Scanning Tunneling Microscopy

Scanning Tunneling Microscopy

  • Mohd Qasim added an answer:
    What is the perfect substrate to study gold nanoplates by STM?

    I want to study gold nanoplates by STM and I need to individually disperse on conductive substrate.

    What is the perfect substrate to study gold nanoplates by STM?

    HOPG? Silicon?

    Mohd Qasim · University of Hyderabad

    drop casting or spin coating of Au dispersion on substrate can be used.

    U can Make dilute dispersion of nano materials in some solvent and they put a drop on substrate. Uniformity of film matter. or do a spin coating. 

  • Seyyedali Hosseini added an answer:
    How can I individually dispersed a gold nanoplate on HOPG?

    I want to study Gold nanoplates by STM and I need to individually disperse on conductive substrate similar to HOPG.
    How can I dispersed gold on HOPG?
    Thanks.

    Seyyedali Hosseini · Sharif University of Technology

    Do you have suggestions on coating the nanoplates on the HOPG?

    thanks.

  • Saeed Hasani added an answer:
    How can I calculate the volume of hexagonal structured nano particles?

    From XRD data the nano particle structure is hexagonal. How can I calculate a,c and volume if my two theta value is slightly deviated from standard value?

    Saeed Hasani · Isfahan University of Technology

    The parameter lattice extracted from XRD is associated with the error. Because, the location of peaks is affected by tension or by nano-sized particle.

    TEM and its diffraction patterns is the best method for determine of parameter lattice e.g. a, and c in hcp materials.

    With Bests

  • Ramesh Mohan Thamankar added an answer:
    For a LHe cooled STM sample, what is the temperature right under the tunnelling junction for RT tips?

    Some STM manufacturers propose variable temperature STMs in which the sample is cooled but the tip is not. It is easy to monitor the overall sample temperature, but given that the tip is very close to the sample and at RT, the tip will certainly heat the tunnelling junction area. Would this temperature increase be significant (more than say 5 Kelvin)? 

    Ramesh Mohan Thamankar · Agency for Science, Technology and Research

    if it a perfectly low temperature, that means both the tip-sample are cooled, then the junction temperature should be same as the sample. But if you are using variable temperature STM, then only sample is cooled. Tip is always at room temperature. Thus the junction temperature is not equal to sample temperature. One needs to be careful while mentioning the temperature. It is neither  helium temperature, nor 300K. There was a study done and published in PRL about this. check this for example Phys. Rev. Lett. 105, 166101.

  • Lars Diekhöner added an answer:
    What is the difference between Surface band gap and bulk band gap?

    I want to correlate band gap values got from two technique 

    1) Tauc plot which will give overall band gap

    2) Scanning tunneling spectra (STS) or Scanning tunneling microscopy

    Lars Diekhöner · Aalborg University

    Let me add a comment on STS: In a band gap measurement using STS you can't directly distinguish between bulk- and surface band gaps. 

  • Hubert Klein added an answer:
    What is the current density for atomic resolution in scanning tunneling microscopy?
    If a current of 10 nA passes through the tunneling junction, which may be of atomic size, a simple calculation suggests a local current density exceeding 10^11 A/sq.mtr- which would ablate the sample if the current flow were one-dimensional. I have not seen any analysis considering the effects of current spreading, short-range ballistic transport, nanoscale heat transfer, etc.
    Hubert Klein · CINaM - Centre Interdisciplinaire de Nanoscience de Marseille

    Following the first answer, there is no dissipation in a tunnel junction, as transmission comes from evanescent waves, there is thus no diffusion and nor heating in the junction. Heating, due to electron phonon interactions, can occur in the surrounding of the junction, but not in the junction itself.

    Noteworthy inelastic processes may occur in the junction, leading for instance to radiative emission by coupling to surface plasmons modes, but quantum yeld of such processes are very low (tipycally 10^-7).

    Even in the case of propagating waves, as in metallic point contacts, where the transport is ballistic, electron-phonon interaction length (typically a few tenth of nm) are larger than the size of the junction. Thus, the electrons cannot release heat in the contact, but rather in the macroscopic electrodes far from the contact. I attach a review of that field.

  • Rui Zhang added an answer:
    How can I make a gauge plate for STM?

