NH3 Nitridation Research Articles

Synthesis of Narrow-Band-Gap GaN:ZnO Solid Solution for Photocatalytic Overall Water Splitting

The solid solution of GaN and ZnO (GaN:ZnO) is a promising photocatalyst applicable to visible-light-driven overall water splitting. However, the band gap of active GaN:ZnO remains as large as ca. 2.7 eV because of the loss of ZnO during the widely applied NH3 nitridation process. Herein, particulate GaN:ZnO exhibiting a band gap of 2.3 eV was synthesized via calcination of a mixture of Ga2O3, Zn, and NH4Cl in a sealed evacuated tube. The synthesis method was also featured with a high nitrogen utilization rate of 87%. The prepared narrow-band-gap GaN:ZnO was active in the overall water-splitting reaction. In the presence of sacrificial reagents, the apparent quantum yields of GaN:ZnO at 420 nm for H2 and O2 generation were 5.1 and 14.3%, respectively. GaN:ZnO was applied as an oxygen evolution photocatalyst to construct a Z-scheme overall water-splitting system with SrTiO3:Rh as a hydrogen evolution photocatalyst, which achieved a solar-to-hydrogen energy conversion efficiency of 3.7 × 10–2% and a remarkable photochemical stability up to 100 h. This work provides an approach to the synthesis of narrow-band-gap GaN:ZnO solid solution and shows the potential of this material in H2 production from water under long-wavelength visible light.

Simultaneously Tuning the Defects and Surface Properties of Ta3N5 Nanoparticles by Mg-Zr Codoping for Significantly Accelerated Photocatalytic H2 Evolution.

The simultaneous control of the defect species and surface properties of semiconducting materials is a crucial aspect of improving photocatalytic performance, yet it remains challenging. Here, we synthesized Mg-Zr-codoped single-crystalline Ta3N5 (Ta3N5:Mg+Zr) nanoparticles by a brief NH3 nitridation process, exhibiting photocatalytic water reduction activity 45 times greater than that of pristine Ta3N5 under visible light. A coherent picture of the relations between the defect species (comprising reduced Ta, nitrogen vacancies and oxygen impurities), surface properties (associated with dispersion of the Pt cocatalyst), charge carrier dynamics, and photocatalytic activities was drawn. The tuning of defects and simultaneous optimization of surface properties resulting from the codoping evidently resulted in the generation of high concentrations of long-lived electrons in this material as well as the efficient migration of these electrons to evenly distributed surface Pt sites. These effects greatly enhanced the photocatalytic activity. This work highlights the importance and feasibility of improving multiple properties of a catalytic material via a one-step strategy.

3D interconnected nanoporous Ta3N5 films for photoelectrochemical water splitting: thickness-controlled synthesis and insights into stability

Solar-driven photoelectrochemical (PEC) water splitting is a promising technology for sustainable hydrogen production, which relies on the development of efficient and stable photoanodes for water oxidation reaction. The thickness and microstructure of semiconductor films are generally crucial to their PEC properties. Herein, three-dimensional (3D) interconnected nanoporous Ta3N5 film photoanodes with controlled thickness were successfully fabricated via galvanostatic anodization and NH3 nitridation. The porous Ta3N5 nanoarchitectures (NAs) of 900 nm in thickness showed the highest PEC performance due to the optimal light-harvesting and charge separation. Compared with the hole-induced photocorrosion, the electrochemical oxidation at high anodic potentials resulted in severer performance degradation of Ta3N5. Although the surface oxide layer on deteriorated Ta3N5 photoanodes could be removed by NH3 re-treatment, the PEC performance was only partially recovered. As an alternative, anchoring a dual-layer Co(OH)x/CoOOH co-catalyst shell on the porous Ta3N5 NAs demonstrated substantially enhanced PEC performance and stability. Overall, this work provides reference to controllably fabricate 3D nanoporous Ta3N5-based photoanodes for efficient and stable PEC water splitting via optimizing the light absorption, hole extraction, charge separation and utilization.

