Layered Black Phosphorus Research Articles

From Amorphous Red Phosphorus to a Few Layers of Black Phosphorus: A Low-cost and Efficient Preparation Process

Abstract: In this work, we present an efficiency synthesis method of phosphorene from red phosphorus by means of black phosphorus. The latter was synthesized by using copper, tin, tin iodide and red phosphorus as precursor at low pressure-temperature. Characterizations with powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), high-resolution TEM (HR-TEM) and Raman spectroscopy were performed to confirm the high quality and purity of black phosphorus crystal. Liquid phase method was used to exfoliate black phosphorus to phosphorene in N-methyl-2-pyrrolidone (NMP) as solvent. Atomic force microscopy and STEM were used to confirm the exfoliation of black phophorus in a few layers of phophorene. Keywords: 2D materials, Red phosphorus, Black phosphorus, Phosphorene, Liquid-phase exfoliation.

Strain-induced vibrational properties of few layer black phosphorus and MoTe2 via Raman spectroscopy

We studied and compared the effect of tensile strain on the Raman spectra of black phosphorus (BP) and molybdenum ditelluride (MoTe2) crystals by using a simple custom strain device. In-situ Raman spectroscopy on BP revealed clear red shifting of all three phonon modes, A1g, B2g and A2g, under tensile stress. From our theoretical analyses, we found that such red shifting strongly depends on the direction of the strain exerted on the system even within the elastic deformation limit (i.e. strain ≤ 1 %). In particular, calculated results for the strain along the armchair direction are consistent with our experimental data, confirming that the strain applied to the sample acts effectively along the armchair direction. In a comparative study, we found that the effect of strain on the Raman shifting is larger for BP than that for MoTe2, presumably due to the smaller Young’s modulus of BP. We also see a remarkable resemblance between donor-type intercalation induced vibrational properties and tensile stress-induced vibrational properties in BP. We anticipate that our method of in-situ Raman spectroscopy can be an effective tool that can allow observation of strain effect directly which is critical for future flexible electronic devices.

Resonant Tunneling and Negative Differential Resistance in Black Phosphorus Vertical Heterostructures

AbstractResonant tunneling diodes with negative differential resistance (NDR) have attracted significant attention due to their unique quantum resonant tunneling phenomena and potential applications in terahertz emission/detection and high‐density logic/memory. In this paper, resonant tunneling devices, where the carriers tunnel through a hexagonal boron nitride (hBN) barrier sandwiched by two black phosphorus (BP) layers, are explored. The resonance occurs when the energy bands of the two black phosphorus layers are aligned. The conductive atomic force microscopy (CAFM) measurements reveal prominent NDR peaks with large peak‐to‐valley ratios at room temperature. It is found that the positions of the NDR peaks are very sensitive to the amplitude and the shape of the voltage waveform used in CAFM, which can be explained by the charge trapping effect. Furthermore, resonant tunneling transistors are demonstrated based on BP/hBN/BP stacks in which the locations of the NDR peaks are tunable by the electrostatic gating. As compared to the traditional tunneling diodes based on bulk materials, the tunneling devices based on thin boron nitride tunneling barrier and high mobility black phosphorus offer ultra‐high‐speed response. This feature, together with the NDR characteristics, provides the potential for applications in THz oscillators and multi‐value logic devices.

Improving room-temperature trace NO2 sensing of black phosphorus nanosheets by incorporating benzyl viologen

