Patent Application
20250116030
This disclosure relates generally to the field of semi-conductor engineering and, more particularly, to growing linear perovskite nanowires for use in photonic circuits and electronics.
Semiconductor nanowires with precisely controlled morphology have captured widespread attention due to their exceptional and versatile properties. These nanostructures with high aspect ratios and subsequent confinement effects lay the foundation for innovative device architectures, optoelectronics. Meanwhile, mechanically flexible and optically anisotropic nanowires further open unique possibilities for customizing light-matter interactions, ultimately contributing to modern photonic integrated circuits and flexible electronics.
Morphological control was traditionally achieved in III-V semiconductor nanowires through the vapor-liquid-solid seeded growth that allows editable size, dimension, and epitaxial structures. However, despite their exceptional electronic properties, inorganic semiconductors are limited with high fabrication cost, elevated processing temperature, and lack of chemical tunability. Alternatively, organic semiconductor nanowires offer cost-effective solution processability, where one-dimensional self-assembly was achieved via anisotropic molecular packing motifs introduced with various supramolecular synthons and intermolecular interactions. Yet, organic derivatives are inherently limited by inferior charge carrier mobility and are subject to aggregation-induced luminescence quenching and high optical loss.
Organic-inorganic hybrid semiconductors, on the other hand, offer the option to synergize chemical tunability and solution processability with optical and electronic properties. These characteristics culminate in the advancement of metal halide perovskites with excellent carrier lifetime, diffusion length, high optical absorption coefficient, and tunable emission across the visible spectrum. Since the development of solution-phase nanowire growth using three-dimensional (3D) halide perovskites, substantial efforts have been dedicated to harnessing organic-inorganic hybrid semiconductors for next-generation nanowire photonics and electronics.
Significant tunability was achieved with the discovery of two-dimensional (2D) halide perovskites. The relaxed goldsmith factor enables the integration of bulky organic spacers to shield inorganic counterparts against ion migration, water, and oxygen, which are the detrimental factors affecting the chemical stability of 3D halide perovskites. Recent studies also aimed to incorporate sophisticated organic cations with engineered band gap and intermolecular π-interactions. Nevertheless, it remains a challenge to achieve precise morphological control in 2D halide perovskites, which, as its name would suggest, typically self-assemble into thin sheets with poor control over in-plane growth directions. Only limited attempts towards 1D growth such as exerting lithography-assisted templated growth or vapor-phase growth of (C4H9NH3)2PbI4 have been reported, which suffers from low aspect ratio, high processing complexity, and limited design flexibility.
These limitations underscore the strong demand for tailor-designed organic spacers to control the morphology of 2D halide perovskite into nanowires for photonics applications. These organic components need to extend beyond single-molecule level and accelerate intermolecular communications as inspired from organic semiconductor nanowires.
Low-dimensional semiconducting materials with precisely controlled nanoscale morphology form the foundation for numerous technological breakthroughs. However, achieving one-dimensional (1D) nanostructures using inherently two-dimensional (2D) materials remains a rare and demanding endeavor. This limitation is addressed herein using hybrid 2D halide perovskites, which inherit the unique tunability of organics. A new “molecular clamp” approach is proposed that breaks the 4-fold symmetry, restricts crystal growth at selected crystal facets, and regulates 1D nanowire growth via tailored secondary bonding interactions. This approach is widely applicable to synthesize a range of high-quality 2D perovskite nanowires with large aspect ratios and tunable organic/inorganic chemical compositions. These nanowires form exceptionally well-defined and flexible cavities that exhibit versatile unusual optical properties including heterogeneous emission polarization, low-loss waveguiding (below 3 dB/mm), and efficient low-threshold light-amplification (below 20 μJ/cm2).
Before the present methods, implementations, and systems are disclosed and described, it is to be understood that this disclosure is not limited to specific synthetic methods, specific components, implementation, or to particular compositions, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting.
As used in the specification and the claims, the singular forms “a, “an” and “the” include plural references unless the context clearly dictates otherwise. Ranges may be expressed in ways including from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another implementation may include from the one particular value. Another implementation may include from the one particular value and/or the other particular value. Similarly, when values are expressed as approximations, for example by use of the antecedent “about,” it will be understood that the particular value forms another implementation. It is to be understood that the use of the term “about” indicates that the value cited may include a range of + or −5 to 50% of the cited value. It will be further understood that the description includes instances where said event or circumstance occurs and instances where it does not.
Several non-limiting embodiments of the disclosure are recited in the clauses listed below.
1. An elongated single crystal layered halide perovskite nanowire with formula II
(A)2PbX4 (II)
2. The elongated single crystal layered halide perovskite nanowire of clause 1, wherein X is Br.
3. The elongated single crystal layered halide perovskite nanowire of clause 1, wherein X is I.
4. The elongated single crystal layered halide perovskite nanowire of clause 2, wherein A is TPA3.
5. The elongated single crystal layered halide perovskite nanowire of clause 2, wherein A is BrCA3.
6. The elongated single crystal layered halide perovskite nanowire of clause 2, wherein A is FCA3.
7. The elongated single crystal layered halide perovskite nanowire of clause 2, wherein A is MeCA3.
8. The elongated single crystal layered halide perovskite nanowire of clause 3, wherein A is TPA3.
9. The elongated single crystal layered halide perovskite nanowire of clause 3, wherein A is BrCA3.
10. The elongated single crystal layered halide perovskite nanowire of clause 1, comprising straight or bent nanowire of (BrCA3)2PbBr4, wherein the elongated single crystal layered halide perovskite nanowire has a maximum length up to 100 μm, a mean length of about 8.45 μm, and a mean diameter/width of about 400 μm.
11. A waveguide comprising the elongated single crystal layered halide perovskite nanowire of clause 10 with nanowire length of about 50 to about 100 μm and wherein the intrinsic light transport optical loss coefficient is about 2.7 dB/mm.
