Messages

16

General Questions and Answers / Re: conductance-gatevoltage results are in contradict with the experiment ?

« on: July 19, 2012, 11:22 »

Thank you,sir.
 [1]At first I re-calculate your script and get the same plot.
 [2]Then I compare mine setup with yours , finding two big differences:1.In A direction, your boundary condition is [Dirichlet, Neumann], while mine is [Neumann, Neumann]
                                                                                                       2.you get the plot by      append( transmission_spectrum.conductance().inUnitsOf(Siemens) * 1e6 ),    which I don't understand.  while, I get the plot by Analyzer>Analyzers>Conductance>Drop NC files.
 [3]Attached is my script with your setup, and Analyzer--produced plot, the plot have different unit. Please tell where i am wrong in ploting.
 [4]Here is the experiments results  http://quantumwise.com/forum/index.php?topic=1713.0
      As is shown, your calculation is still in contradict with the experiments. This needs more discussion and hope to get more attention.

17

General Questions and Answers / conductance-gatevoltage results are in contradict with the experiment ? 4

« on: July 16, 2012, 05:45 »

I dont know how to insert image(in my computer not on the net).
so I have to attach the conductance--gate voltage plot in experiments independedly.
and this is a related paper for reference: http://www.sciencedirect.com/science/article/pii/S0038109808001178


I do not know what mistake I have made in the calculation,
I guess maybe it is a rather physical problem: the conductance in experiments is conceptually different with the one in ATK?
 
hope to attract more discussion and help me solve the problem.

18

General Questions and Answers / uctance-gatevoltage results are in contradict with the experiment ? 3

« on: July 16, 2012, 05:35 »

zigzag-edged graphene.
attached is the related documents:first,conductance--gatevoltage[-8.0,8.0V]every0.25Va point.
                                                    second,conductance--gatevoltage[-0.1,0.1V]every0.02Va point(in order to make sure the problem is not caused by small density of gatevoltage).
                                                     third,script to calculate the transmission
                                                     forth,gatescan script

19

General Questions and Answers / conductance-gatevoltage results are in contradict with the experiment ?2

« on: July 16, 2012, 05:29 »

armchair graphene
                                                    first,conductance--gatevoltage[-8.0,8.0V]every0.25V a point.
                                                    second,transmission spectrum under +8.0V gate voltage.(different with other gate voltage)
                                                     third,script to calculate the transmission
                                                     forth,gatescan script

20

General Questions and Answers / conductance-gatevoltage results are in contradict with the experiment ?

« on: July 16, 2012, 05:24 »

Graphene was widely studied both on theory and experiments. Most basic experiment properties have been tested by simulations.
   I noticed that conductance-gate voltage is very common in experiments, but little simulation by ATK is researched. So I do a lot of work on it.
   However, the result are in contradict with the experiment results.

In experiments, resistance--gate voltage have almost the same trend as following
I did three series of calculations, bulk graphene, armchair-edged graphene, zigzag-edged graphene.

 bulk graphene
attached is the related documents:first,conductance--gatevoltage[-1.0,1.0V]every0.1Va point.
                                                    second,transmission spectrum under all gate voltage.(interesting to find the gate voltage do not affect bulk graphene)
                                                     third,script to calculate the transmission
                                                     forth,gatescan script

21

General Questions and Answers / Re: what kind of Muti-grid should be choosen when calcult graphene_bulk transmission

« on: June 30, 2012, 03:00 »

when metallic and dielectric region are defined, it seems Neumann condition should be used,then I use Neumann in A,B directions, and Periodic in C direction, however, the result get worse

22

General Questions and Answers / what kind of Muti-grid should be choosen when calcult graphene_bulk transmission

« on: June 30, 2012, 02:57 »

http://quantumwise.com/publications/tutorials/mini-tutorials/167
shows the way to calculate the transmission of grpahene_bulk.
   my question is: when a gate voltage is applied to the graphene sheet, ie, in the spatial region define metallic region and dielectric region, what kind of multi-grid in Poission Solver should be choosen?
   In fact, I have done many on the calculations  to get the right choice, but failed.
Attached are the scripts.

23

Scripts, Tutorials and Applications / Re: Boundary Conditions for above and below the gate for my DEVICE?

« on: June 30, 2012, 02:42 »

I am very interested in this problem as well.
according to  http://quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/chap.transmission_spectrum.html#vnl.transmission_spectrum.save
It seems that the device all have Diriklet condition on C direction, and the metallic and dielectric region needs Neumann condition on A,B direction.

and  I would like to know if the device is constructed wiht graphene sheet (not graphene ribbon as above shows) and spatial region. what would it be?