Stable alkali halide vapor assisted chemical vapor deposition of 2D HfSe2 templates and controllable oxidation of its heterostructures

Wenlong Chu, Xilong Zhou, Ze Wang, Xiulian Fan, Xuehao Guo, Cheng Li, Jianling Yue, Fangping Ouyang, Jiong Zhao, Yu Zhou

Front. Phys. ›› 2024, Vol. 19 ›› Issue (3) : 33212.

PDF(4100 KB)
Front. Phys. All Journals
PDF(4100 KB)
Front. Phys. ›› 2024, Vol. 19 ›› Issue (3) : 33212. DOI: 10.1007/s11467-024-1414-7
RESEARCH ARTICLE

Stable alkali halide vapor assisted chemical vapor deposition of 2D HfSe2 templates and controllable oxidation of its heterostructures

Author information +
History +

Abstract

Two-dimensional hafnium-based semiconductors and their heterostructures with native oxides have been shown unique physical properties and potential electronic and optoelectronic applications. However, the scalable synthesis methods for ultrathin layered hafnium-based semiconductor laterally epitaxy growth and its heterostructure are still restricted, also for the understanding of its formation mechanism. Herein, we report the stable sublimation of alkali halide vapor assisted synthesis strategy for high-quality 2D HfSe2 nanosheets via chemical vapor deposition. Single-crystalline ultrathin 2D HfSe2 nanosheets were systematically grown by tuning the growth parameters, reaching the lateral size of 6‒40 μm and the thickness down to 4.5 nm. The scalable amorphous HfO2 and HfSe2 heterostructures were achieved by the controllable oxidation, which benefited from the approximate zero Gibbs free energy of unstable 2D HfSe2 templates. The crystal structure, elemental, and time dependent Raman characterization were carried out to understand surface precipitated Se atoms and the formation of amorphous Hf−O bonds, confirming the slow surface oxidation and lattice incorporation of oxygen atoms. The relatively smooth surface roughness and electrical potential change of HfO2−HfSe2 heterostructures indicate the excellent interface quality, which helps obtain the high performance memristor with high on/off ratio of 105 and long retention period over 9000 s. Our work introduces a new vapor catalysts strategy for the synthesis of lateral 2D HfSe2 nanosheets, also providing the scalable oxidation of the Hf-based heterostructures for 2D electronic devices.

Graphical abstract

Keywords

chemical vapor deposition / HfSe2−HfO2 / nanoelectronics

Cite this article

Download citation ▾
Wenlong Chu, Xilong Zhou, Ze Wang, Xiulian Fan, Xuehao Guo, Cheng Li, Jianling Yue, Fangping Ouyang, Jiong Zhao, Yu Zhou. Stable alkali halide vapor assisted chemical vapor deposition of 2D HfSe2 templates and controllable oxidation of its heterostructures. Front. Phys., 2024, 19(3): 33212 https://doi.org/10.1007/s11467-024-1414-7

1 Introduction

Two-dimensional transition metal chalcogenides have been demonstrated with high carrier mobilities [1], polarization switchable ferroelectricity [2] and tunable magnetic properties of ferromagnetism [3-6], spin glass state [7] and specific surface area with high reaction ability down to monolayer limit [8,9], thus booming in the potential applications of electronic, optoelectronic, magnetic, catalytic conversion and storage devices [4,10-20]. Different from MoS2 and ReS2 material families with weak interlayer interaction, layered hafnium chalcogenides (HfS2 and HfSe2) share much stronger van der Waals force, resulting in the extreme difficulty for the exfoliation and bottom-up synthesis of ultrathin 2D layers [21]. Meantime, layer dependent moderate bandgap from bulk to monolayer of 1.13−1.18 eV for HfSe2, is similar with traditional silicon semiconductor for transistor channel application [22]. The theoretical band structure calculation also has predicted HfSe2 with high phonon-limited mobility of 3500 cm2·V−1·s−1, which is nearly 10 times higher than that of the extensively studied MoS2 (340 cm2·V−1·s−1) [23]. The electronic transport prediction for 2D HfSe2 field effect transistors demonstrated the record on-state current density of 5000 µA·µm−1 (about 650 times that of MoS2) [24]. Moreover, high dielectric constant HfO2 is a compatible oxide of 2D HfSe2, which could be achieved by the slow oxidation process similar to the Si/SiO2 and Bi2O2Se/Bi2SeO5 interface [1,22,25]. Therefore, scalable synthesis of layered 2D HfSe2 and its heterostructure should be highly desirable to realize low-power electronic and optoelectronic devices [24].
Most recently, ultrathin exfoliated HfSe2 nanoflakes from chemical vapor transport synthesized singe crystals demonstrated the promising transistor performance (on/off ratio > 106; on current, 30 μA/μm) due to the interfacial trap free native oxides [22]. Although 2D HfSe2 nanoflakes and their heterostructures have been confirmed with excellent electronic device performance, scalable synthesis of large area 2D HfSe2 nanoflakes and their heterostructures were still rarely reported [22,26-29]. Low pressure chemical vapor deposition with the utilization of the selenolate complexes [Cp2Hf(SeR)2] showed the synthesis of randomly nucleated flower-like nanostructure films [30]. Two-dimensional HfSe2 nanostructures and MoSe2/HfSe2 van der Waals heterostructures were synthesized by molecular beam epitaxy (MBE), also providing the obvious evidence of an ordered Se adlayer by high-resolution scanning tunneling microscopy characterization [31,32]. Polycrystalline wafer-scale 2D HfSe2 thin films were achieved by the MBE with the solid supply of Hf and Se, which were also applied to memristor crossbar array for energy-efficient neural network hardware [33]. Randomly vertical oriented HfS2 nanosheets, polycrystalline small-sized HfSe2 samples, and HfS2(1−x)Se2x alloys were grown by the highly volatile HfCl4 precursors, which are still far from the requirement of electronic devices application in terms of domain size and the lateral flakesgeometry [34-36]. Therefore, the stable synthesis of high-quality 2D single-crystal HfSe2 nanosheets on the diverse substrates laterally is highly desirable, which also could be utilized as scalable oxidation templates for HfO2‒HfSe2 heterostructures, avoiding the nucleation problem of dielectric layer growth on dangling bond free surface [37].
Herein, we report a remote molten salt (NaCl) vapor-assisted stable volatilization of high melting point hafnium-based precursor (HfO2) for the CVD synthesis of high-quality single-crystal HfSe2 nanosheets and thin films on various substrates. The size (6‒40 μm), thickness (~4.5 nm), and shape (hexagonal to circular) of HfSe2 nanosheets can be precisely tuned by varying the growth parameters. High quality HfO2−HfSe2 heterostructures were formed by the slow natural oxidation, which has been confirmed with clear lattice incorporation of oxygen atoms and the formation of surface amorphous oxide layers. Further, we investigated the natural oxidation process of HfSe2 in air and explored the memristor application of HfO2−HfSe2 heterostructures. These findings provide a new idea for the scalable synthesis of two-dimensional hafnium-based chalcogenides laterally and demonstrate that the HfO2−HfSe2 heterostructures hold great promise in the field of information storage devices.

