Patent Application
20230301200
The present invention, in some embodiments thereof, relates to a crystal structure and, more particularly, but not exclusively, to a spin-selective conduction structure,
Spintronics refers to the utilization of electron spin to carry out logic and electronic operations. Spintronics allows for harnessing the spin degree of freedom to realize new functionalities while the energy needed for manipulation of the spin is relatively low compared to classical electronics. Chiral-induced spin-selective (CISS) electronic conduction was demonstrated in bio-inspired chiral thin organic films, such as dsDNA, peptides, and proteins.
Organic-molecule-based magnets have been recently studied [Miller, Organic- and Molecule-Based Magnets. Mater. Today 2014, 17, 224-235; Bogani et al., Molecular Spintronics Using Single-Molecule Magnets. Nat. Mater. 2008. 7, 179-186; Sessoli, Magnetic Molecules Back in the Race. Nature 2017, 548, 400-401; Alexandropoulos et al., Chem. Sci. 2019, 10, 1626-1633; Oshio et al., Superparamagnetic Behavior in an Alkoxo-Bridged Iron(II) Cube. J. Am. Chem. Soc. 2000, 122, 12602-12603; Goodwin et al., Molecular Magnetic Hysteresis at 60 K in Dysprosocenium. Nature 2017, 548, 439-4421; Coronado et al., Synthesis, Chirality, and Magnetic Properties of Bimetallic Cyanide-Bridged Two-Dimensional Ferromagnets. Chem. Mater. 2006, 18, 2670-2681; Shiomi et al., An Enantiopair of Organic Ferromagnet Crystals Based on Helical Molecular Packing of Achiral Organic Radicals. J. Phys. Chem. Lett. 2011, 2, 3036-3039; Dhara et al., Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors, J. Phys. Chem. Lett. 2016, 7, 4988-4995; and Dhara et al., Diamagnetic Molecules Exhibiting Room-Temperature Ferromagnetism in Supramolecular Aggregates. J. Phys. Chem. C 2017, 121, 12159-12167]. Such compounds are known to exhibit magnetic properties, useful for spintronic elements and quantum devices.
According to an aspect of some embodiments of the present invention there is provided a spin-selective conduction structure. The spin-selective conduction structure comprises a crystal. having a monolayer of metal atoms between two layers of chiral organic molecules, wherein each metal atom is coupled to two chiral organic molecules, one at each layer, and wherein a chirality of organic molecules in one of the two layers is the same as a chirality of organic molecules in a to another one of the two layers.
According to some embodiments of the invention the spin-selective conduction structure wherein a chirality of all of the organic molecules in each layer is the same,
According to some embodiments of the invention the crystal is arranged as a stack comprises a plurality of monolayers of the metal atoms, each monolayer being between two layers of the chiral organic molecules.
According to some embodiments of the invention a thickness of the stack, perpendicular to the monolayer, is at least 100 nm, more preferably at least 150 nm, more preferably at least 200 nm, more preferably at least 250 nm, more preferably at least 300 nm.
According to some embodiments of the invention the metal atoms are selected to reduce quantum de-coherence of spin states.
According to some embodiments of the invention the spin-selective conduction structure is characterized by spin-polarization of at least 20%, more preferably at least 25%, more preferably at least 30%.
According to some embodiments of the invention the chiral organic molecules comprise chiral aromatic molecules.
According to some embodiments of the invention the chiral organic molecules self-assemble to form the layers.
According to some embodiments of the invention the crystal is noncentrosymmetric and is characterized by a space group P21.
According to some embodiments of the invention the crystal is noncentrosymmetric and is characterized by a space group P1.
According to some embodiments of the invention the chiral organic molecules comprise chiral amino acid molecules.
According to some embodiments of the invention amino and carboxylic acid moieties of the amino acid molecules are ligands forming the coupling.
According to some embodiments of the invention the chiral amino acid molecules comprise aromatic amino acid molecule.
According to some embodiments of the invention the chiral amino acid molecules comprise D-phenylalanine.
According to some embodiments of the invention the chiral amino acid molecules comprise L-phenylalanine.
According to some embodiments of the invention the chiral amino acid molecules comprise D-pentafluorophenylalanine.
According to some embodiments of the invention the chiral amino acid molecules comprise L-pentafluorophenylalanine.
According to some embodiments of the invention the chiral amino acid molecules comprise D-tryptophan.
According to some embodiments of the invention the chiral amino acid molecules comprise L-tryptophan.
According to some embodiments of the invention the chiral amino acid molecules comprise D-tyrosine.
According to some embodiments of the invention the chiral amino acid molecules comprise L-tyrosine.
