Thermal Annealing In Nitrogen Research Articles

Self-Assembly of Hierarchical High-χ Fluorinated Block Copolymers with an Orthogonal Smectic-within-Lamellae 3 nm Sublattice and Vertical Surface Orientation.

Hierarchical structure-within-structure assemblies offer a route toward increasingly complex and multifunctional materials while pushing the limits of block copolymer self-assembly. We present a detailed study of the self-assembly of a series of fluorinated high-χ block copolymers (BCPs) prepared via postmodification of a single poly(styrene)-block-poly(glycidyl methacrylate) (S-b-G) parent polymer with the fluorinated alkylthiol pendent groups containing 1, 6, or 8 fluorinated carbons (termed trifluoro-ethanethiol (TFET), perfluoro-octylthiol (PFOT), and perfluoro-decylthiol (PFDT), respectively). Bulk X-ray scattering of thermally annealed samples demonstrates hierarchical molecular assembly with phase separation between the two blocks and within the fluorinated block. The degree of ordering within the fluorinated block is highly sensitive to synthetic variation; a lamellar sublattice was formed for S-b-GPFOT and S-b-GPFDT. Thermal analyses of S-b-GPFOT reveal that the fluorinated block exhibits liquid crystal-like ordering. The complex thin-film self-assembly behavior of an S-b-GPFOT polymer was investigated using real-space (atomic force microscopy and scanning electron microscopy) and reciprocal-space (resonant soft X-ray scattering (RSoXS), grazing incidence small- and wide-angle scattering) measurements. After thermal annealing in nitrogen or vacuum, films thicker than 1.5 times the primary lattice spacing exhibit a 90-degree grain boundary, exposing a thin layer of vertical lamellae at the free interface, while exhibiting horizontal lamellae on the preferential (polystyrene brush) substrate. RSoXS measurements reveal the near-perfect orthogonality between the primary and sublattice orientations, demonstrating hierarchical patterning at the nanoscale.

Enhanced anchoring enables highly efficient and stable inverted perovskite solar cells

The immobilization of all-type ions is critical for further enhancing the efficiency and stability of inverted perovskite solar cells as the volatilization of organic cations and migration of halides could cause device degradation and non-radiative recombination. This work reports a novel and effective multidentate molecular “lock”, 2,3,4,5,6-Pentafluorophenylammonium Iodide (F5PhAI), to simultaneously immobilize all types of ions in perovskite with multiple chemical anchoring sites, leading to enhanced stability of perovskite under thermal and ambient conditions, as well as reduced defect density and energy disorder of perovskite films to significantly inhibit the non-radiative recombination. As a result, F5PhAI-modified device achieves an improved PCE of 24.03%, with a VOC of 1.124 V, a JSC of 25.14 mA cm−2, and an FF of 85.03%. Furthermore, the unencapsulated devices exhibit enhanced long-term stability, maintaining 85% and 90% of the initial efficiencies under 85°C thermal annealing in nitrogen for 500 hours and in humid air condition (RH: 60±10%) for 1000 hours, respectively. This work provides a novel and effective multidentate molecular “lock” strategy to achieve high-efficiency and stable inverted perovskite solar cells.

Ultra-small Co/CoO nanoparticles dispersed on N-doped carbon nanosheets for highly efficient electrocatalytic oxygen evolution reaction

In this paper, we report a facile strategy to synthesize Co-BDC-NH2 material, which is used as a precursor towards an excellent OER electrocatalyst by thermal annealing in nitrogen. Ultra-small Co/CoOx nanoparticles were uniformly dispersed on the rhombus N-doped carbon (NC) nanoflakes. Transmission electron microscopic, X-ray diffraction spectrometric, and X-ray photoelectron spectroscopic analyses revealed the coexistence of metallic Co and Co oxides nanoparticles. It was found that Co/CoOx@NC obtained at 500 °C annealing temperature exhibited the highest electrocatalytic OER activity, with 307 and 375 mV overpotential to achieve 10 and 100 mA cm−2 current densities. Besides, thanks to the in-situ annealing process, Co/CoOx@NC showed excellent catalytic stability with 97.4% current density retention after 24 h electrolysis at 1.66 V vs. RHE electrode potential. Further investigations revealed that the ultra-small Co/CoOx nanoparticles distributed on N-doped carbon template contribute significantly towards OER electrocatalysis through enlarging the activity surface areas and enhancing the intrinsic electrochemical activity due to the presence of metallic Co.