    I need a calibration (gauge) plate in order to check a scanning tunneling microscope. For that means I would need two atoms isolated from other atoms in an area of 50 nm (or more) radius on a glass plate? These two atoms must be at a distance of 10-30 nm. I will then look to resolve them.

    My questions are:

    1. Do they sell such plates?

    2, If not how to build one?

    I have an idea to dissolve a small amount of say Cu and then dilute to reach 1 atom in 1 ml. Then pour it on a glass plate and dry. Would this give me the gauge needed?

    Rui Zhang · KTH Royal Institute of Technology

    As the former ( above) said, just using the Si(111) of Au(111) surfaces for STM calibration should be more proper and standard.

  • Christian Wagner added an answer:
    During Current-Voltage measurement, the sample bias and the set current, keeps the STM tip-sample separation fixed. How can I measure the separation?
    When we carry out spectroscopy measurement, at first we stop STM. At that time the sample bias and tunneling set current keeps the tip-sample separation constant. As soon as we do the I-V measurement the feedback loop is switched off and the voltage sweeps across the range and corresponding tunneling current is recorded. If you change the sample bias or set current tip-sample separation changes accordingly. So, how can I measure this tip-sample separation?
    Christian Wagner · Forschungszentrum Jülich
    If you mean the absolute tip-sample separation, this is a highly non-trivial issue and notoriously difficult to measure. One can estimate a lower bound for this distance by going into point contact. Since the tip usually elongates under the influence of short ranged forces this method can only provide said lower estimate. It is in general not possible to obtain the distance from the I, V setpoint alone. If you just want to know the relative tip displacement when changing the setpoint, just look at the change in z-piezo voltage and calculate it from the piezo constant. Your STM software might also have a direct readout for this relative displacement.
  • Jimmie Miller added an answer:
    How would a (commercial) STM behave in high vacuum (~10^(-5)Pa)?
    Scanning Tunneling Microscopy (STM) is usually done in UHV (and sometimes in Air). Doing STM in UHV has many advantages but also imposes greater constraints. In some applications, possibly working in HV only could be more advantageous. So, I wonder exactly what one loses by performing STM in HV (apart from no having perfect surface cleanness). Would the current stability (and tip behaviour) be much worse? What drawbacks would high vacuum imply? Please indicate relevant literature on the subject.
    Jimmie Miller · University of North Carolina at Charlotte
    Don't forget that if you use tungsten tips they oxidize faster in HV environments which will change your ability to image. Also attached is a file showing surface degradation of Si before and after six days of UHV (10-11 Torr) from my ancient dissertation which can be found at the attached link
  • sunil kumar Samji added an answer:
    Is it possible to study the local density of states from phase image of tapping mode? If so how can I do it or interpret it?
    In scanning tunneling microscopy (STM) a contrast in image corresponds to variation in local density of states (LDOS). I learnt that phase mapping (image) in tapping mode is very sensitive technique, is it possible to speak about variation in LDOS from phase contrast , if so, how can I understand it, or interpret it?
    sunil kumar Samji · IIT Madras
    Hi, Swaminathan, Vincent and Nicolas Thanks a lot for the answers.
    I am trying to re frame my question, it requires a bit more understanding will get back after that, Thank you
    @ Nicolas: Thank you very much fro the reference will go through it.
  • Rupali G. Mane added an answer:
    Is it possible to measure the work function of a metal surface with adsorbed gas molecules using STM (scanning tunneling microscopy)?
    We are looking for methods to measure the work function of metal surfaces with polyatomic gas molecules.
    Rupali G. Mane · Bhabha Atomic Research Centre
    Thanks to Jaun De Miguel
  • Ali Salehizadeh asked a question:
    Are there any available lab positions for collaboration in SEM and TEM?
    I am a Physics Engineering PhD Student at the University of Aveiro, Portugal, and looking for an expert lab for electron microscopy, preferably in Europe or the US, to do SEM or TEM and publish a paper. I should mention that my sample is iron oxide nano particles embedded in silica shells.
  • Rainer Christoph added an answer:
    What is the best vibration isolation solution for AFM?
    Are the isolation tables using nitrogen or compressed air supply the best? What do you think about the active isolation platforms available from Herzan and Accurion that runs simply on electricity?
    Rainer Christoph · Nanotecnia
    Whilst working with Heini Rohrer and Christoph Gerber, I learnt that when a hanging suspension elongates 25cm under the combined weight of AFM & support platform, the system oscillates with a main resonance frequency of aprox. 1 s-1. This can be calculated and measured.
  • Daniil Bratashov added an answer:
    Why do I get these streaks in the background in all my AFM images on Mica substrate?