According to some embodiments of the invention the chiral organic molecules comprise chiral peptides, less than 10 amino acids in length, more preferably less than 8 amino acids in length, more preferably less than 6 amino acids in length, more preferably less than 4 amino acids in length, e.g., 2 amino acids in length. According to some of these embodiments, each amino acid residue in the peptide features the same chirality (L or D).
According to some embodiments of the invention the chiral organic molecules comprise chiral metabolites.
According to some embodiments of the invention the metal atoms comprise copper atoms.
According to some embodiments of the invention the metal atoms comprise cobalt atoms.
According to some embodiments of the invention the metal atoms comprise nickel atoms.
According to some embodiments of the invention the metal atoms comprise platinum atoms.
According to an aspect of some embodiments of the present invention there is provided a method of generating current. The method comprises applying energy to the spin-selective conduction structure as delineated above and optionally and preferably as further detailed below, so as to generate flow of charge carriers through the structure.
According to an aspect of some embodiments of the present invention there is provided a method of storing information. The method comprises applying energy to the spin-selective conduction structure as delineated above and optionally and preferably as further detailed below, so as to trap electrons at a preselected spin in the structure.
According to some embodiments of the invention the energy is applied by directing electromagnetic radiation to the structure. According to some embodiments of the invention the energy is applied applying voltage to the structure.
According to some embodiments of the invention the spin-selective conduction structure comprises a semiconductor substrate, wherein one of the layers of chiral organic molecules is deposited on the semiconductor substrate.
According to an aspect of some embodiments of the present invention there is provided a method of generating current. The method provides the spin-selective conduction structure as delineated above and optionally and preferably as further detailed below, and generates condition for charge carriers in the semiconductor substrate to travel through the layers of chiral organic molecules.
According to some embodiments of the invention the method exposes the chiral organic molecules to electromagnetic radiation, so as to generate the condition for the charge carriers in the semiconductor substrate to travel through the layers of chiral organic molecules.
According to some embodiments of the invention the method applies voltage to the semiconductor substrate, so as to generate the condition for the charge carriers in the semiconductor substrate to travel through the layers of chiral organic molecules.
According to an aspect of some embodiments of the present invention there is provided a spintronic circuit. The spintronic circuit comprises the spin-selective conduction structure as delineated above, and optionally and preferably as exemplified herein,
According to an aspect of some embodiments of the present invention there is provided a spintronic circuit. The spintronic circuit comprises an active layer on a semiconductor substrate, wherein the active layer comprises a metal-organic chiral crystal characterized by an electrical resistance that reduces in response to a flow of an electrical current therethrough.
According to some embodiments of the invention the spintronic circuit is incorporated in a device selected from the group consisting of a magnetic field sensor, a memristor, a magnetic memory device, a spintronic transistor, a spin filter device, a spin valve, a spin switch, a spin- polarized light emitting diode (LED), a quantum computer, and a data reading head for reading data from magnetic storage medium.
According to some embodiments of the invention the spintronic circuit comprises a source electrode, a drain electrode, a gate electrode, and a magnetic field generator.
According to some embodiments of the invention the spintronic circuit comprises a controller configure to vary a gate voltage applied to the gate electrode, and a magnetic field applied by the magnetic field generator, so as to provide at least three distinct source-drain current states.
Unless otherwise defined, all technical and/or scientific terms used herein have the same to meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. in case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
Implementation of the method and/or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and/or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.
For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and/or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile storage, for example, a magnetic hard-disk and/or removable media, for storing instructions and/or data. Optionally, a network connection is provided as well. A display and/or a user input device such as a keyboard or mouse are optionally provided as well.
Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings and images. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.
In the drawings:
The present invention, in some embodiments thereof, relates to a crystal structure and, to more particularly, but not exclusively, to a spin-selective conduction structure,
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.
It was found that due to the quantum-mechanical nature of the CISS effect, quantum de-coherence limits the length- and time-scale of the phenomenon to several tens of nanometers. The present disclosure provides a metal-organic chiral crystal that achieves spin-selective conduction using metal atoms and chiral organic molecules. The crystal conducts current in a spin-selective manner, based on the CISS effect, owing to the chiral environment in conjunction with the conducting metal atoms. The inventors experimentally demonstrated spin-selective conduction over a range that is larger than 200 nm. In some embodiments of the present invention the crystal is characterized by an electrical resistance that decreases in response to a flow of an electrical current therethrough. This is unlike conventional oxide-based devices in which the current applied increases the resistance, since the current fills charge trap states.
According to some embodiments of the invention the chiral organic molecules 262 are chiral aromatic molecules.
According to some of any of the embodiments described herein, each of the aromatic molecules comprises an aromatic amino acid.
According to some embodiments of the invention, the chiral organic molecules, e.g., chiral aromatic molecules, self-assemble to form said layers.