MOCVD growth GaN on sapphire

The n-type and p-type a-GaN films were successfully grown on a r-sapphire substrate, according to X-ray diffractometer and SEM results parameters measurement. The growth rate versus the growth temperature was investigated. The holes concentration (8x1017 cm−3) was achieved by the Cp2Mg flow optimization and the parameters of thermal annealing in nitrogen. The GaN film growth rate dependence versus temperature at a constant hydrogen flow through a TEG source was investigated. The results indicate that defects density is reduced upto 104 cm−2, the surface morphology uniformity was improved. During growth the influence from V/III flows ratio was detected.

Role of silver nanoparticles in the dewetting behavior of copper thin films

We report on the effect of added silver on the solid state dewetting behavior of copper thin films, grown by thermal evaporation. The films were annealed under different conditions, conventional furnace annealing in air and argon and rapid thermal annealing in nitrogen. Our results show that for all annealing conditions, addition of silver to copper films suppresses the dewetting when compared to pure copper films. Fully dewet silver–copper films produce roughly spherical nanoparticles, with the amount of silver controlling the particle areal density and size distribution. This provides an additional parameter for controlled synthesis of nanoparticles by a bottom–up approach.

Synthesis and thermal annealing treatment of octylphosphonic acid-capped CdSe-tetrapod nanocrystals for bulk hetero-junction solar cell applications

CdSe-tetrapod nanocrystals (NCs) were synthesized by using octylphosphonic acid (OPA) as a capping ligand and cadmium oxide (CdO) as a cadmium precursor. The effects of thermal annealing in nitrogen (N2) environment on the chemical composition, morphology, crystal structure and optoelectronic properties of the CdSe-tetrapods have been investigated. Remarkable difference in the morphological and optoelectronic properties between as-synthesized and N2-annealed CdSe NCs was observed. The photoluminescence (PL) peak of N2-annealed CdSe NCs shifted to lower energy and UV-vis absorption spectra shifted to longer wavelength, indicating the size increase and improvement of the crystallinity of the CdSe tetrapods. The power conversion efficiency of bulk hetero-junction solar cells made with the annealed CdSe NCs showed higher value compared with the efficiency of cells made with as-synthesized CdSe NCs.

Effects of Thermal Annealing in Nitrogen on Photoluminescence of Sol-Gel Derived ZnO Nanocrystals

The synthesis of ZnO nanocrystals is carried out in alkaline alcoholic solution of zinc acetate dihydrate by sol-gel method. Effects of thermal annealing in nitrogen on photoluminescence (PL) properties of the sol-gel derived ZnO nanocrystals were investigated by PL spectroscopy. With increasing annealing temperature in nitrogen, UV emissions of the ZnO nanocrystals red-shifted from 378 nm to 388 nm while deep-level luminescent bands ranging from 450 to 700 nm with three emission centers at about 502 nm, 538 nm and 602 nm are enhanced, and the green luminescent band gains its intensity at the expense of the yellow and orange luminescent bands. Our results have demonstrated that the origin yellow-green color PL was tuned towards the cyan color PL with increasing the thermal annealing temperature in nitrogen from 344 oC to 813 oC.

