Single-crystal Copper Substrates Research Articles

Interfacial reaction of Sn-1.5Ag-2.0Zn low-silver lead-free solder with oriented copper

High density packaging technology reduces the pad size and the number of grains contained in the pad. When the polycrystalline pad turns into a single crystal pad, the grain orientation has an important impact on the formation of the intermetallic compound (IMC) at the interface. The growth of IMC at the interface between the solder and the single-crystal copper substrate is investigated by selecting the prospective Sn-1.5Ag–2Zn as the solder alloy. Sn-1.5Ag-2.0Zn lead-free solder joints soldered with single crystal (111) copper substrate and polycrystalline red copper substrate are reflowed at 250 °C for 5 min. Samples are subsequently aged at 160 °C. The uneven scallop like Cu6Sn5 IMC layer grows rapidly when the alloy solder contacts with the copper substrate. The Cu6Sn5 grain size formed on the surface of single crystal copper is larger than that of polycrystalline copper. Single crystal copper has no grain boundary to block atomic diffusion, which affects grain nucleation and growth. The growth rate of Cu6Sn5 formed by alloy solder and the single crystal (111) copper solder joint after aging treatment at 160 °C for 20 h is about twice that of the polycrystalline copper solder joint. Then it grows slowly with the increase of aging treatment time. The thick layer Cu6Sn5 breaks due to crack diffusion after 600 h of aging treatment, and the thickness of IMC remains at 3.5 μm. Cu5Zn8 generated at the solder and polycrystalline copper solder joint during aging treatment acts as a barrier layer, preventing the solder from contacting the copper substrate and inhibiting the formation of Cu6Sn5. Cu5Zn8 is broken and decomposed after 300 h of aging treatment, and Cu6Sn5 grows rapidly after the barrier layer disappeared. The thickness of Cu6Sn5 is about 2.8 μm. The thickness of IMC of solder joint on single crystal copper is 0.7 μm more than that on polycrystalline copper. After aging treatment, the IMC formed at the interface between alloy solder and single crystal copper has better compactness and basically no pores, while there are obvious pores between IMC grains at the interface between alloy solder and polycrystalline copper, which can predict that the soldering quality of the interface between alloy solder and single crystal copper is better. This will provide application prospects for solder joint interface reliability research.

Study on interfacial reaction behavior of Sn[sbnd]Ag based lead-free solder with (111) single crystal copper substrate

The morphology and crystal orientation of intermetallic compounds formed by the reaction between SAC305 solder/(111) and SABI333 solder/(111) single crystal copper substrate were investigated. The morphology of Cu6Sn5 at the interface of SAC305 solder/(111) single crystal copper substrate changes from scallop to prismatic with the increase of reflow time. The Cu6Sn5 grains grow parallel to the horizontal direction of the Cu substrate and grow along the vertical direction, and there is an Angle of 60° between different Cu6Sn5 crystals. The calculated b ~ t0.23 relation satisfies the growth kinetics of prismatic Cu6Sn5. In addition, the morphology of Cu6(Sn, In)5 at the interface of SABI333 solder/(111) single crystal copper substrate is between scallop-type and prismatic-type. Cu6(Sn, In)5 grains grow at a certain angle with a single crystal copper substrate due to the addition of In element. Furthermore, it is considered that the deflection mechanism of Cu6(Sn, In)5 grains is controlled by the length and strength of inter-atomic bonds within the grains after the In atom substitution reaction.

Fabrication of three-dimensional sin-shaped ripples using a multi-tip diamond tool based on the force modulation approach

A novel cutting strategy of machining microstructure surface with the multi-tip diamond tool based on the force modulation approach is proposed in this paper. The multi-tip diamond tool with periodic sinusoidal microstructures was prepared by focused ion beam technique. The influence of applied cutting forces on the depths of cut and material removal states was investigated experimentally. MD simulations revealed a significant phenomenon of no material side flow when using the multi-tip diamond tool cutting on single crystal copper substrate. The movement of stacking faults, Lomer-Cottrell locks and Hirth locks jointly governed the formation mechanism of machined surface. To demonstrate the feasibility and effectiveness of this proposed cutting strategy, the fabrication of periodic sinusoidal microstructures under constant forces was successfully realized on the microsphere surface. Furthermore, three-dimensional sin-shaped ripples required variable forces controlling were achieved with high-precision surface quality. The cross-sectional topography of obtained ripples matched the geometry of used MTD tool quite well. In particular, the processing parameters, including the time period of loading forces and cutting speeds, determine the expected wavelength of ripples and play a central role in the surface machining accuracy.

