BBB and BOLS Correlation Theories to the Understanding of Low-Dimensional Chemistry And

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BBB and BOLS Correlation Theories to the Understanding of Low-Dimensional Chemistry and Physics

Chang Q Sun

Dr Sun Chang Qing has been dedicated, since later 1980’s, to uncovering the correlation between the chemical bond, valence band, and surface-potential barrier (BBB) for electronic process of surface chemical reaction involving oxygen, nitrogen and carbon, and the bond-order-length-strength (BOLS) correlation for the impact of atomic coordination-number (CN) imperfection on the physical aspect of surfaces and nanosolids. He has pioneered and extensively verified the respective BBB and BOLS correlation theories using various approaches. Applying the theories to surface reactions, surface-probing technologies, nanostructured solids, and designer materials has led to new scientific knowledge and encouraging discoveries that are beyond the scopes of currently available techniques and theoretical approaches. Achievement has been documented in over 80 principally authored and around 30 co-authored archive journal articles including four authoritative reviews,[1],[2],[3],[4] and two book chapters.[5],[6] Details are described as follows.

I. Bond-band-barrier (BBB) correlation for O(N,C) surface chemistry

• Challenge

Traditionally, chemical reaction between atoms is often discussed in terms of hard spheres interacting with electrostatic forces or ad-atoms resting in the potential well of adsorption. Results probed using crystallography, microscopy, electronic spectroscopy and other techniques are often isolated one from another in analysis. For example, crystallographic and microscopic observations are described in terms of atomic dislocations and electronic spectra are related to a superposition of electronic states of the constituent elements in neutral state1,[7],[8](and refs. therein). A certain adsorbate-induced phase is often accompanied with numerous models arguing about atomic positions. Solutions are referred to the ones optimized with minimization of total energy in theoretical calculations or minimization of R-factor in decoding diffraction data, without involving charge transportation or polarization that dominate in real situation. A huge space of freely adjustable parameters often leads to numerous mathematical solutions that need to be certain in physics. Understanding the electronic process of reaction and the nature and dynamics of surface bonding, and eventually to grip with factors controlling the bond making was recognized as the focusing task for the surface science community in the coming30 years [Surf. Sci. 1993; 300: 678]. The initiated BBB correlation and the associated approaches should be necessary to reconcile the above issues towards bond making in a predictable and controllable way.

• BBB correlation theory

The BBB correlation[9],[10] and its formulation indicate that it is essential for an O (N and C) atom to hybridize its sp-orbital upon interacting with atoms in solid phase, which was ever thought forbidden. In the process of reaction, holes, non-bonding lone pairs, anti-bonding dipoles and hydrogen-like bonds are involved, which add corresponding density-of-states (DOS) features to the valence band or above of the host.[11] Bond forming also alters the sizes and valences of the involved atoms and causes a collective and continuous dislocation of these atoms,[12] which corrugate the morphology or the potential barrier of the surface. The bond nature and the respective DOS should dominate the performance of a compound solid. For example, dipole formation lowers the work function of the surface while overdosing with the adsorbate creates H-like bond that reverses the work function change.1

• Achievement

The power of the BBB premise and the associated approaches are testified by the following major breakthroughs:

(i)The reaction kinetics of over 30 O-derived phases on transition metals Cu,[13] Co,[14] Ag and V,1 noble metals Rh,[15],[16] Ru,[17],[18] and Pd,[19]and non-metallic diamond surfaces[20] and of C/N on Ni(001) surface[21],[22] has been generalized using formulae of reactions with identification of individual atomic valences and bond forming kinetics at the surfaces. This forms the hitherto consistent and comprehensive understanding of the O(C, N) surface bonding kinetics.

(ii)The adsorbate-derived signatures of scanning tunneling microscopy/spectroscopy, low-energy electron diffraction, x-ray diffraction, phtoelectron spectroscopy, thermal desorption spectroscopy, electron energy loss spectroscopy and Raman spectroscopy, have been unified in terms of atomic valence, bond geometry, valence DOS, bond strength and bonding kinetics[23],[24],[25],[26]. This also enhances the capacity of these probing techniques in revealing details of bond forming kinetics and its consequence on the behavior of the involved atoms and valence electronics[27],[28],[29].