Improved thermal stability of nitrogen annealed sputtered hafnium oxide thin films for VLSI technology

PurposeHigh‐dielectric thin films are considered as future dielectric for Si based advanced integrated circuit technology and also for the development of organic thin film transistors and micro sensors. The conventional dielectric SiO2 is grown by thermal oxidation of silicon whereas the HfO2 films are grown by both physical and chemical methods. Depending on film deposition technique, the film and interface characteristics are affected. The purpose of this paper is to investigate the effect of thermal annealing in oxygen and nitrogen ambient on the electrical properties of HfO2‐based metal oxide semiconductor (MOS) capacitor and evaluate thermal stability of the characteristics.Design/methodology/approachHfO2 films are deposited by rf sputtering and Al‐HfO2‐Si MOS capacitor fabricated. The electrical I‐V and C‐V characteristics are measured and the effect of temperature in the range of 25‐200°C is evaluated for films annealed in oxygen and nitrogen.FindingsIt is found that thermal annealing in nitrogen reduces oxide trap density and improves the temperature stability compared to the film annealed in oxygen for MOS devices. From the conductance characteristics Dit oxide trap density in the film is estimated to be 2.1×1011/cm2 for nitrogen and 3.23×1011/cm2 for oxygen, which indicates the role of nitrogen in reducing oxide traps. The thermal activation energy of electron traps is found to be about 0.19 eV for nitrogen and 0.58 eV for oxygen annealed films in the temperature range of 25‐150°C.Originality/valueThe paper examines and compares the role and effect of thermal annealing in nitrogen ambient and oxygen ambient on the electrical properties of sputtered HfO2 thin film for improved MOS device reliability.

Effects of nitrogen doping of ZnO during or after deposition

Effects of nitrogen doping of ZnO (ZnO:N) during deposition and after postdeposition annealing have been studied by optical techniques, electronic properties, and the application to metal-semiconductor-metal photodetectors (MSM-PDs). Films of ZnO, nitrogen doped during rf sputtering, show larger grain size, narrower full width at half maximum, band gap emission shift in photoluminescence, and higher conductivity. Postannealing has been studied using tube furnace and rapid thermal annealing in nitrogen. These annealing methods not only reconstruct the lattice structure but also activate the nitrogen in the film to improve the conductivity of the film. The MSM-PDs having high photo to dark current ratio of 104 and responsive (R) of 1.79 A/W have been fabricated with those films.

The evolution of tungsten oxide nanostructures from nanowires to nanosheets

The self-synthesis of tungsten oxide (W18O49) nanowires/nanosheets on sputtering-deposited tungsten films was obtained by thermal annealing in nitrogen under the thermal budgets of 750 °C for ≥2 h or ≥850 °C for 0.5 h. Experimental evidence of the nanomorphology transformation of tungsten oxide nanostructures from nanowires to nanosheets was presented, which can be attributed to the formation and re-crystallization of an amorphous interface layer between two neighboring parallel-growth nanowires linked together with a low angle misalignment along their growth directions.

Process development and material characterization of polycrystalline Bi2Te3, PbTe, and PbSnSeTe thin films on silicon for millimeter-scale thermoelectric generators

In this work, deposition, patterning, and metallization of vapor-deposited polycrystalline thermoelectric (TE) thin films of Bi2Te3, PbTe, and PbSnSeTe on silicon (Si) substrates are investigated. These fundamental microfabrication methods are intended for use in integrating TE films into thermally powered micro-electro-mechanical systems (MEMS)-based power generators. P-type polycrystalline Bi2Te3, PbTe, and PbSnSeTe films were successfully deposited on thermally oxidized (100) Si substrates to thicknesses ranging from 0.4 to 9 μm. Dry etch rates of about 0.6−0.7 μm/min were achieved for Bi2Te3 and PbTe/PbSnSeTe using methane-based gases. Wet etch rates of ∼3 μm/min were achieved using various acid wet chemistries. Films were electrically characterized using van der Pauw and transfer length method (TLM) test structures. Postdeposition resistivities were measured as low as 23 mΩ cm for Bi2Te3, 134 mΩ cm for PbTe, and 52 mΩ cm for PbSnSeTe. The Seebeck coefficients were measured at up to 94 μV/K for undoped Bi2Te3, and 160 and 42 μV/K for doped PbTe and PbSnSeTe, respectively. Metal contact resistivities (0.18−42 mΩ cm2) were also extracted for a variety of thin film metals (Pt, Au, Cu, Ni, Cr/Pt/Au, Ti/Pt). Various postdeposition annealing treatments were explored for reducing film resistivity that would enable higher power delivery for TE generator applications. Rapid thermal annealing in nitrogen at 400 °C was shown to reduce the resistivity of PbTe and improve film adhesion to oxidized silicon substrates. Also, after successive heatings in air at 200 °C, the resistivity of the PbTe films remained stable while that of the PbSnSeTe increased up to 10×.