    Please see this attached image. I am using tapping mode in air. I have tried different probes, but no help.
    Daniil Bratashov · Saratov State University
    It is harmonic generation with period(s) defined by feedback loop delay and usually it is perpendicular to fast scanning axis (if you clear the highest harmonic from image above, you can see slight vertical lines on Fourier spectrum). Beside this generation, the ill-tuned scanning system can catch another sources of noise (50/60 Hz harmonics from electrical noise, around a 1-3 kHz in acoustic noise from ventilation and electrical from inverter and so on). I have seen up to 5 different noise frequencies in very bad tuned scan in my practice. As noise is sampled with regular interval, it frequency can move to the low freqs. region as difference between sampling and noise freqs. (an so it will appear along slow scanning axis).
  • Gopalakrishnan Ramalingam added an answer:
    Is metal contact between the epitaxial graphene sample and the metal sample substrate imperative in order to take STM images?
    I use a UHV growth chamber for High-T graphitization and the SiC substrate is placed on a metal plate (sample holder). I supposed to transfer the sample into the STM chamber connecting to the growth chamber directly after the graphitization. but i couldn't get stable scan condition, therefore no images. I wonder if it is necessary to make metal contact between the sample and the metal plate(the same sample holder used for graphitization)
    Gopalakrishnan Ramalingam · University of Virginia
    You can use Ag paste in UHV. You just need to pump your sample longer in the loadlock before transferring into the chamber so that the volatiles from the paste are outgassed. We generally outgas our samples overnight to avoid destroying the UHV; try not to use more than necessary. We use Ag paste all the time for good contact between graphite and our Mo-sample plate. Good luck!
  • Meysam Nobakht added an answer:
    Can anyone help me to find a comprehensive review papers about applications of synchrotron?
    I want to know what the advantages are of synchrotron radiation for material analysis in comparison with conventional methods?
    I searched through the internet but I couldn't find anything helpful.
    Meysam Nobakht · University of Isfahan
    thank you dear Timothy Hyde. you help me so much.
  • Sara Ataran added an answer:
    How can I make the thin film top of the surface with STM preparation chamber?
    I used evaporation in preparation chamber, but it was thicker than thin film.
    Sara Ataran · Lund University
    Thank you all for your answers, these are so useful for me.
  • Andrzej Sikora added an answer:
    What are the state of art resolution, operation speed, largest scanable size for main scanning techniques (STM, AFM, TEM)?
    What about the lithography and deposition techniques regarding their resolution, smoothness of surfaces, growth speed, and the largest possible area?
    Andrzej Sikora · Electrotechnical Institute, Wroclaw
    Dear Aref,
    I think that the state of the art in case of AFM is a bit better than Vladimir described. In terms of the resolution, few nanometers may be relatively achieved in the plane, and subnanometer in the vertical scale (please note, that the quantitative height information is delivered only by AFM - the roughness information). But the resolution is also strongly determined by the sample, scanning mode and the settings. The maximum scanning range typically reaches 100 x 100 micrometers in plane and up to 8 micrometers in height.
    There is a significant progress in scanning speed lately. You can purchase the systems allowing to acquire a single image within a minute (at least two producers from USA). It causes however the scanning area.
    I agree with Sridhar, that TEM provides a number of additional analysis. AFM on the other hand also provides imaging of the mechanical, magnetic or electrical properties. Additionally, AFM allows to perform the imaging in the wide range of the environmental conditions (vacuum, gas, liquids, low and high temperatures, magnetic fields). In some experiments its major advantage is the simple preparation (almost none), which would alter the properties of the sample. All those techniques have some potential and in the best solution are used together to provide a complementary source of information as the base on various physical phenomena. So you need to know what your needs are (and the budget, as the prices of the equipment may differ significantly as well).
  • Matúš Dubecký added an answer:
    Does anyone know how Au to Au will be build a schottky contact?
    I have read a artical from Surface Science 600 (2006) 442–447
    which describes that STM tip of Au was used to probe a Au island ,between the tip and island will form a Schottky contact when appropriate gold thickness (such as 0.2nm).
  • Lijo Francis added an answer:
    After a hydrogen molecule, do you think we can see a bigger molecule soon or it is the limit?
    Few days ago, it was announced that researchers in China reported the first visualisation of a hydrogen bond using atomic force microscopy (AFM).In May, Felix Fischer and colleagues at the University of California Berkeley in the US used AFM to image molecules before and after a chemical transformation. The remarkable images showed the formation of covalent bonds in a cyclisation reaction.

