Schematic drawing of the SGM suspended from the mixing chamber plate.
(a) Photo of the SGM mounted on the mixing chamber plate of the CF650 dilution refrigerator. (b) Photo of the scanning stage mounted at the bottom of the cold finger. The sample is seated facing down in the chip socket, and the tip rests on top of a stack of coarse steppers and a piezo scanner.
Cooling power versus temperature for the mixing chamber and the scanner. The cooling power at the scanner is reduced as a side effect of mechanically decoupling the scanner from the pulse tube. A fit to the predicted quadratic dependence of cooling power on temperature is plotted along with experimentally measured values.
Photographs of assembled tuning fork cantilevers. (a) Top view of the tuning fork anchored to a sapphire disk with silver contact pads. (b) Top view of the cantilever and tip epoxied to the end of the tuning fork with a Ti/Au evaporated trace to make electrical contact to the tip.
Vibrations in the vertical direction on the mixing chamber plate as measured with a geophone at room temperature. Harmonics of the pulse frequency (1.40 Hz) are clearly visible in the spectrum when the pulse tube is on.
Vibrations in the vertical direction on the mixing chamber plate and spring stage with the pulse tube on at room temperature. Above 10 Hz, there is a significant attenuation of the pulse tube harmonics at the spring stage.
Tip-sample vibrations while scanning at 15 mK. The integrated RMS vibration between 1 Hz and 1 kHz at 15 mK is 2.1 nm.
Example topographic and gate scans. (a) Optical image of a device based on a GaAs/AlGaAs bilayer 2D electron system. 27 The active region of the device lies between the source and drain gates where the 2D-2D tunnel conductance is measured. (b) Topographic image of the region outlined in yellow in (a). (c) Virtual scanning tunneling microscopy (VSTM) image of the region outlined in red in (b). The change in tunnel conductance with oscillating tip height is plotted in the image. The tip was held 300 nm above the device with a 30 nm RMS oscillation and −6 V applied to the tip.
Low temperature RF filtering and heat sinking stage. (a) The lower half of the stage contains Eccosorb foam for filtering above 1 GHz. Multipole discrete RC filters mounted on sapphire provide heat sinking in the upper half of the stage. (b) Close-up image of the RC filters mounted on sapphire. The sapphire is anchored to the box with two brass screws that also provide ground contact for the RC filters.
Attenuation of the RF filtering stage versus frequency. The measured response is plotted as points and the predicted response is plotted as a solid line, which accounts for parasitics of discrete components.
Coulomb blockade thermometry on a quantum dot. Differential conductance versus plunger gate voltage at zero source-drain bias is plotted along with a fit to Eq. (1), which gives an electron temperature T e = 45 mK. The inset is a plot of differential conductance as a function of plunger gate voltage and source-drain bias. A fit to the slope of the Coulomb diamond gives α = 0.097.
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