Auxiliary plasma sources

In IBAD there is no plasma near the substrate to activate the reactive species so the activation is usually done using an auxiliary plasma source or in a plasma or ion source. 

The plasma can be formed using a number of configurations, as described in Ch. 5. The most common configuration is where an electrically conductive substrate is the cathode. When the substrate or the depositing film is an electrical insulator, the plasma can be formed by making the substrate an rf electrode in an rf plasma system or a pulsed (dc or bipolar) voltage can be used. In some cases, the plasma can be enhanced by an auxiliary electron source or by the electrons used to evaporate the source material. 

The basic set-up and compounds of an ICP-AES and ICP-MS are shown in Fig. 2. The ICP part is almost identical for AES and MS as detection principle. The ICP torch consists of three concentric quartz tubes, from which the outer channel is flushed with the plasma argon at a typical flow rate of 14 1 min-1. This gas flow is both the plasma and the cool gas. The middle channel transports the auxiliary argon gas flow, which is used for the shape and the axial position of the plasma. The inner channel encloses the nebulizer gas stream coming form the nebulizer / spray chamber combination. This gas stream transports the analytes into the plasma. Both the auxiliary and the nebulizer gas flow are typically around 1 1 min-1. The plasma energy is coupled inductively into the argon gas flow via two or three loops of a water-cooled copper coil. A radio frequency of 27.12 or 40.68 MHz at 1-1.5 kW is used as power source. The plasma is... 

In this method the soil sample is dried overnight at 85 °C and ground into an homogeneous mixture. A 1 g soil sample is placed into a beaker and 10 ml of concentrated nitric acid added. The solution is heated to dryness and 5 ml of concentrated nitric acid is added. The uranium is redissolved in 5 ml of 8 N nitric acid and diluted to 25 ml with distilled water. The inductively coupled plasma mass spectrometry system used was an ELAN Model 250. The ion source consists of a modified plasma Thermal Model 2500 control box. The forward power was set at 1200 W with the plasma flow, auxiliary flow and nebuliser pressure set at 131/min, 1.0l/min and 0.27 MPa, respectively. The focusing lenses B, El, P and S2 are set at +5.3 V, -12.5 V, -18.0 V and -7.6 V, respectively. The m/z238 ion was monitored for two sec-... 

This chapter also deals with various types of auxiliary devices used in flow systems including power sources for general purposes and light somces, electronic circuits for controlling solenoid valves, peripheral instruments such as inductively coupled plasma mass spectrometry (ICP-MS) or gas chromatography (GC), and amplifiers. The devices described here have been of great help in constructing our own flow systems. 

Typically, an ECR discharge is established at 1 kW, 2.45 GHz, 800-1000 gauss, and O.l-lOmTorr gas pressure with an electron density of lO -lO electrons/cm and a self-bias (plasma potential) of 10-20 volts in the remote substrate position. Auxiliary magnetic fields may be used in the vicinity of the substrate to increase plasma uniformity over the substrate surface. The ECR sources suffer from the difficulty in scaling them up to large-area sources. 

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