Hydrogen Evolution Reaction and Oxygen Reduction Reaction of Titanium Oxiynitride Catalyzed Activated Carbon in Acid Aqueous Solution

Electrochemical hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are important reactions for realization a renewable energy society. At the present, platinum group metals are known to be the bifunctional electrode catalysts in the acid medium. Unfortunately, these metals are rare, which leads to increase in the cost of the electrochemical reactors such as a water electrolysis and a fuel cell. Recently, we found that titanium oxiynitride catalyzed activated carbons (TiON/ACs) shows a catalytic activity for both HER and ORR in acid aqueous solution [1, 2]. In this presentation, we report the preparation of TiON/ACs (TiON/AC and TiON/ACF), and their activity for these reactions. TiON/AC is successfully obtained through loading of titanium dioxide (TiO2) on AC powder or ACF (activated carbon fiber) and subsequent NH3 nitridation. At first, TiO2 was deposited on the activated carbons by a modified liquid-phase deposition (LPD) method, in where H3BO3 and (NH4)2TiF6 aqueous solutions were used. A desired amount of AC or ACF was added into H3BO3 aqueous solution and then, (NH4)2TiF6 aqueous solution was added with stirring [1, 2]. NH3 nitridation was carried out at over 700oC with flowing NH3 gas. The characterization was performed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). In order to evaluate the HER activity, the water electrolysis experiment was demonstrated in 0.5 mol dm-3 of H2SO4 solution. The working electrode (cathode) was prepared by using TiON/AC and carbon paper as the substance. A carbon paper and Ag|AgCl were used as the counter and the reference electrode, respectively. Hydrogen was quantified by a gas chromatography during chronoamperometry. We carried out a rotating ring electrode technique to evaluate the ORR activity. In this case, the electrolyte solution was 0.1 mol dm-3 of HClO4 solution saturated with O2. TiO2 particles were confirmed on AC or ACF before NH3 nitridation. After NH3 nitridation, the diffraction peaks assigned to TiN and TiO and the broad peak of carbon were found in XRD patterns. The formation of Ti-O-N and O-Ti-N bonding were confirmed in XPS spectra. Therefore, we considered that TiO2 was transformed to TiON during NH3 nitridation. FE-SEM images show that TiON particles were found on AC or ACF substrates. These particles were considered the products composed of titanium, nitrogen and oxygen. The hydrogen production rate was estimated from the results of gas chromatography. The dependency on the loading ratio of TiON was shown in Figure 1. Hydrogen production was confirmed at overpotential = 0.1 V. The TiON/AC with 19 wt% of TiON shows the highest hydrogen production rate. The onset potential for ORR was estimated ca. 0.78 V vs. RHE and it is higher than that of AC. This result shows that TiON has also a catalytic activity for ORR. Thus, we consider that TiON/ACs have a potential to be the bifunctional catalyst for HER and ORR. This work was partially supported by the Matching Planner Program (MP28116808401) from Japan Science and Technology Agency , JST and JSPS KAKENHI Grant Number 16K05940. References T. Kinumoto, et al., Journal of Power Sources, 273(1), 136 -141 (2015).T. Furushiro, et al., The meeting abstract of AiMES2018, #Z01-2091 (2018). Figure 1

Niobium oxynitride prepared by thermal NH3 nitridation as a photoanode material for solar water splitting

Niobium oxynitride (NbON) is a promising photoanode material for photoelectrochemical water splitting using visible light up to ∼600 nm in wavelength. However, the NH3 nitridation method widely used for oxynitride synthesis cannot convert Nb2O5 (Nb5+) to crystalline NbON (Nb5+), due to the generation of NbOxNy (Nb2+−3+). To prevent Nb reduction during nitridation, we added O2 as an oxidant to the NH3 nitridation reaction system. Investigation of the relationship between O2 concentration and the crystal phase of the resulting samples revealed that Nb2O5 nitridation produces crystalline NbON (Nb5+) within a specific O2 concentration range. The O2 concentration required to synthesize NbON increases from 0.05% to over 0.40% upon increasing the nitridation temperature from 600 °C to 750 °C. The photoelectrochemical properties of NbON films were also investigated. Under simulated sunlight illumination, a NbON photoanode produced a photocurrent of 0.6 mA cm-2 at 1.2 V vs. RHE in H2O2 aqueous solution.

