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![a) Crystal structure of α‐MoO3. Mo (black) and O (red) forming distorted octahedra. b) Optical image of as‐grown MoO3 flakes. c) Exfoliated MoO3 flakes. d) HRTEM image of exfoliated MoO3 flakes. e) Selected area electron diffraction (SAED) pattern of exfoliated MoO3 flakes in [010] zone axis.](profile/Brian-Holler-2/publication/343938237/figure/fig1/AS:11431281179398013@1691181946469/a-Crystal-structure-of-a-MoO3-Mo-black-and-O-red-forming-distorted-octahedra-b.png)
a) Crystal structure of α‐MoO3. Mo (black) and O (red) forming distorted octahedra. b) Optical image of as‐grown MoO3 flakes. c) Exfoliated MoO3 flakes. d) HRTEM image of exfoliated MoO3 flakes. e) Selected area electron diffraction (SAED) pattern of exfoliated MoO3 flakes in [010] zone axis.
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The search for smaller electronic and optoelectronic devices is a leading research towards atomically thin graphene‐like 2D semiconductor materials. Due to the decreasing size and unique van der Waals (vdW) nature of these 2D semiconductors, there is an imperative need to find compatible gate dielectrics that can enable high gate coupling efficienc...
Citations
... [11] Gao Xuan P. A. et al. grew thick (5-15 um) MoO3s by physical vapor deposition (PVD) in tube furnace and integrated it as a high-κ gate dielectric in WSe2 FET. [12] Li J o u r n a l P r e -p r o o f ...
Two-dimensional (2D) metal oxide α-MoO3 shows great potentials because of its very high dielectric constant, air stability and anisotropic phonon polaritons. However, a method to produce ultrathin single crystalline α-MoO3 with high transferability for functional device architecture is lacking. Herein, we report on the controllable synthesis of ultrathin α-MoO3 single crystals via chemical vapor deposition (CVD) assisted by plasma pretreatment. We also carried out systematic computational work to explicate the mechanism for the slantly-oriented growth of thin nanosheets on plasma-pretreated substrate. The method possesses certain universality to synthesize other ultrathin oxide materials, such as Bi2O3 and Sb2O3 nanosheets. As-grown α-MoO3 presents a high dielectric constant (≈ 40), ultrathin thickness (≈ 3nm) and high transferability. Memristors with α-MoO3 as the functional layers show excellent performance featuring high on/off ratio of approximately 10 4 , much lower set voltage around 0.5 V, and highly repetitive voltage sweep endurance. The power consumption of MoO3 memristors is significantly reduced, resulted from reduced thickness of the MoO3 nanosheets. Single crystal ultrathin α-MoO3 shows great potentials in post-Moore memristor and the synthesis of CVD assisted by plasma pretreatment approach points to a new route for materials growth.
... 43,44 Two-dimensional MoO 3 layers have been used as a high-k dielectric to fabricate a Ni/WSe 2 based transistor where the MoO 3 will inject holes into the WSe 2 channel layer. 45 This study is focused on the utilisation of CVD grown lamellar MoO 3 multilayered sheets as switching materials and incorporating them as an active part of a synapse that mimics basic functionalities of the biological synapse. In order to ensure the uniform distribution of nanosheets for device fabrication, the prepared multilayers are ultrasonicated for more than two hours in ethanol. ...
Brain-inspired computing systems require a rich variety of neuromorphic devices using multi-functional materials operating at room temperature. Artificial synapses which can be operated using optical and electrical stimuli are in high demand. In this regard, layered materials have attracted a lot of attention due to their tunable energy gap and exotic properties. In the current study, we report the growth of layered MoO3 using the chemical vapor deposition (CVD) technique. MoO3 has an energy gap of 3.22 eV and grows with a large aspect ratio, as seen through optical and scanning electron microscopy. We used transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy for complete characterisation. The two-terminal devices using platinum (Pt/MoO3/Pt) exhibit superior memory with the high-resistance state (HRS) and low-resistance state (LRS) differing by a large resistance (∼MΩ). The devices also show excellent synaptic characteristics. Both optical and electrical pulses can be utilised to stimulate the synapse. Consistent learning (potentiation) and forgetting (depression) curves are measured. Transition from long term depression to long term potentiation can be achieved using the spike frequency dependent pulsing scheme. We have found that the amplification of postsynaptic current can be tuned using such frequency dependent spikes. This will help us to design neuromorphic devices with the required synaptic amplification.