2 Experimental section

2.1 Preparation of HfSe2 nanosheets

Two-dimensional HfSe2 nanosheets were synthesized on Mica, Si/SiO2 substrates using remote molten salt (NaCl)-assisted volatilization of a high melting point hafnium-based precursor (HfO2) in an atmospheric pressure chemical vapor deposition system. Specifically, the high melting point hafnium-based precursor (HfO2, Aladdin, ≥99.9%) was placed in a quartz boat at a high temperature in the center of a tube furnace. The substrate is reversely placed over the precursor. The NaCl (Aladdin, ≥99.5%) powder was placed upstream of the tube furnace at approximately 780 °C. The Se (Aladdin, ≥99.5%) powder was similarly placed upstream of the tube furnace and heated using an external heating band set at 260‒340 °C. Before growth, the quartz tube was purged using high-purity argon (Ar), and then the furnace temperature was increased to 780‒960 °C and kept constant for 10 min under the argon flow rate of 30 sccm. The specific growth schematic is shown in Fig.1(a).
Fig.1 (a) Schematic diagram of remote alkali halide vapor assisted stable sublimation of high melting point hafnium dioxide for controlled synthesis of 2D HfSe2 nanosheets. The NaCl and HfO2 powder were arranged at the separated temperature of 780 °C, and 800 °C, respectively. (b) Schematic atomic structures of 1T-HfSe2 along the ab and bc crystal planes, also for its unit cell. (c) Typical optical image of the synthesized HfSe2 nanosheets on the mica substrate. (d) Raman spectra and (e) XRD pattern of the synthesized HfSe2 nanosheets.

Full size|PPT slide

2.2 Sample characterization

The optical microscope (OM, OLYMPUS BX53M) has been used to obtain the morphology of the HfSe2 nanosheets. The Raman spectrometer (Raman, Renishaw inVia Reflex) with a 532 nm laser as the excitation source was used to collect spectra of HfSe2 nanosheets to determine molecular vibration bonds of the sample. The crystal structures were characterized by X-ray diffraction (XRD, PERSEE XD-3). The thickness of the sample was determined using an atomic force microscope and the surface potential of the samples was tested using Scanning Kelvin Probe Microscopy (OXFORD MFP-3D Origin). Transmission electron microscopy (TEM, FEI Tecnai F20) is used to analyze the crystal structure and elemental composition of the HfSe2 nanosheets.

2.3 Device fabrication and property measurement

The device is fabricated via an Ultraviolet Maskless Lithography machine (TuoTuo Technology (Suzhou) Co., Ltd.). The naturally oxidized 2D HfSe2 (25 °C, 40% humidity, 48 h) were used to fabricate the devices. The transfer platform was used to transfer the sheet to a specific location. Physical vapor deposition equipment (VNANO VZZ-300S) was used to deposit Cr/Au as electrodes. The memristor properties of the devices were tested by a semiconductor analyzer (PDA FS-Pro) connected with a probe station at room temperature.

