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Successive ionic layer adsorption and reaction (SILAR) process has been diversely used for deposition of various metal chalcogenides. SnS is one of them. Owing to the under-utilization of ionic precursor used in SILAR process, recovery of ionic species from solvents is important and critical before disposal. Since a variety of solutes and solvents can be used for the deposition of SnS, we have devised a comparison revealing the diversity of SnS. It is revealed that the residual cationic precursors play an important role in deciding the eventual morphology, purity and thus the photocatalytic performance of nanostructured SnS. We directly compared SnS nanostructures salvaged from ionic precursors of SnSO4 and SnCl2 under similar salvaging conditions and ensued that flower-like SnS can be obtained successfully. Intensive scanning electron microscopy and energy dispersive spectroscopy were utilized to have a closer check on the evolution of morphological and compositional characteristics. Rhodamine B and methylene blue dyes were successfully degraded by both types SnS, however SnS@SnCl2 exhibited superior performance which was credited to its unique flower-like morphology. Significantly, ~ 96.3% removal of methylene blue dye from water was achieved in only 40 min.

In recent years, resistive switching memory devices are attracted much attention for high-density non-volatile memory applications owing to their cell scalability, multilevel operations, and 3D capability in crossbar memory arrays. In this work, we report the forming-free and multilevel resistive switching properties of hydrothermally synthesized hexagonal molybdenum oxide (h-MoO3) microrods. The formation of h-MoO3 microrods was confirmed by using the X-ray diffraction technique and scanning electron microscopy. Different chemical properties of h-MoO3 microrods were determined by energy-dispersive X-ray, photoluminescence, Raman, and X-ray photoelectron spectroscopic techniques. The memory device was fabricated in a Ti/MoO3/FTO structure and its bipolar resistive switching properties were investigated. The memory device shows voltage-dependent tunable I-V properties and shows electroforming-free operation. Moreover, we have calculated the different memristive properties and showed that the device possesses double-valued charge-magnetic flux characteristics, suggesting the dominance of memristive properties in the Ti/MoO3/FTO device. We further explored the multilevel resistive switching property of the device by varying the RESET voltage. The Ti/MoO3/FTO memristive device can able to show four distinct resistive states during endurance and retention tests. The statistical analysis suggested that the device has less variation during the cycle-to-cycle operation. The device conduction mechanism was obtained by fitting different charge transport models, and a possible resistive switching mechanism is presented based on the observed multilevel resistive switching effect of the Ti/MoO3/FTO memristive device.

We examined the chemical and local structural properties of oxidized TiN/ZnS and TiN/ZnO thin films using X-ray absorption spectroscopy (XAS). The composite films were oxidized by post-deposition annealing (PDA) under various oxygen partial pressures (P(O2)). The results of the X-ray absorption near-edge structure (XANES) analyses showed that the S and N vaporized, and a zinc titanate (ZnTiO3)-like phase formed when annealed under the oxygen ambiance. An ab initio XANES simulation as well as the extended X-ray absorption fine structure (EXAFS) analysis further resolved the local structures of ZnTiO3-like phase into high symmetry structures such as ilmenite-like or perovskite-like local structure; for instance, the local structure of TiN/ZnS films annealed with P(O2) = 2 Torr could be described as a mixture of 50% ilmenite ZnTiO3 + 30% perovskite ZnTiO3 + 20% wurtzite ZnO local structures. The formation of ZnTiO3-like local structure is also subject to the temperature during the PDA or the choice of bottom layers (ZnS or ZnO). The temperature of the TiN/ZnS-to-ZnTiO3 local structural phase transformation, was estimated to be 500–600 °C at P(O2) = 2 Torr, and ZnO as bottom layer apparently expedited such local structural evolution by supplying oxygen to TiN.

S passivation of a HfO2 film on an InP substrate is demonstrated using annealing in H2S ambient either before or after ALD of the HfO2 film. We examined the resulting distribution and chemical state of the incorporated S both in the HfO2 film and at its interface with the InP substrate using secondary ion mass spectroscopy and X-ray absorption spectroscopy. Annealing in H2S ambient before ALD of HfO2 resulted in accumulation of S at the interface in the sulfide (S2−) phase (due to lack of oxygen), which effectively suppressed interfacial reactions during ALD and passivated interfacial defect states. On the other hand, annealing in H2S ambient after ALD of the HfO2 film induced a sulfate (S6+) phase in the film due to the abundant oxygen in the film, as well as a sulfide (S2−) phase at the interface. This improved the charge trapping behavior by decreasing the bulk defect density in the HfO2 film.