Agglomeration-free VN nanoparticles with controllable crystallite size prepared by a clapboard approach from Zn-V-O based precursor

Well dispersed vanadium nitride (VN) nanoparticles were successfully prepared by nitridation of Zn3(OH)2(V2O7)·(H2O)2 nanosheets followed by alkaline leaching. ZnO derived from Zn3(OH)2(V2O7)·(H2O)2 during nitridation process acted as a clapboard to prevent VN nanoparticles from growing up and agglomerating. In addition, the effects of NH3 flow rate, nitridation time and temperature on the crystallite size of VN nanoparticles were systemically investigated. The results showed that increasing NH3 flow rate from 100 mL min−1 to 600 mL min−1 resulted in an increase of the crystallite size from 17 nm to 22 nm, and prolonging nitridation time from 2 h to 8 h resulted in an increase from 15 nm to 24 nm. Additionally, the crystallite size of VN increased with the increase of the nitridation temperature. Furthermore, when the nitridation temperature was fixed at 550 °C, agglomeration-free VN nanoparticles with a specific surface area of 62.8 m2 g−1 and crystallite size in the range of 12–15 nm were synthesized. Moreover, this facile synthetic strategy can be extended further to synthesize other dispersed inorganic nanomaterials.

Titanium Oxiynitride Catalyzed Activated Carbons As the Hydrogen Production in Sulfuric Acid Solution

Hydrogen production by water electrolysis is one of the techniques for establishment of the economy using hydrogen as an energy source. At the present, platinum group elements are used as the electrode catalyst for both anode and cathode in the acid medium, leading to be high initial cost of the water electrolysis system. We recently found that titanium oxiynitride catalyzed activated carbon (TiON/AC) has a low overpotential for hydrogen production in the acidic electrolyte. The overpotential is around 40 mV, which is very low among the catalyst based on the non-noble metals. In this presentation, we report the preparation of TiON/AC and its hydrogen production ability. TiON/AC is successfully obtained through two-steps as loading of titanium dioxide (TiO2) on activated carbon powder and then the nitridation. At first, deposition of TiO2 on the activated carbon was carried out by a modified liquid-phase deposition (LPD) method, in where H3BO3 and (NH4)2TiF6 aqueous solutions were used. A desired amount of activated carbon powder [specific surface area is 2343 m2/g purchased from Kuraray. Co., Ltd.] was added into H3BO3 aqueous solution. Then, (NH4)2TiF6 aqueous solution was added under stirring. The product was mounted in an alumina boat. Subsequent NH3 nitridation was carried out at 700, 750, 800 and 900°C. The characterization was performed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). To evaluate hydrogen production ability of TiON/AC, the water electrolysis experiment was demonstrated by using 0.5 mol dm-3 of sulfuric acid solution as the electrolyte. The working electrode (cathode) was prepared by TiON/AC carbon paper. A carbon paper and Ag|AgCl were used as the counter and the reference electrode, respectively. Hydrogen was quantified by a gas chromatography during chronoamperometry. Figure 1 shows the XRD patterns before and after NH3 nitridation at 700, 750, 800 and 900oC. Before the nitridation, the diffraction peaks assigned to both the anatase phase of TiO2 and carbon were recognized. After the nitridation at 700oC, the peaks assigned to TiO2, TiN and TiO were appeared. Furthermore, the peaks assigned to TiN and TiO was obvious and the broad peak of carbon was also recognized when the nitridation temperature was over 750oC. In addition, from the XPS results, the formation of Ti-O-N and O-Ti-N bonding were confirmed. Therefore, we considered that the nitridation of TiO2 to TiON was surely happened over 750oC. Figure 2 shows FE-SEM images of the product after the nitridation of 800oC. The tiny particles as 30 nm were found on AC substrate. These particles were considered the products composed of titanium, nitrogen and oxygen. The hydrogen production rate was estimated from the results of gas chromatography. And, its dependency on the overpotential was shown in Figure 3. Hydrogen production was confirmed at overpotential = 0.1 V for the products after the nitridation of 800 and 900oC. The products obtained at 900oC of the nitridation shows the highest hydrogen production rate. This work was partially supported by the Matching Planner Program from Japan Science and Technology Agency , JST and JSPS KAKENHI Grant Number 16K05940. Figure 1

