Plasma-Assisted Synthesis of High-Mobility Atomically Layered Violet Phosphorus (original) (raw)
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Two-dimensional (2D) nanoflakes have emerged as a class of materials that may impact electronic technologies in the near future. A challenging but rewarding work is to experimentally identify 2D materials and explore their properties. Here, we report the synthesis of a layered material, P 20.56(1) Sb 0.44(1) , with a systematic study on characterizations and device applications. This material demonstrates a direct band gap of around 1.67 eV. Using a laser-cutting method, the thin flakes of this material can be separated into multiple segments. We have also fabricated field effect transistors based on few-layer P 20.56(1) Sb 0.44(1) flakes with a thickness down to a few nanometers. Interestingly, these field effect transistors show strong photoresponse within the wavelength range of visible light. At room temperature, we have achieved good mobility values (up to 58.96 cm 2 /V·s), a reasonably high on/off current ratio (∼10 3), and intrinsic responsivity up to 10 μA/W. Our results demonstrate the potential of P 20.56(1) Sb 0.44(1) thin flakes as a two-dimensional material for applications in visible light detectors.
Applied Materials Today, 2018
Exfoliated few-layer black-phosphorus (BP) has been explored for a variety of electrical and optoelectronic applications. Plasma-assisted thinning of BP has emerged as an exciting pathway to achieve BP crystals of desired thickness. However, to fully realise the true potential of plasma-assisted thinning of BP and other emerging 2D materials, it is critical to understand the effects of different plasma environments on the electrical and optoelectronic properties of the resultant material. Here, we investigate the influence of Ar and O 2 plasma on the electrical and optoelectronic properties of plasma-treated BP flakes. It is revealed that by manipulating the environment under which BP is exposed to the plasma, it is possible to engineer defects that lead to new photoluminescence (PL) emission peaks without compromising the switching ratios or carrier mobilities of BP-based field effect transistors (FETs). Overall, our study finds the use of O 2 plasma as a more suitable approach to retain and enrich the intrinsic (opto)electronic properties of BP. Additionally, our study, for the first time, experimentally reveals the ability of BP to respond to UV excitation.
Nature communications, 2014
Graphene and transition metal dichalcogenides (TMDCs) are the two major types of layered materials under intensive investigation. However, the zero-bandgap nature of graphene and the relatively low mobility in TMDCs limit their applications. Here we reintroduce black phosphorus (BP), the most stable allotrope of phosphorus with strong intrinsic in-plane anisotropy, to the layered-material family. For 15-nm-thick BP, we measure a Hall mobility of 1,000 and 600 cm 2 V À 1 s À 1 for holes along the light (x) and heavy (y) effective mass directions at 120 K. BP thin films also exhibit large and anisotropic in-plane optical conductivity from 2 to 5 mm. Field-effect transistors using 5 nm BP along x direction exhibit an on-off current ratio exceeding 10 5 , a field-effect mobility of 205 cm 2 V À 1 s À 1 , and good current saturation characteristics all at room temperature. BP shows great potential for thin-film electronics, infrared optoelectronics and novel devices in which anisotropic properties are desirable.
Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation
Scientific Reports, 2016
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO 2 /Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using twodimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.
Black phosphorus: narrow gap, wide applications
The recent isolation of atomically thin black phosphorus by mechanical exfoliation of bulk layered crystals has triggered an unprecedented interest, even higher than that raised by the first works on graphene and other two-dimensional, in the nanoscience and nanotechnology community. In this Perspective we critically analyze the reasons behind the surge of experimental and theoretical works on this novel two-dimensional material. We believe that the fact that black phosphorus band gap value spans over a wide range of the electromagnetic spectrum that was not covered by any other two-dimensional material isolated to date (with remarkable industrial interest such as thermal imaging, thermoelectrics, fiber optics communication, photovoltaics, etc), its high carrier mobility, its ambipolar field-effect and its rather unusual in-plane anisotropy drew the attention of the scientific community towards this two-dimensional material. Here we also review the current advances, the future directions and the challenges in this young research field.
Isolation and characterization of few-layer black phosphorus
2014
Isolation and characterization of mechanically exfoliated black phosphorus flakes with a thickness down to two single-layers is presented. A modification of the mechanical exfoliation method, which provides higher yield of atomically thin flakes than conventional mechanical exfoliation, has been developed. We present general guidelines to determine the number of layers using optical microscopy, Raman spectroscopy and transmission electron microscopy (TEM) in a fast and reliable way. Moreover, we demonstrate that the exfoliated flakes are highly crystalline and that they are stable even in free-standing form through Raman spectroscopy and TEM measurements. A strong thickness dependence of the band structure is found by density functional theory (DFT) calculations. The exciton binding energy, within an effective mass approximation, is also calcu- lated for different number of layers. Our computational results for the optical gap are consistent with preliminary photoluminescence results on thin flakes. Finally, we study the environmental stability of black phosphorus flakes finding that the flakes are very hydrophilic and that long term exposure to air moisture etches black phosphorus away. Nonetheless, we demonstrate that the aging of the flakes is slow enough to allow fabrication of field-effect transistors with strong ambipolar behavior. DFT calculations also give us insight into the water-induced changes of the structural and electronic properties of black phosphorus.
