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30 Sep 2002

Volume 81, Issue 14, pp. 2493-2662

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Composition of self-assembled Ge/Si islands in single and multiple layers

O. G. Schmidt, U. Denker, S. Christiansen, and F. Ernst

Appl. Phys. Lett. 81, 2614 (2002); http://dx.doi.org/10.1063/1.1507612 (3 pages) | Cited 47 times

Online Publication Date: 23 September 2002

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The degree of Si alloying in vertically aligned self-assembled Ge islands increases with the number of stacked layers. We find that the Si–Ge interdiffusion coefficient increases by more than two orders of magnitude for stacked hut clusters. Furthermore, we determine the composition profiles through the center of dome-shaped islands, capped with Si. These profiles exhibit a plateau near the base and a Ge enrichment near the apex of the islands. In this case, too, the upper dome island experiences a state of increased alloying with Si. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.65.Ac Multilayers
68.35.Fx Diffusion; interface formation

How nanocavities in amorphous Si shrink under ion beam irradiation: An in situ study

M.-O. Ruault, F. Fortuna, H. Bernas, M. C. Ridgway, and J. S. Williams

Appl. Phys. Lett. 81, 2617 (2002); http://dx.doi.org/10.1063/1.1509854 (3 pages) | Cited 5 times

Online Publication Date: 23 September 2002

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Nanocavities were formed in Si substrates by conventional H implantation and thermal annealing, after which the samples were amorphized by Si ion irradiation. The size evolution of the nanocavities was monitored in situ during further ion irradiation with Si or As at temperatures of 300 or 600 K. The decrease in nanocavity diameter during ion irradiation depended linearly on the ion fluence. The rate of shrinkage differed according to the ion beam-induced atomic displacement rate and had little or no temperature dependence. These in situ results shed new light on possible ion-beam-induced nanocavity shrinkage mechanisms. © 2002 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.43.Dq Amorphous semiconductors, metals, and alloys
61.46.-w Structure of nanoscale materials
61.72.uf Ge and Si
61.82.Fk Semiconductors

Scanning force microscopy jumping and tapping modes in liquids

F. Moreno-Herrero, P. J. de Pablo, R. Fernández-Sánchez, J. Colchero, J. Gómez-Herrero, and A. M. Baró

Appl. Phys. Lett. 81, 2620 (2002); http://dx.doi.org/10.1063/1.1509856 (3 pages) | Cited 17 times

Online Publication Date: 23 September 2002

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In this work theoretical considerations of the performance of scanning force microscopy jumping mode and tapping mode in liquids are discussed. A priori, jumping mode should improve in a liquid environment compared to in air while the situation for tapping mode should become worse. In order to confirm this we present jumping and tapping mode images of DNA molecules absorbed on a mica substrate immersed in water. The experiments demonstrate that jumping mode is a suitable scanning force microscopy method by which to image soft samples in liquid and that it has similar or even better performance than those exhibited by tapping, but without the complex experimental requirements of this mode. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
87.64.Dz Scanning tunneling and atomic force microscopy
68.43.Fg Adsorbate structure (binding sites, geometry)
87.14.G- Nucleic acids

Adhesive forces investigation on a silicon tip by contact-mode atomic force microscope

Vincent Agache, Bernard Legrand, Dominique Collard, and Lionel Buchaillot

Appl. Phys. Lett. 81, 2623 (2002); http://dx.doi.org/10.1063/1.1508806 (3 pages) | Cited 3 times

Online Publication Date: 23 September 2002

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An atomic force microscope operating in contact mode is used in this letter for probing the adhesive forces at the apex of a silicon nanotip with typical radius smaller than 15 nm, fabricated using a combination of high-resolution electron beam lithography and plasma dry etching. The amplitude of the forces is deduced from force versus distance curve measurements. By determining the contact point and the pull-off force from the force curves, the surface topography and the adhesive forces are simultaneously obtained at various locations on the surface. This letter reports both measurements and modeling of adhesive forces versus the contact point on the nanotip. As the nanotip is sharper and has a smaller aperture angle than the employed atomic force microscope tip, the measurements are focused on the nanotip apex. © 2002 American Institute of Physics.
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68.35.Np Adhesion
68.37.Ps Atomic force microscopy (AFM)
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
07.79.Lh Atomic force microscopes
52.77.Bn Etching and cleaning