A g-C3N4@ZnO heterojunction is demonstrated using atomic layer deposition (ALD) of ZnO. A specially designed rotary reactor was used to maintain mechanical dispersion of g-C3N4 powder during the ALD process. Stable, uniform, and intimate heterojunctions between g-C3N4 and ZnO were produced, which induced effective charge separation; thus, the photocatalytic activity of the composites was enhanced. The photocatalytic performance was evaluated by the degradation of methylene blue dye. The photocatalytic reaction rate constant of the optimal g-C3N4@ZnO with five ALD cycles was five times and two times higher than those of pristine g-C3N4 and g-C3N4@TiO2 composite, respectively. Furthermore, the photocorrosion of ZnO was inhibited by coupling with g-C3N4, which was confirmed through cyclic photo-degradation with three consecutive dye degradation tests. The synergistic effects of the g-C3N4@ZnO heterojunction, enhanced photocatalytic activity and photocorrosion resistance were proven.

Size and shape of inorganic materials are known to have great effects on their physical and chemical properties. Here, for the first time we report the visible light driven photocatalytic degradation of erioglaucine – a stable organic dye molecule in the presence of chemically synthesized nanoscale CdS with 1D (nanorods), 2D (nanosheets) and 3D (hierarchical) morphology. Visible light driven photocatalytic degradation efficiency of both 1D and 3D CdS in the removal of erioglaucine are identical. Surprisingly, with 5 min of sonication, the highly crystalline 3D CdS stacked with many thin nanowires containing numerous active surface sites exhibited four-fold enhanced photodegradation efficiency in comparison to 1D and 2D CdS. Scavenger studies revealed that electrons and superoxide radicals are primary reactive species involved in the photodegradation of erioglaucine, while cyclic photodegradation studies revealed the good stability of 3D CdS against photocorrosion. Further, the photocatalytic hydrogen evolution studies also revealed the excellent activity of 3D CdS in comparison to 1D and 2D CdS. Thus, we find that the morphology indeed influences the photocatalytic activity. These results reveal that 3D CdS nanostructures investigated in the present work are efficient photocatalysts that could be fine-tuned for both environmental remediation and hydrogen generation applications.

Ultrathin and conformal ZnS film grown by atomic layer deposition was employed in quantum dot-sensitized solar cells (QDSSCs) as an interfacial layer (IL) between mesoporous TiO2 photoanode and successive ionic layer adsorption and reaction (SILAR)-grown PbS QDs. ZnS IL provided more nucleation sites compared to a bare TiO2 photoanode, which enhanced PbS QDs loading remarkably. As a result, the optical absorbance and thus photocurrent density considerably increased. The power conversion efficiency of QDSSCs increased from 3.4% to 4% by introducing the ZnS IL. However, the β-recombination model obtained from electrochemical impedance spectroscopy revealed the evolution of charge carrier recombination inside QDs as a consequence of enhanced QD loading, which partly dilutes this benefit.

In the present report, a simple and cost-effective successive ionic layer adsorption and reaction method is employed to develop self-rectifying ZnO thin film memory device. The nature of pinched hysteresis loop and frequency dependent I–V characteristics depicts that the developed device behaves like a memristive device. Moreover, significant pinched hysteresis loop at 1 MHz was observed which could be further exploited for the development of new class of high-frequency circuits by using ZnO memristive device. The observed analog memory with scan rate dependent synaptic weights behavior suggests that the ZnO memristive device is a potential candidate for the development of electronic synaptic devices for neuromorphic computing application. Furthermore, multilevel resistive switching with good memory window was obtained at 0.2 V read voltage. The developed device switched successfully in consecutive 10 k resistive switching cycles and can retain multilevel resistance states over 1000 s without any observable degradation in the resistance states. The insights drawn from electrical characterization indicates that the device charge and charge–magnetic flux relations depend upon the frequency of the applied signal. Furthermore, we have presented the criteria for differentiating the experimental device as a memristor or memristive device based on the nature of time domain charge and double valued charge–magnetic flux relation. The resistive switching effect of the present device is manifested due to the unified effect of the Ohmic and Schottky conduction mechanisms.

