A new alloy for Al-chalcogen system AlSe surface alloy on Al 111 En-Ze Shao Kai Liu Hao Xie Kaiqi Geng Keke Bai Jinglan Qiu Jing Wang

2025-04-30 0 0 991.43KB 15 页 10玖币

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A new alloy for Al-chalcogen system: AlSe surface alloy

on Al (111)

En-Ze Shao#, Kai Liu#, Hao Xie, Kaiqi Geng, Keke Bai, Jinglan Qiu, Jing Wang,

Wen-Xiao Wang* and Juntao Song*

College of Physics and Hebei Advanced Thin Films Laboratory, Hebei Normal

University, Shijiazhuang 050024, China

ABSTRACT Metal chalcogenide is a promising material for studying novel

underlying physical phenomena and nanoelectronics applications. Here, we

systematically investigate the crystal structure and electronic properties of the AlSe

surface alloy on Al (111) using scanning tunneling microscopy, angle-resolved

photoelectron spectrometer, and first-principle calculations. We reveal that the AlSe

surface alloy possesses a hexagonal closed-packed structure. The AlSe surface alloy

comprises two atomic sublayers (Se sublayer and Al sublayer) with 1.16 Å along the z

direction. The dispersion shows two hole-like bands for AlSe surface alloy located at

about -2.2 eV, far below the Fermi level, which is sharply different from other

metal chalcogenide and binary alloys. These two bands mainly derive from the in-plane

orbital of AlSe (px and py). These results provide implications for related Al-chalcogen

interface. Meanwhile, AlSe alloy have an advantage of large-scale atomic flatness and

a wide band gap near the Fermi level in serving as an interface for two-dimensional

materials.

INTRODUCTION

Transition metal dichalcogenides (TMDCs) combined with transition metals, like

Mo or W, and chalcogen elements, such as S, Se, or Te, have emerged as promising

materials for diverse applications ranging from optics, nanoelectronics, sensing, and

others. TMDCs include several materials with semiconducting and metallic properties.

Semiconducting TMDCs like MoS2 could serve as many high quantum efficiency

optoelectronic and valleytronic devices 1-3. The metal TMDCs such as NbSe2 and TaSe2

have attracted immense attention due to rich physical properties (superconductivity,

charge density wave (CDW), etc) 1, 4-7.

Other than metal dichalcogenides, metal monochalcogenide alloys are also

emerging, such as CuSe, AgTe, and AgSe8-11. They exhibit abundant structures and

physical properties. CuSe, AgTe and AgSe have remarkable two-dimensional properties

with metal atoms and chalcogenide in a plane forming hexagonal structure. And there

are also metal and chalcogenide alloys with structures of chains, for example, Te on Cu

(111) system with    or    Cu-Te chains 13-16. For electronic

properties, recently, it is reported that CuSe and AgTe possess two dimentional Dirac

nodal line fermions (its Dirac point extend along      high-symmetry line,

forming Dirac nodal line), protected by mirror reflection symmetry8, 9, 11. Moreover, the

chalcogen-based surface alloys are promising to be used as substrates. For example,

CuSe alloy could tune the CDW properties of TiSe2 as a substrate for TiSe212. As a

common metal substrate, aluminum is simple and cheap. And the Al-chalcogen

compounds are also intermediate products in Al-ion battery. So far, the chalcogen -Al

system has not been sufficiently studied. And there are controversy for S/Al (111) and

Se/Al (111) alloy among scientists that whether the structure of AlS and AlSe is planar

or buckling 17-19. It is reported monolayer AlSe is an interface between Si substrate and

Al2Se3 20, 21. However, identifying the electronic properties of AlSe is a challenge due

to the complex energy bands of the Si substrate. Here, we take Se/Al (111) alloy as an

example to clarify the formation process and structure of chalcogen elements/Al (111)

system.

In this study, we systematically investigate the crystal structure and electronic

properties of AlSe alloy on the Al (111) surface combining experiment with calculation.

The atomic arrangement of AlSe on Al (111) is directly revealed using high-resolution

scanning tunneling microscopy (STM). Reflection high-energy electron diffraction

(RHEED) and X-ray photoelectron spectroscopy (XPS) are also carried out to monitor

the formation process of AlSe alloy and its chemical bonding. The interplay between

the substrate and AlSe alloy is analyzed using angle-resolved photoemission

spectroscopy (ARPES) and density functional theory (DFT) calculations. Our results

show a buckled structure of AlSe alloy with a band gap near the Fermi level.

RESULTS AND DISCUSSION

Figure 1 shows the typical XPS spectra of AlSe alloy from the core level of Se 3d.

There are two distinct peaks of Se 3d3/2 and Se 3d5/2 due to the spin-orbit interactions.

In our experiment, the lowest panel of Figure. 1(a) shows the spectrum of Se 3d after

deposition at room temperature. The characteristic peaks of Se can be fitted as four

spectroscopic contributions shown in Figure 1(a). The two red peaks are labeled as Seb1

and Seb2 at a binding energy of 56.10 eV and 55.31 eV, corresponding to the levels

related to bulk Se atoms, in perfect accord with previous studies10. That means they

come from chemical bonds characterized by Se-Se in Se bulk. The two blue peaks are

labeled as Sea1 and Sea2 at a binding energy of 55.30 eV and 54.60 eV, whose binding

energy is shifted by    to lower binding energy. It indicates a charge

transfer process between substrate and Se atoms, after Se atoms deposition on Al (111).

In other words, Se-Al bonds were formed during Se adsorbing on Al (111) substrate.

So, the two chemical environments for Se deposition on Al (111) at room temperature

include Se-Se and Se-Al bonds. The annealing process was taken out to get a single

chemical environment. First, samples were annealed at 200 which significantly

changed the photoemission spectrum. The intensity of the Sea1 and Sea2 peaks increased.

In contrast, Seb1 and Seb2 peaks (indicated Se-Se bond) were reduced, suggesting that

the annealing process either evaporated the excess Se overlayer or promoted Se

interaction with Al . Then the annealing temperature was elevated to 370, the peaks

ascribed to the Se-Se bond (Seb1 and Seb2 peaks) entirely vanished. The only remaining

peaks were related to the Se-Al bond (Sea1 and Sea2 peaks), signifying a single phase of

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摘要：

AnewalloyforAl-chalcogensystem:AlSesurfacealloyonAl(111)En-ZeShao#,KaiLiu#,HaoXie,KaiqiGeng,KekeBai,JinglanQiu,JingWang,Wen-XiaoWang*andJuntaoSong*CollegeofPhysicsandHebeiAdvancedThinFilmsLaboratory,HebeiNormalUniversity,Shijiazhuang050024,ChinaABSTRACTMetalchalcogenideisapromisingmaterialforstudyin...

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A new alloy for Al-chalcogen system AlSe surface alloy on Al 111 En-Ze Shao Kai Liu Hao Xie Kaiqi Geng Keke Bai Jinglan Qiu Jing Wang

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