12. A single crystal layered halide perovskite nanowire laser comprising nanowires of (BrCA3)2SnI4, prepared by the method of clause 26, wherein the single crystal layered halide perovskite nanowire laser has a light amplification threshold at 88 K is below 20 ρJ/cm2.
13. An elongated layered halide perovskite nanowire heterostructure comprising an elongated (BrCA3)2PbI4 core; and an elongated (BrCA3)2PbBr4 shell surrounding and encapsulating the elongated (BrCA3)2PbI4 core.
14. A method of making an elongated single crystal layered halide perovskite nanowire with formula I
(A)2(CH3NH3+)n−1MnX3n+1 (I)
15. The method of clause 14, wherein M is Pb.
16. The method of clause 14, wherein M is Sn.
17. The method of clause 15, wherein X is Br.
18. The method of clause 15, wherein X is I.
19. The method of clause 16, wherein X is I.
20. The method of clause 17, wherein A is TPA3.
21. The method of clause 17, wherein A is BrCA3.
22. The method of clause 17, wherein A is FCA3.
23. The method of clause 17, wherein A is MeCA3.
24. The method of clause 18, wherein A is TPA3.
25. The method of clause 18, wherein A is BrCA3.
26. The method of clause 19, wherein A is BrCA3.
To address the above-referenced limitations of the prior art, disclosed is a new and generalizable “molecular clamp” approach to break the 4-fold symmetry and regulate one-dimensional (1D) growth of two-dimensional (2D) perovskites via secondary bonding interactions. Specifically, in-plane hydrogen bonding, which is simultaneously compatible with the ionic nature and octahedron spacing of halide perovskites, is introduced. With specific molecular engineering, nanowires of 2D halide perovskites were readily assembled in solution facilitated by the formation of 1D H-bonding network in the organic layer. These nanowires with editable lengths and high-quality cavities provided an ideal platform to study anisotropic excitonic behaviors, light propagation, and amplification within 2D halide perovskites. This approach highlights the unique structural tunability of organic-inorganic hybrid semiconducting materials by synergizing the merits of each, which also brings unprecedented opportunities to 2D materials.
Contemporary organic cations designed for 2D perovskites typically impose limited long-range order. For example, an out-of-plane view along the stacking direction of (PEA)2PbBr4 reveals a classical herringbone packing motif in the organic layer (
To direct 1D growth, it was attempted to align the H-bonds with inorganic slabs. An additional COOH unit was introduced in the para position of the existing moiety, forming a backbone that resembles terephthalic acid (TPA). The new candidate was named TPA3 accordingly
However, TPA3-based 2D perovskites exhibited several unsatisfactory morphological and optical properties. Achieving high-quality crystals (
To balance non-covalent H-bonding with ionic assembly, the 1D H-bonding network was partially disrupted by substituting one COOH unit in the TPA backbone with bromine, which acted as a structuring unit to prevent COOH dimers from being twisted back to form interlayer H-bonds. Surprisingly, the new candidate, BrCA3, can maintain a similar in-plane connectivity and form parallelly aligned “partially broken” 1D chains on top of inorganic slabs (
Remarkably, the partially broken 1D connectivity introduced by BrCA3 promoted balanced and rapid self-assembly of 2D perovskites with exceptionally large aspect ratios. These crystals could be further miniaturized into high-quality nanowires via accelerated crystal assembly at the solution-air interface, a type of floating growth method originally developed (D. Pan et al., Nat. Nanotechnol. 16, 159-165 (2021).) for 2D perovskites with sheet morphologies.
The discovery of 2D perovskite nanowires using BrCA3 motivated investigation of their distinctive morphological, physical, optical features, and most importantly, the growth mechanism of these nanowires involving the synergistic effects of organic intermolecular interactions and ionic self-assembly.
Morphological Control with “Molecular Clamps”
While the morphological control of 2D halide perovskite nanowires seems to inherit the 1D connectivity of organic cations, it remains a question whether their growth direction actually follows the H-bond direction created by COOH dimers. To answer this question and unveil the nanowire growth mechanism, single-crystal X-ray diffraction (SC-XRD) and selected-area electron diffraction (SAED) were conducted to face-index bulk crystals and nanowires of (BrCA3)2PbBr4, respectively
Unexpectedly, the COOH dimers act as “molecular clamps”, hindering rather than facilitating the growth of 2D perovskites. This intriguing phenomenon may arise from a combinatory effect of the 1D H-bonding network and the surface-protective attributes of carboxylic acids. The alignment of cations correlates with the distinctive exposure of COOH moieties at the side versus the end facets (here, side facets refer to all the faces that are parallel to the long axis). For instance, the crystal investigated under SC-XRD exhibited six side faces indexed as (
These findings suggested that surface dangling carboxylic acids would slow down crystal growth and lead to the preferred exposure of COOH-abundant surfaces. While it seems to be counter-intuitive, the behavior actually resembles previously reported polymer-assisted synthesis of oxide perovskite Pb(Zr/Ti)O3 nanowires (G. Xu et al., Adv. Mater. 17, 907-910 (2005).), where polymer was hypothesized to reduce the surface tension of certain crystallographic planes. The nanowire growth was thus driven by the coverage of high-energy exposed surfaces and left them as end facets. In the system, surface dangling carboxylic acids protect nanowire side faces by forming robust H-bonds with aqueous solvent molecules, like water. Incoming cations therefore need to break the existing protective H-bonds and overcome steric hinderance. This effect becomes particularly weaker at the (22
The discussion above demonstrated a unique mechanism to achieve morphological control in hybrid 2D perovskites by simultaneously employing directional molecular clamps consisting of CA dimers to drive 1D growth and strategically using partially broken 1D chains to achieve balanced growth conditions. These observed merits highlight the surprising tunability of organic-inorganic hybrid semiconductors and culminate in the formation of nanowires with exceptional crystal quality reflected in their well-defined end-facets. While the hexagonal cylindrical crystal investigated in SC-XRD presented one possibility, miniaturized nanowires of (BrCA3)2PbBr4 displayed diverse morphologies commonly observed as hexagonal or acute trapezoidal end facets (
The “molecular clamp” mechanism featuring directional CA dimers is generally applicable to a wide-range of low-dimensional perovskites with diverse tunability from both organic and inorganic perspectives. For example, BrCA3-based nanowires with [PbI4]2− and [SnI4]2− matrices were readily obtained (
Surprisingly, epitaxial growth of these nanowires originates preferably from their end facets.
