Wedge-shaped copper casting experiment was conducted to study the engulfment behavior of TiB2 particle and the interaction between particle or cluster and the solid/liquid front in commercial pure aluminum matrix. The...Wedge-shaped copper casting experiment was conducted to study the engulfment behavior of TiB2 particle and the interaction between particle or cluster and the solid/liquid front in commercial pure aluminum matrix. The experimental results show that the particle size distribution obeys two separate systems in the whole wedge-cast sample. Furthermore, it is found that the big clusters are pushed to the center of the wedge shaped sample and the single particle or small clusters consisting of few particles are engulfed into the α-Al in the area of the sample edge. The cluster degree of particles varies in different areas, and its value is 0.2 and 0.6 for the cluster fraction in the edge and in the center of the wedge sample, respectively. The cluster diameter does not obey the normal distribution but approximately obeys lognormal distribution in the present work. More importantly, in the whole sample, the particle size obeys two separate log-normal distributions.展开更多
DBC substrates are the standard circuit boardsfor power modules. Using the DBC technologythick copper foils (0.125mm - 0.Tmm) arecladded to Alumina or Aluminum Nitride,The strong adhesion of the copper to ceramicbond ...DBC substrates are the standard circuit boardsfor power modules. Using the DBC technologythick copper foils (0.125mm - 0.Tmm) arecladded to Alumina or Aluminum Nitride,The strong adhesion of the copper to ceramicbond reduces the thermal expansion coefficientin horizontal direction only slightly above theTEC of the ceramic itself. This allows directsilicon attach of large dies without using TECcontrolling layers.As DBC technology is using copper foils,integralleads overhanging the ceramic can be realized...展开更多
The direct deposition of diamond films on copper substrate has been suffered fromadhesion problems due to the mismatch of the thermal expansion coefficients of diamond andcopper. In this paper nuclei with valuable den...The direct deposition of diamond films on copper substrate has been suffered fromadhesion problems due to the mismatch of the thermal expansion coefficients of diamond andcopper. In this paper nuclei with valuable density were directly introduced thirough a submicrondiamond powder layer. The diamond grits partially were buried in the copper substrate leadingto better adhesion. Another method with nickel intermediate layer for enhancing the adhesionwas studied here in detail. It was suggested that Cu-Ni eutectic between the copper substrate andNi interlayer might contribute to the adhesion improvement. The quality of the diamond filmsdeposited wlth rnckel interlayer was investigated by scanning electron microscopy and Ramanspectroscopy.展开更多
Purpose Niobium sputtered on copper has been a popular alternative approach for superconducting radio frequency(SRF)community in the last few decades.Comparing to bulk materials of a few millimeters,high-purity niobiu...Purpose Niobium sputtered on copper has been a popular alternative approach for superconducting radio frequency(SRF)community in the last few decades.Comparing to bulk materials of a few millimeters,high-purity niobium of merely a few microns is sufficient to realize superconductivity on the coated surface.Being niobium thin film,it has been widely acknowledged that surface quality of the substrate plays a vital role in obtaining a superior niobium coating with excellent SRF performance.Therefore,proper chemical treatment of the substrate before coating is crucial and the ultimate goal is to create a smooth and defect-free surface.Prior to the design of a cavity etching system,the mechanism of SUBU as well as two industry-used solutions is studied in detail on samples.Methods Copper samples were first pre-treated by mechanical grinding to remove fabrication damages,obvious defects and visible impurities.Two chemical solutions widely used in industries were subsequently chosen to etch the samples.Finally,the established SUBU solution was used independently on these pre-treated samples for comparison.Surface morphology and etching rate were measured accordingly.Results and conclusions Mirror-like copper surface was created by using the SUBU solution thus qualified for subsequent niobium sputtering,while the other two solutions used in industries were less effective with nonideal surface morphology.The chemical reactions,the experimental requisites and the involved processes are extensively elucidated for all three solutions.Limitations for SUBU were examined,and the optimum ratio of the chemical bath volume to sample surface area was also determined.These investigations will serve as an important guidance for the development of a chemical etching system for elliptical copper cavities.展开更多
