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25 May 1998

Volume 72, Issue 21, pp. 2631-2766

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Observation of chemical shifts of Si 2p level by an x-ray photoelectron spectroscopy system with a laser-plasma x-ray source

Hiroyuki Kondo, Toshihisa Tomie, and Hideaki Shimizu

Appl. Phys. Lett. 72, 2668 (1998); http://dx.doi.org/10.1063/1.121093 (3 pages) | Cited 14 times

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An x-ray photoelectron spectroscopy system with a laser-plasma x-ray source is shown to have energy resolution high enough to observe chemical shifts of Si 2p electrons in SiO2, Si3N4, and pure Si. A boron nitride (BN) plasma x-ray source is produced by irradiation of 100 mJ Q-switched YAG laser pulses. A single line emission at 4.86 nm is selected from the BN plasma by means of carbon foils. Fine spectra are acquired with only 96 laser shots. The results obtained confirm that a laboratory-sized x-ray photoelectron spectroscopy system with submicron spatial resolution and high spectral acquisition speed can be realized. © 1998 American Institute of Physics.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
07.81.+a Electron and ion spectrometers
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Photon emission from Ag and Au clusters in the scanning tunneling microscope

A. Downes and M. E. Welland

Appl. Phys. Lett. 72, 2671 (1998); http://dx.doi.org/10.1063/1.121094 (3 pages) | Cited 14 times

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In principle, chemical information is obtainable from metal surfaces by means of photon emission from the scanning tunneling microscope (STM). However, the photon emission varies significantly with topography and choice of tip. We address the important issue of geometry by studying the emission characteristics of Ag and Au spheres. First, photon maps of Ag clusters, consisting in some cases of just a few atoms, demonstrate that they can be uniquely identified from other nonmetallic particles. Then, the bias at which there is an onset of photon emission for 1 nm Ag and Au clusters is measured and found to be ≈ 3.3 and ≈ 2.1 V, respectively. This allows for the demonstration of the ability of the STM to distinguish different metal particles by their photon emission. The value of the onset bias for each metal can be made almost invariant to sample topography by an appropriate choice of tip; only then is the photon emission related purely to the optical properties of the surface. We envisage a form of chemical microscopy, whereby the bias of emission onset is mapped. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Coupling of GaN- and AlN-like longitudinal optic phonons in Ga1−xAlxN solid solutions

F. Demangeot, J. Groenen, J. Frandon, M. A. Renucci, O. Briot, S. Clur, and R. L. Aulombard

Appl. Phys. Lett. 72, 2674 (1998); http://dx.doi.org/10.1063/1.121095 (3 pages) | Cited 28 times

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Long-wavelength optical phonons of Ga1−xAlxN solid solutions have been identified in a wide compositional range by Raman spectroscopy. The A1 and E1 polar phonon frequencies evolve continuously with x from one-member crystal to the other. The same behavior seems to hold true for the silent B1 mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T. Hon and W. L. Faust, J. Appl. Phys. 1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons. © 1998 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors

The effect of Al3Ti capping layers on electromigration in single-crystal aluminum interconnects

V. T. Srikar and C. V. Thompson

Appl. Phys. Lett. 72, 2677 (1998); http://dx.doi.org/10.1063/1.121096 (3 pages) | Cited 7 times

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Studies of accelerated electromigration were conducted on passivated Al single-crystal interconnects fabricated on oxidized Si, and capped with Al3Ti overlayers. The capping layers were formed by the reaction of the single-crystal Al films with Ti overlayers. The activation energy for electromigration-induced failure was determined to be 0.94±0.05 eV. Previous work on Al single-crystal interconnects without Al3Ti overlayers gave an activation energy of 0.98±0.2 eV and lifetimes of similar magnitude [Y.-C. Joo and C. V. Thompson, J. Appl. Phys. 81, 6062 (1997)]. The similarity of these results suggests that either the rate-limiting mechanism for electromigration-induced failure of single-crystal Al interconnects is not diffusion along the interface of the Al with the surrounding oxide and overlayer, or that, surprisingly, the diffusivity of Al along the Al/Al3Ti interface is approximately the same as, or lower than, the diffusivity of Al along the Al/AlOx interface. © 1998 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Direct observation of the core structures of threading dislocations in GaN

