Semiconductor-to-metal transition in the bulk of WSe<sub>2</sub>upon potassium intercalation

Ahmad, Muhammad; Muller, Eric A.; Habenicht, Carsten; Schuster, R.; Knupfer, M.; Büchner, B.

doi:10.1088/1361-648x/aa63a7

Cited by 8 publications

(12 citation statements)

References 42 publications

(61 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The fact that those new excitations develop in the energy region of the former band gaps and as a result of the intercalation with an electron donor suggests that they represent charge carrier plasmons and that semiconductor-to-metal transitions have occurred. The same phenomenon has been observed in K-intercalated WSe 2 [73] which is also a native semiconductor. The transition can also be seen in the shift of the Fermi energy in the calculated density of states leading to partially filled conduction bands (see Fig.…”

Section: B Semiconductor-to-metal Transitionsupporting

confidence: 76%

“…Once the whole film has reached the minimum stable concentration, the doping level and the plasmon energy position increase smoothly as more potassium is provided. It is interesting that in contrast to those observations, WSe 2 [73], K x CuPc [105], and K 2 MnPc [106] permit only one particular potassium stoichiometry causing the plasmon peak position to be almost unchanged during the intercalation steps. On the other hand, the metallic TMDCs TaSe 2 , TaS 2 , NbSe 2 and NbS 2 appear to accept any alkali metal concentration [70,71].…”

Section: B Semiconductor-to-metal Transitionmentioning

confidence: 58%

“…We combined the two experimental methods with density-functional theory (DFT) calculations to shed light on the effects of doping on crystal structures, the semiconductor-to-metal transitions, the charge carrier plasmons, and the dimensionality of the conduction bands of the title compounds. This research is a continuation of our previous efforts to investigate the effects of alkali-metal doping on TMDCs via EELS for K x TaS 2 , Na x TaSe 2 , K x NbSe 2 , Na x NbSe 2 [70], K x TaSe 2 [71,72], K 2 WSe 2 [73] and K x MoS 2 [74].…”

Section: Introductionmentioning

confidence: 83%

See 2 more Smart Citations

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Habenicht,

Simon,

Richter

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

We have studied potassium-intercalated bulk HfS2 and HfSe2 by combining transmission electron energy loss spectroscopy, angle-resolved photoemission spectroscopy and density functional theory calculations. The results reveal insights into (1) the intercalation process itself, (2) its effect on the crystal structures, (3) the induced semiconductor-to-metal transitions, and (4) the accompanying appearance of charge carrier plasmons and their dispersions.Calculations of the formation energies and the evolution of the energies of the charge carrier plasmons as a function of the potassium content show that certain, low potassium concentrations x are thermodynamically unstable. This leads to the coexistence of undoped and doped domains if the provided amount of the alkali metal is insufficient to saturate the whole crystal with the minimum thermodynamically stable potassium stoichiometry. Beyond this threshold concentration the domains disappear, while the alkali metal and charge carrier concentrations increase continuously upon further addition of potassium.At low intercalation levels, electron diffraction patterns indicate a significant degree of disorder in the crystal structure. The initial order in the out-of-plane direction is restored at high x while the crystal layer thicknesses expand by 33 − 36 %. Calculations suggest that this expansion reaches its maximum at doping levels of x ≈ 0.25 before it reverses slightly for higher concentrations. Superstructures emerge parallel to the planes which we attribute to the distribution of the alkali metal rather than structural changes of the host materials. The in-plane lattice parameters change by not more than 1 %.The introduction of potassium causes the formation of charge carrier plasmons whose nature we confirmed by calculating the loss functions and their intraband and interband contributions. The observation of this semiconductor-to-metal transition is supported by calculations of the density of states (DOS) and band structures as well as angle-resolved photoemission spectroscopy.The calculated DOS hint at the presence of an almost ideal two-dimensional electron gas at the Fermi level for x < 0.6.The plasmons exhibit quadratic momentum dispersions which is in agreement with the behavior expected for an ideal electron gas.

show abstract

Section: B Semiconductor-to-metal Transitionsupporting

confidence: 76%

Section: B Semiconductor-to-metal Transitionmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 83%

See 1 more Smart Citation

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Habenicht,

Simon,

Richter

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…17 Up to now, there are several reported different methods to induce the semiconducting to metallic phase transition, 18−28 and the most effective one is via the intercalation with alkali metal. 29−32 Specifically, owing to the low electron affinities, lithium 29,30 and potassium (K) 31,32 can serve as strong electron donors for the bulk and 2D material. The metallic phase WSe 2 was reported to transform from a semiconducting phase by lithium and K intercalation, forming a compound as Li x WSe 2 and K x WSe 2 , confirmed by X-ray photoelectron spectroscopy (XPS), 14,15,33 Raman, 14,15,29 scanning transmission electron microcscopy (STEM), 26,34 and electron energy-loss spectroscopy (EELS).…”

mentioning

confidence: 99%

Direct Observation of Semiconductor–Metal Phase Transition in Bilayer Tungsten Diselenide Induced by Potassium Surface Functionalization