HfO2/Al2O3/InGaAs MOSCAP Structures and InGaAs Plasma Nitridation Elaborated in a 300mm Pilot Line

The achievement of a good high-k oxide/InGaAs interface quality is a key challenge to obtain high performance MOSFET. Associating Al2O3 and HfO2 in a bilayer oxide is interesting to benefit from the good interface quality obtained with Al2O3 and the better electrostatic control achievable with HfO2. Furthermore, some recent work evidenced the reduction of the interface trap density (Dit) by using a plasma nitridation process [1]. For the first time, we evaluated the passivation properties of a Al2O3/HfO2 bilayer and a nitridation treatment on industrial equipment compatible with 300 mm Si wafers. First, we investigated the number of Al2O3 ALD cycles required to obtain a good interface. Second, we evaluated the effect of a nitridation treatment on the Al2O3/InGaAs interface properties performed on a 300 mm capacitive plasma tool.MOSCAP structures were fabricated on a 27 nm thick In0.53Ga0.47As layer grown on InP substrates. The samples were cleaned in a NH4OH solution (4%) for 1 min at room temperature and rinsed in deionized water. Then, Al2O3 and HfO2 films were deposited in a ALD chamber at 300°C with trimethylaluminium (TMA), Hafnium tetrachloride (HfCl4) and H2O as precursors. The ALD cycle numbers for Al2O3 were 0, 3, 5, 8 and 10 and 32 for HfO2. A post-deposition annealing was carried out at 370°C for 30 min in N2 ambient. For the nitridation study, one InGaAs sample was directly treated with a NH3 plasma for 120 s at 50W and two samples were treated with a NH3 plasma or a N2 plasma for 120 s at 50W after the deposition of Al2O3 (10 ALD cycles) to prevent damages on the III-V layer. After the plasma treatment, Al2O3 was again deposited to reach a 8 nm-thick layer for electrical characterization. Ni/Au gate electrode was deposited through a shadow mask by e-beam evaporation.The sample without Al2O3 (Fig1.a) presents distorted profiles, especially at 10 kHz, sign of a poor InGaAs/HfO2 interface quality. Depositing three Al2O3 cycles (fig.1.b) allows a limited improvement of the characteristics. The dispersion in accumulation of the 10 and 30 kHz curves is reduced but no clear accumulation plateau can be seen. From 5 to 10 cycles, samples (c-e), the situation is significantly improved with a clear accumulation regime. The interface trap densities (Dit) were estimated using the conductance method [2] and were found equal to ~11, 6.1 and 5.5 ×1012 cm-2eV-1 for the 5, 8 and 10 cycles samples respectively. A clear improvement is obtained from 5 to 8 cycles while only a slight improvement is obtained from 8 to 10 cycles. Compare to the Al2O3/InGaAs capacitor (fig.1.f), the best compromise between low Dit and high level capacitance appears to be 8 Al2O3 cycles. Wide frequency dispersion in accumulation can be seen after NH3 treatment without the Al2O3 protection (fig.2c) due to border traps in the dielectric. The plasma treatment prior to the dielectric deposition induces defects at the beginning of the nucleation. This dispersion is reduced when the treatment is implemented through an Al2O3 layer (fig.2b and d). N2 plasma reduces the capacitance whereas NH3 plasma does not deteriorate the C-V characteristics and keeps the same capacitance as the sample without nitridation. According to XPS analysis, N is clearly detected after plasma treatment. The N1s peak can be divided into two components, N1s A at 399.0 eV and N1s B at 397.9 eV. The N1s A component has been attributed to N-O bonds, and N1s B to N-Ga bonds [3]. Residual As oxides are reduced with NH3 (fig. 3e and f) but no As nitride is evidenced. After plasma treatment, the Ga3+ peak increases significantly (fig.3c and d), because of N incorporation at the interface. The Ga3+ component can be attributed to Ga-O and Ga-N bonds resulting in an oxynitride formation [1].In conclusion, Al2O3/HfO2 bilayer was optimized on a 300 mm equipment to achieve low Dit and high level capacitance (1.75 µF/cm²). NH3 nitridation process performed on a 300 mm capacitive plasma tool integrates nitrogen at the InGaAs surface without deterioration of the C-V characteristics. Low Dit is estimated at 2×1012 cm-2eV-1 at room temperature after NH3 plasma which is close to the value shown in [1] obtained with an ECR plasma. Measurements at lower temperature will further explain the Ditenergy distribution. [1] T. Hoshii, J. Appl. Phys., vol. 112, no. 7, p. 073702, 2012.[2] R. Engel-Herbert, Appl. Phys. Lett., vol. 97, no. 6, p. 062905, 2010.[3] T. S. Lay, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct., vol. 22, no. 3, p. 1491, 2004. Figure 1