Specific features of steady-state implantation of crystalline silicon with a molecular oxygen-nitrogen beam: Si L 2, 3 x-ray emission spectra

The local electronic structure of 〈111〉 n-silicon single-crystal samples is studied using Si L2, 3 x-ray emission spectroscopy. The SixOyNz system is formed by implanting the samples with an 16O2+ and 14N2+ ion molecular beam (the oxygen/nitrogen ratio in the molecular beam is 1:1, the implantation energy is 30 keV, the irradiation fluences vary from 2.0 × 1017 to 1.5 × 1018 cm−2, the samples after the implantation are subjected to rapid thermal annealing in nitrogen at 800°C for 5 min). A comparison of the recorded Si L spectra with the spectra of the reference samples reveals clear correlations between the specific features of the electronic structure of the silicon oxynitride formed upon implantation and the ion fluence. It is shown that the implantation at fluences of 2 × 1017 and 1 × 1018 cm−2 results in the predominant formation of Si3N4, whereas the implantation at a fluence of 1.5 × 1018 cm−2 leads primarily to the formation of SiO2 layers in single-crystal silicon. The most probable factors and mechanisms accounting for such implantation of 16O2+ and 14N2+ into the samples under study are discussed. The experimental data obtained are compared with ab initio full-potential linearized augmented plane wave calculations of the band structure.

Thermal stability of CdZnO∕ZnO multi-quantum-wells

The thermal stability of CdZnO∕ZnO multi-quantum-well (MQW) structures was studied using rapid thermal annealing in nitrogen from 300to750°C. Photoluminescence (PL) emission from the MQWs was studied while varying the annealing temperature and time. For 15min annealings, the PL center wavelength showed a 7nm reduction for temperatures up to 650°C. Above 650°C, the wavelength changed rapidly, with a 50nm reduction at 750°C. Annealing at 700°C for up to 20min produced a systematic reduction in PL wavelength up to 39nm. The data suggest that CdZnO∕ZnO MQWs are relatively stable for nitrogen annealing below 650°C for times up to 15min.

Raman Scattering Studies of Electrically Active Impurities in in Situ B-Doped Silicon Nanowires: Effects of Annealing and Oxidation

The concentration of electrically active impurities in in situ boron (B)-doped silicon (Si) nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD) is studied by Raman spectroscopy. B-doped SiNWs exhibit an asymmetric Raman spectrum due to Fano resonance between discrete phonon Raman scattering and continuous electric Raman scattering caused by the excitation of holes in the valence band. To quantitatively evaluate the concentration of active B atoms from the asymmetric spectral shape, the spectra are fitted by a Fano resonance formula and asymmetry parameters are extracted. From the comparison of the asymmetry parameter with those obtained for reference samples, the concentration of active B atoms in SiNWs is estimated. The effects of thermal annealing in nitrogen and oxygen gases on the active B concentration are also studied. The annealing in nitrogen ambience for a short period significantly increases the concentration of active B atoms especially when the doping level is ...

Influence of laser irradiation with hν=1.96 eV on the properties of titanium-silicon contact under thermal annealing in nitrogen

The effect of laser irradiation with hν=1.96 eV (λ=0.63 µm) on the properties of titanium-silicon contacts subjected to steady-state thermal annealing in a nitrogen atmosphere is studied. It is found that treatment-induced changes in the phase composition of the contact modify its electrophysical parameters. The applicability of laser irradiation to the formation of rectifying titanium-silicon junctions with desired parameters is demonstrated.

