Opazovanje relaksacije amorfnega stanja v tantalovem disulfidu z uporabo vrstične tunelske mikroskopije

Aupič, Polona (author), Mihailović, Dragan (mentor)

V magistrskem delu predstavimo eksperimentalno opazovanje relaksacije metastabilnega amorfnega stanja v tantalovem disulfidu proti osnovnem stanju, ki je komenzurabilen val gostote naboja. Za opazovanje uporabimo vrstični tunelski mikroskop. Najprej v tem magistrskem delu obravnavamo relevantne teoretične koncepte, kot so stanje vala gostote naboja, polaroni, metastabilna skrita stanja v trdni snovi in hiperuniformnost. V nadaljevanju se posvetimo uporabljeni eksperimentalni tehniki in predstavimo tunelsko vrstično mikroskopijo. Nato opišemo material 1T-TaS$_2$ in njegov ravnovesni fazni diagram, v katerem nastopa več različnih faz vala gostote naboja. Predstavimo metastabilno skrito stanje, ki ga ni mogoče opaziti na ravnovesnem faznem diagramu in ga lahko vzbudimo z laserskim ali električnim sunkom. Bolj podrobno predstavimo metastabilno amorfno stanje in njegove že znane lastnosti. Nato opišemo eksperiment, v katerem smo s pomočjo konice vrstičnega tunelskega mikroskopa povzročili fazni prehod v amorfno stanje, ter opazovali relaksacijo le-tega pri temperaturi 80 K. Amorfno stanje pri tem interpretiramo kot sistem polaronov. Iz analize pozicij polaronov v zaporednih slikah, pridobljenih z vrstičnim tunelskim mikroskopom, sklepamo, da amorfno stanje pri 80K kaže znake relaksacije proti osnovnem stanju. Za oceno življenjskega časa pa bi bile potrebne izboljšave eksperimenta, ki so naštete v zaključku dela.

• Language: Slovenian
• Keywords: 1T-TaS$_2$, val gostote naboj, polaroni, skrita stanja, relaksacija metastabilnega stanja, vrstična tunelska mikroskopija
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2021
• PID: 20.500.12556/RUL-130548
• COBISS.SI-ID: 76518147
• Publication date in RUL: 16.09.2021

AUPIČ, Polona, 2021, Opazovanje relaksacije amorfnega stanja v tantalovem disulfidu z uporabo vrstične tunelske mikroskopije [online]. Master’s thesis. [Accessed 22 March 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=130548

Secondary language

• Language: English
• Title: Observing relaxation of the amorphous state in tantalum disulfide using scanning tunneling microscopy

Abstract

In this thesis we present the experimental observation of the relaxation of the amorphous state in tantalum disulfide towards the ground state, which is a commensurate charge density wave. We use a scanning tunneling microscope for our observations. First we introduce the relevant theoretical concepts, such as charge density waves, polarons, metastable hidden states in solid matter and hyperuniformity. Then we focus on the used experimental technique and present scanning tunneling microscopy. We then describe the material 1T-TaS$_2$ and its equilibrium phase diagram, which includes several charge density wave states. We briefly present the metastable hidden state, which is not present on the equilibrium phase diagram and can be induced by laser or with electric pulses. We present in more detail the metastable amorphous state and its known properties. Then we describe the experiment, in which we created the amorphous state using a scanning tunneling microscope tip, and then observed its relaxation at the temperature 80 K. We interpret the amorphous state as a system of polarons. We analyze the positions of polarons from sequences of images obtained with a scanning tunneling microscope. From this analysis we conclude the amorphous state at 80 K does show some signs of relaxation towards the ground state, but for evaluating its lifetime, improvements to the experiment would be necessary, they are stated in the conclusion of the thesis.

• Keywords: 1T-TaS$_2$, charge density waves, polarons, hidden states, relaxation of a metastable state, scanning tunneling microscopy