Papers

Papers published before 2000 are listed here.

Methods and Instrumentation for Piezoelectric Motors
B. Drevniok, W. M. P. Paul, K. R. Hairsine and A. B. McLean (submitted Oct. 2011).

Abstract
Because of their compact form factor and rigidity, Pan-style piezoelectric motors are used in scanning probe microscopes that operate at low temperature and in high magnetic field. Here we present detailed information to facilitate the assembly, operation and characterization of a motor of this type. Specifically, a model of the motor is developed and used to identify different regions of operation. Drive electronics, with high slew rate and large output current are described and a step-by-step procedure for assembling piezoelectric shear stacks is detailed. Additionally, a reflective object sensor is described and used to characterize a motor that was designed and assembled using the concepts presented in this paper.

Using Steric Constraints to Template an Organic Array on Si(111)–7x7
A. B. McLean, A. J. Weymouth, G. J. A. Edge, R. H. Miwa and G.P. Srivastava (accepted Physica Status Solidi, September 6, 2011).

Abstract
We show that the Si(111)-7x7 surface reconstruction can be used to template an ordered array of 1,3,5-methyl benzene (mesitylene) molecules. The disorder that normally derives from the multiplicity of admissible adsorption geometries, for small aromatic molecules on 7x7, is suppressed, and the molecules are found to occupy both halves of the 7x7 unit cell with equal probability. It is argued that a steric interaction, associated with the methyl groups, hinders nearest neighbor adsorption and this leads to the formation of an array that has the molecules at the corners of the 7x7 half unit cells. To understand the ordering kinetics we used: scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites and kinetic Monte Carlo modeling to investigate the emergence of translational order in the overlayer.

On Investigation of Ethylene Attachment to Si(111)-7x7 in the Restatom-Adatom Bridging Geometry: Electronic and Vibrational Properties
Zsolt Majzik, Wojciech Kaminski, Alfred Weymouth, Martin Vondracek, Vladimir Zobac, Martin Svec, Andras Berko, Alastair McLean, Kevin Prince, Pavel Jelinek, Vladimir Chab, J. Phys. Chem, 115, 21791-21799 (2011).

Abstract
The adsorption of ethylene on the bridge adatom–restatom position of the Si(111)–7x7 surface was studied with Scanning Tunneling Microscopy, photoelectron spectroscopy and theoretical calculations. The electronic structure and the corresponding vibrational states were calculated for a single molecule adsorbed in different binding sites located within the 7x7 unit cell. We found that there is no significant difference in the electronic structure between the absorption sites that were considered: center and corner adatom–restatom. Moreover, the different electron occupation of the restatoms and adatoms has a strong effect on the electronic structure of the adsorbed molecule near the Fermi level and this leads to the reduction of the molecular symmetry to C2 or even to C1. In the case of the Si 2p core level, beside the previously reported continuous quenching of the restatom state, we found clear evidence for the existence of a peak corresponding to the Si-C bond separated by 0.44 eV from the bulk component. Furthermore, for the vibrational analysis, isotopic substitution of C2H4 with C2D4, gave us more insight for the correct assignment of the modes in the experiment. Specifically, exceptional care must be taken with the allocation of the C-H wagging, twisting and C-C stretching modes.

Directed Assembly of One-Dimensional Magic Cluster Arrays by Domain Boundaries
A. G. Mark and A. B. McLean, (to be submitted).

Abstract
We demonstrate that the most commonly occurring domain boundary (B[bar 2 2]) that separates Ge-5x5 domains grown on Si(111) can be used to direct the assembly of one-dimensional arrays of identical-size magic clusters with a lattice constant of 3.3 nm. A necessary condition for cluster growth is shown to be the presence of faulted dimer-adatom-stacking-fault-7x7 half unit cells within the domain boundary. The assembly technique is illustrated with both In and Ga. This establishes a role for domain boundaries as atomically precise templates.

Templating an Organic Layer with the Si(111)–7x7 Surface Reconstruction using Steric Constraints
A. J. Weymouth, G. J. A. Edge, A. B. McLean, R. H. Miwa and G.P. Srivastava, Physical Review B, 84, 165308 (2011).

