up to about 35 wt %, realizing loading efficiency as high as ten times the maximum value without Al2O3 under the same conditions. Besides, the encapsulation nanolayer of Al2O3 would be degraded under the acidic condition to realize pH-responsive controlled release of the cargo molecules. We further carried out in vitro drug delivery experiments by using human epithelial cervix adenocarcinoma (HeLa) cells as the model and revealed much higher drug delivery efficacy within cancer cells compared to free doxorubicin (Dox) and Dox loaded HMSNP without sealing (HMSNP@Dox). The current work not only clarifies the importance of the surface encapsulation of the nanochannels when using HMSNPs as nanocarriers, but also provides a strategy to prepare fully encapsulated core-shell structures, which holds great potential for physically encapsulating various theranostic reagents in the biomedical field.

Constructing polymers towards ultrathin nanosheets with dual mesopores and intrinsic photoactivity.

We developed ultrathin dual-mesoporous polymer nanosheets by combining co-assembly of different templates with in situ synthesis of functional polymers, which featured inherent smaller and template-directed larger mesopores (2.6 nm and 15 nm, respectively), ultrathin nanolayers (20 nm), high surface area (268 m2 g-1), intrinsic fluorescent properties and effective detectability for organophosphates.

Nanolayer-embedded pseudo-photonic crystals

In recent years, novel high-performance nanophotonic devices have been realized by applying ultrathin two-dimensional nanolayer materials to nanophotonics. In this paper, we propose nanolayer-embedded compact pseudo-photonic crystals (PPCs) that enable strong interaction between ultrathin nanolayers and photonic crystal modes. In typical two-dimensional slab photonic crystals, the transverse-magnetic (TM) photonic crystal bandgap is not well formed, making it difficult to operate the TM photonic crystal waveguide modes. However, by utilizing the low-frequency TM PPC bands, a long propagation TM waveguide mode, a slow TM waveguide mode, and a TM photonic bandgap are all readily available. In particular, the insertion of a nanometer-thick low-refractive-index layer in the vertical center of TM PPC waveguide can localize the electric fields tightly in nanometer space, causing strong field interaction with the inserted nanolayer material. Using the TM slow light near PPC band edges, field interaction with the nanolayer is significantly enhanced. We can also realize nanolayer-embedded high-quality-factor (Q-factor > 104) PPC cavities using the TM PPC bandgap. We believe that the proposed TM PPCs will play an important role in the strong interaction of ultrathin nanolayer materials with photonic crystal modes.

Defect-rich and ultrathin CoOOH nanolayers as highly efficient oxygen evolution catalysts for photoelectrochemical water splitting

Plasma-exfoliation of CoOOH catalysts into defect-rich and ultrathin nanolayers (∼2 nm) significantly improved the photoelectrochemical activities of BiVO4 photoanodes.

Realizing high performance solar water oxidation for Ti-doped hematite nanoarrays by synergistic decoration with ultrathin cobalt-iron phosphate nanolayers

Hematite (α-Fe2O3) is one of the most promising photoanode materials for solar-to-hydrogen (STH) energy conversion by photoelectrochemical (PEC) water splitting. However, the practical application of hematite in PEC water splitting is severely hindered by the intrinsically low charge separation efficiency and sluggish water oxidation kinetics. Here, we reported Ti-doped hematite photoanode nanoarrays decorated with cobalt-iron phosphate (CoFePi) ultrathin nanolayers greatly enhanced bulk and surface charge separation efficiency, as well as passivate surface states for promoting the PEC water oxidation activity. The synergistic interactions of CoFePi nanolayers with the Ti-Fe2O3 photoanode yield current densities of 1.75 mA/cm2 and 2.15 mA/cm2 in 0.1 M KOH and 1 M KOH respectively at 1.23 VRHE under AM 1.5 G illumination, which is 2.3 and 3.1 fold higher than bare hematite photoanode, and also even higher than Ti-Fe2O3 and Ti-Fe2O3 coated with cobalt phosphate (CoPi), iron phosphate (FePi), phosphate (Pi), respectively. A low turn-on voltage of 0.68 VRHE and high incident photon-to-electron conversion efficiency of 46.6% (IPCE, 1.23 VRHE, λ = 340 nm) are achieved with the Ti-Fe2O3/CoFePi photoanode. Collectively, the results demonstrated that the synergistic Ti-Fe2O3/CoFePi photoanode is promising for PEC water oxidation for hydrogen production.

Electrochemical Deposition of MgO@ZnO Shell−Core Nanorod Arrays Largely Enhances the Photoelectrochemical Water Splitting Performance

AbstractWell aligned ZnO nanorod array (NRA) core coated with MgO nanolayer shell was fabricated via a facile pulse electrodeposition method. Using this method, a homogeneous MgO nanolayer could be formed on the surface of the wurtzite ZnO nanorod. This novel nanostructure with controllable shell thickness, provided a high photoinduced current density of 2.4 mA cm−2 at 1 V (vs. Ag/AgCl) under 100 mW cm−2 illumination (AM 1.5), which value is almost three times larger than that of pristine ZnO NRA and also much superior to those of analogous ZnO based photoanodes. The as‐prepared photoanodes exhibited excellent behaviors in photoelectrochemical (PEC) water splitting, significantly improved the photoconversion efficiency. This is attributed to the interface effect and surface hydrophilia provided by the MgO ultrathin nanolayer, suppressing the recombination rate of electron‐hole pairs and improving interfacial charge exchange capacity. Thus, this work provides a cost‐effective route to improve the performance of ZnO based photoanodes, in addition it can be used in other solar energy conversion devices, for example, this hydroxyl groups dominant surface can be employed for other visible light response semiconductors (CdS, CdTe etc.) assembly.

Retarding charge recombination in perovskite solar cells using ultrathin MgO-coated TiO2 nanoparticulate films

MgO ultrathin nanolayers are able to efficiently retard charge recombination in perovskite solar cells.

Efficient Pump Photon Recycling via Gain-Assisted Waveguiding Energy Transfer

We propose a new concept for enhancing the fluorescence of ultrathin nanolayers. In this article, we address the issue of efficient absorption of polymer thin films with nanometer characteristics. ...