By “aromatic molecule” it is meant a molecule (a compound) that comprises a least one aromatic moiety or group.
As used herein, the phrase “aromatic group” or “aromatic moiety” describes a monocyclic or polycyclic moiety having a completely conjugated pi-electron system. The aromatic group can be an all-carbon moiety or can include one or more heteroatoms such as, for example, nitrogen, sulfur or oxygen. The aromatic group can be substituted or unsubstituted, whereby when substituted, the substituent can be, for example, one or more of alkyl, trihaloalkyl, alkenyl, alkynyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, halo, nitro, azo, hydroxy, alkoxy, thiohydroxy, thioalkoxy, cyano and amine.
Exemplary aromatic groups include, for example, phenyl, biphenyl, naphthalenyl, phenanthrenyl, anthracenyl, [1,10]phenanthrolinyl, indoles, thiophenes, thiazoles and, [2,2′]bipyridinyl, each being optionally substituted. Thus, representative examples of aromatic groups that can serve as the side chain within the aromatic amino acid described herein include, without limitation, substituted or unsubstituted naphthalenyl, substituted or unsubstituted phenanthrenyl, substituted or unsubstituted anthracenyl, substituted or unsubstituted [1,10]phenanthrolinyl, substituted or unsubstituted [2,2′]bipyridinyl, substituted or unsubstituted biphenyl and substituted or unsubstituted phenyl. The aromatic group can alternatively be substituted or unsubstituted heteroaryl such as, for example, indole, thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine, quinoline, isoquinoline, quinazoline, quinoxaline, and purine.
In some of any of the embodiments described herein, the aromatic molecule comprises at least one aromatic moiety that is an all-carbon aromatic moiety, e.g., an aryl.
In some of any of the embodiments described herein, the aromatic molecule is or comprises an aromatic amino acid.
In some of any of the embodiments described herein, the aromatic molecule is an aromatic amino acid.
By “aromatic amino acid” it is meant an amino acid, or an amino acid residue in a peptide comprising same, that has an aromatic moiety or group, as defined herein, is its side chain. In exemplary embodiments, an aromatic amino acid has, for example, a substituted or unsubstituted naphthalenyl or a substituted or unsubstituted phenyl, in its side chain. The substituted phenyl may be, for example, pentafluoro phenyl, iodophenyl, biphenyl and nitrophenyl.
According to some embodiments of the invention the chiral organic molecules comprise chiral amino acid molecules. According to some embodiments of the invention the chiral amino acid molecules comprise aromatic amino acid molecule. According to some embodiments of the invention the chiral amino acid molecules comprise D-phenylalanine. According to some embodiments of the invention the chiral amino acid molecules comprise L-phenylalanine, According to some embodiments of the invention the chiral amino acid molecules comprise D-pentafluorophenylalanine. According to some embodiments of the invention the chiral amino to acid molecules comprise L-pentafluorophenylalanine. According to some embodiments of the invention the chiral amino acid molecules comprise D-tryptophan. According to some embodiments of the invention the chiral amino acid molecules comprise L-tryptophan, According to some embodiments of the invention the chiral amino acid molecules comprise D-tyrosine. According to some embodiments of the invention the chiral amino acid molecules comprise L-tyrosine.
According to some embodiments of the invention the chiral organic molecules comprise chiral peptides, less than 10 amino acids in length, more preferably less than 8 amino acids in length, more preferably less than 6 amino acids in length, more preferably less than 4 amino acids in length, e.g., 2 amino acids in length. According to some of these embodiments, each amino acid residue in the peptide features the same chirality (L or D). According to some embodiments of the invention the chiral organic molecules comprise chiral metabolites.
According to some embodiments of the invention the amino and carboxylic acid moieties of the amino acid molecules are ligands forming the coupling between the molecules and the metal atoms. According to some embodiments of the invention the metal atoms 256 are selected to reduce quantum de-coherence of spin states. According to some embodiments of the invention the metal atoms 256 comprise copper atoms. According to some embodiments of the invention the metal atoms 256 comprise cobalt atoms. According to some embodiments of the invention the metal atoms 256 comprise nickel atoms. According to some embodiments of the invention the metal atoms 256 comprise platinum atoms.
According to some embodiments of the invention the crystal is characterized by spin-polarization of at least 20%, more preferably at least 25%, more preferably at least 30%.
According to some embodiments of the invention spin-selective conduction structure 250 comprises a semiconductor substrate 264. One of the layers of the chiral organic molecules 262 is deposited on semiconductor substrate 264. Substrate 264 can comprise any semiconductor material, such as, but not limited to, an elemental semiconductor of Group IV and various combinations of two or more elements from any of Groups III, IV, V and VI of the periodic table of the elements.
