Interfacing a Potential Purely Organic Molecular Quantum Bit with a

Subscriber access provided by YORK UNIV

Surfaces, Interfaces, and Applications

Interfacing a Potential Purely Organic Molecular Quantum Bit with a Real-Life Surface Francesca Ciccullo, Arrigo Calzolari, Katharina Bader, Petr Neugebauer, Nolan M. Gallagher, Andrzej Rajca, Joris van Slageren, and Maria Benedetta Casu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16061 • Publication Date (Web): 06 Dec 2018 Downloaded from http://pubs.acs.org on December 6, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Interfacing a Potential Purely Organic Molecular Quantum Bit with a Real-Life Surface Francesca Ciccullo,† Arrigo Calzolari,§ Katharina Bader,‡ Petr Neugebauer§‡ Nolan M. Gallagher,⊺ Andrzej Rajca⊺, Joris van Slageren, ‡ Maria Benedetta Casu†* †Institute

of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen,

Germany §

CNR-NANO Istituto Nanoscienze, Centro S3, I-41125 Modena, Italy

‡Institute §Central

of Physical Chemistry, Universität Stuttgart, 70569 Stuttgart, Germany

European Institute of Technology, CEITEC BUT, Technická 3058/10, 61600, Brno,

Czech Republic ⊺Department

of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United

States

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

ABSTRACT. By using a multidisciplinary and multi-technique approach, we have addressed the issue of attaching a molecular quantum bit to a real surface. First, we demonstrate that an organic derivative of the pyrene-Blatter radical is a potential molecular quantum bit. Our study of the interface of the pyrene-Blatter radical with a copper-based surface reveals that the spin of the interface layer is not cancelled by the interaction with the surface and that the Blatterradical is resistant in presence of molecular water. Although the measured pyrene-Blatter derivative quantum coherence time is not the highest value known, this molecule is known as a “super stable” radical. Conversely, other potential qubits show poor thin film stability upon air exposure. Therefore, we discuss strategies to make molecular systems candidates as qubits competitive, bridging the gap between potential and real applications.

KEYWORDS organic radicals, quantum bits, interfaces, spinterfaces, X-ray spectroscopies.


Page 3 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION The well-known Moore’s law describes the number of transistors on a microprocessor developing over time. The semiconductor industry followed this trend until the beginning of the 21st century, when Moore’s law started showing signs of saturation.1 Heat is one of the main problems causing the slower pace and that has been addressed, for example, by limiting the clock rates and using more than one processor in each chip. Soon the chip’s continuous rescaling will face quantum effects in silicon. This may represent a problem once the limit is reached, but it is also pushing science and industry towards new directions: quantum computing and all-spin-logic are two ways that are presently being explored.1 Analogously to the classical bit, a qubit is the unit of quantum information in quantum computing,2-4 with the quantum coherence time, i.e., the lifetime of the superposition state, which corresponds to the time available for the quantum calculation. Understanding and exploring the use of spins not only involved inorganic materials, but also opened the way to organic spintronics5 and molecular nanomagnets.6-7 Molecular systems are promising materials that intersect with many different fields such as organic/molecular spintronics and electronics, organic magnetism and quantum computing, not least because of their tremendous flexibility by chemical design.2-3, 8-12Among them, organic radicals have been recently proposed as molecular spin qubits.13-15 Implementing a new material in technology is a process that goes beyond controlled laboratory conditions. This is particularly true for molecular spin qubits because of the proposed configurations that imply contacting the molecular qubits for their control and manipulation.16-19 There are several challenges that must be faced in order to retain their magnetic properties for applications. Irregardless of the chosen substrate (metallic or not), the interaction with the substrate (weak versus strong), the presence of defects, contaminants, of OH groups and molecular water cannot be avoided. They might affect the quantum bit, its spin and its interaction with mobile charge carriers, as well as the array organization. Other important aspects that must be considered are stability 3 ACS Paragon Plus Environment


Page 4 of 23

upon air exposure, thermal stability, and capability to adjust to non-controlled operando environments. These challenges prompted us to investigate the interfacial layer of a pyrene-Blatter radical derivative20 (Figure 1) deposited on commercially available copper beryllium (Cu:98%, Be:2%) micro-plates.21 Copper is a metal ubiquitously present in industry for applications ranging from electronics to mechanics. It is very often used as a composite material to improve its good electrical conductivity and mechanical strength.22-30 The use of beryllium as a doping element led to one of the most successful combinations because the presence of beryllium atoms improves at the same time conductivity and mechanical properties of copper.25, 31-33 This is important in case of nano-contacts because copper interconnects might become brittle at the nano-scale.24 The electronic properties of the real-life CuBe surfaces in practical applications do not differ from those of the ideal Cu systems, as characterized in controlled laboratory conditions.21 Here, we denote as “real-life” the surfaces that are the standard in devices, dust-free and prepared in clean rooms, but intrinsically “dirty”, with unintentional contaminants (e.g., O-based compounds) that may interact changing the properties of the interface/spinterface, i.e., an interface with spin-dependent density of state.3435

To investigate this system, we have adopted the methodology that is usually applied to

atomically cleaned and controlled surfaces. This includes density functional theory (DFT) calculations used to model surfaces with contaminants, and organic molecular beam deposition (OMBD) that allows growing thin films under controlled conditions, making the film growth reproducible and tunable,36-37 keeping the radical character intact.37 Previous research published so far13-15 has not addressed the issues of thermal and air stability when using a radical as a quantum bit. In contrast, this is the first aspect that we have considered. Thus, we have reasoned that an “on-purpose” choice of the radical is the fundamental starting point to face the mentioned challenges. In fact, molecular structure and


Page 5 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


degree of delocalization of the unpaired electron play an important role when considering the stability of thin layers based on radicals.37 During the last decades different families of radicals with high chemical stabilities have been synthesized.38-44 We have chosen a pyrene-Blatter radical derivative20 because the Blatter radical is known as a “super stable” radical.45 The specific derivative used in this work, characterized by a significant delocalization of spin density into the pyrene moiety, was synthesized to fulfill the thermodynamic conditions to obtain stable films and interfaces.20 Its films show constant electron paramagnetic resonance (EPR) peak heights over three months in air, indicating exceptionally good spin stability at ambient conditions, and no chemical changes upon annealing,20 making it an ideal candidate not only for electronics and spintronics, but also for investigations in environments beyond solutions/powders. Consequently, because of the characteristics of the two systems, the Blatter radical/CuBe is a model interface suitable for discussing in detail the processes occurring at a real metal-organic quantum bit interface, underlining the applicability of our results for progress towards real applications.

