Black Phosphorus Films Research Articles

Black phosphorus film as Q-switcher in neodymium-doped fiber laser

We present the successful development of a 1089.4 nm Q-switched laser employing a neodymium-doped fiber (NDF) as the active fiber and black phosphorus (BP) as the saturable absorber (SA). The BP SA was fabricated by inserting BP compound into a polyvinyl alcohol (PVA) host polymer, exhibiting a saturable absorption of 2.8 %. Integrated into an NDFL ring cavity, the SA modified the cavity loss, enabling the production of Q-switched pulses. With an increase in the 808 nm pumping power from 108.6 to 155.9 mW, the laser output pulse duration decreased from 3.74 to 3.54 μs, while the repetition rate improved from 40.6 to 51.0 kHz. The laser demonstrated a stable pulse train output, with a fundamental frequency signal to background noise ratio of 45.78 dB. The highest pulse energy of 1.3 nJ was recorded at 155.9 mW pump power. To the best of our knowledge, this represents the first utilization of BP as a SA or Q-switcher within an NDFL cavity.

A clean transfer approach to prepare centimetre-scale black phosphorus crystalline multilayers on silicon substrates for field-effect transistors

Recently reported direct growth of highly crystalline centimetre-sized black phosphorus (BP) thin films on mica substrates by pulsed laser deposition (PLD) has attracted considerable research interest. However, an effective and general transfer method to incorporate them into (opto-)electronic devices is still missing. Here, we show a wet transfer method utilizing ethylene-vinyl acetate (EVA) and an ethylene glycol (EG) solution to transfer high-crystalline large-area PLD-BP films onto SiO2/Si substrates. The transferred films were used to fabricate BP-based bottom-gate field-effect transistor (FET) arrays exhibiting good uniformity and continuity, with carrier mobility and current switching ratios comparable to those obtained in as-grown BP films on mica substrates. Our work presents a promising transfer strategy for scalable integration of on-substrate grown 2D BP into devices with more complex structures and further investigation of material properties.

Large-area solution-processable black phosphorus for electronic application

Two-dimensional (2D) layered black phosphorus (BP), with a direct band gap and high carrier mobility, has shown great potential for next generation electronics and optoelectronics. However, how to prepare a large-area 2D material film is still a big problem for realizing its practical applications. Herein, an improved one-step solution-processable method is put forward to solving this problem to get uniform and large-area BP film. Our results show that the designed electrodes can be fully covered by BP flakes and the corresponding FET reveals relatively high performance. Our study opens a new avenue in fabricating large-area ultra-thin BP films.

Anisotropic Sensing Performance in a High-Sensitivity Surface Plasmon Resonance Sensor Based on Few-Layer Black Phosphorus.

Few-layer black phosphorus (FLBP) is a highly promising material for high sensitivity label-free surface plasmon resonance (SPR) sensors due to its exceptional electrical, optical, and mechanical properties. FLBP exhibits inherent anisotropy with different refractive indices along its two main crystal orientations, the zigzag and armchair axes. However, this anisotropic property is often overlooked in FLBP-based sensors. In this study, we conducted a comprehensive investigation of the SPR reflectivity and phase in a BK7-Ag-FLBP structure to understand the influence of the stacking sequence and the number of FLBP layers on the sensing performance. Clear resonant angle shifts caused by different stacking sequences of FLBP could be observed both theoretically and experimentally. In the theoretical study, the highest reflective and phase sensitivities were achieved with a 12-layer black phosphorus (BP) structure. The reflectivity sensitivity reached 287.9°/refractive index units (RIU) with the zz stacking 12-layer BP film exhibiting a sensitivity 76°/RIU higher than the ac stacking structure. Similarly, the phase sensitivity reached 1162°/RIU with the zz stacking 12-layer BP structure showing a sensitivity 276.9°/RIU higher than the ac stacking structure. The electric field distribution of the 12-layer BP structure with four different stacking sequences has also been analyzed. In the experiment study, the well-known Attenuated Total Reflection (ATR) θ-2θ SPR setup is utilized to detect the reflectivity and phase of BK7-Ag-FLBP structures. The FLBP samples with the same thickness but different stacking sequences show significant resonant angle shift (0.275°) and maximum phase difference variation (34.6°). The FLBP sample thickness and crystal orientations have been demonstrated using the angular-resolved polarized Raman spectroscopy (ARPRS). These theoretical and experimental results provide strong evidence that the stacking sequences of FLBP have a significant impact on the sensing performance of SPR sensors. By harnessing the anisotropic properties of materials like FLBP, novel structures of anisotropic-2D material-based SPR sensors could open up exciting possibilities for innovative applications.