Abstract
We demonstrate that the Si(111)-7x7 surface reconstruction can be used to template an ordered array of 1,3,5-methyl benzene molecules, that are uniformly distributed over both the faulted and unfaulted halves of the 7x7 unit cell, by covalent attachment in vacuo. An intermolecular steric interaction, which hinders nearest neighbor adsorption, is shown to play an important role in the formation of the ordered array. The stable equilibrium structure is shown to be one where the molecules are located at the corner of the half unit cells maximizing the inter-molecular separation.
In addition to the intermolecular steric interaction there is an interaction between the molecule and the surface that plays a important role in reducing disorder in the array. Moreover, as the coverage is increased, there is a switch in site preference, from edge to corner, that mitigates the effect of the intermolecular interaction. To investigate this system we used: scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites and Monte Carlo modeling to examine the emergence of translational order in the overlayer. The switch in site preference from edge to corner is faithfully reproduced by the kinetic Monte Carlo model when an interaction term is included.

Templating an organic array with Si(111)–7x7
A. J. Weymouth, R. H. Miwa, G. J. A. Edge, G.P. Srivastava and A. B. McLean, Chem. Commun. 47, 8031-8033 (2011).

Abstract
We demonstrate that nearest neighbor molecular adsorption can be sterically hindered on the Si(111)-7x7 surface reconstuction. This breaks the energetic equivalence of corner and edge di-sigma attachment geometries and allows a translationally ordered organic layer to be templated directly on the 7x7 reconstruction.

Domain Boundaries of the Si(111)-Ge5x5 Reconstruction
A. G. Mark and A. B. McLean, Physica Status Solidi C7, No. 2, 185-188 (2010).

Abstract
The boundaries that form between domains of the 5x5 reconstruction of Si(111)-Ge are examined. A notation for indexing the boundaries is developed, and their symmetry properties are discussed. A preparation procedure that enhances the density of such boundaries while encouraging their uniform growth is described. The notation is illustrated using a selection of examples.

The Role of a Precursor State in Thiophene Chemisorption on Si(111)–7x7
A. J. Weymouth, R. H. Miwa, G.P. Srivastava and A. B. McLean, Physica Status Solidi C7, No. 2, 240-243 (2010).

Abstract
The adsorption of thiophene on Si(111)–7x7 has been studied with scanning tunneling microscopy (STM) and kinetic Monte Carlo (kMC) modelling. Previous experimental studies of this system clearly demonstrated that thiophene prefers to chemisorb on the faulted half of the 7x7 unit cell. The STM studies reported here concur with this and provide further information about thiophene site preference as a function of coverage. Additionally, an ab initio theoretical investigation of this system demonstrated that the occupancy of available adsorption sites could not be explained using equilibrium binding energies, as these were calculated to be the same for all experimentally identified adsorption sites (~ 1.0 eV). To investigate the possibility that site selection is kinetically controlled, a kMC model was developed. This model places the molecule in a mobile precursor state, allowing the molecule to traverse the surface before chemisorbing. The kMC model was found to reproduce the STM data, providing compelling evidence that site occupancy in this system is indeed kinetically controlled at room temperature. Activation energy differences, for each the four unique chemisorption geometries, could be extracted from a fit of the kMC model predictions to the experimental data.

Ab initio study of thiophene chemisorption on Si(111)-(7x7)
R. H. Miwa, A. J. Weymouth, G.P. Srivastava and A. B. McLean, Phys. Rev. B, 80, 115317 (2009).

Abstract
The adsorption of thiophene on has been studied using density functional theory within the generalized gradient approximation. For all adsorption geometries that have been experimentally identified, equilibrium binding energies have been calculated using a full 7×7 supercell to a depth of six Si monolayers. Despite the structural heterogeneity of the surface, all adsorption geometries are calculated to have the same binding energy, irrespective of their location within the unit cell. A parallel survey of chemisorption sites, performed with scanning tunneling microscopy, demonstrated that thiophene prefers the faulted half of the unit cell over the unfaulted half, and edge over corner sites, in agreement with previous experimental studies. The theoretical and experimental results suggest that the activation energy barriers for chemisorption are site dependent. The physical factors leading to site dependent activation energies are briefly discussed.

Si(557)-Ag: A metallic quasi-one-dimensional system
J. A. Lipton-Duffin, A. G. Mark, J. M. MacLeod and A. B. McLean, Phys. Rev. B, 77, 125419 (2008).

