Lattice Transformation from 2 -D to Quasi 1-D and Phonon Properties of Exfoliated ZrS 2 and ZrSe 2 Awsaf Alsulami1 Majed Alharbi1 Fadhel Alsaffar12 Olaiyan Alolaiyan1 Ghadeer Aljalham1

2025-05-03 0 0 1.82MB 28 页 10玖币

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Lattice Transformation from 2-D to Quasi 1-D and

Phonon Properties of Exfoliated ZrS2 and ZrSe2

Awsaf Alsulami1, Majed Alharbi1, Fadhel Alsaffar1,2, Olaiyan Alolaiyan1, Ghadeer Aljalham1,

Shahad Albawardi1, Sarah Alsaggaf1, Faisal Alamri1, Thamer A. Tabbakh3, and Moh R. Amer1,4*

1Center of Excellence for Green Nanotechnologies,

Joint Centers of Excellence Program

King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia

2Department of Mechanical and Aerospace Engineering

University of California, Los Angeles, Los Angeles, CA, 90095

3National Center for Nanotechnology,

Materials Science Institute,

King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia

4Department of Electrical and Computer Engineering

University of California, Los Angeles, Los Angeles, CA, 90095

* Please send all correspondence to mamer@seas.ucla.edu

Abstract:

Recent reports on thermal and thermoelectric properties of emerging 2-Dimensional (2D) materials

have shown promising results. Yet, most of these emerging materials are underrepresented or lack

a consistent and thorough investigation. Among these materials are Zirconium based

chalcogenides such as Zirconium Disulfide (ZrS2) and Zirconium Dieselenide (ZrSe2). Here, we

investigate the thermal properties of these Zirconium based materials using confocal Raman

spectroscopy. We observed 2 different and distinctive Raman signatures for exfoliated ZrX2

(where X = S or Se). These Raman modes generally depend on the shape of the exfoliated

nanosheets, regardless of the incident laser polarization. These 2 shapes are divided into 2D- ZrX2

and quasi 1D- ZrX2. For 2D- ZrX2, Raman modes are in alignment with those reported in literature.

However, for quasi 1D-ZrX2, we show that Raman modes are identical to exfoliated ZrX3

nanosheets, indicating a major lattice transformation from 2D to quasi-1D. We also measure

thermal properties of each resonant Raman mode for each ZrX2 shape. Based on our

measurements, most Raman modes exhibit a linear downshift dependence with temperature.

However, for ZrS2, we see an upshift (blueshift) with temperature for A1g mode, which is attributed

to non-harmonic effects caused by dipolar coupling with IR-active modes. Moreover, the observed

temperature dependence coefficient for some phonon modes of quasi 1D-ZrX2 differ dramatically,

which can be caused by the quasi 1D lattice. Finally, we measure phonon dynamics under optical

heating for each of 2D-ZrX2 and quasi 1D-ZrX2 and show phonon confinement in quasi 1D-ZrX2

nanosheets. We extract the thermal conductivity and the interfacial thermal conductance for each

of 2D-ZrX2 and quasi 1D-ZrX2 nanosheets. Our calculations indicate lower interfacial thermal

conductance for quasi 1D-ZrX2 compared to 2D-ZrX2, which can be attributed to the phonon

confinement in 1D. Based on our model, we show low thermal conductivity for all ZrX2

nanosheets. Our results demonstrate exceptional thermal properties for ZrX2 materials, making

them ideal for future thermal management strategies and thermoelectric device applications.

Keywords: Zirconium Disulfide, Zirconium Dieselenide, phonons, Raman spectroscopy, lattice

transformation, thermal conductivity.

Introduction:

Since the beginning of graphene about a decade ago, new classes of 2D materials have emerged

ranging from single elements such as silicene [1-3], phosphorene [4-7], and Tellurene [8-11], to

Transition Metal dichalcogenides or TMDCs. These TMDCs are composed of MX2 where M is a

transition metal, X is a chalcogen material. Although there have been intense research efforts on

TMDCs, especially, Molybdenum Disulfide (MoS2) and Tungesten Diselenide (WSe2) [12, 13],

there are other branches of transition metal chalcogenides known as transition metal

monochalcogenides (TMMCs) such as GeS, GeSe, [14, 15], and transition metal trichalcogenides

(TMTCs) known as ZrSe3, ZrS3 [16-18]. Recent reports on these classes of materials have shown

exceptional properties ranging from quantum tunneling, structural phase transitions, high thermal

transport, and high thermoelectric properties [19-23].

