Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interfacial structure of sub-micron Al2O3 particles in aluminum matrix

The surfaces of ellipsoidal Al₂O₃ particles with average size of 0.15 μm and the interfaces between the Al₂O₃ particles and 1070Al were investigated by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM).The results show that the surfaces of Al₂O₃ particles appear to be polyhedrons consisting of crystal planes with small angle, while every plane of the polyhedrons could be considered as a stepped structure composed of close-packed planes along the close-packed direction. The interfaces of the 0.15 μm Al₂O₃p/1070Al composite bond well, without any interfacial reaction products. It is proposed that there are several kinds of crystallographic orientation relationships between the aluminum matrix and Al₂O₃particles due to the polyhedral structure. In our study, such orientation relationships are found to be {110} _Al ||{1100} _Al2O3 and ?110? _Al ||?1126? _Al2O3 .     

Characterization of laser-induced plasma plume: Comparison between Al and Al2O3 targets

Characterization of the plasma plume produced by laser ablation from Al and Al₂O₃ targets was carried out on the basis of the line profile analysis of Al(I) (²P°–²S) emission. The spatial distribution and density parameters of electrons and Al atoms in the plume were obtained by comparing observed spectral line profiles with a theoretical calculation. The results showed different behavior for the Al and Al₂O₃ targets. The Al atoms from the Al₂O₃ target were populated in a smaller region than those from the Al target. PACS 52.38.MF; 52.70.Kz; 52.25.Os     

Magnetism and electronic correlations in the iron aluminides R Fe2Al10 (R = Y,Yb)

YFe₂Al₁₀ and YbFe₂Al₁₀ are new additions to the currently investigated rare‐earth (R) series of compounds RT₂Al₁₀ in which T is Fe, Ru, or Os. Unusual physical properties are drawing considerable attention to this group of compounds. Intriguingly, very small moments order in CeRu₂Al₁₀ at as high as 27 K, whereas CeFe₂Al₁₀ is a Kondo insulator with very strong hybridization of the Ce magnetic moments and no magnetic ordering at all. Here we present the first results of two further iron‐based compounds YFe₂Al₁₀ and YbFe₂Al₁₀ as a timely contribution to the knowledge of the physics at work in this system. In YFe₂Al₁₀ we find signatures of correlated electrons and the low‐temperature results of specific heat, magnetic susceptibility and electrical resistivity are indicative of ferromagnetic quantum criticality. In YbFe₂Al₁₀ localized f‐electron spins of Yb become involved in correlations with a moderately enhanced electronic specific heat that classifies it as a non‐ordered heavy‐fermion compound. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Neutron diffraction study of crystal structure and antiferromagnetic ordering in the heavy fermion compound CePd2Al3

Nuclear and magnetic structures of an annealed polycrystalline sample of the heavy-fermion compound CePd₂Al₃ prepared by arc-melting were investigated by neutron powder diffraction. The chemical structure corresponds well to the ordered hexagonal PrNi₂Al₃-type structure. The antiferromagnetic structure of CePd₂Al₃ with an ordered magnetic moment _Ce=0.47(2) _B at saturation is remarkably similar to that in the heavy fermion superconductor UPd₂Al₃. The additional incommensurate magnetic structures reported previously both for UPd₂Al₃ and CePd₂Al₃ are not observed in the present sample of CePd₂Al₃. At 1.4 K the magnetoresistivity of CePd₂Al₃ measured up to 14 T indicates only one field-induced phase transition at 3.0 T.     