Abstract
A quasi-1D system was fabricated by adsorbing one fifth of a monolayer of Ag onto a Si(557) surface. Structural investigations performed with electron diffraction and scanning tunneling microscopy provided evidence of a mid-terrace row of Si adatoms with 2x periodicity along [1-1 0], parallel to the step edges. A similar feature is also found in the Si(557)-Au system. However, the lattice gas of extra Si adatoms that is a distinctive feature of Si(557)-Au [KirakosianPRB2003] is absent in Si(557)-Ag. Inverse photoemission studies of the Si(557)-Ag energy bands revealed a Fermi level crossing parallel to the step-edges along Gamma K at (0.5 pm 0.1) 1/A. In the orthogonal direction (Gamma M'), the dispersion of this band is flat. Consequently, the adlayer system has quasi-1D symmetry. Another state with anisotropic dispersion was found just below the vacuum level. Its dispersion is free-electron-like along Gamma K but, once again, flat along Gamma M'. This is likely to be an image state that is in resonance with the bulk bands of Si and also perturbed by the quasi-1D surface reconstruction.

Phys. Rev. B 89Preprint.pdf 89Fig1.pdf 89Fig2.pdf 89Fig3.pdf 89Fig4.pdf 89Fig5.pdf 89Fig6.pdf 89Fig7.pdf

Patterned Growth of Nanoscale In Clusters on the Si(111)-7x7 and Si(111)-Ge(5x5) Reconstructions
J. M. MacLeod, D. Psiachos, A. G. Mark, M. J. Stott and A. B. McLean, Proceedings of ICN+T Conference, Basel, August 2006, J. Phys. Conference Series, 61, 800-804 (2007).

Abstract
Results of a study designed to investigate the possibility of using the Si(111)-Ge(5x5) surface reconstruction as a template for In cluster growth are described. As with Si(111)-7x7, the In adatoms preferentially adsorb in the faulted half-unit cell, but on Si(111)-Ge(5x5) a richer variety of cluster geometries are found. In addition to the clusters that occupy the faulted half-unit cell, clusters that span two and four half-unit cells are found. The latter have a triangular shape spanning one unfaulted and three, nearest neighbor, faulted half-unit cells. Triangular clusters in the opposite orientation were not found. Many of the faulted half-unit cells have a streaked appearance consistent with adatom mobility.

Journal of Physics 88Preprint.pdf 88Fig1.pdf 88Fig2.pdf 88Fig3.pdf 88Fig4.pdf 88Fig5.pdf 88Fig6.pdf

Nanolines on silicon surfaces (Invited Review Article)
A. B. McLean, I. G. Hill, J. A. Lipton-Duffin, J. M. MacLeod, R. H. Miwa and G. P. Srivastava, International Journal of Nanotechnolgy (to be published in 2008, accepted 2007).

Abstract
Although a wide range of periodic surface nets can be grown on low index silicon surfaces, only a few of these have quasi-one dimensional symmetry. If high index silicon surfaces, such as (553) and (557), are used instead, the surface unit cell contains steps. It is possible to fabricate a number of quasi-one dimensional nanoline systems on the terraces and some of these have nested energy bands near the Fermi level. In some cases, the bands have fractional filling factors. These nano-scale systems may support exotic many-electron states produced by enhanced electron correlations and a reduction in electron screening in one spatial dimension. In this article, our groups’ experimental and theoretical studies of nanolines phases, grown on both low index and vicinal silicon surfaces are reviewed. These studies give us insight into the electronic properties of artificial nanoline structures.

• International Journal of Nanotechnology
• 87Preprint.pdf
• 40 Pages
• 30 Figures
• Table ofContents

Abstract
The adsorption of In on the Si(111)-Ge(5x5) surface reconstruction has been studied with scanning tunneling microscopy and ab initio calculations to investigate the possibility of using this reconstruction as a template for cluster formation. As with In adsorption on Si(111)-7x7 at low substrate temperatures and low In fluences, the In adatoms are found to preferentially adsorb on the faulted half-unit cell. However, in contrast to In adsorption on Si(111)-7x7, the In adatoms are also frequently found in the unfaulted half-unit cell at low coverages. The filling of unfaulted unit cell halves is primarily due to the formation of large clusters that span multiple substrate half-unit cells. Moreover, many of the faulted half-unit cells have a streaked appearance that indicates that surface atoms within them are mobile.