METHODS EXPERIMENTS CuBe surface preparation, this film deposition and X-ray photoelectron spectroscopy (XPS) measurements were performed in an ultra-high vacuum (UHV) system consisting of a substrate preparation chamber and an OMBD-dedicated chamber, connected to an analysis chamber (base pressure 4 x 10-10 mbar) equipped with a SPECS Phoibos 150 hemispherical electron analyzer and a monochromatic Al Kα source (SPECS Focus 500). Copper Beryllium (Cu:98%, Be:2%) 25 m thick micro-plates were used as a substrate. They were cleaned following the methods described elsewhere.21 Their degree of cleanness was verified by XPS. Thin films of the pyrene-Blatter radical, synthesized according to Ref. 20, were deposited in 5 ACS Paragon Plus Environment


Page 6 of 23

situ by OMBD using a Knudsen cell (evaporation rate = 2 Å /min, substrate at room temperature). The evaporation rate was measured with a quartz crystal microbalance, and the nominal thickness was cross-checked by using the attenuation of the XPS substrate signal (Cu 2p) after deposition of the radical. Survey and detailed XPS spectra were measured with electron pass energy of 50 eV and 20 eV, respectively. The binding energy was calibrated by using the Fermi edge of the CuBe substrate. No beam-induced degradation of the samples was observed on the time scale of all discussed experiments. Pulsed EPR measurements were performed on a home-built46 pulsed Q-band spectrometer (ν = 35 GHz), equipped with an Oxford Instruments CF935 continuous flow helium cryostat. A typical π/2 pulse length was 20 ns. The Hahn Echo pulse sequence was used for both echodetected spectra and phase memory time determination. The inversion recovery sequence was used for T1 determination. The spectrometer is controlled by SpecMan software. Highfrequency EPR spectra were recorded on a home-built spectrometer.47 Its radiation source is a 0 – 20 GHz signal generator (VDI) in combination with an amplifier-multiplier chain (VDI) to obtain the required frequencies (80 – 1100 GHz). It features a quasi-optical bridge (Thomas Keating) and induction mode detection. The detector is a QMC Instruments magnetically tuned InSb hot electron bolometer. The sample is mounted inside an Oxford Instruments 15/17T cryomagnet equipped with a variable temperature insert (1.5 – 300K). The spectrometer control program was written in LabView.

CALCULATION DETAILS Structural and electronic ground state properties of the interface are evaluated from first principles simulations based on DFT as implemented in the Quantum Espresso (QE) suite of codes.48 The exchange and correlation functional is expressed by using the PBE formulation,49 and the spin degrees of freedom were treated within the local spin density (LSP) approximation. Grimme-D2 correction50 is used to model the van der Waals type interactions. The convergence 6 ACS Paragon Plus Environment

Page 7 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


thresholds for the geometrical optimizations are set to 0.03 eVÅ-1. The electron ion interactions were described by using ultrasoft pseudopotentials of Vanderbilt’s type.51 Single particle electronic wave functions (charge) were expanded in a plane wave basis set up to an energy cutoff of 28 Ry (280 Ry). The unit supercell (15.40 x 15.40 x 40.00) Å3 has an hexagonal (6 x 6) lateral periodicity and includes 7 layers of Cu(111), Be dopants (ca. 1.7 %), O and OH fragments and the pyreneBlatter radical. Slab replicas are separated by ~15 Å of vacuum in the direction perpendicular to the surface. A regular (2 x 2) grid of k-points was used to sample the 2D Brillouin zone of the interface.

RESULTS AND DISCUSSION Our first step was to assess the potential of the pyrene-Blatter compound as a molecular qubit. We have studied its spin dynamics in dilute frozen solution (toluene-d8, 0.001 M) by means of pulsed EPR (Figure 1) spectroscopy. The fact that an echo detected spectrum can be recorded at all demonstrates that coherent manipulations of the electron spin in the pyreneBlatter radical are possible and, thus, that it is a potential molecular qubit. The spin lattice time was determined by means of the inversion recovery pulse sequence. The inversion recovery curve turned out to be biexponential leading to two spin-lattice relaxation times of T1,f = 12 ± 7 and T1,s = 116 ± 8 ms, respectively. A Hahn echo measurement yielded a quantum coherence or phase memory time of TM = 7.2 ± 0.1 μs. This quantum coherence time is not the highest value known, but compares favorably with many other molecular systems.52 Importantly, it can be likely further enhanced by deuteration of the compound, in view of the fact that weak interactions with proton nuclear spins are typically the limiting factor of the coherence time.53 A valuable tool for investigating the phenomena occurring at the interface between two materials and for addressing the stability of the radical in films and onto a surface is 7 ACS Paragon Plus Environment