Lei

Pan

et al. 2018

ACS Nano

View full text Add to dashboard Cite

Structures determine properties of materials, and controllable phase transitions are, therefore, highly desirable for exploring exotic physics and fabricating devices. We report a direct observation of a controllable semiconductor-metal phase transition in bilayer tungsten diselenide (WSe) with potassium (K) surface functionalization. Through the integration of in situ field-effect transistors, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy measurements, and first-principles calculations, we identify that the electron doping from K adatoms drives bilayer WSe from a 2H phase semiconductor to a 1T' phase metal. The phase transition mechanism is satisfactorily explained by the electronic structures and energy alignment of the 2H and 1T' phases. This explanation can be generally applied to understand doping-induced phase transitions in two-dimensional (2D) structures. Finally, the associated dramatic changes of electronic structures and electrical conductance make this controllable semiconductor-metal phase transition of interest for 2D semiconductor-based electronic and optoelectronic devices.

show abstract

“…21 The ability to store (release) alkali atoms by intercalation (de-intercalation) also makes transition metal dichalcogenides possible electrode materials, both as cathode 22 and anode, [23][24][25] for Li-ion batteries. Electrodonor intercalants promote a structural phase transition from a semiconducting phase to a metallic one, [26][27][28][29][30][31][32][33][34][35] with potential applications in data storage and reconfigurable electrical circuitry.…”

Section: Introductionmentioning

confidence: 99%

Decoupling Molybdenum Disulfide from its Substrate by Cesium Intercalation

Sant,

Lisi,

Nguyen

et al. 2020

Preprint

View full text Add to dashboard Cite

Intercalation of alkali atoms within the lamellar transition metal dichalcogenides is a possible route toward a new generation of batteries. It is also a way to induce structural phase transitions authorizing the realization of optical and electrical switches in this class of materials. The process of intercalation has been mostly studied in three-dimensional dichalcogenide films. Here, we address the case of a single-layer of molybdenum disulfide (MoS 2 ), deposited on a gold substrate, and intercalated with cesium (Cs) in ultra-clean conditions (ultrahigh vacuum). We show that intercalation decouples MoS 2 from its substrate. We reveal electron transfer from Cs to MoS 2 , relative changes in the energy of the valence band maxima, and electronic disorder induced by structural disorder in the intercalated Cs layer. Besides, we find an abnormal lattice expansion of MoS 2 , which we relate to immediate vicinity of Cs. Intercalation is thermally activated, and so is the reverse process of de-intercalation. Our work opens the route to a microscopic understanding of a process of relevance in several possible future technologies, and shows a way to manipulate the properties of two-dimensional dichalcogenides by "under-cover" functionalization.tion is thermally activated, being completed after few tens of minutes at a temperature of 550 K. Above 850 K, deintercalation is efficient and completed within a few tens of minutes.Intercalated cesium forms a a Cs monolayer with an ill-ordered structure compatible with a ( √ 3 × √ 3)R30 • reconstruction with respect to Au(111). We reveal electron transfer from Cs to MoS 2 , modifications of the relative positions of the valence band maxima in MoS 2 , and electronic disorder induced by structural disorder in the intercalated layer. Upon intercalation, MoS 2 is lifted, and adopts an unusually large lattice parameter. Our analysis combines scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED), grazing incidence X-ray diffraction (GIXRD), reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), and angle-resolved photoemission spectroscopy (ARPES) all performed under ultrahigh vacuum, in some cases in operando during intercalation. Further insights are brought by density functional theory (DFT) calculations. MethodsThree ultrahigh vacuum systems were used for our experiments. A first one is coupled to the X-ray synchrotron beam delivered at the BM32 beamline of the ESRF. It has a base pressure of 3×10 −10 mbar and is equipped with a quartz micro-balance and a RHEED apparatus. The second one, at Institut Néel (Grenoble), with a base pressure of 2×10 −10 mbar, is part of a larger ultrahigh vacuum system comprising a STM, a RHEED apparatus, and a quartz microbalance. The samples were prepared in each system before being investigated by RHEED, STM, GIXRD, and XRR. Temperatures were measured with a pyrometer in both systems. Note that the pyrometers and the chamber configurations are different in the two systems, which implies a plausible variability...

show abstract

Semiconductor-to-metal transition in the bulk of WSe₂upon potassium intercalation

Cited by 8 publications

References 42 publications

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Direct Observation of Semiconductor–Metal Phase Transition in Bilayer Tungsten Diselenide Induced by Potassium Surface Functionalization

Decoupling Molybdenum Disulfide from its Substrate by Cesium Intercalation

Contact Info

Product

Resources

About

Semiconductor-to-metal transition in the bulk of WSe2upon potassium intercalation

Cited by 8 publications

References 42 publications

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Potassium-intercalated bulk HfS$_2$ and HfSe$_2$: Phase stability, structure, and electronic structure

Direct Observation of Semiconductor–Metal Phase Transition in Bilayer Tungsten Diselenide Induced by Potassium Surface Functionalization

Decoupling Molybdenum Disulfide from its Substrate by Cesium Intercalation

Contact Info

Product

Resources

About

Semiconductor-to-metal transition in the bulk of WSe₂upon potassium intercalation