Physical Review B 86Preprint.pdf 86Fig1.pdf 86Fig2.pdf 86Fig3.pdf

Abstract
The unoccupied energy bands of the quasi one-dimensional Si(557)-Au system have been studied with momentum-resolved inverse photoemission. A band is found that lies (0.4 ± 0.4) eV above the Fermi level at the center of the surface Brillouin zone (Γ). It disperses to higher binding energy, along the ΓK direction, and crosses the Fermi level at k_|| = 0.5 ± 0.1 Å^-1. The corresponding direction in real space is parallel to both the rows of silicon adatoms and the rows of embedded gold atoms that are distinctive features of this surface reconstruction. The location of the crossing is in good agreement with previously published photoemission data (Altmann et al. Phys. Rev. B, 64, 035406, 2001; Ahn et al. Phys. Rev. Lett. 91, 196403, 2003), where two closely spaced bands were found to disperse from the K zone boundary to lower binding energy and then cross the Fermi level. In addition to the band mentioned above, a band was found that has parabolic dispersion along ΓK, the direction that is parallel to the rows of embedded gold atoms. The band minimum for the parabolic band lies (0.8 ± 0.4) eV below the vacuum level and it has an effective mass m^* = (1.0 ± 0.1)m_e, where m_e is the free electron mass. Perpendicular to the rows of gold atoms, as expected for a state with quasi-1D symmetry, it has flat dispersion. This band may be an image state resonance, overlapping the silicon conduction band continuum, that it is spatially localized to the edge of the silicon terraces.

		Physical Review B 85Preprint.pdf 85Fig1.pdf 85Fig2.pdf 85Fig3.pdf 85Fig4.pdf 85Fig5.pdf 85Fig6.pdf 85Fig7.pdf 85Fig8.pdf 85Fig9.pdf 85Fig10.pdf

A compact nano-positioning stage with high vibrational eigenfrequencies
S.J. Ball, C. Folsom and A.B. McLean, Review of Scientific Instruments, 76, 113702 (7 pages) (2005). Also published in the Virtual Journal of Nanoscale Science and Technology, Volume 12, Issue 21, Nov 21, 2005.

Abstract
A compact nano-positioning stage is described that has high vibrational eigenfrequencies and is, therefore, insensitive to external vibrations. The high eigenfrequencies are produced by a rigid structure that is designed so that it does not degrade the motional performance of the stage. Preliminary performance evaluations are presented. We describe how a positioning stage of this type could be used as an integral part of a proximal probe.

	Virtual Journal of Nanoscale Science and Technology Review of Scientific Instruments 83Preprint.pdf 83Fig1.pdf 83Fig2.pdf 83Fig3.pdf 83Fig4.pdf 83Fig5.pdf 83Fig6.pdf 83Fig7.pdf 83Fig8.pdf

The equilibrium geometry and electronic structure of Bi nanolines on clean and hydrogenated Si(001) surfaces
R.H. Miwa, J. M. MacLeod, A.B. McLean and G.P. Srivastava, Nanotechnology, 16, 2427-2435 (2005)

Abstract
The equilibrium geometry, electronic structure and the energetic stability of Bi nanolines on clean and hydrogenated Si(001) surfaces have been examined by means of ab initio total energy calculations and scanning tunneling microscopy. For the Bi nanolines on a clean Si surface the two most plausible structural models, the Miki or M model [Phys. Rev. B 59, 14868 (1999)] and the Haiku or H model [Phys. Rev. Lett. 88, 226104 (2002)], have been examined in detail. The results of the total energy calculations support the stability of the H model over the M model, in agreement with previous theoretical results. For Bi nanolines on the hydrogenated Si(001) surface, we find that an atomic configuration derived from the H model is also more stable than an atomic configuration derived from the M model. However, the energetically less stable (M) model exhibits better agreement with experimental measurements for equilibrium geometry. The electronic structure of the H and M models are very similar. Both models exhibit a semiconducting character, with the the highest occupied Bi-derived bands lying at approx. 0.5 eV below the valence band maximum. Simulated and experimental STM images confirm that at a low negative bias the Bi lines exhibit an "antiwire'' property for both structural models.