Page 8 of 23

thickness-dependent XPS.37, 54 Its sensitivity to the modification of the electronic structure induced at the interface has been very recently exploited to describe spinterfaces.37, 54-56 One can observe that the C 1s core level spectra of the thicker films of the pyrene-Blatter deposited on CuBe (Figure 2) are characterized by a main line, which is attributed to photoelectrons emitted from the carbon atoms of the aromatic sites (C-C and C-H bound carbons). A second feature at higher binding energies is related to the photoelectrons from carbon atoms bound to nitrogen atoms (C-N).20 The ratio of the integrated signal intensities of the different lines are in full stoichiometric agreement with the chemical formula of the pyrene-Blatter radical (Tables S1 and S2 in the Supporting Information) indicating that the molecules are intact upon evaporation and deposition.20 These results are mirrored by the N 1s core level spectra (Figure 2b, and Table S3 in the Supporting Information). The thicker film N 1s core level spectra are characterized by three contributions, as expected for an intact pyrene-Blatter radical20 that has three nitrogen atoms with different chemical environments. The contribution at around 401.0 eV is associated with electrons emitted from nitrogen atoms bound to a phenyl ring and a nitrogen atom (N1), the contribution at 399.3 eV is attributed to photoelectrons from the imine-like nitrogen atoms bound to a carbon atom and a nitrogen atom (N2), whereas the contribution at around 398.3 eV is assigned to electrons emitted from the nitrogen radical atoms (N4 = Nrad).20 In addition, a rich satellite structure is evident, typical in photoemission core level spectra of aromatic hydrocarbon ring molecules. It is due to electronic relaxation effects, occurring as a response to the core−hole creation.57

NH2

N Ph

NHPh

PhHN

N

Ph

Ph

NH Pd/C, air DBU

Cl

toluene reflux (8-15%)

2 1 N Ph N 4N

DCM, rt (34-60%)

8

ACS Paragon Plus Environment

3

1

Page 9 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (upper panel) The Pyrene-Blatter radical derivative molecular structure. (lower panel) Echo detected Q-band EPR spectrum of a 0.001 M solution of pyrene-Blatter in toluene-d8 at 25 K and 35.000 GHz (blue), together with a fit using a minimal model including an axial g-tensor (g= 2.0042(1), g// = 1.9989(1)) and two different isotropic nitrogen hyperfine coupling constants (A1 = 39(3) MHz and A2= 33(3) MHz), with a simulation linewidth of 0.5 mT (peak to peak). The arrow indicates the field position at which relaxation experiments were performed. (top left inset) Inversion recovery curve recorded under the same conditions (symbols) and fit to a biexponential curve (line). (top right inset) Hahn echo decay curve recorded under the same conditions (symbols) and fit to a monoexponential decay (line).

Considering the high sensitivity of XPS for the chemical environment of the single atoms in the molecule, a correspondence between XPS features and EPR patterns in radicals can be expected58-59: stoichiometric XPS features correspond to the expected EPR patterns. On the contrary, when EPR indicates the presence of a different or degraded radical, the XPS spectra



show concomitant changes, due to a different chemical environment of the nitrogen atoms carrying the unpaired spin.37, 58-59

N 1s

C 1s

78 Å

Intensity / a. u.

Intensity / a. u.

78 Å 51 Å 35 Å

35 Å 17 Å

14 Å

14 Å 404 400 396 Binding Energy / eV

a)

b) N 1s N2 N1

78 Å C-H

14 Å

C-C

C-N

292 288 284 Binding Energy / eV

Intensity / a. u.

C 1s

c)

51 Å

17 Å

292 288 284 Binding Energy / eV

Intensity / a. u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 23

78 Å

Nrad S

N*

14 Å 404 402 400 398 Binding Energy /eV

d)

Figure 2. Thickness dependent C1s (a) and N1s (b) core level spectra of the pyrene-Blatter thin films deposited on the CuBe surfaces, together with the peak fit analysis (see the 10 ACS Paragon Plus Environment

Page 11 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Supporting Information) of the C1s (c) and N 1s (d) spectrum of the pyrene-Blatter for the thickest film (upper panel) and the thinnest film (lower panel). The film nominal thicknesses are also indicated.

The thick film XPS features in Figure 2 are typical for the pyrene-Blatter films with the expected EPR pattern corresponding to an intact radical.20 Thus, we can confidently conclude that the radical character is preserved in the pyrene-Blatter thicker films. To corroborate this finding, we have investigated the stability of the pyrene-Blatter radical films by highfrequency EPR (HFEPR). HFEPR spectra were recorded on a 30 Å nominally thick film on a CuBe surface at 320 GHz (Figure 3a). The 60 K spectrum displays a clear single resonance line. Because of its corresponding g-value (2.00368) and narrow width (1 mT peak-to-peak), the resonance line must be due to a radical species, i.e., the pyrene-Blatter radical. In contrast, after washing the radical off of the surface, the substrate shows no signal under the same measurement conditions. Hence, the HFEPR results are fully concomitant with those obtained by XPS. A small shift of the EPR resonance line upon decreasing the temperature is observed (effective g-value change from 2.00368 to 2.00261), together with an increasing asymmetry and broadening of the resonance line (Figure 3b). This may indicate the occurrence of dynamic phenomena in the film and it is promising that EPR is sensitive in that respect. Interestingly, no spectral shifts were observed in HFEPR measurements on bulk samples. In addition, a broad feature can be observed, whose origin is unclear at the moment, but which may originate from intermolecular magnetic interactions. The linewidths are larger than those found in frozen solution Q-band measurements, which may be explained by the presence of g-strain that broadens the spectra at higher fields.



Page 12 of 23

Figure 3. a) High-frequency EPR spectrum recorded on a 30 Å nominally thick film of pyrene-Blatter at 320 GHz and different temperatures as indicated, as well as, of the substrate after removing the radical film. b) g-value and linewidth versus temperature.

