STM Blog
(This is a kind of logbook page. You can report daily progress, if you find it relevant for the STM users)
03-02-2006
The RHK SPM 1000 Rev.8E control electronics has been modified in order to reduce the output XYZ, XYZ-offsets voltages from +/- 215V to +/- 140V. This has been done in order to protect scanning tubes thinner than 1mm from being depoled by too high voltages. All the details will be soon uploaded under the RHK electronics wiki page.
06-02-2006
The first RT, on the table, imaging of the topography of a “flat” gold film (res: 256×256). Here after some pictures. Note that the size of such Au islands should be roughly 10-20nm. Note a “tip crash site” in the first image.
07-02-2006
Now the STM is hanging vertical. Other images of the same film.
08-02-2006 and 09-02-2006
STM is cold. Images at 200K (08020634.png) and at 100K (09020602.png).
10-02-2006
Tested small biases (3mV instead of 300mV used for the above pictures). Tested “Vortex” pre-amp. Topographic imaging works well, at small bias, with both pre-amps (“Vortex” and “Oxides”).
Tested IV-spectroscopy: a very large offset on the bias (3mV) prevents full bipolar I-V sweep at small bias 
Check this out!
These images are at small bias (3mV) instead of 300mV used for the previous ones. Used “Oxides” preamp.
These images are at small bias (3mV) and the “Vortex” preamp has been used.
13-02-2006
Are these terraces or artefacts (not enough Z-position resolution)?
I-V spectroscopy, “Oxides” preamp. 5 different I-Vs and the avarage of 8 I-V curves on the same spot. T=190K.
Note the large V-offset (-400mV): check this out!
15-02-2006
STM out. Tested magnet with Cryogenics Limited power supply.
Set Field=2.0 Tesla, Driven mode, OK.
Set Persisten Mode, OK.
Set Field=0.8 Tesla, Driven, OK.
Set Persistent Mode, OK.
Set ZERO.
17-02-2006
Au/Mica (Au-100nm, sputtered by Ruud Hendrikx in the ATC, about 1 month ago).
Images on the table reveal a not so flat sample. Nevertheless on the top of the plateaus the surface is very flat. Unfortunately some 415Hz distorted some of the higher res. images. When the STM was inserted in the cryostat the 415Hz made scanning impossible. Internal mechanical vibration is suspected. Took the STM out.
07-03-2006
Cooled down STM with a Au/Mica sample and using a 0.25mm Titanium spring (“flapper type”), with the fixing screws (4) released up such to have a static friction limit of ~ 30gr. The sample is not great (an image under), but the Z-motor worked down to base T this time. Piezo drive settings: Delta_V=210 Volts, 5 steps + try_for_tunneling_current, tau=200 micro_seconds, parabolic pulse. See logbook for details. Further testing required to prove that the Z-motor really works now with the Ti-spring.
09-03-2006
Cooled down STM, after taking it out to air and changing sample (HOPG, now). The Z motor works again, down to 5K (did not go lower). Here after IV on HOPG, 200K (used “Oxides” preamp.) and dI/dV, showing a ~ 1V semiconducting gap.
03-04-2006
18:15, 7.88 Tesla: The Great White Plume…
12-04-2006
I-V curves on some places of LSMO(62nm)/STO. Magnetic field dependence at RT.
25-04-2006
Cryostat warmed up for Easter. Pumped vacuum spaces last week, precooled with LN2 yesterday.
Today, when expelling LN2 from He-tank the following issue arised: nitrogen gas (in large quantities) was ending up in the helium recovery line (gas meter rotating fast). After a quick debugging I relised the N2 gas was entering the helium recovery line from the λ-plate pumping port. Either there's a hole in the pumping tube of the λ-plate or the nitrogen gas was coming into the line from somewhere else. Phoned to Cryogenic Ltd. (spoked with Mr. Mitchell). He says that an occasional overpressure in the λ-plate circuit (cooling tube/capillary/pumping line) can cause the pumping tube to be pulled down. This causes a gap on the top at the piston coupling, and that's where the gas can go into the line. He says that it should not be any problem to cool down like this. He says that the next time the cryostat is warmed up the insert should be lifted and the joint between the pumping tube and the cooling loop checked.
22-06-2006
Line scan of the superconducting gap of a BSCCO crystal (optimally doped) at 4K.
25-08-2006
Nice results on LCMO/Nb:STO. Shown are AFM and STM topography images and STM conductivity maps for different magnetic fields (in this case: light color=metallic).
28-08-2006
Problems with the magnet power supply model SMS120C. Contacted Cryogenics Ltd. Here is the email about the issue:
Using now SMS80C (max. 80 Amp.) controller from AMC group while waiting for repair of SMS120C.
10/12-2006
Measuring LCMO on NGO (strain free, ~ 50nm). Measurements on insulating NGO substrate are possible. Discoveries:
- Sharp tips are critical requirement for stable and long (2 weeks) measurements.
- If tips are cut lousily (very easy to do that), minitips form, and tunneling from different minitips occurs. This is of course bad for imaging (see tip mirroring features here under) and spectroscopy (noisy and unreliable).
- Tested etched W-tip. Good, but not long lasting (due to oxidation).
- Discovered the “square” or “rectangular” anisotropic growth of LCMO on NGO (and possibly on STO), see images under. Film roughness is high (10 nm or more, data confirmed by AFM).
- Mitra et al. T-dependence of G(0) confirmed, although contamination (condensation of water et al.) makes measurements occasionally less sensitive than in a UHV environment (large tunneling gaps are then required).
05-12-2006
Problems with the He probe of the green cryostat. Probe broken. Contact Cryogenic LTD for repair/new probe on 20-12-2006. Email communication and quotation for new probe (really expensive!!) here under: