The effect of electric current and surface oxidization on the growth of Sn whiskers

Electric current was applied on pure Sn-plated leadframes to evaluate the effects of current-induced stress on the growth of Sn whiskers. The samples were stored at room temperate and 55 °C/85% relative humidity (RH) conditions with an induced current range of 0.1 A to 0.5 A. The samples stored at the room temperature did not grow the whiskers at any of the current conditions until 3000 hrs. As the current flow increased, irregular intermetallic compounds (IMCs) grew at the interface between the Sn finish and Cu substrate. However, various lengths of columnar and bent whiskers were observed under all current conditions, after exposure to 55 °C/85% RH conditions for 1000 hours. At the same temperature, the higher current levels showed longer whiskers than lower current levels. The Sn oxide had the α-SnO₂ structure of the rutile phase which was non-uniformly formed on the surface of the Sn finish. The grain size of the SnO₂ was estimated to be several nanometers. The SnO₂ film was up to a thickness of ∼23 nm on the Sn whisker surface stored at 55 °C/85% RH conditions for 3000 hours.     

Growth and kinetic studies of lead carbonate whiskers in silica gel

Lead carbonate whiskers were grown by diffusion of ammonium carbonate in the silica gel charged with lead nitrate. It is found that low pH is preferred to the whisker growth. In addition to straight whiskers gently curved whiskers are also found. Curving of whiskers is found to be maximum at high concentration of carbonate ions. Growth kinetics of whiskers are studied by changing the parameters of gel growth. It is found that the parabolic relationship between dimension and growth period is obeyed in this.     

Interaction between neighbouring phase-slip centers in a superconducting Zn whisker

We fabricated multi-potential-probe samples with a Zn whisker as measuring whisker and four Sn whiskers as potential probes and investigated the interaction effect between two neighbouring phase-slip centers in the Zn whisker. An active phase-slip center changes the critical current of a neighbouring phase-slip center. This change depends on the temperature and the relative polarity of the currents through the influencing and influenced phase-slip center. An interpretation of the observed effect is proposed.     

二元金属须的强度和形变特点

测量了直径20—300微米的大量的Fe鬚、Fe-Cu鬚、Fe-Co鬚、Cu鬚和Cu-Co鬚的室温和高温拉断强度,结果指出,弥散型的二元金属鬚如Fe-Cu鬚和Cu-Co鬚的强度较高于单元金属鬚,而固溶型的二元金属鬚如Fe-Co鬚则否。根据应力应变曲线的测量和金相观测的结果,认为弥散型的Fe-Cu鬚的强度所以较高,可能是由于高强度的铁铜弥散混合层的出现,而它的范性所以较好,可能是由于这种鬚具有范性较好的铜心轴。讨论了弥散型和固溶型二元金属鬚在变粗当中所包含的基本过程,以及与它们所表现的强度和形变特点的联系。并且指出,生长弥散型混合鬚的原理和方法给制备强度较高和范性较好的复合材料提供了一个值得参考的途径。 关键词：     

由汽态还原生长金属须的机制

进行了用蒸汽还原法生长铜须和铁须的实验。研究了须的生长机制,为的是找出能够生出又粗又长而强度又极高的金属须的有效措施。实验指出,当生长槽材料的晶体结构与生长须的金属的晶体结构相同时,可以促进须的生长。由此所得的结论是,须的生长是通过沿轴线的螺型位错的机制。观测了所生的铜须和铁须在生长槽上的分布和排列取向的各种方式,由此推论到这些须是由顶端生长的。此外,实验还指出,氯化亚铜(或亚铁)蒸汽是优先在须的顶端还原的,这可能是由于螺型位错在须顶端所产生的表面台阶对于这种还原有一种催化作用。观测了直径50—120微米的大铜须的生长情况,发现了片状生长、堆垛生长和层状生长。这种特殊生长方式可能与一维和二维成核生长的交互更迭发生有关。讨论了通过适当选择和控制生长条件和方式的途径来获得基本上不含位错的大块晶体的可能性。     