Mid-Infrared, Optically Active Black Phosphorus Thin Films on Centimeter Scale.

Black phosphorus (BP) is a narrow bandgap (∼0.3 eV) semiconductor with a great potential for optoelectronic devices in the mid-infrared wavelength. However, it has been challenging to achieve a high-quality scalable BP thin film. Here we present the successful synthesis of optically active BP films on a centimeter scale. We utilize the pulsed laser deposition of amorphous red phosphorus, another allotrope of phosphorus, followed by a high-pressure treatment at ∼8 GPa to induce a phase conversion into BP crystals. The crystalline quality was improved through thermal annealing, resulting in the observation of photoluminescence emission at mid-infrared wavelengths. We demonstrate high-pressure conversion on a centimeter scale with a continuous film with a thickness of ∼18 nm using a flat-belt-type high-pressure apparatus. This synthesis procedure presents a promising route to obtain optical-quality BP films, enabling the exploration of integrated optoelectronic device applications such as light-emitting devices and mid-infrared cameras on a chip scale.

Luminescence of black phosphorus films: Exfoliation-induced defects and confined excitations

Luminescence of black phosphorus films: Exfoliation-induced defects and confined excitations

Multilayer graphene and black phosphorus thin-film frequency doublers using direct-current bias

Multilayer graphene and black phosphorus films exhibit strong nonlinearity under voltage modulation. In this paper, according to the nonlinear characteristics of graphene and black phosphorus, the frequency doubling characteristics of graphene and black phosphorus are introduced, and the nonlinear SDD model of graphene is established in EDA, and the simulation results are basically consistent with the measured results. Under the regulation of DC bias voltage, the second harmonic output power of both graphene frequency doubler and black phosphorus frequency doubler is larger than their third harmonic output power when the operating frequency is 800–1100 MHz. The experimental results show that the minimum conversion loss of the black phosphorus multiplier is 24.22 dB when the input voltage is 0.9 V and the input power is 12 dBm, and the minimum conversion loss of the graphene multiplier is 32.15 dB when the input voltage is 1.6 V. The experimental results show that the conversion loss of the black phosphorus multiplier is better than that of the graphene multiplier, and the conversion efficiency is higher.

Tip-enhanced two-photon excited fluorescence spectroscopy of monolayer black phosphorus

The optical properties of monolayer black phosphorus (BP) in two-photon excited fluorescence (TPEF) are pivotal for photoluminescence applications at the single molecular level. In this study, we theoretically examine the TPEF properties of monolayer BP using a tip-enhanced spectroscopy system. We detail the influence of parameters such as the tip radius, the distance between the tip and the BP film, the incidence angle and the tip half-cone angle on the fluorescence excitation and emission enhancement of monolayer BP. This examination employs the finite element method. Our findings reveal that the signal enhancement in TPEF is substantially improved, approximately two orders of magnitude greater than that in single-photon excited fluorescence (SPEF), attributed to the high-order nonlinear coupling effect. By optimising the system configuration, we determined that the TPEF enhancement factor with monolayer BP can reach as high as eight orders of magnitude under an excitation wavelength of 800 nm. The highest spatial resolutions achievable for TPEF and SPEF spectroscopy are also 4.4 nm and 5.3 nm, respectively. These results provide an in-depth understanding of the TPEF enhancement mechanism and are invaluable for designing and applying BP-based optoelectronic devices.

