Scanning Tunneling Microscopy

Scanning Tunneling Microscopy

  • Jeffrey J Weimer added an answer:
    In preparation of sample for STM is there any alternative for LB deposition?

    to obtain monolayer of nanoparticles, according to several protocols for preparation of nanoparticles langmuir-schafer technique is used. Due to lack of Langmuir Trough I need to seek alternative. Do you have any suggestion for alternative preparation of sample for scanning tunneling microscopy? 

    Jeffrey J Weimer

    @S Rucman: I do not know the chemistry of your systems. The bonding of nano-particles to the substrate may or may not need to be strong (chemisorption), or it could suffice to be strictly van der Waals (physisorption). Certainly, an atomic force microscope could move phyisorbed nanoparticles around when it would scan in contact mode. Perhaps not at all scanning in tapping mode. An STM has no "lateral force" with particles, so chemisorption should not be needed to scan in this case; just modestly strong physisorption.

    The important point here also is, to distinguish a nanoparticle at 6-10nm diameter on a substrate, you have to see many of them in a sufficient scan range to image with good statistical confidence. That means, imaging at 50-100nm scan range. At this scan size, your substrate needs to have a roughness significantly below the size of the particles, or you will only see the substrate convolved with the particles.

  • Nikolay A Vinogradov added an answer:
    Does anyone know what to do if the probe just doesn't land in STM?

    Calibration sample shows the tip is not broken. But it just never lands on my sample which is semiconducting.

    Nikolay A Vinogradov

    In addition to the above answer, check that there is a good electrical contact between the sample and (its) holder, and tht the sampleholder is inserted correctly in the STM stage. Otherwise, your sample might not be grounded (if the tip is biased in your setup), or there is no net current flowing (if the sample is biased).



  • Ahmed El-barbary added an answer:
    How can the web reinforcement affect on the strut and Tie model?

    while the analysis of deep beams using the strut and tie model , it was sometimes difficult to show the role of web reinforcement. i ask anyone who know how to implemented the affect of web reinforcement in STM analysis?

    Ahmed El-barbary

    Thank you Dr. Ahmed Ramadan for your kindly reply

  • Kun Wang added an answer:
    What kind of molecules dissolved in STM solvent will cause leakage current during STM measurement?

    I want to do some in situ reaction and observe the changes using STM. The reaction will need CuCl and pyridine. I wonder if they would cause leakage current?

    Kun Wang

    Hi, the solvent causing significant leaking current must be something polarized. If you have Cl- ions in the solution, it will for sure induced leakage current. I would suggest you coat the STM tip with insulating wax (e.g., Apiezon Wax), and then you are free to use most of the solvents as long as the solvent does not dissolve the wax.

    Hope this will be helpfully. 

    Good luck. 

  • Margret Giesen 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.
  • Khaled Kaja added an answer:
    What are the proper substrates to use for Peak-force TUNA and Conductive AFM?

    For running Peak-force TUNA and C-AFM, we need a substrate which is conductive enough to pass the current to the sample; however, it should not be too conductive to saturate the current. What do you suggest as a proper substrate?

    Thank you so much for your help in advance. 

    Khaled Kaja


    If the surface of interest or structures on the surface could be connected to ground, your PF TUNA measurements should normally work.

    As an example think of carbon nanotubes on silicon oxide. if the nanotubes are electrically connected to an electrode that you ground, PF TUNA will give you the conductivity of these nanostructures. Current though will then flow through the nanotubes rather than vertically through the silicon oxide substrate. 

    So I would say, as long as you can electrically ground the part of interest on the surface of your sample, the substrate should not matter.

    You could check this application note in the attached link that shows the example that I mentioned in figure 11.

    good luck :)


  • Sujoy Sarkar added an answer:
    Why do I loose the STM image whenever I turn on the cell or run CV during ECSTM ?

    During ECSTM whenever i turn on cell or run CV i loose STM image, it shows that tip is crashed or completely retracted. I cannot have simultaneously STM image and electrochemistry. I am using nanoscope 4.

    Sujoy Sarkar

    Check the controller whether they are synchronized properly or not???

  • Alexander Loskutov added an answer:
    Is there a better approach than the Simmons analysis for MIM diodes having small electrode gaps?