原位生长高度定向ZnO晶须

采用大气压金属有机化合物化学气相沉积(AP-MOCVD)方法，以Zn(C₅H₇O₂)₂为原料，在玻璃基片上制备出高度定向的ZnO晶须.扫描电子显微镜观察发现晶须垂直基片取向生长，规则排列，长度、形状几乎一致.晶须直径为100nm—800nm,长径比为8—15，尖端曲率半径仅为50nm，甚至更小.x射线衍射(XRD)分析结果表明ZnO晶须为六方晶系纤锌矿结构，并沿c轴高度取向.采用热分析对反应前驱物进行了研究,同时也讨论 关键词： ZnO 取向生长 晶须 MOCVD     

Observations of the spontaneous growth of tin whiskers on tin-manganese alloy electrodeposits

The spontaneous growth of tin whiskers on electrodeposited tin-manganese alloy coatings has been observed. This growth is distinct from any previously reported whisker growth on either pure tin or other tin-based alloy electrodeposits. It has an extremely short incubation period of a few hours only, followed by a spectacularly rapid and profuse growth. During the whole period of whisker growth, the tin-manganese electrodeposits were found to be in a tensile residual stress state. This rules out the commonly accepted explanation of a compressive stress as the driving force for tin whisker growth.     

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.     

Dependence of the growth rate of crystal whiskers on their diameter

The growth kinetics of silicon crystal whiskers is investigated in this paper. An explanation is given of the results obtained on the basis of the kinetic equation of crystal whisker (CW) growth. An equation is proposed to describe CW growth under the condition that seed formation is the limiting stage of the growth process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 18–22, December, 1986.     

Effect of Sn particle size on the intermetallic compound formations of cold sprayed Sn-Ni coatings

Comparative studies on the intermetallic compound (IMC) formations of small (aggregated) and large Sn (irregular) with Ni and Cu in cold gas dynamic sprayed coatings were carried out. The Sn with high purity were selected and prepared as raw materials mixture in order to be sprayed onto Ni and Cu plate-shape substrates. The small particles of Sn (<1 μm) were successfully coated under conventional coating parameters when they are mixed with larger powder materials. And microstructural observation regards to compound formation similarly worked out for both small and large Sn mixture. However, the intermetallic formation behavior was turned out to be different. After post-annealing, the larger Sn particles in the composite coating formed larger amount of IMC with Ni than small Sn although, owing to larger interfacial area, more intensive reactivities were expected. Also, there were significant differences in the size and distribution of eutectic pores as well.     

Effects of polyethylenimine on morphology and property of ZnO films grown in aqueous solutions

Morphologies and properties of well-aligned ZnO films were controlled using zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine as a surfactant. Porous and dense ZnO films were fabricated with and without polyethylenimine, respectively. The addition of polyethylenimine proceeded to form porous ZnO whiskers film by preferential adsorption to nonpolar crystal faces and modifications of the surface free energy and growth rate. Dense ZnO film showed high transmittance of 80%, and low intensity of fluorescence and photo-induced current. Porous ZnO whiskers film showed low transmittance of 70%, while high intensity of fluorescence and high photo-induced current were detected because the porous ZnO nanowhisker film possessed a large interior surface area which can capture large amounts of DNA molecules labeled with dye molecules on the surface of ZnO crystals. High performance dye-sensitized sensors can be produced using ZnO whisker films prepared from an aqueous solution.     

Size, position and direction control on GaAs and InAs nanowhisker growth

The self-organized, position-controlled and parallel growth of GaAs and InAs nanowhiskers is successfully demonstrated by using a metal–organic chemical vapour deposition method. The growth takes place preferentially along the 111 As direction with the aid of the catalytic effect of Au nanodroplets, and not along 111 Ga or In directions. The diameter and length of the whisker can be controlled artificially down to 10 nm and to over 1 μm, respectively. Doping and composition control of p- or n-type such as GaAs–InAs heterostructure formation are possible along the length direction of the whisker by changing the source gases. In order to control the growth position of the whisker, positioning of a Au nanodroplet is essential and realized by a lithographic method. By choosing the [111]B direction to the substrate surface and normal to the patterned side edges, and by positioning the Au nanodroplet on the side wall, the positioned planar nanowhisker growth and bridging are successfully demonstrated. The growth mechanism of the nanowhiskers is revealed by the scanning and transmission electron microscope observations. Nanometer-size Au-alloy droplets play an important role in the growth of the whiskers. The whisker growth process is governed by the vapor–liquid–solid growth mechanism.     