(iii)Most strikingly, a Cu3O2 bond geometry and its four-stageforming kinetics on the O-Cu(001) surface has been quantified using LEED and STM calculations as: one bond forms first and then the other follows; the sp-orbital then hybridizes with creation of lone pairs that induce dipoles. (please refer to: The four-stage bonding kinetics holds general to other analyzed systems based on various observations.

(iv)It has been uncovered that formation of the basic tetrahedron, and consequently, the four-stage bond forming kinetics and the adsorbate-derived DOS features, are intrinsically common for all the analyzed systems though the patterns of observations may vary from situation to situation. What differs one surface phase from another in observations are: (a) the site selectivity of the adsorbate, (b) the order of the ionic bond formation and, (c) the orientation of the tetrahedron at the host surfaces. The valences of adsorbate, the scale and geometrical orientation of the host lattice and the electronegativity of the host elements determine these specific differences extrinsically.

II. Bond order-length-strength (BOLS) correlation for the impact of atomic CN imperfection

• Challenge

Properties of solids determined by their shape and size are indeed fascinating and form the basis of the emerging field of nanoscience and nanotechnology that has been recognized as the key significance in science, technology, and economics in the concurrent century. Overwhelming works have been reported on atomic imaging and manipulating, nanosolid synthesizing, functioning, and chracterising as well as structuring patterning. However, understanding of the mechanism behind the nanosolid tunability remains yet infancy. For a single phenomenon, there are often numerous theories discussing from various perspectives. A description of all observations in a comprehensive yet simple theory is high challenge. Furthermore, structural miniaturization provides one with an additional freedom that not only allows us to tune the properties by changing the shape and size, but also challenges us to gain certain kinds information that is beyond traditional approaches.

• BOLS correlation theory

The BOLS correlation[30],[31] indicates that the CN imperfection of atoms at sites surrounding defects or near the surface edges dictates the tunability of a nanosolid of which the portion of such lower-coordinated atoms increases when the solid size is reduced. Atomic CN imperfection causes the remaining bonds of the lower-coordinated atom to contract spontaneously associated with magnitude rise in bond energy. Bond contraction localizes the electrons and enhances the charge density in the relaxed region, which contribute to the work function and the magnetization of the solid. Bond strengthening enhances the energy density per unit volume in the relaxed region, which perturbs the Hamiltonian of an extended solid and the associated properties such as the band-gap, core-level shift, Stokes shift (electron-phonon interaction), and dielectrics. The joint effect of bond strengthening and CN-reduction lowers the cohesive energy per atom of the lower-coordinated system, which dictates the thermodynamic process of the solid such as self-assembly growth, atomic vibration, phase transition, diffusitivity, sinterbility, chemical reactivity, and thermal stability. The joint effect of atomic cohesive energy depression and energy density enhancement dictates the mechanical strength (surface stress, surface energy, and Young’s modulus), and compressibility (extensibility, or ductility) of a nanosolid below the melting point that drops with the solid dimension.

• Achievement

The BOLS correlation has enabled the following major breakthroughs:

(i)The unusual behavior of a nanosolid in mean lattice contraction,[32],[33] mechanical strength,[34],[35] phase transition,[36],[37],[38] thermal stability,[39] acoustic and optical phonons,[40],[41],[42] optoelectronics,[43],[44],[45] magnetism,[46] dielectrics,[47],[48],[49] and chemical reactivity[50],[51] has been consistently understood and systematically formulated as functions of atomic CN imperfection and its derivatives. Description of photoluminescence blue shift at the lower end of the size limit has been solved, which is beyond the scope of traditional ‘quantum confinement’ theory.[52]

(ii)The bonding identities such as the length, strength, extensibility, and thermal and chemical stability,[53] in metallic monatomic chains[54],[55] and in the carbon nanotubes[56] have been determined. Understanding has been extended to the mechanical strength and ductility of metallic nanowires.

