ABSTRACT
Liquid layers adhered to solid surfaces and that are in equilibrium with the vapor phase are common in printing, coating, and washing processes as well as in alveoli in lungs and in stomata in leaves. For such a liquid layer in equilibrium with the vapor it faces, it has been generally believed that, aside from liquid lumps, only a very thin layer of the liquid, i.e., with a thickness of only a few nanometers, is held onto the surface of the solid, and that this adhesion is due to van der Waals forces. A similar layer of water can remain on the surface of a wall of a microchannel after evaporation of bulk water creates a void in the channel, but the thickness of such a water layer has not yet been well characterized. Herein we showed such a water layer adhered to a microchannel wall to be 100 to 170 nm thick and stable against surface tension. The water layer thickness was measured using electron energy loss spectroscopy (EELS), and the water layer structure was characterized by using a quantitative nanoparticle counting technique. This thickness was found for channel gap heights ranging from 1 to 5 µm. Once formed, the water layers in the microchannel, when sealed, were stable for at least one week without any special care. Our results indicate that the water layer forms naturally and is closely associated only with the surface to which it adheres. Our study of naturally formed, stable water layers may shed light on topics from gas exchange in alveoli in biology to the post-wet-process control in the semiconductor industry. We anticipate our report to be a starting point for more detailed research and understanding of the microfluidics, mechanisms and applications of gas-liquid-solid systems.
ABSTRACT
We demonstrate direct electron beam writing of a nano-scale Cu pattern on a surface with a thin aqueous layer of CuSO4 solution. Electron beams are highly maneuverable down to nano-scales. Aqueous solutions facilitate a plentiful metal ion supply for practical industrial applications, which may require continued reliable writing of sophisticated patterns. A thin aqueous layer on a surface helps to confine the writing on the surface. For this demonstration, liquid sample holder (K-kit) for transmission electron microscope (TEM) was employed to form a sealed space in a TEM. The aqueous CuSO4 solution inside the sample holder was allowed to partially dry until a uniform thin layer was left on the surface. The electron beam thus reduced Cu ions in the solution to form the desired patterns. Furthermore, the influence of e-beam exposure time and CuSO4(aq) concentration on the Cu reduction was studied in this work. Two growth stages of Cu were shown in the plot of Cu thickness versus e-beam exposure time. The measured Cu reduction rate was found to be proportional to the CuSO4(aq) concentration.
ABSTRACT
The enhanced lifetime stability for the carbon nanotubes (CNTs) by coating hybrid granular structured diamond (HiD) films on Au-decorated CNTs/Si using a two-step microwave plasma enhanced chemical vapor deposition process was reported. Electron field emission (EFE) properties of HiD/Au/CNTs emitters show a low turn-on field (E0) of 3.50 V/µm and a high emission current density (Je) of 0.64 mA/cm(2) at an applied field of 5.0 V/µm. There is no notable current degradation or fluctuation over a period of τ(HiD/Au/CNTs) = 360 min for HiD/CNTs EFE emitters tested under a constant current of 4.5 µA. The robustness of the HiD/CNTs EFE emitter is overwhelmingly superior to that of bare CNTs EFE emitters (τ(CNTs) = 30 min), even though the HiD/Au/CNTs do not show the same good EFE properties as CNTs, which are E0 = 0.73 V/µm and Je = 1.10 mA/cm(2) at 1.05 V/µm. Furthermore, the plasma illumination (PI) property of a parallel-plate microplasma device fabricated using the HiD/Au/CNTs as a cathode shows a high Ar plasma current density of 1.76 mA/cm(2) at an applied field of 5600 V/cm with a lifetime of plasma stability of about 209 min, which is markedly better than the devices utilizing bare CNTs as a cathode. The CNT emitters coated with diamond films possessing marvelous EFE and PI properties with improved lifetime stability have great potential for the applications as cathodes in flat-panel displays and microplasma display devices.
ABSTRACT
A colorimetric immunoassay biosensor is developed employing CNTs as a label material, which allowed direct observation of the sensing result by the naked eye. Implemented for HSA, the detection limit is 3 × 10-5 mg ml-1 when characterized using UV-Vis.
