Large-area fabrication of 2D layered topological semimetal films and emerging applications

Figures & data

Figure 1. Schematic illustration of the band structures and crystal structures of topological Dirac semimetals and topological Weyl semimetals. (a). The splitting of a Dirac point (DP) into a pair of Weyl points with opposite chirality (WP±) through time-reversal symmetry (TRS) or inversion symmetry (IS) breaking. The green line represents a surface Fermi arc (SFA) between the Weyl points reproduced from reference. Reproduced from [130]. (b). Type-II Weyl semimetal and type-II Dirac semimetal with tilted Weyl or Dirac cones. Reproduced from [130]. (c). Crystal structures of layered topological materials. Blue and purple spheres represent metal and chalcogenide atoms, respectively.

Figure 2. CVD growth of MoTe₂ and PtTe₂ by tellurizing corresponding metal films. (a). Top is a two-zone furnace growth schematic. Middle and bottom are TEM cross-section images of a 14-cycle MoO_x film and converted MoTe₂ film, respectively. Reproduced from [62]. (b). Schematic of the CVD process with a half-open quartz tube. Reproduced from [67]. (c). The photograph of wafer-scale PtTe₂ films with different thicknesses of ≈ 5 nm (top) and ≈ 10 nm (bottom). Reproduced from [67]. (d). Photo image of PtTe₂ films on different substrates. Reproduced from [68].

Figure 3. MBE growth of MoTe₂ and WTe₂ films. (a). Schematic diagram of the MBE growth setup for MoTe₂. Reproduced from [76]. (b). Growth process control of the MBE growth of 1T’ and 2H MoTe₂. Reproduced from [76]. (c). Raman spectra of the MoTe₂ films grown at different temperatures. Reproduced from [76]. (d). RHEED patterns of graphene substrate (top) and sub-monolayer 1T’ WTe₂ (bottom). Reproduced from [50]. (e). Core level spectra of 1T’ WTe₂. Reproduced from [50]. (f). Atomically resolved STM image of 1T’ WTe₂. Reproduced from [50].

Figure 4. Preparation and characterization of PLD growth of WTe₂ films. (a). Schematic diagrams of the PLD and post annealing apparatus for WTe₂ films. Reproduced from [94]. (b). Raman spectra of the WTe₂ films annealed for different time intervals. Reproduced from [94]. (c). Cross-section HAADF image of a multilayered Bi₂Te₃-WTe₂ film grown on mica. Reproduced from [96]. (d). Higher magnification scan of the boxed area shown in Figure 4(c). Reproduced from [96].

Figure 5. (a). Schematic illustration of the post annealing SiO₂/MoTe₂/SiO₂ heterostructure. Reproduced from [102]. (b). Schematic diagram of the co-sputtering deposition of MoTe₂. Reproduced from [54]. (c). Plot of deposition rate and the Te/Mo ratio (inset) vs. temperature. Reproduced from [54]. (d). Schematic illustration of the transformation of the as-deposited MoTe₂ films. Reproduced from [103].

Table 1. List of large-area growth conditions for 2D layered topological semimetals