3 Results and discussion

To achieve high-quality two-dimensional (2D) HfSe2 nanosheets as the heterostructure template, we propose a remote alkali halide vapor assisted chemical vapor deposition [Fig.1(a)]. Different from the normal growth using the precursor mixtures, our design strategy separated the location of HfO2 and NaCl to avoid the precursor supply shortage or erupt [38]. The alkali halide powder was placed around its melting temperature of 780 °C, separately arranging the HfO2 powers (800−940 °C), which could continuously provide the vapor phase of alkali halide molecule to react with the HfO2 surface for stable sublimation. The freshly exfoliated mica or SiO2/Si substrate was settled on the top of HfO2 powders, in which the reaction species were transported to the substrate surface and formed the nuclei. Thus, the nuclei could epitaxially grow towards in-plane direction to form 2D HfSe2 under the continuous mild supply, avoiding the small sizes or the vertical nanosheets formation [36,39-41]. Fig.1(b) shows the schematic crystal structure of 1T phase HfSe2 (−4.550 eV), which has a lower formation energy than 2H-HfSe2 (−4.045 eV). In details, 1T-HfSe2 belongs to the hexagonal crystal system with space group of P3¯m1, showing the lattice parameters of a = b = 3.744 Å, c = 6.155 Å, α = β = 90°, γ = 120° [27]. Monolayer 1T-HfSe2 consists of two layers of Se atoms sandwich a layer of Hf atoms with interlayer covalent bonding, in which the Hf atoms are located at the center of an octahedron composed of Se atoms, with a spacing distance of 0.62 nm [Fig.1(b)] [42].
Fig.1(c) shows an OM image of 2D single crystalline HfSe2 nanosheets synthesized on a mica substrate, which are obtained by the separated precursor strategy. The HfSe2 nanosheets exhibit a regular hexagonal geometry with uniform optical contrast and an average domain size of about 6.4 μm. The typical growth results of 2D single crystalline HfSe2 nanosheets are better than the previously reported polycrystalline HfSe2 thin films or vertical small size nanosheets (HfS2) [34,41], which are due to the high nucleation sites from high volatilization of low melting point HfCl4. Similarly, the normal precursor mixtures could provide erupt chemical supply, resulting in high nucleation sites for randomly vertical 2D HfSe2 [Fig. S1 of the Electronic Supplementary Materials (ESM)] [34,39]. Therefore, such a design enables NaCl vapor to continuously interact with HfO2, promotes the stable volatilization of the metal precursor, and achieves a smooth and continuous supply of reactants, thus facilitating the synmthesis of high-quality lateral epitaxy of 2D HfSe2 nanosheets [43]. Raman spectra of the prepared saples [Fig.1(d)] were obtained using a 532 nm excitation laser for the identification of HfSe2 nanosheets. The in-plane Eg mode of 146.7 cm−1 and the out-of-plane A1g mode of 198.6 cm−1 were observed, both of which are in good agreement with previously reported results [31,41]. Three clear and sharp diffraction peaks at 2θ = 14.4°, 44.2°, and 60.1° that correspond to the (001), (003), and (004) crystal planes of HfSe2 were shown, which matched well with the standard PDF card of the HfSe2 crystals (PDF#01-084-6304), indicating that the grown HfSe2 samples have a 1T-phase structure with specific growth direction [Fig.1(e)] [33]. Therefore, high-quality 2D HfSe2 thin nanosheets were achieved by the remote alkali halide vapor assisted chemical vapor deposition.
The thickness, domain size, and surface morphology of 2D material have a great influence on its physical properties such as band gap and carrier mobility [11,36,44]. Therefore, it is crucial to realize the precise control for achieving large-size and ultrathin 2D single-crystal. Herein, the temperature dependence of growth procedures has been systematically carried out to tune the thickness, domain size, and surface morphology. Fig.2(a)−(e) show the optical images of hexagonal HfSe2 nanosheets grown on mica substrates at different temperatures, in which other growth conditions were kept as argon flow rate of 30 sccm, Se temperature of 280 °C and NaCl temperature of 780 °C. Two obvious growth results trends were observed according to the above optical images analysis. First, the optical contrast of the HfSe2 nanosheets changes from light blue to white and finally to silver-pink with the increased growth temperature, indicating that the thickness of the nanosheets is gradually getting much thicker. This is reflected more clearly in the corresponding AFM images [Fig.2(f‒j)] and the thickness statistics histogram [Fig.2(k)]. The thickness of HfSe2 nanosheets increased from 4.5 to 338.2 nm when the growth temperature was increased from 800 to 940 °C. It is worth noting that 4.5 nm is not the thinnest sample we could obtain, due to the easily oxidizable property of HfSe2 making the samples less than 4.5 nm thick are difficult to measure (Fig. S2 of the ESM). Secondly, the average domain size of HfSe2 nanosheets increases gradually with the increased growth temperature. As shown in Fig.2(l), the average domain size of HfSe2 nanosheets increased from 6.3 to 20.2 μm when the temperature was increased from 800 to 940 °C. At lower growth temperatures, the low diffusivity of active reactive precursors prefers to bond with the active edge of two-dimensional HfSe2 sheet at the substrate surface, which tends to produce thin two-dimensional HfSe2 nanosheets. As the growth temperature increases, the concentration of active reactants is elevated and the migration rate of precursors on the substrate surface is enhanced, which promote both in-plane and out-of-plane growth of 2D nanosheets, resulting in large and thick materials with lower surface energy. 2D HfSe2 nanosheets grown on SiO2/Si substrates (Fig. S3 of the ESM) exhibit the similar temperature dependent thickness and domain size regularity. The HfSe2 morphology changes from hexagonal to circular nanosheets and large area thin films were also realized by the tuned ratio of Hf to Se precursor (Fig. S4 of the ESM), and the decreased gas flow rate, respectively (Fig. S5 of the ESM). Thus, the systematic growth results of 2D HfSe2 were carefully explored and shown with high-quality samples under the wide range of synthesis conditions [41,45].
Fig.2 (a−e) Optical images of HfSe2 nanosheets grown on mica substrates at different growth temperatures: 800 °C, 820 °C, 840 °C, 870 °C, and 940 °C, respectively, under the argon flow rate of 30 sccm, Se temperature of 280 °C and growth time of 10 min. (f‒j) Corresponding representative AFM images. (k) Statistical graph of the thickness of HfSe2 nanosheets at different growth temperatures. (l) Statistical graphs of HfSe2 nanosheet domain sizes at different growth temperatures.

Full size|PPT slide

In order to further investigate the microstructure, elemental composition, and crystallinity of 2D HfSe2 nanosheets, the measurement of transmission electron microscopy was carried out. Vertically grown HfSe2 was pressed directly onto a TEM copper grid for the clean surface quality (Fig. S6 of the ESM). A low-resolution TEM image of a HfSe2 nanosheet exhibited a regular hexagonal corner [Fig.3(a)]. Fig.3(b) shows the corresponding high-resolution TEM image with the clear lattice stripes showing the excellent crystallinity, in which the lattice spacing of 0.32 and 0.16 nm can be indexed to the (100) and (020) crystal planes of HfSe2, respectively [22]. The selected-area electron diffraction pattern of the HfSe2 nanosheet was shown with regular hexagonal pattern in Fig.3(c), in which single crystalline diffraction patterns are consistent with the simulated electron diffraction and other electron diffraction from different regions (Fig. S7 of the ESM). Fig.3(f) and (g) show the corresponding elemental mappings of Hf and Se for the samples in Fig.3(e), in which the Hf and Se elements are uniformly distributed throughout the nanosheets. The elemental analysis spectra of HfSe2 nanosheets [Fig.3(d)] indicates that the stoichiometric ratio of Hf to Se is around 1:2.2, which is close to the theoretical chemical ratio.
Fig.3 (a) Low-resolution TEM image and (b) High-resolution TEM image of 2D HfSe2 nanosheet. (c) Corresponding selected-area electron diffraction pattern (SAED). (d) EDS elemental analysis spectra of 2D HfSe2 nanosheet and the inset shows the stoichiometric ratio of Hf and Se. (e) Dark-field TEM image of 2D HfSe2 nanosheet. (f, g) EDS mapping images of Hf and Se, respectively.