... Most of the 2D MOs show an excellent optical response to the ultraviolet (UV) region, which is suitable for building UV detectors. Similar to the 2D black phosphorus, 2D MO can be achieved by several exfoliation techniques such as mechanical exfoliation [61][62][63] and liquid-phase exfoliation [61,64]. Also, the 2D MOs can be fabricated by liquid-phase synthesis, such as adaptive ionic layer [65], self-assembly [66], and salt-templated epitaxy [67]. ...
Two-dimensional (2D) nanomaterials like silicene, MXenes, transition metal dichalcogenides (TMDs), and phosphorene have earned substantial interest where charge carrier mobility concerning whole body participation plays a significant role in required physical, electrical, chemical, and optical properties. The obligatory recommendations are bequeathed mainly to 2D materials with an atomic-thin layer structure and large surface area. To eliminate difficulties for device applications, the fabrication of heterostructure with weak interlayer van der Waals interaction is conceived for molding composites. Thus, new composites engender tunable band gap engineering with reduced charge carrier scattering encompassing defects. In this regard, phosphorene with a puckered structure and prominent anisotropy may unleash a new potential application in the new and stable 2D arena for next-generation photovoltaic (PV) cells, better anode material for energy storage, improved performance than lithium and sodium ion batteries, and supercapacitors. This article examines the existing literature, density functional theory (DFT) approximation mainly for complex heterostructures, and recent advances in 2D materials with a specific focus on phosphorene in relation to surface protection, layer structure alignment, and strain conditions for field applications. This review also explains and discusses major applications of phosphorene in sensors, catalysis, field effect transistors, and batteries.
... An additional important aspect of MoO 3 is its layered structure, i.e., its adjacent two-dimensional (2D) crystalline layers are bound by weak van der Waals interactions [2,13]. This allows the easy preparation of ultra-thin films or even monolayers using simple techniques, such as the scotch tape exfoliation method [14], although it has been also successfully grown in 2D form using the hot plate thermal deposition technique [15]. The 2D layers have the potential to be used in flexible and stretchable electronics due to their mechanical properties and transparency [16]. ...
Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO3 monolayer.
... Ultrathin films are thin films with thicknesses of a few nanometers, making them ultra-compact and highly reactive [1][2][3][4]. These films possess exceptional properties, including a high surface area, electrical conductivity, and optical transparency, which make them ideal for applications in electronics, ferromagnetism, catalytic, optics, and energy storage [1,3,[5][6][7]. Molybdenum trioxide (MoO 3 ) is a metal oxide with several interesting properties, making it a popular material for the fabrication of thin films and ultrathin films. MoO 3 is an interesting material to study due to its distinctive electrical and optical characteristics [8,9]. ...
... MoO 3 is an interesting material to study due to its distinctive electrical and optical characteristics [8,9]. As an n-type semiconductor, it has high electron mobility, making it practical for use in electronic devices such as energy storage devices, transistors, solar cells, and supercapacitors [5,10,11]. Additionally, MoO 3 also serves as a good gas sensor [12] and can detect various gases, including oxygen and nitrogen oxides. The combination of optical transparency, high conductivity, wide bandgap, strong electro-optical properties, and environmental stability make α-MoO 3 an attractive material for use in optoelectronic devices. ...
Ultrathin MoO3 semiconductor nanostructures have garnered significant interest as a promising nanomaterial for transparent nano- and optoelectronics, owing to their exceptional reactivity. Due to the shortage of knowledge about the electronic and optoelectronic properties of MoO3/n-Si via an ALD system of few nanometers, we utilized the preparation of an ultrathin MoO3 film at temperatures of 100, 150, 200, and 250 °C. The effect of the depositing temperatures on using bis(tbutylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum source for highly stable UV photodetectors were reported. The ON–OFF and the photodetector dynamic behaviors of these samples under different applied voltages of 0, 0.5, 1, 2, 3, 4, and 5 V were collected. This study shows that the ultrasmooth and homogenous films of less than a 0.30 nm roughness deposited at 200 °C were used efficiently for high-performance UV photodetector behaviors with a high sheet carrier concentration of 7.6 × 1010 cm−2 and external quantum efficiency of 1.72 × 1011. The electronic parameters were analyzed based on thermionic emission theory, where Cheung and Nord’s methods were utilized to determine the photodetector electronic parameters, such as the ideality factor (n), barrier height (Φ0), and series resistance (Rs). The n-factor values were higher in the low voltage region of the I–V diagram, potentially due to series resistance causing a voltage drop across the interfacial thin film and charge accumulation at the interface states between the MoO3 and Si surfaces.