The investigation of the thicker films gives us a deep insight into the electronic structure of the films free from interface effects. These findings are a reference to understand in detail the interfacial layer, focusing on the behavior of the radical that carries the magnetic moment. In fact, the comparison between films of different thicknesses allows distinguishing between chemi- and physisorption. Strong interactions with the substrate deform the involved molecular orbitals leading to differences in the XPS features of the layer close to the surface.37, 56, 60 Comparing the XPS core level spectra of the thicker and the thinnest film (Figures 2a and 2b, and Tables S4 and S5 in the Supporting Information), we can observe that the C 1s core level spectra stay essentially unperturbed close to the interface. In contrast, the N 1s core level spectra show a few changes (evidenced also by a best fit procedure, as shown in Figures 2c and 2d) leading to an intense new feature (N*) that appears at around 400.2 eV, overlapping the satellite line. The deviation of the interface N 1s spectral lines from those of the thick 12 ACS Paragon Plus Environment

Page 13 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


films indicates a perturbation of the molecular orbitals at the interface, hinting at several phenomena occurring between the pyrene-Blatter radical and the CuBe surface. These phenomena involve especially the benzotriazine ring in the Blatter radical, while the two phenyl groups and the pyrene substituent do not substantially contribute. At this point a detailed knowledge of the substrate is useful21: in order to mimic application conditions, the substrate is a CuBe metallic surface with OH groups, molecular water, and residual carbon adsorbed on top, and it is slightly oxidized, mostly at the Be atom sites.21 This represents the key to understand the CuBe/pyrene-Blatter radical interface: the binding energy of the N* contribution at 400.2 eV is closely related to the Cu-N energy shown by several organic molecules after Cu metallization,61-63 suggesting an interaction of the molecules with the copper surface. At the same time, the feature at around 398 eV (Nrad), assigned to the photoelectron emitted from the radical, is still clearly visible at the interface (see Figure 2 and Tables S3 and S5 in the Supporting Information). Thus, the XPS core level spectrum at the interface can be explained as a superposition of contributions: due to i) pyrene-Blatter radicals that interact with the substrate where the surface has a metallic nature, quenching the radical magnetic moment,55-56, 64 and to ii) pyrene-Blatter radicals that keep their spin density preserved because they interact locally with passivated sites. (For a detailed quantitative discussion of the fit results see the Supporting Information). To support our interpretation and shed light on the electronic phenomena that take place at the interface, we have performed first principles DFT calculations on a radical/CuBe surface model. The initial configuration for the CuBe substrate, a (111) surface, was derived from the previous characterization of the “real-life” CuBe surface,21 which includes not only intentional Be dopants, but also structural defects (e.g., Cu vacancies) and unintentional impurities (e.g., O-derivatives). The choice of a (111) substrate-lattice geometry is grounded by the evidence that metals with the face centered cubic crystal structure prevalently grow exposing the (111) geometry orientation at the surface.65-66 13 ACS Paragon Plus Environment


Page 14 of 23

The simulated Cu(111) surface (Figure 4a) includes Be dopants (1 %) either in the outermost surface layer configuration or in the central bulk section of the slab; one oxygen adatom and one OH unit, both adsorbed close to surface Be atoms; and one surface copper vacancy (VCu). The pyrene-Blatter radical derivative was initially set with the pyrene unit parallel to the surface at a distance of about 3.4 Å.67 After total-energy-and-force optimization, the radical approaches the surface with a small tilting angle due to the presence of the O-derived protrusions that remove the initial pyrene/surface parallelism. The Blatter radical undergoes a localized distortion, with the benzotriazine ring that loses the initial planarity and the N2 and N4 atoms (Figure 1) that move inward and outward toward the surface plane. The electronic structure of the optimized interface is summarized in Figure 4. Panel (b) shows the total (gray area) and moleculeprojected (green area) density of states (DOS) of the system. The DOS spectrum for the isolated molecule in gas phase (blue line) is superimposed for comparison. The formation of the interface entails a small but not-negligible molecule-to-surface charge transfer that partially empties the former singly occupied molecular orbital (SOMO) of the radical. This is confirmed by the analysis of the single particle electronic state of the interface at the Fermi level (Figure 4c, top view) that maintains the SOMO character of the isolated molecule. We may also notice that at the interface, the reported orbital has contributions delocalized on the Cu substrate (Figure 4c, side view), which indicates a delocalized electronic coupling between the CuBe and the Blatter radical. Albeit evidently the radical is not simply physisorbed on the surface, the interaction cannot be considered as a standard chemisorption, associated with the formation of directional covalent (e.g., site specific) chemical bonds. It rather results in a weak but extended superposition of the -like SOMO orbital of the molecule and the s-band of Cu surface at the Fermi level. The partial depletion of the pristine SOMO has two direct consequences: (i) a partial reduction of the magnetic moment of the radical from 1.0 to 0.75 Bohr magneton/molecule, and (ii) the spin density (up-dw) remains localized around the 14 ACS Paragon Plus Environment

Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


radical, with no contributions from the surface, as shown in panel (d). Thus, our calculations confirm the experimental observation of an interaction with the CuBe substrate, which does not cancel the magnetic character of the radical. Note that a possible oxidation/hydrogenation of the films would lead to the presence of a spectroscopic line in the binding energy range observed for N*.20 However, we can confidently exclude that N* is due to such reactions because our calculations do not indicate any interaction of the Blatter radical with OH groups and oxygen atoms. Moreover, experimental results obtained for films grown on clean SiO2 in presence of residual water partial pressure20 do not exhibit any spectroscopic lines in this binding energy range.

Figure 4. (a) Side view of pyrene-Blatter/CuBe interface. Labels identify the chemical species of the system. (b) Total (gray area) and molecule-projected (green) DOS. DOS spectrum for the isolated molecule (blue line) is superimposed for comparison. Zero energy reference is set to Fermi level (EF) of the interface. Isosurface plot of (c) SOMO orbitals and 15 ACS Paragon Plus Environment


Page 16 of 23

(d) spin density of interface and isolated molecule. In panel (c) a separation blue slice, parallel to the pyrene core, is inserted to highlight the similarities with molecular SOMO. In panel (d) VCu marks the position of the Cu surface vacancy.

