High-resolution Photoelectron Spectroscopy Research Articles

Precision Measurement of the Electron Affinity of Chlorine via High-Resolution Photoelectron Spectroscopy.

Chlorine (Cl2) is a diatomic molecule used as an important industrial gas. However, the electron affinity (EA) of Cl2, a fundamental parameter for understanding chemical reactions, has no accurate experimental result available. The latest result of the EA value of Cl2 is 2.50(20) eV reported in 1983. In the present work, we report the precision measurement of the EA of Cl2 with the successive difference method via the high-resolution photoelectron spectroscopy of cryogenically cold chlorine anions Cl2-. The EA of Cl2 is determined to be 19432(9) cm-1 or 2.4093(11) eV.

Spectroscopic Quantification of the Inverted Singlet-Triplet Gap in Pentaazaphenalene.

We report the direct and accurate spectroscopic quantification of the inverted singlet-triplet gap in 1,3,4,6,9b-pentaazaphenalene. This measurement is achieved by directly probing the lowest singlet and triplet states via high-resolution cryogenic anion photoelectron spectroscopy. The assignment of the first excited singlet state is confirmed by visible absorption spectroscopy in an argon matrix at 20 K. Our measurements yield an inverted singlet-triplet gap with ΔEST= -0.047(7) eV. The accurate quantification of the singlet-triplet gap presented here allows for direct evaluation of various computational electronic structure methods and highlights the critical importance of the proper description of the double excitation character of these electronic states. Overall, this study validates the idea that despite Hund's multiplicity rule, useful organic chromophores can have inherently inverted singlet-triplet gaps.

Momentum-Resolved Electronic Structures and Strong Electronic Correlations in Graphene-like Nitride Superconductors.

Although transition-metal nitrides have been widely applied for several decades, experimental investigations of their high-resolution electronic band structures are rare due to the lack of high-quality single-crystalline samples. Here, we report on the first momentum-resolved electronic band structures of titanium nitride (TiN) films, which are remarkable nitride superconductors. The measurements of the crystal structures and electrical transport properties confirmed the high quality of these films. More importantly, from a combination of high-resolution angle-resolved photoelectron spectroscopy and first-principles calculations, the extracted Coulomb interaction strength of TiN films can be as large as 8.5 eV, whereas resonant photoemission spectroscopy yields a value of 6.26 eV. These large values of Coulomb interaction strength indicate that superconducting TiN is a strongly correlated system. Our results uncover the unexpected electronic correlations in transition-metal nitrides, potentially providing a perspective not only to understand their emergent quantum states but also to develop their applications in quantum devices.

Probing the activated complex of the F + NH3 reaction via a dipole-bound state

Experimental characterization of the transition state poses a significant challenge due to its fleeting nature. Negative ion photodetachment offers a unique tool for probing transition states and their vicinity. However, this approach is usually limited to Franck-Condon regions. For example, high-lying Feshbach resonances with an excited HF stretching mode (vHF = 2-4) were recently identified in the transition-state region of the F + NH3 → HF + NH2 reaction through photo-detaching FNH3− anions, but the direct photodetachment failed to observe the lower-lying vHF = 0,1 resonances and bound states due apparently to negligible Franck-Condon factors. Indeed, these weak transitions can be resonantly enhanced via a dipole-bound state (DBS) formed between an electron and the polar FNH3 species. In this study, we unveil a series of Feshbach resonances and bound states along the F + NH3 reaction path via a DBS by combining high-resolution photoelectron spectroscopy with high-level quantum dynamical computations. This study presents an approach for probing the activated complex in a reaction by negative ion photodetachment through a DBS.