Investigation of the adhesive contact between a diamond indenter and single-Crystal copper substrate at low temperatures

ABSTRACT Considering the elastoplastic deformation of a single-crystal copper substrate, based on the atomic scale, a mixed potential function (EAM and Morse) and the Verlet algorithm were used to simulate the adhesion contact and separation process between a hemispherical diamond indenter and a single-crystal copper substrate at low temperatures. The influences of the temperature on the micro/nanomechanical properties of the material surface and on the mechanism of the subsurface deformation process were analysed. The results show that as the simulated temperature decreases, the time for adhesion to occur is delayed, and the adhesion forces increase slightly. While the indenter is being pressed, the temperature affects the generation and interaction of the dislocations in the substrate. As the temperature decreases, a large number of dislocations in the substrate are generated and then relatively reduced, and the load on the indenter fluctuates. A calculation of the mechanical properties of the material found that the contact stiffness was related to the elastic recovery energy. A smaller elastic recovery energy leads to a greater contact stiffness; thus, the indentation hardness is related to the plastic deformation energy. An increased plastic deformation energy results in a decreased indentation hardness.

Fast growth of centimeter-scale single-crystal copper foils with high-index planes by the edge-incision effect

Single-crystal copper substrates have gained importance for the preparation of high-quality graphene and hexagonal boron nitride monolayer films by chemical vapor deposition (CVD). Especially, large-scale single-crystal copper foils with high-index planes are synthesized recently and attract great interests. However, the current synthesis methods of single-crystal copper foils and films are energy and time-consuming. Here, we show a rapid and efficient approach for the preparation of centimeter-scale single-crystal copper foils by making small incisions at the edges of polycrystalline copper foils before high-temperature annealing. 1.5 cm × 4 cm pieces of grain-boundary-free copper foils can be prepared by annealing at 1080 °C for 60 min. The annealed copper foil manifests a single high-index plane and is grain-boundary-free over the whole area. We also show that CVD of graphene on the high-index single-crystal copper affords a higher growth rate than on low-index copper substrates.

Influence of Nanoscale Textured Surfaces and Subsurface Defects on Friction Behaviors by Molecular Dynamics Simulation.

In nanomaterials, the surface or the subsurface structures influence the friction behaviors greatly. In this work, nanoscale friction behaviors between a rigid cylinder tip and a single crystal copper substrate are studied by molecular dynamics simulation. Nanoscale textured surfaces are modeled on the surface of the substrate to represent the surface structures, and the spacings between textures are seen as defects on the surface. Nano-defects are prepared at the subsurface of the substrate. The effects of depth, orientation, width and shape of textured surfaces on the average friction forces are investigated, and the influence of subsurface defects in the substrate is also studied. Compared with the smooth surface, textured surfaces can improve friction behaviors effectively. The textured surfaces with a greater depth or smaller width lead to lower friction forces. The surface with 45° texture orientation produces the lowest average friction force among all the orientations. The influence of the shape is slight, and the v-shape shows a lower average friction force. Besides, the subsurface defects in the substrate make the sliding process unstable and the influence of subsurface defects on friction forces is sensitive to their positions.

Effect of material removal state on the selection of theoretical models when scratching single-crystal copper using the load modulation approach

This article presents a constant force–controlled cutting approach with two different geometries of cutting tools. The methodologies for establishing two theoretical models were proposed to quantitatively predict the required applied normal forces at the expected machined depths, which were obtained with a solution to the horizontal projection of the sample–tip contact area and the multi-edge form tip based on a generalized cutting approach, respectively. The selection of the proposed theoretical models is dependent on the two material removal states, respectively, in which one is plowing for a regular triangular pyramid and the other one is cutting chips for a single-point diamond tip. To verify the feasibility and effectiveness of the proposed theoretical models and cutting strategy, a constant normal force cutting of microgrooves was implemented on a single-crystal copper substrate, while realizing constant cutting depths. The difference between the setting normal forces and the theoretical normal forces was analyzed by comparing the experimental results and the model prediction results. The aim of the present study was to investigate the effect of the geometry of the cutting tools on the material removal state and on the selection of the theoretical models.