Gas-phase nanoparticle formation during AlGaN metalorganic vapor phase epitaxy

J. R. Creighton, W. G. Breiland, M. E. Coltrin, and R. P. Pawlowski

Appl. Phys. Lett. 81, 2626 (2002); http://dx.doi.org/10.1063/1.1510580 (3 pages) | Cited 9 times

Online Publication Date: 23 September 2002

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Using in situ laser light scattering, we have directly observed the formation of gas-phase nanoparticles during AlN, GaN, and AlGaN metalorganic vapor phase epitaxy. The nanoparticles are sharply distributed in height 6 mm from the surface, in good agreement with a model based on a balance between thermophoretic and convective forces. By measuring the angular dependence of the scattering intensity, we determined that the AlN particle sizes were 35–50 nm, and particle densities were 1–6×108 cm−3, which corresponds to 20%–80% of the input Al being converted into nanoparticles. © 2002 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Ya Chemistry of MOCVD and other vapor deposition methods

Dopant profiling on semiconducting sample by scanning capacitance force microscopy

Kei Kobayashi, Hirofumi Yamada, and Kazumi Matsushige

Appl. Phys. Lett. 81, 2629 (2002); http://dx.doi.org/10.1063/1.1510582 (3 pages) | Cited 17 times

Online Publication Date: 23 September 2002

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Scanning capacitance force microscopy (SCFM) capable of mapping differential capacitance (∂C/∂V) on semiconducting sample based on atomic force microscopy (AFM) without an external capacitance sensor is introduced. While an electric field alternating at an angular frequency ω is applied between the tip and the sample, an induced electrostatic force (ESF) oscillating at its third harmonic frequency (3ω) is detected by a lock-in amplifier. Owing to the fact that the magnitude of the induced ESF is proportional to the square of the magnitude of the applied electric field and the fact that the capacitance of the semiconducting sample is also modulated at ω, the amplitude and the phase of the induced ESF oscillating at 3ω contain information on ∂C/∂V. We present ∂C/∂V images on a Si test sample obtained by SCFM using both contact-mode AFM and dynamic-mode AFM, showing clear contrasts depending on species and density of dopants. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
61.72.S- Impurities in crystals
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Fabrication of stable nanopatterns on metals

Daiichiro Sekiba, Stefania Bertero, Renato Buzio, Francesco Buatier de Mongeot, Corrado Boragno, and Ugo Valbusa

Appl. Phys. Lett. 81, 2632 (2002); http://dx.doi.org/10.1063/1.1511534 (3 pages) | Cited 5 times

Online Publication Date: 23 September 2002

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Nanopatterns on metal surfaces can be easily created by ion sputtering. However, due to the fast diffusion processes characterizing these materials, the nanostructures are often unstable at room temperature and above. This effect prevents the use of such patterned substrates in nanotechnology applications. In this letter, we present a simple oxidation process able to stabilize these features durably. The method has been tested on Cu, but its generality suggests that it can be applied to many other metals. © 2002 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Pr Micro- and nano-oxidation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Generation of palladium clusters on Au(111) electrodes: Experiments and simulations

M. Del Popolo, E. Leiva, H. Kleine, J. Meier, U. Stimming, M. Mariscal, and W. Schmickler

Appl. Phys. Lett. 81, 2635 (2002); http://dx.doi.org/10.1063/1.1511285 (3 pages) | Cited 18 times