Recently, graphitic carbon nitride (g-C3N4) possessing two-dimensional structure has received great concern by virtue of its attractive optoelectronic properties, nontoxicity, stability, and cost-effectiveness. However, undesirable charge carrier recombination confines its photocatalytic efficiency. In this work, a hydrothermal process was used to form ternary g-C3N4/rGO/SnO2 nanocomposite simply. The effective photocatalytic activity pertained to the nanocomposite was owed to the combined effect of three core processes: effectual charge separation, multistep charge transfers, and higher visible-light absorbance. The ternary g-C3N4/rGO/SnO2 complex demonstrated excellent photocatalytic activity due to large number of nano/heterojunction in contrast with pristine g-C3N4, and the other hydrothermally synthesized composites namely, g-C3N4/rGO, and g-C3N4/SnO2 in degradation of Rhodamine-B (RhB) dye. The optimal nanocomposite (i.e. g-C3N4/5-rGO/SnO2) demonstrated an approximate 40% increase in dye degradation efficiency. The physical, morphological, optical, electrochemical, and photocatalytic characteristic have been studied by X-ray diffractometer, scanning/transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence, FTIR spectroscopy, UV–Vis spectroscopy and electrochemical impedance spectra. This work presents newer heterojunction, revealing the individual roles of three-components of this system, as well as an enhancing the absorption ability of light to construct efficient ternary nano/hetero junctions photocatalyst which is cost effective as well.

Atomic layer deposition (ALD) of TiO2 films from (CpMe5)Ti(OMe)3 as precursor and O3 as co-reactant was examined. The high thermal stability of (CpMe5)Ti(OMe)3 enabled ALD reaction up to a high temperature of 345 °C. A wide temperature window from 182 to 345 °C was achieved in the ALD process, and the growth per cycle increased with increasing the temperature from 0.025 to 0.06 nm/cycle in the ALD window. The impurity content of the films decreased with increasing growth temperature. Above 291 °C, the carbon content in the films decreased to the level in a single crystalline Si substrate. The morphology with patterns spreading radially from the multiple points developed above 236 °C, and the size of the grains decreased as the growth temperature increased. Eventually, a uniform morphology with fine grains was obtained at temperatures > 300 °C. The films grown at the high temperatures exhibited superior dielectric properties. Other common metalorganic precursors of Ti usually restrict the use of high-temperature ALD because they are thermally unstable and decompose below 300 °C. Therefore, (CpMe5)Ti(OMe)3 is favorable for forming dense and high-purity TiO2 films by ALD.

Atomic layer deposition (ALD) is proposed to synthesize ZnS-coated g-C3N4 photocatalysts which form an effective heterojunction for charge separation by reducing carrier recombination. It also, enables decrease in processing time from few days to several hours and circumvents collection process of synthesized powder which leads improvement in the productivity. In ZnS/g-C3N4 heterojunction composite, ZnS quantum-dots are uniformly distributed on g-C3N4 rather than conformal ZnS film due to hydrophobic nature of g-C3N4 surface. Photocatalytic activity of the ZnS/g-C3N4 heterojunction composites is enhanced up to 2.6 times compared to pristine g-C3N4 by tailoring ZnS ALD cycles. A range of ALD cycles from 2 to 50 have applied, out of which 5 cycles are found optimum for best efficiency, above and below 5 cycles it becomes either saturated or less potent, respectively.

Macroporous titanium dioxide (TiO2) layer was formed through selective etching of silica (SiO2) microspheres incorporated in TiO2/SiO2 composite layer, resulting in a significant increase in the photovoltaic performance of PbS quantum-dot-sensitized solar cells (QDSSCs). Strategic incorporation of macroporous TiO2 layer on top of a mesoporous layer improved the light absorption characteristics, which is concurrently attributed to light scattering behaviour of macropores and increased loading of quantum dots (QDs) via successive ionic layer adsorption and reaction process. Thereby, a direct increase in the photocurrent density of PbS-QDSSC was ensued. Open-circuit voltage decay analysis combined with in-depth electrochemical impedance spectroscopy revealed a significant improvement in the electron life time and recombination resistance of QDSSC which was credited to the barrier effect of more uniformly loaded PbS QDs inside macroporous TiO2 photoanode.

Surface passivation of a nanostructured Si solar cells plays a crucial role in collecting photogenerated carriers by mitigating carrier recombination at surface defect sites. Interface modification by additional sulfur (S) incorporation is proposed to enhance the field-effect passivation performance. Here, we report that simple annealing in a H2S ambient induced additional negative fixed charges at the interface between atomic-layer-deposited Al2O3 and nanostructured Si. Annealing at various temperatures allowed us to control the S concentration and the fixed charge density. The optimized S incorporation at the interface significantly enhanced the negative fixed charge density and the minority carrier lifetime up to ~5.9 × 1012 cm−2 and ~780 μs, respectively. As a result, the internal quantum efficiency was nearly two times higher in the blue response region than that of control cells without S incorporation. Copyright © 2017 John Wiley & Sons, Ltd.

