4 Probe measurements on "lifted" nanowires
(Result of the month 09/2005)

Four-probe scanning tunnelling microscope with atomic resolution for electrical and electro-optical property measurements of nanosystems.

We demonstrate a special four-probe scanning tunnelling microscope (STM) system in ultrahigh vacuum (UHV), which can provide coarse positioning for every probe independently with the help of scanning electron microscopy (SEM) and fine positioning down to nanometre using the STM technology. The system allows conductivity measurements by means of a four-point probe method, which can draw out more accurate electron transport characteristics in nanostructures, and provides easy manipulation of low dimension materials. All measurements can be performed in variable temperature (from 30 K to 500 K), magnetic field (from 0 to 0.1 T), and different gas environments. Simultaneously, the cathodoluminescence (CL) spectrum can be achieved through an optical subsystem. Test measurements using some nanowire samples show that this system is a powerful tool in exploring electron transport characteristics and spectra in nanoscale physics.

Image 1: STM image of Boron nanowires; (a) Overview scan showing two nanowires, Iset = 500 pA, Vgap = 300 mV; (b) Zoom-in to the left corner of image (a), Iset = 500 pA, Vgap = 300 mV.

Image 2: Process of hooking a nanorod. (a), (c) and (d) show A-type, B-type and C-type hooks respectively.

Image 3: (a) to (c): The probe with a hook at the end is hooking a nanostick; (d) A nanostick suspended with four probes.

Image 4: (a) A perylene nanostick is suspended with two probes. (b) I-V curve () of the perylene nanostick measured by two probes and I-V curve () of the leak current.

Image 5: The exponential curve shows the electrical conductivity-temperature characteristics of the sample. Image 6: SEM image (a) of ZnO nanostick and CL spectrum.