Infrared-to-visible up-conversion emissions and thermometric applications of Er 3+-doped Al 2 O 3

Er³⁺-doped Al₂O₃ has been prepared by a sol–gel method, using aluminium isopropoxide [Al(OC₃H₇)₃]-derived Al₂O₃ sols with addition of erbium nitrate [Er(NO₃)₃·5H₂O]. The phase structure of θ-(Al,Er)₂O₃ phase was obtained for the 0.1 mol. % Er³⁺-doped Al₂O₃ at the sintering temperature of 1273 K. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ² H _11/2, ⁴ S _3/2→⁴ I _15/2 and ⁴ F _9/2→⁴ I _15/2 transitions of Er³⁺, were detected by a 978-nm semiconductor laser diode excitation. The temperature dependence of green up-conversion emissions was studied over a wide temperature range of 295–725 K, and reasonable agreement between the calculated temperatures obtained by the fluorescence intensity ratio theory and the measured temperature was obtained, which proved that Er³⁺-doped Al₂O₃ has a good potential for the development of high-temperature sensors. It has some advantages compared to glasses due to its higher thermal and mechanical resistance and allows measurements in a large temperature range. PACS 78.55.Hx; 81.40.Tv     

Al2O3Hx(x=1—3)分子团簇的结构与光谱研究

用密度泛函理论(DFT)的B3lyp方法在6-311++g(d,p)水平上对Al₂O₃H_x(x=1—3)分子的几何构型, 电子结构, 振动频率等性质进行了系统研究. 并给出了它们可能基态结构的总能量(E_T), 零点能(E_z), 摩尔热容(C_v), 标准熵(S), 原子化能(ΔE_m), 垂直电离能(IP)及垂直电子亲和能(E_A). Al₂O₃H和Al₂O₃H₂分子可能的基态的几何构型都为平面结构. Al₂O₃H₃的两个可能为基态的几何构型都是在立体Al₂O₃(D_3h)的几何结构基础上加三个氢原子构成. 这三个分子的能量最低结构为Al₂O₃H(²A′)C_s, Al₂O₃H₂(¹A′) C_s, Al₂O₃H₃ (²A) C₁.     

Hf3Al2 and Zr3Al2 Isostructural Aluminides Studied by PAC with 181Ta and 111Cd Probes

The electric quadrupole hyperfine interactions for ¹⁸¹Hf/¹⁸¹Ta and for ¹¹¹In/¹¹¹Cd probes in polycrystalline Zr₃Al₂ and Hf₃Al₂ compounds were measured in the temperature range 24–1100 K. The hyperfine quadrupole interaction parameters were determined after different doping techniques and heat treatments of the samples.¹⁸¹Hf/¹⁸¹Ta was found to substitute the Hf/Zr sites and the ¹¹¹In/¹¹¹Cd impurities appear to substitute both the 8(j) Al sites and the three nonequivalent Hf/Zr sites.     

First-principles investigation on vibrational,anisotropic elastic and thermodynamic properties for L12 structure of Al3Er and Al3Yb under high pressure

To better clarify the physical properties for Al₃RE precipitates, first-principles calculations are performed to investigate the vibrational, anisotropic elastic and thermodynamic properties of Al₃Er and Al₃Yb. The calculated results agree well with available experimental and theoretical ones. The vibrational properties indicate that Al₃Er and Al₃Yb will keep their dynamical stabilities with L1₂ structure up to 100 GPa. The elastic constants are satisfied with mechanical stability criteria up to the external pressure of 100 GPa. The mechanical anisotropy is predicted by anisotropic constants A^G, A^U, A^Z and 3D curved surface of Young’s modulus. The calculated results show that both Al₃Er and Al₃Yb are isotropic at zero pressure and obviously anisotropic under high pressure. Further, we systematically investigate the thermodynamic properties and provide the relationships between thermal parameters and pressure. Finally, the pressure-dependent behaviours of density of states, Mulliken charge and bond length are discussed.     

Ab initio calculations of electric field gradients detected by impurities in TiO2, Al2O3 and CaCO3

We present ab initio calculations of electric field gradients (EFGs) at impurity sites in ionic crystals TiO₂, Al₂O₃ and CaCO₃. The electronic structure was calculated self-consistently by the KKR method in the framework of the local spin density approximation of the density functional theory. The system with a single impurity was simulated by the super cell method. It was found that EFGs for the transition metal impurities (Sc, Nb, Cd and Ta) in TiO₂ were well reproduced by the calculations if the charge state of them in TiO₂ was taken into account. The present method was applied to the determination of the implantation sites of N and O nuclei in TiO₂. The calculation of EFGs at a Si impurity in Al₂O₃ and at Ca site in CaCO₃ were used to derive the quadrupole moments of ²⁷Si and ³⁹Ca from their quadrupole coupling constants. This revised version was published online in August 2006 with corrections to the Cover Date.     

