Electrical properties of MoS$_2$ nanotubes

Malok, Matjaž (author), Remškar, Maja (mentor)

The demand for ultra-low-power, high-performance computing devices continues to drive the advancement of electronic technologies. Among emerging materials, molybdenum disulfide (MoS$_2$) has attracted significant attention due to its favorable electronic and quantum properties, particularly when transitioning from bulk to two-dimensional structures. While MoS$_2$ monolayers have been extensively studied, the electrical behavior of MoS$_2$ nanotubes remains largely unexplored. In this work, MoS$_2$ nanotubes in cylindrical and collapsed shapes synthesized via chemical vapor transport are investigated, revealing low defect densities and a continuous chiral interface. The surface morphology of collapsed nanotubes is found to be non-uniform and wrinkled, where elevated regions exhibit higher conductivity than depressed areas. In contrast, the highly curved edges display pronounced conductivity variations, ranging from insulating to highly conductive behavior, suggesting localized electron confinement. Charge injections are shown to significantly modify the surface potential of the nanotubes. Due to the strong anisotropy between in-plane and out-of-plane conductivity in MoS$_2$, injected charge carriers predominantly propagate laterally. However, this transport is influenced by structural imperfections such as defects, edge terminations, and interfacial strain. Additionally, overlapping nanotubes and surface flakes alter local electronic properties through mechanisms including charge trapping, electrostatic gating, and strain-induced scattering. Furthermore, charge injections induce reversible geometrical changes in cylindrical and in collapsed nanotubes. These deformations, observed as helical twisting along the nanotube axis and gradual plastic deformation, are attributed to a rotational component of the inverse piezoelectric effect inherent to chiral structures. The magnitude of this response depends on factors such as nanotube diameter, chirality, and prior charge injection history. Notably, the long-term persistence of these shape changes was observed, which can be attributed to the accumulation of structural defects and the associated strain, potentially enabling memory-like charge confinement. The choice of substrate can shift the work function of MoS$_2$ nanotubes by several hundred millivolts, directly influencing Schottky barrier heights, charge injection, and contact resistance - findings critical for contact engineering and device fabrication. Overall, these findings highlight the importance of nanoscale structural and electrical characterization for understanding and engineering charge transport in MoS$_2$ nanotubes. This insight is essential for the development of defect-tolerant, high-performance devices based on transition metal dichalcogenides.

• Language: English
• Keywords: MoS$_2$, Nanotubes, Collapse, Electrical properties, Surface potential modulation, Piezoelectric effect
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2026
• PID: 20.500.12556/RUL-184225
• COBISS.SI-ID: 283423491
• Publication date in RUL: 02.07.2026

Secondary language

• Language: Slovenian
• Title: Električne lastnosti MoS$_2$ nanocevk

Abstract

Povpraševanje po računalniških napravah z izjemno nizko porabo energije in visoko zmogljivostjo je gonilna sila za nadaljnji razvoj elektronskih naprav. Med perspektivnimi materiali je molibdenov disulfid (MoS$_2$), ki izkazuje ugodne elektronske in kvantne lastnosti pri prehodu iz “bulk” v tanke plasti. Kljub temu, da so plastni kristali MoS$_2$ že obsežno raziskani, ostajajo električne lastnosti nanocevk MoS$_2$ razmeroma slabo raziskane. V doktorski disertaciji sem obravnaval nanocevke MoS$_2$ v cilindrični in sploščeni geometriji, ki so bile sintetizirane s kemijsko transportno reakcijo. Zanje je značilna nizka gostota strukturnih napak in ohranjena zvezna kiralna struktura. Ugotovili smo, da je površina sploščenih nanocevk nagubana, pri čemer so privzdignjeni predeli bolj električno prevodni kot poglobljeni. Močno ukrivljeni robovi izkazujejo izrazite razlike v prevodnosti, od neprevodnih do visoko prevodnih območij, kar nakazuje na lokalno ujetje elektronov. Injiciranje naboja vpliva na površinski potencial nanocevk. Zaradi izrazite anizotropije med prevodnostjo znotraj plasti in pravokotno med plastmi se v MoS$_2$ injiciran naboj širi predvsem lateralno. Vendar pa na lateralno širjenje naboja vplivajo zaključeni sloji, mehanske napetosti zaradi upogibanja slojev in nanocevke ter luske, ki se nahajajo na površini sploščenih nanocevk. Te strukturne nepravilnosti vplivajo na lokalne elektronske lastnosti prek ujetja naboja, elektrostatičnega vpliva in sipanja elektronov zaradi mehanskih napetosti ter posledično pomembno vplivajo na širjenje naboja. Injiciranje naboja povzroča tudi povratne geometrijske spremembe tako pri sploščenih kot ne-sploščenih nanocevkah. Te deformacije, ki se kažejo kot vijačno sukanje vzdolž osi nanocevke in postopna plastična deformacija, pripisujemo rotacijski komponenti inverznega piezoelektričnega efekta v kiralnih strukturah. Izrazitost efekta je odvisna od premera nanocevke, kiralnosti in zgodovine predhodnih injiciranj naboja. Te deformacije so obstojne nepričakovano dolgo, kar razlagamo s kopičenjem strukturnih defektov in s tem povezanih napetosti, kar vodi do spominskega učinka in dolgotrajne spremembe površinskega potenciala. Izbira substrata lahko spremeni izstopno delo nanocevk MoS$_2$ za več sto milivoltov, kar neposredno vpliva na višino Schottkyjeve pregrade, injiciranje naboja in kontaktno upornost – ugotovitve, ki so ključne za kontaktno inženirstvo in izdelavo naprav. Ti rezultati poudarjajo ključno vlogo strukturne in električne karakterizacije na nanometrski skali za razumevanje prenosa naboja in načrtovanje visoko zmogljivih naprav na osnovi dikalkogenidov prehodnih kovin.

• Keywords: MoS$_2$, nanocevke, sploščitev, električne lastnosti, spreminjanje površinskega potenciala, piezoelektrični efekt