ZrX2 and ZrX3 (where X = S or Se) based materials are classified as TMDCs and TMTC,

respectively. Both exhibit different lattice structures, which grand them different and promising

properties. For instance, ZrS2 and ZrSe2 exhibit high carrier mobilities reaching 1200 cm2V-1s-1

and 2300 cm2V-1s-1, respectively [24]. The bandgap for both ZrS2 and ZrSe2 is indirect with values

close to 1.12eV and 1.07eV, which is close to silicon band gap [25, 26]. Such properties make

ZrX2 materials attractive for future device applications. On the other Hand, ZrS3 and ZrSe3

materials exhibit a layered anisotropic 1D superlattice chain [20]. For both of these materials, the

indirect band gap energy is higher than ZrX2 materials, reaching 1.88eV and 1.54eV for ZrS3 and

ZrSe3, respectively [20, 27]. Both materials, ZrX2 and ZrX3, have shown exceptional

thermoelectric properties with figure of merit reaching higher than 1 [27, 28].

Although there have been recent efforts to investigate the properties of ZrX2 materials,

there is still a noticeable gap in rigorous experimental work to understand the fundamental

properties of ZrX2 materials. Here, we investigate the optical properties of ZrX2 materials by

means of confocal Raman spectroscopy and show a lattice transformation from 2D to quasi-1D

structure for ZrS2 and ZrSe2, evident by a radical change in the measured Raman spectra. We also

investigate the temperature dependence of these Raman active modes and study the phonon

dynamics for ZrX2 materials. Finally, we demonstrate and discuss optothermal measurements for

ZrX2 materials and extract the thermal conductivity and interfacial thermal conductance for each

material.

Results:

Figure 1a shows the lattice structure schematic of ZrX2 and the primitive cell. This lattice

structure exhibit trigonal shape with P-3m1 space group. Each Zr atom is connected to 6 different

sulfide/selenide atoms. Atoms have a stronger bond in ab plane compared to c-axis, which makes

it easier to mechanically exfoliate atomically thin ZrX2. Layers are stacked and connected via a

weak van der Waals force in the c-axis. The Raman-active modes for ZrX2 materials are illustrated

schematically in figure 1b. These Raman modes can be resolved spectrally as shown in figure 2a

and 2b. For ZrSe2, in-plane Eg mode and out-of-plane A1g mode have frequencies at 147 cm-1 and

194.16 cm-1, respectively, while for ZrS2, these phonon modes occur at frequencies 250 cm-1 and

333 cm-1, respectively. In addition, ZrS2 exhibits overlapping peaks at 316 cm-1 and 358 cm-1. The

origin of these peaks can be explained on the bases of anharmonicity effects observed for A1g mode

where a noticeable dipolar coupling occurs between IR-active A2u and Eu modes with A1g mode,

giving rise to the observed broadening at A1g Raman shift [29]. These spectra in figures 2a and 2b

have been reported previously by different groups [21, 30, 31].

In figures 2c and 2d, 3 anomalous Raman modes are detected from exfoliated ZrSe2 and

ZrS2, respectively, which deviates greatly from typical Raman modes reported in figures 2a and

2b. These modes exhibit a Lorentzian shape with Raman shifts at 178 cm-1, 234 cm-1, and 302 cm-

1 for ZrSe2 and 150 cm-1, 281 cm-1, and 320.2 cm-1 for ZrS2. Based on the optical images illustrated

in figure 2c and 2d, these Raman modes only appear from exfoliated nanosheets that exhibit a

noticeably narrow 1D-rectangular shape, where one axis is exceedingly longer than the other in

the lateral direction (ab plane). In fact, due to the randomness of the exfoliation process, typical

Raman modes reported in literature appear from non-rectangular (referred to as 2D-ZrX2)

nanosheets, while these new Raman modes in figures 2c and 2d are exclusively measured from

these narrow rectangular ZrX2 nanosheets (referred to as quasi 1D-ZrX2).

