Pengpeng Zhang

Bio: Pengpeng Zhang is an academic researcher from Michigan State University. The author has contributed to research in topics: Scanning tunneling microscope & Thin film. The author has an hindex of 15, co-authored 46 publications receiving 1045 citations. Previous affiliations of Pengpeng Zhang include Beijing Normal University & Pennsylvania State University.

Electronic transport in nanometre-scale silicon-on-insulator membranes

Abstract: The widely used ‘silicon-on-insulator’ (SOI) system consists of a layer of single-crystalline silicon supported on a silicon dioxide substrate. When this silicon layer (the template layer) is very thin, the assumption that an effectively infinite number of atoms contributes to its physical properties no longer applies, and new electronic, mechanical and thermodynamic phenomena arise1,2,3,4, distinct from those of bulk silicon. The development of unusual electronic properties with decreasing layer thickness is particularly important for silicon microelectronic devices, in which (001)-oriented SOI is often used5,6,7. Here we show—using scanning tunnelling microscopy, electronic transport measurements, and theory—that electronic conduction in thin SOI(001) is determined not by bulk dopants but by the interaction of surface or interface electronic energy levels with the ‘bulk’ band structure of the thin silicon template layer. This interaction enables high-mobility carrier conduction in nanometre-scale SOI; conduction in even the thinnest membranes or layers of Si(001) is therefore possible, independent of any considerations of bulk doping, provided that the proper surface or interface states are available to enable the thermal excitation of ‘bulk’ carriers in the silicon layer.

Hybrid strategies in nanolithography

Abstract: Hybrid nanoscale patterning strategies combine the registration and addressability of conventional lithographic techniques with the chemical and physical functionality enabled by intermolecular, electrostatic and/or biological interactions. This review aims to highlight and to provide a comprehensive description of recent developments in hybrid nanoscale patterning strategies that enhance existing lithographic techniques or can be used to fabricate functional chemical patterns that interact with their environment. These functional structures create new capabilities, such as the fabrication of physicochemical surfaces that can recognize and capture analytes from complex liquid or gaseous mixtures. The nanolithographic techniques we describe can be classified into three general areas: traditional lithography, soft lithography and scanning-probe lithography. The strengths and limitations of each hybrid patterning technique will be discussed, along with the current and potential applications of the resulting patterned, functional surfaces.

Self-Assembly of Carboranethiol Isomers on Au{111}: Intermolecular Interactions Determined by Molecular Dipole Orientations

Abstract: Self-assembled monolayer (SAM) structures and properties are dominated by two interactions: those between the substrate and adsorbate and those between the adsorbates themselves. We have fabricated self-assembled monolayers of m-1-carboranethiol (M1) and m-9-carboranethiol (M9) on Au{111}. The two isomers are nearly identical geometrically, but calculated molecular dipole moments show a sizable difference at 1.06 and 4.08 D for M1 and M9 in the gas phase, respectively. These molecules provide an opportunity to investigate the effect of different dipole moments within SAMs without altering the geometry of the assembly. Pure and co-deposited SAMs of these molecules were studied by scanning tunneling microscopy (STM). The molecules are indistinguishable in STM images, and the hexagonally close-packed adlayer structures were found to have (√19 × √19)R23.4° unit cells. Both SAMs display rotational domains without the protruding or depressed features in STM images associated with domain boundaries in other SAM ...

Self-organization of semiconductor nanocrystals by selective surface faceting

Abstract: The formation and ordering of Si nanocrystals in dewetting and agglomeration of the thin single crystalline Si layer in silicon-on-insulator has been investigated using low-energy electron microscopy. The evolution of the Si dewetting and agglomeration is captured in real time, revealing the detailed process for the formation and ordering of the nanocrystals. A surface faceting mechanism governing this self-organized process is proposed and supported with first-principles calculations.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Abstract: Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Stretchable form of single crystal silicon for high performance electronics on rubber substrates

Abstract: The present invention provides stretchable, and optionally printable, semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Stretchable semiconductors and electronic circuits of the present invention preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention may be adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

X-ray photoelectron spectroscopy sulfur 2p study of organic thiol and disulfide binding interactions with gold surfaces

Abstract: The presence of two sulfur species was detected in X-ray photoelectron spectroscopy (XPS) studies of thiol and disulfide molecules adsorbed onto gold surfaces. These species are assigned to bound thiolate (S2p3/2 binding energy of 162 eV) and unbound thiol/disulfide (S2p3/2 binding energy from 163.5 to 164 eV). These assignments are consistent with XPS data obtained from different thiols (C12, C16, C18, and C22 alkane thiols, a fluorinated thiol, and a cyclic polysiloxane thiol) and different adsorption conditions (solvent type, thiol concentration, temperature, and rinsing). In particular, the use of a poor solvent for thiol adsorption solutions (e.g., ethanol for long chain alkanethiols) and the lack of a rinsing step both resulted in unbound thiol molecules present at the surface of the bound thiolate monolayer. This has implications for recent studies asserting the presence of multiple binding sites for gold−thiolate species in organic monolayers.

Multivalency as a chemical organization and action principle.

Abstract: Multivalent interactions can be applied universally for a targeted strengthening of an interaction between different interfaces or molecules. The binding partners form cooperative, multiple receptor-ligand interactions that are based on individually weak, noncovalent bonds and are thus generally reversible. Hence, multi- and polyvalent interactions play a decisive role in biological systems for recognition, adhesion, and signal processes. The scientific and practical realization of this principle will be demonstrated by the development of simple artificial and theoretical models, from natural systems to functional, application-oriented systems. In a systematic review of scaffold architectures, the underlying effects and control options will be demonstrated, and suggestions will be given for designing effective multivalent binding systems, as well as for polyvalent therapeutics.