Full size|PPT slide

Thin Hf-based oxide nanostructure or ultrathin film has attracted much interest in recent years, which is highly derisible to develop scalable synthesis methods rather than only relying on atomic layer deposition, etc.. [46] The nonlayered crystal structure and high melting temperature make it difficult to synthesize in large scale 2D forms and get high crystal quality with the cheap semiconductor procedure [47]. Herein, high-quality 2D HfSe2 nanosheets with low Gibbs free formation energy were proposed as the ultrathin template, oxidating into the nonlayered HfO2‒HfSe2 heterostructure, which could be much easier to implement compared to stable 2D HfS2 [48]. Fig.4(a) illustrates the schematic natural oxidation of 2D HfSe2 in air, where the unstable 2D HfSe2 is exposed to the moist air. The microelectrochemical charge transfer may occur between the material basal plane and the water redox pairs, thus leading to surface oxidation of 2D HfSe2, where the selenium clusters segregate onto the surface of the material in the form of amorphous selenium. The active oxygen atoms could replace the selenium atoms and generate Hf−O chemical bonds, eventually forming the HfO2−HfSe2 heterostructure or entire HfO2 amorphous structures. Fig.4(b) shows the relative standard molar Gibbs free energies of HfSe2 and HfO2, which are much lower for HfO2 (−1162.4 kJ/mol) than for HfSe2, which confirms the thermodynamical possibility of the transformation of HfSe2 into HfO2. An air-exposed of ~40 nm HfSe2 nanosheet was used to record Raman spectra at different oxidation time. The optical contrast of HfSe2 nanosheet changes from light blue to dark brown with the increase of exposure time, and there are obvious dark spots appearing on the surface of 2D HfSe2 (Fig. S8 of the ESM). In the time dependent Raman spectrum, it can be seen that after 12 h of natural oxidation, in addition to the representative peaks A1g of HfSe2, a new active peak at 253.7 cm−1 appeared [Fig.4(e)]. This Raman characteristic peak can be indexed as amorphous Se and the peak intensity increases with time. The above results fully confirm that HfSe2 has amorphous Se production during the oxidation process with the maintained Hf‒Se chemical bonds. High-resolution TEM images of oxidized HfSe2 nanosheets with corresponding EDS elemental analyses are shown in Fig.4(c) and (d), respectively. The high-resolution TEM image of oxidized HfSe2 nanosheets showed the clear disordered structures with amorphous diffraction rings, indicating the formation of amorphous HfO2 surface layers [Fig.4(c)]. The relatively uniform Hf and O elemental mapping and the discrete elemental distribution of weak Se intensities also indicate the chemical oxidation induced by the surface reaction. The unusual FFT diffraction spots of other different regions reveal other specific orientation formation of HfSe2, which may arise the volumetric expansion and lattice strain in the heterostructure (Fig. S9 of the ESM). The surface potential of 2D HfSe2 nanosheets before and after oxidation was measured by the kelvin probe force microscopy, in which the samples were transferred on the gold substrates shown with small roughness change [Fig.4(f) and Fig. S10 of the ESM]. The surface potential image of HfO2 layers demonstrated the uniform potential distribution, indicating the slow oxidation kinetics process [Fig.4(f)]. The surface potential of HfO2 is higher by 80.5 mV compared to the fresh grown HfSe2, indicating the lowering Fermi level and the decreased electron density [49]. The above results clearly confirm the formation of high-quality HfO2‒HfSe2 heterostructures with the controllable oxidation process.
Fig.4 (a) Schematic of natural oxidation of 2D HfSe2 nanosheets in air, forming Se clusters on the surface of HfO2‒HfSe2 heterostructure under the H2O and O2 atmosphere. (b) Schematic of the relative magnitudes of standard molar Gibbs free formation energies of HfSe2 and HfO2. (c) High-resolution TEM image of HfSe2 nanosheets after 48 h oxidation in air, and the inset image is the corresponding FFT of amorphous HfO2 structure. (d) Corresponding EDS elemental mapping for Hf, Se, and O, respectively. (e) Raman spectra of HfSe2 nanosheets naturally oxidized in air for different oxidation times. (f) Surface potentials comparison of 2D HfSe2 nanosheets before and after the oxidation.