From the perspective of organic cations, the design of BrCA3 can be expanded by facile replacement of bromide with other structuring units such as fluorine or methyl. These new candidates can sustain the one-dimensional growth of 2D perovskite nanowires, as illustrated with their [PbBr4]2− derivatives (
Morphologically restricting the growth of 2D perovskites into 1D nanowires facilitates the investigation of distinctive optical properties along or perpendicular to the stacking directions of these layered structures. It was initially observed that PL from nanowires of (BrCA3)2PbBr4 and (BrCA3)2MAPb2Br7 displayed weak linear polarization that approximately propagated along their long axes (
2D perovskites possess intrinsic emission polarization due to the in-plane confinement of excitons. While such phenomenon is challenging to observe in contemporary 2D perovskites with stacking direction typically parallel to the substrates, nanowires offer ready accessibility to their side facets. Therefore, when viewing perpendicular to the stacking direction, strong linearly polarized PL could be revealed which propagates perpendicular to the long axes, corresponding with the observation from nanowires of (BrCA3)2PbI4.
More interestingly, a piece of twisted (BrCA3)2PbI4 nanowire was examined to unequivocally resolve the origin of its polarization dependence (
While the intrinsic anisotropic excitonic properties of 2D halide perovskites was revealed via morphological control, miniaturized nanowires also create unique cavities to study their light propagation behavior. In this regard, nanowires of our 2D perovskites are exceptional candidates for active waveguides inspired by their editable length, emission tunability, and bendable morphology. Waveguide losses were assessed from a few ca. 100 μm long nanowires of (BrCA3)2PbBr4 according to their propagation-distance-dependent relative tip emission intensity collected and analyzed with far-field PL images (METHODS). Nanowires of (BrCA3)2PbBr4 exhibited intrinsic loss coefficients as low as 2.7 dB/mm as observed in straight candidates (
Furthermore, waveguides can be coupled and transport light to adjacent crystals, creating complex optical network. A few coupled nanowires were examined through tip-tip interactions or cross-intersections (
The low-loss waveguiding behavior of BrCA3-based 2D perovskite nanowires suggested their promise as Fabry-Perot cavities for optical amplification. Building on the pioneering efforts on semiconductor nanowire lasers and subsequent lasing in 3D perovskites, the lasing behavior of BrCA3-based 2D perovskite nanowires was investigated. In lead-based 2D halide perovskites, lasing threshold is often constrained by the strong exciton-phonon interaction or Auger recombination. Enhanced lasing performances are commonly pursued in quasi-2D systems. Tin-based 2D halide perovskites, on the other hand, may exhibit lasing performances surpassing their lead counterparts, as shown in recent studies on thin films and exfoliated crystals. However, their lasing threshold are still pinned in the ˜100 ρJ/cm2 regime with significant sample-to-sample variation, both due to the lack of well-established cavity. To examine the lasing potential of our materials, nanowires of (BrCA3)2SnI4 were investigated. Interestingly, emission from the two end facets gradually took dominance with increasing pump fluence (
2D perovskite nanowires based on BrCA3 have displayed a diverse array of unusual optical properties. On one aspect, the intrinsic exciton behavior of 2D halide perovskites enables facile observation and control of polarized emission. Concurrently, these nanowires also revealed exceptional cavity qualities, thereby fostering active waveguides with low loss coefficients and facilitating light-amplification with notable low thresholds.
The method to manipulate the morphology of 2D halide perovskites by introducing robust intermolecular interactions between organic cations is distinctive to the special crystal structures of organic-inorganic hybrid materials and requires more comprehensive investigations. As disclosed herein, the CA dimer was originally exploited to enforce one-dimensional orientation within the organic layer. Nevertheless, this type of directionality appears to hamper rather than facilitate the 1D growth of 2D perovskites, which complicated the establishment of morphological control in an unforeseen manner. However, through an examination of side and end facets, the synergistic role of CA dimers was discovered, which simultaneously created aligned organic cation network and therefore protected side surfaces with dangling CA moieties. While 1D nanowire growth can be achieved through this molecular clamp mechanism, achieving optimal optical and morphological properties requires more delicate molecular engineering to promote balanced and rapid self-assembly of 2D perovskites into miniaturized nanowires. In this context, TPA3 was replaced by BrCA3 with partially broken 1D chains of CA dimers.
Morphological control with directional supramolecular synthons proves to be a generally applicable strategy for 2D and quasi-2D halide perovskites, with potential extension to diverse organic cations. However, its merit extends to a broad range of organic-inorganic hybrid semiconductors. Particularly, the selection of functional groups and intermolecular interactions to be incorporated within the organic layer transcends far beyond CA dimers and H-bonding network. For instance, x effect (R-T, 1-p, or x-d interactions) between organic cations, electrostatic interactions, and even chirality, could also be readily implemented. Further explorations in this regard will introduce enhanced versatility in these hybrid materials as the next-generation semiconductors, where the collective benefits of conventional organic and inorganic counterparts readily converge.