... These low values of J-V characteristic parameters may be due to the inappropriate selection of transport layers concerning the LaFeO 3 perovskite absorber. To optimize the performance of our proposed device, further simulation works were carried out with the same approach by taking a variety of oxide materials as ETL (TiO 2 [21], In 2 O 3 [22], and IGZO [23]) and as HTL (NiO [21], MoO 3 [24,25] , and WO 3 [24,26,27]). To compare PSC's performance with that of ZnO ETL and Cu 2 O HTL, the thickness of these ETL and HTL materials is kept at 100 and 200 nm, respectively. ...
Mott insulator-based heterostructures have been proposed as good candidates for highly efficient solar cells. Mott insulating transition metal oxide (LaFeO3) containing earth-abundant elements have long-term stability and the strong electron–electron correlation found in them enhances the quantum efficiency of the device. This paper represents a simulation work to access the energy conversion ability of Mott insulator-based solar cell with LaFeO3 as its absorbing layer using a solar cell capacitance simulator (SCAPS). This work explores the influence of the electron transport layer (ETL), hole transport layer (HTL), active perovskite layer thickness, and defect density on device performance. The simulation showed that In2O3 and MoO3 are the most competent materials for ETL and HTL layers. Additionally, the impact of other optoelectronic parameters of different layers is also investigated and discussed. An efficiency of 9.11 % (with Voc = 1.997 V, Jsc = 6.75 mA/cm², and fill factor of 67.55 %) has been achieved with Nb:STO/In2O3/LaFeO3/MoO3/Au solar cell architecture. The simulated model has great potential for making stable solar cell devices by using Mott insulator perovskite materials.
... More importantly, α-MoO 3 has high dielectric constant. It has been shown that α-MoO 3 has the relative dielectric constant as high as 35, near 10 times that of SiO 2 [12]. In addition, the unique vdW characteristics can be easily integrated with other 2D vdW semiconductors, promising applications in future 2D electronics and optoelectronics [13,14]. ...
Two-dimensional van der Waals crystals (2D vdW) are recognized as one of the potential materials to solve the physical limits caused by size scaling. Here, vdW metal oxide MoO3 is applied with the gate dielectric in a 2D field-effect transistor (FET). Due to its high dielectric constant and the good response of MoS2 to visible light, we obtained a field effect transistor for photodetection. In general, the device exhibits a threshold voltage near 0 V, Ion/Ioff ratio of 105, electron mobility about 85 cm2 V−1 s−1 and a good response to visible light, the responsivity is near 5 A/W at low laser power, which shows that MoO3 is a potential material as gate dielectric.
... Recently, MoO 3 thin films were also found to have a high dielectric constant and were used as the gate oxide in thin film transistors. 6 From a more fundamental science point of view, MoO 3 is an excellent candidate oxide for exfoliation to mono-or few-layer ultrathin films. 7 In that sense, it is comparable to V 2 O 5 because in both cases, the transition metal is in its highest possible valence state and they both form layered crystals with weak van der Waals interactions between the neutral layers. ...
Orthorhombic α−MoO3 is a layered oxide with various applications and with excellent potential to be exfoliated as a 2D ultra-thin film or monolayer. In this paper, we present a first-principles computational study of its vibrational properties. Our focus is on the zone center modes, which can be measured by a combination of infrared and Raman spectroscopy. The polarization dependent spectra are simulated. Calculations are also performed for a monolayer form in which “double layers” of Mo2O6, which are weakly van der Waals bonded in the α-structure, are isolated. Shifts in phonon frequencies are analyzed.
... [171,172] Recently MoO 3 has also been investigated for its applications in 2D field effect transistors (FETs) as both the conducting channel [173,174] and as the gate oxide dielectric material. [175] As mentioned in Sec. I, MoO 3 has an orthorhombic α-phase which allows for simple mechanical exfoliation. ...