Black phosphorus (BP), an appealing two-dimensional (2D) material, has attracted considerable attention in gas sensing by virtue of large specific surface area, high carrier mobility and small out-plane conductivity, but undesirably hindered by incomplete recovery and fragile reproducibility especially toward strongly oxidizing NO2 gas. To overcome these limitations, in this report we attempt to incorporate benzyl viologen (BV) with few-layer BP nanosheets to detect trace NO2 at room temperature (20 °C). Compared with BP sensor, BP-BV one showed superior recovery characteristics, repeatability, selectivity and humidity-repelling features. In addition, the sensor response remained quite large and nearly unchanged after BV incorporation (-33 % for BP-BV-1 sensor vs. -32 % for BP counterpart toward 50 ppb NO2, which was among the best cases of BP-involving NO2 detection). Herein, BP layers not only interacted with NO2 gas but also transported electrons. BV mainly played dual roles in the composites during sensing tests. On the one hand, BV offered additional electrons to NO2 gas to compensate for NO2 adsorption loss arising from BV-induced partial covering of some high-energy sorption sites on BP nanosheets. On the other hand, BV effectively passivated BP through occupying these sites, thus maintaining a reversible recovery and a repeatable response. This work revealed an improved NO2 sensing of BP nanosheets by incorporating BV material of optimal content, enriching the alternative strategies for reversible and sensitive operation of novel BP-related sensors.

Synthesis of Highly Stable One-Dimensional Black Phosphorus/h-BN Heterostructures: A Novel Flexible Electronic PlatformSupported by the National Natural Science Foundation of China (Grant Nos. 11804184, 11974208, and 21905159) and the Shandong Provincial Science Foundation (Grant Nos. ZR2019MA054, 2019KJJ020, and ZR2019BA010).

Layered black phosphorus (BP) has recently emerged as a promising semiconductor because of its tunable band gap, high carrier mobility and strongly in-plane anisotropic properties. One-dimensional (1D) BP materials are attractive for applications in electronic and thermal devices, owing to their tailored charge and phonon transports along certain orientations. However, the fabrication of 1D BP materials still remains elusive thus far. We herein report the successful synthesis and characterization of nanotube-like BP for the first time by a selective composite with hexagonal boron nitride (h-BN) nanotubes under high pressure and high temperature conditions. The produced 1D BP/h-BN composites possess flexible diameter, length and thickness by adjusting the experimental synthesis parameters. Interestingly, it is important to notice that the stability of our BP sample has been significantly improved under the formation of heterostructures, which can actively promote their commercial applications. Our experimental work, together with first-principles calculations, presents a new scalable strategy of designing 1D tube-like BP/h-BN heterostructures that are promising candidates for flexible and high efficiency electronic platform.

Gold-black phosphorus nanostructured absorbers for efficient light trapping in the mid-infrared.

We propose a gold nanostructured design for absorption enhancement in thin black phosphorus films in the 3-5 µm wavelength range. By suitably tuning the design parameters of a metal-insulator-metal (MIM) structure, lateral resonance modes can be excited in the black phosphorus layer. We compare the absorption enhancement due to the resonant light trapping effect to the conventional 4n2 limit. For a layer thickness of 5 nm, we achieve an enhancement factor of 561 at a wavelength of 4 µm. This is significantly greater than the conventional limit of 34. The ability to achieve strong absorption enhancement in ultrathin dielectric layers, coupled with the unique optoelectronic properties of black phosphorus, makes our absorber design a promising candidate for mid-IR photodetector applications.

Studies on covalent functionalization of single layer black phosphorus from GW calculations based on the many body perturbation theory

The major challenge of black phosphorus (BP) is its fast-oxidative degradation in air. Organic covalent chemical modification of BP flakes could suppress the chemical degradation. Here we focus on the effects of covalent chemical modification on the electronic structures of single layer BP. We employed the state-of-the-art first principles GW method, which is based on the many body green functions, to study the covalent modification of single layer BP by forming P–C bonds. Our results show that the functional group chemisorbed at perfect lattice site results in deep in-gap state, which may deteriorate its performance, while the P–C bonds forming at single vacancies are electrically inactive. In addition, our results show that functional groups at low concentration would be preferably chemisorbed at single vacancies. At high concentration, functional groups would lead to the breaking of P–P bonds, and hence, oxygen impurity will easily insert in the interstitial position. Finally, we propose that functional groups at low concentration would protect BP from deterioration, and at high concentrations, functional groups would accelerate the deterioration of BP performance.