(iii)Most strikingly, single energy levels of an isolated Si, Pd, Au, Ag and Cu atoms and their shift upon bulk and nanosolid formation have been quantified by matching predictions to the observed size and shape dependence of the XPS and Auger photoelectron coincidence spectroscopy (APECS)[57]data. This in turn enhances the capability of the XPS and APECS, and provides a new way, determining the intra-atomic trapping energy of an isolated atom and the crystal binding intensity to the specific electrons[58],[59]. Achievement is beyond the reach of techniques such as the combination of XPS and laser cooling that only measures the energy level separation of the slowly moving atoms/clusters in gaseous phase.[60]

(iv)Quantitative information about dimmer vibration40 and electron-phonon interaction[61] has been obtained by matching predictions to the measured shape and size dependence of Raman and photoemission/absorption spectra of Si and other III-V and II-VI compounds. The phase stability of ferromagnetic, ferroelectric and superconductive nanosoilds has been reconciled to the CN imperfection of different orders.[62]

New knowledge derived from the BBB and BOLS premises has enabled discoveries of new measures or functional materials for blue-light emission,[63] photonic switch,[64] electron emission,[65] diamond-metal adhesion,[66] nitride self-lubrication,[67] magnetization modulation,[68] and other systems[69],[70],[71] as well as consistent insight into the joint effects of chemical passivation and physical miniaturization on the behavior of numerous kinds of nanosolids.30-71

Achievements testify the originality, the novelty, the power and the potential of the originated premises and approaches in revealing information that goes beyond conventional approaches. With innovated ways of thinking and approach, the unique BBB and BOLS premises provide guidelines for theoretical refinement and for materials design, which should open up new branches of study.

References (list of key publications)

1

[1]Sun CQ, Oxidation electronics: bond-band-barrier correlation and its applications. PROG. MATER. SCI. 2003; 48: 521-685.

[2]Sun CQ, O-Cu(001): I. Binding the signatures of LEED, STM and PES in a bond-forming way. SURF REV LETT 2001;8:367-402.

[3]Sun CQ, O-Cu(001): II. VLEED quantification of the four-stage Cu3O2 bonding kinetics. SURF REV LETT 2001;8:703-34.

[4]Sun CQ, The sp hybrid bonding of C, N and O to the fcc(001) surface of nickel and rhodium. SURF REV LETT 2000;7:347-63.

[5]Jennings PJ and Sun CQ. Low-energy electron diffraction. In the Surface Analysis Methods in Materials Science, Eds O'Connor DJ, Sexton BA and Smart RC, BerlinSpringer-Verlag, New York 2003.

[6] Thurgate SM, Hitchen G and Sun CQ, Surface structural determination by VLEED analysis.In the Surface Science: Principles and Applications, Eds MacDonald R J, Taglauer E C and Wandelt KR, Springer-Verlag, 1999.

[7] Thurgate SM, Sun CQ.Very-low-elnergy electron diffraction analysis of oxygen on Cu(001). PHYS REV 1995;B51:2410-7.

[8]Sun CQ, Li S, Tay BK, et al. Solution certainty in the Cu(110)-(2×1)-2O2- surface crystallography. INT J MOD PHYS 2002;B16:71-8.

[9]Sun CQ, Li S. Oxygen-derived DOS features in the valence band of metals. SURF REV LETT 2000;7:213-7.

[10]Sun CQ, Bai CL. Modeling of non-uniform electrical potential barriers for metal surfaces with chemisorbed oxygen. J PHYS-CONDENS MAT 1997;9:5823-36.

[11]Sun CQ, A model of bonding and band-forming for oxides and nitrides, APPL PHYS LETT 1998;72:1706-8.

[12]Sun CQ. Exposure-resolved VLEED from the O-Cu(001): Bonding dynamics. VACUUM 1997;48: 535-41.

[13]Sun CQ. Origin and processes of O-Cu(001) and the O-Cu(110) biphase ordering. INT J MOD PHYS 1998;B12:951-64.

[14]Sun CQ. On the nature of the O-Co(1010) triphase ordering. SURF REV LETT 1998;5:1023-8.

[15]Sun CQ. Driving force behind the O-Rh(001) clock reconstruction. MOD PHYS LETT B 1998;12:849-57.