Nanotechnology 82Preprint.pdf 82Fig1.pdf 82Fig2.pdf 82Fig3.pdf 82Fig4.pdf 82Fig5.pdf 82Fig6.pdf 82Fig7.pdf 82Fig8.pdf 82Fig9.pdf 82Fig10.pdf 82Fig11.pdf 82Fig12.pdf 82Fig13.pdf

7-Azaindolyl and 2,2'-Dipyridylamino Functionalized Molecular Stars with 6-fold Symmetry: Structures, Luminescence and Supramolecular Assembly
Wen-Li Jia, Rui-Yao Wang, Datong Song, S.J. Ball, A.B. McLean and Suning Wang, Chemistry - a European Journal, 11 (3): 832-842 JAN 21 2005.

• Chemistry - A European Journal

A simplified Besocke scanning tunneling microscope with linear approach geometry
S.J. Ball, G.E. Contant and A.B. McLean, Rev. Sci. Instrum., DEC 2004, 75, 12, 5293-5301, 2004.

Abstract
Besocke-style scanning tunneling microscopes are used in low and variable temperature applications because they are compact and the tip-sample spacing is insensitive to thermal drift. It is demonstrated that the economical Besocke design can be simplified even further if a linear approach geometry is used. In this geometry, the sample has only to be moved along two orthogonal axes and just 11 wires are required to control both tip-sample approach and image acquisition. This simplifies the control electronics, increases the reliability of the microscope and, if the microscope is operated in a cryostat, it weakens the thermal link between low and room temperature. Nevertheless, all of the advantages of the Besocke design are retained including thermal compensation of the tip-sample spacing. A self-aligning mechanism is also described that automatically locates the sample relative to the scanner before tip-sample approach. This feature is particularly useful because the microscope is designed for remote operation in a cryostat where there is restricted visual access. Graphite was used as a test surface and images are presented of beta-site corrugation, moire supermeshes

Rev. Sci. Instrum. 80Preprint.pdf 80Fig1.pdf 80Fig2.pdf 80Fig3.pdf 80Fig4.pdf 80Fig5.pdf 80Fig6.pdf 80Fig7.pdf 80Fig8.pdf 80Fig9.pdf 80Fig10.pdf 80Fig11.pdf 80Fig12.pdf 80Fig13.pdf 80Fig14.pdf

The geometry of Bi nanolines on Si(001)
R.H. Miwa, J. M. MacLeod, G.P. Srivastava and A.B. McLean, Proceedings of the International Conference on Solid Films and Surfaces (ICSFS-12), Japan, June 2004, Applied Surface Science, 244, 1-4, 157-160 MAY 2005.

Abstract
A study of the Bi nanoline geometry on Si(001) has been performed using a combination of an ab initio theoretical technique and scanning tunnelling microscopy (STM). Our calculations demonstrate decisively that the recently proposed Haiku geometry is a lower energy configuration than any of the previously proposed line geometries. Furthermore, we have made comparisons between STM constant-current topographs of the lines and Tersoff-Hamann STM simulations. Although Haiku and the Miki geometries both reproduce the main features of the constant-current topographs, the simulated STM images of the Miki geometry have a dark stripe between the dimer rows that does not correspond well with experiment.

• Applied Surface Science
• 79Preprint.pdf
• 79Fig1.pdf
• 79Fig2.pdf
• 79Fig3.pdf

Bismuth nanolines on Si(001) and their influence on mesoscopic surface structure
J. M. MacLeod, C. P. Lima, R.H. Miwa, G.P. Srivastava and A.B. McLean, Proceedings of the International Conference on Nanomaterials and Nanomanufacturing, London, UK, 15-16th December, 2003. Materials Science and Technology, 20 (8), 951-954 AUG 2004.

Abstract
Experimental studies of Bi heteroepitaxy on Si(001) have recently uncovered a self-organized nanoline motif which has no detectable width dispersion. The Bi lines can be grown with an aspect ratio that is greater than 350:1. In this paper, we describe a study of the nanoline geometry and electronic structure using a combination of scanning tunneling microscopy (STM) and ab initio theoretical methods. In particular, we examine the effect that the lines have on Si(001) surface surface structure at large length scales; l >100 nm. We have found that Bi line growth on surfaces that have regularly spaced single-height steps results in a 'preferred' nanoline domain.