Y. Xin, S. J. Pennycook, N. D. Browning, P. D. Nellist, S. Sivananthan, F. Omnès, B. Beaumont, J. P. Faurie, and P. Gibart

Appl. Phys. Lett. 72, 2680 (1998); http://dx.doi.org/10.1063/1.121097 (3 pages) | Cited 86 times

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Here we present the first direct observation of the atomic structure of threading dislocation cores in hexagonal GaN. Using atomic-resolution Z-contrast imaging, dislocations with edge character are found to exhibit an eight-fold ring core. The central column in the core of a pure edge dislocation has the same configuration as one row of dimers on the {10-10} surface. Following recent theoretical work, it is proposed that edge dislocations do not have deep defect states in the band gap, and do not contribute to cathodoluminescence dislocation contrast. On the other hand, both mixed and pure screw dislocations are found to have a full core, and full screw dislocation cores were calculated to have states in the gap. © 1998 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Influence of oxygen plasma treatments on the structural properties of c-Si

N. H. Nickel and I. Sieber

Appl. Phys. Lett. 72, 2683 (1998); http://dx.doi.org/10.1063/1.121098 (3 pages) | Cited 3 times

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The effects of hydrogen and oxygen plasma treatments on the structural properties of n-type c-Si were examined. Specimens were exposed to either an oxygen or a hydrogen electron-cyclotron-resonance plasma in a temperature range of 240–385 °C. Hydrogenations performed at low temperatures (<300 °C) introduced platelets. On the other hand, oxygen plasma treatments did not result in the formation of platelets. Analysis of O and H concentration depth profiles, measured by secondary-ion-mass spectrometry (SIMS), reveal that O and H migrate with a similar diffusion coefficient of Deff ≈ 1012 cm2 s−1. Moreover, the O concentration exceeds the H concentration by roughly a factor of 2.5. This suggests that one H atom and 2–3 O atoms migrate as a cluster. Furthermore, evidence of deep traps for H and O was found from the SIMS depth profiles. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.S- Impurities in crystals
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
71.55.Cn Elemental semiconductors

Low temperature fabrication and properties of sol-gel derived (111) oriented Pb(Zr1−xTix)O3 thin films

Yoon J. Song, Yongfei Zhu, and Seshu B. Desu

Appl. Phys. Lett. 72, 2686 (1998); http://dx.doi.org/10.1063/1.121099 (3 pages) | Cited 44 times

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A novel processing method is developed for preparing sol-gel derived Pb(Zr1−xTix)O3 (x = 0.47) thin films on Pt/Ti/SiO2/Si substrates. Using a modified precursor solution and a rapid heat treatment without pyrolysis, it was possible to obtain highly (111) oriented PZT thin films with high perovskite content at a low annealing temperature of 550 °C. The low temperature processing was assisted by taking advantage of the heterogeneous nucleation of the PZT films, which reduces the activation energy for perovskite phase formation. Using this method, the PZT thin films exhibited better dielectric and ferroelectric properties at 550 °C than those reported by other methods. For example, the PZT films annealed at 550 °C showed a well-saturated hysteresis loop at an applied voltage of 5 V with Pr and Ec of 12 μC/cm2 and 38 kV/cm, and their dielectric constant and dissipation factor at a frequency of 100 kHz were 410 and 0.021, respectively. The leakage current density was lower than 10−8 at an applied electric field of 150 kV/cm. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)

Investigation of the interface formation between calcium and tris-(8-hydroxy quinoline) aluminum