Online Publication Date: 23 September 2002

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The properties of palladium clusters, generated with the electrochemical scanning tunneling microscope, have been investigated both by experiments and by computer simulations. The clusters are found to be larger and more stable if the tip is moved further towards the electrode surface in the generation process. The simulations suggest that the larger clusters consist of a palladium–gold mixture, which is more stable than pure palladium. Dissolution of the clusters occurs from the edges rather than layer by layer. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
82.45.Qr Electrodeposition and electrodissolution
81.16.Be Chemical synthesis methods
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.07.-b Nanoscale materials and structures: fabrication and characterization
82.33.Hk Reactions on clusters

Effect of H2O adsorption on electron transport in a carbon nanotube

Ranjit Pati, Yiming Zhang, Saroj K. Nayak, and Pulickel M. Ajayan

Appl. Phys. Lett. 81, 2638 (2002); http://dx.doi.org/10.1063/1.1510969 (3 pages) | Cited 47 times

Online Publication Date: 23 September 2002

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We have studied the adsorption of H2O molecules on a single-wall carbon nanotube (NT) using first-principles gradient-corrected density-functional theory. Subsequently, Green’s function-based Landauer–Büttiker multichannel formalism within a tight-binding model is used to calculate the electron transport, and our results suggest that H2O molecules adsorbed on the NT surface reduce the electronic conduction in the tube in agreement with recent experimental measurements. The decrease of conductance with water adsorption is explained on the basis of charge transfer between the adsorbate and the NT. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Operation of nanomechanical resonant structures in air

L. Sekaric, M. Zalalutdinov, R. B. Bhiladvala, A. T. Zehnder, J. M. Parpia, and H. G. Craighead

Appl. Phys. Lett. 81, 2641 (2002); http://dx.doi.org/10.1063/1.1511287 (3 pages) | Cited 15 times

Online Publication Date: 23 September 2002

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We report on the resonant operation of high-quality-factor silicon nanomechanical structures in air and at room temperature. We describe techniques used to actuate and detect nanomechanical structures in atmosphere, resulting in the enhancement of the effective quality factor to above 1000 and demonstrate the potential for successful sensor operation of resonant nanomechanical structures under ambient conditions. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems

Formation of a quantum dot in a single-walled carbon nanotube using the Al top-gates

J. W. Park, J. B. Choi, and K.-H. Yoo

Appl. Phys. Lett. 81, 2644 (2002); http://dx.doi.org/10.1063/1.1510578 (3 pages) | Cited 9 times

Online Publication Date: 23 September 2002

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We have fabricated gate-controlled carbon-nanotube single-electron devices by utilizing the line-shaped Al top-gates. A quantum dot is formed in the single-walled carbon nanotube between two Al top-gates fabricated using the electron-beam lithography technique. The deposited top-gates flatten the single-walled carbon nanotube locally and the deformed regions play the role of tunneling barrier, whose potential is controlled by the top-gates. We have also investigated the temperature dependence of the conductance G for the devices with the Al top-gates. The power-law dependence, G∝Tα, is observed at high temperatures. However, the exponent α increases as the barrier potential is enhanced. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots

Raman characterization of boron-doped multiwalled carbon nanotubes

J. Maultzsch, S. Reich, C. Thomsen, S. Webster, R. Czerw, D. L. Carroll, S. M. C. Vieira, P. R. Birkett, and C. A. Rego

Appl. Phys. Lett. 81, 2647 (2002); http://dx.doi.org/10.1063/1.1512330 (3 pages) | Cited 41 times

Online Publication Date: 23 September 2002

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We present first- and second-order Raman spectra of boron-doped multiwalled carbon nanotubes. The Raman intensities are analyzed as a function of the nominal boron concentration. The intensities of both the D mode and the high-energy mode in the first-order spectra increase with increasing boron concentration, if normalized with respect to a second-order mode. We interpret this result as an indication that the high-energy mode in carbon nanotubes is defect-induced in a similar way as the D mode. Based on this result, we provide a preliminary quantitative relation between the boron concentration and the Raman intensity ratios. © 2002 American Institute of Physics.
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78.67.Ch Nanotubes
78.30.Hv Other nonmetallic inorganics
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
63.20.kp Phonon-defect interactions
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