Indium Phosphide Nanocrystals Research Articles

Localizing Oleylamine Ligands on Amine–Halide Copassivated Indium Phosphide Nanocrystals

The surface capping of organic ligands is a full part of a colloidal nanocrystal (NC) that provides colloidal stability, helps passivating electronic trap-states, or governs charge hopping between adjacent NCs. A central aspect to understanding this ligand shell is its inherently heterogeneous nature caused by, for example, site- or facet-dependent adsorption energies. Even so, the identification of ligands bound to different surface sites remains highly challenging. In this work, we propose a case study on oleylamine/chloride copassivated InP NCs, for which we show that the heterogeneous broadening of 1H resonances in the nuclear magnetic resonance spectrum enables ligands adsorbed to facets to be distinguished from edge- or corner-bound ligands. More specifically, we demonstrate by means of the recovery of spectral holes burned in the alkene resonance of surface-bound oleylamine that the ligand shell consists of spatially distinct pools of oleylamine characterized by a different average chemical shift. Combining this observation with classical molecular dynamics simulations, we assign the downfield and upfield side of the alkene resonance to oleylamine bound to facets, or edges and corners, respectively. Importantly, we show that this proposed spectral fingerprint of surface-localization of ligands agrees with the change in shape of the alkene resonance when increasing the NC size and when exchanging part of the oleylamine for hexadecanethiol. Given the general applicability of the methodology introduced here, we believe this work offers a starting point to assess ligand localization for a broad range of colloidal NCs and develop a better understanding of the binding and packing of ligands on NC surfaces.

Synthesis of single‐crystalline InP tetrapod nanocrystals via addition of ZnCl2

AbstractRecently, single‐crystalline indium phosphide (InP) tetrapods, which allow an exciton to act in a true tetrapodal geometry, were successfully synthesized and proved as a useful platform to study multiple exciton behaviors. We used ZnCl2 precursor, a commonly used additive in the synthesis of aminophosphine‐based InP nanocrystals to enhance the optical performance, and successfully synthesized InP tetrapods (InP‐ZnCl2) with the narrower arm length distribution. Interestingly, no distinct enhancement in photoluminescence was observed while the arm length of the InP tetrapod was suppressed with the addition of ZnCl2. Further shell growth on InP‐ZnCl2 successfully preserved tetrapodal geometry in InP‐ZnCl2/ZnSe and showed higher photoluminescence than that of tetrapodal InP/ZnSe. The crystal structure of InP‐ZnCl2 was also retained even along with various Zn feed ratios as observed in x‐ray diffraction (XRD) patterns and showed no peak shift as Zn only passivates the surface of InP tetrapods. These results provide a platform to study the role of Zn precursor.

Heteroepitaxial chemistry of zinc chalcogenides on InP nanocrystals for defect-free interfaces with atomic uniformity

Heteroepitaxy on colloidal semiconductor nanocrystals is an essential strategy for manipulating their optoelectronic functionalities. However, their practical synthesis typically leads to scattered and unexpected outcomes due to the intervention of multiple reaction pathways associated with complicated side products of reactants. Here, the heteroepitaxy mechanism of zinc chalcogenide initiated on indium phosphide (InP) colloidal nanocrystals is elucidated using the precursors, zinc carboxylate and trialkylphosphine selenide. The high magnetic receptivity of 77Se and the characteristic longitudinal optical phonon mode of ZnSe allowed for monitoring the sequence of epilayer formation at the molecular level. The investigation revealed the sterically hindered acyloxytrialkylphosphonium and diacyloxytrialkylphosphorane to be main intermediates in the surface reaction, which retards the metal ion adsorption by a large steric hindrance. The transformation of adsorbates to the crystalline epilayer was disturbed by surface oxides. Raman scattering disclosed the pathway of secondary surface oxidation triggered by carboxylate ligands migrated from zinc carboxylate. The surface-initiated heteroepitaxy protocol is proposed to fabricate core/shell heterostructured nanocrystals with atomic-scale uniformity of epilayers. Despite the large lattice mismatch of ZnS to InP, we realised a uniform and interface defect-free ZnS epilayer (~0.3 nm thickness) on InP nanocrystals, as evidenced by a high photoluminescence quantum yield of 97.3%.

Anisotropic and hyperbranched InP nanocrystals via chemical transformation of in situ produced In2O3.

We synthesized indium phosphide (InP) nanoparticles of different shapes and sizes, utilizing triphenyl phosphite (TPOP) as the phosphorus source. We show that this reaction proceeds via the formation of in situ formed In2O3 nanoparticles followed by subsequent transformation with triphenyl TPOP acting as the phosphorus source. Our findings open up new synthetic possibilities utilizing a cost-effective, non-pyrophoric and non-toxic phosphorus precursor. The large surface area of hyperbranched InP NCs might be ideally suited for surface-driven processes such as catalysis and energy storage.