Ohmic contact engineering in few–layer black phosphorus: approaching the quantum limit

Achieving good quality Ohmic contacts to van der Waals materials is a challenge, since at the interface between metal and van der Waals material different conditions can occur, ranging from the presence of a large energy barrier between the two materials to the metallization of the layered material below the contacts. In black phosphorus (bP), a further challenge is its high reactivity to oxygen and moisture, since the presence of uncontrolled oxidation can substantially change the behavior of the contacts. Here we study three of the most commonly used metals as contacts to bP, chromium, titanium, and nickel, and investigate their influence on contact resistance against the variability between different flakes and different samples. We investigate the gate dependence of the current–voltage characteristics of field–effect transistors fabricated with these metals on bP, observing good linearity in the accumulation regime for all metals investigated. Using the transfer length method, from an analysis of ten devices, both at room temperature and at low temperature, Ni results to provide the lowest contact resistance to bP and minimum scattering between different devices. Moreover, we observe that our best devices approach the quantum limit for contact resistance both for Ni and for Ti contacts.

Chemically Functionalized Phosphorene As a 2D Material Emerging Toward Sensitive Biosensors

The interest of phosphorene as 2D material is high due to its excellent mechanical, electrical and optical properties [1]. However, the possibility of its application in the area of biosensors is a result of low cytotoxic cell-viability effects and excellent cytocompatibility [2]. Phosphorene has much higher surface to volume ratio compared to graphene and transition metal dichalcogenides. This due to its “puckered” lattice structure. These properties are advantages in sensing applications [3]. But puckered layer is quite reactive to oxygen and water adsorbed on the surface of phosphorene [4]. One way to change it and improve the ambient stability of layered black phosphorus is to modify the surface so that covalently or non-covalently attached chemical compounds passivate the surface to prevent damage [4, 5].The biosensing device consists of chemical part and biological unit with unique specifities towards corresponding analytes for example proteins.In this work the biosensor of bacteria has been prepared in several steps: phosphorene preparation, functionalization with 4-azidobenzoic acid, followed by coating with an antibody layer.Phosphorene (few layered black phosphorus, FLBP) was prepared from pre-crushed black phosphorus (BP) dispersed in anhydrous dimethylformamide or toluene under an argon atmosphere by the liquid exfoliation. Afterwards, the resultant suspension was centrifuged to remove the residual un-exfoliated particles, yielding supernatant.We functionalized few layered black phosphorus (FLBP) by direct bonding of the phosphorus atom bearing lone electron pair with nitrogen during reaction with 4-azidobenzoic acid, leading to the formation of P=N double bonds, which passivate the reactive FLBP effectively. A covalent combining few-layered black phosphorus (FLBP) with 4-azidobenzoic acid can function as a bridge between FLBP and biomolecules. The functionalized phosphorene (f-FLBP) results in the possibility of using it as a biosensor platform for the detection of Heamophillus Influenza - one of the most common bacteria that cause infections in humans [6, 7]. It is very important to determine the presence of a given bacterial strain, because nowadays strains resistant to numerous antibiotics are more and more often observed. In the US alone, antibiotic-resistant bacteria cause at least 2 million infections and 23,000 deaths per year, which cause losses of 55-70 billion dollars a year [8].The efficient functionalization of BP flakes was revealed by infrared spectroscopy. The cyclic voltammetry and electrochemical impedance spectroscopy measurements were carried out in Na2SO4 solution containing reference redox systems: [Fe(CN)6]3−/4−.Heamophillus Influenza bacteria were detected by the impedimetric method. The changes of the charge transfer resistance (Rct) can be attributed to the selective protein binding on the surface of the electrode. This was preceded by the attachment of antibodies to f-FLBP and obtaining a stable sensory surface. The procedure is shown in Figure 1.Consequently:- the benzoic groups enhance electric conductivity delivering fast direct electron transfer.- antibody-coated functionalized phosphorene were used to detect a bacteria (Haemophilus influenzae).- modified FLBP can work as surface for determination of organic molecules, e.g., nucleic acid bases or peptides and proteins, while it offers the promising possibility for biosensing. ACKNOWLEDGEMENTS This work was supported by the Polish National Science Centre [2016/22/E/ST7/00102]; and the National Centre for Science and Development [347324/12/NCBR/2017]. The DS funds of the Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged.

