The Local Structure of Amorphous Silicon

Paracrystalline Amorphous silicon has traditionally been represented by a continuous random network model in which there is no long-range ordering for the atoms, and some have less than fourfold coordination, which form dangling bonds—a type of defect. Treacy and Borisenko (p. 950; see the Perspective by Gibson) used fluctuation electron microscopy to explain that models including regions of crystalline order are needed to fit the observed local variations in structure. Thus, on the 1- to 2-nanometer-length scale, this material should be thought of as having a paracrystalline structure containing localized crystalline regions. Amorphous silicon is more accurately described by a paracrystalline model, not the idealized continuous random network. It is widely believed that the continuous random network (CRN) model represents the structural topology of amorphous silicon. The key evidence is that the model can reproduce well experimental reduced density functions (RDFs) obtained by diffraction. By using a combination of electron diffraction and fluctuation electron microscopy (FEM) variance data as experimental constraints in a structural relaxation procedure, we show that the CRN is not unique in matching the experimental RDF. We find that inhomogeneous paracrystalline structures containing local cubic ordering at the 10 to 20 angstrom length scale are also fully consistent with the RDF data. Crucially, they also matched the FEM variance data, unlike the CRN model. The paracrystalline model has implications for understanding phase transformation processes in various materials that extend beyond amorphous silicon.

[1]  G. Wang,et al.  Transformation-mediated ductility in CuZr-based bulk metallic glasses. , 2010, Nature materials.

[2]  Parthapratim Biswas,et al.  Reverse Monte Carlo modeling of amorphous silicon , 2004 .

[3]  P. Munroe,et al.  Structural characterization of pressure-induced amorphous silicon , 2009 .

[4]  J. L. Robertson,et al.  High-energy x-ray diffraction study of pure amorphous silicon , 1999 .

[5]  David Alan Drabold,et al.  Real space information from fluctuation electron microscopy: applications to amorphous silicon , 2007, 0707.4012.

[6]  S. Elliott,et al.  Ab Initio computer simulation of the early stages of crystallization: application to Ge(2)Sb(2)Te(5) phase-change materials. , 2011, Physical review letters.

[7]  P. Voyles,et al.  Reverse Monte Carlo structural model for a zirconium-based metallic glass incorporating fluctuation microscopy medium-range order data , 2009 .

[8]  R. Bisseling,et al.  Device-size atomistic models of amorphous silicon , 2001, cond-mat/0107358.

[9]  Winer,et al.  Computer generation of structural models of amorphous Si and Ge. , 1985, Physical review letters.

[10]  De Nyago Tafen,et al.  Experimentally constrained molecular relaxation: The case of glassy Ge Se 2 , 2005 .

[11]  Gerard T. Barkema,et al.  Raman spectra and structure of amorphous Si , 2001 .

[12]  Keiji Watanabe,et al.  Critical-like behaviour of glass-forming liquids. , 2010, Nature materials.

[13]  M. Treacy,et al.  Substantial crystalline topology in amorphous silicon. , 2010, Physical review letters.

[14]  K. B. Borisenko,et al.  Applications of electron reduced density function analysis to the study of amorphous materials: An example of Zr64.13Cu15.75Ni10.12Al10.0 and Zr55Cu30Ni5Al10 metallic glasses , 2010 .

[15]  D. Cockayne.  The Study of Nanovolumes of Amorphous Materials Using Electron Scattering , 2007 .

[16]  Evan Ma,et al.  Relationship between structure, dynamics, and mechanical properties in metallic glass-forming alloys , 2008 .

[17]  D. Turnbull,et al.  Structure of amorphous semiconductors , 1972 .

[18]  D. Muller,et al.  Fluctuation microscopy in the STEM. , 2002, Ultramicroscopy.

[19]  Gerard T. Barkema,et al.  Fitting the Stillinger–Weber potential to amorphous silicon , 2001 .

[20]  W. Zachariasen,et al.  THE ATOMIC ARRANGEMENT IN GLASS , 1932 .

[21]  J. Abelson,et al.  Absence of an abrupt phase change from polycrystalline to amorphous in silicon with deposition temperature. , 2001, Physical review letters.

[22]  S. C. Moss,et al.  Evidence of Voids Within the As-Deposited Structure of Glassy Silicon , 1969 .

[23]  R. Mcgreevy,et al.  Structural modelling of glasses using reverse Monte Carlo simulation , 1990, Nature.

[24]  Linn W. Hobbs,et al.  Network properties of crystalline polymorphs of silica , 1990 .

[25]  M. Treacy,et al.  Medium-range order in amorphous silicon investigated by constrained structural relaxation of two-body and four-body electron diffraction data , 2012 .

[26]  Medium-range order in molecular materials: fluctuation electron microscopy for detecting fullerenes in disordered carbons. , 2009, Ultramicroscopy.

[27]  P. Voyles,et al.  Schläfli cluster topological analysis of medium range order in paracrystalline amorphous semiconductor models , 2000 .

[28]  Ulf R. Pedersen,et al.  Geometry of slow structural fluctuations in a supercooled binary alloy. , 2009, Physical review letters.

[29]  J. Abelson,et al.  Quantifying nanoscale order in amorphous materials: simulating fluctuation electron microscopy of amorphous silicon , 2007 .

[30]  G. T. Barkema,et al.  High-quality continuous random networks , 2000 .

[31]  M. Treacy,et al.  Paracrystallites found in evaporated amorphous tetrahedral semiconductors , 1998 .

[32]  J. Robertson,et al.  Density, sp 3 fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy , 2000 .

[33]  Shanks,et al.  Vibrational spectrum of amorphous silicon: Experiment and computer simulation. , 1987, Physical review. B, Condensed matter.

[34]  S. G. Bishop,et al.  Observation of the Role of Subcritical Nuclei in Crystallization of a Glassy Solid , 2009, Science.

[35]  J. Tersoff,et al.  Empirical interatomic potential for silicon with improved elastic properties. , 1988, Physical review. B, Condensed matter.

[36]  N. Jakse,et al.  Glass forming ability and short-range order in a binary bulk metallic glass by ab initio molecular dynamics , 2008 .