	Materials Science and Technology 78Preprint.pdf 78Fig1.pdf 78Fig2.pdf 78Fig3.pdf 78Fig4.pdf 78Fig5.pdf

The electronic structure of Si(001)-Bi(2xn)
A.G. Mark, J.A. Lipton-Duffin, J. M. MacLeod, R.H. Miwa, G.P. Srivastava and A.B. McLean, Journal of Physics: Condensed Matter, 17 (4): 571-580 FEB 2 2005.

Abstract
A Bi 2xn surface net was grown on the Si(001) surface and studied with inverse photoemission, scanning tunneling microscopy and ab initio and empirical pseudopotential calculations. The experiments demonstrated that Bi adsorption eliminates the dimer related pi_1^* and pi_2^* surface states, produced by correlated dimer buckling, leaving the bulk band gap clear of unoccupied surface states. Ab initio calculations support this observation and demonstrate that the surface states derived from the formation of symmetric Bi dimers do not penetrate the fundamental band gap of bulk Si. Since symmetric dimers are thought to be an important structural component of the recently discovered Bi nanolines, that self-organize on Si(001) above the Bi desorption temperature, these results suggest that the nanolines should also be semiconducting.

Journal of Physics: Condensed Matter 76Preprint.pdf 76Fig1.pdf 76Fig2.pdf 76Fig3.pdf 76Fig4.pdf 76Fig5.pdf 76Fig6.pdf 76Fig7.pdf

The electronic origin of contrast reversal in bias-dependent STM images of nanolines
J. M. MacLeod, R.H. Miwa, G.P. Srivastava and A.B. McLean, Surface Science, 576 (1-3): 116-122 FEB 10 2005

Abstract
Self-organized Bi lines that are only 1.5 nm wide can be grown without kinks or breaks on Si(001) surfaces to lengths of up to 500 nm. Constant-current topographical images of the lines, obtained with the scanning tunneling microscope, have a striking bias dependence. Although the lines appear darker than the Si terraces at biases below approx |1.2| V, the contrast reverses at biases above approx |1.5| V. Between these two ranges the lines and terraces are of comparable brightness. It has been suggested that this bias dependence may be due to the presence of a semiconductor-like energy gap within the line. Using ab initio calculations it is demonstrated that the energy gap is too small to explain the experimentally observed bias dependence. Consequently, at this time, there is no compelling explanation for this phenomenon. An alternative explanation is proposed that arises naturally from calculations of the tunneling current, using the Tersoff-Hamann approximation, and an examination of the electronic structure of the line.

Surface Science 75Preprint.pdf 75Fig1.pdf 75Fig2.pdf 75Fig3.pdf 75Fig4.pdf 75Fig5.pdf 75Fig6.pdf 75Fig7.pdf 75Fig8.pdf

Ultramicroscopy 74Preprint.pdf 74Fig1.pdf 74Fig2.pdf 74Fig3.pdf 74Fig4.pdf 74Fig5.pdf 74Fig6.pdf 74Fig7.pdf

Two linear beetle-type scanning tunneling microscopes
J. M. MacLeod, Antje Moffat, J. A. Miwa, A.G. Mark, G. K. Mullins, R. H. J. Dumont, G. E. Contant and A.B. McLean, Review of Scientific Instruments, 74, 4, 2429-2437 (2003). Also published in the April 7th, 2003 issue of the Virtual Journal of Nanoscale Science and Technology.

Abstract
Two beetle-type scanning tunneling microscopes are described. Both designs have the thermal stability of the Besocke beetle and the simplicity of the Wilms beetle. Moreover, sample holders were designed that also allow both semiconductor wafers and metal single crystals to be studied. The coarse approach is a linear motion of the beetle towards the sample using inertial slip-stick motion. Ten wires are required to control the position of the beetle and scanner and measure the tunneling current. The two beetles were built with different sized piezo-legs, and the vibrational properties of both beetles were studied in detail. It was found, in agreement with previous work, that the beetle bending mode is the lowest principal eigenmode. However, in contrast to previous vibrational studies of beetle-type scanning tunneling microscopes, we found that the beetles did not have the rattling modes that are thought to arise from the beetle sliding or rocking between surface asperities on the raceway. The mass of our beetles is 3-4 times larger than the mass of beetles where rattling modes have been observed. We conjecture that the mass of our beetles is above a 'critical beetle mass'. This is defined to be the beetle mass that attenuates the rattling modes by elastically deforming the contact region to the extent that the rattling modes can't be identified as distinct modes in cross-coupling measurements.

