edfas.org 1 1 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 25 NO . 1 1. 2KScanWave: sMIMoperated in a dry or liquid cryostat withaheliumexchangegas sampleenvironment. Thebase temperature can reach below 2 K and the system can be operated up to room temperature (300 K). 2. mKScanWave: sMIMoperated inadilution refrigerator. The base temperature can reach below 100 mK and the system can be operated up to 300 mK. 3. UHV ScanWave: sMIM operated in a low temperature, UHV environment. The base temperature can reach be- low500mK and operates up to room temperature (300 K). The sample ismeasured in UHVwith in-situ sample transfer capability. Figure 4 shows the components and wiring of the 2K LT ScanWave system. A low temperature AFM with an sMIM probe interface module is integrated in a cryostat and a laser interferometer is used to detect the cantilever deformation for topographic feedback. The front-end electronics are installed in the cold chamber to minimize noise that may otherwise enter the system from the long wiring required to reach the room temperature part of the electronics. The LT sMIM systems comewith an option to install solenoid magnets or vector magnets that can reach up to 12 Tesla for testing samples under magnetic fields. To reach sub 100 mK, dilution refrigeration is used as shown in Fig. 5a. The insert shown in Fig. 5b holds the AFM stage and ScanWave probe. The probe is inserted, and the sample is mounted on the AFM stage in air and at room temperature before loading the insert from the top. A sample with an array of thin aluminum rectangles surrounded by dielectric was imaged at 90 mK as shown in Fig. 6. The measurement conditions were: 10 µm scan width, 500 nm/s scanning speed, and -10 dB microwave power. The native oxide on the aluminumplate has a different dielectric k-value than the surrounding silicon dioxide and this is imaged with high contrast (hundreds of millivolts, Fig. 6, middle) in the capacitance signal indicating that very high sensitivity is achievable at sub 100 mK. CASE STUDIES QUANTUMWELL DEVICES In the study of quantum spin Hall effects in HgTe quantum wells, modeling predicted that the edge conductivity would disappear once an applied magnetic field reached 3.8 Tesla. However, sMIM images (Fig. 7b and c) taken at a temperature of a few Kelvin and varying magnetic fields demonstrated that the edge conductivity continued to persist well above 3.8 Tesla and even above 9 Tesla.[8] It took an even higher magnetic field for the edge conductivity to become insulating, which indicates that the model did not accurately represent the behavior of this device. PHASE TRANSITION IN MANGANITES Manganites are known to have complex phase diagrams andwhenobserved at themacro scale, twoormore phases can appear to co-exist. Using sMIMat temperatures fromabout 15 K to 250 K andmagnetic fields up to 9 Tesla, conductivity mapping of Nd1/2Sr1/2MnO3 thin films grown Fig. 5 mKelvin system images (a) dilution refrigeration and (b) insert with AFM and ScanWave probe. (a) (b) Fig. 4 Diagram of the 2K LT ScanWave system.
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