In operation, bulk bromide perovskite single crystals were obtained through slow-cooling a solution composed of HBr, PbBr2, and the organic ammonium salts. The iodide counterparts were obtained with PbI2 and the organic ammonium salts in HI and H3PO2 as solvents. MABr or MAI were added to obtain n>1 structures. Additionally, dimethylformamide (DMF) was added to assist the formation of (BrCA3)2MAPb2Br7 single crystals only. The detailed crystal growth parameters such as the ratio of solvents and the concentration of each precursor are specified in TABLE 1.
aSC: slow cooling; SCsolve: crystal quality suitable for solving the structure with SC-XRD; FG: floating growth; FC: fast-cooling.
bDMF is necessary for growing (BrCA3)2MAPb2Br7. Without DMF addition, slow-cooling resulted in either n = 1 or 3D perovskites as majority. Other additives (ethanol, isopropanol) were screened as well, but did not result in formation of n = 2 crystals.
cPhase-pure n > 1 iodide crystals were extremely difficult to obtain. Listed here are a few precursor solutions used. Slow-cooling typically gave a cloudy suspension of crystals with mixed phases. Toluene was identified as a suitable additive to drive the formation of phase-pure n = 2 or n = 3 iodide crystals. Other additives were screened: methanol, ethanol, isopropanol were unsuitable for our system which drove liquid phase separation; acetonitrile and acetone did not lead to phase separation, but did not drive the formation of n = 2 or n = 3 iodide species; chlorobenzene and 1,2-dichlorobenzene could be used to replace toluene.
The precursors and solvents were mixed in a 2 mL scintillation vial. After being tightly capped, the sample vial was heated carefully with a heat gun over 100° C. to induce mild refluxing of the solvents until materials were completely dissolved and the solution was clear. This process was carried out with great cautions in a fume hood with sash closed. Sonication was occasionally used to assist the dissolution of materials but magnetic stirring was avoided. To avoid rapid precipitation upon placing the vial in a boiling water bath, the mixture was then stabilized on a 90° C. hotplate to ensure no precipitate was observed even with mild evaporation of solvents inside the vial and condensation on the wall thereafter. Then, the vial was transferred to and sealed in a Dewar flask containing boiling water, which was then stored at ambient conditions to allow slow-cooling for about 72 to about 96 hours until the water bath reached room temperature. The crystal was stored in solution until being removed for structure determination and face indexing.
Nanowires of perovskite single crystals were grown with a variety of methods including floating growth and fast cooling. The preparation methods of precursor solution were similar to those mentioned above for perovskite single crystal growth. The exact composition of solution varied in each scenario and is documented in TABLE 1.
Floating growth was used for n=1 [PbBr4]2−, n=1 [PbI4]2−, and n=2 bromide nanowires. The method accelerates the crystal growth at air-liquid interface and has been well-documented. In detail, a clear and refluxing solution containing perovskite precursors was cooled to 70° C. and kept undisturbed until the temperature had stabilized, sometimes indicated by the formation and stabilization of precipitates. The exact temperature varies depending on the material composition, precursor concentration, etc. A few (1-5) μL of the supernatant were extracted with a 10 μL micropipette onto a glass substrate at ambient conditions in air. Nucleation and growth quickly initiated at the air-droplet interface. This process was be monitored under an optical microscope. Nanocrystals grown with this method were then picked-up by gently touching the droplet surface with various substrates including TEM grids, silicon (Si), Si/silica (SiO2) for SEM, Si/SiO2 or polydimethylsiloxane substrates (from GelPak, PF-30-X4) for optical characterizations. Leftover solvents were gently absorbed with a piece of filter paper.
Fast cooling was used to synthesize n=1 [SnI4]2−. This method was same as slow cooling except that the cooling speed was accelerated to a few minutes. In detail, the clear and refluxing precursors solution was cooled to room temperature without external control and kept undisturbed until a precipitate formed. The precipitated crystals were then transferred to various substrates with similar methods as described before.
For n>1 lead-iodide nanowires, regular slow-cooling was used.
This method uses longitudinal epitaxial nanowire heterostructures with (BrCA3)2PbI4 core and (BrCA3)2PbBr4 shell as example. First, (BrCA3)2PbI4 nanowires were prepared on Si/SiO2 or pdms substrates. (BrCA3)2PbBr4 shell was further grown with the floating growth method starting from a 70° C. droplet. The droplet was left cooled-down for a few seconds giving an oversaturated solution. A few particles might already crash out at the air-liquid interface. Then, the substrate having core nanowires was placed upside-down to cover the shell droplet leading to immediate epitaxial growth of shell materials on the as-grown core. The substrate was then removed from the droplet and leftover solvent was dried.
Lead bromide (PbBr2, 99.999% trace metals basis, #398853), lead iodide (PbI2, 99.999% trace metals basis, perovskite grade, #900168), tin iodide (SnI2, AnhydroBeads™, −10 mesh, 99.99% trace metals basis, #409308), hydrobromic acid (HBr, 48 wt. % in H2O), hydroiodic acid (HI, 57 wt. % in H2O), hypophosphorous acid (H3PO2, 50 wt. % in H2O) were purchased from Millipore Sigma. Methylammonium bromide (MABr, >99.99%, #SKU MS301000), Methylammonium iodide (MAI, >99.99%, #SKU MS101000) were purchased from Greatcell Solar Materials. Deuterated dimethyl sulfoxide (DMSO-d6) and deuterated chloroform (CDCl3) were purchased from Millipore Sigma. Anhydrous solvents used in organic synthesis were purchased from Millipore Sigma. Precursors used are specified in following sections.
Bulk bromide perovskite single crystals were obtained through slow-cooling a solution composed of HBr, PbBr2, and the organic ammonium salts. The iodide counterparts were obtained with PbI2 and the organic ammonium salts in HI and H3PO2 as solvents. MABr or MAI were added to obtain n>1 structures. Additionally, dimethylformamide (DMF) was added to assist the formation of (BrCA3)2MAPb2Br7 single crystals only. The detailed crystal growth parameters such as the ratio of solvents and the concentration of each precursor are specified in TABLE 1.