Virtual Journal of Nanoscale Science and Technology. Review of Scientific Instruments 73Preprint.pdf 73Fig1.pdf 73Fig2.pdf 73Fig3.pdf 73Fig4.pdf 73Fig5.pdf 73Fig6.pdf 73Fig7.pdf 73Fig8.pdf 73Fig9.pdf 73Fig10.pdf 73Fig11.pdf 73Fig12.pdf

An inverse photoemission system with large solid angle of detection and adjustable optical bandpass
J.A. Lipton-Duffin, A.G. Mark, G.K. Mullins,G.E. Contant and A.B. McLean, Review of Scientific Instruments, 75, 2, 445-454 (2004).

Abstract
A high-brightness, low energy electron source and dual Geiger-Muller-type isochromat photon detectors are combined to create a versatile new inverse photoemission system. The bandpass of the photon detector can be set to one of the following discrete values: 0.37 +/- 0.02, 0.43 +/- 0.02, 0.56 +/- 0.02 or 0.73 +/- 0.04 eV by using ethanol, 1-propanol, 1-butanol or a dimethyl ether/ethanol mixture respectively as the detection gas(es). All of the alcohols are self-quenching and do not require the addition of an additional quench gas. The design of the photon detectors, the electron gun, and the circuits that perform the dead time gating are described in detail. The capabilities of the new system are illustrated using spectra from both metal (Cu) and semiconductor (Si) surfaces.

Review of Scientific Instruments 72Preprint.pdf 72Fig1.pdf 72Fig2.pdf 72Fig3.pdf 72Fig4.pdf 72Fig5.pdf 72Fig6.pdf 72Fig7.pdf 72Fig8.pdf 72Fig9.pdf 72Fig10.pdf 72Fig11.pdf 72Fig12.pdf 72Fig13.pdf

Photon Detection with n-Propanol and C2H6O Isomers
J.A. Lipton-Duffin, A.G. Mark and A.B. McLean, Review of Scientific Instruments, 73, 9, 3149-3153 (2002).

Abstract
We demonstrate that a Geiger-Muller-type bandpass photon detector, suitable for inverse photoemission experiments, can be constructed from a MgF_2 entrance window that has a high energy transmission threshold of 10.97eV, and ethanol, a detection gas with an ionization potential of 10.48eV. The photon detector has a mean detection energy of hbar omega_d=(10.89 pm 0.07)eV and a bandpass of Delta hbar omega_d=(0.37 pm 0.05)eV. A photon detector can also be constructed from n-propanol/MgF_2 with a mean detection energy of hbar omega_d=(10.76 pm 0.07)eV and a bandpass Delta hbar omega_d=(0.41 pm 0.05)eV. These two new detection gas/window combinations have a higher detection energy and a narrower bandpass than the dimethyl ether/MgF_2 detector (Delta hbar omega_d=(0.71 pm 0.04)eV and hbar omega_d=10.60 eV). Since all three detectors utilize a MgF_2 entrance window, the photon bandpass can be changed straightforwardly by changing the detection gas. For systems that can be easily damaged by electron beams, having the freedom to open up the detector bandpass is an advantage because it can reduce the total electron exposure time during measurement.

Review of Scientific Instruments 71Preprint.pdf 71Fig1.pdf 71Fig2.pdf 71Fig3.pdf 71Fig4.pdf 71Fig5.pdf

Probing the internal structure of nanowires
A.B. McLean and I.G. Hill, Proceedings of the 5th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, July 6-9, 1999, Aix en Provence, France. Applied Surface Science, 162-163, 620-624, 2000.

Abstract
Si(111)-In(4x1) is a fascinating quasi-1D system that contains a repeated nanowire motif. The nanowires contain only two rows of In atoms. We demonstrate that it is possible to infer the spacing between the rows from a study of the dispersion of the image state band, measured using inverse photoemission. Our analysis suggest that the rows of In atoms are separated by 4 +/-0.5 A. This value is in excellent agreement with estimates of the spacing by both STM and surface x-ray diffraction.

Applied Surface Science 69Preprint.pdf 69Fig1.pdf 69Fig2.pdf 69Fig3.pdf 69Fig4.pdf 69Fig5.pdf