To shed some light on the origin of these quasi 1D-ZrX2 Raman modes, Raman

measurements of exfoliated ZrX3 materials have been measured and compared to quasi 1D-ZrX2

nanosheets. In figure 3a and 3b, Raman spectra of quasi-1D ZrS2 and ZrSe2 are compared against

Raman modes measured for exfoliated ZrS3 and ZrSe3, respectively. The detected Raman peaks

from quasi 1D-ZrX2 nanosheets remarkably overlap with the measured Raman modes of ZrX3,

mimicking the exact Raman spectra. Therefore, we can assign the measured peaks as A3g, A5g, and

A6g for quasi 1D-ZrS2 and A5g, A6g, and A8g for quasi 1D-ZrSe2. The lattice structure and the

observed phonon modes for ZrX3 are schematically illustrated in figure 2c and 2d, respectively.

The reason behind this identical overlapping of phonons can be attributed to lattice transformation

of exfoliated 2D-ZrX2 into quasi-1D structure, identical to ZrS3 and ZrSe3, as will be shown later.

We also measured the anisotropy behavior of 2D-ZrX2 and quasi 1D-ZrX2 nanosheets. In

figure S1, polar plots of Raman intensity at different polarization angles are illustrated for both

shapes of ZrX2 nanosheets. From these plots, one can see the Raman intensity for all modes

changes with changing laser polarization angle, indicating the existence of anisotropy in 2D- ZrX2

and quasi 1D-ZrX2 materials. This Raman intensity modulation occurs for all Raman modes with

a different modulation degrees. For quasi-1D ZrX2, the anisotropy trend is remarkably analogous

to ZrX3 materials reported previously [32], which further indicates the nature of the lattice

transformation to quasi-1D structure for ZrX2 rectangular shaped nanosheets.

Temperature dependence of Raman modes:

The Raman modes temperature dependence of 2D-ZrX2 and quasi 1D-ZrX2 nanosheets are

measured and analyzed. Here, exfoliated nanosheets have been deposited on SiO2/Si substrate. The

sample is then inserted inside an enclosed temperature-controlled stage with an optical window

for Raman measurements. Figure 4 shows the Raman spectra at 2 different temperatures and the

change in the Raman shift vs. temperature ( Δω = ωT – ωo) for all different ZrX2 structure. For 2D-

ZrSe2 in figure 4a and 4b, we see an equal downshift of both Raman modes with increasing

substrate temperature, mainly Eg and A1g modes. However, for 2D-ZrS2 nanosheet, a different

trend is observed. E1g and A2u modes show similar downshift magnitudes with increasing

temperature while A1g mode exhibits a weak upshift instead of a downshift, as demonstrated in the

Raman spectra and Raman shift vs. temperature in figures 4c and 4d, respectively. This anomalous

behavior can be attributed to the origins of A1g mode where anharmonicity effects are strong and

caused by hyperdization between A1g, A2u, and acoustic phonons [30, 33]. The phonon behavior

for each of 2D-ZrSe2 and 2D-ZrS2 has been observed in additional nanosheets, as shown in figure

S2a to S2d.

We also measured Raman temperature dependence of quasi 1D-ZrX2 nanosheets. In figure

4e, and 4f, we show the Raman spectra of quasi 1D-ZrS2 nanosheets at 2 different temperatures

and the change in the Raman shift with increasing temperatures. Although all phonon modes

downshift with increasing temperature, A3g mode shows a weak Raman dependence with

temperature compared to A5g and A6g. This weak dependence of A3g mode stems from the quasi-

1D nature of the transformed lattice of rectangular ZrS2 nanosheet, where rigid interchain

interaction between atoms in the 1D lattice model dominates A3g mode, leading to this weak

temperature dependence. While for A5g and A6g modes, we see a higher downshift with

temperature indicating higher sensitivity to the surrounding temperature compared to A3g mode.

In figure S3a and S3b, other quasi 1D-ZrS2 nanosheets showed analogous trend, confirming the

observation of this phonon behavior.

Figure 4g and 4h show Raman spectra at 2 different temperatures and the change in the

Raman shift with increasing temperatures for quasi 1D-ZrSe2 nanosheet. Here, A5g, A6g, and A8g

Raman modes downshift with increasing temperature. However, it is observed that A6g and A8g

modes exhibit higher downshift compared to A5g mode, leading to a higher temperature sensitivity.

Figure S3c and S3d also demonstrates this trend on another quasi 1D-ZrSe2 nanosheet.

