倒装芯片上金属布线/凸点互连结构中原子的定向扩散

采用倒装芯片互连凸点串联回路研究了高温、高电流密度条件下倒装芯片上金属布线/凸点互连结构中原子的定向扩散现象,分析了互连结构中受电应力和化学势梯度作用的各相金属原子的扩散行为.在电迁移主导作用下,Ni(V)镀层中的Ni原子的快速扩散导致原本较为稳定的Ni(V)扩散阻挡层发生快速的界面反应,造成Al互连金属与焊料的直接接触.Al原子在电子风力作用下沿电子流方向向下迁移造成窗口附近焊料中Al原子含量逐步上升,同时,空位的反向迁移、聚集形成过饱和,导致Al互连中形成大面积空洞.焊料中的Sn,Pb原子在化学势梯度 关键词： 倒装芯片 凸点 电迁移 扩散     

Structural origin of the Sn 4d core level line shape in Sn/Ge(111)-(3x3)

High-resolution photoemission of the Sn 4d core level of Sn/Ge(111)-(3x3) resolves three main components in the line shape, which are assigned to each of the three Sn atoms that form the unit cell. The line shape found is in agreement with an initial state picture and supports that the two down atoms are inequivalent. In full agreement with these results, scanning tunnel microscopy images directly show that the two down atoms are at slightly different heights in most of the surface, giving rise to an inequivalent-down-atoms (3x3) structure. These results solve a long-standing controversy on the interpretation of the Sn 4d core-level line shape and the structure of Sn/Ge(111)-(3x3).     

Direct observation of Sn crystal growth during the lithiation and delithiation processes of SnO(2) nanowires

Tin (Sn) crystal growth on Sn-based anodes in lithium ion batteries is hazardous for reasons such as possible short-circuit failure by Sn whiskers and Sn-catalyzed electrolyte decomposition, but the growth mechanism of Sn crystals during battery cycling is not clear. Here we report different growth mechanisms of Sn crystal during the lithiation and delithiation processes of SnO(2) nanowires revealed by in situ transmission electron microscopy (TEM). Large spherical Sn nanoparticles with sizes of 20-200nm grew instantaneously upon lithiation of a single-crystalline SnO(2) nanowire at large current density (j>20A/cm(2)), which suppressed formation of the Li(x)Sn alloy but promoted agglomeration of Sn atoms. Control experiments of Joule-heating (j≈2400A/cm(2)) the pristine SnO(2) nanowires resulted in melting of the SnO(2) nanowires but not Sn particle growth, indicating that the abnormal Sn particle growth was induced by both chemical reduction (i.e., breaking the SnO(2) lattice to produce Sn atoms) and agglomeration of the Sn atoms assisted by Joule heating. Intriguingly, Sn crystals grew out of the nanowire surface via a different "squeeze-out" mechanism during delithiation of the lithiated SnO(2) nanowires coated with an ultra-thin solid electrolyte LiAlSiO(x) layer. It is attributed to the negative stress gradient generated by the fast Li extraction in the surface region through the Li(+)-conducting LiAlSiO(x) layer. Our previous studies showed that Sn precipitation does not occur in the carbon-coated SnO(2) nanowires, highlighting the effect of nanoengineering on tailoring the electrochemical reaction kinetics to suppress the hazardous Sn whiskers or nanoparticles formation in a lithium ion battery.     

LEED crystallographic investigation of ultrathin films formed by deposition of Sn on the Pt(111) surface

Deposition of Sn on the Pt(111) surface followed by annealing at 1000 K leads to the formation of ordered phases showing (2 × 2 and ( LEED patterns, depending on the surface coverage of Sn. Both these phases were studied by LEED dynamical analysis. The best agreement between experimental and calculated I–V curves was obtained by means of models based on the formation of mixed Pt-Sn layers on the surface where Pt and Sn atoms are nearly coplanar with a slight upward buckling of Sn atoms. The structures of these phases are similar to those already observed for the Pt₃Sn(111) surface.     