Synthesis of black phosphorus films.

Synthesis of black phosphorus films.

Growth of uniformly doped black phosphorus films through versatile atomic substitution

Growth of uniformly doped black phosphorus films through versatile atomic substitution

Growth of single-crystal black phosphorus and its alloy films through sustained feedstock release

Black phosphorus (BP), a fascinating semiconductor with high mobility and a tunable direct bandgap, has emerged as a candidate beyond traditional silicon-based devices for next-generation electronics and optoelectronics. The ability to grow large-scale, high-quality BP films is a prerequisite for scalable integrated applications but has thus far remained a challenge due to unmanageable nucleation events. Here we develop a sustained feedstock release strategy to achieve subcentimetre-size single-crystal BP films by facilitating the lateral growth mode under a low nucleation rate. The as-grown single-crystal BP films exhibit high crystal quality, which brings excellent field-effect electrical properties and observation of pronounced Shubnikov-de Haas oscillations, with high mobilities up to ~6,500 cm2 V-1 s-1 at low temperatures. We further extend this approach to the growth of single-crystal BP alloy films, which broaden the infrared emission regime of BP from 3.7 μm to 6.9 μm at room temperature. This work will greatly facilitate the development of high-performance electronics and optoelectronics based on BP family materials.

Enhanced near-field thermal radiation between black phosphorus with high electron density by BP/hBN heterostructures

ABSTRACT The black phosphorus (BP)/hexagonal boron nitride (hBN) Van der Waals heterostructure has great potential application in BP-based devices due to its higher stability than monolayer BP film. The near-field thermal radiation (NFTR) between two identical BP/hBN heterostructures with high electron density is studied to promote the application of BP-based devices. The BP/hBN heterostructures show a higher heat transfer coefficient (HTC) at a 10 nm gap distance compared to BP films with electron density n larger than 1 × 1013 cm−2, due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). Especially at n ≥ 3 × 1013 cm−2, the improvement is more than 100%. The SPPs and the HPPs couple into surface plasmon-phonon polaritons (SPPPs) out of the hyperbolic region and hyperbolic plasmon-phonon polaritons (HPPPs) inside. The SPPPs can achieve photon tunneling in the broader wavevector region than SPPs, making most of the contribution to heat transfer. The influences of the thickness of the hBN sheet and gap distance are also discussed. This scheme only effectively enhances NFTR for BP with high electron density at small nanogaps. After structural optimization, h = 2 nm is the optimal thickness for BP/hBN configuration with low electron density, such as n = 1 × 1013 cm−2. In contrast, large thickness h = 500 nm is optimal for BP with high electron density. At high electron density, a thick hBN sheet is prominent in enhancing the SPPPs in the frequencies below the type-I region and the HPPPs inside the type-II region. We further propose BP/hBN/BP heterostructures and find that HTC is further enhanced by 4.4% ~ 30.8% due to the more robust surface modes. Our work may contribute to developing BP-based near-field thermal devices and promote understanding the NFTR mechanism of BP/hBN heterostructure.

Electrochemically exfoliated phosphorene nanosheet thin films for wafer-scale near-infrared phototransistor array

Two-dimensional (2D) black phosphorus (BP), or phosphorene, has recently emerged as a promising 2D semiconductor because of its p-type charge transport behavior and near-infrared photoresponsivity. However, the application of BP in practical electronic and optoelectronic devices is hindered by challenges in producing high-quality BP films over large areas. In this manuscript, we present a facile solution-based process to create wafer-scale BP films for fabrication of p-channel field-effect transistors that are responsive to near infrared light. Few-layer BP nanosheets are first exfoliated from the bulk crystal via electrochemical intercalation of cationic molecules and then vacuum-filtered through an anodic aluminum oxide membrane. The resulting BP film can be transferred onto an SiO2-coated silicon substrate, thereby allowing for realization of field-effect transistors after electrode deposition and thermal annealing. The transistor array exhibits spatial uniformity in electrical performance with an average hole mobility of ~0.002 cm2 V−1 s−1 and on/off ratio of 130. Furthermore, gate-induced modulation of the BP channel allows for enhancement in the photoresponsivity for 1550-nm light illumination up to 24 mA W−1, which benefits the application of the phototransistor array for near infrared imaging.

