Dell 3100 Especificaciones descargar pdf (Pagina 208)

Scanning Tunneling Microscopy (STM)

Troubleshooting Operation of STM

188 Dimension 3100 Manual Rev. D

A comparison to STM imaging reveals two somewhat conﬂicting requirements. As a good starting

point, the sample and tip should produce consistent STM images. The images should repeat well

from frame to frame and be fairly free of noise or areas on the surface that appear unstable. For

current-versus-voltage type plots, the spectroscopic plots may be nice and smooth and repeat well,

but switching back to the STM imaging mode reveals images which are quite noisy. This can be

attributed to the fact that the quality and uniformity of the tip is probably more critical for imaging

than for making the rather simple spectroscopic plots. This is generally not true for the I vs. S plots.

Some general recommendations for acquiring spectroscopic plots are:

1. Low settings for the Integral gain are preferred. Since the tip is not tracking any topography,

the lower gains are acceptable and tend to make the plots more stable.

2. The maximum input range of ±100nA on the NanoScope with the standard preamps will

restrict the current-versus-voltage plots.

3. The spectroscopic functions do not adjust for any loss of bias voltage due to IR losses caused

by the input impedance of the preamplifier. This has different effects for the STS i(v) and

STS i(s) functions which are discussed individually below:

STS i(v)

The spectroscopic plots do not correct for reductions in bias voltage caused by the preampliﬁer,

which for current-versus-voltage is typically small, anyway. For example, a 1V scan on the bias

voltage, producing a 50nA response in the tunneling current would have a 5 percent error at the

extremes of the scan (50nA x 1 MΩ = 50mV or 5 percent of 1V).

Input impedance of the preampliﬁer leads to reduced bias voltages at increased tunneling currents.

This effect can cause the I vs. S plot to be inaccurate. For example, a bias voltage of 20mV will

restrict the upper limit of the tunneling current to 20nA since that level of current would effectively

reduce the bias voltage to zero. Even before the tunneling current gets to 20nA, the reduced bias

voltage will make the measured current appear lower than it should be for a given tip height.

11.5 Troubleshooting Operation of STM

This section addresses errors or malfunctions encountered during the operation of the STM.

11.5.1 Head and Microscope-Related Problems

This section deals with problems related to the scan heads or the microscope. If a problem exists

with a scan head, try a second one under the same conditions, if possible. Otherwise, the following

list of symptoms and cures may be helpful:

1 2 ... 203 204 205 206 207 208 209 210 211 212 213 ... 375 376

Sin comentarios

Dell 3100 Especificaciones Pagina 208