Interfacial reactions and failure mechanism of Cu/Ta/SiO 2/Si multilayer structure in thermal annealing

The integrity of Cu/Ta/SiO 2/Si multilayer structure under nitrogen thermal annealing has been examined by sheet resistance measurement, X-ray diffraction, scanning electron microscopy, secondary ion mass spectroscopy, Rutherford backscattering spectrometry and cross-section transmission electron microscopy analysis. According to electrical measurement it was found that Ta diffusion barrier could preserve the integrity of the Cu/Ta/SiO 2/Si structure up to 650 °C in N 2 for 35 min. There are two causes by which the Cu/Ta/SiO 2/Si structure became degraded. One is the out diffusion Ta atoms towards the Cu film. The other factor is the formation of Cu, Ta and Cu–Ta oxide. Hence, Cu penetration is not the only reason to cause the failure; oxidation, phase transformation and interfacial reactions are also associated problems during thermal annealing.

The Blue Laser Diode. The Complete Story

The story of Shuji Nakamura and the blue laser diode is remarkable. It is clear from this book that he enjoys this fact and wishes his readers to become familiar with his success. Nakamura was a little known researcher at a small but successful Japanese company, Nichia Chemical, on Shikoku, one of Japan's four main islands. One of their successful lines was phosphors for fluorescent lights. In 1989, Nakamura was given a few million dollars by the company's Chairman Nobuo Ogawa. Nakamura chose to research into blue light emitters using gallium nitride, a material that had been studied by Pankove at RCA some 20 years earlier and largely written off by the conventional semiconductor industry. In spite of many factors against progress, this second edition of The Blue Laser Diode testifies to the success of this gamble. The book is subtitled `The complete story'. This is an unlikely epithet for the book because there is still a long way to go. The book is written with a mixture of academic integrity and commercial trumpet blowing. There is too often a lack of detail and logical order. There is inadequate discussion of the case for and against other materials such as ZnSe. One feels that the commercial pressure not to give away all the answers about gallium nitride has triumphed over the wish for scientific disclosure to enable results to be repeated. The book clearly reports the two most significant difficulties faced by gallium nitride. First, it appeared from Pankove's work that it would not to be easy to find an appropriate p-type dopant that could make suitable p-n junctions. Two chapters consider this problem, starting with low energy electron beam irradiation and then in the second chapter considering thermal annealing in nitrogen. The writing and detail suggest that it is still a technology rather than science (or, perhaps more unkindly, cook-book recipes of time and temperature). The second important difficulty is that gallium nitride has too many dislocations for long-life laser action. Growth on sapphire with appropriate buffer layers is described as an initial step in reducing the dislocations. Later in the book, it is recognized that InxGa1-xN offers greater versatility, and this is considered in more detail along with InGaN/AlGaN double heterostructures. Regrettably it is not easy though to dig out from this book all the details of lattice matching that are required and how successful lattice matching has been in removing dislocations and increasing lifetime. Clearly the general trend of longer lifetimes means that there has been useful success. Blue laser diodes are now claimed to be commercially available with lifetimes measured in thousands of hours while blue light emitting diodes, with their lower current densities, are said to have lifetimes measurable in years. The book has a little for everyone. Applications are noted briefly as well as blow-by-blow accounts of the manufacturing technology of double heterostructure, multi-quantum well lasers and progress to room temperature operation. Applications range from the mundane traffic light, through full colour displays to 15-20 Gbyte optically read data storage discs. Interestingly it is the mundane applications that may have the biggest financial impact. A statistic that appears on the Internet is that if all the traffic signals in Japan could be switched to suitable LEDs then one could save the construction of at least one nuclear power plant. Although Nakamura is an admirer of Pankove's work, the writing and scientific style does not match that of Pankove. Nevertheless the book records a thorough solid achievement and as such there should be a similar solid basis for many readers in materials science and laser technology wishing to read this book. The book regrettably gives no indication why Nakamura has left Nichia for a Professorship at Santa Barbara after such magnificent early support by Nichia. Nor does the book explain why Nakamura's co-author Gerhard Fasol is undercutting the joint venture by selling for $15 over the web a 28 page summary about blue laser diodes using gallium nitride. However, if price is no consideration, there is also advertised on the web a 222 page report SC-23 from Strategies Unlimited entitled `Gallium Nitride 2000 - Technology Status, Applications, and Market Forecast' for a modest $3950. Clearly the present book cannot be `the complete story'. That will run for quite a time yet. John Carroll