(Invited) Momentum-Resolved Dielectric Response of Free Standing Black Phosphorus Down to the Monolayer

Atomic layers of Black Phosphorus (BP) have been recently isolated, ten years after graphene. BP stands out in the 2D-materials panorama by its unique semiconducting properties: direct bandgap which can be tuned by the layer number in a wide range of wavelengths from visible (monolayer) to midinfrared (bulk) [1]. This tunability combined the anisotropy of the structure therefore offers promising perspectives in various fields such as electronics and photonics. However, the fast photooxidation in ambient condition, coupled to a high sensitivity to quantum confinement and dielectric environment in ultrathin BP, make very difficult the investigations on its intrinsic optical properties [2]. Further, as screening effects may strongly affect electronic and spectroscopic properties of 2D materials, it is highly desirable to investigate intrinsic properties of free-standing layers as well the ones of the bulk material which remain poorly known.To start with, we have investigated photoluminescence (PL) and absorption properties of high quality BP single crystals at 2K [FTIR]. The PL intensity appears comparable to high quality InAs crystals confirming the suitability of BP for infrared applications. Two peaks are evidenced at 0.275 eV and 0.26 eV. The highest energy peak is particularly narrow (FWHM = 3.8meV) and is tentatively attributed to exciton recombination, thanks to the temperature dependence of PL spectra from 2K to 300K. Further, we have measured the gap related energy shift of the PL spectra as a function of the BP thickness in a series of mechanically exfoliated samples with thicknesses down to 10 nm, complementary to the previous measures done on thinner samples [3].As far as the thinnest layers are concerned, which cannot manipulated in air, we have shown that Angular resolved Electron energy loss spectroscopy implemented in Transmission Electron Microscopy (Ar-EELS-TEM) offers a unique way to investigate dielectric response of free-standing layers related to valence band and plasmon excitations with the advantage to get access to their q dispersion and their symmetry properties [4]. By combining this technique with suitable ab initio calculations, we have studied the dielectric response of free-standing BP layers as a function of the number of layers. We found optical bandgap values of 1.9 eV, 1.4 eV and 1.1 eV for the mono- bi- and trilayer respectively. Moreover, by combining our results with a simple variational model, we correlate the exciton energy with the dielectric screening. We hence demonstrate that the variations of the electronic gap are sizeably larger than the variations of the binding energy. Finally, we probe and analyze the volume and surface plasmons dispersion as a function of momentum for the 1-3 BP layers and bulk and highlight a deviation and linearization of the parabolic dispersion with strong anisotropic fingerprints [5].[1] G. Zhang et al., Nat. Com., 8, 14071, (2017)[2] A. Favron, E. Gaufres et al Nature Mat. 14 (2015) 826.[3] C. Chen et al., NanoLett., (2019)[4] F. Fossard et al, Phys. Rev. B 96, 115304 (2017)[5] E. Gaufres et al, Nanoletters (2019); DOI: 10.1021/acs.nanolett.9b03928

Plasma Thinning of Large Black Phosphorus Flakes

The growing interest over the 2D materials has led to the discovery of exfoliated black phosphorus (bP), a semiconductor with a thickness-dependent bandgap. The direct bandgap energy varies from 0.3 eV for bulk materials to 1.9 eV for the monolayer of black phosphorus. The fabrication of thin layers is, however, difficult because the layers photo-oxidize in air into phosphoric acid with kinetic that gets faster for thinner layers1. Inspired by a new method to produce thin layers of black phosphorus using oxygen plasma, we work to optimise the process for making large few-layers bP flakes2. Using ICP-RIE oxygen plasma, exfoliated flakes of black phosphorus were etched in a controlled way and Raman spectroscopy was used to evaluate the quality of the flakes after plasma treatments. The results show no sign of high-degradation of the bP crystal structure after the plasma treatment. Here we show that the method can be adapted to produce high quality thin flakes of black phosphorus towards incorporation into electronic and optoelectronic applications. 1 Favron, A., Gaufrès, E., Fossard, F. et al. Photooxidation and quantum confinement effects in exfoliated black phosphorus. Nature Mater 14, 826–832 (2015) 2 Pei, J., Gai, X., Yang, J. et al. Producing air-stable monolayers of phosphorene and their defect engineering. Nat Commun 7, 10450 (2016)

Autogenous Formation of Gold on Layered Black Phosphorus for Catalytic Purification of Waste Water.