As used herein, the term “group” is given its usual definition as understood by one of ordinary skill in the art. For instance, group III elements include Al, Ga, In and Tl; Group IV
elements include C, Si, Ge, Sn and Pb; Group V elements include N, P, As, Sb and Bi; and Group VI elements include O, S, Se, Te and Po.
For example, when substrate 264 comprises silicon, substrate 264 can comprises can be a silicon oxide or silicon nitride. Other example include, without limitation, silicon oxynitride, aluminum oxide, aluminum oxynitride, hafnium oxynitride, hafnium aluminum oxide, hafnium silicon oxide, hafnium silicon oxynitride, zirconium silicate, hafnium dioxide and zirconium dioxide and the like.
Other types of substrates that are contemplated for use as substrate 264 include, without limitation, binary-III-V semiconductor alloys, such as, but not limited to, InAs, InSb, InP GaSb, GaAs and AlSb, ternary III-V semiconductor alloys such as, but not limited to, InGaAs, InAsSb, InAsP, AlInAs, AlAsSb, GaAsP and InSbP, and quaternary semiconductor alloys such as, but not limited to, GaInAsSb.
Spin-selective conduction structure 250 can be incorporated in a spintronic circuit. According to some embodiments of the invention the spintronic circuit is incorporated in a magnetic field sensor. According to some embodiments of the invention the spintronic circuit is incorporated in a magnetic memory device. According to some embodiments of the invention the spintronic circuit is incorporated in a spintronic transistor. According to some embodiments of the invention the spintronic circuit is incorporated in a spin filter device. According to some embodiments of the invention the spintronic circuit is incorporated in a spin valve. According to some embodiments of the invention the spintronic circuit is incorporated in a spin switch. According to some embodiments of the invention the spintronic circuit is incorporated in a spin-polarized light emitting diode. According to some embodiments of the invention the spintronic circuit is incorporated in a quantum computer. According to some embodiments of the invention the spintronic circuit is incorporated in a data reading head for reading data from magnetic storage medium.
Spin-selective conduction structure 250 can be used for generating current. For example, energy can be applied to structure 250, to generate flow of charge carriers through the structure.
Spin-selective conduction structure 250 can be used for storing information. For example, energy can be applied to structure 250, to trap electrons at a preselected spin in the structure.
The energy can be applied, for example, by directing electromagnetic radiation to the structure, or by applying voltage to the structure.
In some embodiments of the present invention conditions are generated for charge carriers in semiconductor substrate 264 to travel through the layers 254, 258, 260 of crystal 252.
This can be done in more than one way. In some embodiments of the present invention the structure 250 is exposed to electromagnetic radiation, for example, to light. This can be done by means of an electromagnetic radiation source 266, such as, but not limited to, a light source, configured for generating electromagnetic radiation 268. In various exemplary embodiments of the invention radiation 268 is monochromatic radiation wherein the wavelength of radiation 268 is selected to generate the condition for charge carriers in semiconductor substrate 264 to travel through the layers 254, 258, 260.
In some embodiments of the present invention voltage is applied to the semiconductor substrate 264 by means of a source electrode 270 and a drain electrode 272, connected to a voltage source 274, as to generate the condition for the charge carriers in the semiconductor substrate to travel through the layers of chiral organic molecules 254, 258, 260.
A representative example of a spintronic circuit 300, according to some embodiments of the present invention is illustrated in
The term “memristor” is short for “memory resistor.” A memristor is a nonlinear component combines a persistent memory with electrical resistance. In other words, a memristor has a non-linear resistance that can act as a universal memory that enables logic operations. The memristor of the present embodiments acts differently from known oxide-based inorganic memristors. In particular, the memristor of the present embodiments comprises a crystal, such as, but not limited to, crystal 252, that is characterized by an electrical resistance that decreases in response to a flow of an electrical current therethrough. This is unlike conventional-based inorganic memristors in which the current applied increases the resistance, since the current fills charge trap states.
Spintronic circuit 300 comprises an active crystal, such as, but not limited to, crystal 252 on substrate 264, source electrode 270, and drain electrode 272. In some embodiments of the present invention circuit 300 also comprises a gate electrode 302 for applying a gate voltage to substrate 264, and optionally and preferably also a magnetic field generator 304 for applying a magnetic field to crystal 252. Preferably, but not necessarily, the magnetic field lines are generally parallel to the source-drain direction defined between source electrode 270 and drain electrode 272. The Inventors found that such a configuration allows memristor 300 to exhibit multilevel memory states. In particular, it was found that different directions of the magnetic fields, and different gate voltages induce different memory states in memristor 300. Thus, a controller 306 is optionally and preferably configure to vary the gate voltage applied to gate electrode 306, and the magnetic field applied by magnetic field generator 304, so as to provide a plurality (e.g., three or more) distinct memory states. As demonstrated in the Examples section that follows, the Inventors successfully fabricated a memristor that exhibits six memory states using two levels for the gate voltage and three different magnetic field characteristics.