Large-scale growth of copper oxide nanowires was realized on surfaces of various copper-containing substrates, including copper grids, high-purity copper foils, and small copper blocks, by the stress-induced method. A...Large-scale growth of copper oxide nanowires was realized on surfaces of various copper-containing substrates, including copper grids, high-purity copper foils, and small copper blocks, by the stress-induced method. A relatively low heating temperature of 340 ~C was demonstrated to give rise to dense nanowire growth with fine crystal structures and high aspect ratio of approximately 300. Gradual cooling process, which is positive for the growth of nanowires on multi-layer substrates, is shown to have no effect on the nanowire growth on other pure copper substrates. Diameter of as-obtained nanowires is mainly dependent on the heating temperature. Moreover, the nanowires growing on copper grids are much longer than those growing on two other substrates.展开更多
Purpose Surface quality of the substrate is widely acknowledged to be essential for the niobium thin film deposition. Mucheffort has thus been spent to improve the surface roughness by using various chemical etching t...Purpose Surface quality of the substrate is widely acknowledged to be essential for the niobium thin film deposition. Mucheffort has thus been spent to improve the surface roughness by using various chemical etching techniques. However, surfacepreparation before the chemical etching also plays a part in obtaining a satisfactory substrate, but has rarely been studiedbefore. This paper aims to define a specification for the pre-polished copper substrate prior chemical etching and searches forsuitable alternative non-chemical grinding methods for the copper cavity.Methods Copper samples were mechanically pre-polished at first by using flap sanding wheels of different grits and thenchemically etched by using the well-established SUBU solutions. Surface roughness, as a figure of merit, was measuredand compared before and after SUBU. Optimum practice for pre-polishing may therefore be determined. The mechanicalgrinding was subsequently applied on the 1.3-GHz mono-cell copper cavity. Meantime, the previously reported centrifugalbarrel polishing method was also applied with new abrasive materials and modified schemes. A comprehensive study ofetching rate, surface roughness and morphologies was conducted.Results and conclusions The specification for surface roughness prior SUBU was determined. Due to a complex geometryand curved surfaces possessed by the 1.3-GHz copper cavity, the traditional mechanical grinding was proved to be not ideal.Satisfactory surface quality was obtained by using the alternative centrifugal barrel polishing on the cavity. The proposed newscheme and new abrasive materials were demonstrated to be effective, and a mirror-like surface was achieved on the coppercavity. The traditional mechanical grinding can therefore be replaced. This constitutes a dedicated study on pre-polishing ofthe 1.3-GHz copper cavity substrate prior chemical etching for niobium sputtering.展开更多
文摘Wedge-shaped copper casting experiment was conducted to study the engulfment behavior of TiB2 particle and the interaction between particle or cluster and the solid/liquid front in commercial pure aluminum matrix. The experimental results show that the particle size distribution obeys two separate systems in the whole wedge-cast sample. Furthermore, it is found that the big clusters are pushed to the center of the wedge shaped sample and the single particle or small clusters consisting of few particles are engulfed into the α-Al in the area of the sample edge. The cluster degree of particles varies in different areas, and its value is 0.2 and 0.6 for the cluster fraction in the edge and in the center of the wedge sample, respectively. The cluster diameter does not obey the normal distribution but approximately obeys lognormal distribution in the present work. More importantly, in the whole sample, the particle size obeys two separate log-normal distributions.
文摘DBC substrates are the standard circuit boardsfor power modules. Using the DBC technologythick copper foils (0.125mm - 0.Tmm) arecladded to Alumina or Aluminum Nitride,The strong adhesion of the copper to ceramicbond reduces the thermal expansion coefficientin horizontal direction only slightly above theTEC of the ceramic itself. This allows directsilicon attach of large dies without using TECcontrolling layers.As DBC technology is using copper foils,integralleads overhanging the ceramic can be realized...
文摘The direct deposition of diamond films on copper substrate has been suffered fromadhesion problems due to the mismatch of the thermal expansion coefficients of diamond andcopper. In this paper nuclei with valuable density were directly introduced thirough a submicrondiamond powder layer. The diamond grits partially were buried in the copper substrate leadingto better adhesion. Another method with nickel intermediate layer for enhancing the adhesionwas studied here in detail. It was suggested that Cu-Ni eutectic between the copper substrate andNi interlayer might contribute to the adhesion improvement. The quality of the diamond filmsdeposited wlth rnckel interlayer was investigated by scanning electron microscopy and Ramanspectroscopy.