CONCLUSIONS We have shown several phenomena at the interface between the pyrene-Blatter, a potential purely organic quantum bit, and a copper surface that simulates real contacts: 1) the interaction of the Blatter radical with passivated surfaces does not influence the pyreneBlatter spin density at the interface. 2) Interactions with metallic copper perturb but do not cancel the magnetic moment at the interface. 3) The pyrene substitute is not involved in a localized covalent bond with the CuBe surface. The presence of “intrinsic” molecular water (i.e., present on the substrate during film deposition) is known to play a role in the degradation mechanisms in organic devices, such as organic light emitting,68 and hybrid perovskite-based devices.69 Importantly, our results show that the Blatter radical is resistant to molecular water. On the other hand, its full protection could be achieved taking advantage from the chemical flexibility by design of molecular systems and considering that the pyrene substituent does not covalently interact with the surface. We could consider synthesizing pyrene-Blatter derivatives by using an approach based on a building block point of view, i.e., identifying three blocks: a functional group, the pyrene substituent, and the Blatter radical. The functional group would be chosen with a strong chemical affinity towards specific substrate sites (e.g., copper), acting as the anchor of the radical derivative on the substrate. The pyrene would be the spacer between the anchor and the radical. In case of the Blatter radical this has a two-fold role: it enhances the unpaired electron delocalization and keeps the molecular qubit intact and available for the wished logic operations. This method would also allow controlling the distance between molecules 16 ACS Paragon Plus Environment

Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


attached to a surface, i.e., between their spin centers, and, thus, controlling their correlation or, in other words, their entanglement.16, 18 While discussing the criteria for quantum calculation is far outside the scope of this fundamental study, we note that in case of a radical two criteria are fulfilled by the fact that it is a S=1/2 system and it is paramagnetic at room temperature. A further key criterium is a long coherence time, thus, significant efforts have been focused on enhancing coherence in molecular systems up to room temperature.70 The usual investigations are performed on bulk samples, such as frozen solutions and doped powders. Although the pyrene-Blatter derivative quantum coherence time is not the highest value known, the films of the pyrene-Blatter derivative show unprecedented stability, by being resistant under X-ray, vacuum conditions, annealing, air exposure, and “intrinsic” molecular water. Stability, beyond solutions or powders, should be considered as a primary issue when synthesizing potential molecular quantum bits. Some of them form thin films and/or interfaces that are relatively weak, when not in solution,37, 71 making their transition to applications very difficult. For example, thin films of a vanadyl complex, a potential qubit with exceptional quantum coherence, show oxidation effects after few hours of air exposure,71 while thin films of a pentacene-TEMPO derivative are extremely sensitive on a shorter time scale.37, 72 70Our approach indicates that a significant role is played by the interface stability in environments that simulate device working conditions and its full consideration will in time bridge the gap between potential and real applications.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI:



Page 18 of 23

Stoichiometric and experimental elemental ratios for a thicker film. Fit results for energy position and relative intensities of the photoemission lines in the C 1s and N 1s spectra for a 78 and 14 Å nominally thick film, respectively, as shown in Figure 2.

AUTHOR INFORMATION Corresponding Author * [email protected]

Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors would like to thank T. Chassé for the access to the photoelectron spectroscopy lab at the University of Tübingen, H. Adler and E. Nadler for technical support, and M. Pink for the X-ray structure of the radical. Financial support from the Institutional Strategy of the University of Tübingen (DFG, ZUK 63), German Research Foundation (DFG) under the contracts CA852/5-2, CA852/11-1, SL104/3-2, PN1900/3-2 (SPP1601), INST41/863 and the Fonds der Chemischen Industrie is gratefully acknowledged. REFERENCES (1) Waldrop, M. M., The Chips Are Down for Moore’s Law. Nature 2016, 530, 144-147. (2) Bader, K.; Dengler, D.; Lenz, S.; Endeward, B.; Jiang, S.-D.; Neugebauer, P.; van Slageren, J., Room Temperature Quantum Coherence in a Potential Molecular Qubit. Nat Commun 2014, 5, 5304. (3) Troiani, F.; Affronte, M., Molecular Spins for Quantum Information Technologies. Chem. Soc. Rev. 2011, 40, 3119-3129. (4) Nielsen, M. A.; Chuang, I. L., Quantum Computation and Quantum Information. Cambridge University Press: 2011. (5) Sanvito, S., Molecular Spintronics. Chem. Soc. Rev. 2011, 40, 3336-3355. 18 ACS Paragon Plus Environment