Effects of postannealing on the electrical properties of Ta2O5 thin films deposited on TiN/T

The effects of postannealing on the structural and leakage current characteristics of Ta2O5 thin films deposited on a TiN/Ti bottom electrode by chemical-vapor deposition at 350 °C were investigated. The Ta2O5 film of 50 nm thickness shows an amorphous phase and smooth surface morphology after annealing in N2O plasma at 350 °C, but the film treated with rapid thermal annealing in nitrogen (RTN) at 750 °C prior to N2O plasma annealing at 350 °C has an orthorhombic structure and rugged surface morphology. In addition, the TiSi phase also appears in the specimen of RTN-treated Ta2O5 film. Moreover, the residual carbon can be effectively eliminated and the oxygen deficiency can be well compensated by the N2O plasma annealing for both amorphous and crystalline Ta2O5 films. The I–V relation of the amorphous Ta2O5 films is asymmetric with respect to the biasing polarity, which indicates that the leakage current is primarily dominated by the Schottky emission. On the other hand, the crystalline Ta2O5 film has a symmetrical I–V relation, suggesting that the non-Ohmic leakage in the crystalline Ta2O5 film is related to the Poole–Frenkel effect. The barrier heights φB for the non-Ohmic leakage in the amorphous and crystalline Ta2O5 films, as evaluated from the temperature dependence of the I–V relation, are 0.52 and 0.82 eV, respectively.

Thermal Stability and Oxidation Resistance of W, TiW, W(N) and TiW(N) Thin Films Deposited on Si

The thermal stability and oxidation resistance of ∼100-nm-thick W, TiW, W(N) and TiW(N) thin films deposited on Si substrate by rf magnetron sputtering were investigated by X-ray diffraction, resistivity measurement, X-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. All films showed good thermal stability against rapid thermal annealing in nitrogen (RTN) at 800°C for 1 min, except the W(N) film which decomposed to W and N2 at 800°C. The films also exhibited differences in oxidation resistance against rapid thermal annealing in oxygen (RTO). Both W and W(N) films were significantly oxidized at temperatures above 450 and 500°C, respectively, while TiW and TiW(N) films showed much better oxidation resistance up to temperatures of 750 and 650°C, respectively. In general, nitridized films, i.e., W(N) and TiW(N), exhibit better resistance against oxidation than metallic films. However, TiW films exhibit better oxidation resistance than nitridized films at RTO temperatures ≧600°C due to a change in surface oxide formation from a uniform oxide to a Ti-rich oxide. Once the films were completely oxidized, they were peeled off.

Roughness at Si/SiO2 interfaces and silicon oxidation

With a plan-view transmission electron microscopy technique of directly imaging buried Si/SiO2 interfaces, we studied the interface roughness resulting from the oxidation process. Our results show that thermal annealing in nitrogen at 900 °C can dramatically remove the interface roughness for Si(100)/SiO2 interfaces [X. Chen and J. M. Gibson, Appl. Phys. Lett. 70, 1462 (1997)]. In contrast, Si(111)/SiO2 interfaces, which tend to be smoother than Si(100)/SiO2 interfaces, are not affected by annealing. A model to link interface roughness and silicon oxidation kinetics was developed. This model not only qualitatively explains the difference between Si(111) and Si(100) interfaces that we saw but also shows that oxidation dynamics is the origin of the interface roughness. Hence, it might be a new approach to understand oxidation dynamics through studying interface roughness.