Layered black phosphorus (BP) is a member of a layered material family with anisotropic properties and layer-dependent band gaps that can be exfoliated down to single-layered phosphorene. Compared with graphene, few-layered BP and its single-layer phosphorene are significantly more reactive, and this reactivity can be applied for the autogenous reduction of gold ions to metallic gold nanoparticles supported by few-layered BP (Au/BP). Few-layered BP and gold are well-known oxidation catalysts important in organic synthesis and also in the catalytic treatment and purification of industrial wastewater. The treatment of organic contamination present in industrial wastewater presents serious problems and is an important issue for current catalysis. Here, we show the high catalytic activity of the gold supported on few-layered black phosphorus (Au/BP) for wet oxidation of acrylic acid, including samples of industrial wastewater with complex composition. The catalyst Au/BP exhibits high stability, which allows utilization of its easily accessible 2D surface for the preparation of 2D material-supported metal catalysts.

Pressure-induced evolution of band structure in black phosphorus studied by P31 NMR

Two-dimensional layered semiconductor black phosphorus (BP), a promising pressure induced Dirac system as predicted by band structure calculations, has been studied by $^{31}$P-nuclear magnetic resonance. Band calculations have been also carried out to estimate the density of states $D(E)$. The temperature and pressure dependences of nuclear spin lattice relaxation rate $1/T_1$ in the semiconducting phase are well reproduced using the derived $D(E)$, and the resultant pressure dependence of semiconducting gap is in good accordance with previous reports, giving a good confirmation that the band calculation on BP is fairly reliable. The present analysis of $1/T_1$ data with the complemental theoretical calculations allows us to extract essential information, such as the pressure dependences of $D(E)$ and chemical potential, as well as to decompose observed $1/T_1$ into intrinsic and extrinsic contributions. An abrupt increase in $1/T_1$ at 1.63GPa indicates that the semiconducting gap closes, resulting in an enhancement of conductivity.

Stable One-Dimensional Single Crystalline Black Phosphorus Nanowires for Gas Sensing

Layered black phosphorus (BP), as a well-known type of two dimensional (2D) materials, has exhibited many fascinating properties in the fields of electronics, photonics, and chemical applications. ...

Wavelength-Tunable Mid-Infrared Lasing from Black Phosphorus Nanosheets.

Van der Waals layered semiconductor materials own unique physical properties and have attracted intense interest in developing high-performance electronic and photonic devices. Among them, black phosphorus (BP) is distinct for its layer number-tuned direct band gap which spans from near- to mid-infrared (MIR) waveband. In addition, the puckered honey comb crystal lattice endows the material with highly linear-polarized emission and marked anisotropy in carrier transportation. These unique material properties render BP as an intriguing and promising building block for constructing mid-infrared-ranged coherent light sources. Here, a room temperature surface-emitting MIR laser based on single crystalline BP nanosheets coupled with a distributed Bragg reflector cavity is reported. MIR stimulated emission at 3611 nm is achieved with a near-unity linear polarization, which exhibits robust thermal stability up to 360 K. Most importantly, the lasing wavelength can be tuned from 3425 to 4068 nm by varying the cavity length via thickness control of BP layer. The demonstrated highly polarized lasing output and wavelength-tunable capacity of the proposed device scheme in MIR spectral range opens up promising opportunities for a broad array of applications in polarization-resolved IR imaging, range-finding, and free space quantum communications.