As used herein the term “about” refers to ±10%.
The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to”.
The term “consisting of” means “including and limited to”.
The term “consisting essentially of” means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.
As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof
Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6, This applies regardless of the breadth of the range.
Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging/ranges between” a first indicate number and a second indicate number and “ranging/ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.
Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.
Utilization of thiolated double stranded DNA (dsDNA) as a spin-selective component in a spin filter device 10 is illustrated
This Example describes a particular bioinspired class of a metal-organic chiral crystals comprising Cu(II) atoms arranged in two-dimensional (2D) layers of D- or L-enantiomers of phenylalanine or pentafluorophenylalanine. This Example shows experimental observation of a thermally activated ferromagnetic component, occurring at temperatures higher than about 50 K. This makes the materials potentially weakly multi-ferroic, that is, possessing a combination of ferroelectric and ferromagnetic properties. Such behavior has, to date, been identified at room temperature only in inorganic materials. The onset of ferromagnetism is accompanied by a significant increase in long-range (above 300 nm), spin-selective electron conduction. Without wishing to be bound to any particular theory, the Inventors, based on electron paramagnetic resonance (EPR) studies and density functional theory (DFT) calculations, attribute the unexpected magnetic behavior to an indirect exchange interaction between the Cu(II) ions through the chiral lattice. It is expected that the discovered combination of chirality and magnetic properties, exists also in other chiral metal-organic crystals, and can also be used in spin-based devices.
In an exemplified embodiment of the present invention, the spin-selective conduction structure comprises bio-inspired self-assembled organometallic crystals formed by D- or L-phenylalanine and with copper (D/L-Phe—Cu, respectively) and/or D- or L-pentafluorophenylalanine with copper (D/L-F5Phe—Cu, respectively). In experiments performed by Inventors of the present invention, these materials self-assembled in water into a structure in which two chiral amino acid molecules coordinate a copper (II) ion. This formed a crystalline structure made up of a continuous layer of copper atoms sandwiched between the chiral amino acid environment.
It was experimentally found that the Phe—Cu and F5Phe—Cu crystallized into non-centrosymmetric crystal structures, where D- and L-Phe—Cu are mirror images of each other and D- and L-F5Phe—Cu are non-symmetric. These crystals are plate-like, with a diameter ranging from 500 nm to 1 mm in diameter, proving relatively simple to use in nano-, micro- and macro-sized applications.
It was experimentally found that the formed crystals conduct current in a spin-selective manner, based on the CISS effect, owing to the chiral amino acid environment in conjunction with the conducting metallic centers. The inventors demonstrated spin-selective conduction for long ranges (more than 200 nm) with good spin-polarization values of about 30%.
Methods
All materials were purchased from Sigma-Aldrich (Israel) unless noted otherwise, Pentafluorophenylalanine was purchased from Chem Impex (USA). All amino acid-copper crystals were obtained using the following general method: 1 equiv of the CuCl2 (99.999% CuCl2 purity, 5 mM) aqueous solution was slowly added to 2 equiv of an amino acid (10 mM) alkaline solution containing 2 equiv of NaOH (10 mM) under heating at 60° C. Spontaneously, plate-like blue crystals started growing at the liquid-air interface. The crystals were filtered off, washed with deionized water, and dried under vacuum.
Blue plate-like crystals suitable for diffraction were coated with Paratone oil (Hampton Research) and mounted on a MiTeGen loops and flash frozen in liquid nitrogen. All X-ray diffraction measurements were done at 100 K. Diffraction measurements for L-Phe—Cu were done at ESRF synchrotron, station ID23-1. Data were collected and processed using MXCube and the automated XDS pipeline. Data for D-Phe—Cu were measured in-house on a Bruker ApexKappaII. Data were collected and processed using the Bruker Apex2 software suite, D/L-F5Phe—Cu crystals were measured in-house on a Rigaku XtaLabPro full Kappa diffractometer. Data were collected and processed with CrysAlisPro. All structures were solved by direct methods using SHELXT-2013 or SHELXT 2016/4, The structures were refined by fill-matrix least-squares against F2 with SHELXL 2016/4. The crystallographic data are given in Table 1, below. The structure was illustrated using Mercury 3.9 (Cambridge Crystallographic Data Centre, Cambridge, UK).
CD spectra were obtained at 25° C. using an Applied Photophysics Chirascan CD spectrometer, equipped with a temperature-controlled cell, at 1 nm resolution, as an average of three measurements. Spectra were subtracted and smoothed using the Pro-Data software (Applied Photophysics).
