Thermal switching of the electrical conductivity of Si(111)()Ag due to a surface phase transition

Abstract

The temperature-dependent surface conductivity of the Si(111)([Formula: see text])Ag surface was measured using a microscopic four-point probe. The conductivity was found to undergo a sharp increase of about three orders of magnitude when the system was heated above about 220 K. This strong conductivity change is reversible and attributed to the phase transition which is generally believed to occur on this surface. It is also shown that, in order to find the true surface conductivity, it is necessary to separate it from the contribution of the bulk and space charge layer. In this work, this is achieved by using a finite-element model. A percolating network of Ag islands on Si(111) was also studied and a much simpler behaviour (compared to that of Si(111)([Formula: see text])Ag) was found. The temperature-dependent conductivity of this system was found to display typical metallic behaviour. The absolute value of the conductivity is comparable to the value expected by modelling the Ag film as exhibiting the bulk Ag transport properties.

The conductivity of Bi(111) investigated with nanoscale four point probes

“…Further details of the probes with the ultrahigh vacuum instrument and measurement procedure can be found elsewhere. 20,23,24 In order to vary the contact spacing, two different techniques are employed. First, since each monocantilever probe has 12 contacts and since only 4 are required to perform the conductivity measurement, the contact spacing can be changed by simply selecting different contacts.…”

“…20 Four point probes have successfully been used to determine the surface conductance of semiconductor surfaces for cases where the conductance of the space charge layer and the bulk are negligible compared to that of the surface. [21][22][23][24] If the goal of the experiment is to determine the conductance due to the surface states of Bi, the best approach for doing this is to use a Bi single crystal as a sample, not a thin film with concomitant problems of quantum size effects and carriers induced at the film-substrate interface. We therefore performed our measurements on the ͑111͒ surface of Bi for which the electronic structure and even the lifetime of the surface states are well known.…”

“…We therefore performed our measurements on the ͑111͒ surface of Bi for which the electronic structure and even the lifetime of the surface states are well known. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] growth direction for thin films. Our findings have direct relevance for the study of the semimetal to semiconductor transitions in these films.…”

A complementary metal-oxide-semiconductor compatible monocantilever 12-point probe for conductivity measurements on the nanoscale

“…Four-point probes have been scaled down to sizes of a few micrometers 2 and applied for investigations on a wide range of materials. [3][4][5] The standard microscopic four-point probe, which consists of four individual Au-coated SiO 2 cantilevers, cannot meet the recent demands of the semiconductor industry for small pitched complementary metal-oxide-semiconductor ͑CMOS͒ compatible probes. In order to meet the criteria of CMOS compatibility, the probes cannot contain metals or silicides with high mobility, since such materials could greatly affect the properties of the investigated samples.…”

“…Measurements in ultrahigh vacuum were performed using a system in Aarhus. 3 The Bi͑111͒ surface was prepared in situ by repeated cycles of Ar ion bombardment and annealing to 150°C. The surface order was checked using low energy electron diffraction.…”