    In 1963 Simmons [1] gave a general expression (Eq. 20) with a separate expression for low voltages (Eq. 24) for the tunneling current in a MIM diode as a function of the applied bias.  These equations have frequently been applied in the analysis of experimental data for MIM diodes as in scanning tunneling microscopy.   Both of these equations fail when the electrode spacing "d" is small, which may be understood because they were derived using the WKB approximation which assumes a quasi-opaque barrier.   As the spacing becomes small Eq. (20) has a change in sign followed by a singularity of order 1/d^2, whereas Eq. (24) has no sign change but a singularity of order 1/d.  Others have used the Landauer formula or other approaches to obtain closed-form expressions for the tunneling current with ultrathin barriers.  I am interested in applications for modeling a STM, and have introduced the spreading resistance of the sample in Eq. (24).   For a tungsten tip and sample I find that a typical spreading resistance of about 300 Ohms, corresponding to the spot size for the tunneling current, avoids the singularity in Eq. (24) and gives I-V curves that are consistent with the observation that the current does not have a dramatic increase in tip-crash.  I question whether it is necessary to simulate the effects of ultrathin barriers because this effect would be dominated by the spreading resistance. My questions are as follows:

    1. Is it appropriate to allow for a spreading resistance, and if so what would be an appropriate spot size?  That is, beyond what radius could we consider only classical transport of electrons within the metal sample of an STM? 

    2. Is it reasonable to consider that adding the spreading resistance to the model  could provide a "patch", as I have suggested, to connect the contact mode (where the tip and sample make electrical contact) to tip-sample distances where the WKB approximation is reasonable?

    I would appreciate any answers, comments, or suggestions.


    [1] J.G. Simmons,  J. Appl. Phys. 34 (1963) 1793-1803.

    Alexander Loskutov

    Very interesting question. Indeed eq. 20 in Simmons article  for ultrathin barriers is not suitable. Two main reasons. The first - the inadequacy of the WKB approximation of the tunneling probability for thin barriers. The reason is that accurate wave function inside the barrier, i.e. in the classically inaccessible region, contains the sum of two exponents - descending and ascending. Usually one always leaves the first descending, but the second ascending for broad barriers neglects. The coefficients in front of them are determined by the usual boundary conditions at the edges of the barrier: the continuity of the wave function and its first derivative. It is important not to confuse the two exponents with the eq. (20), because (20) shows the sum of the currents in the two opposite directions - on the probe with the sample and vice versa, wherein each in WKB approximation. In the exact general expression there should be four such terms. In this case the signs will be all right. Of course, the sign of the current, ie its direction,  is determined by the sign of U. In principle, with one-dimensional approximation for a rectangular barrier, this problem is considered in any good textbook on quantum mechanics (eg Landau). The only problem is that the exact wave function in the probe and, especially in the sample, which should be stapled at the boundaries of the barrier to the sum of two exponents, we do not know. In the probe, according to Tersoff and Haman, it can take as s-wave, ie, decreasing depth probe exponent. As for the sample we must know Bloch functions for surface superstructure, which is practically impossible. Furthermore, in the electric field, these wave functions are deformed, which also must be considered carefully. Therefore, the only way - to use the approximate solutions. Here we come to the second reason - inadequate Simmons  eq.- neglecting the pre-exponential factor, whose influence on the current and the shape of the CVC even more than tunneling exponents. It is easy to see from the eq. for low voltages, in which exponents simply do not contain U, so purely resistive dependence is realized . To learn how you can take into account the pre-exponential factor for the different types of symmetry of surface electronic states – see for example: Journal of Computational and Theoretical Nanoscience . 01/2015; 12 (1-8). DOI: 10.1166 / jctn.2015.4078. If you enter a "spreading resistance" related to the current gathering area - it is possible to take into account the multidimensional problems, but, of course,  the situation with the correct limiting transition to small d does not improve. Coanswer with Arkadii Mandel.

  • Shahnaz Khosravian asked a question:
    Is there any experimental result by STM technique for deposition of oxygen on Cu(111) at 100-190 K?

    Ph.D fellow

    • [Show abstract] [Hide abstract]
      ABSTRACT: The adsorption and dissociation of dioxygen on the Cu(1 1 1) surface have been studied using periodic self-consistent density functional calculations. Two types of di-σ-type chemisorbed molecular precursors are identified: a non-magnetic type located over threefold hollows and a paramagnetic type over bridge sites, both with a binding energy of ca. −0.50 eV with respect to a gas-phase O2 molecule. Atomic oxygen is found to prefer threefold hollows, with a binding energy of ca. −4.3 eV with respect to a gas-phase O atom. Possible pathways for the dissociation of O2 are explored, and the lowest activation energy is calculated to be ca. 0.20 eV. Expansive strain parallel to the surface plane is shown to enhance the binding of atomic and molecular oxygen on the surface as well as to decrease the transition state energy of O2 dissociation.
      No preview · Article · Nov 2001 · Surface Science
  • Ahmad Razmdideh added an answer:
    How can we calculate current of cnt fet with stone walls defect?

