Electron Transmission Experiments Research Articles

Mean Free Path of Electrons in Organic Photoresists for Extreme Ultraviolet Lithography in the Kinetic Energy Range 20-450 eV.

The blur caused by the nonzero mean free path of electrons in photoresists exposed by extreme ultraviolet lithography has detrimental consequences on patterning resolution, but its effect is difficult to quantify experimentally. So far, most mean free path calculations use the dielectric formalism, which is an approximation valid in the optical limit and fails at low kinetic energy. In this work, we used a modified substrate-overlayer technique that exploited the attenuation of the Si 2p core level originating specifically from the native silicon dioxide to evaluate the attenuation of electrons traveling through 2 and 4 nm of photoresist overlayers to provide a close estimation of the inelastic mean free path relevant for photoresist lithography patterning and for electron microscopy. The photoemission spectra were collected in the proximity of the Si 2p edge (binding energy ∼101 eV) using synchrotron light of energy ℏω ranging between 120 and 550 eV. The photoresist films were prototypical chemically amplified resists based on organic copolymer of poly hydroxystyrene and tertbutyl methacrylate with and without triphenyl sulfonium perfluoro-1-butanesufonate photoacid generator and trioctylamine quencher. The inelastic mean free path of electrons, in the range that is relevant for photoresist exposure in extreme ultraviolet lithography (20-92 eV), was found to be between 1 and 2 nm. At higher kinetic energy, the mean free path increased, consistently with the well-known behavior. The presence of the photoacid generator and quencher did not change the mean free path, within experimental error. Our results are discussed and compared with the existing literature on organic molecules measured via dielectric formalism and electron transmission experiments.

Joint experimental and theoretical study on electron scattering from titanium tetrachloride (TiCl4) molecule.

Absolute grand-total cross section for electron scattering from titanium tetrachloride, TiCl4, molecule was measured at electron-impact energies ranging from 0.3 to 300eV, in the linear electron-transmission experiment. The elastic integral, differential, momentum transfer, and total ionization cross sections for TiCl4 molecule were also calculated for low and intermediate collisional energies at the level of various theories. The low-energy elastic integral, differential, and momentum transfer cross sections were calculated with the Schwinger multichannel method implemented with pseudopotentials, in the static-exchange and static-exchange plus polarization levels of approximation, for energies up to 30eV. The integral cross section calculated for low-energy electron scattering with the R-matrix method within the static-exchange and static-exchange plus polarization approximations for energies up to 15eV are also reported. By the inspection of the cross sections, the presence of resonances is discussed. In particular, the calculated integral cross sections and the measured total cross section display a minimum at around 1eV, which is consistent with the presence of a Ramsauer-Townsend minimum and a sharp increase at low energies, which is consistent with the presence of a virtual state. Additionally, interactions in elastic and ionization channels for intermediate collision energies were investigated with the additivity rule and the binary-encounter-Bethe methods.

Electron scattering from tin tetrachloride (SnCl4) molecules

Absolute grand-total cross section (TCS) for electron scattering from a tin tetrachloride, SnCl4, molecule was measured at electron-impact energies ranging from 0.6 to 300 eV, in the linear electron-transmission experiment. The measured TCS energy dependence shows two very pronounced enhancements peaking near 1.2 eV and around 9.5 eV, separated with a deep minimum centered close to 3 eV. The low energy structure is attributed to the formation of two short-living negative ion states. Additional weak structures in the TCS curve are also perceptible. We also calculated the integral elastic and ionization cross sections for SnCl4 up to 4 keV within the additivity rule approximation and the binary-encounter-Bethe approach, respectively. To examine the role of the central atom of tetrachloride target molecules in collisions with electrons, we compared the experimental TCS energy functions for XCl4 molecules (X = C, Si, Ge, Sn).

Electron collisions with X(CH3)4 molecules (X = C, Si, Ge).

Absolute grand-total cross sections (TCSs) for electron scattering from tetramethylmethane [C(CH3)4], tetramethylsilane [Si(CH3)4], and tetramethylgermane [Ge(CH3)4] molecules have been measured at electron-impact energies extending from around 0.5 to 300 eV in the linear electron-transmission experiment. The measured TCS energy dependences show very pronounced broad enhancement, peaking near 5.5 eV for Si(CH3)4 and Ge(CH3)4 molecules and around 6.5 eV for C(CH3)4. Additional weak structures are also located at higher electron energies. We attributed the TCS features to the resonant processes involved in the electron-molecule scattering. To examine the role of permethylation in the scattering, the measured TCS energy functions for X(CH3)4 compounds (X = C, Si, Ge) have been compared to the TCS curves for XH4 molecules. Additionally, the integral elastic cross section (ECS) and ionization cross section (ICS) have been calculated from intermediate to high electron-impact energies using model methods. At energies above 50 eV, the sum of ECS and ICS for the investigated targets is in satisfactory agreement with the respective measured TCS. The computed ECS+ICS values can be used as rough estimation of TCS at energies above 300 eV.

