20.500.12556/RUL-173508 Merjenje specifične upornosti s štiri-točkovno in Van der Pauw metodo Measuring resistivity with the four-point probe and the Van der Pauw method Natančno merjenje specifične upornosti v materialih nizke upornosti predstavlja izziv zaradi vpliva parazitnih upornosti merilnih vodnikov in kontaktov. V tej zaključni nalogi opisujem implementacijo, sistematično vrednotenje in uporabo Van der Pauw metode, ki omogoča natančne meritve na vzorcih poljubne oblike. Za ta namen smo v laboratoriju za električne in magnetne meritve na Fakulteti za matematiko in fiziko, Univerze v Ljubljani, razvili in izdelali namenski kabel s preklopno škatlo za merilni sistem QD PPMS® 9T. Sistem smo najprej testirali z meritvami na vzorcih iz aluminijaste folije. Referenčna štiri-točkovna meritev na vzorcu v obliki kvadra je dala specifično upornost ρ(300 K) = 3,1 ± 0,4 μΩ·cm, kar je v skladu z vrednostmi v literaturi. Sledile so meritve z Van der Pauw metodo na petih vzorcih različnih geometrij (kvadrat, krog, grški križi). Rezultati so potrdili veljavnost metode, saj so vse meritve dale med seboj skladne vrednosti specifične upornosti, s čimer smo dokazali neodvisnost metode od oblike vzorca. Preverjeno merilno tehniko sem nato uporabil za preiskovanje superprevodnih lastnosti vzorca niobija z visokim razmerjem preostale upornosti (RRR = 45,26). Pri ničelnem magnetnem polju sem določil kritično temperaturo Tc = 9,250 K. Z meritvami v zunanjih magnetnih poljih do 0,5 T sem opazoval zniževanje kritične temperature in uspešno konstruiral H-T fazni diagram, ki opisuje mejo med superprevodnim in normalno prevodnim stanjem. Delo dokazuje uspešno implementacijo zanesljivega sistema za karakterizacijo električnih transportnih lastnosti materialov. Accurate measurement of specific resistivity in low-resistance materials is a challenge due to the influence of parasitic resistances from the measurement leads and contacts. In this thesis, I describe the implementation, systematic evaluation, and application of the Van der Pauw method, which allows for precise measurements on samples of arbitrary shape. For this purpose, in the Laboratory for Electrical and Magnetic Measurements at the Faculty of Mathematics and Physics, University of Ljubljana, we developed and built a custom cable with a switchbox for the QD PPMS® 9T measurement system. The system was first tested with measurements on samples made from aluminum foil. A baseline four-point probe measurement on a strip-shaped sample yielded a specific resistivity of ρ(300 K) = 3.1 ± 0.4 μΩ·cm, which is in agreement with literature values. This was followed by Van der Pauw method measurements on five samples of different geometries (square, circle, Greek crosses). The results confirmed the validity of the method, as all measurements yielded consistent values for specific resistivity, thereby demonstrating the method’s independence from sample shape. I then used the validated measurement technique to investigate the superconducting properties of a niobium sample with a high residual-resistance ratio (RRR = 45.26). At zero magnetic field, I determined the critical temperature to be Tc = 9.250 K. With measurements in external magnetic fields up to 0.5 T, I observed the suppression of the critical temperature and successfully constructed the H-T phase diagram, which describes the boundary between the superconducting and normal conducting states. The work demonstrates the successful implementation of a reliable system for the characterization of electrical transport properties of materials. specifična upornost Van der Pauw metoda štiri-točkovna metoda meritve nizke upornosti superprevodnost niobij fazni diagram specific resistivity Van der Pauw method four-point probe method low-resistance measurements superconductivity niobium phase diagram true false false Slovenski jezik Angleški jezik Zaključna naloga 2025-09-18 08:15:16 2025-09-18 08:15:21 2025-11-10 03:34:50 0000-00-00 00:00:00 2025 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 153903 250400771 19447.pdf 19447.pdf 1 D9F02D34EDA1DD3F2E76AB47A5C738D7 e701855aec34527787631c1e1dd7b70fdded6140820b2d0564cb87802e1ae8ad ae6e7bdd-9456-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=218023 Fakulteta za matematiko in fiziko 0 0 0