Full size|PPT slide

The vertical memristor devices were constructed by the layer-by-layer transfer and fabrication, using the natural oxidized HfO2−HfSe2 heterostructure as the active layers [Fig.5(a)]. A layer of Cr/Au (4/8 nm) was made on the SiO2/Si surface as the bottom electrode, and the naturally oxidized HfSe2 nanosheets were transferred to the bottom electrode surface. Finally, the top electrode was deposited a layer of Cr/Au (10/70 nm). The characteristic I−V switching curves for this typical memristor were measured by the cyclic voltage scanning in the range 0‒6 V with 0.1 V step [Fig.5(a)]. As the applied positive voltage increases, the device switches from the high-resistance state to the low-resistance state at about 4.1 V. When the voltage drops to 2.3 V, the device spontaneously and gradually switches from the low-resistance state to the high-resistance state. It is possible the surface HfO2 layer helps reduce lower resistance states of the memristor to obtain a high switching ratio. The symmetrical characteristic IV relation was also observed for our devices. The CVD derived HfO2‒HfSe2 heterostructure memristor has demonstrated a switching ratio of up to 105. In addition, the device could spontaneously and gradually switch from a low-resistance state to a high-resistance state when the external electric field decreases, indicating that the device is volatile, and shown as a threshold switching devices. In order to understand the working mechanism of HfO2‒HfSe2 memristors, the inert metal of Au layers was used as the top and bottom electrodes [Fig.5(b)]. A significant facile amnesic behavior was observed in several devices [Fig.5(b) and Fig. S11 of the ESM], in which the immobile gold atoms inferred oxygen vacancy filament is the main reason of resistance conductivity transition. When a forward bias is applied to the device, the enriched oxygen vacancies in the amorphous HfO2 layer could gradually move to the bottom electrode. The oxygen vacancies are continuously enriched and migrated, and eventually form a conducting channel across the dielectric layer and show a low resistance state. When the forward voltage decreased, the oxygen vacancy conducting filaments could rupture at the most fragile part, bringing the device back to the high-resistance state [Fig.5(c)].
Fig.5 (a) Typical I−V switching curve of the HfO2‒HfSe2 heterostructure memristor with Cr/Au top electrode and Cr/Au bottom electrodes. The inset picture shows the schematic device structure. (b) Typical I−V switching curve of the HfO2‒HfSe2 heterostructure memristor with inert Au top electrode and Au bottom electrodes. The inset picture shows the schematic device structure. (c) Schematic mechanism diagram of oxygen vacancies dominated resistance change in the HfO2−HfSe2 heterostructure. (d) I−V switching curves of the HfO2−HfSe2 memristor under different limiting currents. (e) Holding characteristics of the high and low resistance states of the HfO2−HfSe2 memristor. (f) The multiple cycling stability measurement of the HfO2−HfSe2 memristor devices.

Full size|PPT slide

The HfO2−HfSe2 memristor was operated and measured under different limiting currents of 10−8, 10−7 and 10−6 A, where the device maintained a switching ratio of over 103 with a clear memristor windows even the current is as low as 10 nA [Fig.5(d)]. High device performance at low current density helps to reduce the power consumption of the memristor device and attenuates the adverse effects of high current density on device’s lifetime. The hold-up characteristics in the high-resistance and low-resistance states at bias voltages of 3.2 V were measured [Fig.5(e)]. The measured results showed that the high/low resistive states are virtually unchanged over the experimental time scale of 9000 seconds, indicating that the device is virtually unaffected by read disturbances. The multiple scanning performance of this HfO2‒HfSe2 memristor is shown in Fig.5(f), demonstrating the voltages window with small fluctuation within two small ranges of 3.8‒4.1 V and 2‒2.9 V, which indicates the good cycling stability. The relatively high performance and scalable fabrication of HfO2−HfSe2 heterostructure devices clearly confirm our excellent stable synthesis strategy, which also reveal the oxygen vacancies dominated working mechanism of the memristor.

4 Conclusion

In conclusion, we have successfully and controllably synthesized high-quality 1T-HfSe2 nanosheets on mica and SiO2/Si substrates using stable molten salt-assisted volatilization of high melting point hafnium-based precursors by chemical vapor deposition. The lateral-size, thickness, and micro-morphology can be precisely adjusted by changing the growth parameters. The high-quality HfO2−HfSe2 heterostructures were achieved by the easy natural oxidation, in which the selenium clusters segregated onto the surface forming amorphous selenium and oxygen atoms incorporated into HfSe2 lattice replacing the Se atoms. The fabricated HfO2‒HfSe2 heterostructures demonstrated excellent performance of a high switching ratio of 10 [5], and long retention time of over 9000 s under low current density. Our work provides a new synthesis strategy for epitaxy growth of lateral Hf-based layered materials and its heterostructure for high performance scalable electronic devices.