In detail, the precursors and solvents were mixed in a 2 mL scintillation vial. After being tightly capped, the sample vial was heated carefully with a heat gun over 100° C. to induce mild refluxing of the solvents until materials were completely dissolved and the solution was clear. This process was carried out with great cautions in a fume hood with sash closed. Sonication was occasionally used to assist the dissolution of materials but magnetic stirring was avoided. To avoid rapid precipitation upon placing the vial in a boiling water bath, the mixture was then stabilized on a 90° C. hotplate to ensure no precipitate was observed even with mild evaporation of solvents inside the vial and condensation on the wall thereafter. Then, the vial was transferred to and sealed in a Dewar flask containing boiling water, which was then stored at ambient conditions to allow slow-cooling for 72-96 hours until the water bath reached room temperature. The crystal was stored in solution until being removed for structure determination and face indexing.
Nanowires of perovskite single crystals were grown with a variety of methods including floating growth and fast-cooling. The preparation methods of precursor solution were similar to those mentioned above for perovskite single crystal growth. The exact composition of solution varied in each scenario and is documented in TABLE 1.
Floating growth was used for n=1 [PbBr4]2−, n=1 [PbI4]2−, and n=2 bromide nanowires. The method accelerates the crystal growth at air-liquid interface and has been well-documented in D. Pan, et al. (2021). In detail, a clear and refluxing solution containing perovskite precursors was cooled to 70° C. and kept undisturbed until the temperature had stabilized, sometimes indicated by the formation and stabilization of precipitates. The exact temperature varies depending on the material composition, precursor concentration, etc. A few (1-5) μL of the supernatant were extracted with a 10 μL micropipette onto a glass substrate at ambient conditions in air. Nucleation and growth quickly initiated at the air-droplet interface. This process was be monitored under an optical microscope (
Fast-cooling was used to synthesize n=1 [SnI4]2−. This method was same as slow-cooling except that the cooling speed was accelerated to a few minutes. In detail, the clear and refluxing precursors solution was cooled to room temperature without external control and kept undisturbed until a precipitate formed. The precipitated crystals were then transferred to various substrates with similar methods as described before.
For n>1 lead-iodide nanowires, regular slow-cooling was used.
This method uses longitudinal epitaxial nanowire heterostructures with (BrCA3)2PbI4 core and (BrCA3)2PbBr4 shell as example. First, (BrCA3)2PbI4 nanowires were prepared on Si/SiO2 or pdms substrates. (BrCA3)2PbBr4 shell was further grown with the floating growth method starting from a 70° C. droplet. The droplet was left cooled-down for a few seconds giving an oversaturated solution. A few particles might already crash out at the air-liquid interface. Then, the substrate having core nanowires was placed upside-down to cover the shell droplet leading to immediate epitaxial growth of shell materials on the as-grown core. The substrate was then removed from the droplet and leftover solvent was dried.
Single crystals of the investigated compounds were coated with a trace of Fomblin oil and were transferred to the goniometer head of a Bruker Quest diffractometer. Data for (TPA3)2PbI4, (TPA3)2PbBr4 (296 K), (BrCA3)2PbI4, (BrCA3)2PbBr4 (300 K) and (BrCA3)2PbBr4 (150 K) were collected on an instrument with a fixed chi angle, a Mo Kα wavelength (λ=0.71073 Å) sealed tube fine focus X-ray tube, a single crystal curved graphite incident beam monochromator, and a Photon II area detector. Data for (BrCA3)2 (MA) Pb2Br7, (TPA3)2PbBr4 (150 K) and (mCA1)2PbBr4 were collected on an instrument with kappa geometry, a Cu Kα wavelength (λ=1.54178 Å) I-μ-S microsource X-ray tube, a laterally graded multilayer (Goebel) mirror for monochromatization, and a Photon III C14 area detector. Both instruments were equipped with an Oxford Cryosystems low temperature device and examination and data collection were performed at 150 K, except for (TPA3)2PbBr4 and (BrCA3)2PbBr4, which were measured at both 150 K and 296 or 300 K, respectively. In particular, (BrCA3)2PbBr4 displayed a phase change between 150 and 300 K, and the crystal structure at 300 K was used for presentation materials.
Data were collected, reflections were indexed and processed, and the files scaled and corrected for absorption using APEX4 (Bruker (2022). Apex4, SAINT, Bruker AXS Inc.: Madison (WI), USA) and SADABS or TWINABS (L. Krause, R. Herbst-Irmer, G. M. Sheldrick & D. Stalke, J. Appl. Cryst. 48, 3-10 (2015)). The space groups were assigned using XPREP within the SHELXTL suite of programs (SHELXTL suite of programs, Version 6.14, 2000-2003, Bruker Advanced X-ray Solutions, Bruker AXS Inc., Madison, Wisconsin: USA, G. M. Sheldrick, A short history of SHELX. Acta Cryst. A64, 112-122 (2008)) and solved by dual methods using ShelXT (G. M. Sheldrick, SHELXT-Integrated space-group and crystal-structure determination. Acta Cryst. A71, 3-8 (2015)) and refined by full matrix least squares against F2 with all reflections using Shelxl2018 or Shelxl2019 (G. M. Sheldrick, Crystal structure refinement with SHELXL. Acta Cryst. C71, 3-8 (2015)) using the graphical interface Shelxle (C. B. Hübschle, G. M. Sheldrick & B. Dittrich, ShelXle: a Qt graphical user interface for SHELXL. J. Appl. Cryst. 44 (6), 1281-1284, (2011)).
Where not specified otherwise H atoms were handled as follows: H atoms attached to carbon and nitrogen atoms as well as hydroxyl hydrogens were positioned geometrically and constrained to ride on their parent atoms. C—H bond distances were constrained to 0.95 Å for aromatic and alkene C—H moieties, and to 0.99 and 0.98 Å for aliphatic CH2 and CH3 moieties, respectively. Methyl CH3, ammonium NH3+ and hydroxyl H atoms were allowed to rotate but not to tip to best fit the experimental electron density. Water H atom positions were refined and O—H distances were restrained to 0.84 (2) Å. Where necessary, water H ··· H distances were restrained to 1.36 (2) Å, and H atom positions were further restrained based on hydrogen bonding considerations. Uiso (H) values were set to a multiple of Ueq (C) with 1.5 for CH3, NH3+ and OH, and 1.2 for C—H and CH2 units, respectively.