Page 19 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Gatteschi, D.; Sessoli, R.; Villain, J., Molecular Nanomagnets. Oxford University Press Inc.: New York, 2006. (7) Miller, J. S., Magnetically Ordered Molecule-Based Materials. Chem. Soc. Rev. 2011, 40, 3266-3296. (8) Pedersen, K. S.; Ariciu, A.-M.; McAdams, S.; Weihe, H.; Bendix, J.; Tuna, F.; Piligkos, S., Toward Molecular 4f Single-Ion Magnet Qubits. J. Am. Chem. Soc. 2016, 138, 5801-5804. (9) Fernandez, A.; Moreno Pineda, E.; Muryn, C. A.; Sproules, S.; Moro, F.; Timco, G. A.; McInnes, E. J. L.; Winpenny, R. E. P., G-Engineering in Hybrid Rotaxanes to Create Ab and Ab2 Electron Spin Systems: EPR Spectroscopic Studies of Weak Interactions between Dissimilar Electron Spin Qubits. Angew. Chem. Int. Ed. 2015, 54, 10858-10861. (10) Fernandez, A.; Ferrando-Soria, J.; Pineda, E. M.; Tuna, F.; Vitorica-Yrezabal, I. J.; Knappke, C.; Ujma, J.; Muryn, C. A.; Timco, G. A.; Barran, P. E.; Ardavan, A.; Winpenny, R. E. P., Making Hybrid [n]-Rotaxanes as Supramolecular Arrays of Molecular Electron Spin Qubits. Nat Commun 2016, 7, 10240. (11) Shiddiq, M.; Komijani, D.; Duan, Y.; Gaita-Ariño, A.; Coronado, E.; Hill, S., Enhancing Coherence in Molecular Spin Qubits Via Atomic Clock Transitions. Nature 2016, 531, 348-351. (12) Zadrozny, J. M.; Niklas, J.; Poluektov, O. G.; Freedman, D. E., Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit. ACS Central Science 2015, 1, 488-492. (13) Lehmann, J.; Gaita-Arino, A.; Coronado, E.; Loss, D., Quantum Computing with Molecular Spin Systems. J. Mater. Chem. 2009, 19, 1672-1677. (14) Nakazawa, S.; Nishida, S.; Ise, T.; Yoshino, T.; Mori, N.; Rahimi, R. D.; Sato, K.; Morita, Y.; Toyota, K.; Shiomi, D.; Kitagawa, M.; Hara, H.; Carl, P.; Höfer, P.; Takui, T., A Synthetic Two-Spin Quantum Bit: g-Engineered Exchange-Coupled Biradical Designed for Controlled-Not Gate Operations. Angew. Chem. Int. Ed. 2012, 51, 9860-9864. (15) Sato, K.; Nakazawa, S.; Rahimi, R.; Ise, T.; Nishida, S.; Yoshino, T.; Mori, N.; Toyota, K.; Shiomi, D.; Yakiyama, Y.; Morita, Y.; Kitagawa, M.; Nakasuji, K.; Nakahara, M.; Hara, H.; Carl, P.; Hofer, P.; Takui, T., Molecular Electron-Spin Quantum Computers and Quantum Information Processing: Pulse-Based Electron Magnetic Resonance Spin Technology Applied to Matter Spin-Qubits. J. Mater. Chem. 2009, 19, 3739-3754. (16) Ghirri, A.; Candini, A.; Affronte, M., Molecular Spins in the Context of Quantum Technologies. Magnetochemistry 2017, 3, 12. (17) Vincent, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F., Electronic Read-out of a Single Nuclear Spin Using a Molecular Spin Transistor. Nature 2012, 488, 357. (18) Jenkins, M. D.; Zueco, D.; Roubeau, O.; Aromi, G.; Majer, J.; Luis, F., A Scalable Architecture for Quantum Computation with Molecular Nanomagnets. Dalton Trans. 2016, 45, 16682-16693. (19) Moreno-Pineda, E.; Godfrin, C.; Balestro, F.; Wernsdorfer, W.; Ruben, M., Molecular Spin Qudits for Quantum Algorithms. Chem. Soc. Rev. 2018, 47, 501-513. (20) Ciccullo, F.; Gallagher, N. M.; Geladari, O.; Chasse, T.; Rajca, A.; Casu, M. B., A Derivative of the Blatter Radical as a Potential Metal-Free Magnet for Stable Thin Films and Interfaces. ACS Appl. Mater. Interfaces 2016, 8, 1805–1812. (21) Glaser, M.; Ciccullo, F.; Giangrisostomi, E.; Ovsyannikov, R.; Calzolari, A.; Casu, M. B., Doping and Oxidation Effects under Ambient Conditions in Copper Surfaces: A "RealLife" Cube Surface. J. Mater. Chem. C 2018, 6, 2769-2777. (22) Fadlallah, M. M.; Eckern, U.; Schwingenschlögl, U., Defect Engineering of the Electronic Transport through Cuprous Oxide Interlayers. Sci. Rep. 2016, 6, 27049. (23) Josell, D.; Brongersma, S. H.; Tőkei, Z., Size-Dependent Resistivity in Nanoscale Interconnects. Annu. Rev. Mater. Res. 2009, 39, 231-254. 19 ACS Paragon Plus Environment