Fractal contact behavior of single crystal copper substrate and rigid plane

The micro-nanoscopic morphology of the contact surfaces directly affects the tribological behavior between the contact surfaces. In this paper, a single crystal copper substrate with nano rough surfaces is characterized based on the fractal theory, and the nano rough contact model which could exist stably at room temperature (298 K) is established. The contact behavior between rigid plane and elasto-plastic rough substrate is analyzed. It is found that only a few higher asperities enter the contact area at the initial contact stage, causing large fluctuations in contact force. However, due to the small interaction between the asperities, the contact area is approximately linear with the contact force. If the ratio of real contact area to nominal contact area is greater than 17%, the contact force and contact area both increase with the increase of indentation depth, but the contact area-contact force curve deviates from the linear relationship gradually due to the intensification of material deformation and the interaction between asperities.

The Influence of Velocity Variation on the Adhesive Contact Behavior and the Deformation of Substrate Based on Molecular Dynamics Method

The contact behavior between indenter and single crystal copper substrate is performed to investigate based on EAM and Morse potentials and Verlet algorithm. Effects of different velocities on the contact behavior and substrate deformation are compared and analyzed. The results show that the single crystal copper material’s resist deformation level is limited by low velocity, and more dislocated atoms were accumulated under the direction of indenter moving in higher indenting velocity. During sliding process, lager chip volume is produced in front of the indenter as the sliding speed or sliding distance increases. The dislocated band in basis lies at the angle of 45 degrees with the direction of indenter moving in indenting and sliding process. Furthermore, the contact force, friction force and normal force increase with the rising of speed. On the contrary, the friction coefficient decrease gradually with higher sliding speed.

An AFM Evaluation of Rhenium-Nickel Electrodeposit Nucleation on Copper

The electrodeposition of rhenium and rhenium alloys is well documented both in acidic1-5 and alkaline6,7 solutions. The effect of complexing agents as well as the catalytic effect of divalent nickel ions has also been extensively investigated2-4. It has been shown that Re-Ni electrodeposits consist of alternating layers of Ni-rich and Re-rich phases2. However, a detailed explanation of the origin of such layers as well as the electrodeposit nucleation process is still missing. The objective of the present work is threefold. First, we seek to elucidate the nucleation mechanism of Re-Ni alloys. AFM will be used to document the formation and growth of electrodeposit nuclei and delineate the progressive vs. instantaneous nucleation mechanism. Second, the multilayered structure of the Re-Ni deposits will be addressed by documenting the formation of the initial layer and its evolution over time. Finally, nickel deposits will be used as substrates for pure rhenium electrodeposition to test the hypothesis that a strike layer of nickel is necessary to promote the deposition of pure rhenium.Galvanostatic pulse methods were used to electrodeposit pure nickel and pure rhenium salts separately from citrate solutions on (111) single crystal copper substrates as well as mica-supported copper films. The results are compared with the electrodeposition behavior of Re-Ni bath mixtures. A very small time scale is needed to deposit a monolayer of nickel. Distinct differences in frictional force of the initial deposit nuclei was captured by AFM. Figure 1 shows the difference in frictional force between a bare copper surface (111) and nickel deposit on a copper (111) surface. Nickel was deposited electrochemically by exposing a copper surface (111) to a 96 mM nickel sulfamate solution under galvanostatic polarization for 1 ms at -53.0 mA/cm2. The spots observed in the frictional image are attributed to islands of nickel atoms that are too thin to be detected in the topography mode. Acknowledgements The authors gratefully acknowledge the financial support from AFOSR under grant FA9550-10-1-0520. References 1) S. Szabó and I. Bakos, J. Electroanal. Chem., 492, 103 (2000). 2) A. Naor, N. Eliaz, and E. Gileadi, Electrochim. Acta, 54, 6028 (2009). 3) A. Naor, N. Eliaz, L. Burstein, and E. Gileadi, Electrochem. and Solid-State Letters, 13, D91 (2010). 4) A. Naor, N. Eliaz, and E. Gileadi, J. Electrochem. Soc., 157, D442 (2010). 5) E. Méndez, M. F. Cerdá, A. M. Castro Luna, C. F. Zinola, C. Kremer, and María E. Martins, J. Colloid. Int. Sci., 263, 119 (2003). 6) L. E. Netherton and M. L. Holt, J. Electrochem. Soc., 99, 44 (1954). 7) A. Vargas-Uscategui, E. Mosquera and L. Cifuentes, Electrochim. Acta, 109, 283 (2013). 8) A. Duhin, A. Inberg, N. Eliaz, and E. Gileadi, Electrochim. Acta, 56, 9637 (2011).

