The change of microstructure in deuteron-implanted aluminum under electron irradiation

Abstract

As known for a long time, bubbles in liquid would emit light under ultrasonic waves. This experiment, called sonoluminescence, has attracted many people to research on it, but its mechanism is not yet clear. It is reasonable to think that similar phenomenon involving bubbles may happen in solid materials, but its opacity prevents researchers to detect such a kind of phenomenon. This paper investigates the change of gas bubbles by transmission electron microscope (TEM), being able to overcome the difficulty of opacity of materials. Thin film samples of pure aluminum are prepared for TEM experiment by jet chemical polishing. The samples are implanted first by deuterium or hydrogen at room temperature using ion accelerator, followed by electron irradiation under 200 kV TEM. Gas bubbles will form in aluminum after ion implantation, and then grow into larger ones or be collapsed under electron irradiation. Electron diffraction rings of polycrystals appear together with the change of gas bubbles. This kind of diffraction rings of polycrystals could be observed both in deuterium-implanted and hydrogen-implanted aluminum, but would never be found in the case of electron irradiation on the aluminum without implantation of hydrogen or deuterium. The polycrystals of aluminum are not due to the heating effect of electron beam, even electron beam could make a hole in the film sample finally. For the sample of aluminum containing no hydrogen or deuterium, only dislocation loops can be observed during electron irradiation. It may be that a kind of heat emission occurs when the gas bubbles are irradiated by electron beams, but the heat emission would not be due to deuterium fusion reaction because the electron beam-induced polycrystals occur not only in deuterium case, but also in hydrogen case, indicating that the implanted deuterium is not the necessary condition for heat emission. In addition, the energy dispersive spectrometer in TEM is used to detect the possible unique X-ray signals, but none of any special peak below 40 keV in the X-ray spectrum can be found. The plasmatization of gas in the bubbles under electron beam irradiation is used to try to explain the mechanism of such heat emission.