Two-Dimensional Phosphorus: From the Synthesis Towards the Device Integration
Zenodo (CERN European Organization for Nuclear Research), 2021
hosphorus and silicon two-dimensional (2D) allotropes have been the forerunners among the postgraphene monoelemental 2D materials. The scientific and technological advantages of these materials require the development of processing methods to guarantee their effective integration in new devices for nanoelectronics. In the present thesis work, some of the unresolved bottlenecks along the device integration path of 2D elemental phosphorus allotropes have been examined considering specifically the case of the-P (single-layer black phosphorus or phosphorene) and-P (blue phosphorene) 2D polymorphs. The integration of the 2D-P phase in devices has been the subject of extensive investigations and nowadays relies on an almost consolidated path that has led to applications spanning a wide range of fields. One of the few remaining obstacles on this path is the lack of a scalable method to produce 2D-P layers on large areas and with accurate control of the thickness. In particular, such control is difficult to achieve in the exfoliation of layered black phosphorus (BP) crystals. In this respect, micro-Raman spectroscopy has been used both as a metrological tool to determine the thickness of the exfoliated flakes and as method to achieve their controllable thickness reduction employing the laser thinning technique. However, thickness determination methods based on the calibration of the intensity of the Raman bands have been poorly investigated in the case of multilayer BP flakes due to difficulties caused by optical interferences and anisotropy effects. In this thesis work, we have proposed a novel Raman spectroscopy approach that, carefully accounting for these effects, allowed the quick discrimination of the thickness of exfoliated BP flakes between 5 nm and 100 nm. Moreover, in order to achieve a better control of the laser thinning process down to the ultimate 2D limit, we have also investigated the effects of the substrate on the laser heating and ablation of multilayer BP flakes. Raman thermometry experiments and numerical calculations of the heat diffusion problem have elucidated that optical, thermal, and mechanical effects caused by the substrate may act differently on the laser heating and ablation of multilayer flakes depending on their thickness. An effective device integration route for the 2D-P phase, instead, is still missing due to more stringent requirements in the synthesis, based on epitaxial techniques, and to the instability issue outside the UHV growth environment. These obstacles are commonly shared with other members of the family of 2D epitaxial Xenes and, in this work, have been investigated considering the case of-P epitaxially grown on Au(111)/mica substrates. The details of its atomic structure and the chemical reactivity to ex-situ and in-situ oxygen exposure have been analyzed with the aid of Scanning Tunneling Microscopy (STM) and X-Ray Photoelectron Spectroscopy (XPS). The air-instability issues have been tackled by developing an encapsulation strategy based on the in-situ growth of an Al2O3 capping layer that, in turn, allowed the handling of epitaxial phosphorus along the preliminary steps of a device integration process. In this respect, two novel approaches for the transfer of the epitaxial membrane from the growth substrate towards target substrates have been surveyed. Both the transfer methods can be generalized to the whole class of 2D epitaxial Xenes grown on metal/mica paving the way for the establishment of methodological standards for their manipulation. In particular, the universality of such approaches has been exploited for the successful fabrication of back-gated FET and MIM devices on Al2O3/multilayer silicene/Ag(111) and Al2O3/epitaxial phosphorus/Au(111) mica-delaminated samples, respectively. The epitaxial phosphorus MIM devices may open intriguing perspectives to study of the nonvolatile resistive switching in monoelemental 2D materials.
Ultrathin black phosphorus, or phosphorene, is the second known elementary two-dimensional material that can be exfoliated from a bulk van der Waals crystal. Unlike graphene it is a semiconductor with a sizeable band gap and its excellent electronic properties make it attractive for applications in transistor, logic, and optoelectronic devices. However, it is also the first widely investigated two dimensional electronic material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation affects the physical transport properties and to enable future application of phosphorene. Here we demonstrate that atomically thin graphene and hexagonal boron nitride crystals can be used for passivation of ultrathin black phosphorus. We report that few-layer pristine black phosphorus channels passivated in an inert gas environment, without any prior exposure to air, exhibit greatly improved n-type charge transport resulting in symmetric electron and hole trans-conductance characteristics. We attribute these results to the formation of oxygen acceptor states in air-exposed samples which drastically perturb the band structure in comparison to the pristine passivated black phosphorus.
arXiv (Cornell University), 2014
Thin layers of black phosphorus have recently raised interest for their two-dimensional (2D) semiconducting properties, such as tunable direct bandgap and high carrier mobilities. This lamellar crystal of P atoms stacked together by weak van der Waals forces can be exfoliated down to the stratophosphane monolayer (also called phosphorene) using procedures similar to those used for graphene. Properties of this 2D material are however challenging to probe due to a fast and ubiquitous degradation upon exposure to ambient conditions. Herein, we investigate the crystal degradation using in-situ Raman and transmission electron spectroscopies and highlight a process involving a photo-induced oxidation reaction with adsorbed oxygen in water. The experimental conditions to prepare and preserve mono-, bi-and multilayers of stratophosphane in their pristine states were determined. Study on these 2D layers provides new insights on the effect of confinement on the chemical reactivity and the vibrational modes of black phosphorus.