References

[1]
T.LiT.Tu Y.SunH. FuJ.YuL.XingZ.Wang H.WangR. JiaJ.WuC.TanY.Liang Y.ZhangC. ZhangY.DaiC.QiuM.Li R.HuangL. JiaoK.LaiB.YanP.Gao H.Peng, A native oxide high-κ gate dielectric for two-dimensional electronics, Nat. Electron. 3(8), 473 (2020)
[2]
Y. Zhou, D. Wu, Y. Zhu, Y. Cho, Q. He, X. Yang, K. Herrera, Z. Chu, Y. Han, M. C. Downer, H. Peng, K. Lai. Out-of-plane piezoelectricity and ferroelectricity in layered α-In2Se3 nanoflakes. Nano Lett., 2017, 17(9): 5508
CrossRef ADS Google scholar
[3]
C. Chen, X. Chen, C. Wu, X. Wang, Y. Ping, X. Wei, X. Zhou, J. Lu, L. Zhu, J. Zhou, T. Zhai, J. Han, H. Xu. Air-stable 2D Cr5Te8 nanosheets with thickness-tunable ferromagnetism. Adv. Mater., 2022, 34(2): 2107512
CrossRef ADS Google scholar
[4]
B. Li, Z. Wan, C. Wang, P. Chen, B. Huang, X. Cheng, Q. Qian, J. Li, Z. Zhang, G. Sun, B. Zhao, H. Ma, R. Wu, Z. Wei, Y. Liu, L. Liao, Y. Ye, Y. Huang, X. Xu, X. Duan, W. Ji, X. Duan. Van der Waals epitaxial growth of air-stable CrSe2 nanosheets with thickness-tunable magnetic order. Nat. Mater., 2021, 20(6): 818
CrossRef ADS Google scholar
[5]
X. Fan, R. Xin, L. Li, B. Zhang, C. Li, X. Zhou, H. Chen, H. Zhang, F. OuYang, Y. Zhou. Progress in the preparation and physical properties of two-dimensional Cr-based chalcogenide materials and heterojunctions. Front. Phys. 19, 2023, (2): 23401
CrossRef ADS Google scholar
[6]
B. Lei, A. Li, W. Zhou, Y. Wang, W. Xiong, Y. Chen, F. Ouyang. Room-temperature ferromagnetism and half-metallicity in monolayer orthorhombic CrS2. Front. Phys. 19, 2024, (4): 43200
CrossRef ADS Google scholar
[7]
X. Zhu, H. Liu, L. Liu, L. Ren, W. Li, L. Fang, X. Chen, L. Xie, Y. Jing, J. Chen, S. Liu, F. Ouyang, Y. Zhou, X. Xiong. Spin glass state in chemical vapor-deposited crystalline Cr2Se3 nanosheets. Chem. Mater., 2021, 33(10): 3851
CrossRef ADS Google scholar
[8]
Y. Zhou, C. Li, Y. Zhang, L. Wang, X. Fan, L. Zou, Z. Cai, J. Jiang, S. Zhou, B. Zhang, H. Zhang, W. Li, Z. Chen. Controllable thermochemical generation of active defects in the horizontal/vertical MoS2 for enhanced hydrogen evolution. Adv. Funct. Mater., 2023, 33(46): 2304302
CrossRef ADS Google scholar
[9]
R. Xie, W. Luo, L. Zou, X. Fan, C. Li, T. Lv, J. Jiang, Z. Chen, Y. Zhou. Low-temperature synthesis of colloidal few-layer WTe2 nanostructures for electrochemical hydrogen evolution. Discover Nano, 2023, 18(1): 44
CrossRef ADS Google scholar
[10]
Y. Zhou, J. L. Silva, J. M. Woods, J. V. Pondick, Q. Feng, Z. Liang, W. Liu, L. Lin, B. Deng, B. Brena, F. Xia, H. Peng, Z. Liu, H. Wang, C. M. Araujo, J. J. Cha. Revealing the contribution of individual factors to hydrogen evolution reaction catalytic activity. Adv. Mater., 2018, 30(18): 1706076
CrossRef ADS Google scholar
[11]
Y. Zhou, H. Jang, J. M. Woods, Y. Xie, P. Kumaravadivel, G. A. Pan, J. Liu, Y. Liu, D. G. Cahill, J. J. Cha. Direct synthesis of large-scale WTe2 thin films with low thermal conductivity. Adv. Funct. Mater., 2017, 27(8): 1605928
CrossRef ADS Google scholar
[12]
Y. Wen, Q. Wang, L. Yin, Q. Liu, F. Wang, F. Wang, Z. Wang, K. Liu, K. Xu, Y. Huang, T. A. Shifa, C. Jiang, J. Xiong, J. He. Epitaxial 2D PbS nanoplates arrays with highly efficient infrared response. Adv. Mater., 2016, 28(36): 8051
CrossRef ADS Google scholar
[13]
G. Wu, L. Xiang, W. Wang, C. Yao, Z. Yan, C. Zhang, J. Wu, Y. Liu, B. Zheng, H. Liu, C. Hu, X. Sun, C. Zhu, Y. Wang, X. Xiong, Y. Wu, L. Gao, D. Li, A. Pan, S. Li. Hierarchical processing enabled by 2D ferroelectric semiconductor transistor for low-power and high-efficiency AI vision system. Sci. Bull. (Beijing), 2024, 69(4): 473
CrossRef ADS Google scholar
[14]
H. Liu, C. Zhu, Y. Chen, X. Yi, X. Sun, Y. Liu, H. Wang, G. Wu, J. Wu, Y. Li, X. Zhu, D. Li, A. Pan. Polarization-sensitive photodetectors based on highly in-plane anisotropic violet phosphorus with large dichroic ratio. Adv. Funct. Mater., 2023, 34(17): 2314838
CrossRef ADS Google scholar
[15]
X. Sun, C. Zhu, J. Yi, L. Xiang, C. Ma, H. Liu, B. Zheng, Y. Liu, W. You, W. Zhang, D. Liang, Q. Shuai, X. Zhu, H. Duan, L. Liao, Y. Liu, D. Li, A. Pan. Reconfigurable logic-in-memory architectures based on a two-dimensional van der Waals heterostructure device. Nat. Electron., 2022, 5(11): 752
CrossRef ADS Google scholar
[16]
J. Zhu, L. Wang, J. Wu, Y. Liang, F. Xiao, B. Xu, Z. Zhang, X. Fan, Y. Zhou, J. Xia, Z. Wang. Achieving 1.2 fm/Hz1/2 displacement sensitivity with laser interferometry in two-dimensional nanomechanical resonators: Pathways towards quantum-noise-limited measurement at room temperature. Chin. Phys. Lett., 2023, 40(3): 038102
CrossRef ADS Google scholar
[17]