Resonant photoemission studies on Fe-Ni alloys

This paper investigates the electronic structure of Fe1−xNix (x = 0.32, 0.36, 0.4, 0.5) alloys employing high resolution photoelectron spectroscopy using synchrotron radiation. The valence bands and the core levels have been recorded at various on-resonance and off-resonance photon energies of Fe and Ni. An anti-resonance dip observed in the valence bands taken at Fe 3p → 3d resonance lies closer to the Fermi level compared to that observed at Ni 3p → 3d resonance, indicating larger density of itinerant Fe 3d electrons. Whereas, Ni 3d states are comparatively less itinerant in these alloys. The hybridization effects increase with increase of Fe content in the alloy system. The intensity of Ni L3M4,5M4,5 Coster-Cronig Auger transition observed with 853 eV (Ni 2p → 3d resonance) photon energy, drops down drastically for the Invar alloy (Fe0.64Ni0.36) as compared to other Fe-Ni alloys due to the existence of Ni in more than one local chemical surroundings as expected for Invar alloy. The electron-electron interaction energy (Udd) of Ni 3d shell is found to decrease with the decrease of Ni concentration. The 3p and 3s core levels of Fe and Ni recorded at 707 eV (Fe 2p → 3d resonance) are overwhelmed by various intense resonant Auger features such as Fe L3M2,3M2,3, Fe L3M2,3M4,5 and Fe L3M1M4,5. The 1S state of Fe L3M2,3M2,3 is greatly enhanced in the Invar alloy as compared to other alloys. The microscopic compositional in-homogeneity present in Invar alloy plays a crucial role in the screening of holes in Ni sites but does not contribute in screening the holes in Fe sites.

High-Resolution Photoelectron Spectroscopy of the Ground and First Excited Electronic States of MgXe.

We report on the characterization of the X+ 2Σ+ ground and the A+ 2ΠΩ (Ω = 1/2, 3/2) and B+ 2Σ+ electronically excited states of MgXe+. Rotationally cold MgXe in the a 3Π0(v″ = 0) metastable electronic state was generated in a laser-ablation supersonic-beam source. Following single-photon excitation from the metastable state, the vibrational structure of the X+ state of MgXe+ was measured by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy, and the adiabatic ionization energy of the X+ ← a ionizing transition was determined to be EI/(hc) = 37,468.3(6) cm-1. Spectra of the A+ ← X+ and B+ ← X+ transitions were recorded by using the method of isolated-core Rydberg-dissociation spectroscopy. The observation of the Mg+(3p) 2P1/2 + Xe 1S0 dissociation limit enabled the determination of the dissociation energies of the X+ [D0(X+) = 2970(7) cm-1] and A+ states [D0(A1/2+) = 9781(7) cm-1 and D0(A3/2+) = 9603(7) cm-1]. We compare these results with those of earlier experimental studies and ab initio quantum-chemical calculations.

High-resolution photoelectron spectroscopy of the very weakly bound MgNe molecule

ABSTRACT We report on the characterisation of the X + 2 Σ + ground electronic state of MgNe + by photoionisation, mass-analysed threshold-ionisation (MATI) and pulsed-field-ionisation zero-kinetic-energy photoelectron (PFI-ZEKE-PE) spectroscopy and the observation of the metastable a 3 Π 0 state of MgNe. Rotationally cold MgNe was generated in a laser-ablation supersonic-beam source in both the X 1 Σ + ( v ″ = 0 ) ground state and a 3 Π 0 ( v ″ = 0 ) metastable electronic state. PFI-ZEKE-PE spectra with full resolution of the vibrational structure and partial resolution of the rotational structure were recorded from the X 1 Σ + ground state following resonant ( 1 + 1 ′ ) two-photon excitation via selected rovibrational levels of the C 1 Π intermediate state and from the a 3 Π 0 metastable state following single-photon excitation. The lowest six vibrational levels of the X + 2 Σ + state were observed, covering 80% of the X + 2 Σ + potential-well depth. The experimental data were used to determine potential-energy functions, dissociation energies, and molecular constants for the X 1 Σ + , a 3 Π 0 and C 1 Π states of MgNe and the X + 2 Σ + state of MgNe + . With dissociation energies D 0 of 12(3) cm−1 and 10(3) cm−1, respectively, the X 1 Σ + and a 3 Π 0 states of 24 Mg 20 Ne are extremely weakly bound. In contrast, the X + 2 Σ + state of 24 Mg 20 Ne + has a dissociation energy D 0 of 185(3) cm − 1 and 12 bound vibrational levels. From the difference between the adiabatic ionisation energies of the X 1 Σ + (61 498.5(4) cm − 1 ) and the a 3 Π 0 (39 645.1(3) cm − 1 ) states, the term value of the a 3 Π 0 ground vibrational level is determined to be 21 853.4(5) cm − 1 . These results are compared with those of earlier experimental studies and ab initio quantum-chemical calculations.