The crystal structure of SnYb3Rh4Sn12, a new ternary superconducting stannide

The crystal structure of superconducting SnYb₃Rh₄Sn₁₂ has been determined from single-crystal X-ray diffraction data. This compound is cubic, space group Pm3n, $\text{a}{}_{\mathrm{o}}\text{= 9.676}\text{A}\text{?}$ (1) and has two formulae per unit cell. The structure was solved from Patterson and subsequent Fourier synthesis. The least squares refinement was based on 375 independent reflections. The final R and wR factors were 0.015 and 0.014, respectively. The two Sn(1) atoms occupy the 2a (000) positions, the six Yb atoms the 6d ($\text{1}\text{4}$$\text{1}\text{2}$ 0) positions, the eight Rh atoms the 8e ($\text{1}\text{4}$$\text{1}\text{4}$$\text{1}\text{4}$) positions and the twenty-four Sn(2) atoms the 24k (Oyz) positions (y ～ 0.31, z ～ 0.15). The Sn(2) atoms form a tridimensional array of corner-sharing trigonal prisms whose centers are occupied by the rhodium atoms. The Sn(1) and the Yb atoms occupy the icosahedral and cuboctahedral holes of this array, respectively. They form a sublattice which has the arrangement found in the structure of the A15 compounds. The structure of SnYb₃Rh₄Sn₁₂ can be described as containing two interpenetrated structures, namely Yb₃Sn and RhSn₃, or as having an A15 arrangement of clusters of atoms such as (SnSn₁₂) and (YbSn₁₂). These clusters are bound together by face-sharing among them; and by the rhodium atoms. An analogy is drawn between SnYb₃Rh₄Sn₁₂ and the perovskite-like ternary oxides A′A″₃B₄O₁₂.     

Cross-section measurements for (n, 2n) reactions on stannum isotopes in the neutron energy range of 13.5 to 14.6 MeV

Cross-sections for (n, 2n) reactions have been measured on stannum isotopes at the neutron energies of 13.5 to 14.6 MeV using the activation technique. Data are reported for the following reactions:112Sn(n, 2n)111Sn, 118Sn(n, 2n)117Sn and 124Sn(n, 2n)123mSn. The neutron fluences were determined using the monitor reaction 93Nb(n, 2n)92mNb or 27Al(n, α)24Na. The results of present work were compared with data published previously.     

Magnetic and electronic properties of Mn2Sn thin films: First-principles calculations and high temperature series expansions

In this paper, first-principles calculations have been performed in order to study the electronic and magnetic properties of the bulk and the (0 0 1) surface of Mn₂Sn thin films using self-consistent ab initio calculations, based on the density functional theory approach and using the product of the muffin-tin radius and the maximum reciprocal space vector, R_MT. K_max, we full potential linear augmented plane wave methods. Spin-polarized calculations within the framework of density-functional theory are a powerful tool for describing the magnetism of itinerant electrons in solid state materials. The total and partial density of states of Mn₂Sn thin films were calculated. The magnetic moments considered to lie along the c axes are computed. The data obtained from the ab initio calculations are used as an input for the high temperature series expansions calculations used to compute other magnetic parameters. The critical temperature and exchange interactions between the magnetic atoms in the Mn₂Sn thin films are obtained using high temperature series expansions and mean field theory, respectively.     

Low temperature CEMS of Sn-implanted SiO2

Conversion electron Mössbauer spectroscopy (CEMS) at room and low temperature has been used to study thin SiO₂ films implanted with Sn atoms and annealed at 900°C. This work focuses on the determination of the Debye temperature (θ _D) and Debye–Waller factors (f) of the Sn oxidized phases formed in this system. The Sn²⁺ oxidation state is the predominant one, even if a small percentage of the Sn atoms is in the Sn⁴⁺ oxidation state. The real Sn-oxides fractions are calculated by normalizing the resonant areas to the f values, as calculated from the temperature dependence of the related resonant areas within a Debye model. The Sn⁴⁺ oxidation state, possibly related to Sn atoms close to the SiO₂ surface, represents less than 20% of the Sn atoms. For the Sn²⁺ oxidation state, two different electronics configurations a and b, having different Debye temperature and hyperfine parameters are identified. The component a, with a lower θ _D (137 K), is the predominant one and might be related to small (2–3 nm) amorphous SnO _x clusters in the SiO₂ matrix. The component b could be related to substitutional Sn atoms in the SiO₂ network forming a local Sn environment similar to the SnO amorphous compound.     

Determination of the Sn 4d line shape of the Sn/Ge(111) radical3 x radical3 and 3x3 surfaces

The Sn 4d line shapes of the Sn/Ge(111) sqrt[3]xsqrt[3] and 3x3 surfaces are currently under debate. By employing LEED, core-level, and valence band spectroscopy we have been able to determine the correct Sn 4d line shapes for these surfaces. Contrary to a recent study we conclude that the majority of the earlier reports present line shapes close to the correct ones. At 70 K we identify three 4d components in the 3x3 spectrum, two of which are identified with the two types of Sn atoms in the 3x3 cell. The third component is attributed to Sn atoms surrounding Ge substitutional defects.     