Theoretical study of the ammonia nitridation rate on an Fe (100) surface: a combined density functional theory and kinetic Monte Carlo study.

Ammonia (NH3) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (Eb) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (Eb) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH3 nitridation rate on the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH3 nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH3 nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH3 nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.

V2O5 precursor-templated synthesis of textured nanoparticles based VN nanofibers and their exploration as efficient field emitter

Textured Vanadium Nitride (VN) nanofibers are prepared from hydrothermally derived V2O5 nanofibers by NH3 reduction and nitridation approach. The reaction temperature is seen to be a crucial parameter to prepare pure VN phase. VN produced via this route has distinctive structural characteristics. The crystal structure, morphology, and oxidation states of the elements of VN nanofibers are characterized by XRD, FESEM, TEM, HRTEM, and XPS studies. Field emission properties for these textured VN nanofibers have been explored. The field emission properties show the reproducible turn-on field of 3.4 V/μm for the emission current density of 10 μA/cm2. The observed turn-on field is found to be quite superior compare to carbide, nitride and oxide nanostructures. High emission current density of 44 μA/cm2 has been found at a field of 4 V/μm. Emission current stability for the preset current of 5 μA has been recorded for the period of 2 h. Present results indicate the considerable potential for the utilizing VN nanofibers as a cold cathode in the field emitter devices.

Nitridated Si–Ti–Ni alloy as an anode for Li rechargeable batteries

Nitridated Si–Ti–Ni (STN) ternary alloy as an anode for lithium ion batteries is prepared by the NH3 nitridation of STN alloy. The nitridated STN electrode shows 14% increased reversible capacity and 4 times higher rate capability at 3 C compared to those of pristine STN electrode. These improvements are attributed to the formation of nitride compounds (such as SiNx/SiNxOy, TiNx/TiNxOy and NiNx/NiNxOy) on STN alloy, which benefits both mechanics and kinetics.