[16]Sun CQ. On the nature of the O-Rh(110) multiphase ordering. SURF SCI 1998;398: L320-6.

[17]Sun CQ. O-Ru(0001) surface bond and band formation. SURF REV LETT 1998;5:465-71.

[18]Sun CQ. Oxygen interaction with Rh(111) and Ru(0001) surfaces: Bond-forming dynamics. MOD PHYS LETT 2000; B14:219-27.

[19]Sun CQ. Nature and dynamics of the O-Pd(110) surface bonding. VACUUM 1998;49:227-32.

[20]Sun CQ, Xie H, Zhang W, Preferential oxidation of diamond {111}, J PHYS D 2000;33:2196-9.

[21]Sun CQ, Hing P. Driving force and bond strain for the C-Ni(100) surface reaction. SURF REV LETT 1999;6:109-14.

[22]Sun CQ. Mechanism for the N-Ni(100) clock reconstruction. VACUUM 1999;52:347-51.

[23]Sun CQ, Zhang S, Hing P, et al. Spectral correspondence to the evolution of chemical bond and valence band in oxidation. MOD PHYS LETT B 1997;11:1103-13.

[24]Sun CQ, Bai CL. A model of bonding between oxygen and metal surfaces. J PHYS CHEM SOLIDS 1997;58:903-12.

[25]Sun CQ. Oxygen-reduced inner potential and work function in VLEED.VACUUM 1997;48:865-9.

[26]Zhao ZW, Tay BK, Sun CQ, and Ligatchev V.,Oxygen lone-pair states near the valence-band edge of aluminum oxide thin films. J. Appl. Phys. In press.

[27]Sun CQ. Time-resolved VLEED from the O-Cu(001): Atomic processes of oxidation. VACUUM 1997;48: 525-30.

[28]Sun CQ. Angular-resolved VLEED from O-Cu(001): Valence bands, chemical bonds, potential barrier, and energy states. INT J MOD PHYS B 1997;11: 3073-91.

[29]Sun CQ. Spectral sensitivity of the VLEED to the bonding geometry and the potential barrier of the O-Cu(001) surface. VACUUM 1997;48:491-8.

[30]Sun CQ, Tay BK, Zeng XT, et al., Bond-order-length-strength (BOLS) correlation mechanism for the shape and size dependency of a nanosolid. J. Phys. Condens Matt. 2002;14:7781-95.

[31]Sun CQ, Gong HQ, Hing P, et al. Behind the quantum confinement and surface passivation of nanoclusters. SURF REV LETT 1999;6:L171-6.

[32]Sun CQ, Li S, and Tay BK,Laser-like mechanoluminescence in ZnMnTe-diluted magnetic semiconductor. APPL. PHYS. LETT. 2003;82:3568-9.

[33]Sun CQ. The lattice contraction of nanometre-sized Sn and Bi particles produced by an electrohydrodynamic technique. J PHYS-CONDENS MAT 1999;11:4801-3.

[34]Sun CQ, et al.Atomic coordination-number imperfection reverses the Hall-Petch relationship at nanometer regime. ACTA MATER, In press.

[35] Zeng XT, Zhang S, Sun CQ, Liu YC. Nanometric-layered CrN/TiN thin films: mechanical strength and thermal stability. Thin Solid Films 2003;424:99-102.

[36] Zhong WH, Sun CQ, et al. Curie temperature suppression of ferromagnetic nanosolids. J. PHYS. CONDENS MATT. 2002;14:L399-405.

[37] Pan LK, Huang HT, Sun CQ. Dielectric transition and relaxation of nanosolid silicon. J APPL PHYS 2003;94:2695-700.

[38] Ye HT, Sun CQ, Huang HT, et al. Dielectric transition of nanostructured diamond films. APPL PHYS LETT 2001;78:1826-8.

[39]Sun CQ, Wang Y, Tay BK, et al. Correlation between the melting point of a nanosolid and the cohesive energy of a surface atom. J. Phys. Chem. 2002;B106:10701-5.

[40]Sun CQ, Pan LK, Li CM. Si-Si dimmer vibration derived from size dependence of Raman shift. J Phys. Chem B, in press

[41]Sun CQ,Pan LK, Fu YQ, et al. Size dependent 2p-level shift of nanosolid silicon. J Phys Chem 2003; B107:L5113-5.