Characterisation of the ground X+ 2ΠΩ and first excited A+ 2Σ+ electronic states of MgO+ by high-resolution photoelectron spectroscopy.

Despite the importance of MgO+ for understanding the electronic structure and chemical bonds in alkaline-earth metal oxides and its potential astrophysical relevance, hardly any spectroscopic information is available on this molecular cation. We report on a high-resolution photoelectron spectroscopic study of MgO using a resonant (1 + 1') two-photon excitation scheme in combination with PFI-ZEKE photoelectron spectroscopy. By carrying out the resonant excitation via selected rotational levels of several intermediate states of different electronic configurations, total electronic spins, and internuclear distances, a broad range of vibrational levels of the X+ 2ΠΩ (Ω = 3/2, 1/2) ground and A+ 2Σ+ first excited states of MgO+ were observed for the first time. The new data provide a full characterisation of the rovibronic level structure of MgO+ up to 2 eV (16 000 cm-1) of internal energy. A full set of vibrational, rotational and spin-orbit-coupling molecular constants were extracted for these two electronic states. The adiabatic ionisation energy and the singlet-triplet interval of 24Mg16O were determined to be 64 577.65(20) cm-1 and 2492.4(3) cm-1, respectively.

Ferroelectric-enabled significant carbon dioxide molecular adsorption on BaTiO3(001)

Carbon dioxide is reversibly adsorbed and desorbed from ferroelectric (001) oriented, BaO-terminated barium titanate, as revealed in real time by high resolution ultrafast photoelectron spectroscopy and certified by low energy electron diffraction.

Role of Polarization Interactions in the Formation of Dipole-Bound States.

Even though there is a critical dipole moment required to support a dipole-bound state (DBS), how molecular polarizability may influence the formation of DBSs is not well understood. Pyrrolide, indolide, and carbazolide provide an ideal set of anions to systematically examine the role of polarization interactions in the formation of DBSs. Here, we report an investigation of carbazolide using cryogenic photodetachment spectroscopy and high-resolution photoelectron spectroscopy (PES). A polarization-assisted DBS is observed at 20 cm-1 below the detachment threshold for carbazolide, even though the carbazolyl neutral core has a dipole moment (2.2 D) smaller than the empirical critical value (2.5 D) to support a dipole-bound state. Photodetachment spectroscopy reveals nine vibrational Feshbach resonances of the DBS, as well as three intense and broad shape resonances. The electron affinity of carbazolyl is measured accurately to be 2.5653 ± 0.0004 eV (20,691 ± 3 cm-1). The combination of photodetachment spectroscopy and resonant PES allows fundamental frequencies for 14 vibrational modes of carbazolyl to be measured. The three shape resonances are due to above-threshold excitation to the three low-lying electronic states (S1-S3) of carbazolide. Resonant PES of the shape resonances is dominated by autodetachment processes. Ultrafast relaxation from the S2 and S3 states to S1 is observed, resulting in constant kinetic energy features in the resonant PES. The current study provides decisive information about the role that polarization plays in the formation of DBSs, as well as rich spectroscopic information about the carbazolide anion and the carbazolyl radical.

FlexPES: a versatile soft X-ray beamline at MAX IV Laboratory.

