Transfer line method

At this stage, a technique that would enable independent access to the channel and contact resistances is needed. Such a feature is offered by the transfer line method (TLM) [38-41, 89], a method adapted from a classical technique use to estimate contact resistance, and first developed for the amorphous silicon thin-film transistor [42]. The method consists of measuring the channel resistance for different channel lengths. The measured resistance is actually the sum of the channel and contact resistances. As long as the measurement is performed in the linear regime (small drain voltage) the channel resistance is proportional to L (see Eq. 1) and the width-normalized (Rx W) total resistance is given by ... 

Fig. 6.9. A model for contact resistance. A real device is modeled as an ideal device which exhibits no contact resistance and a contact resistance in series at the source and drain (a). If a longer but otherwise identical device is fabricated, the contact resistance should remain constant, while the ideal transistor scales (b). Comparison of different length devices is the basis for the transfer line method of transistor contact resistance extraction.

This technique can be applied at a range of gate biases and plotted as a function of channel charge density, gate voltage, or applied lateral electric field. Non-linear models have been proposed for the contact resistance as a function of the applied bias (see, for example, [ffS]), which generally assume a Schottky or other diode-like charge injection from the contact into the channel. The transfer line method can also be used to extract a purely empirical model. 

It is of crucial importance that the extracted field-effect mobility and threshold voltage obtained from transistor characteristics are therefore not exclusively channel properties but influenced by the contact formation at the source and drain electrodes. Commonly, the transfer line method (TLM) is used to extract the contact resistance from the OFET current/voltage dependence [69]. The method stems from a conventional technique to estimate contact resistances, and was developed for amorphous silicon TFTs. The prevailing contact resistance is determined by varying the channel length L of the transistor. Since the total resistance is the sum of the channel resistance Vd//d and the total contact resistance R =Ris, +I id), the total resistance 7 tot in the linear region can be written as... 

Manipulations involving materials sensitive to air or water vapour can be carried out by these procedures. Vacuum-line methods make use of quantitative transfers, and P(pressure)-V(volume)-T(temperature) measurements, of gases, and trap-to-trap separations of volatile substances. 

A natural question is just how big does Mq have to be to see this ordered phase for M > Mq. It was shown in Ref 189 that Mq <27, a very large upper bound. A direct computation on the Bethe lattice (see Fig. 2) with q neighbors [190,191] gives Mq = [q/ q — 2)f, which would suggest Mq 4 for the square lattice. By transfer matrix methods and by Pirogov-Sinai theory asymptotically (M 1) exact formulas were derived [190,191] for the transition lines between the gas and the crystal phase (M 3.1962/z)... 

Coupled liquid chromatography-gas chromatography is an excellent on-line method for sample enrichment and sample clean-up. Recently, many authors have reviewed in some detail the various LC-GC transfer methods that are now available (1, 43-52). For the analysis of normal phase eluents, the main transfer technique used is, without doubt, concurrent eluent evaporation employing a loop-type interface. The main disadvantage of this technique is co-evaporation of the solute with the solvent. 

Conditions apparatus, Hewlett-Packard HP5890 equipped with an HP5972 mass-selective ion detector (quadruple) column, PTE-5 (30 m x 0.25-mm i.d.) with 0.25- am film thickness column temperature, 50 °C (1 min), increased at 20 °C min to 150 °C(5 min) and then at 4 °Cmin to 280 °C (30 min) inlet and detector (GC/MS transfer line) temperature, 250 and 280 °C, respectively gas flow rate, He carrier gas ImLmin" injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70eV scan rate, 1.5 scanss scanned-mass range, m/z 50-550. The retention times of benfluralin, pendimethalin and trifluralin are 15.2, 25.1 and... 

Chlornitrofen and nitrofen conditions for GC/MS column, cross-linked methyl silicone capillary (12 m x 0.22-mm i.d., 0.33- am film thickness) column temperature, 60 °C (1 min), 18 °C min to 265 °C inlet, transfer line and ion source temperature, 260, 200 and 200 °C, respectively He gas column head pressure, 7.5 psi injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70 eV scan rate, 0.62 s per scan cycle scanned mass range, m/z 100-400. The retention times for chlornitrofen and nitrofen were 11.8 and 11.3 min, respectively. The main ions of the mass spectrum of chlornitrofen were at m/z 317, 319 and 236. Nitrofen presented a fragmentation pattern with the main ions at m/z 283, 202 and 285. ... 

The polymer/additive system in combination with the proposed extraction technique determines the preferred solvent. In ASE the solvent must swell but not dissolve the polymer, whereas MAE requires a high dielectric solvent or solvent component. This makes solvent selection for MAE more problematical than for ASE . Therefore, MAE may be the preferred method for a plant laboratory analysing large numbers of similar samples (e.g. nonpolar or polar additives in polyolefins [210]). At variance to ASE , in MAE dissolution of the polymer will not block any transfer lines. Complete dissolution of the sample leads to rapid extractions, the polymer precipitating when the solvent cools. However, partial dissolution and softening of the polymer will result in agglomeration of particles and a reduction in extraction rate. 

Parameters influencing the performance of headspace methods include sample preparation, sample temperature, equilibration time, carrier gas pressure, pressurisa-tion time, sampling time and transfer line temperature. For validation of headspace instrumentation, see Kolb and Ettre [207],... 

The temperature of molten polymer process streams is commonly measured using a thermocouple positioned through a transfer line wall and partially immersed in the polymer stream. Process stream temperature measurements that use an exposed-tip thermocouple, however, can be misleading since the temperature of the thermocouple junction is a balance between the heat transferred from the polymer stream and from the thermocouple assembly [39]. Due to the low heat transfer rate between the polymer and the exposed tip and the high thermal conductivity of the thermocouple sheath, the temperatures measured can be different by up to 35°C depending on conditions. Extrudate temperatures, however, can be accurately measured using a preheated, handheld thermocouple probe. This method minimizes thermal conduction through the probe sheath. 

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