微弧等离子喷涂碳纳米管/纳米Al2O3-TiO2复合涂层的吸波性能研究

将碳纳米管与纳米Al₂O₃-TiO₂陶瓷粉末超声共混制备了碳纳米管/纳米Al₂O₃-TiO₂复合粉末,测试了复合粉末在2—18GHz波段的电磁参数.研究表明：随着碳纳米管质量分数的增加,碳纳米管/纳米Al₂O₃-TiO₂复合粉末的复介电常数和损耗角不断增大.当碳纳米管质量分数和厚度增加时,复合粉末对电磁波的反射率峰值先增加后减小,而谐振频率不断向低频移动.采用微弧等离子喷涂制备了7wt%碳纳米管/纳米Al₂O₃-TiO₂复合吸波涂层,当厚度为1.5mm时,涂层最小反射率为-24.0dB,当厚度为2.0mm时,涂层小于-10dB的频带宽为3.60GHz,当温度为500℃高温时,1.0mm厚的涂层最小高温反射率为-12.2dB,小于-10dB频带宽为2.0GHz.复合涂层的实际厚度D与理论厚度d呈线关系：d=0.898D+0.515. 关键词： 等离子喷涂 碳纳米管 2O₃-TiO₂')" href="#">纳米Al₂O₃-TiO₂ 吸波性能     

A new heavy-fermion superconductor: UNi2Al3

Measurements of the resistivity, susceptibility and specific heat are reported which clearly show that the hexagonal compound UNi₂Al₃ is a heavy-fermion magnet belowT _N=4.6 K and a heavy-fermion superconductor belowT _c=1 K.On leave from Institute of Low Temperature and Structure Research, Polish Academy of Sciences PL-50-950, Wroclaw 2, Poland     

Atomic-scale mapping of twins and relevant defective structures in Al20Cu2Mn3 decagonal approximant

Twins or multiple twins occur frequently in the orthorhombic Al₂₀Cu₂Mn₃ approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al₂₀Cu₂Mn₃ approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al₂₀Cu₂Mn₃ approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.     

Stacked and nanolaminated Al2O3/TiO2 for surface passivation and encapsulation of silicon

Silicon solar cells passivated with Al₂O₃ require a capping layer that protects the passivation layer from humidity because of sensitivity of Al₂O₃ to moisture. Al₂O₃/TiO₂ stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field‐effect passivation. In this work, degradation of this Al₂O₃/TiO₂ stack, when exposed to humidity, is examined, and an attempt is made for a humidity‐resistant encapsulation layer by adding Al₂O₃/TiO₂ nanolaminates that can be deposited in‐situ without breaking vacuum. Placing the nanolaminate on top of the TiO₂ and Al₂O₃ stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Microstructure characterization of Al2O3 nanowires with networked rectangular nanostructure

L-shaped and U-shaped Al₂O₃ nanowires were synthesized using a vapor phase deposition method. The as-grown nanowires are single crystalline and structurally uniform at the junction of the branches. Detailed TEM analysis revealed that the growth direction of the nanowires is parallel to the a- or b-axis directions, and switched growth from one direction to another forms the rectangular morphology of the peculiar L-shaped or U-shaped nanowires. Possible growth mechanism of the Al₂O₃ nanowires was explained. Our results can provide evidence to understand the growth mechanism of the complicated nanostructure.     