Complete crystallographic data, in CIF format, have been deposited with the Cambridge Crystallographic Data Centre (CCDC), with the deposition number 2292512-2292519. CCDC contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
A suitable well-shaped single crystal representative of the bulk of each sample was selected using Carl Zeiss Discovery. V8 crystal microscope and mounted with the help of a trace of Fomblin oil on a MiTeGen micromesh mount (80 μm diameter mesh area with 15 μm openings). The mounted crystal was transferred to the goniometer head of the molybdenum wavelength Bruker Quest diffractometer described above (the same as used for data collection) precooled to the specified temperature. Data for a unit cell determination were collected using APEX4 (three times 12 frames with 0.5° frame width). After determination of a preliminary unit cell, the crystal was rotated around phi (360° rotation) and an image was collected every one degree. Full data were then collected and the structure was determined to establish the standard unit cell, and this unit cell was then loaded by reimporting the result of the integration of all data. Then, using the Apex4 subroutine for face indexing, crystal faces with indices<3 for h, k and 1 along the viewing direction of each image were identified, and the distance to the center of rotation was measured until all visible crystal faces were accounted for and the shape of the crystal determined from crystal faces did match the actual shape of the crystal. Results were used for absorption correction (for samples not twinned by non-merohedry) and to establish the shape and habit of crystals.
All bright-field images were collected with a custom Olympus BX53 microscope equipped with a polarizer. All PL images were taken using an X-Cite Series 120 Q lamp as the excitation source. A coherent continuous wave OBIS 375 nm laser excitation source was used for PL spectrum measurements and selected-area excitation in waveguide study. PL spectra were collected with a SpectraPro HRS-300 spectrometer.
Nanowires on Si/SiO2 substrates were optically pumped with a 400 nm femtosecond beam generated with a Ti: Sapphire seed laser and ultrafast amplifier (Spectra-Physics, Solstice Ace; 1 kHz, 100 fs, 800 nm, linear polarization) and second harmonic generation. An electronic shutter controlled the number of pulses per exposure, and a variable neutral-density optical attenuator was used to control the excitation power. The sample was mounted in a N2-filled. Experiments were performed at 88 K. The cryostat was placed on an inverted microscope. Laser beam was defocused to cover the entire crystal under investigation. A 420 nm long pass dichroic mirror beam splitter was used to eliminate collection of excitation light. The spectra were collected using a grating spectrometer (50 μm slit width, 1200 g/mm blaze holographic grating, and liquid-nitrogen-cooled Si CCD array detector). The sample exposure time was varied between 200 ms and 2 s. The laser fluence was calculated based on the spot size measured under microscope and the average power determined using a calibrated power meter.
Instead of analyzing PL spectra, PL images were collected with an emission polarizer and analyzed with imageJ. In detail, a region of interest (ROI) unique to each nanowire to avoid analyzing the waveguided light at the edge which would complicate the results. The total ROI-specific intensity at each polarizer angle was calculated and used for data plots. Exposure time used to collect the PL images was same across one measurement set and was chosen carefully so that both the tip and body emission (i.e. emission near the excitation spot) were below saturation. Regarding the twisted nanowire in
Waveguide losses were assessed according to the propagation-distance-dependent relative tip emission intensity collected and analyzed with far-field PL images and imageJ. In detail, the 375 nm laser beam (ø: ca. 15 nm) was focused at various positions on each nanowire and the distances from the focal point to the tip were calculated as light propagation distances (D). Exposure time used to collect the PL images was same across one measurement set and was chosen carefully so that both the tip and body emission (i.e. emission near the excitation spot) were below saturation. ROI was used to analyze the total intensity of tip and body emission. Each PL image was separated into red, green, and blue channels. Green channels were used to represent the material inherent waveguide loss while blue channel was affected by self-absorption, and red channel had low signal/noise ratio. Relative tip emission (Itip/Ibody) was calculated and plotted against/). The data plot was fitted with the waveguide loss equation (Itip/Ibody=Ae−αD) to obtain the loss coefficient.
Scanning Electron Microscopy (SEM) was conducted with a Hitachi S-4800 Field Emission SEM. The Transmission Electron Microscopy (TEM) image and electron diffraction pattern were obtained on a 200 kV JEOL JEM-F200 field-emission microscope equipped with a CMOS camara (Gatan Rio16). Atomic Force Microscopy (AFM) was conducted with an Asylum Cypher ES AFM.
NMR was acquired at room temperature with a Bruker Avance III HD 400 MHZ spectrometer equipped with a 2-channel Nanobay console and a 5 mm BBFO Z-gradient SmartProbe, or Bruker NEO 500 MHz equipped with prodigy liquid-nitrogen cooled cryoprobe with BBFO configuration. NMR spectra were analyzed with Mestrenova.
The program Mercury (C. F. Macrae, et al., J. Appl. Cryst. 41, 466-470, (2008).) was used for crystal structure illustration in this article. Bright field, PL, and SEM images were analyzed in imageJ. Translations and rotations were executed when necessary. The Blender software was used for 3D modeling in
The boc-protected amine, 3-(((tert-butoxycarbonyl)amino)methyl)benzoic acid (from Ambeed, 1 mmol, 1 eq.) was added to a 4 mL vial. Then, 48% aqueous HBr solution (3 mL, excess) was added to cleave the boc protecting group and form the ammonium bromide in-situ. The mixture was stirred vigorously at 50° C. overnight, during which the heterogenous mixture gradually became a homogenous suspension. Water was added to obtain a clear solution, which was washed 3 times with dichloromethane. Then, the water phase was collected and concentrated. The product was recrystallized in water, filtered, and dried in vacuum at 60° C. to give a white solid. Yield: 47.0%. 1H NMR (500 MHZ, DMSO-d6) δ 13.09 (s, 1H), 8.19 (s, 3H), 8.09 (s, 1H), 7.95 (d, J=7.8 Hz, 1H), 7.71 (d, J=7.8 Hz, 1H), 7.56 (t, J=7.7 Hz, 1H), 4.12 (s, 2H). 13C NMR (126 MHZ, DMSO-d6) δ 166.94, 134.43, 133.43, 131.11, 129.87, 129.32, 128.92, 41.91.