Growth of Si whiskers by MBE: Mechanism and peculiarities

We analyzed the stress-driven mechanism of MBE Si whisker growth. It is shown that the driving force for MBE whisker growth is determined by the relaxation of elastic energy stored in the overgrown layer L_s due to gold intrusion. In this case the supersaturation is determined by the interplay between elastic stresses and surface energy. The latter is considerably decreased due to decoration of the Si surface by gold resulting in formation of thin liquid Si/Au eutectic layer. This suggests that in our case the Si supersaturation is not an independent growth parameter as it is in the chemical vapor deposition growth method. Instead it is determined by stress in the overgrown Si layer. This approach allows us to explain quite well the growth kinetic and the relationship between the radius and the length of the whiskers. The whisker growth in our case can be considered as a stress relaxation mechanism, where the stress relaxation occurs due to transition from the two-dimensional system to the three-dimensional one.     

High-resolution transmission electron microscopy on silicon carbide whiskers

SiC whiskers were grown from the reaction of silicon monoxide (SiO) with activated carbon containing iron impurities. Growth proceeds through a VLS growth mechanism with SiO and CO as reacting gases. HRTEM combined with EDS shows that the SiC whisker is topped by a Fe₃Si catalyst droplet. The SiC whisker is found to be one-dimensionally disordered along the [111] growth direction of an fcc crystal structure. Although the catalyst droplet is usually larger than the top face of the whisker, we observed a number of situations where the diameter of the droplet was smaller. The study of the SiC-Fe₃Si interface showed that the growth is nucleated from the edges.     

On the general regularities of the growth of micro-and nanoscale si whiskers

On the basis of the investigations of the processes of synthesis nano-and microscale silicon whiskers, general regularities of their quasi-one-dimensional growth are established: the presence of the catalyst drop liquid at the top, the same preferred orientation <111> of the growth axis, presence of pedestal in the whisker base, decrease in radius over the crystal length (conicity), branching and formation of bends, flat crystallization front under the drop, two-stage character of the process (axial and radial growth), etc. Some individual features, inherent in the nanocrystal growth, are also established.     

Nature of the “yield tooth” under torsion in plastic-deformed whiskers

The plastic torsion of whiskers with high Peierls barriers has been studied. As the samples for the studies we chose p-type germanium whiskers with <111> growth axis. The diameter of the whisker was (5–60)·10^–6 m and the gauge length was (1–4)·10^–3 m. The whiskers were dislocation-free in the initial state. Within the framework of the continuum model developed by us for the plastic deformation of whiskers under torsion, we analyze the anomalies of the torsional stress-strain diagram under different testing conditions and with preliminary deformation. The flow tooth during the torsion of a whisker is attributable to the nonuniform distribution of dislocations over the cross section of the whisker and high barriers to the dislocation motion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–8, July, 1987.     

Control Al/Mg intermetallic compound formation during ultrasonic-assisted soldering Mg to Al

To prevent the formation of Al/Mg intermetallic compounds (IMCs) of Al₃Mg₂ and Al₁₂Mg₁₇, dissimilar Al/Mg were ultrasonic-assisted soldered using Sn-based filler metals. A new IMC of Mg₂Sn formed in the soldered joints during this process and it was prone to crack at large thickness. The thickness of Mg₂Sn was reduced to 22 μm at 285 °C when using Sn-3Cu as the filler metal. Cracks were still observed inside the blocky Mg₂Sn. The thickness of Mg₂Sn was significantly reduced when using Sn-9Zn as the filler metal. A 17 μm Mg₂Sn layer without crack was obtained at a temperature of 200 °C, ultrasonic power of Mode I, and ultrasonic time of 2 s. The shear strengths of the joints using Sn-9Zn was much higher than those using Sn-3Cu because of the thinner Mg₂Sn layer in the former joints. Sn whiskers were prevented by using Sn-9Zn. A cavitation model during ultrasonic assisted soldering was proposed.     

