Instrument Design

Adam Z. Stieg @ the CNSI - UCLA

| home | back to Research |

Overview | Electrochemical Scanning Tunneling Microscopy ( EC-STM ) / in-situ STM | Instrument Design | Images & Performance | Sponsors, Suppliers, & Collaborators

The major design criteria for an instrument of this type fall into fivemain categories that are addressed in a number of ways.

1. Mechanical stability : Control of tip-sample separation is essential due to the exponential dependence of the tunneling current on barriew width. Since this current is our signal and measurement are carried out with the tip-sample separation commonly maintained on the order of a few Angstroms, stability is of the utmost importance. This is addressed through the selection of the proper materials. The method of tip-sample approach is also important in this regard. Finally, the minimization and/or elimination of externally excited vibrations and acoustic noise serves to enhance the overall stability of the instrument described above.

2. Electronic Noise Reduction : Since our signal is on the order of nanoamperes or less, it is important to isolate the system form any sources of electromagnetic noise coupling, whether from internal or external sources. To address these issues it is important to use low-noise amplifiers and power supplies, minimize ground loops and isolate the system from external sources of EMI. Both the HV amplifiers and I/V converter preamplifier are supplied by RHK Technologies. The bipotentiostat is supplied by Pine Instruments.

3. Tip isolation : The reduction of Faradaic currents at the tip is essential for STM measurements carried out in the electrolytic environment. Common methods of tip insulation include coating the tip with materials such as nail polish or apiezon wax.

4. Environmental Control : Maintanence of a clean and stable environment in which to carryout measurements is the final important consideration. Early success in high resolution imaging was commonly done in the UHV environment in an attempt to isolate the tip and sample as best as possible from contamination and environmental variations such as temperature gradients etc. Hence, the electrochemical cell design & outer casing for the instrument are also important variables.

5. Control Electronics : In its original caoncept, the EC-STM was to be developed alongside a project aimed at writing open source control software developed in house and interfaced with the Signal Ranger DSP board by Soft dB. As this component was not realized due to variables outside my control, I have recently interfaced the STM with the Nanonis Universal Controller.


	Adam Z. Stieg @ the CNSI - UCLA \| home \| back to Research \| Overview \| Electrochemical Scanning Tunneling Microscopy ( EC-STM ) / in-situ STM \| Instrument Design \| Images & Performance \| Sponsors, Suppliers, & Collaborators The major design criteria for an instrument of this type fall into fivemain categories that are addressed in a number of ways. 1. Mechanical stability : Control of tip-sample separation is essential due to the exponential dependence of the tunneling current on barriew width. Since this current is our signal and measurement are carried out with the tip-sample separation commonly maintained on the order of a few Angstroms, stability is of the utmost importance. This is addressed through the selection of the proper materials. The method of tip-sample approach is also important in this regard. Finally, the minimization and/or elimination of externally excited vibrations and acoustic noise serves to enhance the overall stability of the instrument described above. 2. Electronic Noise Reduction : Since our signal is on the order of nanoamperes or less, it is important to isolate the system form any sources of electromagnetic noise coupling, whether from internal or external sources. To address these issues it is important to use low-noise amplifiers and power supplies, minimize ground loops and isolate the system from external sources of EMI. Both the HV amplifiers and I/V converter preamplifier are supplied by RHK Technologies. The bipotentiostat is supplied by Pine Instruments. 3. Tip isolation : The reduction of Faradaic currents at the tip is essential for STM measurements carried out in the electrolytic environment. Common methods of tip insulation include coating the tip with materials such as nail polish or apiezon wax. 4. Environmental Control : Maintanence of a clean and stable environment in which to carryout measurements is the final important consideration. Early success in high resolution imaging was commonly done in the UHV environment in an attempt to isolate the tip and sample as best as possible from contamination and environmental variations such as temperature gradients etc. Hence, the electrochemical cell design & outer casing for the instrument are also important variables. 5. Control Electronics : In its original caoncept, the EC-STM was to be developed alongside a project aimed at writing open source control software developed in house and interfaced with the Signal Ranger DSP board by Soft dB. As this component was not realized due to variables outside my control, I have recently interfaced the STM with the Nanonis Universal Controller.