Fatigue of metals at nanoscale: Metal thin films and conductive interconnects for flexible device application

As electrodes and electrical interconnects in flexible electronic devices,metal films are one of the weakest components in the system against mechanical deformation in daily use.Fatigue reliability at nanoscale becomes a practical concern for these flexible electronic devices.This review introduces state-of-the-art fatigue testing techniques and evaluation methods for thin metal films and conductive interconnect materials constrained by a substrate.Then,experimental results about fatigue damage behaviors,fatigue properties and fatigue life prediction are summarized.Furthermore,fundamental insights into fatigue mechanisms of metals at the nanoscale and the size effects on fatigue properties are elucidated.Finally,the perspectives of studies on fatigue of thin metal films constrained by a substrate are proposed.

Electric Current-induced Failure of 200-nm-thick Gold Interconnects

200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The failure behavior of the Au interconnects under three kinds of electric currents were characterized in-situ by scanning electron microscopy. It is found that the formation of voids and subsequent growth perpendicular to the interconnect direction is the fatal failure mode for all the Au interconnects under three kinds of electric currents. The failure mechanism of the ultrathin metal lines induced by the electric currents was analyzed.

Distribution of nitric oxide synthase positive neurons in the substantia nigra of rats with liver cirrhosis

BACKGROUND：Nitrogen monoxide plays an important role in the physiological activity and pathological process of striatum in substantia nigra, and the nitric oxide synthase in substantia nigra may have characteristic changes after liver cirrhosis.OBJECTIYE： To observe the distribution and forms of nitric oxide synthase （NOS） positive neurons and fibers in substantia nigra of rats with liver cirrhosis.DESIGN： A comparative observational experiment.SETTINGS： Beijing Friendship Hospital; Capital Medical University.MATERIALS： Twenty 4-month-old male Wistar rats （120 - 150 g） of clean grade, were maintained in a 12-hour light/dark cycle at a constant temperature with free access to standard diet and water. Cryostat microtome （LEICA, Germany）; All the reagents were purchased from Sigma Company.METHODS： The experiment was carried out in the Department of Anatomy （key laboratory of Beijing city）,Capital Medical University from July 2000 to March 2002. The rats were randomly divided into normal group （n=10） and liver fibrosis group （n=10）. Rats in the liver fibrosis group were subcutaneously injected with 60% CCl4 oil at a dose of 5 mL/kg for the first time, and 3 mL/kg for the next 14 times, twice a week,totally 15 times. Liver fibrosis of grades 5 - 6 was taken as successful models. Whereas rats in the normal group were not given any treatment. Four months after CCl4 treatment, all the rats were anesthetized to remove brain, and frontal frozen serial sections were prepared. The expressions of nitric oxide synthase positive neurons in substantia nigra of rats were observed under inverted microscope. The number and gray scale of cell body of nitric oxide synthase positive neurons in substantia nigra were detected with NADPH-diaphorase staining.MAIN OUTCOME MEASURES： ①Number and gray scale of cell body of nitric oxide synthase positive neurons in substantia nigra; ②Expressions of nitric oxide synthase positive neurons in substantia nigra.RESULTS： All the 20 rats were involved in the analysis of results. ①The nitric oxide synthase positive neurons in substantia nigra were obviously fewer in the liver cirrhosis group than in the normal group （P〈0.01）, and the gray scale of the positive cell body was higher in the liver cirrhosis group than in the normal group （P〈0.05）. ② Abundant nitric oxide synthase positive neurons were observed in substantia nigra of neurons in substantia nigra were obviously fewer in the liver cirrhosis group than in the normal group （P〈0.01）, and the gray scale of the positive cell body was higher in the liver cirrhosis group than in the normal normal rats, the cell body of nitric oxide synthase positive neurons was clear and transparent, with short own cloudy processes. In substantia nigra of rats with liver cirrhosis, the body of nitric oxide synthase positive neurons were observed shrink obviously, less fibrin than normal.CONCLUSION： Rats with liver cirrhosis may suffer from the physiological dysfunction of neurons due to lack of fibers. The nitric oxide synthase positive neurons in substantia nigra can shrink and reduce.

Microstructural Characterization and Hardness Behavior of a Biological Saxidomus purpuratus Shell

The microstructures of the Saxidomus purpuratus shell were observed.It was found that the inner and middle layers of the shell are composed of crossed lamellae,while the outer layer exhibits porous structures.With the characteristic structure of each layer,the hardness of inner layer with narrow domains in crossed lamellar structure is the highest,and that of middle layer with wide domains is lower,while the outer layer has the lowest hardness.The damage morphologies of the indentations change a lot,depending not only upon the magnitude of the indentation load,but also upon the orientation between the indentation direction and the crossed lamellae in the microstructure of the shell,which illustrates the anisotropy in mechanical properties of such shells.