Luminescent Anisotropic Wurtzite InP Nanocrystals.

Indium phosphide (InP) nanocrystals are emerging as an alternative to heavy metal containing nanocrystals for optoelectronic applications but lag behind in terms of synthetic control. Herein, luminescent wurtzite InP nanocrystals with narrow size distribution were synthesized via a cation exchange reaction from hexagonal Cu3P nanocrystals. A comprehensive surface treatment with NOBF4 was performed, which removes excess copper while generating stoichiometric In/P nanocrystals with fluoride surface passivation. The attained InP nanocrystals manifest a highly resolved absorption spectrum with a narrow emission line of 80 meV, and photoluminescence quantum yield of up to 40%. Optical anisotropy measurements on ensemble and single particle bases show the occurrence of polarized transitions directly mirroring the anisotropic wurtzite lattice, as also manifested from modeling of the quantum confined electronic levels. This shows a green synthesis path for achieving wurtzite InP nanocrystals with desired optoelectronic properties including color purity and light polarization with potential for diverse optoelectronic applications.

Accelerated screening of colloidal nanocrystals using artificial neural network-assisted autonomous flow reactor technology.

Colloidal semiconductor nanocrystals with tunable optical and electronic properties are opening up exciting opportunities for high-performance optoelectronics, photovoltaics, and bioimaging applications. Identifying the optimal synthesis conditions and screening of synthesis recipes in search of efficient synthesis pathways to obtain nanocrystals with desired optoelectronic properties, however, remains one of the major bottlenecks for accelerated discovery of colloidal nanocrystals. Conventional strategies, often guided by limited understanding of the underlying mechanisms remain expensive in both time and resources, thus significantly impeding the overall discovery process. In response, an autonomous experimentation platform is presented as a viable approach for accelerated synthesis screening and optimization of colloidal nanocrystals. Using a machine-learning-based predictive synthesis approach, integrated with automated flow reactor and inline spectroscopy, indium phosphide nanocrystals are autonomously synthesized. Their polydispersity for different target absorption wavelengths across the visible spectrum is simultaneously optimized during the autonomous experimentation, while utilizing minimal self-driven experiments (less than 50 experiments within 2 days). Starting with no-prior-knowledge of the synthesis, an ensemble neural network is trained through autonomous experiments to accurately predict the reaction outcome across the entire synthesis parameter space. The predicted parameter space map also provides new nucleation-growth kinetic insights to achieve high monodispersity in size of colloidal nanocrystals.

Continuous Nucleation and Size Dependent Growth Kinetics of Indium Phosphide Nanocrystals

Aminophosphines derived from N,N′-disubstituted ethylenediamines (R–N(H)CH2CH2N(H)–R; R = ortho-tolyl, phenyl, benzyl, iso-propyl, and n-octyl) were used to adjust the kinetics of InP nanocrystal f...

Synthesis and Spectroscopy of Emissive, Surface-Modified, Copper-Doped Indium Phosphide Nanocrystals

Aminophosphine precursors were used to synthesize copper-doped indium phosphide nanocrystals (InP NCs) via direct doping in a slow-injection bottom-up method and postsynthetic cation exchange. By both methods, the amount of copper incorporated into the NCs could be tuned simply by varying the molar ratio during synthesis. Common postsynthetic surface modifications such as Lewis acid treatment and zinc chalcogenide shelling were performed on these samples, resulting in an enhancement of the copper-based emission from 10% to 40%. For samples with thick shells, the copper-based photoluminescence quantum yield reached over 60%, a record value for doped InP NCs. Time-resolved photoluminescence spectroscopy showed increasing carrier lifetimes after surface treatments concurrent with the disappearance of a 2 ns decay process previously attributed to surface trapping in native InP NCs, showing the broad applicability and consistent impacts of the surface treatments. In this way, we have successfully developed a route to obtain high-quality near-infrared emitters utilizing less toxic alternatives to the popular lead- and cadmium-containing materials.

Mechanistic Insights into Size-Focused Growth of Indium Phosphide Nanocrystals in the Presence of Trace Water

Indium phosphide (InP) nanocrystals have emerged as a viable alternative to heavy metal-based colloidal quantum dots for optoelectronic applications. Traditionally, the presence of trace amounts of...

Unraveling the role of zinc complexes on indium phosphide nanocrystal chemistry.