Radical graft polymerization from carbon whisker initiated by peroxyester groups introduced onto the surface

The radical graft polymerization of vinyl monomers onto carbon whiskers, i.e. vapor grown carbon fibers, initiated by tert-butyl peroxyester groups that are introduced onto the surface was investigated. The introduction of tert-butyl peroxyester groups onto the carbon whisker surface was achieved by the reaction of acyl chloride groups on the surface with tert-butyl hydroperoxide. The carbon whisker having acyl chloride groups was prepared by the following three methods: (1) reaction of surface carboxyl groups with thionyl chloride, (2) reaction of surface phenolic hydroxyl groups with succinyl dichloride, and (3) reaction of surface phenolic hydroxyl groups with phthaloyl dichloride. The carbon whiskers having tert-butyl peroxyester groups prepared from these three methods were abbreviated as CW-POE 1, 2, and 3, respectively. The peroxyester group content of CW-POE 1, 2, and 3 was determined to be 0.06, 0.05, and 0.17 mmol/g, respectively. It was found that the radical polymerization of vinyl monomers such as methyl methacrylate, styrene, and N-vinylcarbazole was successfully initiated in the presence of CW-POE 2 and 3, and the corresponding polymers were grafted onto the surface. However, CW-POE 1 failed to initiate the radical graft polymerization, because surface phenyl radicals formed by the thermal decomposition of the tert-butyl peroxyester groups are stabilized by the aromatic rings of the carbon whisker surface.     

Driving force and mechanism for spontaneous metal whisker formation

The room temperature spontaneous growth of low melting point metal whiskers, such as Sn, poses a serious reliability problem in the semiconducting industry; a problem that has become acute with the introduction of Pb-free technology. To date, this 50+ year old problem has resisted interpretation. Herein we show that the driving force is essentially a reaction between oxygen and the sprouting metal. The resulting volume expansion creates a compressive stress that pushes the whiskers up. The model proposed explains our observations on In and Sn whiskers and many past observations. The solution is in principle simple: diffusion of oxygen into the metal must be prevented or slowed down. This was demonstrated by coating the active surfaces with a polymer coating.     

Effect of Ni on growth kinetics,microstructural evolution and crystal structure in the Cu(Ni)–Sn system

Abstract

The role of Ni addition in Cu on the growth of intermetallic compounds in the Cu–Sn system is studied based on microstructure, crystal structure and quantitative diffusion analysis. The diffraction pattern analysis of intermetallic compounds indicates that the presence of Ni does not change their crystal structure. However, it strongly affects the microstructural evolution and diffusion rates of components. The growth rate of (Cu,Ni)₃Sn decreases without changing the diffusion coefficient because of the increase in growth rate of (Cu,Ni)₆Sn₅. For 3 at.% or higher Ni addition in Cu, only the (Cu,Ni)₆Sn₅ phase grows in the interdiffusion zone. The elongated grains of (Cu,Ni)₆Sn₅ are found when it is grown from (Cu,Ni)₃Sn. This indicates that the newly formed intermetallic compound joins with the existing grains of the phase. On the other hand, smaller grains are found when this phase grows directly from Cu in the absence of (Cu,Ni)₃Sn indicating the ease of repeated nucleation. Grain size of (Cu,Ni)₆Sn₅ decreases with further increase in Ni content, which indicates a further reduction of activation barrier for nucleation. The relations for the estimation of relevant diffusion parameters are established considering the diffusion mechanism in the Cu(Ni)–Sn system, which is otherwise impossible in the phases with narrow homogeneity range in a ternary system. The flux of Sn increases, whereas the flux of Cu decreases drastically with the addition of very small amount of Ni, such as 0.5 at.% Ni, in Cu. Analysis of the atomic mechanism of diffusion indicates the contribution from both lattice and grain boundary for the growth of (Cu,Ni)₆Sn₅ phase.