... Since α-MoO 3 intrinsically has a band gap of ∼3eV, it seems natural to realize its function as a dielectric material for 2D semiconductor devices. In a recent paper, Holler et al. [175] demonstrated that MoO 3 can act as the top-gating material in layered 2D semiconductor FETs. This was motivated by experimental claims of thin-film MoO 3 having a large dielectric constant. ...
In the field of atomically thin 2D materials, oxides are relatively unexplored in spite of the large number of layered oxide structures amenable to exfoliation. There is an increasing interest in ultrathin film oxide nanostructures from applied points of view. In this Perspective paper, recent progress in understanding the fundamental properties of 2D oxides is discussed. Two families of 2D oxides are considered: (1) van der Waals bonded layered materials in which the transition metal is in its highest valence state (represented by V 2O 5 and MoO 3) and (2) layered materials with ionic bonding between positive alkali cation layers and negatively charged transition metal oxide layers (LiCoO 2). The chemical exfoliation process and its combination with mechanical exfoliation are presented for the latter. Structural phase stability of the resulting nanoflakes, the role of cation size, and the importance of defects in oxides are discussed. Effects of two-dimensionality on phonons, electronic band structures, and electronic screening are placed in the context of what is known on other 2D materials, such as transition metal dichalcogenides. The electronic structure is discussed at the level of many-body-perturbation theory using the quasiparticle self-consistent G W method, the accuracy of which is critically evaluated including effects of electron–hole interactions on screening and electron–phonon coupling. The predicted occurrence of a two-dimensional electron gas on Li-covered surfaces of LiCoO 2 and its relation to topological aspects of the band structure and bonding is presented as an example of the essential role of the surface in ultrathin materials. Finally, some case studies of the electronic transport and the use of these oxides in nanoscale field-effect transistors are presented.
... [167,168] Recently MoO 3 has also been investigated for its applications in 2D field effect transistors (FETs) as both the conducting channel [169,170] and as the gate oxide dielectric material. [171] As mentioned in Sec. I, MoO 3 has an orthorhombic α-phase which allows for simple mechanical exfoliation. ...
... Interestingly, this effect was observed to be reversible upon annealing the exposed flakes in an inert atmosphere, returning the α-MoO 3 to an insulating state. F presence was observed al. [171] with permission. ...
... Since α-MoO 3 intrinsically has a band gap of ∼3eV, it seems natural to realize its function as a dielectric material for 2D semiconductor devices. In a recent paper, Holler et al. [171] demonstrated that MoO 3 can act as the top-gating material in layered 2D semiconductor FETs. This was motivated by experimental claims of thin-film MoO 3 having a large dielectric constant. ...
In the field of atomically thin 2D materials, oxides are relatively unexplored in spite of the large number of layered oxide structures amenable to exfoliation. There is an increasing interest in ultra-thin film oxide nanostructures from applied points of view. In this perspective paper, recent progress in understanding the fundamental properties of 2D oxides is discussed. Two families of 2D oxides are considered: (1) van der Waals bonded layered materials in which the transition metal is in its highest valence state (represented by V$_2$O$_5$ and MoO$_3$) and (2) layered materials with ionic bonding between positive alkali cation layers and negatively charged transition metal oxide layers (LiCoO$_2$). The chemical exfoliation process and its combinaton with mechanical exfoliation are presented for the latter. Structural phase stability of the resulting nanoflakes, the role of cation size and the importance of defects in oxides are discussed. Effects of two-dimensionality on phonons, electronic band structures and electronic screening are placed in the context of what is known on other 2D materials, such as transition metal dichalcogenides. Electronic structure is discussed at the level of many-body-perturbation theory using the quasiparticle self-consistent $GW$ method, the accuracy of which is critically evaluated including effects of electron-hole interactions on screening and electron-phonon coupling. The predicted occurence of a two-dimensional electron gas on Li covered surfaces of LiCoO$_2$ and its relation to topological aspects of the band structure and bonding is presented as an example of the essential role of the surface in ultrathin materials. Finally, some case studies of the electronic transport and the use of these oxides in nanoscale field effect transistors are presented.