A common way to identify ferroelectricity in a material is by measuring the change of the permittivity as a function of an applied electric field (ε-E) or the equivalent capacitance versus applied voltage (C-V) curves. The or C-V measurements are typically done by applying simultaneously on the sample a variable DC voltage and a constant small AC voltage of relatively high frequency (I kHz or above). The AC voltage is used to measure the capacitance, which is then plotted as a function of the DC bias field or voltage. In this example, the C-V curve of L-Phe—Cu crystals was measured using an impedance analyzer (Alfa; Novocontrol) at 1 kHz AC frequency.
Magnetic measurements of L-Phe—Cu crystal were performed using MPMS3 SQUID magnetometer (LOT-Quantum Design Inc.) by applying a vibrating sample mode. The sample was placed in a standard brass holder. The temperature dependence of the magnetic moment was taken at FCH mode: the sample was cooled to 2 K under a 1000 Oe magnetic field. Samples were measured while heating from 2 to 300 K. Magnetic field dependencies were taken at different temperatures in the intervals while the magnetic field H was decreased and increased in the range −20 kOe≤H≤+20 kOe (at some cases the interval was lengthened: ±60 kOe). The lamellar shape of the crystals before their grinding completely corresponds to the orientation of the layers in the crystal structures (
CW-EPR spectra were recorded on a Bruker Elexsys E580 spectrometer operating at X-band (9.5 GHz) and Q-band (35 GHz) frequencies and outfitted with an EN411.8X-MD4 resonator for X-band measurements and with an EN-5107-D2 for Q-band measurements. The temperature was controlled by an Oxford Instruments CF935 continuous flow cryostat using liquid He. Experimental conditions were 2000 points, with a microwave power of 2 mW, 0.1 ml modulation amplitude, and 100 kHz modulation frequency for X-band measurements. The sweep range was 200 mT. For Q-band measurements, the experimental conditions were 2000 points, with microwave power of 1.6 mW, 0.1 mT modulation amplitude and 50 kHz modulation frequency. The sweep range was 200 mT.
Gold electrodes, 3 μm apart from each other, were fabricated in a van der Pauw geometry on a thermal oxide (SiO2—100 nm) p-type silicon wafer.
With reference to
Substrate surfaces were prepared by sputtering a 120 nm layer of nickel, followed by an 8 nm layer of gold on top of a silicon wafer with a 2 μm thermal silicon oxide layer, with an 8 nm titanium layer for adhesion. The use of the Ni/Au surfaces for the mAFM measurements allowed magnetic-field-induced spin polarization of the electrons injected from the surface to the crystal, All surfaces were cleaned by boiling first in acetone and then in ethanol for 10 min, followed by a UV-ozone cleaning for 15 min and a final incubation in warm ethanol for 40 min. The solution of the crystal was drop-casted on the surface and kept in vacuo for evaporation.
Magnetic-field-dependent current versus voltage (I-V) characteristics of the crystals were obtained using a multimode magnetic scanning probe microscopy system built with Beetle Ambient AFM and an electromagnet equipped with a R9 electronics controller (FMK Technology). Voltage spectroscopy for I-V measurements were performed by applying voltage ramps with a Pt tip (DPE-XSC11, μmasch with spring constant 3-5.6 N m−1) in contact with the sample at an applied force of 5 nN. At least 100 I-V curves were scanned for both magnetic field orientation (field UP and DOWN). The crystals were deposited on a gold-coated nickel (Ni 120 nm, Au 8 nm) silicon substrate. The magnetization direction of the nickel layer (up or down) was controlled by an external magnetic field, oriented perpendicular to the Ni plane.
Geometric structure optimizations and electronic structure calculations were performed using the Vienna ab Initio Simulation Package plane wave basis code. Crystal geometric optimizations were performed for the ferromagnetic and antiferromagnetic states separately using the Perdew-Burke-Ernzerhof generalized-gradient approximation exchange-correlation functional, augmented by Tkatchenko-Scheffler van der Waals (TS-vdW) dispersion corrections. Ionic cores were addressed by the projector augmented wave method. The Brillouin zones of all examined crystals were sampled using a Monkhorst-Pack k-point grid of 3×5×3, with a plane wave energy cutoff of 600 eV, following convergence tests with respect to both parameters. For electronic structure calculations, the screened-hybrid functional of Heyd, Scuseria, and Ernzerhof was used. These methods were found to produce reliable results in molecular crystalline materials. Magnetization was calculated by subtracting the up and down spin densities of the crystal and illustrated using the VESTA software.