Cross sections for electron collision with pyridine [C5H5N] molecule

ABSTRACTThe absolute grand -total cross section (TCS) for electron scattering from pyridine, C5H5N, molecules has been measured at impact energies from 0.6 to 300 eV in the linear electron-transmission experiment. The obtained TCS energy dependence appears to be typical for targets of high electric-dipole moment; the cross section generally decreases with rising energy, except for the 3–20 eV range, where a broad enhancement peaked near 8.5 eV is clearly visible. Below 10 eV, some weak structures which can be attributed to resonant scattering processes are also discernible. The present TCS energy dependence is compared with TCS experimental data reported very recently. Comparison with TCS for benzene is also made to search how the replacement of the CH group in the benzene ring with the nitrogen atom influences the electron-scattering process. In addition, for pyridine and its halogenated derivatives: 2-chloropyridine [2-CHClN] and 2-bromopyridine [2-CHBrN], integral elastic (ECS) and ionisation (ICS) cross sections have been calculated at intermediate and high electron-impact energies within semiempirical approaches. For pyridine the sum of ECS and ICS is in reasonable agreement with the measured TCS above 40 eV.

Cross-sections for electron-scattering from 2-methyl-1-buten-3-yne, C5H6, molecules

Cross-sections for electron collisions with the 2-methyl-1-buten-3-yne [H2CC(CH3)CCH] molecule were measured and calculated. Absolute grand-total electron-scattering cross-section (TCS) was taken at impact energies from 0.6 to 300eV in the linear electron-transmission experiment. The TCS energy dependence for the electron–C5H6 collision has two prominent enhancements separated with a deep minimum located near 1.8eV. In addition, in the low-energy TCS function two noteworthy features occur: (i) near 1eV, a change in a slope on rapidly declining side of the TCS curve; (ii) between 2 and 5eV, a distinct hump superimposed on the opposite, rising part of the curve. To search for the origin of these features in the TCS curve for C5H6, the comparison was made with results of the electron-scattering studies for selected hydrocarbon molecules. These features were attributed to the formation of short-living negative ions (resonant states). Elastic (ECS) and ionization (ICS) cross-sections for C5H6 and C4H2 (1,3-butadiyne) were computed up to 3keV by means of the additivity rule (AR) approximation and the binary-encounter-Bethe (BEB) approach, respectively. For the C5H6 molecule, the sum ECS+ICS is in good agreement with the experimental TCS for energies above about 40eV.

Total cross section of furfural by electron impact: Experiment and theory

We present experimental total cross sections for electron scattering from furfural in the energy range from 10 to 1000 eV, as measured using a double electrostatic analyzer gas cell electron transmission experiment. These results are compared to theoretical data for furfural, as well as to experimental and theoretical values for the structurally similar molecules furan and tetrahydrofuran. The measured total cross section is in agreement with the theoretical results obtained by means of the independent-atom model with screening corrected additivity rule including interference method. In the region of higher electron energies, from 500 eV to 10 keV, the total electron scattering cross section is also estimated using a semi-empirical model based on the number of electrons and dipole polarizabilities of the molecular targets. Together with the recently measured differential and integral cross sections, and the furfural energy-loss spectra, the present total cross section data nearly complete the data set that is required for numerical simulation of low-energy electron processes in furfural, covering the range of projectile energies from a few electron volts up to 10 keV.

Six laws of low-energy electron scattering in solids

Relativistic partial wave elastic scattering (Mott cross-sections) and dielectric energy losses with the full dispersion relation and corresponding momentum changes should explain the anomalous decrease of electron backscattering towards the sub-keV energy region. Respective Monte Carlo programs are in good agreement with electron backscattering and transmission experiments. As a main result, several scattering and transport quantities can be correlated with the total backscattering ratio η B0( Z, E 0) including the dependence on the atomic number Z of the target material as well as on the initial electron energy E 0. All depth distributions can be expressed by the reduced depth x/ R related to the maximum electron range R( E 0). Thus a much easier access, e.g. to the angle-dependent backscattering, to the mean energy of backscattered electrons, to the electron penetration rate, and to the energy transfer profile in solid targets is given.

