Diaphragm atrophy developing during mechanical ventilation strongly impacts clinical outcomes. Targeting an inspiratory effort level similar to that of healthy subjects at rest might accelerate liberation from ventilation.

The nature of the surface-state charge (Qss) associated with thermally oxidized silicon has been studied experimentally using MOS structures. The effects of oxidation conditions, silicon orientation, annealing treatments, oxide thickness, and electric field were examined, as well as the physical location of the surface-state charge. The results indicate that the surface-state charge can be reproducibly controlled over a range 1010-1012 cm -2, and that it is an intrinsic property of the silicon dioxide-silicon system. It appears to be due to an excess silicon species introduced into the oxide layer near the silicon during the oxidation process.In much of the early work on the properties of semiconductor surfaces, experimental results were interpreted within the framework of two quantities: fast and slow surface states (1). "Fast surface states" are electronic states within Che forbidden gap of the semiconductor, located at the surface, which are in good electrical communication with the semiconductor bulk. Because of this, they can act as surface recombination centers. Their density per unit area for both clean germanium and silicon surfaces has been generally found to be of the same order as the surface atom density. If the semiconductor is covered by an adsorbed layer, or an oxide, the density of fast states has been found to decrease to 1011-101~ cm-2. "Slow states," in contrast, have been attributed to ionic contamination within an oxide covering the semiconductor surface. Because of their relatively large distance from the semiconductor, they are in poor electrical communication with it. Their density is a strong function of the ambient and surface treatment of the sample, but generally ranges in the neighborhood of 1012-1013 am-2 In the past several years, the thermally oxidized silicon surface has been investigated very intensively, partly due to its extreme technological importance and partly to the ease with which its characteristics can be studied (2). As a result of these investigations, a detailed picture of this system has emerged which is not explainable strictly within the framework of fast and slow surface states. Vol. 114, No. 3 SURFACE-STATE CHARGE OF OXIDIZED Si 267An idealized representation of the current picture of the thermally oxidized silicon system is depicted in Fig. 1. Fast surface states have been identified, but in many cases their density has been found to be less than 5 x 10 TM cm-2 (3), considerably lower than in other systems, thus leading to the low surface recombination velocity of passivated silicon devices (4). While slow surface states, in the customary sense, have not been evident, ionic space charges within the oxide have been observed. These were found to result from either contamination by relatively mobile ions such as sodium (5, 6), or from exposure to ionizing radiation (7). They are evidently in poor electrical contact with the underlying silicon even when located very near the oxide-silicon interface.These charges within the oxide, which have general...

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