The Study on Deposition Process and Mechanical Properties of Deposited Cu Thin Films Using Molecular Dynamics

This paper studies the deposition process and mechanical properties of Cu thin films deposited on single crystal copper substrates with various surface roughnesses by molecular dynamics (MD). In the effect of vacancy concentration (Cv) of substrate, the Young's modulus of sample decreased as the Cv of substrate increased but the adhesion force will increase as the Cv of substrate increases. The effect of substrate roughness on the peak intensity of crystal orientation has little. And the greater Cv of substrate, the surface roughness of the deposited thin film also increased. In the effect of numbers of deposited atoms, the deposited thin film thickness increases, the surface will be relatively flat and the Young's modulus will also increase. By the XRD pattern, the principal growth directions of thin film are the (220) and (200) in the early stage of growth during deposition. However, with the thickness increasing, the (111) will be the preferred orientation.

Electronic structure of graphene on single-crystal copper substrates

The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low-energy electron microscopy, low-energy electron diffraction, and angle-resolved photoemission spectroscopy. On both substrates the graphene is rotationally disordered and interactions between the graphene and substrate lead to a shift in the Dirac crossing of $\ensuremath{\sim}$$\ensuremath{-}$0.3 eV and the opening of a $\ensuremath{\sim}$250 meV gap. Exposure of the samples to air resulted in intercalation of oxygen under the graphene on Cu(100), which formed a ($\sqrt{2}\ifmmode\times\else\texttimes\fi{}2\sqrt{2}$)R45${}^{\mathrm{o}}$ superstructure. The effect of this intercalation on the graphene $\ensuremath{\pi}$ bands is to increase the offset of the Dirac crossing ($\ensuremath{\sim}$$\ensuremath{-}$0.6 eV) and enlarge the gap ($\ensuremath{\sim}$350 meV). No such effect is observed for the graphene on the Cu(111) sample, with the surface state at $\ensuremath{\Gamma}$ not showing the gap associated with a surface superstructure. The graphene film is found to protect the surface state from air exposure, with no change in the effective mass observed, as for one monolayer of Ag on Cu(111).

STM investigation of energetic insertion during direct ion deposition

ABSTRACTThin copper films have been deposited on single crystal copper substrates and characterized using a UHV Scanning Tunneling Microscope to probe the effect of atomic insertions during hyperthermal ion deposition. At low temperatures, atomic insertions are predicted to provide a net downhill current that offsets the roughening effect due to uphill “Schwoebel” currents leading to a net smoothing of the surface. Films have been grown at several different energies targeted to observe a crossover from insertion driven smoothing to adatom-vacancy dominated roughening. Copper thin films are deposited near 20 eV using a mass selected ion deposition system that allows precise control (+/− 2 eV) over the energy of constituent atoms. Experimental observations are compared with a sophisticated Kinetic Monte Carlo and Molecular Dynamics hybrid (KMC-MD) simulation.

Induced Crystallographic Orientations in Electrodeposited Ni‐Cu Multilayers

The results of controlling the preferential crystallographic orientation of electrodeposited Ni‐Cu multilayers by means of electrochemical methods are reported. These multilayers were grown on pulse electrodeposited and dc electrodeposited copper foils of (111) and (220) preferential crystallographic orientation, respectively. Since multilayers have a tendency to grow epitaxially, the multilayers grown on these substrates exhibited (111) or (220) preferential crystallographic orientation. Results of electrodeposition of multilayers on cold‐rolled copper foil and on titanium are also presented. Similar results can be obtained using polycrystalline copper foil as compared to single crystal copper substrates. © 1999 The Electrochemical Society. All rights reserved.