Mesoporous TiN Microspheres with Hierarchical Chambers and Enhanced Visible Light‐Driven Hydrogen Evolution

Mesoporous titanium nitride (TiN) microspheres with tunable chamber structures were synthesized through NH3 nitridation of organotitania obtained via solvothermal alcoholysis. Owing to high content of organic species in organotitania, which stabilized the original structure and also promoted the nitridation at low temperature, TiN duplicated the solid, yolk-shell, and hollow chambers of organotitania in NH3 nitridation and also formed the mesoporous structure after removing organic species. During visible light-induced photocatalytic water splitting, the yolk-shell TiN demonstrated a higher H2 evolution efficiency than the solid, hollow, and crushed TiN; the yolk-shell TiN obtained through N2 nitridation; and other semiconductor photocatalysts reported so far without the aid of noble metals. This could be attributed mainly to the narrow energy band gap for absorbing visible light, high surface area, and excellent electrical conductivity, which facilitated light harvesting, reactant adsorption, and photoelectron-hole separation to suppress their recombination. Moreover, it could be easily recycled and thus used repetitively.

Crack-Free Thick AlN Films Obtained by NH3 Nitridation of Sapphire Substrates

We demonstrate that NH3 nitridation of sapphire substrates effectively suppresses cracks in AlN epilayers. The sapphire nitridation promoted three-dimensional (3D) growth at the initial stage, in contrast to the 2D growth mode on non-nitrided sapphire. The coalescence of 3D columnar grains in the process created voids, which act as strain absorber and thus crack-free thick epilayers were obtained. The control of nitridation period is also found important. The optimum nitridation period realized an atomically-smooth epilayer with superior structural quality. On the other hand, the least nitrided sapphire exhibited high twist mosaic of the grains which complicate the epilayer smoothing process, and the longer nitridation promoted slow recovery of a smooth epilayer.

Effect of NH3 plasma treatment on the interfacial property between ultrathin HfO2 and strained Si0.65Ge0.35 substrate

The effect of NH3 plasma treatment on the interfacial property between ultrathin HfO2 and strained Si0.65Ge0.35 substrate has been investigated by high-resolution cross-sectional transmission electron micrographs, x-ray photoelectron spectroscopy, VBS, capacitance-voltage (C-V), and current density-voltage (J-V). TEM and XPS results confirm that interfacial layer with N–Hf and N–Si/O-N-Si bonds acts as a barrier layer against interdiffusions during annealing in some degree. The valence-band offsets ΔEV of HfO2/SiGe interfaces with and without nitridation are determined to be 3.02 ± 0.05 eV and 2.91 ± 0.05, respectively while the conduction-band offsets ΔEC are found to be 1.79 ± 0.05 and 1.90 ± 0.05 eV. The largest total dielectric constant (k) of 15.0 and smallest equivalent oxide thickness of 0.78 nm has been calculated from the accumulation capacitance of the capacitor with NH3 nitridation before post-deposition annealing (PDA). Moreover, the nitrided capacitor after PDA shows a small C-V hysteresis loop of ∼239 mV and low leakage current density (J) of ∼6.53 × 10−7 A/cm2 at a gate bias of Vg = −2.0 V.

Effect of plasma N2 and thermal NH3 nitridation in HfO2 for ultrathin equivalent oxide thickness

Two methods of HfO2 nitridation including plasma N2 nitridation and thermal NH3 anneal were studied for ultrathin HfO2 gate dielectrics with <1 nm equivalent oxide thickness (EOT). The detailed nitridation mechanism, nitrogen depth profile, and nitrogen behavior during the anneal process were thoroughly investigated by XPS and SIMS analysis for the two types of nitridation processes at different process conditions. Intermediate metastable nitrogen was observed and found to be important during the plasma nitridation process. For thermal NH3 nitridation, pressure was found to be most critical to control the nitrogen profile while process time and temperature produced second order effects. The physical analyses on the impacts of various process conditions are well correlated to the electrical properties of the films, such as leakage current, EOT, mobility, and transistor bias temperature instability.