Area-selective atomic layer deposition has attracted considerable interest as a means for enabling versatile fabrication of selectively formed thin films in both vertical and lateral direction in extremely downscaled 3D semiconductor devices. Herein, we report a methodology for an enhanced selectivity ALD process with a discrete feeding method (DFM), capable of improving the chemisorption density of small alkylating agents onto desired substrates. Using the DFM strategy of (N, N-diethylamino)trimethylsilane as an aminosilane inhibitor to render surface alkyl groups, we explored its efficacy with regard to improving its blocking capability against subsequent Ru ALD on various substrates such as Si, SiO2, and SiN substrates to provide H-, OH-, and NHx-terminated surface groups, respectively. As a result, a denser chemisorption layer could be selectively obtained on OH-terminated SiO2 and NH-terminated SiN but not on H-terminated Si, which in turn led to significant growth retardation on both SiO2 and SiN during Ru ALD. Adding a process sequence composed of intermittent Ru etching followed by DFM retreatment on both SiO2 and SiN allowed for selective removal of Ru moieties and restoration of inhibitory alkyl groups. In this way, we finally achieved enhanced deposition selectivity with a combination of sequential DFM and Ru ALD-etch supercycles.

The HfO 2 films grown by atomic layer deposition (ALD) at a low temperature (100 °C) necessarily has a large amount of residual impurities due to lack of thermal energy for stable ALD reactions such as ligand removal and oxidation, which degrades various properties. However, Al 2 O 3 incorporation into the film significantly decreased the residual impurities despite of a low growth temperature. The decrease in C impurity is attributed to the reduced oxygen vacancies by the incorporated Al 2 O 3 phase or the high reactivity of Al precursor. Consequently, the electronic band structure of the film, and thereby the electrical properties were improved significantly.

Surface sulfur (S) passivation on InP substrate was performed using a dry process – rapid thermal annealing under H2S atmosphere for III–V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process – (NH4)2S solution treatment. The H2S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH4)2S solution treatment, although S profiles at the interface of HfO2/InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H2S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H2S annealing.

Conventional secondary antibodies for immunoassays are generally obtained from live animals or expensive mammalian cell culture systems. These antibodies are then conjugated with enzymes that repeatedly convert inactive substrates to signal-generating active products by secondary antibody mimics of low-abundance target molecules in a concentration-dependent manner. In this study, we constructed recombinant immunoglobulin G (IgG)-binding nanobody-based secondary antibody mimics using a well-established SpyTag/SpyCatcher protein ligation system. We prepared SpyCatcher as a scaffold protein, chemically conjugated it with an activated horseradish peroxidase (HRP), and fused SpyTag to two IgG-binding nanobodies specific for the Fc regions of mouse IgG1 and rabbit IgG, which is denoted as MG1Nb and RNb, respectively. We selectively ligated HRP-conjugated SpyCatcher with SpyTag-fused MG1Nb or RNb depending on the original species of primary antibodies and amplified signals of target molecules in a plug-and-playable manner. We successfully demonstrated that HRP:MG1Nb and HRP:RNb selectively bind to target-bound mouse IgG1 or rabbit IgG, respectively, and serve as excellent target-specific signal amplifiers in various immunoassays such as western blot, enzyme-linked immunosorbent assay (ELISA), and multiplex tyramide signal amplification (TSA) cell and tissue imaging. These recombinant signal-amplifying IgG-binders can be simple and reliable alternatives to conventional secondary antibodies in various immunoassays.

Atomic layer deposition (ALD) was employed to obtain superior deposition of a conformal ZnO shell on SiO2 spherical particles passivating the limitations of wet-chemical deposition routes which yield inferior surface-related physicochemical characteristics of resultant SiO2-ZnO particles. It was established that ALD route for deposition of ZnO on SiO2 enables us to have reasonably crystalline ZnO shell over amorphous SiO2 (SZCSPs), without any evolution of corresponding silicates of zinc that may lower the performance of SZCSPs. Detailed scanning and transmission electron microscopy along with X-ray diffraction analysis were utilized to elucidate the morphological contrast of SZCSPs particles, concomitantly revealing the structural superiority, conformality and effectiveness of ALD deposition in comparison with the wet-chemical route. Concurrently, improved optoelectronic properties were recorded for superior photocatalytic performance of the SZCSPs under UV-irradiation for degradation of rhodamine-B dye. Furthermore, the dye degradation performance was investigated by scavenging experiment, revealing the mechanism of generation of reactive species and their interaction with rhodamine-B dye molecules.