To quantify the observed Raman downshift with temperature for each measured Raman

peak, the Raman temperature dependence of each mode can be expressed as:



Where  is the Raman shift in cm-1,  is the Raman shift when the temperature goes to

absolute zero, and  is the temperature coefficient of the Raman mode of interest. Using this

relation, one can extract the temperature coefficient for all ZrX2 nanosheets. Figure S4 shows

independent plots for each Raman mode measured with changing temperature. Accordingly, the

obtained temperature coefficient () and Raman shift at 0K () for each Raman mode are

summarized in table 1. We can deduce from this table that Eg and A1g modes show similar

Eq. 1

downshift for 2D-ZrSe2. While for 2D-ZrS2, A1g show a weak and anomalous upshift with

temperature compared to Eg and A2u modes.

As mentioned above, for quasi 1D-ZrSe2, all phonon modes downshift. However, the

temperature coefficient for A8g is higher than other Raman modes confirming this high temperature

sensitivity. Similarly, the temperature coefficient of A5g and A6g for quasi 1D-ZrS2 show almost

equal values, suggesting equal downshift with temperature. Nevertheless, the temperature

coefficient of A3g mode shows 3 orders of magnitude less than A5g and A6g, confirming this weak

downshift with temperature as explained above.

Table 1: Raman shift () and the temperature coefficient () of each Raman mode for

2D-ZrX2 and quasi 1D-ZrX2

Material

Raman mode

 (cm-1)

 (cm-1/K)

2D-ZrSe2

146.4209

-0.01343

A1g

194.58626

-0.01282

2D-ZrS2

250.09365

-0.01869

A1g

333.13913

0.00589

A2u

317.27941

-0.0201

Quasi 1D-ZrSe2

A5g

178.17638

-0.01153

A6g

235.24741

-0.01133

A8g

302.72557

-0.01558

Quasi 1D-ZrS2

A3g

150.48667

-0.00768

A5g

280.72034

-0.02188

A6g

319.56597

-0.02046

Localized Laser Heating of Raman modes:

To gain a deeper understanding of the phonon dynamics of ZrX2-based materials with

different shapes, localized laser-induced optothermal experiment is carried out on exfoliated ZrX2

nanosheets. In this experiment, a laser source is used to induce localized heat on the targeted ZrX2

nanosheets, while Raman spectra are detected and measured simultaneously. It is possible to

extract the temperature of a specific Raman mode with increasing laser power by obtaining the

empirical relationship between this Raman mode and temperature based on equation 1. This

method has been applied previously to extract the thermal conductivity of various 2D materials

including graphene, MoS2, and MoSe2 [34-36].

Figure 5 shows the optothermal measurements obtained for 2D-ZrX2 and quasi 1D-ZrX2

nanosheets. For 2D-ZrSe2 and 2D-ZrS2 nanosheets, A1g and A2u modes were chosen to extract

nanosheet temperature, respectively. Figures 5a,b and 5c,d show the Raman spectra at 2 different

laser powers and the extracted temperature vs. laser power for each 2D nanosheet. A monotonic

increase in temperature is observed with temperatures reaching as high as 171oC for ZrSe2 and 282

oC for ZrS2.

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LatticeTransformationfrom2-DtoQuasi1-DandPhononPropertiesofExfoliatedZrS2andZrSe2AwsafAlsulami1,MajedAlharbi1,FadhelAlsaffar1,2,OlaiyanAlolaiyan1,GhadeerAljalham1,ShahadAlbawardi1,SarahAlsaggaf1,FaisalAlamri1,ThamerA.Tabbakh3,andMohR.Amer1,4*1CenterofExcellenceforGreenNanotechnologies,JointCentersof...

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Lattice Transformation from 2 -D to Quasi 1-D and Phonon Properties of Exfoliated ZrS 2 and ZrSe 2 Awsaf Alsulami1 Majed Alharbi1 Fadhel Alsaffar12 Olaiyan Alolaiyan1 Ghadeer Aljalham1.pdf

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Lattice Transformation from 2 -D to Quasi 1-D and Phonon Properties of Exfoliated ZrS 2 and ZrSe 2 Awsaf Alsulami1 Majed Alharbi1 Fadhel Alsaffar12 Olaiyan Alolaiyan1 Ghadeer Aljalham1

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