FlexPES is a soft X-ray beamline on the 1.5 GeV storage ring at MAX IV Laboratory, Sweden, providing horizontally polarized radiation in the 40-1500 eV photon energy range and specializing in high-resolution photoelectron spectroscopy, fast X-ray absorption spectroscopy and electron-ion/ion-ion coincidence techniques. The beamline is split into two branches currently serving three endstations, with a possibility of adding a fourth station at a free port. The refocusing optics provides two focal points on each branch, and enables either focused or defocused beam on the sample. The endstation EA01 at branch A (Surface and Materials Science) is dedicated to surface- and materials-science experiments on solid samples at ultra-high vacuum. It is well suited not only to all flavours of photoelectron spectroscopy but also to fast (down to sub-minute) high-resolution X-ray absorption measurements with various detectors. Branch B (Low-Density Matter Science) has the possibility to study gas-phase/liquid samples at elevated pressures. The first endstation of this branch, EB01, is a mobile setup for various ion-ion and electron-ion coincidence techniques. It houses a versatile reaction microscope, which can be used for experiments during single-bunch or multi-bunch delivery. The second endstation, EB02, is based on a rotatable chamber with an electron spectrometer for photoelectron spectroscopy studies on primarily volatile targets, and a number of peripheral setups for sample delivery, such as molecular/cluster beams, metal/semiconductor nanoparticle beams and liquid jets. This station can also be used for non-UHV photoemission studies on solid samples. In this paper, the optical layout and the present performance of the beamline and all its endstations are reported.

High-Resolution Photoelectron Spectroscopy of Vibrationally Excited Vinoxide Anions.

High-resolution photoelectron spectra of vibrationally pre-excited vinoxide anions (CH2CHO-) are reported using the recently developed IR-cryo-SEVI technique. This method is combined with a newly developed implementation of vibrational perturbation theory that can readily identify relevant anharmonic couplings among nearly degenerate vibrational states. IR-cryo-SEVI spectra are obtained by resonant infrared excitation of vinoxide anions via the fundamental C-O (ν4, 1566 cm-1) or isolated C-H (ν3, 2540 cm-1) stretching vibrations prior to photodetachment. Excitation of the ν4 mode leads to a well-resolved photoelectron spectrum that is in excellent agreement with a harmonic Franck-Condon simulation. Excitation of the higher-energy ν3 mode results in a more complicated spectrum that requires consideration of the calculated anharmonic resonances in both the anion and the neutral. From this analysis, information about the zeroth-order states that contribute to the nominal ν3 wave function in the anion is obtained. In the neutral, we observe anharmonic splitting of the ν3 fundamental into a polyad feature with peaks at 2737(22), 2 835(18), and 2910(12) cm-1, for which only the center frequency has been previously reported. Overall, 9 of the 12 fundamental frequencies of the vinoxy radical are extracted from the IR-cryo-SEVI and ground-state cryo-SEVI spectra, most of which are consistent with previous measurements. However, we provide a new estimate of the ν5 (CH2 scissoring) fundamental frequency at 1395(11) cm-1 and attribute the discrepancy with previously reported values to a Fermi resonance with the 2ν11 overtone (CH2 wagging).

The primary gas phase hydration shell of hydroxide.

The number of water molecules in hydroxide's primary hydration shell has been long debated to be three from the interpretation of experimental data and four from theoretical studies. Here, we provide direct evidence for the presence of a fourth water molecule in hydroxide's primary hydration shell from a combined study based on high-resolution cryogenic experimental photoelectron spectroscopy and high-level quantum chemical computations. Well-defined spectra of OH-(H2O)n clusters (n=2 to 5) yield accurate electron binding energies, which are, in turn, used as key signatures of the underlying molecular conformations. Although the smaller OH-(H2O)3 and OH-(H2O)4 clusters adopt close-lying conformations with similar electron binding energies that are hard to distinguish, the OH-(H2O)5 cluster clearly has a predominant conformation with a four-coordinated hydroxide binding motif, a finding that unambiguously determines the gas phase coordination number of hydroxide to be four.