In this work, we modified the conventional wet chemical route used for synthesis of ZnO hierarchical structure (HS), and successfully obtained superior optical, photochemical and antimicrobial characteristics for ZnO-HS as a consequence of incorporation of hydrofluoric acid (HF). ZnO-HS is unique owing to its morphology with 2D interconnected nanosheets. Strategic use of HF led to appreciable reduction in sheet thickness (up to ~15 nm) of ZnO-HS while physicochemical attachment of Fluorine (F) was also realized. Antimicrobial activity of ZnO-HS against Escherichia coli was measured via pour plate method, and found to be significantly increased as a consequence of HF-based modification of ZnO-HS. In addition, resultant ZnO-HS exhibited higher deposition of CdS quantum-dots via pseudo-successive ionic layer adsorption and reaction (p-SILAR), affirming higher photocatalytic performance of ZnO/CdS hierarchical composite (HC). It was established that congo red (CR) dye was degraded ~15% more, when ZnO/CdS HC incorporating HF-based surface modification was used as a photocatalyst. Characteristic improvements in ZnO-HS were affirmed using diffuse reflectance spectroscopy, FTIR spectroscopy and SEM.

SiO2/TiO2 core/shell nanoparticles (ST-NPs) with an ultrathin and conformal TiO2 shell were fabricated via atomic layer deposition (ALD) technique with a specially-designed rotary reactor. We successfully employed the ST-NPs as light scattering centers in a mesoporous TiO2 photoanode in quantum dot (QD)-sensitized solar cells (QDSSCs). ST-NPs enhanced the light scattering in the TiO2 photoanode without deterioration of QD loading behavior. Consequently, visible light absorbance was improved in the PbS QDs-sensitized TiO2 photoanode, and thus the photocurrent density increased from 14 to 17 mA/cm2. Detailed electron microscopy was utilized to reveal the uniqueness of the ultrathin TiO2 shell in ST-NPs, and in-depth electrochemical impedance spectroscopy divulged the increase in photogenerated carrier lifetime and improved recombination resistance for the QDSSC with ST-NPs.

The non-linear nature in the current-voltage relationship and good resistive switching characteristics were demonstrated with the help of TiO2 nanorods-functionalized multiwalled carbon nanotube (fMWCNT) composite grown by the low-cost hydrothermal method. The composites were characterized by X-ray diffraction, scanning electron microscopy, Raman, photoluminescence, and X-ray photoelectron spectroscopy to investigate the structural, morphological, and chemical composition of composite films. The resistive switching characteristics of the TiO2-fMWCNT nanocomposites were found to be strongly dependent on the fMWCNT concentration. The enhanced switching performance is associated with the surface nanostructure and chemical composition of the nanocomposites. Owing to the hierarchical rutile TiO2 nanorods and opportune fMWCNT content, the nanocomposite based device with 0.03 wt % fMWCNT exhibited the best resistive switching performance with good endurance and retention non-volatile memory properties. Interestingly, with the optimized stoichiometric composition and operation conditions, forming-free, low operational voltage, self-rectifying like properties have been simultaneously achieved, which are some of the prerequisites for next-generation memory devices. In addition to this, the double-valued charge-magnetic flux nature of the developed devices was demonstrated. The experimental current-voltage characteristics are well-matched with the Ohmic and Schottky conduction mechanisms.

Although perovskite tin titanate (SnTiO3, STO) has been predicted to have ferroelectricity with a large spontaneous polarization, the implementation of metastable perovskite STO remains a great challenge. In this study, the atomic layer deposition of STO films was attempted using bis(1-dimethylamino-2-methyl-2-propoxy)tin(II) as the Sn source, titanium-tetrakis-isopropoxide as the Ti source, and water as the oxygen source. It was found that during the process, adsorption of both the precursors was enhanced on the heterogeneous reaction surface because of the correlation growth behavior. STO films remained amorphous below 250 °C. Furthermore, although the film was crystallized at 270 °C, the perovskite phase was not identified. Despite the use of the Sn precursor with Sn2+, Sn ions in all the films transformed into Sn4+. Although the postdeposition annealing process in a forming gas atmosphere was conducted for the perovskite conversion, the STO film transformed into Ti5Sn3, an intermetallic compound, at 500 °C.