BrCA3, TPA3, FCA3, and MeCA3 were synthesized according to the following general scheme.
Hydroxybenzoates (1.0 eq.), potassium carbonate (K2CO3, from Millipore Sigma, 2.0 eq.), and tert-butyl (2-bromoethyl) carbamate (from Millipore Sigma, 1.5-2.0 eq.) were added to round-bottom flask charged with a stir bar. After a brief purge with Ar, anhydrous acetonitrile (MeCN, 0.1-0.2 M) was added. After extensive purging with Ar, the suspension was stirred at 90-95° C. to induce refluxing of MeCN for 12-24 h. The reaction can be further accelerated by addition of cesium carbonate (Cs2CO3, from Millipore Sigma, 0.5-1.0 eq.) or by replacing the solvent with anhydrous dimethylformamide (DMF) but without increasing the temperature.
Water was added, and the crude product was extracted with dichloromethane, dried over magnesium sulfate, filtered, and concentrated before been further purified with silica column chromatography (hexane/ethyl acetate). Product (boc-protected amine) and starting material (hydroxybenzoate) typically have similar Rf values and can be indistinguishable during column chromatography. Hence, considerable consumption of the starting material is crucial to obtain products with decent purity. However, a small amount of starting material in the final product can be further removed during the purification after converting the product to the ammonium salts.
Materials: dimethyl 2-hydroxyterephthalate (TPA-OH, 3.034 mmol, 1 eq.), K2CO3 (3.034 mmol, 1 eq.), Cs2CO3 (3.034 mmol, 1 eq.), tert-butyl (2-bromoethyl) carbamate (6.068 mmol, 2 eq.), anhydrous DMF (20 mL, 0.15 M). Near 100% starting material consumption. Final product: yellow gel. Yield 90.1%. 1H NMR (400 MHZ, CDCl3) δ 7.85 (d, J=8.0 Hz, 1H), 7.67 (dd, J=8.0, 1.4 Hz, 1H), 7.61 (d, J=1.3 Hz, 1H), 5.48 (s, 1H), 4.18 (t, J=5.0 Hz, 2H), 3.94 (s, 6H), 3.59 (q, J=5.2 Hz, 2H), 1.45 (s, 9H).
Materials: methyl 4-bromo-3-hydroxybenzoate (4.328 mmol, 1 eq.), K2CO3 (8.656 mmol, 2 eq.), tert-butyl (2-bromoethyl) carbamate (6.492 mmol, 1.5 eq.), anhydrous MeCN (35 mL, 0.125 M). Hydroxybenzoate not fully consumed. Final product: pale yellow powder (ca. 6 mol % hydroxybenzoate). Yield 86.2%. 1H NMR (400 MHZ, CDCl3) δ 7.61 (d, J=8.6 Hz, 1H), 7.53 (dq, J=3.8, 1.8 Hz, 2H), 5.05 (s, 1H), 4.14 (t, J=5.0 Hz, 2H), 3.91 (s, 3H), 3.61 (q, J=5.4 Hz, 2H), 1.46 (s, 9H).
Materials: methyl 4-fluoro-3-hydroxybenzoate (5.462 mmol, 1 eq.), K2CO3 (10.924 mmol, 2 eq.), Cs2CO3 (2.731 mmol, 0.5 eq.), tert-butyl (2-bromoethyl) carbamate (8.194 mmol, 1.5 eq.), anhydrous MeCN (55 mL, 0.125 M). Hydroxybenzoate fully consumed. Final product: white powder. Yield 85%, 1H NMR (400 MHZ, CDCl3) δ 7.72-7.57 (m, 2H), 7.12 (dd, J=10.6, 8.6 Hz, 1H), 5.02 (s, 1H), 4.14 (t, J=5.1 Hz, 2H), 3.91 (s, 3H), 3.58 (q, J=5.3 Hz, 2H), 1.45 (s, 9H).
Materials: methyl 3-hydroxy-4-methylbenzoate (8.728 mmol, 1 eq.), K2CO3 (17.656 mmol, 2 eq.), Cs2CO3 (4.364 mmol, 0.5 eq.), tert-butyl (2-bromoethyl) carbamate (13.092 mmol, 1.5 eq.), anhydrous MeCN (70 mL, 0.125 M). Hydroxybenzoate poorly consumed. Final product: white powder with 29 mol % hydroxybenzoates. Yield: 70%. 1H NMR (500 MHz, CDCl3) δ 7.58 (d, J=7.71, 1H), 7.45 (1H), 7.20 (d, J=7.75, 1H), 4.92 (s, 1H), 4.08 (t, J=5.1, 2H), 3.90 (s, 3H), 3.59 (q, J=4.6, 2H), 2.28 (s, 3H), 1.46 (s, 9H).
To a round-bottom flask charged with a stir bar was added the boc-protected amine from the previous reaction (1 mmol, 1 eq.), followed by anhydrous dioxane (10 mL, 0.1 M). After complete dissolution, 48% HBr (aq. 10 mmol, 10 eq.) was added. After extensive Ar purging, the solution was heated at 95° C. to induce mild refluxing of solvents for 12 h. Similarly, 57% aqueous HI was used to synthesize iodide salts. The reaction mixtures will gradually turn yellow for the bromides and black for iodides.