The Tl-Ba-Ca-Cu-O superconducting ceramics containing Al2O3

The Tl-Ba-Ca-Cu-O superconducting ceramics containing Al₂O₃ have been prepared utilizing the reaction, Tl₂O₂+BaCuO₂+Ca₂CuO₃+A1₂O₃ or Tl₂O₃+BaCuO₂ +Ca₂CuO₃+AlCuO_2.5. It is shown that the resulting ceramics show the superconductivity at temperatures over 100 K when the Al/Cu molar ratio is kept below 0.5. EPMA analyses revealed that there is always an Al₂BaO₄ layer between the superconducting Tl-Ba-Ca-Cu-O and Al₂O₃ phases, leading to the separation between the superconducting and A1₂O₃ phases.     

EPMA mapping method for small particles of Al3Fe,Al6Fe, α‐AlFeSi and β‐AlFeSi in 1050‐H18 aluminum sheets

We developed an EPMA mapping method for small Al_aFe_bSi_c particles in 1050‐H18 aluminum sheet, which is one of the base materials coated by photoresist in advance called PS plate (pre‐sensitized printing plate). In this method, we used the ratios of relative x‐ray intensities, I_Fe/I_Al and I_Fe/I_Si instead of the mass ratios, Fe/Al and Fe/Si, of the main elements which constitute the particles and tried to determine the ratios of relative x‐ray intensities using Monte Carlo calculations. Furthermore, using this developed mapping method, we performed the mapping of small Al_aFe_bSi_c particles such as Al₃Fe (0–3%Si as impurities), Al₆Fe (0–1%Si as impurities), α‐AlFeSi(Al_8.3Fe₂Si) and β‐AlFeSi(Al_8.9Fe₂Si₂) in 1050‐H18 aluminum sheets. We found that the discrimination of these particles was achieved with this mapping method. We confirmed that this method is useful for the mapping of Al_aFe_bSi_c particles in 1050‐H18 aluminum sheets. Copyright © 2004 John Wiley & Sons, Ltd.     

Silicon solar cells with Al2O3 antireflection coating

The paper presents the possibility of using Al₂O₃ antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al₂O₃ thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al₂O₃ antireflection coating by ALD method. Results and their analysis allow to conclude that the Al₂O₃ antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al₂O₃ the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al₂O₃ on the bulk passivation of the silicon.     

Silicon surface passivation by atomic‐layer‐deposited Al2O3 facilitated in situ by the combination of H2O and O3 as reactants

We investigate the effect of O₃ and H₂O oxidant pre‐pulse prior to Al₂O₃ atomic layer deposition for Si surface passivation. Interfacial oxide SiO_x formed by the O₃ pre‐pulse is more beneficial than that by H₂O to a high level of surface passivation. The passivation of thinner H₂O–Al₂O₃ films is more improved by this O₃ pre‐pulse. O₃ pre‐pulse for 10 nm H₂O–Al₂O₃ reduces saturation current density in boron emitter to 18 fA cm^–2 by a factor of 1.7. Capacitance–voltage measurements reveal this interfacial oxide plays a role of decreasing interface trap density without detrimental effect to negative charge density of Al₂O₃. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

The diffusion of silicon atoms in stack structures of La2O3 and Al2O3

The interfacial reactions and electrical characteristics of stack structures of La₂O₃ and Al₂O₃ were investigated as a function of the annealing temperature. In the case of Al₂O₃/La₂O₃/Si (ALO structure), the La₂O₃ in contact with the Si substrate was readily transformed into La-silicate by the diffusion of Si atoms, while in the case of La₂O₃/Al₂O₃/Si (LAO structure), interfacial reactions between the Al₂O₃ layer and the Si substrate were suppressed. After an annealing treatment at 700 °C, the Al₂O₃ in the ALO structure can play an effective role in blocking the hydration of La₂O₃, resulting in an unchanged interfacial layer. However, the Al₂O₃ layer in the LAO structure was unable to suppress the diffusion of Si atoms into the La₂O₃ film. When the annealing temperature reached 900 °C, both structures showed a similar depth distribution with a high content of Si atoms diffused into the films. The change in the elemental distributions via the diffusion and reaction of Si atoms affected the electrical characteristics at the interface between ALO/LAO structure and Si substrate, specifically the trap charge density (D_it) and band gap (E_g) values.