Results and Discussion
D- and L-enantiomers of phenylalanine and pentafluorophenylalanine were separately crystallized with copper ions (D/L-Phe—Cu and D/L-F5Phe—Cu, respectively) and characterized by X-ray crystallography and circular dichroism (CD) spectroscopy (see the Methods section for details). The asymmetric units of both types of crystals comprise an amino acid dimer coordinating a copper atom (
The ferroelectric response of the crystals was examined. The equivalent capacitance versus applied voltage (C-V) curves of L-Phe—Cu crystals using an impedance analyzer at a frequency of 1 kHz. At very low temperature, 2 K, the samples behave as a perfect capacitor, showing no maximum in the capacitance with the applied DC voltage. At 30 K (
Magnetic properties of these materials were measured using a superconducting quantum interference device (SQUID). The inventors used ultrapure materials for the crystallization and repeated the measurements for different batches, ruling out bulk contamination. Furthermore, measurements were performed on both single crystals and microcrystalline powders to rule out surface contamination. For the single crystals,
The behavior of the magnetization as a function of temperature, measured at a 1000 Oe magnetic field, is further analyzed using the Curie-Weiss equation, χ−1=(T−Θ)/X, where χ is the magnetic susceptibility, T is the absolute temperature, and C and Θ are, respectively, the Curie-Weiss constant and temperatures (
To further support the magnetic data, EPR spectra were measured for the L—Phe—Cu crystalline powder at both the Q- and X-bands (
The magnetic measurements were augmented by temperature-dependent conduction measurements, performed using four gold contacts in a Van der Pauw geometry (
To explore spin-dependent conduction, room-temperature spin-dependent electron conduction studies were performed using a magnetic conductive probe atomic force microscope CP-AFM), based on a setup shown in
Based on the CISS effect alone, the current magnitude for the L-enantiomer with the up-magnetized substrate should be the same as that for the D-enantiomer with the down-magnetized substrate.
To gain insight into the unconventional electronic and magnetic properties of the crystals, DFT calculations were performed. Computational details are given in the Methods section. Computational results for the L-enantiomer are shown in
Both ferromagnetic and an antiferromagnetic state were stabilized in the DFT calculations, with the energy of the antiferromagnetic state being lower by about 3.5 meV per unit cell. The density of states for the ferromagnetic and antiferromagnetic phases of L-Phe—Cu is given in
Interpreting the energy difference between the ferromagnetic and an antiferromagnetic states as the thermodynamic energy needed to flip the spin density at and around one Cu2+ ion in the unit cell, these results suggest that no ferromagnetic response is expected below about 40 K, which, given the approximations inherent in the calculations, is in good qualitative agreement with experiment. At higher temperatures, one can expect some filling of the ferromagnetic state and therefore coexistence of ferromagnetic and antiferromagnetic states, explaining the onset of ferromagnetic hysteresis and its above-discussed impact on transport. The spin density suggests to that for a given spin-polarized electron these states facilitate transport from one Cu2+ ion to its adjacent neighbor for the ferromagnetic state but not for the antiferromagnetic state, where the same spin polarization occurs only on the second-nearest neighboring Cu2+ ion. This explains why the conductivity drops for temperatures low enough such that the antiferromagnetic state dominates (see
It is noted that dynamic phenomena may also explain temperature-activated ferromagnetism. Magnetic order may form owing to the interaction of the spin on the copper ion with lattice dynamics in the crystals, or by a magnetic field created locally by acoustic chiral phonons, which is manifested as an enhanced long-range exchange interaction. A possible role of chirality in obtaining temperature-activated ferromagnetism is that when the Cu2+ ion vibrates against the chiral lattice, it causes charge polarization. Because of the chirality, the charge polarization is accompanied by spin polarization, which in turn induces spin polarization on the next Cu ion. Such a dynamic effect would be consistent with the EPR results presented above.
This Example showed that bioinspired chiral metal-organic crystals support room-temperature, long-range, chirality-induced spin-selective electron conduction. These crystals are found to be weakly ferromagnetic and ferroelectric. The observed ferromagnetism is thermally activated, so that the crystals are antiferromagnetic at low temperatures and become ferromagnetic above about 50 K. Without wishing to be bound to any particular theory, this unexpected behavior can be explained in terms of indirect interaction between the unpaired electrons on the Cu ions, mediated via the chiral lattice, which results in a low-lying thermally populated ferromagnetic state,
This Example describes the use of chiral metal-organic crystals with non-conventional magnetic properties, for the fabrication of an organic chiral spin nonlinear spin memory-resistor (memristor), based on the CISS effect. The device described in this Example consists of an irregular memristor loop, which depends on both the charges and spin trapping. This Example demonstrates that a simple device can exhibit multilevel controlled states, generated by the magnetization of the source. In this Example, changing the source magnetization slows a six-level readout for two terminal organic devices.