Structural evolution, electronic and magnetic properties investigation of V3Sin− (n = 14–18) clusters based on photoelectron spectroscopy and density functional theory calculations

Silicon clusters doped with a transition metal (TM) atom have been intensively studied due to their novel properties and superior stability for possible usage as building blocks of future nanoelectronics. Besides the selection of the doped element, introducing the number of dopant atoms as another dimension adds versatility to tuning the cluster properties. However, there are few studies of silicon clusters doped with multiple TM atoms. Here, we present a study of V3Sin− (n = 14–18) by combining high-resolution photoelectron spectroscopy (PES) measurements with a search of their global minimum energy structures based on a homemade genetic algorithm coupled with density functional theory (DFT) for energy calculations. The simulated photoelectron spectra of the putative global minimum structures are in fair agreement with the experimental ones, which gives evidence for their authenticity as the ground-state structures. In these clusters the three V atoms always bond with each other and form an acute triangle, which can be seen as a nanoscale analogue of phase segregation in the bulk. For the size range n = 14–17, each of the ground-state structures has a silicon basket-like structure with the vanadium triangle inside, while V3Si18− has a baseball-mitt-like structure almost completely encapsulating the V3 triangle. The average binding energy of TMSin− (TM = V1, V2, V3) indicates that the more V atoms are doped the more stable the clusters are. Among these clusters, only V3Si14− have a total magnetic moment of 2 μB, making it a potential structural unit for magnetic storage devices. Mulliken population analysis and the electron spin density show that V atoms at different positions have different contributions to the total magnetic moments, and d electrons in V atoms contribute the most.

Surface charge dynamics on air-exposed ferroelectric Pb(Zr,Ti)O3(001) thin films.

Probing of the free surface ferroelectric properties of thin polar films can be achieved either by estimating the band bending variance under the top-most layer or by studying the extent of the extrinsic charge accumulated outside the surface. Photoemitted or incoming low-energy electrons can be used to characterize locally both properties in a spectromicroscopic approach. Thin ferroelectric lead zirco-titanate (PZT) is investigated by combining low energy/mirror electron microscopy (LEEM/MEM) with photoemission electron microscopy (PEEM) and high-resolution photoelectron spectroscopy (XPS). Significant extrinsic negative compensation charge is proven to accumulate on the surface of the outward polarized thin film, indicated by high MEM-LEEM transition values, up to 15.3 eV, and is correlated with the surface electrostatic potential, which can be partially screened either by electrons interacting with the sample or by soft X-rays through the ejection of secondary electrons and generation of positive charge under the surface. A radiation-induced surface charge compensation effect is observed. The study indicates that air-exposed high quality ferroelectric thin films show large negative surface potentials, determined locally on the surface, which are nevertheless sensitive to beam damage and molecular desorption. These values represent a confirmation of previously estimated surface potential energy values determined from the LEED data on clean surfaces.

High-resolution photoelectron spectroscopy of the ground and first excited electronic states of MgKr+

We report on the characterisation of the lowest three electronic states of MgKr, the X ground state associated with the Mg(3s) + Kr(4p) dissociation limit and the A and B excited states associated with the Mg(3p) + Kr(4p) dissociation limits. The vibrational structure of the X ground state was measured by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy starting from the a metastable state of MgKr generated by laser ablation of a Mg rod in a Kr supersonic beam. The vibrational assignment was derived from the isotopic structure of the spectra and the adiabatic ionisation energy of the ionising transition was determined to be 38182.4(2.0) cm. Partially rotationally resolved spectra of the A X and B X transitions were recorded by monitoring the yield of Mg ions produced by dissociation of MgKr using the technique of isolated-core Rydberg-dissociation spectroscopy. Analytical potential-energy functions of the X, A, and B states were derived using a global model of these states that includes the spin-orbit interaction. The observation of the highest vibrational levels of the B state and the onset of the Kr + Mg(3p) dissociation continuum enabled the precise determination of the dissociation energies of the X, A and B states of MgKr and of the a state of MgKr. The X, A and B states of MgKr are important stepping stones to access the Rydberg states of MgKr and the ground state of MgKr by resonant multiphoton excitation.