Solvents were then completely removed from the solution through rotary evaporation, including water contained in HBr or HI. Then, the crude product was reprecipitated at least thrice by dissolution in acetone followed by addition of diethyl ether. The crude products usually have decent solubility in acetone for the iodine salts, but bromides are only poorly soluble. Thus, the crude bromide salts were extensively sonicated in acetone before addition of ether.
Materials: TPA3-Boc (1.128 mmol, 1 eq.), anhydrous dioxane (0.1 M), HBr (11.28 mmol, 10 eq.). Product reprecipitated with acetone/ether. The last reprecipitation was done with acetone/methanol/ether. Product: white powder. Yield: 67.4%. 1H NMR (500 MHZ, DMSO-d6) δ 13.25 (s, 2H), 7.91 (s, 3H), 7.79 (d, J=7.8 Hz, 1H), 7.69-7.62 (m, 2H), 4.32 (q, 2H), 3.26-3.21 (m, 2H). 13C NMR (126 MHz, DMSO-d6) δ 166.72, 166.35, 156.68, 134.93, 131.02, 126.24, 122.32, 115.77, 66.43, 38.43.
Materials: TPA3-Boc (0.8556 mmol, 1 eq.), anhydrous dioxane (0.2 M), HI (8.5 mmol, 10 eq.). Product reprecipitated with acetone/ether. Product: pale yellow powder. Yield: 52.1%. 1H NMR (500 MHZ, DMSO-d6) δ 13.28 (s, 2H), 7.86 (s, 3H), 7.79 (d, J=7.9 Hz, 1H), 7.68-7.62 (m, 2H), 4.32 (t, J=5.3 Hz, 2H), 3.24 (s, 2H). 13C NMR (126 MHz, DMSO-d6) δ 166.72, 166.35, 156.69, 134.94, 131.03, 126.25, 122.34, 115.85, 66.45, 38.45.
Materials: BrEs3-Boc (0.8572 mmol, 1 eq.), anhydrous dioxane (0.1 M), HBr (8.57 mmol, 10 eq.). Product reprecipitated with acetone/ether. Product: white powder. Yield: 81.9%. 1H NMR (500 MHz, DMSO-d6) δ 13.26 (s, 1H), 8.00 (s, 3H), 7.76 (d, J=8.2 Hz, 1H), 7.60 (d, J=1.8 Hz, 1H), 7.51 (dd, J=8.2, 1.8 Hz, 1H), 4.33 (t, J=5.3 Hz, 2H), 3.29-3.26 (m, 2H). 13C NMR (126 MHz, DMSO-d6) δ 166.46, 154.21, 133.49, 131.71, 123.69, 116.84, 114.49, 66.03, 38.15.
Materials: BrEs3-Boc (1.5549 mmol, 1 eq.), anhydrous dioxane (0.1 M), HI (15.5 mmol, 10 eq.). Product reprecipitated with acetone/ether. Last reprecipitation with acetone/methanol/ether. Product: white powder. Yield: 49.7%. 1H NMR (500 MHZ, DMSO-d6) δ 13.27 (s, 1H), 7.93 (s, 3H), 7.76 (d, J=8.2 Hz, 1H), 7.61 (d, J=1.8 Hz, 1H), 7.52 (dd, J=8.2, 1.8 Hz, 1H), 4.32 (t, J=5.3 Hz, 2H), 3.29-3.25 (m, 2H). 13C NMR (126 MHz, DMSO-d6) δ 166.46, 154.20, 133.48, 131.71, 123.71, 116.84, 114.53, 66.09, 38.18.
Materials: FEs3-Boc (3 mmol, 1 eq.), anhydrous dioxane (0.1 M), HBr (30 mmol, 10 eq.). Product reprecipitated with acetone/ether. Product: white powder. Yield: 67.0%. 1H NMR (500 MHz, DMSO-d6) δ 13.14 (s, 1H), 7.96 (s, 3H), 7.70 (dd, J=8.2, 1.8 Hz, 1H), 7.63 (ddd, J=8.3, 4.4, 1.9 Hz, 1H), 7.39 (dd, J=11.0, 8.5 Hz, 1H), 4.32 (t, J=4.8 Hz, 2H), 3.27 (t, J=4.7 Hz, 2H). 13C NMR (126 MHz, DMSO-d6) δ 166.25, 154.66 (d, JCF=252.7 Hz), 145.58 (d, JCF=11.2 Hz), 127.71 (d, JCF=2.8 Hz), 123.75 (d, JCF=7.8 Hz), 116.43 (d, JCF=18.9 Hz), 116.22, 65.99, 38.23. 19F NMR (470 MHz, DMSO-d6, uncalibrated) δ −127.05.
Materials: MeEs3-Boc (2 mmol, 1 eq.), anhydrous dioxane (0.1 M), HBr (20 mmol, 10 eq.). Product reprecipitated with acetone/ether. Last reprecipitation with acetone/methanol/ether. Product: white powder. Yield: 56.4%. 1H NMR (500 MHz, DMSO-d6) δ 12.88 (s, 1H), 7.93 (s, 3H), 7.51 (d, J=7.7 Hz, 1H), 7.44 (s, 1H), 7.30 (d, J=7.7 Hz, 1H), 4.22 (t, J=4.2 Hz, 2H), 3.29-3.24 (m, 2H), 2.28 (s, 3H). 13C NMR (126 MHz, DMSO-d6) δ 167.64, 156.28, 132.50, 131.15, 130.20, 122.78, 112.11, 65.07, 38.94, 16.68.
Thus, while the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.
This application claims priority under 35 U.S.C. § 119 (e) to U.S. Provisional Application No. 63/589,121, filed Oct. 10, 2023, the entirety of the disclosure of which is incorporated herein by reference.
This invention was made with government support under 2143568-DMR and 2110706-DMR awarded by the National Science Foundation and under DE-SC0022082 and DE-EE0009519 awarded by the Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63589121 | Oct 2023 | US |
