Digital instrumentation

In the past decade there has been an increasing use of digital instrumentation21,22 this involves controlling experiments with a microprocessor inside the instrument or by an external microcomputer. These can also be used for direct analysis of the data obtained. 

Since a digital instrument functions at fixed points, that is discontinuous, any direct microprocessor control of an experiment has to be in steps. For example, a linear sweep appears as a staircase instead of a continuous ramp. To minimize these effects there are two possibilities  

The second of these options, although involving fewer steps, is only now becoming important with the advent of 16-bit and 32-bit microprocessors and microcomputers at reasonably accessible prices. 

Digital instrumentation is especially useful where it is necessary to apply pulses of potential to the working electrode, i.e. a succession of steps, with current sampling (the microprocessor s internal clock is used). There has recently been a lot of progress in this area of pulse voltammetry (Section 10.9). 

Sawyer and J. L. Roberts, Experimental electrochemistry for chemists, Wiley, New York, 1974. 

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Fig. 5.5. Schematic view of the deflection sensing system as used in the NanoScope III AFM (Digital Instruments, Santa Barbara, CA, USA). The deflection ofthe cantilever is amplified by a laser beam focused on the rear ofthe cantilever and reflected towards a split photodiode detector.

Digital Instruments GmbH Janderstrafie 9 68199 Mannheim Germany www.digital-instruments.com STM, AFM... 

It is worth to note that the authors experience has been accumulated working with scanning probe microscopes MultiMode and DimensionSOOO (both products of Digital Instruments/Veeco Instruments) but most of the results and conclusions are also relevant for practical work with scanning probe microscopes of other manufacturers. 

Although A/D interface technology is still widely used, there is a continued push by the pharmaceutical industry towards digital instrument control. Much of this is being driven by two factors information-rich detectors which are more commonplace in today s laboratories, and the regulatory pressure that is associated with electronic records (21 CFR... 

Digital electrochemical noise. The digital Instrumentation used for the noise studies comprised the following ... 

Fig, 19, Differences between noncontact and tapping mode AFM, The signal for the former is dependent on the change in oscillation due to the force gradient, while the latter is dependent on the oscillation change due to the contact, (Courtesy of Digital Instruments, Veeco... 

Fig. 20. Illustration of the actual AFM probe in tapping mode above and in contact with the surface. A laser beam is used to help amplify the change in oscillation. (Courtesy of Digital Instruments, Veeco Metrology Group, Santa Barbara, CA.)...

Dimension 5000 Scanning Probe Microscope Instruction Manual, Digital Instruments, Veeco Metrology Group, Santa Barbara, CA, 1997. 

For example. Park Scientific Instruments, 1171 Borregas Ave., Sunnyvale, California 94089 Digital Instruments, Inc.. 6780 Cortona Drive, Santa Barbara, CA 93117. 

Similarly, STMs are being developed commercially at an astonishing speed. As of summer 1991, over 30 companies have manufactured and marketed STMs and parts. Many beginning companies dedicated to STMs and AFMs are seeing their business expand rapidly. The recent performance of Digital Instruments, Park Scientific Instruments, WA Technology, Angstrom... 

At this writing it is possible to link digital instrumentation with notebook computers and even achieve portability. Developments have been so rapid in this area that it is difficult to imagine what will come next. General-purpose processor-based electroanalytical instruments are now available from Amel, Bioanalytical Systems, Cypress Systems, EcoChemie, Metrohm, Tacussel, and Princeton Applied Research. 

Note that digital instrumentation approximates the linear potential ramp as a staircase waveform [3, 6, 7]. There is a good agreement between the linear and staircase currents for ls/r = 0.25 — 0.30 for reversible processes (with ts being the time between the application of the potential pulse and the current sampling), if the potential step AE is less than 8 mV. 

This nanotransistor is made of two tiny electrodes joined by a carbon nanotube that controls the flow of electric current through the system. (Digital Instruments/Veeco/ Photo Researchers, Inc.)... 

Infrared spectra of the unfilled and filled copolymers were measured using a Perkin-Elmer model 1700 FTIR spectrometer. The 13C CP/MAS NMR measurements were conducted on a Bruker 300 instrument operating at 75.51 MHz. The samples were rotated with a spectra width of 40.0 Hz, the CP time was 5 ms. l3C lI distortionless enhancement by polarization transfer (DEPT) technique was applied for analysis of monomers. The process was performed at 75.51 MHz, rotated with a spectral width of 0.75 Hz and a CP time of 15 ms. Atomic force microscopy measurements were carried out using a Nanoscope Ilia controlled Dimension 3000 AFM (Digital Instrument, Santa Barbara, CA). 

Atomic Force Microscopic images were obtained with a NanoScope III (Digital Instruments, USA) apparatus working in Tapping Mode. Powder samples were prepared by hand pressing using a glass plate. 

A multimode AFM instrument and a NanoScope IV-D3100 (Digital Instruments, Santa Barbara) were operated in the tapping mode. Silicon tips with a radius of 10-20 nm, a spring constant of 30N/m and a resonance frequency of 250-300 kHz were used. 

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