ASTER-System

FIG. 2. The dependence of the carbon fraction. v = Cl/(lSi] + [C ) on the gas-flow ratio r = [CH4]/([SiH4] -I- ICH4I) for films deposited in the ASTER system [ASTI (filled circles) and AST2 (filled triangles)] and for films deposited in a similar system (ATLAS) [ATLI (open circles) and ATL2 (open triangles)]. (From R, A. C. M. M. van Swaaij, Ph.D. Thesis, Universiteit Utrecht, Utrecht, the Netherlands, 1994. with permission.)... 

In the ASTER system (see Section 1.2.4), experiments were performed in order to test this scaling law. To this end, a newly designed RF electrode assembly was retrofitted to a deposition chamber. With this electrode setup, it was possible to change the electrode distance from the outside, without breaking the vacuum. A large data set was taken, consisting of 420 data points [162] at three values of the pressure (0.1 < p < 0.45 mbar), five of the RF power (5 < P < 25 W), seven of the electrode distance (12 < L < 30 mm), and four of the RF frequency (13.56 < o)/2n < 50 MHz). 

In this sub-subsection the results of the ID model are shown together with data taken from experiments in the ASTER system. Both the partial pressures of the... 

In the ASTER system a data series is measured for an argon and a hydrogen plasma running at 13.56 MHz, in which the power (5-30 W) and pressure (5-50 Pa) are varied [265,295], The probe tip is positioned exactly between powered and grounded electrode, at the center of the discharge. 

Probe measurements in silane discharges have been reported [296,297]. Apparently, no difficulties were experienced, as the deposited amorphous silicon layer on the tip was sufficiently photoconductive. For typical silane discharge conditions values for are found to be between 2 and 2.5 eV. Electron densities are around 1 x 10 cm - [296]. Probe measurement in the ASTER system failed due to strong distortions of the probe current, even after following cleaning procedures. 

The partial pressures of the stable neutral molecules in the discharge (silane, hydrogen, disilane, trisilane) can be measured by a quadrupole mass spectrometer (QMS). The QMS usually is mounted in a differentially pumped chamber, which is connected to the reactor via a small extraction port [286]. In the ASTER system a QMS is mounted on the reactor that is used for intrinsic material deposition. The QMS background pressure (after proper bake-out) is between 10 and 10 mbar. The controllable diameter in the extraction port is adjusted so that during discharge operation the background pressure never exceeds 10"" mbar. 

The ASTER-System (EPA, 1991) provides estimates of chemical properties, environmental fate and toxicity and access to the AQUIRE database. 

FIG. 5. Schematic representation of the ASTER deposition system. Indicated are (I) load lock. (2) plasma reactor for intrinsic layers. (3) plasma reactor for />-type layers. (4) plasma reactor for t -type layers, (5) metal-evaporation chamber (see text). (6) central transport chamber. (7) robot arm. (8) reaction chamber, (9) gate valve, (10) gas supply. (11) bypass. (12) measuring devices, and (13) tur-bomolecular pump. 

The ID fluid discharge model has been applied to the ASTER deposition system (see Section 1.2.4). The deposition reactor has an inner volume of 10 1 and an inner diameter of 20 cm. The upper electrode is grounded (see Fig. 4a), and the powered electrode is located 2.7 cm lower. Other typical silane-hydrogen discharge parameters are summarized in Table IV. 

The SiHa H2 ratio was 20% 80% in all simulations. As most experiments in the ASTER deposition system are performed at a constant total power, the... 

FIG. 40. The influence of deposition temperature on (a) the hydrogen concentration, (b) the microstructure parameter, and (c) the Raman half width P/2. The labels A and P refer to the ASTER and the PASTA deposition system. Series A1 was prepared from a SiH4 H2 mixture at 0.12 mbar. Series A2 and A3 were deposited from undiluted SiHa at 0.08 and 0.12 mbar. respectively. Series PI was deposited from undiluted SiHa. (From A. J. M. Bemtsen. Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands, 1998, with permission.)... 

A systematic study of the role of the ions in the deposition process and their influence on the quality of the layers has been performed by Hamers et al. [163, 301, 332] in the ASTER deposition system. More specifically, a study has been made on the relation between the plasma parameters and the material properties in both the a- and the y -regime at typical deposition conditions. Here, the... 