Sulfur was embedded in atomic-layer-deposited (ALD) HfO2 films grown on Ge substrate by annealing under H2S gas before and after HfO2 ALD. The chemical states of sulfur in the film were examined by S K-edge X-ray absorption spectroscopy. It was revealed that the valences of S-ions were mostly –2 at Ge/HfO2 interface (GeSx or HfO2–ySy to passivate the interface), while they were mostly +6 in HfO2 layers (sulfates; HfO2–z(SO4)z). The leakage current density in post-deposi-tion-treated film was lower than that in pre-deposition-treated one. This suggests that the passivation of defects in oxide layer by sulfate ions is more effective to lower the leakage current rather than the interface defect passivation by S2– ions. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

SnO 2 thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp) 2 ) and O 3 in a temperature range of 100–230 °C. The ALD window was found to be in the range of 100–200 °C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042 nm/cycle. Above 230 °C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp) 2 precursor. The SnO 2 films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn 4+ in SnO 2 . The concentration of carbon and nitrogen in the all SnO 2 films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO 2 films with respect to the growth temperature. The ALD process with Sn(dmamp) 2 and O 3 shows excellent conformality on a hole structure with an aspect ratio of ∼9. This demonstrates that the ALD process with Sn(dmamp) 2 and O 3 is promising for growth of robust and highly pure SnO 2 films.

Atomic-layer-deposited Al 2 O 3 films were grown on ultrathin-body In 0.53 Ga 0.47 As substrates for III-V compound-semiconductor-based devices. Interface sulfur (S) passivation was performed with wet processing using ammonium sulfide ((NH 4 ) 2 S) solution, and dry processing using post-deposition annealing (PDA) under a H 2 S atmosphere. The PDA under the H 2 S atmosphere resulted in a lower S concentration at the interface and a thicker interfacial layer than the case with (NH 4 ) 2 S wet-treatment. The electrical properties of the device, including the interface property estimated through frequency dispersion in capacitance, were better for (NH 4 ) 2 S wet-treatment than the PDA under a H 2 S atmosphere. They might be improved, however, by optimizing the process conditions of PDA. The PDA under a H 2 S atmosphere following (NH 4 ) 2 S wet-treatment resulted in an increased S concentration at the interface, which improved the electrical properties of the devices.

A single-step pyrolysis assisted route towards the large scale fabrication of metal oxide nanoparticles (Fe 2 O 3 , Co 3 O 4 and NiO) ingrained in graphitic carbon nitride (GCN) is demonstrated. Urea, an abundantly available precursor, plays a dual role during the synthesis: while it acts as a reducing agent, it also gets converted to GCN. The formation of GCN and the in-situ growth and embedment of oxide nanoparticles are discussed on the basis of the experimental results. The wide absorption of the samples in the visible light region makes them suitable for nonlinear transmission and photocatalytic activity studies. Visible light photocatalytic activities of the samples are studied by monitoring the degradation of Rhodamine B dye. Optical limiting properties of the prepared samples are studied through the open aperture z -scan technique using 5 ns laser pulses at a wavelength of 532 nm. The cost-efficient and time saving synthetic approach is complemented by the magnetic behaviour of the samples, which enables their use as recyclable photocatalyst and magnetically controllable optical limiters.

The effects of oxidant (H2O) feeding time and growth temperature on the C- and N-related impurities and Si diffusion behavior in the atomic-layer-deposition (ALD) of La2O3 films were examined using in situ X-ray photoelectron spectroscopy analysis. Longer H2O pulse time assisted in a complete ligand exchange reaction during ALD, which suppressed the accumulation in the film of residual C- and N-related byproducts/impurities with low bonding energy that originated from incompletely reacted ligands and carboxyl compound intermediate phases. In addition, this phenomenon slightly increased the growth rate of the La2O3 film even under the nominal growth-saturated ALD conditions because the concentration of residual C- and N-related byproducts/impurities, which disturb the formation of the active sites, was reduced. The band gap energy of the films increased slightly with H2O feeding time due to the reduction of C impurities. The residual C- and N-related byproducts/impurities and carboxyl compound intermediate phases in the La2O3 films were effectively reduced by increased growth temperature. However, increased growth temperature enhanced the Si out-diffusion from the substrate into the films and decreased the film growth rate because the surface functional groups for sequential film growth during ALD were reduced. The enhanced Si out-diffusion increased the band gap of the film and the valence band off-set with respect to the Si substrate.

