タイトルまたは説明
We offer Electron Spin Resonance Spectrometer, in recent years
Magnetic Resonance has developed into a very useful and powerful
tool in solid state research. In this method, use is made of the
Zeeman interaction of the magnetic dipoles associated with the
nucleus or electron, when placed in an external magnetic field.
Accordingly, they are identified as NMR (Nuclear Magnetic
Resonance) or ESR (Electron Spin Resonance). This form of
spectroscopy finds many applications in the investigation of
crystal structures, environmental effects, dynamic effects, defects
in solids and in many diverse branches of Physics, Chemistry and
Biology.
Features
- FET based marginal R.F. Oscillator
- Digital display of frequency
- Excellent peaks display
- Digital display of Helmoltz Coil Current
- Compatible with general purpose CRO in X-Y mode
Description of the ESR Spectrometer
A block diagram of the ESR Spectrometer is given below in Fig. 1,
and a brief description follows.
Basic Circuit
The first stage of the ESR circuit consists of a critically
adjusted (marginal) radio frequency oscillator with *-digit
frequency display. This type of oscillator is required here, so
that the slightest increase in its load decreases the amplitude of
oscillation to an appreciable extent. The sample is kept inside the
tank coil of the oscillator, which in turn, is placed in the *0Hz
magnetic field, generated by the Helmholtz coils. At resonance,
i.e. when the frequency of oscillation equal to the Larmour’s
frequency of the sample, the oscillator amplitude registeres a dip
due to the absorption of power by the sample. This obviously,
occurs periodically four times in each complete cycle of the supply
voltage. The result is an amplitude modulated carrier which is then
detected using a FET demodulator and amplified by an op-amp
circuit.
Highly stabilised and almost ripple free power supply for the above
circuit is obtained using an integrated circuit regulator.
Phase Shifter
This can compensate the undermined phase difference which may be
introduced in the amplification stages of the spectrometer and
oscilloscope.
*0Hz Sweep Unit
A *0Hz current flows through Helmholtz coils which provides a low
frequency magnetic field to the sample. As the resonance is
observed at few gauss only, no static magnetic field is
applied.
Oscilloscope (not supplied with the Spectrometer)
Any inexpensive oscilloscope normally available in the laboratory
would be quite suitable.
Advantages and Limitations of our Spectrometer
- The instrument is basically designed for postgraduate
laboratories keeping in view their requirements and
limitations.
- The observation of ESR at low magnetic fields and consequently
in radio-frequency region makes its instrumentation and working a
lot simple and within the reach of a postgraduate students. Good
resonance peaks can be obtained as a class room exercise.
- The spectrometer is complete in all respects including a sample
DPPH (except a CRO).
The experiment is complete in all respect.
