The binding energies are referred to the common Fermi level. Immediately outside the copper surface, conservation of energy givesThis is the emitted photoelectron energy at the sample. On reaching the electrically connected, unbiased analyser, its energy is instead . The 0.4 eV difference is the contact-potential correction, not an additional binding-energy shift. Distinguishing these two reference positions is essential for the retarding-voltage calculation.
The hemispherical component needs 100.0 eV electrons, whereas electrons arrive at its entrance optics with 111.4 eV. The optics must therefore remove 11.4 eV, requiring a retarding-potential magnitude of 11.4 V. For a negative electron, moving to a more negative electrostatic potential increases potential energy, so the retarding region is 11.4 V negative relative to the analyser entrance. Equivalently the hemisphere entrance is 11.8 V negative relative to the sample vacuum reference after including the 0.4 V contact step. Reporting 11.8 V as the additional instrument retardation would count the contact correction twice.
Fixed entrance retardation and fixed pass energy select the same pre-retardation kinetic energy, 111.4 eV. The required photon energy is thereforeIt is lower than the original excitation by exactly the difference between the two core binding energies, 114.4 eV.
Define the retard ratio using the kinetic energy at the analyser entrance before the deliberate retardation: . Initially . With the original excitation, a carbon photoelectron arrives with . ThusThe new deliberate retardation is . For fixed slits, angular acceptance and hemisphere radii, the geometrical fractional energy width is approximately constant, so the absolute analyser width grows in proportion to pass energy: about 2.03 times poorer absolute energy resolution. Counts may improve, but closely separated chemical shifts become harder to resolve. An alternative definition gives 0.114 rather than 1.114 for the same physical setting and leads to the same final pass energy when used consistently.
The large resonance at the smallest field-to-normal angle identifies an unoccupied orbital whose transition dipole is mainly normal to the surface. An N 1s initial state is approximately spherical; the dipole matrix element for a transition is directed along the normal to the adsorbate's aromatic plane. Consequently the adsorbate rings lie predominantly parallel to the copper surface. For perfectly flat molecules the resonance strength scales as , which decreases strongly from to as observed.
For azimuthally disordered molecular normals tilted by from the surface normal, averaging gives . Strong dichroism therefore implies a large orientational order parameter, but the plotted qualitative curves alone do not determine a unique tilt angle or distribution. Background subtraction, incident polarization and intensity normalization would be needed for such a fit. This experiment identifies the orientation of the pi system; it does not by itself identify a particular nitrogen–copper bonding topology.
The initial nitrogen environment loses intensity on heating, and a lower-binding-energy component becomes prominent near the highest temperatures. A change of surface chemical species accompanies loss or conversion of the original adsorbate. Plausible processes include thermally activated decomposition with nitrogen-containing fragments remaining on copper, desorption of intact material or fragments, and rearrangement of the coordination environment. The extra components at intermediate temperatures suggest coexistence rather than a rigid, uniform shift of every molecule.
The individual curves have vertical offsets, so their baseline height is not a coverage measurement. Integrated, sensitivity-corrected N and C peak areas, a clean heated substrate control, and evolved-gas mass spectrometry would help distinguish loss of material from chemical conversion. binding energy alone cannot establish a unique fragment structure: local charge, metallic screening and coordination all affect it.
A step elastically reflects a surface-state wave. Interference between and produces a local density oscillation at , so the measured spatial period is , not . Thus and . Write with . The two points giveHere . The fitted minimum is above the Fermi level. This assumes the bias measures sample excitation energy, parabolic dispersion over the measured interval, and no wave-vector-dependent phase contribution that changes the fitted period.
inverse photoemission spectroscopy is appropriate: the fitted minimum lies above the Fermi level, so the state is unoccupied in equilibrium. Injection of electrons followed by photon emission probes unoccupied states. Ordinary ultraviolet photoemission removes electrons from occupied states and cannot map this empty minimum without an additional population mechanism.
The same wave vectors now differ in energy by only 0.070 eV, so the curvature is . ThereforeThe nearly free-electron in-plane mass and high unoccupied energy suggest an image-potential-derived state, with an electron confined outside the film by its image attraction and surface barrier but relatively free parallel to it. Relative to the supplied clean-platinum vacuum level, its minimum is 0.84 eV below vacuum, a plausible scale for an image state. gold adsorption can change the work function, so 0.84 eV is conditional on using the supplied clean-surface value; an adsorbate work-function measurement is needed for a quantitative assignment. The dispersion alone supports the interpretation without proving it uniquely.
An Au(111) Shockley state requires the near-surface band structure and projected bulk gap of a sufficiently thick gold region. In an ultrathin film, its wavefunction reaches the platinum interface, where hybridization and leakage into platinum states can shift, broaden or destroy the bound surface state. As the gold thickness exceeds the relevant decay length, the top surface becomes electronically decoupled from the substrate and the gold-like state emerges. A monolayer's atomic identity is insufficient to guarantee a bulk-gold surface electronic structure.
When reaches a vibrational quantum, a tunnelling electron can lose energy by exciting that vibration. Opening an inelastic channel changes at both voltage polarities. If the conductance increases in each direction, has a positive feature at positive threshold and a negative feature at the corresponding negative threshold. Approximate antisymmetry follows from approximate symmetry of the conductance; unequal tip and sample electronic structures can make amplitudes unequal.
The three energy scales are 8, 48 and 375 meV, corresponding to about 65, 387 and 3025 cm. A plausible assignment is a low-energy frustrated lateral translation or rotation, an adsorbate–metal stretch or hindered molecular mode at 48 meV, and a C–H stretching vibration at 375 meV. The terminal carbon of methyl isocyanide supplies a plausible adsorption contact, but exact mode assignment requires calculated normal modes or independent vibrational measurements. In particular the 48 meV band should not be labelled a C–N stretching vibration simply because the molecule contains that bond: its frequency is far too low for the usual internal stretching mode.
The 375 meV pair should shift most fractionally, towards zero bias, because C–H stretching has strong hydrogen displacement. A reduced-mass estimate givesso the pair would move approximately from to mV. A frozen-carbon estimate gives , or about 265 mV; the actual normal mode includes coupled motion. Whole-molecule modes change much less: the molecular mass rises only from approximately 41 to 44, giving a translational estimate .
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