The addition of zinc complexes to the syntheses of indium phosphide nanocrystals (InP NCs) has become commonplace, due to their ability to alter and significantly improve observed optical properties. In this paper, the role of zinc complexes on the synthesis and observed properties of InP is carefully examined. Produced InP and InP:Zn2+ NCs are thoroughly characterized from both structural (core and surface) and optical perspectives over a wide range of Zn2+ compositions (0%-43% atomic content). We find no differences in the physical (NC size and polydispersity) and structural properties (crystallographic phase) of InP and InP:Zn2+ NCs. Optically, significant changes are observed when zinc is added to InP syntheses, including blueshifted absorption edges and maxima, increased quantum yields, and the near elimination of surface state emission. These improved optical properties result from surface passivation by zinc carboxylate moieties. Changes to the optical properties begin at zinc concentrations as low as 5%, demonstrating the high sensitivity of InP optical properties to exogenous species.

Effects of Surface Chemistry on the Photophysics of Colloidal InP Nanocrystals.

Indium phosphide (InP) semiconductor nanocrystals (NCs) provide a promising alternative to traditional heavy-metal-based luminescent materials for lighting and display technologies, and implementation of InP NCs in consumer products is rapidly increasing. As-synthesized InP NCs typically have very low photoluminescence quantum yields (PLQY), however. Although empirical methods have led to NCs with near-unity PLQYs, a fundamental understanding of how specific synthetic and post-synthetic protocols can alter the electronic landscape of InP NCs is still lacking. Here, we have studied a series of homologous InP NCs prepared from InP clusters using a combination of room-temperature and low-temperature time-resolved spectroscopies to elucidate how specific charge-carrier trapping processes are affected when various surface modifications are performed. The data allow identification of large PLQY increases that occur specifically through elimination of surface electron traps and provide a rationale for understanding the microscopic origins of this trap suppression in terms of elimination of undercoordinated surface In3+ ions. Despite essentially complete elimination of surface electron trapping when surface In3+ is addressed, hole trapping still exists. This hole trapping is shown to be partially suppressed by even very thin shell growth, attributable to elimination of undercoordinated surface phosphides. We also observe signatures of bright-dark excitonic splitting in InP NCs with only submonolayer surface coverage of select additives (divalent Lewis acids or fluoride anions)-signatures that have only been previously observed in thick-shelled InP NCs. Together, these synthetic and spectroscopic results improve our understanding of relationships between specific InP NC surface chemistries and the resulting NC photophysics.

Chemical Synthesis and Applications of Colloidal Metal Phosphide Nanocrystals.

Colloidal nanocrystals (NCs) have emerged as promising materials in optoelectronic devices and biological imaging application due to their tailorable properties through size, shape, and composition. Among these NCs, metal phosphide is an important class, in parallel with metal chalcogenide. In this review, we summarize the recent progress regarding the chemical synthesis and applications of colloidal metal phosphide NCs. As the most important metal phosphide NCs, indium phosphide (InP) NCs have been intensively investigated because of their low toxicity, wide and tunable emission range from visible to the near-infrared region. Firstly, we give a brief overview of synthetic strategies to InP NCs, highlighting the benefit of employing zinc precursors as reaction additive and the importance of different phosphorus precursors to improve the quality of the InP NCs, in terms of size distribution, quantum yield, colloidal stability, and non-blinking behavior. Next, we discuss additional synthetic techniques to overcome the issues of lattice mismatch in the synthesis of core/shell metal phosphide NCs, by constructing an intermediate layer between core/shell or designing a shell with gradient composition in a radial direction. We also envision future research directions of InP NCs. The chemical synthesis of other metal phosphide NCs, such as II–V metal phosphide NCs (Cd3P2, Zn3P2) and transition metal phosphides NCs (Cu3P, FeP) is subsequently introduced. We finally discuss the potential applications of colloidal metal phosphide NCs in photovoltaics, light-emitting diodes, and lithium ion battery. An overview of several key applications based on colloidal metal phosphide NCs is provided at the end.

Electronic Structure and Dynamics of Copper-Doped Indium Phosphide Nanocrystals Studied with Time-Resolved X-ray Absorption and Large-Scale DFT Calculations

The recent development of time-resolved X-ray absorption spectroscopy (TR-XAS) has opened avenues for fundamental research on doped semiconductors. Reported herein are results on the successful doping of indium phosphide nanocrystals (NCs) with copper and subsequent characterization with time-resolved X-ray studies and large-scale density functional theory (DFT) calculations. The synthetic protocol that was based on the cluster seed method afforded control of both the doping level and the quantity of NCs produced in a batch. The stability of the colloidal dispersion allowed us to monitor the photophysical properties of copper guest ions with static and TR-XAS at the copper K-edge. These data reveal that copper captures a hole from the photoexcited InP NC, and relaxation to the ground state occurs via multiple timescales likely due to the presence of interior and surface-bound dopant ions as well as recombination with surface- and defect-trapped electrons. Large-scale DFT calculations reveal a striking dep...