V.-E. Choong, M. G. Mason, C. W. Tang, and Yongli Gao

Appl. Phys. Lett. 72, 2689 (1998); http://dx.doi.org/10.1063/1.121100 (3 pages) | Cited 103 times

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X-ray and ultraviolet photoemission spectroscopy investigations reveal strong interactions between Ca and tris-(8-hydroxy quinoline) aluminum (Alq3) during the Ca/Alq3 interface formation. The details of the interaction depend on the direction of the interface formation. For the case of Ca deposited on Alq3, a staged interface reaction is observed. For low Ca coverages (ΘCa ⩽ 4 Å), negatively charged Alq3 radical anions are formed by electron transfer from the Ca. The emergence of new states in the energy gap is observed in the UPS spectra. At higher coverages, the Ca reacts with the phenoxide oxygen resulting in the decomposition of the Alq3 molecule. On the other hand, for the case of Alq3 deposited on Ca, a strong chemical reaction takes place as soon as Alq3 is deposited, and Ca attacks every constituent of Alq3. Finally, no interaction occurs between Alq3 and the Ca substrate if the substrate has been passivated by oxygen prior to the Alq3 deposition. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Nonlinearity and scaling behavior in donor-doped lead zirconate titanate piezoceramic

Volkmar Mueller and Q. M. Zhang

Appl. Phys. Lett. 72, 2692 (1998); http://dx.doi.org/10.1063/1.121101 (3 pages) | Cited 28 times

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Two different effective thresholds for the onset of nonlinearity in the dielectric and piezoelectric coefficients of donor-doped lead zirconate titanate (soft PZT) piezoceramics at electric ac fields Ec1 ≈ 100 V/cm and Ec2 ≈ 1 V/cm are found. Both are characterized by a scaling behavior x = x0+A[E−Ec)/Ec]ϕ above the respective threshold, where x is the dielectric or piezoelectric coefficient. The values of the effective exponent ϕ are apparently independent of the particular ceramic system which suggests a universal behavior in soft PZT. We suggest that the nonlinearity is dominated by the dynamics of domain walls in a randomly pinned medium. © 1998 American Institute of Physics.  
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)

The kinetic glass transition of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass former-supercooled liquids on a long time scale

R. Busch and W. L. Johnson

Appl. Phys. Lett. 72, 2695 (1998); http://dx.doi.org/10.1063/1.121102 (3 pages) | Cited 72 times

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Viscosity and enthalpy relaxation from the amorphous state into the supercooled liquid state was investigated in the bulk metallic glass forming Zr46.75Ti8.25Cu7.5Ni10Be27.5 alloy below the calorimetric glass transition. At different temperatures, the viscosities relax into states that obey the same Vogel–Fulcher–Tammann relation as the data obtained at higher temperatures in the supercooled liquid. Enthalpy recovery experiments after relaxation in the same temperature range show that the enthalpy of the material reaches values that also corresponds to the supercooled liquid state. The glass relaxes into a metastable supercooled liquid state, if it is observed on a long time scale. Equilibration is possible far below the calorimetric glass transition and very likely even below the isentropic temperature. © 1998 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
65.20.-w Thermal properties of liquids
65.40.gd Entropy
66.20.-d Viscosity of liquids; diffusive momentum transport
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Manipulation and writing with Ag nanocrystals on Si(111)-7×7

S. Jay Chey, Lin Huang, and J. H. Weaver

Appl. Phys. Lett. 72, 2698 (1998); http://dx.doi.org/10.1063/1.121103 (3 pages) | Cited 6 times

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Manipulation of Ag nanocrystals derived from up to 200 000 atoms was performed using the tip of a scanning tunneling microscope. By varying the scanning conditions, it was possible to move them laterally on contamination-free Si(111)-7×7 surfaces or to remove them. In both cases, thin Ag tracks were left behind. This demonstrates the concepts of nano patterning and nano painting with metals on clean semiconductor surfaces. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
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