Page 20 of 23

(24) Association, S. I., International Technology Roadmap for Semiconductors (Itrs). 2013; Vol. Interconnect Section. (25) O'Keeffe, M.; Moore, W. J., Electrical Conductivity of Monocrystalline Cuprous Oxide. J. Chem. Phys. 1961, 35, 1324-1328. (26) Isseroff, L. Y.; Carter, E. A., Electronic Structure of Pure and Doped Cuprous Oxide with Copper Vacancies: Suppression of Trap States. Chem. Mater. 2013, 25, 253-265. (27) Crone, W. C.; Shield, T. W., Experimental Study of the Deformation near a Notch Tip in Copper and Copper–Beryllium Single Crystals. J Mech. Phys. Solids. 2001, 49, 2819-2838. (28) Kikuchi, N.; Tonooka, K., Electrical and Structural Properties of Ni-Doped Cu2O Films Prepared by Pulsed Laser Deposition. Thin Solid Films 2005, 486, 33-37. (29) Wei, M.; Braddon, N.; Zhi, D.; Midgley, P. A.; Chen, S. K.; Blamire, M. G.; MacManus-Driscoll, J. L., Room Temperature Ferromagnetism in Bulk Mn-Doped Cu2O. Appl. Phys. Lett. 2005, 86, 072514. (30) Kale, S. N.; Ogale, S. B.; Shinde, S. R.; Sahasrabuddhe, M.; Kulkarni, V. N.; Greene, R. L.; Venkatesan, T., Magnetism in Cobalt-Doped Cu2O Thin Films without and with Al, V, or Zn Codopants. Appl. Phys. Lett. 2003, 82, 2100-2102. (31) Liu, J. F.; Krawczyk, F. L.; Kurennoy, S. S.; Schrage, D. L.; Shapiro, A. H.; Tajima, T.; Wood, R. L., Rf Surface Resistance of Copper-on-Beryllium at Cryogenic Temperatures Measured by a 22-Ghz Demountable Cavity. Proceedings of the 2003 Particle Accelerator Conference 2003, 3, 2083-2085. (32) Gallo, P.; Berto, F.; Lazzarin, P.; Luisetto, P., High Temperature Fatigue Tests of CuBe and 40CrMoV13.9 Alloys. Procedia Materials Science 2014, 3, 27-32. (33) Berto, F.; Gallo, P.; Lazzarin, P., High Temperature Fatigue Tests of a Cu-Be Alloy and Synthesis in Terms of Linear Elastic Strain Energy Density. Key Eng. Mater. 2014, 627, 77-80. (34) Sanvito, S., Molecular Spintronics: The Rise of Spinterface Science. Nat. Phys. 2010, 6, 562-564. (35) Cinchetti, M.; Dediu, V. A.; Hueso, L. E., Activating the Molecular Spinterface. Nat. Mater. 2017, 16, 507. (36) Forrest, S. R., Ultrathin Organic Films Grown by Organic Molecular Beam Deposition and Related Techniques. Chem. Rev. 1997, 97, 1793-1896. (37) Casu, M. B., Nanoscale Studies of Organic Radicals: Surface, Interface, and Spinterface. Acc. Chem. Res. 2018, 51, 753-760. (38) Hicks, R. E., Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron Compounds. Wiley: 2010. (39) Rajca, A.; Shiraishi, K.; Pink, M.; Rajca, S., Triplet (S = 1) Ground State Aminyl Diradical. J. Am. Chem. Soc. 2007, 129, 7232-7233. (40) Rajca, A.; Olankitwanit, A.; Wang, Y.; Boratyński, P. J.; Pink, M.; Rajca, S., HighSpin S = 2 Ground State Aminyl Tetraradicals. J. Am. Chem. Soc. 2013, 135, 18205-18215. (41) Ullman, E. F., Stable Free Radicals. VIII. New Imino, Amidino, and Carbamoyl Nitroxides. J. Org. Chem. 1970, 35, 3623-3631. (42) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Rey, P., Toward Molecular Magnets: The Metal-Radical Approach. Acc. Chem. Res. 1989, 22, 392-398. (43) Sun, Z.; Zeng, Z.; Wu, J., Zethrenes, Extended p-Quinodimethanes, and Periacenes with a Singlet Biradical Ground State. Acc. Chem. Res. 2014, 47, 2582-2591. (44) Constantinides, C. P.; Koutentis, P. A., Chapter Seven - Stable N- and N/S-Rich Heterocyclic Radicals: Synthesis and Applications. In Adv. Heterocycl. Chem., Eric, F. V. S.; Christopher, A. R., Eds. Academic Press: 2016, pp 173-207. (45) Constantinides, C. P.; Koutentis, P. A.; Krassos, H.; Rawson, J. M.; Tasiopoulos, A. J., Characterization and Magnetic Properties of a “Super Stable” Radical 1,3-Diphenyl-7Trifluoromethyl-1,4-Dihydro-1,2,4-Benzotriazin-4-Yl. J. Org. Chem. 2011, 76, 2798-2806. 20 ACS Paragon Plus Environment

Page 21 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46) Tkach, I.; Baldansuren, A.; Kalabukhova, E.; Lukin, S.; Sitnikov, A.; Tsvir, A.; Ischenko, M.; Rosentzweig, Y.; Roduner, E., A Homebuilt ESE Spectrometer on the Basis of a High-Power Q-Band Microwave Bridge. Appl. Magn. Reson. 2008, 35, 95-112. (47) Neugebauer, P.; Bloos, D.; Marx, R.; Lutz, P.; Kern, M.; Aguila, D. A.; Vaverka, J.; Laguta, O.; Dietrich, C.; Clerac, R.; van Slageren, J., Ultra-Broadband EPR Spectroscopy in Field and Frequency Domains. Phy. Chem. Chem. Phys. 2018, 20, 15528-15534 (48) Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; Dal Corso, A.; de Gironcoli, S.; Fabris, S.; Fratesi, G.; Gebauer, R.; Gerstmann, U.; Gougoussis, C.; Kokalj, A.; Lazzeri, M.; MartinSamos, L.; Marzari, N.; Mauri, F.; Mazzarello, R.; Paolini, S.; Pasquarello, A.; Paulatto, L.; Sbraccia, C.; Scandolo, S.; Sclauzero, G.; Seitsonen, A. P.; A., S.; Umari, P.; M., W. R., Quantum Espresso: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys.: Condens. Matter 2009, 21, 395502. (49) Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. (50) Stefan, G., Semiempirical Gga‐Type Density Functional Constructed with a Long‐Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. (51) Vanderbilt, D., Soft Self-Consistent Pseudopotentials in a Generalized Eigenvalue Formalism. Phys. Rev. B 1990, 41, 7892-7895. (52) Eaton, S. S.; Eaton, G. R., Relaxation Times of Organic Radicals and Transition Metal Ions. In Distance Measurements in Biological Systems by EPR, Berliner, L. J.; Eaton, G. R.; Eaton, S. S., Eds. Springer US: Boston, MA, 2002, pp 29-154. (53) Ardavan, A.; Rival, O.; Morton, J. J. L.; Blundell, S. J.; Tyryshkin, A. M.; Timco, G. A.; Winpenny, R. E. P., Will Spin-Relaxation Times in Molecular Magnets Permit Quantum Information Processing? Phys. Rev. Lett. 2007, 98, 057201. (54) Mugnaini, V.; Calzolari, A.; Ovsyannikov, R.; Vollmer, A.; Gonidec, M.; Alcon, I.; Veciana, J.; Pedio, M., Looking inside the Perchlorinated Trityl Radical/Metal Spinterface through Spectroscopy. J. Phys. Chem. Lett. 2015, 6, 2101-2106. (55) Kakavandi, R.; Calzolari, A.; Borozdina, Y. B.; Ravat, P.; Chassé, T.; Baumgarten, M.; Casu, M. B., Unraveling the Mark of Surface Defects on a Spinterface: The Nitronyl Nitroxide/TiO2(110) Interface. Nano Res. 2016, 9, 3515–3527. (56) Kakavandi, R.; Savu, S.-A.; Caneschi, A.; Chasse, T.; Casu, M. B., At the Interface between Organic Radicals and TiO2(110) Single Crystals: Electronic Structure and Paramagnetic Character. Chem. Commun. (Cambridge, U. K.) 2013, 49, 10103-10105. (57) Enkvist, C.; Lunell, S.; Sjögren, B.; Brühwiler, P. A.; Svensson, S., The C1s Shakeup Spectra of Buckminsterfullerene, Acenaphthylene, and Naphthalene, Studied by High Resolution X‐Ray Photoelectron Spectroscopy and Quantum Mechanical Calculations. J. Chem. Phys. 1995, 103, 6333-6342. (58) Savu, S.-A.; Biswas, I.; Sorace, L.; Mannini, M.; Rovai, D.; Caneschi, A.; Chassé, T.; Casu, M. B., Nanoscale Assembly of Paramagnetic Organic Radicals on Au(111) Single Crystals. Chem.-Eur. J. 2013, 19, 3445-3450. (59) Kakavandi, R.; Ravat, P.; Savu, S. A.; Borozdina, Y. B.; Baumgarten, M.; Casu, M. B., Electronic Structure and Stability of Fluorophore–Nitroxide Radicals from Ultrahigh Vacuum to Air Exposure. ACS Appl. Mater. Interfaces 2015, 7, 1685-1692. (60) Savu, S. A.; Biddau, G.; Pardini, L.; Bula, R.; Bettinger, H. F.; Draxl, C.; Chasse, T.; Casu, M. B., Fingerprint of Fractional Charge Transfer at the Metal/Organic Interface. J. Phys. Chem. C 2015, 119, 12538–12544. (61) Diller, K.; Klappenberger, F.; Allegretti, F.; Papageorgiou, A. C.; Fischer, S.; Wiengarten, A.; Joshi, S.; Seufert, K.; Écija, D.; Auwärter, W.; Barth, J. V., Investigating the Molecule-Substrate Interaction of Prototypic Tetrapyrrole Compounds: Adsorption and SelfMetalation of Porphine on Cu(111). J. Chem. Phys. 2013, 138, 154710. 21 ACS Paragon Plus Environment