Measurements of absolute total cross sections for electron scattering from triatomic polar molecules: SO 2 and H 2S

Absolute total electron-scattering cross sections (TCSs) have been measured in the energy range from 0.5 to 370 eV for SO 2 and from 6 to 370 eV for H 2S molecules. Measurements have been carried out using modified electron spectrometer working in a linear transmission mode. The present results are compared to published experimental TCS data. Some aspects important for achieving accurate absolute total cross sections in an electron transmission experiment are discussed.

Low Energy Electron Transmission Study of Indium/(perylene-3,4,9,10-tetracarboxylic dianhydride) System

Low-energy electron transmission (LEET) experiments were performed for the indium/perylene-3,4,9,10-tetracarboxylic dianhydride (In/PTCDA) system prepared by a sequential deposition of PTCDA and In on a MoS2 single crystal surface. The dependence of LEET spectra and the work function change (Δφ=φfilm-φsubstrate) on the deposition amount of In on the PTCDA monolayer showed that the organic-metal compound of In4PTCDA was formed at the In/PTCDA interface. The result is in good agreement with that previously obtained using metastable atom electron spectroscopy. Furthermore, from the temperature dependence of LEET spectra and Δφ for the In/PTCDA system, we propose that in the as-grown In4PTCDA at room temperature In atoms are located out of the PTCDA plane, and after heat treatment, it becomes a planer structure.

Formation of anion fragments from gas-phase glycine by low energy (0–15 eV) electron impact

We have measured the formation of anion fragments in gas phase glycine (H2NCH2COOH) via dissociative electron attachment (DEA) reactions in the 0–15 eV electron energy range, using a monochromatic electron beam and mass spectrometric detection of the negative ions. By far the most intense product observed is the closed shell glycine anion (H2NCH2COO)− which appears from a low-energy resonance with a peak located at 1.4 eV and a cross section in the range 10−16 cm2. The corresponding precursor ion can be characterized by electron attachment into the empty π* orbital of the −COOH group as recently assigned from electron transmission experiments and ab initio self-consistent field calculations [Aflatooni, Hitt, Gallup, and Burrow, J. Chem. Phys. 115, 6489 (2001)]. This precursor state is also observed to decompose (with much lower intensity) yielding a negative ion fragment with 58 amu, which is attributed to anions of the stoichiometric composition H2C2O2− or H4C2NO−. A further prominent DEA peak is observed at 6 eV, which is likely associated with a core excited resonance, and leads to formation of at least six different negative ion fragment species with the following mass numbers: 16 amu (O−/NH2−), 17 amu (OH−), 26 amu (CN−), 28 amu (H2CN−), 45 amu (HCO2−), 56 amu (H2C2NO−).

Low-energy electron transmission experiments on graphite

Low-energy-electron transmission (LEET) spectra were measured for graphite using electron energies below 30 eV. The observed LEET spectra have broadened square-wave-like features, and comparison with the conduction-band density of states above the vacuum level measured by ultraviolet photoemission and inverse photoemission spectroscopies indicated that the conduction-band density of states was not observed in the LEET spectra except band gaps. It is concluded that band gaps are more strongly reflected in LEET spectra than other features in the density-of-states. It is expected that electron-interference effects along the surface normal dominate LEET features, even for a very thick sample, where the energy dependence of electron-transmission probability through a one-dimensional periodic potential along the surface normal does not reflect the variation of the density of states (except band gaps).

FCN- and FNC- radical anions

The radical anions FCN− and FNC− are studied at high ab initio levels of theory. Both anionic isomers possess a weak so-called three-electron bond, and highly correlated methods are necessary to predict their geometric parameters. At their respective equilibrium structures both anions represent electronically stable species but the associated neutrals FCN and FNC exhibit negative vertical electron affinities. Our computed electron affinities show that both anionic isomers are stable with respect to adiabatic electron loss. FCN− represents the global minimum of the FCN-plus-electron system, and FNC− can decay only ia rearrangement and simultaneous autodetachment, but is predicted to exhibit a very long lifetime. The temporary anion states associated with vertical electron attachment to the neutrals are investigated within the framework of the complex absorbing potential method. Short-lived 2Π resonance states are identified and predicted to be observable in an electron transmission experiment. In spite of their close relation, the two isomeric anions FCN− and FNC− show surprisingly different properties. FNC− can be characterised as a typical pseudo-dihalogen anion, whereas FCN− is more similar to the isovalent CO2−.