B. Liu, W. Chu, S. Liu, Y. Zhou, L. Zou, J. Fu, M. Liu, X. Fu, F. Ouyang, Y. Zhou. Engineering the nanostructures of solution proceed In2SexS3−x films with enhanced near-infrared absorption for photoelectrochemical water splitting. J. Phys. D Appl. Phys., 2022, 55(43): 434004
CrossRef ADS Google scholar
[18]
M. Li, H. Sun, J. Zhou, Y. Zhao. Engineering phonon thermal transport in few-layer PdSe2. Front. Phys. 19, 2023, (3): 33203
CrossRef ADS Google scholar
[19]
T. Zhu, Y. Zhang, X. Wei, M. Jiang, H. Xu. The rise of two-dimensional tellurium for next-generation electronics and optoelectronics. Front. Phys., 2023, 18(3): 33601
CrossRef ADS Google scholar
[20]
Y. Wang, X. Guo, S. You, J. Jiang, Z. Wang, F. Ouyang, H. Huang. Giant quartic-phonon decay in PVD-grown α-MoO3 flakes. Nano Res., 2023, 16(1): 1115
CrossRef ADS Google scholar
[21]
S. H. Chae, Y. Jin, T. S. Kim, D. S. Chung, H. Na, H. Nam, H. Kim, D. J. Perello, H. Y. Jeong, T. H. Ly, Y. H. Lee. Oxidation effect in octahedral hafnium disulfide thin film. ACS Nano, 2016, 10(1): 1309
CrossRef ADS Google scholar
[22]
M. J. Mleczko, C. Zhang, H. R. Lee, H. H. Kuo, B. Magyari-Köpe, R. G. Moore, Z. X. Shen, I. R. Fisher, Y. Nishi, E. Pop. HfSe2 and ZrSe2: Two-dimensional semiconductors with native high-κ oxides. Sci. Adv., 2017, 3(8): e1700481
CrossRef ADS Google scholar
[23]
W. Zhang, Z. Huang, W. Zhang, Y. Li. Two-dimensional semiconductors with possible high room temperature mobility. Nano Res., 2014, 7(12): 1731
CrossRef ADS Google scholar
[24]
G. Fiori, F. Bonaccorso, G. Iannaccone, T. Palacios, D. Neumaier, A. Seabaugh, S. K. Banerjee, L. Colombo. Electronics based on two-dimensional materials. Nat. Nanotechnol., 2014, 9(10): 768
CrossRef ADS Google scholar
[25]
N. Peimyoo, M. D. Barnes, J. D. Mehew, A. De Sanctis, I. Amit, J. Escolar, K. Anastasiou, A. P. Rooney, S. J. Haigh, S. Russo, M. F. Craciun, F. Withers. Laser-writable high-κ dielectric for van der Waals nanoelectronics. Sci. Adv., 2019, 5(1): eaau0906
CrossRef ADS Google scholar
[26]
L. Yin, K. Xu, Y. Wen, Z. Wang, Y. Huang, F. Wang, T. A. Shifa, R. Cheng, H. Ma, J. He. Ultrafast and ultrasensitive phototransistors based on few-layered HfSe2. Appl. Phys. Lett., 2016, 109(21): 213105
CrossRef ADS Google scholar
[27]
M. Kang, S. Rathi, I. Lee, D. Lim, J. Wang, L. Li, M. A. Khan, G. H. Kim. Electrical characterization of multilayer HfSe2 field-effect transistors on SiO2 substrate. Appl. Phys. Lett., 2015, 106(14): 143108
CrossRef ADS Google scholar
[28]
M. Kang, S. Rathi, I. Lee, L. Li, M. A. Khan, D. Lim, Y. Lee, J. Park, S. J. Yun, D. H. Youn, C. Jun, G. H. Kim. Tunable electrical properties of multilayer HfSe2 field effect transistors by oxygen plasma treatment. Nanoscale, 2017, 9(4): 1645
CrossRef ADS Google scholar
[29]
T.KangJ. ParkH.JungH.ChoiS.M. Lee N.LeeR. G. LeeG.KimS.H. KimH.Kim C.W. YangJ. JeonY.H. KimS.Lee, High-κ dielectric (HfO2)/2D semiconductor (HfSe2) gate stack for low-power steep-switching computing devices, Adv. Mater. 2312747, doi: 10.1002/adma.202312747 (2024)
[30]
A. L. Hector, W. Levason, G. Reid, S. D. Reid, M. Webster. Evaluation of group 4 metal bis-cyclopentadienyl complexes with selenolate and tellurolate ligands for CVD of ME2 films (E = Se or Te). Chem. Mater., 2008, 20(15): 5100
CrossRef ADS Google scholar
[31]
R. Yue, A. T. Barton, H. Zhu, A. Azcatl, L. F. Pena, J. Wang, X. Peng, N. Lu, L. Cheng, R. Addou, S. McDonnell, L. Colombo, J. W. P. Hsu, J. Kim, M. J. Kim, R. M. Wallace, C. L. Hinkle. HfSe2 thin films: 2D transition metal dichalcogenides grown by molecular beam epitaxy. ACS Nano, 2015, 9(1): 474
CrossRef ADS Google scholar
[32]
K. E. Aretouli, P. Tsipas, D. Tsoutsou, J. Marquez-Velasco, E. Xenogiannopoulou, S. A. Giamini, E. Vassalou, N. Kelaidis, A. Dimoulas. Two-dimensional semiconductor HfSe2 and MoSe2/HfSe2 van der Waals heterostructures by molecular beam epitaxy. Appl. Phys. Lett., 2015, 106(14): 143105
CrossRef ADS Google scholar
[33]
S. Li, M. E. Pam, Y. Li, L. Chen, Y. C. Chien, X. Fong, D. Chi, K. W. Ang. Wafer-scale 2D hafnium diselenide based memristor crossbar array for energy-efficient neural network hardware. Adv. Mater., 2022, 34(25): 2103376
CrossRef ADS Google scholar
[34]
B. Zheng, Y. Chen, Z. Wang, F. Qi, Z. Huang, X. Hao, P. Li, W. Zhang, Y. Li. Vertically oriented few-layered HfS2 nanosheets: Growth mechanism and optical properties. 2D Mater., 2016, 3(3): 035024
CrossRef ADS Google scholar
[35]
D. Wang, X. Zhang, H. Liu, J. Meng, J. Xia, Z. Yin, Y. Wang, J. You, X. M. Meng. Epitaxial growth of HfS2 on sapphire by chemical vapor deposition and application for photodetectors. 2D Mater., 2017, 4(3): 031012