Page 22 of 23

(62) Diller, K.; Klappenberger, F.; Marschall, M.; Hermann, K.; Nefedov, A.; Wöll, C.; Barth, J. V., Self-Metalation of 2H-Tetraphenylporphyrin on Cu(111): An X-Ray Spectroscopy Study. J. Chem. Phys. 2012, 136, 014705. (63) Uvdal, K.; Bodö, P.; Liedberg, B., L-Cysteine Adsorbed on Gold and Copper: An XRay Photoelectron Spectroscopy Study. J. Colloid Interface Sci. 1992, 149, 162-173. (64) Javaid, S.; Bowen, M.; Boukari, S.; Joly, L.; Beaufrand, J. B.; Chen, X.; Dappe, Y. J.; Scheurer, F.; Kappler, J. P.; Arabski, J.; Wulfhekel, W.; Alouani, M.; Beaurepaire, E., Impact on Interface Spin Polarization of Molecular Bonding to Metallic Surfaces. Phys. Rev. Lett. 2010, 105, 077201. (65) R. Rosenberg; D. C. Edelstein; C.-K. Hu, a.; Rodbell, K. P., Copper Metallization for High Performance Silicon Technology. Annu. Rev. Mater. Res. 2000, 30, 229-262. (66) Zhang, X.; Han, J.; Plombon, J. J.; Sutton, A. P.; Srolovitz, D. J.; Boland, J. J., Nanocrystalline Copper Films Are Never Flat. Science 2017, 357, 397-400. (67) The one-to-one comparison between simulated and experimental structure goes beyond the aim of this work that is, instead, focused on the microscopic understanding of the electronic properties of the spinterface. (68) Scholz, S.; Kondakov, D.; Lüssem, B.; Leo, K., Degradation Mechanisms and Reactions in Organic Light-Emitting Devices. Chem. Rev. (Washington, DC, U. S.) 2015, 115, 8449-8503. (69) Deretzis, I.; Smecca, E.; Mannino, G.; La Magna, A.; Miyasaka, T.; Alberti, A., Stability and Degradation in Hybrid Perovskites: Is the Glass Half-Empty or Half-Full? J. Phys. Chem. Lett. 2018, 9, 3000-3007. (70) Sproules, S., Molecules as Electron Spin Qubits. In Electron Paramagnetic Resonance: Volume 25, The Royal Society of Chemistry: 2017, pp 61-97. (71) Tesi, L.; Lucaccini, E.; Cimatti, I.; Perfetti, M.; Mannini, M.; Atzori, M.; Morra, E.; Chiesa, M.; Caneschi, A.; Sorace, L.; Sessoli, R., Quantum Coherence in a Processable Vanadyl Complex: New Tools for the Search of Molecular Spin Qubits. Chem. Sci. 2016, 7, 2074-2083. (72) Arantes, C.; Chernick, E. T.; Gruber, M.; Rocco, M. L. M.; Chasse, T.; Tykwinski, R. R.; Casu, M. B., Interplay between Solution-Processing and Electronic Structure in MetalFree Organic Magnets Based on a Tempo Pentacene Derivative. J. Phys. Chem. C. 2016, 120, 3289–3294.


Page 23 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC GRAPHICS

The Blatter radical is a quantum bit

1

0 also at real-life interfaces


Interfacing a Potential Purely Organic Molecular Quantum Bit with a

Recommend Documents