[42]Sun CQ, Sun XW, Gong HQ, et al. Frequency shift in the photoluminescence of nanometric SiOx: surface bond contraction and oxidation. J PHYS-CONDENS MAT 1999;11:L547-50.

[43]Sun CQ, Li S, Tay BK, Chen TP, Upper limit of blue shift in the photoluminescence of CdSe and CdS nanosolids, Acta Materialia 2002;50: 4687-93.

[44] Pan LK, Sun CQ, Tay BK, et al. Photoluminescence of Si nanosolid near the lower end of the size limit. J Phys Chem 2002;B106:11725-7.

[45]Sun CQ, et al. Effects of surface passivation and interfacial reaction on the size-dependent 2p-level shift of supported coppernanosolids. ACTA MATERIALIA 2003;51:4631-6.

[46]Zhong WH, Sun CQ, Li S, et al. Magnetism of ferromagnetic nanosolids: A Monte Carlo Study. Phys Rev B in press.

[47] Huang HT, Sun CQ, Zhang TS, et al. Grain-size effect on ferroelectric Pb(Zr1-xTix)O-3 solid solutions induced by surface bond contraction. PHYS REV 2001; B63:184112.

[48] Huang HT, Sun CQ, Hing P. Surface bond contraction and its effect on the nanometric sized lead zirconate titanate. J PHYS-CONDENS MAT 2000;12:L127-32.

[49]Sun CQ, Sun XW, Tay BK, et al. Dielectric suppression and its effect on photoabsorption of nanometric semiconductors. J PHYS D 2001;34:2359-62.

[50]Sun CQ, Pan LK, Bai HL, et al. Effects of surface passivation and interfacial reaction on the size-dependent 2p-level shift of supported coppernanosolids. ACTA MATER 2003;51:4631-6.

[51] Pan LK, Sun CQ, Yu GQ, Band gap expansion, core level shift and dielectric suppression of nanosolid Si passivated by plasma fluorination. J. VAC. SCI. TECHNOL in press.

[52]Sun CQ, Chen TP, Tay BK, et al. An extended 'quantum confinement' theory: surface-coordination imperfection modifies the entire band structure of a nanosolid. J PHYS D 2001;34:3470-9.

[53]Sun CQ, Bai HL, LiS, et al. Size effect on the electronic structure and the thermal stability of a gold nanosolid. ACTA MATER, 52(2), 501-5 (2004).

[54]Sun CQ, Bai HL, LiS, et al. Length, strength, extensibility and thermal stability of an Au-Au bond in the gold monatomic chain. J Phys Chem B. IN PRESS

[55]Sun CQ, Li C, and Li S. Breaking limit of atomic distance in the monatomic chain.COMMUNICATED

[56]Sun CQ, Bai HL, Tay BK, et al. Dimension, strength, and chemical and thermal stability of a single C-C bond in carbon nanotubes. J Phys Chem 2003;B107:7544-6.

[57]Sun CQ, et al. Effects of screen shielding and catalytic recharging on the simultaneous shift of 3d5/2 and 2p3/2 levels of Cu. COMMUNICATED

[58]Sun CQ. Atomic-coordination-imperfection-enhanced Pd-3d5/2 crystal binding energy Surf Rev Lett In press

[59]Sun CQ. Surface and Nanosolid Core-level Shift: Impact of Atomic Coordination Number Imperfection. PHYS REV 2004; B??

[60]Sun CQ, Tay BK, Fu YQ, Discriminating crystal bonding from the atomic trapping of a core electron at energy levels shifted by surface relaxation or nanosolid formation. J Phys Chem 2003;B107:L411-4.

[61] Pan LK, Sun CQ. Coordination imperfection enhanced electron-phonon interaction in porous silicon. J APPL PHYS IN PRESS

[62]Sun CQ, Zhong WH, Li S, et al. Coordination imperfection suppressed phase stability of ferromagnetic, ferroelectric, and superconductive nanosolids. J PHYS CHEM B IN PRESS