On-surface synthesis of disilabenzene-bridged covalent organic frameworks

Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C4Si2) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSix film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C4Si2-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C4Si2 ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C4Si2 rings were converted into C4Si pentagonal siloles by further annealing.

Electron affinity of tantalum and excited states of its anion.

The tantalum anion has the most complicated photoelectron spectrum among all atomic anions of transition elements, which was the main obstacle to accurately measure its electron affinity via the generic method. The latest experimental value of the electron affinity of Ta was 0.323(12) eV, reported by Feigerle et al. [J. Chem. Phys. 74, 1580 (1981)]. In the present work, we report the high-resolution photoelectron spectroscopy of Ta- via the slow-electron velocity-map imaging method combined with a cryogenic ion trap. The electron affinity of Ta was measured to be 2652.38(17) cm-1 or 0.328859(23) eV. Three excited states 5D1, 3P0, and 5D2 of Ta- were observed, and their energy levels were determined to be 1169.64(17) cm-1 for 5D1, 1735.9(10) cm-1 for 3P0, and 2320.1(20) cm-1 for 5D2 above the ground state 5D0, respectively.

Microscopic Views of Ge Segregation and Scavenging Ge on Thin Si on Epi-Ge(001)

Si capping layer is the most notable approach used in Ge metal-oxide-semiconductor (MOS);1-2 however, the Ge segregation and diffusion occurred during the growth of Si.3-4 The formation of undesirable GeOx is detrimental to the Ge nMOS reliability.5 This work focuses on using the scavenging process to reduce the segregated Ge atoms and to completely remove GeOx in the high-k/epi-Si/epi-Ge(001). We used high-resolution synchrotron radiation photoelectron spectroscopy (SRPES) to show the detailed development of Ge segregation and scavenging Ge using in-situ film growth, oxidation, and annealing. The Si films in 8Å thickness were grown on the epi-Ge(001) in a semiconductor molecular beam epitaxy (MBE) chamber.2 These samples were in-situ transferred to National Synchrotron Radiation Research Center in Taiwan for electronic structure studies using photoemission. Molecular oxygen was exposed to the epi-Si/epi-Ge(001) surfaces at 300°C in the photoemission chamber. The samples were then in-situ annealed at 500°C for 5 min under an ultra-high vacuum (UHV).The topmost surface of epi-Ge(001) is terminated with Ge-Ge buckled dimers.6 In the case of room-temperature grown amorphous Si (a-Si) film, the intensity of the Ge down-dimer component from the underlying epi-Ge remains as it is. The Ge up-dimer atoms were partly diffused into the a-Si film, and some of them were segregated to the top of the a-Si surface. The epi-Si grown at 260 - 280°C causes the rest of the Ge down-dimer atoms to move to the epi-Si surface to become both segregated Ge (segGe) and diffused Ge (diff-Ge). The growth of Si merely affects the topmost surface, and the Ge atoms in the second layer of the epi-Ge remain intact. A comparison of the amount of GeOx for HfO2/epi-Si/epi-Ge(001) and HfO2/epi-Ge(001) shows that the epi-Si has greatly reduced the amount of GeOx. However, the GeOx, segGe and diff-Ge components are still observed in the HfO2/epi-Si/Ge(001) samples.We have previously reported that three-time scavenging cycles have greatly reduced the amount of segGe and diff-Ge atoms in high-κ/epi-Si/n-Ge(001), thus