In the ASTER deposition system, experiments have been carried out in which the excitation frequency was varied between 13.56 and 65 MHz [169]. The other process conditions were kept constant at a power of 10 W, a pressure of 0.16 mbar, gas flows of 30 seem SiHa and 30 seem H2, and a substrate temperature of 250°C. As in Section 1.6.2.3, plasma properties that are deduced from lED measurements are compared with material properties in Figure 63. The lEDs of SiH at four frequencies are shown in Figure 64. 

The plasma potential is about 25 V (Figure 63a). This value of the plasma potential is typical for the silane plasmas in the asymmetric capacitively coupled RF reactors as used in the ASTER deposition system, and is also commonly found in argon or hydrogen plasmas [170, 280, 327]. From the considerable decrease of the dc self-bias with increasing frequency (Figure 63a) it is inferred that the... 

Prototype electrostatic loudspeakers where the graphite is replaced by a-Si H have been made, where a Mylar foil (area 10 x 10 cm-, thickness 6 /im) is used [657]. Deposition of the a-Si H layer was carried out in the ASTER deposition system. Uniform deposition (standard deviation of thickness, 1.5%) was achieved by diluting the SiHa with Ht with SiHa Hi = 1 2 [370]. The deposition was at room temperature. The hydrogen content amounted to 18 at.%, and the bandgap was 1.81 eV. The dark conductivity and AM 1.5 photoconductivity were 7.5 X 10 and 1.8 x 10 cm" , respectively. In practice the film would not... 

Russom, C. L., Anderson, E. B., Greenwood, B. E., Pilli, A. ASTER An integration of the AQUIRE data base and the QSAR system for use in ecological risk assessments. Sci. Total Environ. 1991, 109/110, 667-670. 

Ocean surface temperature AYHRR, ATSR-2/ERS-2, AATSR/ENYISAT, MODIS/ EOS-Terra/Aqua, AMSR-E/EOS-Aqua, OCTS/ADEOS. Spaceborne system EOS/Terra is equipped with radiometer ASTER to measure thermal radiation and its reflection from the ocean surface, spectrometers MODIS and MISRC, as well as MOPITT and CERES instruments to record pollutant and energy fluxes, respectively. 

Bupleurum falcatum (Chai hu plants) is an important tonic herb for the liver and circulatory system of humans and can alleviate hepatitis. Chang et al. (2004) reported aster yellows phytoplasma associated with Bupleurum falcatum plant in Canada. Diseased plants showed resetting, proliferation of auxiliary shoots at the nodes of the stem, witches - broom, virescence and phyllody symptoms. 

J.W. Dolan and L.R. Snyder, Troubleshooting LC Systems, Aster, Chester, 1989. 

Direct irradiation of the silyl ketone (9) affords the products shown in scheme 2. The same products can be obtained on sensitised irradiation. An analysis of the reaction suggests that two reaction paths are operative.The asters (10) are photochemically reactive in methanol. The preference for the reaction paths observed is dependent upon the substituent in the naphthyl ring. Thus with unsubstitution or with a 4-methyl substituent the reaction mode is dominated by C-0 bond heterolysis yielding intermediates from which the ether (11) and the acid (12) are formed. With a 4-cyano substituent the reaction is dominated by C-0 homolysis yielding the alkane (13) as the major product. The introduction of a 3-mathoxy substituent produces a system which is intermediate between the two extremes. 

Even though the flotation process involves three phases and three interfaces, most research work has been solely on the behavior of the solid-liquid interface. This is in spite of the fact that ndsorption at the solid-liquid interface, as shown In Fig. 16,3-10, is of a considerably smaller megnitede than diet at the solid-gas or liquid-gas interface. It is to be noted that excellent correlation has been obtained recently between surfactant ndsorption at the liquid-gas interface and flotation for the hemadte-oleate system (see Fig. 16.3-11). It is also important to note thel the migration of the surf at rent at the liquid-ges interface is faster than its diffusion from bulk to the interface, as least for this system.w Such a migration at the interface can help toward (aster attainment of required surfactant ndsorption density at the solid-gas interface upon the contact of the bubble with the panicle. 

The model is solved numerically by means of the finite element code ASTER. The equations are discretized within a finite element formulation. The time discretization is implicit and the coupling is solved by means of a global inversion of the system, as explained in Chavant (2(X)1). 

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