Phase diagram of Ge:(C,Sn)

We present the self-assembling conditions of 1C4Sn tetrahedral nanoclusters with carbon atoms in their centers in Ge:(C, Sn) in the wide temperature range as a function of the impurity contents and temperature. These conditions are the phase diagram of Ge:(C, Sn) since nanocluster occurrence and completion of self-assembling when all carbon atoms are in nanoclusters are results of the continuous phase transitions. The significant decrease of the strain energy after formation of nanoclusters is a cause of self-assembling. It is shown that the nanocluster occurrence temperature depends only on the Sn content. The impurity content conditions when all carbon atoms are in 1C4Sn nanoclusters are obtained for the temperatures up to 855 ^°C.     

A molecular dynamics investigation of the micro-mechanism for vacancy formation between Ag3Sn and βSn under electromigration

In this paper, the vacancy formation at the interface between different grains (Ag₃Sn and βSn) induced by electromigration was investigated from the perspective of atom diffusion. To explain the micro-mechanism of void formation near the interface, the diffusion coefficient was specifically studied here via molecular dynamics (MD) simulation. By comparing the atom diffusion rates of atoms in βSn and Ag₃Sn, a significant difference could be observed when the temperature is up to 400 K. The Sn atoms in βSn have a higher diffusion coefficient (8E ? 9 cm²/s) than atoms in Ag₃Sn (4E ? 9 cm²/s), which indicated that the void would be prone to appear in βSn near the interface. Moreover, the effect of grain size and pressure on atom diffusivity was studied. Results show that the atom diffusivity depends heavily on the grain size of Ag₃Sn. When the thickness of Ag₃Sn is increased from 4 to 12 nm, this difference is significant when the temperature is only 375 K. On the other hand, the atom diffusion character of Ag₃Sn and βSn changes substantially under constant pressure. The difference of the atom diffusion rate would be inhibited by pressure perpendicular to the interface, which indicated voids have less possibility to appear herein.     

Determination of the number of atoms of the long-lived nuclide ~(126)Sn by γ-ray spectrometry

By using HPGe γ-ray spectrometry, the activity of the long-lived fission product 126Sn in a SnOB2 sample was measured. The number of 126Sn atoms and the ratio of 126Sn to Sn were calculated based on the half-life value of 2.35×105a and the chemical stoichiometry. The result of the ratio of 126Sn to Sn, (1.033±0.037)×10-8, is consistent with the results measured by the accelerator mass spectrometry (AMS) within uncertainty limits, which confirms our procedures in the measurement of 126Sn by AMS and lays a foundation for the AMS measurement of 126Sn at much lower levels.     

Autoionization of triply excited rydberg series

The Auger rates of triply excited Rydberg series are shown to behave rather differently from doubly excited series. It is shown that in hollow atoms the Auger decay rates for Rydberg series of the type 2l2l(')nl(") with n>/=2 are expected to be nearly independent of n, while for doubly excited series of the type 2lnl(') the decay rate in general decreases with increasing n. In addition the ratio between the rates for 2l2l(')nl(") Rydberg series with different l(") values will be fixed and often the ratio will be equal to one.     

Local environment and dynamic characteristics of the 119Sn(II) and 119Sn(IV) Mössbauer probes on the surface of Cr2O3 exposed to hydrogen sulfide atmosphere

Tin dopant located on the surface of Cr₂O₃ crystallites interacts easily, at room temperature, with adsorbed H₂S molecules. Contrary to the initial oxygen-surrounded tin species, the resulting Sn(II) and Sn(IV) sulfur-surrounded entities exhibit no spin polarization, at least down to 4.6 K, which shows that they are more distant from the magnetically ordered oxide substrate. Additionally, their thermal vibration amplitudes are greater than in oxygen-surrounding, which denotes a weaker bonding of the tin within the H₂S adsorbed layer. Moreover, for Sn(II), sufficiently large quadrupole splitting allows the Goldanski-Karyagin effect to be seen. Thermal vibration amplitudes of Sn(II) are then found to be greater in the plane of the three neighbouring sulfur atoms than in the perpendicular direction.     

A first-principles study on the lower-valence coexisting Cr2TiX (X=Al, Ga, Si, Ge, Sn, Sb) Heusler alloys

The electronic, magnetic, and bonding properties of the Cr₂TiX (X=Al, Ga, Si, Ge, Sn, Sb) Heusler alloys have been investigated using first-principles calculations. The results show that Cr₂TiSb exhibits a half-metallic nature and Cr₂TiGa and Cr₂TiSn exhibit a nearly half-metallic nature. From analysis of the density of states and the electron density difference along the Ga→Sn→Sb series for sp atoms, we found that the Cr-Ti bond demonstrates covalent character with more or less the ionic and metallic nature. In addition, the Cr-Ti bonding strength increases along this series. All the compounds have a negative total magnetic moment, most of which are confined to the Cr atoms. There exists a 1.0μ_B increasing trend of the total moment along the III→IV→V main group for sp atoms, and only the total moment of Cr₂TiSb coincides well with the Slater-Pauling behavior.     