decreasing electron traps.7 Each scavenging cycle includes room-temperature oxidation followed by thermal annealing. In this study, the oxidation of the as-grown epi-Si/epi-Ge(001) samples was performed at 300°C. It is worth noting that there is no GeOx formation on the surface after the thermal oxidation, which is different from the room-temperature oxidation of the epi-Si/epi-Ge(001) surfaces. In addition, the oxidation at 300°C affects part of the diff-Ge atoms to evaporate from the surface, which is also different from our previous work, where the diff-Ge component shows no change in intensity since the oxidation occurred at room temperature. The subsequent in-situ annealing at 500°C moved the residual Ge-boned Si (diff-Ge) inside the epi-Si to the surface to become part of the segGe atoms. In conclusion, we have used the aforementioned process to further reduce the segregated Ge, and thus the GeOx, on top of the epi-Si/epi-Ge(001).To whom the correspondence is addressed: mhong@phys.ntu.edu.tw (M. Hong), raynien@phys.nthu.edu.tw (J. Kwo), and pi@nsrrc.org.tw (T. W. Pi)AcknowledgmentsThis work is supported by MOST 110-2112-M-002-036-, 110-2622-8-002-014-, 110-2923-M-002-001-, and 110-2112-M-213-012- of the Ministry of Science and Technology in Taiwan.Reference 1 H. Arimura, E. Capogreco, A. Vohra, C. Porret, R. Loo, E. Rosseel, A. Hikavyy, D. Cott, G. Boccardi, L. Witters, G. Eneman, J. Mitard, N. Collaert, and N. Horiguchi, IEEE Int. Electron Devices Meet., 2.1.1−2.1.4 (2020). 2 H. W. Wan, Y. J. Hong, Y. T. Cheng, C. K. Cheng, C. H. Hsu, C. T. Wu, T. W. Pi, J. Kwo, and M. Hong, M., ACS Appl. Electron. Mater. 3, 2164−2169 (2021). 3 R. Loo, H. Arimura, D. Cott, L. Witters, G. Pourtois, A. Schulze, B. Douhard, W. Vanherle, G. Eneman, O. Richard, P. Favia, J. Mitard, D. Mocuta, R. Langer, N. Collaert, ECS J. Solid State Sci. Technol. 7, 66−72 (2018). 4 Y. T. Cheng, H. W. Wan, C. K. Cheng, C. P. Cheng, J. Kwo, M. Hong, T. W. Pi, Appl. Phys. Express 13, 085504 (2020). 5 J. Franco, B. Kaczer, P. J. Roussel, J. Mitard, S. Sioncke, L. Witters, H. Mertens, T. Grasser, G. Groeseneken, IEEE Int. Electron Devices Meet., 15.2.1−15.2.4 (2013). 6 Y. T. Cheng, Y. H. Lin, W. S. Chen, K. Y. Lin, H. W. Wan, C. P. Cheng, H. H. Cheng, J. Kwo, M. Hong, T. W. Pi, Appl. Phys. Express 10, 075701 (2017). 7 Y. T. Cheng, H. W. Wan, T. Y. Chu, T. W. Pi, J. Kwo, M. Hong, ACS Appl. Electron. Mater. 3, 4484-4489 (2021).

Fluorination of the silicon-terminated (100) diamond surface using C60F48

Fluorination of the silicon terminated (100) diamond surface under ultra-high vacuum using a molecular fluorine source (C60F48) is investigated with a combination of high resolution photoelectron spectroscopy and low energy electron diffraction. The C60F48 fluorinates the dangling bonds of the silicon-termination on contact, resulting in an inhomogeneous fluorine termination, which remains when the C60F48 is removed by a 550 °C anneal. Despite removing approximately 50% of the surface silicon in the process, the two domain (3 × 1) surface symmetry of the silicon-terminated (100) surface is retained. When exposed to ambient conditions, while some fluorine is displaced by atmosphere exposure, partial fluorination remains. While further optimsation of this process is required for fluorinating diamond in cases where homogeniety and minimised surface damage are desirable, this work demonstrates the potential of the silicon-terminated (100) diamond surface for enabling engineering of the surface properties of diamond.