Electrochemical exfoliation of two-dimensional layered black phosphorus and applications

With the discovery of graphene, black phosphorus (BP) has been rediscovered as a two-dimensional (2D) layered material. Since its first preparation in 2014, 2D BP has elicited immense interest, and has exhibited excellent properties, such as distinct pleated structures in layers, adjustable direct bandgap, high carrier mobility, moderate on/off ratio, large specific surface area, and various interesting in-layer anisotropies. However, the realization of these excellent properties depends on the preparation of high-quality 2D BP sheets. Electrochemical exfoliation methods are typically performed under mild conditions, thus, these methods are convenient, controllable, and can produce high-quality 2D BP sheets. This review summarizes research progress in BP sheets preparation through anodic, cathodic, and electrolyte exfoliation in recent years. Different exfoliating methods affect the quality of 2D BP sheets. Moreover, possible exfoliating mechanisms and the potential applications of different exfoliating methods are summarized and discussed in detail. Lastly, the shortcomings of existing research on electrochemical exfoliation are presented, and suggestions and prospects for future research on the electrochemical exfoliation of 2D BP are proposed.

Interlayer Band‐to‐Band Tunneling and Negative Differential Resistance in van der Waals BP/InSe Field‐Effect Transistors

AbstractAtomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 108 and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature.

Black phosphorus modified soluble microneedle patch for painless, effective and accurate body slimming

Compared with painful and difficult overall weight-loss, a surgery-free method was developed to achieve local accurate body slimming. A layer of black phosphorus was modified on the back of the rosiglitazone (Rosi)-loaded soluble microneedle patch. Under near-infrared (NIR) irradiation, Rosi could be delivered to the target adipose tissues efficiently and painlessly, thus achieving accurate body slimming. Based on the experiments in a mouse model with high-fat-induced obesity, after one month, the mice lost about 8% of their body weight while their waist circumference (target region) dropped about 21%. In addition, an interesting phenomenon of adipose tissue dynamic compensation was discovered and discussed for the first time.

Layered black phosphorus as a reducing agent – decoration with group 10 elements

Black phosphorus is prone to surface oxidation under ambient conditions. This attribute is often seen as a negative property of this interesting material. However, its proneness to oxidation – thus the reductive properties – can also be employed in modification of its surface and in preparation of composite materials. Here we describe the process of decoration of BP particles with nickel, palladium and platinum in form of a phosphide or in metallic form, respectively. The deposits have forms of films or nanoparticles and the reported method represents a general way of modifying the surface of black phosphorus with metals or their respective compounds for desired applications.

An Interdigital Capacitive Humidity Sensor With Layered Black Phosphorus Flakes as a Sensing Material

Black phosphorus (BP) atomic layers have received significant attention for chemical sensing applications due to its exceptional electrical, mechanical, and surface properties. However, they are known to undergo chemical degradation in ambient conditions. In this paper, an interdigital capacitive humidity sensor with layered BP flakes as a sensing material is reported. The BP flakes were prepared from crystal powders by the mechanical exfoliation and then deposited on the interdigital electrode (IDE) structures by a spin-coating method. The deposited BP flakes were characterized by the atomic force microscope (AFM) and Raman spectroscopy, which demonstrated the uniformity of highly crystalline BP flakes. The interdigital capacitive humidity sensors were measured under different relative humidity (RH) levels. The results obtained show that the capacitance increases gradually as the RH levels with the sensitivity of about 0.2pF/%RH at the low RH levels (<45%RH) while the capacitance increases rapidly as the RH levels with the high sensitivity of about 10pF%RH. The maximum hysteresis was measured to be about 3%RH. Stability measurement showed that the capacitance of the sensors increased in the first 15 hours and then tended to be stable. Good repeatability was observed in the measurement, suggesting that degradation was prevented. Oxide layers were formed on the surface instead and the inside layers of BP kept intact. The estimated response and recovery time of the capacitive sensors was about 17s and 4.7s, respectively. The equivalent RC networks model for the capacitive sensors is proposed to explain the mechanisms. The fast response and excellent sensitivity of the capacitive sensors at the high RH levels showed potential applications in high RH monitoring areas.