Advanced Spectroscopy

The section on "Normalization of spectroscopy data" describes the basic commands involved in analysis of the spectroscopy. However, in some situations more advanced commands may be needed. For example, consider the situation in which one wants to average together spectra acquired with the SAME voltage parameters but DIFFERENT delta-z parameters. In that case, one should normalize each data set to constant-z (using a measured value of the inverse decay length, kappa), than average together the data sets. In the example below, this constant-z data in then output (for plotting on a logarithmic scale). Alternatively, one could do the same procedure on both the current and conductance, and then perform normalization of the spectra in a manner appropriate for constant-z data.

in
011222.145	;first set of conductance data
hyst
50
av/b
4
2
su		;sum into a FIRST buffer
1
su
2
in
011222.147
hyst
50
av/b
4
2
su
2
in
011222.150
hyst
50
av/b
4
2
su
2
in
011222.152
hyst
50
av/b
4
2
su
2
su		;compute the average of FIRST buffer
3
ze		;subtract zero level
-0.05,.4
2
norm		;get correct absolute magnitude
0,7.e-3
z1		;normalize to constant z
0.6666
s2		;sum into a SECOND buffer
1
s2
2
in		;second set of conductance data
011222.156
hyst
10
av/b
4
2
su		;sum into the FIRST buffer
1
su
2
in
011222.158
hyst
10
av/b
4
2
su
2
in
011222.164
hyst
10
av/b
4
2
su
2
su		;compute the average of FIRST buffer
3
ze		;substract zero level
-0.05,.4
2
norm		;get correct absolute magnitude
0,7.e-3
z1		;normalize to constant z
0.6666
s2		;sum into SECOND buffer
2
s2		;get average of SECOND buffer
3
ou/vd
61_200bc.con1
61_200bc.con2
pl
qu

New commands in the above, and others, are described below:


Sum2
arguments: action (integer)

For computing the average of several data arrays, in a separate data buffer than that used in the SUm command. For action=1 will initialize the auxiliary array into which the subsequent values are summed (NOTE: this action=1 command must be issued after the first array is INput, since only then does the program know how large to make the auxiliary array). For action=2 will sum into the auxiliary array the contents of the data array, and for action=3 will compute the average of all the summed arrays (i.e. divide by the number of summed arrays) and that result is put back into the main data array.


Znormalize1
argument: kappa (real)

Normalizes data acquired with a V-shaped type of z(V) curve, by multiplying the data by exp(-2*kappa*z(V)) where z(V) is known from the header of the spectroscopic data file.


DidV
argument: action (integer)

This is a general purpose spectroscopic analysis command, whose performance depends on the value of action:

action=1
input current vs voltage data into a temporary data array.
action=2
input conductance vs voltage data into a temporary data array.
action=3
input delta-z vs voltage data into a temporary data array (it may be necessary to generate this curve, which can be done with the ZGen command).
action=4
compute the logarithmic derivative, (dI/dV)/I. From this quantity one can derive values of kappa as a function of voltage.
action=5
derive values of kappa as a function of voltage. Before this command is executed one must have used the DidV command with all of the action values of 1, 2, 3, and 4. The kappa values thus generated can be plotted, or listed, to obtain an average value. (For plotting it may be necessary to limit, i.e. clip, the observed values, which can be done with the MOD/z command).

other specialized action values of 6-12 are available, but their functions are not listed here.


ZGenerate
arguments: none

Generates a z(V) curve, based on the header of the spectroscopic data file.