基金Wewould like to thank Dr.ChaoDong for helping with sample characterizations.We are especially grateful to LNER-team at IHEP for providing the laboratory and necessary facilities for chemical experiments.This work has been supported by the Platform for Advanced Photon Source Technology(PAPS)project and Pioneer“Hundred Talents Program”of Chinese Academy of Sciences.
文摘Purpose Niobium sputtered on copper has been a popular alternative approach for superconducting radio frequency(SRF)community in the last few decades.Comparing to bulk materials of a few millimeters,high-purity niobium of merely a few microns is sufficient to realize superconductivity on the coated surface.Being niobium thin film,it has been widely acknowledged that surface quality of the substrate plays a vital role in obtaining a superior niobium coating with excellent SRF performance.Therefore,proper chemical treatment of the substrate before coating is crucial and the ultimate goal is to create a smooth and defect-free surface.Prior to the design of a cavity etching system,the mechanism of SUBU as well as two industry-used solutions is studied in detail on samples.Methods Copper samples were first pre-treated by mechanical grinding to remove fabrication damages,obvious defects and visible impurities.Two chemical solutions widely used in industries were subsequently chosen to etch the samples.Finally,the established SUBU solution was used independently on these pre-treated samples for comparison.Surface morphology and etching rate were measured accordingly.Results and conclusions Mirror-like copper surface was created by using the SUBU solution thus qualified for subsequent niobium sputtering,while the other two solutions used in industries were less effective with nonideal surface morphology.The chemical reactions,the experimental requisites and the involved processes are extensively elucidated for all three solutions.Limitations for SUBU were examined,and the optimum ratio of the chemical bath volume to sample surface area was also determined.These investigations will serve as an important guidance for the development of a chemical etching system for elliptical copper cavities.
文摘Large-scale growth of copper oxide nanowires was realized on surfaces of various copper-containing substrates, including copper grids, high-purity copper foils, and small copper blocks, by the stress-induced method. A relatively low heating temperature of 340 ~C was demonstrated to give rise to dense nanowire growth with fine crystal structures and high aspect ratio of approximately 300. Gradual cooling process, which is positive for the growth of nanowires on multi-layer substrates, is shown to have no effect on the nanowire growth on other pure copper substrates. Diameter of as-obtained nanowires is mainly dependent on the heating temperature. Moreover, the nanowires growing on copper grids are much longer than those growing on two other substrates.
文摘Purpose Surface quality of the substrate is widely acknowledged to be essential for the niobium thin film deposition. Mucheffort has thus been spent to improve the surface roughness by using various chemical etching techniques. However, surfacepreparation before the chemical etching also plays a part in obtaining a satisfactory substrate, but has rarely been studiedbefore. This paper aims to define a specification for the pre-polished copper substrate prior chemical etching and searches forsuitable alternative non-chemical grinding methods for the copper cavity.Methods Copper samples were mechanically pre-polished at first by using flap sanding wheels of different grits and thenchemically etched by using the well-established SUBU solutions. Surface roughness, as a figure of merit, was measuredand compared before and after SUBU. Optimum practice for pre-polishing may therefore be determined. The mechanicalgrinding was subsequently applied on the 1.3-GHz mono-cell copper cavity. Meantime, the previously reported centrifugalbarrel polishing method was also applied with new abrasive materials and modified schemes. A comprehensive study ofetching rate, surface roughness and morphologies was conducted.Results and conclusions The specification for surface roughness prior SUBU was determined. Due to a complex geometryand curved surfaces possessed by the 1.3-GHz copper cavity, the traditional mechanical grinding was proved to be not ideal.Satisfactory surface quality was obtained by using the alternative centrifugal barrel polishing on the cavity. The proposed newscheme and new abrasive materials were demonstrated to be effective, and a mirror-like surface was achieved on the coppercavity. The traditional mechanical grinding can therefore be replaced. This constitutes a dedicated study on pre-polishing ofthe 1.3-GHz copper cavity substrate prior chemical etching for niobium sputtering.