CrossRef ADS Google scholar
[36]
L. Fu, F. Wang, B. Wu, N. Wu, W. Huang, H. Wang, C. Jin, L. Zhuang, J. He, L. Fu, Y. Liu. Van der Waals epitaxial growth of atomic layered HfS2 crystals for ultrasensitive near-infrared phototransistors. Adv. Mater., 2017, 29(32): 1700439
CrossRef ADS Google scholar
[37]
W. Li, J. Zhou, S. Cai, Z. Yu, J. Zhang, N. Fang, T. Li, Y. Wu, T. Chen, X. Xie, H. Ma, K. Yan, N. Dai, X. Wu, H. Zhao, Z. Wang, D. He, L. Pan, Y. Shi, P. Wang, W. Chen, K. Nagashio, X. Duan, X. Wang. Uniform and ultrathin high-κ gate dielectrics for two-dimensional electronic devices. Nat. Electron., 2019, 2(12): 563
CrossRef ADS Google scholar
[38]
C. Li, R. Xin, C. Y. Jiao, Z. Zhang, J. Qin, W. Chu, X. Zhou, Z. Li, Z. Wang, J. Xia, Y. Zhou. Synthesis of hetero-site nucleation twisted bilayer MoS2 by local airflow perturbations and interlayer angle characterization. J. Cent. South Univ., 2023, 30(10): 3187
CrossRef ADS Google scholar
[39]
X. Zhu, L. Wong, X. Fan, J. Zhao, Y. Zhou, F. Ouyang. Role of the spatial distribution of gas flow for tuning the vertical/planar growth of nonlayered two-dimensional nanoplates. Cryst. Growth Des., 2022, 22(1): 763
CrossRef ADS Google scholar
[40]
W. Chu, R. Xin, L. Zou, X. Fan, X. Zhou, C. Li, Y. Zhou. Synthesis of nonlayered 2D α-Fe2O3 nanosheets by ultralow concentration precursor with Se catalysts design. Phys. Status Solidi R., 2023, 2023: 2300102
CrossRef ADS Google scholar
[41]
D. Wang, X. Zhang, G. Guo, S. Gao, X. Li, J. Meng, Z. Yin, H. Liu, M. Gao, L. Cheng, J. You, R. Wang. Large-area synthesis of layered HfS2(1−x)Se2x alloys with fully tunable chemical compositions and bandgaps. Adv. Mater., 2018, 30(44): 1803285
CrossRef ADS Google scholar
[42]
Q. Yao, L. Zhang, P. Bampoulis, H. J. W. Zandvliet. Nanoscale investigation of defects and oxidation of HfSe2. J. Phys. Chem. C, 2018, 122(44): 25498
CrossRef ADS Google scholar
[43]
F. Cui, X. Zhao, B. Tang, L. Zhu, Y. Huan, Q. Chen, Z. Liu, Y. Zhang. Epitaxial growth of step-like Cr2S3 lateral homojunctions towards versatile conduction polarities and enhanced transistor performances. Small, 2022, 18(4): 2105744
CrossRef ADS Google scholar
[44]
F. Zhang, Z. Mo, B. Cui, S. Liu, Q. Xia, B. Li, L. Li, Z. Zhang, J. He, M. Zhong. Bandgap engineering of BiIns nanowire for wide-spectrum, high-responsivity, and polarimetric-sensitive detection. Adv. Funct. Mater., 2023, 33(49): 2306077
CrossRef ADS Google scholar
[45]
Z. Mo, F. Zhang, D. Wang, B. Cui, Q. Xia, B. Li, J. He, M. Zhong. Ultrafast-response and broad-spectrum polarization sensitive photodetector based on Bi1.85In0.15S3 nanowire. Appl. Phys. Lett., 2022, 120(20): 201105
CrossRef ADS Google scholar
[46]
H. Chen, X. Zhou, L. Tang, Y. Chen, H. Luo, X. Yuan, C. R. Bowen, D. Zhang. HfO2-based ferroelectrics: From enhancing performance, material design, to applications. Appl. Phys. Rev., 2022, 9(1): 011307
CrossRef ADS Google scholar
[47]
H. Chen, L. Tang, H. Luo, X. Yuan, D. Zhang. Modulation of ferroelectricity in atomic layer deposited HfO2/ZrO2 multilayer films. Mater. Lett., 2022, 313: 131732
CrossRef ADS Google scholar
[48]
S. Lai, S. Byeon, S. K. Jang, J. Lee, B. H. Lee, J. H. Park, Y. H. Kim, S. Lee. HfO2/HfS2 hybrid heterostructure fabricated via controllable chemical conversion of two-dimensional HfS2. Nanoscale, 2018, 10(39): 18758
CrossRef ADS Google scholar
[49]
X. Fan, L. Zou, W. Chu, L. Wang, Y. Zhou. Synthesis of high resistive two-dimensional nonlayered Cr2S3 nanoflakes with stable phosphorus dopants by chemical vapor deposition. Appl. Phys. Lett., 2023, 122(22): 222101
CrossRef ADS Google scholar

Declarations

The authors declare that they have no competing interests and there are no conflicts.

Electronic supplementary materials

The online version contains supplementary material available at https://doi.org/10.1007/s11467-024-1414-7 and https://journal.hep.com.cn/fop/EN/10.1007/s11467-024-1414-7.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. U23A20570 and 51902346), the Science and Technology Innovation Program of Hunan Province (“HuXiang Young Talents”, Grant No. 2021RC3021), the Key Project of the Natural Science Program of Xinjiang Uygur Autonomous Region (Grant No. 2023D01D03), and the Natural Science Foundation of Hunan Province (Grant No. 2021JJ40780). This work was supported by Double Cs-corrected TEM Laboratory of the State Key Laboratory of Powder Metallurgy.

RIGHTS & PERMISSIONS

2024 Higher Education Press
AI Summary AI Mindmap
PDF(4100 KB)

Supplementary files

fop-24417-of-zhouyu_suppl_1 (4237 KB)

586

Accesses

5

Citations

Detail

Sections
Recommended

/