    A Stone–Wales defect is the rearrangement of the six-membered rings of graphene into pentagons and heptagons.[ This rearrangement is a result of π/2 (90°) rotation of a C–C bond. The density of Stone–Wales defects is usually small due to the high activation barrier of several eV for the bond rotation. However, the defects has been imaged using scanning tunneling microscopy as well as resonant–vibrational spectroscopy techniques[clarifyA number of theoretical studies have shown that the absorption energies and charge transfer energies for single-walled carbon nanotubes are larger than the corresponding values on pristine carbon nanotubesThe diminished resonance and higher strain energy of this defect increased the probability of nucleophilic attack which provides a possible explanation for the enhanced reactivity. Research has also shown the incorporation of defects along a carbon-nanotube network can program a carbon-nanotube circuit to enhance the conductance along a specific path. These defects lead to a charge de localization which redirects and incoming electron down a given trajectory/as shown as a attachment file

    now how we can calculate current of cnt fet with stone walls defect?

    Ahmad Razmdideh

    tanks my dear zahedi but intrest for me analiticalay calculate with out soft ware.. best regards

  • William Cullen added an answer:
    Is scanning tunneling microscopy in air like "snow plowing" through oxides?

    My simulations suggest that if analog PI or integral (I) feedback control is used a recoverable "tip bounce" is likely to occur. I would expect this problem to be more prominent in air than in vacuum where the sample and tip are both cleaned.  Our by SEM images show marked disfigurement of the tip (like a corkscrew) immediately after measurements in air with a commercial STM.    

    William Cullen

    I think the answer is in many cases "yes".

    I was told many years ago that the conventional wisdom was to avoid tungsten tips for ambient STM work - use Pt-Ir instead. I think your observation of "corkscrewing" the tip is not surprising. The clean gold surface should be robust for ambient tunneling, I think, but probably not the tungsten tip. I would be curious to know if your experiment is possible using Pt-Ir tips without damaging them.

    Simulations involving temporal response of the STM feedback loop (digital, analog, I vs. PI, whatever) may be missing the point here. As pointed out in the replies by Gan and Giessibl, the issue is force at the tunnel junction. Unfortunately, STM feedback has no sensitivity to forces but the forces are there nonetheless. I think it is a question of what forces are involved in bringing the juntion into the required conductance (set by the current setpoint and voltage bias). STM will always drive the tip in until the current setpoint is maintained.
    If the tungsten tip is sufficiently oxidized, then the tip and sample may have to be in mechanical contact before current can flow at, say 100 pA level. If the tip is initially sharp - a high-aspect-ratio needle - then it will almost certainly bend over and curl up under this force. I've seen it many times, even in UHV. But my point is that if a moderately strong repulsive force is needed to establish current flow, then STM feedback won't change the behavior no matter how good it is - AFM feedback should be used instead.

  • Michael Leitner added an answer:
    Is there any commercial AFM that uses piezoelectric cantilever for tapping mode deflection measurements?

    I was wondering if any commercial Atomic Force Microscope (AFM) has been made by any company that only uses piezoelectric cantilevers instead of laser beam sensor for deflection measurement of the cantilever tip.

    Michael Leitner

    There is an Austrian company ( producing and selling self sensing cantilevers based on piezo resistive sensing and thermal actuation. They are especially designed to be used for purposes where laser read out is not possible or where free space above the cantilever is required. For a prototpye this cantilevers have been implemented on a Keysight (Agilent) 5500 AFM at JKU and used for conatct and tapping mode imaging in dry state as well as in liquid. An additional application for this cantilevers comes from GETec ( using them for an AFM-SEM combination by using a special commercial available scanner.

  • 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

    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?

    Seyyedali Hosseini

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


  • 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

    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

    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

    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/ 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

    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

    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
    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.
  • 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
    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
    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
    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
    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
    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
    thank you dear Timothy Hyde. you help me so much.

About Scanning Tunneling Microscopy

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

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