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NPL at the Royal Institution of Great Britain

Graphene and 2D materials

Electrical transport measurements in variable environments

Cutting-edge electronics testing for advanced materials in variable environmental conditions

Hall effect measurements to characterise electrical properties of advanced materials and devices

NPL has electrical measurements services capable of characterising the electrical transport properties: the electrical resistivity (or conductivity), majority carrier type (electrons or holes), charge carrier density and mobility. These measurements can be done in a wide range of conditions:

  • ambient
  • vacuum (down to 10-5 mbar pressure)
  • controlled relative humidity (0 to 80%)
  • over a wide temperature range (2 K to 400 K)
  • controlled gas environment
  • large magnetic field capability (±9 T)
  • DC or AC (up to 100 kHz) electrical excitation.

NPL’s capabilities enable the development and optimisation of new devices to be accelerated, including for environmentally-sensitive applications.

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The measurements can be done using two techniques:

  1. Custom-built electrical transport measurements in variable environments setup (ETMiVE),

  2. Quantum design physical properties measurement system (PPMS).  

Both systems enable:

  • Quick and reliable identification of the electronic properties of continuous films without the need for expensive and time-consuming patterning
  • Monitoring of the electronic properties which are dependent on short- and long-term environmental changes 
  • The response of advanced materials to be monitored as changes are made in environmental pollutants

Electrical transport measurements in variable environments setup (ETMiVE)

The custom-built setup is capable of electrical transport measurements in the following conditions:

  • Ambient

  • Vacuum (down to 10-5 mbar pressure)
  • Controlled relative humidity (0 to 80%)
  • Controlled gas environment
  • Temperature ranging from 300 K to 400 K
  • Magnetic field range of ±25 mT
  • AC electrical excitation (up to 100 kHz)

The electrical transport measurements are automated and can be performed continuously in a fixed or varying environment. Further customisation is possible upon request, such as 2-wire device measurements, DC excitation and mixed gas environments.

 

Measurement chamber (top). Sample holder probing a continuous conductive film (bottom – left) and a microscale device on a chip (bottom – right). The electrical contacts of the microscale device are extended to a chip carrier via wire bonding.

 Measurement chamber. Sample holder probing a continuous conductive film and a microscale device on a chip. The electrical contacts of the microscale device are extended to a chip carrier via wire bonding.

Representative results from a CVD grown graphene film on SiO2 (left) and a water-based conductive ink printed on a glass substrate (right). The environment changes from vacuum to air for the graphene sample (left). The response in the electrical properties is very clear: the sheet resistance drops and the majority carrier type switches from electrons to holes. For the printed ink device, the relative humidity is varied between 80% and 10% (right).  Orders of magnitude change in the sheet resistance is captured as a result. Representative results from a CVD grown graphene film on SiO2 (left) and a water-based conductive ink printed on a glass substrate (right). The environment changes from vacuum to air for the graphene sample (left). The response in the electrical properties is very clear: the sheet resistance drops and the majority carrier type switches from electrons to holes. For the printed ink device, the relative humidity is varied between 80%25 and 10%25 (right). ¬†Orders of magnitude change in the sheet resistance is captured as a result.

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Physical Properties Measurement System (PPMS)

PPMS is able to perform the electrical transport measurements in the following conditions:

  • Temperature ranging from 2 K to 400 K

  • Magnetic field range of ±9 T

  • Low pressure He environment (10 mbar at 300 K)
  • DC and AC electrical excitation (up to 200 Hz)
  • Simultaneous measurements of up to 3 devices

Custom electrical measurements are available by integrating external measurement equipment with PPMS, such as transistor measurements, 2-wire device measurements.

PPMS (left) and its sample holder with a graphene FETs chip (top – right) and a thin film on SiO2/Si substrate (bottom – right)

Representative results from a CVD grown graphene film on SiO2 (left) and a water-based conductive ink printed on a glass substrate (right). The environment changes from vacuum to air for the graphene sample (left). The response in the electrical properties is very clear: the sheet resistance drops and the majority carrier type switches from electrons to holes. For the printed ink device, the relative humidity is varied between 80%25 and 10%25 (right).  Orders of magnitude change in the sheet resistance is captured as a result.

Download this information as a PDF

Measurement chamber. Sample holder probing a continuous conductive film and a microscale device on a chip. The electrical contacts of the microscale device are extended to a chip carrier via wire bonding.

Representative PPMS results: Temperature-dependent mobility for 3 different materials: a graphene Hall bar device (top), a composite film (middle), conductive ink printed on a glass substrate (bottom).

Case study

Validating the effectiveness of shielding and thermal paints at high temperatures and humidity

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Case study

Revealing new markets for graphene sensors

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An unparalleled range of measurements

Capability

ETMiVE

PPMS

Temperature range

300 K to 400 K 2 K to 400 K

Conditions

  • Ambient
  • Vacuum (~10-5 mbar)
  • Controlled relative humidity (0 to 80%)
  • Mixed gas
  • Low pressure He environment (~10 mbar at 300 K)

Electrical excitation

AC (up to 100 kHz) DC, AC (up to 200 Hz)

Magnetic field

±25 mT ±9 T

Simultaneous measurements

1 2 for AC, 3 for DC

Sample dimensions

< 1 cm < 1 cm

Sample type

van der Pauw van der Pauw
Hall bar

Upper R limit

0.1 MΩ 1 MΩ

Lower mobility limit

10 cm2 V-1 s-1 < 1 cm2 V-1 s-1

For van der Pauw measurements:

  • The sample must be homogenous, continuous, and isotropic
  • The thickness must be uniform
  • The film thickness must be known for calculation of the resistivity (conductivity) and volume carrier density.

Applications

The service could support the following applications and sectors:

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Contact our Customer Services team on +44 20 8943 7070