Sintering of silver and copper nanoparticles on (001) copper observed by in-situ ultrahigh vacuum transmission electron microscopy

The sintering of copper and silver nanoparticles with single crystal copper substrates has been studied using a novel in-situ ultrahigh vacuum transmission electron microscope (UHV TEM). The system is equipped with a UHV DC sputtering attachment enabling metal nanoparticles to be generated in-situ and transferred directly into the microscope in the gas phase. In both cases, we find the particles to be of initially random orientation on the substrate. Upon annealing, however, the particles reorient and assume the same orientation as the substrate. The process apparently occurs by a mechanism involving sintering and grain growth. In the case of silver on copper, grain growth cannot occur since the metals are immiscible. Our observations show that, upon annealing, the particles wet the substrate surface and form epitaxially oriented islands by surface diffusion and grain boundary migration. The post-anneal islands exhibit the orientation relationship (111) Ag∥001) Cu, [110] Ag∥[110] Cu.

Direct observations of the sintering of silver nanoparticles on single crystal copper by in-situ uhv tem

ABSTRACTUsing a novel ultrahigh vacuum (UHV) transmission electron microscope with in-situ UHV sputtering attachment we have studied the sintering of copper and silver nanoparticles with single crystal copper substrates. Copper and silver particles deposited on (001) copper initially assume random orientations. Upon annealing, however, the particles reorient and assume an epitaxial orientation with the substrate. In the case of copper on copper, homoepitaxy occurs by a process involving sintering and grain growth. In the case of silver on copper, we have observed the particles to wet the substrate surface and sinter to form a thin epitaxial film with the orientation relationship (111)Ag // (001)Cu, [110]Ag // [110]Cu.

Magnetoresistance in electrodeposited NiFeCu/Cu multilayers

Multilayers of NiFeCu/Cu have been electrodeposited from a single electrolyte onto polycrystalline (100) textured and (100) single crystal copper substrates. Bilayer thicknesses as low as 30 Å have been achieved, as confirmed by X-ray diffraction. Room temperature magnetoresistance measurements show the presence of giant magnetoresistance (GMR) and an anisotropic magnetoresistance (AMR) component in the films.

Growth of TiO x overlayers by chemical vapour deposition on a single-crystal copper substrate

The deposition of ultrathin titania films by chemical vapour deposition from titanium tetraisopropoxide has been studied on a Cu(100) substrate using the surface analytical techniques of X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). The titania initially grows as a near-uniform layer with a well defined hexagonal structure, possibly related to the rutile structure. There is no evidence for a strong electronic interaction between the oxide overlayer and substrate. At higher exposures further growth at 600 K proceeds by 3D crystallite nucleation.

Mechanism for diamond nucleation and growth on single crystal copper surfaces implanted with carbon

The nucleation and growth of diamond crystals on single-crystal copper surfaces implanted with carbon ions has been studied. Microwave plasma-enhanced chemical vapor deposition was used for diamond growth. The single-crystal copper substrates were implanted either at room temperature or at elevated temperature (∼820 °C) with carbon ions prior to diamond nucleation. This procedure leads to the formation of a graphite film on the copper surface which greatly enhances diamond crystallite nucleation. From our study we construct a simple lattice model for diamond growth on graphite as 〈111〉diamond parallel to 〈0001〉graphite and 〈110〉diamond parallel to 〈112̄0〉graphite.

Sputtering-induced surface topography on F.C.C. metals

High fluence ion implantation of solids is known both to lead to new phase evolution and to modify, by sputtering, the surface topography of the solid. In the past the two processes have been separated by the use of only intermediate, but variable species, fluences in the former (e.g. by mixing of two-layer systems) or high fluence, inert gas or self-iron irradiation in the latter type of study. In the present study a variety of very high fluence (greater than 10 19 ions cm −2) implants into polycrystalline and single-crystal copper substrates have been studied to elucidate both mixing (and possible phase formation) and topographic evolution effects. The species were chosen to exert similar ballistic or collisional processes but different chemical or metallurgical effects in the substrate.