Effect of Film Morphology and Thickness on Charge Transport in Ta3N5/Ta Photoanodes for Solar Water Splitting

Photoelectrochemical water splitting is one of many approaches being studied to harvest sunlight and produce renewable H2. Tantalum nitride (Ta3N5) is a promising photoanode candidate as its band edges straddle the water redox potentials and it absorbs a large portion of the solar spectrum. However, reported photocurrents for this material remain far from the theoretical maximum. Previous results indicate Ta3N5 may be hindered by charge transport limitations attributed to poor bulk charge transport, charge transport across grain boundaries, and/or charge transfer across the interface at the back contact. The primary goal of this work was to study these mechanisms, especially bulk hole and electron transport, to determine which processes limit device efficiency. Crystalline thin films (60–780 nm) of Ta3N5 (Eg = 2.1 eV) on Ta foils were synthesized by oxidation of Ta metal in air at 550 °C and subsequent nitridation in NH3 at 900 °C. Scanning electron microscopy revealed that thermal stresses and difference...

Investigation of inversion domain formation in AlN grown on sapphire by MOVPE

AbstractFor certain growth conditions pronounced roughening has been observed for AlN layers grown on c‐plane sapphire by metal‐organic vapour phase epitaxy. TEM investigations revealed inversion domains correlated with the rough regions of the wafer. Al‐polar material was found at hillocks and N‐polar AlN in the valleys. We have investigated the early stages of growth and found three determining factors for the polarity development in AlN on c‐plane sapphire: substrate treatment by NH3 (nitridation) or TMAl preflow, substrate treatment by annealing under H2 atmosphere and the influence of parasitic depositions in the reactor. We propose a correlation between the sapphire surface termination and the polarity of AlN. Oxygen termination of sapphire is suggested to lead to N‐polarity and aluminium termination to Al‐polar AlN. By optimising the reactor condition, substrate treatment and growth conditions, smooth Al‐polar AlN layers were obtained for the subsequent growth of deep UV‐LED heterostructures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The NH3 Nitridation Effects on a Al2O3 Passivation by Atomic Layer Deposition (ALD) in the HfO2/GaAs Systems

We investigated the nitridation effects on a passivating Al2O3 layer formed by atomic layer deposition (ALD) process at the interface of HfO2/GaAs. Results reveal that formation of Ga-O is suppressed greatly when annealed under NH3 ambient for the HfO2/GaAs system. Moreover if the Al2O3 layer is thick enough, diffusion of Ga into the high-k dielectric is blocked effectively, even after heat treatment at 500oC. This not only suppresses formation of interfacial oxide, but also improves the electrical properties. The nitrogen contents present in NH3 ambient lead to a decrease in the interfacial layer, which in turn decreases the effective oxide thickness (EOT). Results of chemical analyses by x-ray photoelectron spectroscopy (XPS) and micro-structure analyses by high-resolution transmission electron microscopy (HR-TEM) are presented.

The NH3 Nitridation Effects on a Al2O3 Passivation by Atomic Layer Deposition (ALD) in the HfO2/GaAs Systems

not Available.

Fabrication of Si3N4-based composite containing needle-like TiN synthesized using NH3 nitridation of TiO2 nanofiber

Abstract A Si3N4 composite containing needle-like TiN particles (7 vol%) was fabricated. Needle-like TiN particles several micrometers long were synthesized using NH3 nitridation of TiO2 nanofiber, which was obtained using hydrothermal treatment. A mixed powder of α-Si3N4 and the needle-like TiN particles with additives was hot pressed at 24 MPa and 1850 °C for 1 h in N2 atmosphere. Mechanical properties of the composite were compared with those of a composite containing rounded TiN particles and a monolithic β-Si3N4 ceramic. The Si3N4 matrix of the composites containing TiN was mainly a-phase, suggesting that the α–β phase transformation of Si3N4 was inhibited by the presence of TiN. Although fracture strength of the composites was lower, fracture toughness was comparable to that of monolithic β-Si3N4 ceramics. Hardness of the composites was about 19 GPa and was greater than that of the monolithic β-Si3N4 ceramic.