Calculations of Rydberg energy levels for Ni ⅩⅧ using the weakest bound electron potential model theory

Martin expression about the quantum defect of single-valence atoms is extended to many-valence atoms by identifying the weakest bound electron (WBE) under the weakest bound electron potential model(WBEPM) theory. Six Rydberg series energy levels of 2p6np2P°1/2 (n ≥ 3), 2p6np2P°3/2 (n ≥ 3), 2p6nd2D3/2(n ≥ 3), 2p6nd2D5/2 (n ≥ 3), 2p6nf2F°5/2 (n≥4), and 2p6nf2F°7/2 (n ≥ 4) for Ni ⅩⅧ are calculated by this method. The calculated results are in good agreement with the experimental results.     

Density-functional study of the CO chemisorption on bimetallic Pd–Sn(1 1 0) surfaces

We study the ordered PdSn c(2 × 2), (2 × 1), and PdSn₂ (3 × 1) overlayers deposited on Pd(1 1 0) by using first-principles density-functional calculations. It appears that the two PdSn structures are almost degenerate in the energy. Pd–Sn surfaces we consider do not display the marked buckling with Sn atoms displaced towards vacuum that is common for Pt–Sn surfaces. Low-coverage CO chemisorption at these overlayers and on analogous surface structures on Pd₃Sn is considered. It is shown that inclusion of an empirical correction to the CO adsorption energy changes the stable adsorption site from the long-bridge to the top one in most cases. The adsorption energy decreases with the number of Sn atoms in the vicinity of the adsorption site, and this property correlates well with the position of the centre of gravity of the local Pd d-electron band, and also with the variation of the local density of d-electron states at the Fermi level. The centre-of-gravity value is used to assess the core-level shifts for Pd atoms in various geometries. Most of the calculated data compare rather well with the recent measurements on Pd–Sn overlayers at Pd(1 1 0) as well as with other data on related bimetallic systems.     

Binding states of Ga and Sn on W and Mo: Structures,evaporation field and its temperature dependence

Binding states of deposited Ga and Sn on the W and Mo substrates were studied by measuring the evaporation fields of the deposited metal atoms at various temperatures. Ga and Sn form two layers: an overlayer and an underneath pseudomorphic layer which directly contacts the substrate surface. The evaporation fieds of the overlayer Ga and Sn atoms were found to be the same on various crystal planes and significantly lower than that of the pseudomorphic Ga and Sn atoms, indicating that the binding between the overlayer atoms and the pseudomorphic atoms is much weaker than that between the pseudomorphic atoms and the substrate W and Mo atoms. The finding that the evaporation field of the pseudomorphic atoms on W is very close to that on Mo while the evaporation field of W is significantly higher than that of Mo was unexpected. Another interesting finding is that the field emission current from the (011) plane is not noticeably affected by the coverage of the mono-atomic Ga layer arranged in the superstructure while the current from other crystal planes covered by the pseudomorphic layer having the same atomic arrangement with the substrate surface is minimized. Furthermore, it has been found that the evaporation field of the Ga overlayer is lower than that of Sn, while the Ga pseudomorph is more stable than Sn pseudomorph on W surface at temperatures below about 100 K. The temperature dependence of the evaporation field was also examined and compared with existing models.     

Pd-Sn双金属催化剂催化1,3-丁二烯加氢反应的仲氢诱导极化研究

本文首先利用等体积共浸渍法合成了一系列Pd/Sn比(原子比)不同的Pd₁-Sn_x/Al₂O₃双金属催化剂,然后通过多相催化仲氢诱导极化(PHIP)技术研究了Pd-Sn/Al₂O₃双金属催化剂上1,3-丁二烯选择性加氢反应．结果发现催化剂的Pd/Sn比会影响1,3-丁二烯反应活性和丁烯选择性：随着Pd/Sn比的下降,反应中1,3-丁二烯转化率降低,丁烯选择性提高．利用PASADENA(parahydrogen and synthesis allow for dramatically enhanced nuclear alignment)技术,发现Pd/Sn比的变化影响了1-丁烯与2-丁烯之间的异构化过程：随着Pd/Sn比的下降,1-丁烯异构化率降低,这是由于Sn组分含量的提高减少了表面暴露的Pd组分,使得催化剂反应活性降低;Sn组分含量的提高同时导致了Pd电子密度的上升,使得选择性还原产物丁烯更易脱附,阻止其进一步加氢生成丁烷,并抑制了1-丁烯异构化反应过程...