Material	Phase	Preparation method	Precursors or target	Growth temperature	Substrate	Ref
WTe2	Td	CVD	WOx film, Te	600°C	SiO2	[44]
	1T’	CVD	W film, NixTey film	500°C	SiO2	[63]
	Td	CVD	W film, Te	800°C	SiO2	[65]
	1T’	MBE	W, Te	280°C	SiC(0001)	[50]
	1T’	MBE	W, Te	275°C	Bi2Te3, MoS2, graphite	[86]
	Td	PLD	WTe2	300°C (growth), 700°C (annealing)	mica	[52,92,94]
	1T’	PLD	WTe2	210°C	Bi2Te3	[96]
	amorphous	sputtering	WTe2	RT	SiO2	[100]
	amorphous	sputtering	WTe2	50–150°C	SiO2	[101]
MoTe2	2H and 1T’	CVD	Mo/MoO3 film, Te	650–700°C	SiO2	[45–47]
	2H and 1T’	CVD	MoO3 film, Te	650–800°C	SiO2	[48]
	2H and 1T’	CVD	MoOx film, Te	500°C	Si	[60]
	2H and 1T’	CVD	MoO3 film, Te	650°C	SiO2	[61]
	2H and 1T’	CVD	MoOx film, Te	580°C	SiO2	[62]
	1T’	CVD	Mo film, Te	470°C	SiO2	[64]
	2H and 1T’	MOCVD	Mo(CO)6, (C4H9)2Te	400°C	SiO2	[56,57]
	2H	MBE	Mo, Te	350°C	Al2O3(0001)	[77]
	2H	MBE	Mo, Te	450°C	MoS2	[78]
	2H and 1T’	MBE	Mo, Te	250–400°C	HOPG	[80]
	1T’	MBE	Mo, Te	280°C	SiC(0001)	[82]
	2H	PLD	MoTe2	300°C (growth), 800°C (annealing)	SiO2	[51]
	2H and 1T’	sputtering	MoTe2	400°C (growth), 650°C (annealing)	SiO2	[102]
	2H	sputtering	MoTe2	200°C (growth), 700–850°C (annealing)	SiO2	[103]
PtTe2	1T	CVD	Pt film, Te	400°C	SiO2	[49,66]
	1T	CVD	Pt film, Te	460°C	SiO2	[67]
	1T	CVD	Pt film, Te	450°C	Al2O3, STO, YSZ, mica, SiO2, etc.	[68]
	1T	CVD	Pt (111)	200°C	Pt (111)	[69]
	1T	MBE	Pt, Te	300°C	SiC(0001)	[71]
PdTe2	1T	CVD	Pd (111)	570°C	Pd (111)	[69]
	1T	MBE	Pd, Te	237°C	SiC(0001)	[70]
ZrTe2	1T	MBE	Zr, Te	400°C	InAs(111)/Si(111)	[75]
	1T	PLD	ZrTe5	550°C	STO(110)	[97]

Figure 6. The transport characteristics of the MBE growth PdTe₂ films. (a). The resistance of PdTe₂ films with different thickness as a function of the temperature. The inset is the schematic of four-probe measurements. Reproduced from [112]. (b). T_c and H_c2 (T = 0) dependence of the film thickness. The circles and squares represent the H_c2 (0) derived from the two-band model and Ginzburg-Landau formula, respectively. Reproduced from [112]. (c). The sheet resistance R_s of PdTe₂ films under the conditions of different perpendicular magnetic fields from 0 to 0.897 T. Reproduced from [113]. (d). The evolution of Rs-B curves at different temperatures ranging from 20 to 450 mK. The inset curves are some crossing points from the Rs-B. Reproduced from [74].

Figure 7. Photoelectric detection researches of PtTe₂ films. (a). The photoresponse of PtTe₂ at different wavelengths. The inset is the schematic illustration of photodetector. Reproduced from [72]. (b). Anisotropic photoresponse for the linear-polarized excitation at 10.7 μm. Reproduced from [72]. (c). The schematic illustration of the temporal photo-responsiveness of PtTe₂/p-Si devices. Reproduced from [49]. (d). Relative balance as a function of illumination modulation frequency, defined as (I_max− I_min)/I_max. Reproduced from [49]. (e). The rise (τ_r) and fall (τ_f) times are obtained in the magnified view of photo-switching characteristics at 150 kHz. Reproduced from [49]. (f). Photographs and images of the PtTe₂-based arrays device. Reproduced from [118]. (g), (h). The THz detecting devices and mechanisms of PtTe₂ and graphene heterojunction, respectively. Reproduced from [121]. (i). THz image of the metal nut. Reproduced from [121].

Figure 8. The spin orbit torque measurements in the WSMs and DSMs. (a). Illustration of the second harmonic measurement on WTe_x(3, 5, 8 nm)/CoFeB(6 nm) Hall bar device. Reproduced from [100]. (b). The thickness dependent DL torque and FL torque of the sample in Figure 8(a). Reproduced from [100]. (c). The DL torque efficiency of different thickness and Te concentration in WTe_x films. Reproduced from [101]. (d), (e). The schematic illustration and image of the Py/WTe₂ devices. Reproduced from [125]. (f). MOKE images of Py before (left) and after (right) applying a pulsed DC current I (indicated by the purple arrow) along the x-axis. Reproduced from [125]. (g). The schematic illustration of the torque generation in the Py/PtTe₂ heterojunction. Reproduced from [67]. (h). The inverse of the SOT efficiency as an evolution of the inverse of the Py thickness in Pt/Py and PtTe₂/Py. Reproduced from [67]. (i). ξ_SOT (circle line) and spin Hall conductivity (circle) with different PtTe₂ thicknesses. Reproduced from [67].

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