Transmission and spin motion of electrons across ferromagnets

`Complete’ spin-polarized electron transmission experiments across free standing Au/Co/Au films are presented. If the spin polarization of the primary beam P 0 is parallel to the in-plane Co-film magnetization M , these films can be used as analyzer foils for spin-polarized electrons or as polarizer foils for initially unpolarized electrons, in analogy to polarizer foils for linearly polarized light. Furthermore by choosing P 0 perpendicular to M , the spin polarization rotates into the direction of M and simultaneously also rotates out of the film plane. The first rotation is caused by the spin filtering of the two wavefunction components along M . The second rotation is the electron analogue to the Faraday rotation observed with light. It is caused by the phase difference that develops between the two wavefunction components due to the spin dependence of the inner potential.

Asymmetric scattering of polarized electrons by organized organic films of chiral molecules

Electron transmission experiments demonstrate a large asymmetry in the scattering probability of polarized electrons by thin organized films of chiral molecules. This large asymmetry results from the interaction of the electron's wavefunction with many scatterers (molecules) in the organized monolayer structure and represents a manifestation of quantum interference on the scale of supramolecular lengths.

Absolute total cross-section measurements for electron scattering from silicon tetrachloride, SiCl

The absolute total cross-sections for electron scattering on SiCl4 molecules have been measured in two distinct electron-transmission experiments, in Gdansk and in Trento laboratory, for impact energy ranging from 0.3 to 250 eV and from 75 to 4000 eV, respectively. The e--SiCl4 total cross-section function shows two very distinct resonant-like features: the strong peak at 1.9 eV and much broader main maximum centered near 10 eV with some additional substructure close to 5 eV. The present results are compared with low-energy total experimental data and elastic theoretical calculations for electron collisions with silicon tetrachloride molecules.

Low-energy electron scattering from hydrocarbons and their perfluorinated derivatives: I. Elastic differential cross section for e- scattering

A crossed-beam experiment has been performed to measure differential elastic and vibrationally inelastic cross sections for electron scattering from ethane in the energy range E = 0.3-10 eV. In the present paper, the results for elastic scattering are reported. The energy and angular dependence of the cross sections is determined. Absolute values of the differential cross sections (DCS) are obtained by using -He scattering as a reference system. By use of phase-shift analysis (PSA) and modified effective-range theory (MERT), the measured DCS are extrapolated into the experimentally inaccessible regions. Integral and momentum transfer cross sections are determined which can be compared with the results of electron transmission experiments and swarm experiments. The most important features in the elastic scattering cross section of ethane are a Ramsauer-Townsend minimum below 1 eV and a broad resonance structure at about 7.5 eV.

Very low energy electron collisions with molecular chlorine

Electron transmission experiments are reported involving the measurement of absolute total cross-sections for scattering of electrons by for energies between 20 meV and 9.5 eV, with an energy resolution in the incident electron beam of between 3 and 4 meV full-width half-maximum. These data represent the first absolute values of scattering cross-sections recorded for . Results are also reported for scattering in the presence of an axial magnetic field of 20 G over an energy range which extends from 16 meV to 250 meV. Strong evidence is found for electron attachment at very low impact energies, in agreement with the results of other groups. Data suggest that attachment occurs through the p-partial wave. A resonance in the form of a doublet in the total scattering cross-section has been found between 70 and 200 meV. This structure is absent in the spectrum obtained in the presence of an axial magnetic field. A qualitative mechanism is suggested for the formation of the observed structure involving virtual excitation of the first vibrational quantum of . The doublet nature of the resonance is attributed to the intervention of the excited -states of . The plausibility of the proposed mechanism could be checked by accurate calculations of excited state potentials for and by measurement of the yield of ions as a function both of the electron energy and the temperature of the target gas.

New Survey of Electron Impact Cross Sections for Photoelectron and Auroral Electron Energy Loss Calculations

Newly surveyed sets of energy loss cross sections are presented for N2, O2, and O. The work was motivated by a number of new electron energy loss measurements in the late 1980s and early 1990s and recent selected review articles. Each set includes a total ionization cross section and excitation cross sections that correspond to all important non-ionizing energy loss channels for that species. A total cross section for each species is constructed by summing the elastic scattering cross section with the ionization and excitation cross sections. The sum is compared to a measured total cross section obtained from electron transmission experiments. Good agreement is achieved for each of the three species. A loss function is also constructed for each species and compared with the Bethe formula above 100 eV. Good agreement is also achieved in energy loss which is dominated by ion and secondary electron production. Fluxes of photoelectrons and auroral electrons have been calculated for the new sets of energy loss cross sections as well as our previous sets. No substantial differences occur using the new description of energy loss.

Absolute total cross section measurements for electron scattering on benzene molecules

The absolute total cross section for electron scattering on C 6H 6 molecules has been measured in two distinct electron-transmission experiments for impact energies between 0.6 eV and 3.5 keV. The present results are compared with other total cross section experimental data.