The synthesis of CdO, Ag2O (5nm) and Ag (~20~30 nm) nano-objects is achieved simultaneously by nanosecond-pulsed discharges in liquid nitrogen between one cadmium electrode and one silver electrode. Oxidation occurs w...The synthesis of CdO, Ag2O (5nm) and Ag (~20~30 nm) nano-objects is achieved simultaneously by nanosecond-pulsed discharges in liquid nitrogen between one cadmium electrode and one silver electrode. Oxidation occurs when liquid nitrogen is fully evaporated and nanoparticles are in contact with the air. No alloy is formed, whatever the conditions, even though both elements are present simultaneously, as showed by timeresolved optical emission spectroscopy. This lack of reactivity between elements is attributed to the high pressure within the discharge that keeps each metallic vapor around the electrode it comes from. Each element exhibits a specific behavior. Cubic Cd particles, formed at 4 kV, get elongated with filamentary tips when the applied voltage reaches 7 and 10 kV. Cd wires are formed by assembly in liquid nitrogen of Cd nanoparticles driven by dipole assembly, and not by dielectrophoresis. On the contrary, silver spherical particles get assembled into 2D dendritic structures. The anisotropic growth of these structures is assumed to be due to the existence of pressure gradients.展开更多
A simple method to synthesise hexagonal lead sheets,which belong to the class of two-dimensional materials,is proposed.These objects are collected on a substrate located under two lead electrodes, between which nanose...A simple method to synthesise hexagonal lead sheets,which belong to the class of two-dimensional materials,is proposed.These objects are collected on a substrate located under two lead electrodes, between which nanosecond-pulsed spark discharges are ignited in liquid nitrogen.The hexagonal sheets are single crystals produced by gas phase condensation.Once nitrogen completely evaporates,the sheets change to PbO2by oxidation in air.The oxidation process induces stress that pleats the uppermost sheets or open cracks at the centre.The thickness of the individual objects typically varies from 4to 20nm.When the number of discharges is more than about 2000,in addition to sheets,two types of PbO2 sticks start to form:bundles composed of nanosticks (length 5p.m and diameter 50nm)and isolated sticks (length 20μm and diameter 500nm).These new nanostructures mainly form because of the way the discharge erodes the lead electrodes.Initially,anisotropic erosion driven by the orientation of the crystallographic planes of the lead crystals produces octahedra and nanosticks,and the nanosticks grow on the electrode surfaces as discharge proceeds.After about 2000discharges,the nanosticks are sufficiently long that they can be easily broken,probably by mechanical stress,and they fall onto the underlying substrate.展开更多
文摘The synthesis of CdO, Ag2O (5nm) and Ag (~20~30 nm) nano-objects is achieved simultaneously by nanosecond-pulsed discharges in liquid nitrogen between one cadmium electrode and one silver electrode. Oxidation occurs when liquid nitrogen is fully evaporated and nanoparticles are in contact with the air. No alloy is formed, whatever the conditions, even though both elements are present simultaneously, as showed by timeresolved optical emission spectroscopy. This lack of reactivity between elements is attributed to the high pressure within the discharge that keeps each metallic vapor around the electrode it comes from. Each element exhibits a specific behavior. Cubic Cd particles, formed at 4 kV, get elongated with filamentary tips when the applied voltage reaches 7 and 10 kV. Cd wires are formed by assembly in liquid nitrogen of Cd nanoparticles driven by dipole assembly, and not by dielectrophoresis. On the contrary, silver spherical particles get assembled into 2D dendritic structures. The anisotropic growth of these structures is assumed to be due to the existence of pressure gradients.
文摘A simple method to synthesise hexagonal lead sheets,which belong to the class of two-dimensional materials,is proposed.These objects are collected on a substrate located under two lead electrodes, between which nanosecond-pulsed spark discharges are ignited in liquid nitrogen.The hexagonal sheets are single crystals produced by gas phase condensation.Once nitrogen completely evaporates,the sheets change to PbO2by oxidation in air.The oxidation process induces stress that pleats the uppermost sheets or open cracks at the centre.The thickness of the individual objects typically varies from 4to 20nm.When the number of discharges is more than about 2000,in addition to sheets,two types of PbO2 sticks start to form:bundles composed of nanosticks (length 5p.m and diameter 50nm)and isolated sticks (length 20μm and diameter 500nm).These new nanostructures mainly form because of the way the discharge erodes the lead electrodes.Initially,anisotropic erosion driven by the orientation of the crystallographic planes of the lead crystals produces octahedra and nanosticks,and the nanosticks grow on the electrode surfaces as discharge proceeds.After about 2000discharges,the nanosticks are sufficiently long that they can be easily broken,probably by mechanical stress,and they fall onto the underlying substrate.