Various array types of 1-diode and 1-resistor stacked crossbar array (1D1R CA) devices composed of a Schottky diode (SD) (Pt/TiO2/Ti/Pt) and a resistive switching (RS) memory cell (Pt/TiO2/Pt) are fabricated and their performances are investigated. The unit cell of the 1D1R CA device shows high RS resistance ratio (≈103 at 1.5 V) between low and high resistance state (LRS and HRS), and high rectification ratio (≈105) between LRS and reverse-state SD. It also shows a short RS time of

Effect of ozone (O"3) concentration (90, 300g/Nm^3) on atomic layer deposition of HfO"2 thin films on GaAs wafers using tetrakis (dimethylamino)hafnium (TDMAHf) as Hf precursor was systematically studied including MISCAP performance and related microstructure. High-resolution transmission electron microscopy analyses show that oxidation of the GaAs substrate enhances with O"3 concentration which leads to an increase in interfacial layer (IL) thickness between the high-k dielectric and the substrate. The thin IL was maintained after PDA, while the high-k (HfO"2) layer experienced shrinkage of ~12% due to densification. However HfO"2 film deposited using O"3 concentration of 300g/Nm^3 produced relatively thicker IL and thinner high-k layer which both did not show a noticeable change after PDA. This led to C"m"a"x variations depending on the different O"3 concentration. In the case of O"3 concentration of 90g/Nm^3, increase of leakage current density by an order was observed and corresponding micro-structural change is discussed.

Electrical properties and thermal stability of LaHfO"x nano-laminate films deposited on Si substrates by atomic layer deposition (ALD) have been investigated for future [email protected] gate dielectric applications. A novel La precursor, tris(N,N'-diisopropylformamidinato) lanthanum [La(^iPrfAMD)"3], was employed in conjunction with conventional tetrakis-(ethylmethyl)amido Hf (TEMA Hf) and water (H"2O). The capacitance-voltage curves of the metal oxide semiconductor capacitors (MOSCAPs) showed negligible hysteresis and frequency dispersion, indicating minimal deterioration of the interface and bulk properties. A systematic shift in the flat-band voltage (V"f"b) was observed with respect to the change in structure of nano-laminate stacks as well as La"2O"3 to HfO"2 content in the films. The EOTs obtained were in the range of ~1.23-1.5nm with leakage current densities of ~1.3x10^-^8A/cm^2 to 1.3x10^-^5A/cm^2 at V"f"b-1V. In addition, the films with a higher content of La"2O"3 remained amorphous up to 950^oC indicating very good thermal stability, whereas the HfO"2 rich films crystallized at lower temperatures.

La"2O"3 films were grown by atomic layer deposition technique using a novel formamidinate precursor, tris(N,N'-diisopropylformamidinato) lanthanum [La(^iPrfAMD)"3], with H"2O and O"3 as an oxidant. La"2O"3 films grown with H"2O in the film exhibited a parasitic chemical vapor deposition type growth possibly due to a La(OH)"x component. However, the use of O"3 as the oxidant revealed a stable ALD process window. A post-deposition annealing (PDA) of the deposited La"2O"3 films using O"3 significantly reduces leakage current density by four orders of magnitude relative to as-deposited samples. The dielectric constant of La"2O"3 films with a TaN metal gate is found to be ~29, which is higher than reported values for CVD and ALD La"2O"3 films.

A thin (~ 0.5 nm) layer of Hf metal was deposited on an atomic layer deposited (ALD) HfO"2 film by the DC sputtering method. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses showed that the Hf metal layer transformed into HfO"2 during the post-deposition annealing process. It appears that the HfO"2 layer formed by the oxidation of Hf metal provided the underlying ALD HfO"2 layer with the nucleation sites necessary to decrease the grain-boundary density of the crystallized HfO"2 film. The decrease in the grain-boundary density resulted in a reduction in the Hf-silicate formation and interfacial layer growth during post deposition annealing. This eventually resulted in a smaller increase in the capacitance equivalent thickness (CET) and high-k characteristics in the CET vs. leakage current density curve even after post deposition annealing at 1000 ^oC.