Tunable spectral manifestation of Tamm plasmon-polaritons in a hybrid structure with 2d black phosphorus in the terahertz range

ABSTRACT A structure consisting of the 2d black phosphorus (BP) film and a rugate filter (RF) divided by a liquid crystal (LC) layer is theoretically studied as a system in which Tamm plasmon-polaritons (TPP) can be excited. The spectral distribution of the reflection coefficient of the system in the RF band gap region is calculated for the cases when the band gap is in the regions of 1 and 10 THz. It is shown that, in both cases, the reflection coefficient dip associated with TPP excitation near the 2d BP film appears in the RF band gap region. The spectral position and magnitude of the reflection coefficient dip depend on the harmonic profile parameters of the RF refractive index, concentration and effective mass of the 2d BP charge carriers, and the LC layer thickness and refractive index. It was found that the TPP wavelength is a periodic function of the LC layer thickness and its refractive index, and with their increase, two or more TPP can appear at wavelengths within the RF band gap. The possibility of controlling the TPP spectral position using an external electric field is noted.

Ag decoration-enabled sensitization enhancement of black phosphorus nanosheets for trace NO2 detection at room temperature

Black phosphorus (BP), one rising star of two-dimensional (2D) materials, has showcased a huge capability for ppb-level NO2 detection. However, sluggish reaction kinetics and fragile stability frustrate its further application. In this regard, for the first time we prepared Ag nanoparticles modified BP nanosheets as the sensing layer via one feasible method to recognize trace NO2 at room temperature. With respect to individual BP, the composition-optimized BP-Ag nanocomposites (BP-Ag-1 sensor) achieved a favorable performance primarily in terms of boosted response (39.9% vs. 11.8%, 100 ppb NO2), accelerated response speed (190 s vs. 486 s, 100 ppb NO2) and strengthened operation stability, together with ultralow theoretical detection limit of 0.25 ppb. Furthermore, a protection layer comprised of polylactic acid (PLA) was anchored onto the surface of BP-Ag-1 sensor to keep the water molecules physically from the sensing layer and retain a distinguishable signal toward trace NO2 at high moisture environments. The introduction of Ag and PLA separately reduced the lone electron pairs from P atoms and suppressed the water penetration into the BP film, thereby offering an alternative way to passivate BP for its optoelectronic applications in the future.

Field canalization using anisotropic 2D plasmonics

Optical devices capable of suppressing diffraction nature of light are of great technological importance to many nanophotonic applications. One important technique to achieve diffractionless optics is to exploit field canalization effect. However, current technological platforms based on metamaterial structures typically suffer from strict loss-confinement trade-off, or lack dynamic reconfigurability over device operations. Here we report an integrated canalization platform that can alleviate this performance trade-off. It is found that by leveraging material absorption of anisotropic 2D materials, the dispersion of this class of materials can flatten without increasing propagation losses and compromising confinement. The realization of such plasmon canalization can be considered using black phosphorus (BP), where topological transition from elliptic to hyperbolic curves can be induced by dynamically leveraging material absorption of BP. At the transition point, BP film can support long range, deeply subwavelength, near-diffractionless field propagation, exhibiting diffraction angle of 5.5°, propagation distance of 10λspp, and λspp < λ0/300.

Molecularly Engineered Black Phosphorus Heterostructures with Improved Ambient Stability and Enhanced Charge Carrier Mobility.