Synthesis of indium phosphide nanocrystals by sonochemical method and survey of optical properties

Indium phosphide semiconductor materials (InP) have various applications in the field of semiconductor optoelectronics because of its advantages. But the making of this material is difficult due to the very weak chemical activity of In element. In this report we present a simple method to synthesize InP nanocrystals from inorganic precursors such as indium chloride (InCl 3 ), yellow phosphorus (P 4 ), reduction agent NaBH 4 at low temperature with the aid of ultrasound. Structural, morphological and optical properties of the formed InP nanocrystals were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersed X-ray analysis (EDS), Raman scattering, absorption and photoluminscence (PL) spectroscopy. After the surface treatment of InP nanocrystals with liquid hydrofluoric (HF) acid, the luminescence spectra have an enhanced intensity and consist of the peaks in the region from 500 nm to 700 nm. The intensity of these peaks strongly depends on the concentration and etching time of HF.

Investigation of Indium Phosphide Nanocrystal Synthesis Using a High‐Temperature and High‐Pressure Continuous Flow Microreactor

The important parameters for the synthesis of indium phosphide nanocrystals (InP NCs) are examined in a continuous three-stage microfluidic system (see figure). InP NC growth is largely independent of the experimental parameters that are significant in CdSe NC syntheses, such as mixing temperature and reagent concentrations. However, the concentration of myristic acid (MA) is important role for the growth of InP NCs. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production

Efficient production of solar fuels is an imperative for meeting future fossil-fuel-free energy demands. Hydrogen that is derived from the splitting of water by solar energy is clearly attractive as a clean energy vector, and there have been many attempts to construct viable molecular and biomolecular devices for photohydrogen production. A common approach in the construction of such devices is the utilization of tris(bipyridine)ruthenium, zinc porphyrin, or related molecular materials as photosensitizers in conjunction with a tethered or free electrocatalyst or enzymic system. Apart from cost, such systems suffer from having limited lifetimes, which may be attributed at least in part to the intrinsic reactivity of the organic N-donor ligands in the radical anion form of the photoexcited state and photodegradation pathways.

Synthesis of InP nanocrystals from indium chloride and sodium phosphide by solution route

Indium phosphide nanocrystals have been synthesized by the direct reaction of sodium phosphide and indium trichloride pre-combined with n-trioctylphosphine in 4-ethylpyridine as a suitable solvent for terminating the particles growth. The formation of InP particles with the size of c.a. 3–7 nm was evidenced by the analysis of powder X-ray diffraction, solution UV–vis spectra and transmission electron microscopy.

Functional InP Nanocrystals as Novel Near-infrared Fluorescent Sensors for Mercury Ions

Abstract Water-soluble indium phosphide nanocrystals capped with mercaptoacetic acid were synthesized. The nanocrystals fluoresce in the near-infrared region with maximum excitation and emission wavelengths at 750 and 826 nm, respectively. The fluorescence intensity is significantly enhanced in the presence of Hg2+ ions. Under the optimum conditions, the fluorescence enhancement is in proportional to the concentration of Hg2+.

Indium phosphide nanocrystals formed in silica by sequential ion implantation

Fused silica substrates were implanted with: (1) phosphorus only, (2) indium only, and (3) phosphorus plus indium ions. Vibrational and electronic characterizations have been performed on the P only and In only samples to obtain an understanding of the thermal annealing behavior in order to obtain a meaningful guide for the fabrication of InP quantum dots (QDs) formed by sequential ion implantation of In and P in SiO 2. Thermal annealing procedures for InP synthesis have been established and InP quantum dots are confirmed by TEM, XRD and far infrared measurements. Far IR spectra show a single resonance at 323 cm −1 rather than two absorption peaks in its counterpart of bulk InP crystals. The single band absorption is attributed to the surface phonon of InP quantum dots which will appear between transverse optical (TO) and longitudinal optical (LO) phonon modes of the bulk.

Organometallic chemical vapor deposition and characterization of indium phosphide nanocrystals in Vycor porous glass

Indium phosphide has been deposited in 40 and 150 Å Vycor porous glass by the reaction of trimethylindium with excess PH3. X-ray diffraction (XRD) of the red, transparent samples confirms the presence of crystalline indium phosphide. The amount of III-V material deposited within the glass matrix (loading) and annealing conditions influence the crystallinity and particle size of the nanocrystallites. The absorption spectra of vacuum-annealed samples is blue shifted with respect to bulk InP, with maxima ranging from 500 to 700 nm for both the 40 and 150 Å samples and is consistent with size quantization. The nonlinear optical properties of these nanocrystallite composites have been evaluated by Z-scan measurements and are characterized by a defocusing refractive nonlinearity influenced by a substantial nonlinear loss presumed to be caused by two-photon absorption.