We have investigated the effect of trimethyl aluminum (TMA) and water (H2O) half-cycle treatments on HF-treated, and O3-oxidized GaN surfaces at 300 °C. The in-situ X-ray photoelectron spectroscopy results indicate no significant re-growth of Ga–O–N or self-cleaning on HF-treated and O3-oxidized GaN substrates with exposure to water and TMA. This result is different from the self-cleaning effect of Ga2O3 seen on sulfur-treated GaAs or InGaAs substrates. O3 causes aggressive oxidation of GaN substrate and direct O–N bonding compared to H2O. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The local structural order of amorphous ${\text{HfO}}_{2}$ films $(a{\text{-HfO}}_{2})$ was examined using $\text{Hf}\text{ }{L}_{3}$-edge x-ray absorption spectroscopy and fine structure analyses. The fine structure simulation successfully reproduced the spectral evolution of the crystalline-to-amorphous phase transition by reducing the characteristic radius for atomic ordering to $\ensuremath{\sim}3.5\text{ }\text{\AA{}}$. Detailed path-by-path analyses further showed that the vibrational displacement of oxygen atoms in $a{\text{-HfO}}_{2}$ films is highly anisotropic showing mainly lateral dispersion perpendicular to a Hf-O bond. This anisotropic structural disorder is responsible for enhancing the dielectric constant accompanying phonon mode softening in the $a{\text{-HfO}}_{2}$ film.

Fabrication of three-dimensional (3D) TiO2 nanoscale architectures with spindle, tube and rod shapes, by a novel deformation assisted approach is demonstrated. Plausible growth mechanisms are predicted based on morphological investigations. Improved photocatalytic reduction of Cr(VI) is observed using the fabricated nanostructures under visible light irradiation.

Transparent analog capacitors using indium tin oxide (ITO) electrodes and HfO 2 (and Al 2 O 3 ) high-k dielectrics were examined for optical device applications. The adoption of ITO bottom and top electrodes for the capacitors did not degrade the electrical properties of the capacitors compared to titanium nitride (TiN) and Pt electrodes. Compared to conventional analog capacitors using TiN electrodes, capacitors using ITO electrodes show a larger capacitance at the negative voltages in the capacitance-voltage (C-V) curve. This suggests the presence of a thicker depletion layer at the top electrode, which is probably due to the high resistivity of the Sn-rich top ITO initial layer on the dielectric film. Before and after a subsequent thermal annealing, the C-V curve of ITO/Al 2 O 3 /ITO was barely changed, while that of ITO/HfO 2 /ITO showed significant variations. This was attributed to the change in the composition at the interface (i.e., Hf diffusion and oxygen deficiency) rather than to the change in the crystallinity of ITO and HfO 2 .

Interfacial barrier layers (IBLs), such as a thermally grown SiO 2 using O 3 , thermally nitrided SiO x N y using NH 3 , and an atomic layer deposited (ALD) HfO 2 layer, were used as an interface layer between a sputtered SrTiO 3 film and a Si substrate. Sr-silicate phase formation at the interface between the SrTiO 3 film and Si substrate was suppressed by these IBLs. The ALD HfO 2 layer was the most effective diffusion/reaction barrier against Si diffusion and the interfacial reactions among the IBLs examined. However, the crystallinity of the SrTiO 3 layer deteriorated as a result of a chemical reaction with the underlying ALD HfO 2 layer, which decreased the permittivity of the SrTiO 3 layer. The SrTi0 3 film with a SiO x N y IBL showed lower Si diffusion and better crystallinity, which provided the optimum dielectric properties of the film.

This paper reports the fabrication and characterization of metal-insulator-semiconductor (MIS) capacitors using a ZnO semiconducting layer and Al 2 O 3 insulating layer deposited by plasma-enhanced atomic layer and thermal atomic layer deposition, respectively. The sample stack structure is Al 2 O3 / ZnO/ITO. The effects of the ZnO deposition conditions, such as plasma power, film thickness, and oxygen flow rate, on the electrical characteristics of the MIS capacitors were investigated. The thicknesses of the ZnO and Al 2 O 3 layers were changed independently in order to examine the influence of full depletion of carriers on the capacitance-voltage (C-V) characteristics. It was found that the electrical properties of the ZnO thin films changed according to their thickness. This was attributed to a chemical interaction with the under-indium-tin-oxide (ITO) layers during the long growth time (over 2 h), which made it difficult to determine the semiconductor parameters, such as the carrier density. During the process of Al 2 O 3 film deposition, an interfacial layer was grown between the ZnO and Al 2 O 3 films. This interfacial layer deteriorated the C-V characteristics of the MIS capacitors because of the interface state increment. It was found that there was a certain range of ZnO and Al 2 O 3 thicknesses where the optimal properties were achieved.