Positivity bias

Figure 14-4. MIS junction under negative and positive bias (a) flat-band, (b) accumulation (l/<0), (c) depletion (l/>0), and (d) inversion (V>0, Ef>E,).

Figure 8-12. Field-induced differential transmission spectra (A7/T)a)/.- for a positive bias of 13 V and different pump-probe delays (front Ref. [401 with permission).

In the case of negative bias, the Fermi level moves closer to the valence band edge. Consequently, the concentration of the majority of carriers (holes) at die insulator-semiconductor interface becomes laiger than in the bulk. This corresponds to the accumulation regime. When a positive bias is applied to die metal, the... 

The first realization of a conjugated polymer/fullerene diode [89] was achieved only recently after the detection of the ultrafasl phoioinduced electron transfer for an lTO/MEH-PPV/CW)/Au system. The device is shown in Figure 15-18. Figure 15-19 shows the current-voltage characteristics of such a bilayer in the dark at room temperature. The devices discussed in the following section typically had a thickness of 100 nm for the MEH-PPV as well as the fullerene layer. Positive bias is defined as positive voltage applied to the 1TO contact. The exponential current tum-on at 0.5 V in forward bias is clearly observable. The rectification ratio at 2 V is approximately l()4. 

To prevent withdrawal of the ions thus produced by penetration of the main accelerating field, either a small positive bias is applied to plate 6 or alternatively (31) the exit slit from the ionization chamber is covered by a transparent wire mesh. The ions are withdrawn from the ionization chamber by a voltage pulse of proper sign applied either to the repeller plate (plate 3) or to the ion withdrawal plate (plate 6). 

We note also that, experimentally, the STM contrast is found to change as much as 0.5 A depending on the applied (positive) bias and specific tips. On these grounds, it is reasonable to expect that different tips would result in scaling factors different from the ones reported in [4]. In this respect, simultaneous AFM and STM of the surface acquire additional importance for the identification of experimental tip structures, and consequently, the scaling factor required to gain quantitative agreement between... 

Table 35-4 reports ANOVA comparing the METHOD B procedure to the METHOD A procedure for combined laboratories. Thus the combined METHOD B analyses for each sample were compared to the combined METHOD A analyses for the same sample. This statistical test indicates whether there is a significant bias in the reported results for each method, irrespective of operator or location. An apparent trend is indicated using this statistical analysis, that trend being a positive bias for METHOD B as compared to... 

The fundamental figure of merit for rectification, the rectification ratio, RR, is defined as the current at a positive bias V divided by the absolute value of the current at the corresponding negative bias —V RR = I(V)/ /(—V) I. Commercial doped Si, Ge, or GaAs pn junction rectifiers have RR between 10 and 100. 

Method 2 in graph (b) shows a constant positive bias compared with Method 1. 

Specificity is the ability to detect only the test substance. Lack of specificity will result in false positive results if the method is qualitative and positive bias in quantitative results. The nature of any interfering substance for particular methods will be discussed in the appropriate sections but it is important to appreciate that specificity is often linked to sensitivity. It is possible to reduce the sensitivity of a method with the result that interference effects become less significant and the method is specific although less sensitive to the test substance. In such a situation false positives (interfering substances) will not occur, but false negatives (undetected low concentrations) may and it is necessary to decide whether maximum sensitivity or specificity is required. 

The use of bromcresol green for the measurement of albumin has been criticized on several counts. There is a tendency for the protein-dye complexes to precipitate at pH 4.2, which is very near the iso-ionic pH of albumin. It is claimed that the method is not absolutely specific for albumin and particularly with serum samples shows a positive bias in results. There is also some variability in the intensity of the colour produced with albumins from different sources, a fact which makes the choice of the standard material important. 

Etching of silicon in alkaline solutions occurs under evolution of hydrogen with a ratio of two molecules H2 per dissolved Si atom. This ratio is found to be reduced under positive bias [Pa6] or by addition of oxidizing agents like H202 [Sc6], If the anodic bias is increased beyond the passivation potential (PP), the dissolution rate is reduced by orders of magnitude. 

The characteristic shape of the anodic voltammogram of a Si electrode in aqueous fluoride media, as shown for example in Fig. 3. Id, is surprisingly stable against changes in fluoride concentration (cF) or pH. When the potential of a p-type Si electrode is swept anodic of OCP a steep current rise near 0 V is observed, followed by a sharp peak (Jj) and a narrow plateau (J2). Then a second broad maximum (Ji) is found around a positive bias of 1.5-2.5 V, followed by a broad plateau (J4) extending over several volts, as shown in Fig. 4.7. When electrode rotation is used, these curves are pen-reproducible for a given solution. The hysteresis of the curves approaches zero for slow sweeps [Ch3]. 

But even in a homogeneously doped material an etch stop layer can be generated by an inhomogeneous charge carrier distribution. If a positive bias is applied to the metal electrode of an MOS structure, an inversion layer is formed in the p-type semiconductor. The inversion layer passivates in alkaline solutions if it is kept at the PP using a second bias [Sm5], as shown in Fig. 4.16b. This method is used to reduce the thickness variations of SOI wafers [Og2]. Illuminated regions... 

Because an infrared result is calculated as if the aromatics in the sample were present in the same ratio as in the calibration standard, accuracy depends on use of a calibration standard as similar to the type of contamination as possible. Use of a dissimilar standard will tend to create a positive bias in highly aliphatic samples and a negative bias in highly aromatic samples. 

In summary, infrared methods are prone to interferences (positive bias) from nonpetroleum sources since many organic compounds have some type of alkyl group associated with them, whether petroleum-derived or not. 

In addition, positive bias is often introduced as a result of (1) product differences in molar absorbtivity, (2) partitioning of soluble aromatics from the bulk... 

Positive bias a result that is incorrect and too high. 

Based on the Bradford HiU criteria, a positive association is indicated if the following criteria are met (1) no identifiable positive bias, (2) possibility of positive confounding considered, (3) association unlikely to be due to chance alone, (4) association strong, and (5) dose-response relationship. 

The CH stretching VCD for (—)-cyclohexanone-2,6-<(2. 23, consists of a number of bands of alternating sign, with an overall positive bias. FPC calculations are in qualitative agreement with part of the VCD in this region. 

VCD in L-alanine-C(3-d3-N-ti3 and the positive bias in L-alanine-V-d3. These two models allow for electronic motion (LMO centroid displacement or charge flow along bonds) in parts of the molecule distant from the primary nuclear motion. The observed and calculated spectra using the LMO model are compared in Figure 13 and an example of the calculated nuclear and LMO centroid displacements are presented in Figure 14 for the methine stretching mode. 

In addition to the VCD from the methine C H stretching vibration, which alone gives rise to a strong positive bias in the CH stretching region, the CH stretching VCD of amino acids contains contributions from two other sources. Minor features can be attributed to combination bands of the very intense antisymmetric carboxylate stretch at 1610 cm with the symmetric carboxylate... 

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