Our laboratory has several equipment to perform electrical transport measurements under different conditions of temperature, magnetic field, frequency and different ranges of resistance, both in macro and micro and nanoscopic samples.
- Magnetotransport with rotating field
- Magnetotransport with high fields
- Seebeck effect, high and low electrical resistance and capacitance
- High electrical resistance and pyroelectric currents
Magnetotransport with rotating field
This equipment allows electrical resistance measurements of conductive samples as a function of temperature, magnetic field and field angle with respect to the sample. It has a Janis SVT300 cryostat with optical window that allows regulating the temperature between 4K and 300K, and an electromagnet that reaches fields of ±1.2 T. This equipment is particularly useful if you want to have fine control of the magnetic field at low fields. The electromagnet is mounted on a rotating platform that rotates manually with a precision of 1º. The electrical transport measurements are performed with a Keithley 6220 precision current source and a HP34401A multimeter.
Note: Currently and until further notice, the equipment works only between 77K and 300K.
Magnetotransport with high magnetic field
This equipment is used to obtain electrical resistance measurements of conductive samples depending on temperature and magnetic field. It has a Janis cryostat with a superconducting magnet, which allows regulating the temperature between 4 K and 300 K and reaching ± 9T magnetic fields. The measurement of electrical transport are performed with a Keithley 220 current source and an HP 34420A nanovoltmeter. For capacity measurements, an Andeen Hagerling 2500A 1kHz ultra-precision capacitance bridge is used.
Seebeck effect, high and low electrical resistance and capacitance
In the Magnetic Resonance Laboratory there is a multipurpose equipment which has a cryostat and an oven, which allow experiments to be carried out at temperatures between 4 K and 500 K. It is equipped with two sample sample holders prepared for conductive systems or high resistance (up to 1011 Ω). To measure the Seebeck effect, it has two LakeShore 330 temperature controllers and an HP 34420A nanovoltmeter. For electrical resistivity measurements, they are made with a “home made” source (0.1 mA-100 mA) and the same nanovoltmeter. For temperature-dependent capacity measurements, an Andeen Hagerling 2500A 1kHz ultra-precision capacitance bridge is used. The combination of measures of Seebeck effect and electrical resistivity can be useful to describe the mechanisms of electrical transport, polaron detection, influence of chemical disorder, etc
High electrical resistance and pyroelectric currents
This equipment has a cryostat that allows experiments to be carried out at temperatures between 4K and 300K. It is equipped with a sample lance prepared for high resistance systems (up to 1011 Ω). For high electrical resistivity measurements are made with a Keithley 6221 current source and a Keithley 6517A electrometer. For pyroelectric current measurements, the same electrometer is used.
This equipment consist of an impedance analyzer (Agilent 4294A), a cryostat and an oven, which allow characterizing the impedance of macroscopic samples as a function of temperature (between 100 K and 1000 K) and frequency (between 40 Hz and 110 MHz). In addition to frequency dependence, it is possible to perform measurements as a function of excitation amplitude (between 5 mVrms and 1 Vrms) and bias voltage / current (from 0 to 40V and 0 to 100 mA).
For low temperature measurements (100 K – 320 K), it is pssible to use a LakeShore DRC-91CA temperature controller and a cryogenic head that is inserted into a thermos filled with liquid nitrogen. In the high temperature range (300 K – 1000 K), the set-up has a Delta DTB4848 controller and the temperature measurement on the sample is carried out with an R/S thermocouple and an temperature controller Omega CN3201 model.
The nanomanipulator consists of a stage that operates within a SEM microscope chamber, equipped with 4 small robotic arms (based on picomotors and actuators) alternately controlled by a joystick. 4 tungsten probes can be brought close to the object and moved it with an accuracy of 5 nm. The scanning electron microscope allows the image of the object and of the work carried out with the tips to be obtained simultaneously and in real time. A Keithley SCS 4200 electrical characterization device with resolution in the range of fA and nV at 100 mA is connected through pass-through connectors, allowing the measurement of resistances up to Tohm and I-V curves. The tungsten tips (around 50 nm-radius) allow to touch and measure the electrical properties of different nanostructures: nanotube, sphere, bar, etc. The sample temperature can be varied in the range -50 °C to 150 °C. This equipment allows the specific study of the contribution to the electrical resistance of grain edges, nanostructures and electrode/material interfaces to study the existence of physical barriers (Schottky or tunnel type) that cause non-linear phenomena in electrical conduction.