The main application found for organic materials in electronic applications is the organic light-emitting diodes (OLED). For memory applications, organic materials suffer from having relatively low conductivity and large variability. In spintronics, although organic materials having a notable relatively long spin lifetime, the low conduction and the need to interface organic materials with inorganic ferromagnetic electrodes make the use of organic materials a challenge.
This Example presents chiral metal-organic crystals (MOCs), as organic materials that have relatively good conduction and in addition, interesting magnetic properties, and demonstrates the use of these crystals as spin memory-resistors (memristors) that act differently from the known oxide-based inorganic memristors. These MOCs can have more than 2 bits of memory and the fabricated devices are chemically and structurally stable.
A memristor is a nonlinear component with properties that cannot be replicated with any combination of the other fundamental components, combines a persistent memory with electrical resistance. In other words, a memristor has a non-linear resistance that can act as a universal memory that enables logic operations. The device presented in this Example combines a memristor's behavior with multilevel logic.
The CISS effect offers a unique approach for meeting the challenge of simple and small memristor fabrication. Because of the CISS effect, chiral molecules and crystals can act as efficient spin filters. The MOC described in this example consists of Cu-phenylalanine crystals that are chiral. Example 1 above showed that these crystals were shown to have good conduction and ferromagnetic properties at room temperature.
D-enantiomers of the amino acid phenylalanine were crystallized with copper ions and characterized by X-ray analysis and circular dichroism (CD) spectroscopy. The asymmetric units of the crystal consist of phenylalanine dimer coordinating a copper atom, and the unit-cell consists of two dimers, as shown in
All the electrical measurements were performed in a planar architecture when the device is located on a thermal oxide (SiO2—100 nm) p-type silicon wafer. The optical microscope image and the graphic sketch of the right-handed D-enantiomers of phenylalanine MOC crystals located between two gold pads are shown in the inset in
Example 1 showed that conduction through the crystals is spin selective, due to the CISS effect. Since the excitation by circular polarized light results in exciting one spin direction, following the excitation, there is an electron in the excited state with one specific spin and the hole in the ground state has the same specific spin. In accordance with the two-band conduction model, the hole conduction is expected to be improved as a result of the scattering reduction for the same spin. When this spin is the spin preferred for conduction through the chiral system, a large photocurrent is produced. A similar improvement in conductivity after magnetizing the Cu atoms is presented shown in
In this Example, three different types of devices have been used to study the spin memristor behaviour: a Hall device, a gated device, and a gated device with magnetic leads.
The first configuration studied is a Hall configuration. As shown in
The device of the present embodiments exhibits a strong dependence of the hysteresis on the current sweep frequency and the hysteresis decays at a high frequency. This frequency dependence is presented in
Note that different devices exhibit similar behaviour, for example, when comparing
This is because the sign of the spin transported is reversed when the current direction is flipped. The large correlation between the Hall signal hysteresis and the drain-source hysteresis can be used in some embodiments of the present invention to reduce the device's noise.
Example 1 showed that the phenylalanine crystals exhibit ferromagnetic behaviour at room temperature, but the crystals become antiferromagnetic below 50 K. Therefore, it is expected that a hysteresis that relates to the magnetic properties of the material disappears at low temperatures. The temperature dependence I vs. the V curves of a device is presented in
Direct magnetization measurements, as a function of temperature, are presented in
The current-induced magnetization effect was used to generate a multi-level spin memristor, as shown in
The multi-level logic is shown in
The observed memristor behaviour results from the special properties of the crystal, which combine chirality and ferromagnetism at room temperature. The current through the chiral crystal is spin selective, due to the CISS effect. The spin current induces the magnetization of the unpaired electrons on the Cu+2 ions. Hence, the hysteresis in resistance and non-linearity results from reducing scattering within the crystal, upon the formation of ferromagnetic domains. The copper ions are responsible for the relatively good conduction of the crystals at room temperature. As was observed by calculations, the ions states lie just above the highest lying molecular orbitals (HOMO) and they indicate a barrier of about meV for conduction. In addition, as shown in
This Example showed that by using organic materials can be used for fabricating devices with new properties that are stable for a long time at ambient conditions. The ability to combine chirality and magnetism with good conduction makes the crystal of the present embodiments useful for many spintronic applications, particularly devices having a size on the order of tens of nanometers.
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Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is/are hereby incorporated herein by reference in its/their entirety.
This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/986,700 filed on Mar. 8, 2020, the contents of which are incorporated herein by reference in their entirety.
The project leading to this application has received funding from the European Research Council (ERC) under the European Union's BISON research and innovation project (grant agreement No. 694426).
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IL2021/050253 | 3/8/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62986700 | Mar 2020 | US |