    In the latest study to visualise molecules, Xiaohui Qiu and colleagues at the National Centre for Nanoscience and Technology, China, went one step further. They used the same non-contact AFM as Fischer, but instead of looking for covalent bonds they tweaked it to look for weaker interactions.
    Do you think we had reached the limit of magnification or we can see bigger molecule soon?
    http://www.rsc.org/chemistryworld/2013/09/first-pictures-hydrogen-bonds-unveiled-afm
  • A. Bensouici asked a question:
    What are the parameters to be considered in account to obtain accurate results in I-V measurements using home-made STM?
    STM measurements of semiconducting surfaces.
  • Régis Bisson asked a question:
    Can you suggest a power inverter to protect instruments against overvoltage/power-cut without inducing spurious signal in discriminator/electrometer?
    I am looking for power inverter (220V, 50Hz) suitable for protection of sensitive instruments like STM / EELS / AES / QMS (power consumption ~250W) against overvoltage from power-provider and power cut up to 4-5 hours. It should specifically not induce any spurious signal in measurements from discriminators / electrometers when running on battery during a power cut.
    I would very much appreciate any advice and feedback on any devices you may have tried.
  • Joshua S White added an answer:
    How are SDH STM-1 multiplexors synchronized?
    STM-1 synchronization
    How are SDH STM-1 multiplexors synchronized?
    Joshua S White · State University of New York Institute Polytechnic Institute
    To build on what Yaakov Stein said, the Stratum levels are a standard for NTP (Network Time Protocol - See RFC 1305). A Stratum 0 clock uses GPS for synchronism among network elements. Stratum1 servers / network devices get there information from a stratum 0 system and pass it on over the network, and so on for the various levels. Typical SONET networks use a stratum 0 device at their core and source there clocks from it. STM-1 multiplexers rely on the Stratum 1 that results.
  • Berndt Koslowski added an answer:
    Why do we get negative voltages in barrier height images and how to remove them?
    Barrier height imaging is auxilary to scanning tunneling microscope. The barrier height images are collected from lock-in-amplifier. Observation: some times there is an amplitude dampening (of the applied modulation to the z-piezo) in the signal (observed from an oscilloscope) even before it enters the lock-in-amplifier.
    Berndt Koslowski · Universität Ulm
    Since I(z) is strictly monotonic (non-resonant tunneling, no strange effects) sign reversal of the lock-in signal must be an artifact. There are many sources of such artifacts. The most prominent may be scanning too fast such that the tunneling current undergoes changes (feedback too slow). Another source may be time dependent distortions in the tunneling current. Check your tunneling current signal for unexpected changes/distortions.
  • Tanya Dahms added an answer:
    Our AFM does not seem to be working.
    We have an AFM/STM from Veeco. It was working fine but a few days ago we purchased a vibration proof table for it. When it was installed the AFM did not working. It shows a message saying "Invalid floating point operation". Can anyone help us to sort out this problem.
    Tanya Dahms · University of Regina
    Yes, computer. I agree with Peter - contact Bruker - they should be helpful. Good luck!
  • Jagadish Chandra Mahato asked a question:
    During Current-Voltage measurement, the sample bias and the set current, keeps the stm tip-sample separation fixed. How can I measure the separation?
    Actually when we are to carry out spectroscopy measurement, at first we stop STM. At that time the sample bias and tunneling set current keeps the tip-sample separation constant. As soon as we do the I-V measurement the feedback loop is switched off and the voltage sweeps across the range and corresponding tunneling current is recorded. If you change the sample bias or set current tip-sample separation changes accordingly. So, how can I measure this tip-sample separation?
  • Yabin Chen asked a question:
    Is there any simple method to know the Eii value of SWNTs, and the tubes are grown on the surface by CCVD?
    Eii value is one of the most important constant of SWNTs. Normally it can be obtained by RRS and low temperature STM. Are there any other methods?

About Scanning Tunneling Microscopy

A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level.

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