Overcoming the intrinsic instability and preserving unique electronic properties are key challenges for the practical applications of black phosphorus (BP) under ambient conditions. Here, it is demonstrated that molecular heterostructures of BP and hexaazatriphenylene derivatives (BP/HATs) enable improved environmental stability and charge transport properties. The strong interfacial coupling and charge transfer between the HATs and the BP lattice decrease the surface electron density and protect BP sheets from oxidation, resulting in an excellent ambient lifetime of up to 21 d. Importantly, HATs increase the charge scattering time of BP, contributing to an improved carrier mobility of 97 cm2 V-1 s-1 , almost three times of the pristine BP films, based on noninvasive THz spectroscopic studies. The film mobility is an order of magnitude larger than previously reported values in exfoliated 2D materials. The strategy opens up new avenues for versatile applications of BP sheets and provides an effective method for tuning the physicochemical properties of other air-sensitive 2D semiconductors.

Air Stable Nickel-Decorated Black Phosphorus and Its Room-Temperature Chemiresistive Gas Sensor Capabilities.

In the rapidly emerging field of layered two-dimensional functional materials, black phosphorus, the P-counterpart of graphene, is a potential candidate for various applications, e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelectrics, solar cells, and sensors. Black phosphorus has shown superior chemical sensing performance; in particular, it is selective for the detection of NO2, an environmental toxic gas, for which black phosphorus has highlighted high sensitivity at a ppb level. In this work, by applying a multiscale characterization approach, we demonstrated a stability and functionality improvement of nickel-decorated black phosphorus films for gas sensing prepared by a simple, reproducible, and affordable deposition technique. Furthermore, we studied the electrical behavior of these films once implemented as functional layers in gas sensors by exposing them to different gaseous compounds and under different relative humidity conditions. Finally, the influence on sensing performance of nickel nanoparticle dimensions and concentration correlated to the decoration technique and film thickness was investigated.

Black phosphorus thin film integrated long-period fiber grating for highly refractive index and biomolecules detection

We have developed a sensing platform using a long-period fiber grating (LPFG) integrated black phosphorus (BP) thin film from the numerical simulation analysis and experimental process verification. Due to the high optical absorption of BP, the attenuated depth of the cladding mode in the BP coated LPFG (named BP-LPFG) sensor can be varied by the change of external environment. Benefited from the BP film, the sensing system shows a superior enhancement in the refractive index (RI) detection compared to the use of bare LPFG. The sensitivity can reach 122.1 dB/RIU, 139.5 dB/RIU, and 931.9 dB/RIU in the RI regions of 1.33–1.38, 1.39–1.44, and near 1.455, respectively. Moreover, this sensing system has been applied to implement the highly sensitive and label-free detection for the bovine hemoglobin (BHb) molecules, with a sensitivity of 5.6 dB/(mg/mL) and a detection limit of 0.05 mg/mL achieved. The detection limit is 2600 times lower than the hemoglobin threshold for the confirmation of men’s anemia illness, defined by the World Health Organization (WHO). This newly sensing platform is promising in the early clinical diagnose for anemia illness.

Recent progress in epitaxial growth of two‐dimensional phosphorus

AbstractPhosphorus is an important non‐metal element with many allotropes and tunable electronic properties. As one of the most important allotropes of phosphorus, two‐dimensional (2D) black phosphorus (BP) possesses many extraordinary properties, such as high charge carrier mobility with high on/off ratio, thickness‐dependent direct bandgap varying from 0.3 to 2 eV, and anisotropic electrical, optical and thermal properties. Inspiring by the success of 2D BP, other 2D phosphorus allotropes with intriguing properties for next‐generation electronic and optoelectronic devices have also attracted much attention. However, large‐scale growth of high‐quality 2D single/few‐layer phosphorus remains a great challenge. In this review, we highlight recent progress achieved on 2D phosphorus, with special focus on the epitaxial growth of 2D BP films, blue phosphorus (BlueP) monolayers as well as phosphorus‐metal porous networks. The remaining challenges and future perspectives on the development of monolayer phosphorus or phosphorus‐metal alloys are also provided.