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28 Jun 2004

Volume 84, Issue 26, pp. 5299-5475

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Appl. Phys. Lett. 84, 5398 (2004); http://dx.doi.org/10.1063/1.1767591 (3 pages)

E. Menard, K. J. Lee, D.-Y. Khang, R. G. Nuzzo, and J. A. Rogers
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Nanopillar growth mode by vapor-liquid-solid epitaxy

J. L. Taraci, J. W. Dailey, T. Clement, David J. Smith, Jeff Drucker, and S. T. Picraux

Appl. Phys. Lett. 84, 5302 (2004); http://dx.doi.org/10.1063/1.1766076 (3 pages) | Cited 8 times

Online Publication Date: 17 June 2004

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We report epitaxial growth of Ge nanopillars (NPs) on Si (100) by vapor-liquid-solid (VLS) growth from digermane. This growth morphology is characterized by short, low-aspect-ratio pillars and is markedly different from the long, narrow nanowires (NWs) previously reported for VLS growth. The NP growth mode occurs at low digermane pressures. It is attributed to surface-diffusion-induced lateral growth in combination with an insufficient Ge concentration gradient in the AuGe eutectic to catalyze NW growth. High resolution electron microscopy confirms that the NPs are epitaxial with the Si (100) substrate and are fully relaxed and strain free.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Controlled carbon nanotube sheathing on ultrafine InP nanowires

L. W. Yin, Y. Bando, Y. C. Zhu, and M. S. Li

Appl. Phys. Lett. 84, 5314 (2004); http://dx.doi.org/10.1063/1.1766079 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2004

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Controlled carbon nanotube sheathing on ultrafine InP nanowires has been realized through a simple vapor–solid process. The synthesized InP–C nanocables were composed of crystalline InP core about 13–15 nm in diameter and parallel carbon sheath layers about several nanometers in thickness. The growth of the C layers takes place via a layer-by-layer process. The carbon tube sheathing can be controlled from several to more than 10 parallel layers by adjusting the deposition time. Both the carbon tube sheath and InP nanowire core show a higher degree of crystalline perfection. Graphitic carbon could act as chemically inert protecting layers for the ultrafine InP nanowires. This method could be applied to a wide range of materials and result in various hetrostructures, which may serve as potential building blocks in various nanodevices.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Vertical alignment of printed carbon nanotubes by multiple field emission cycles

Yong C. Kim, K. H. Sohn, Y. M. Cho, and Eun H. Yoo

Appl. Phys. Lett. 84, 5350 (2004); http://dx.doi.org/10.1063/1.1766403 (3 pages) | Cited 21 times

Online Publication Date: 17 June 2004

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The effect of field emission cycles on printed carbon nanotubes was investigated using scanning electron microscopy and current–voltage measurement. After multiple emission cycles, the printed nanotubes irreversibly deformed to orient themselves parallel to the field direction and, from them, remarkably enhanced emission image with good uniformity was demonstrated. Corresponding gradual decrease in the field emission threshold and increase of field enhancement factor (β) were also observed during field emission cycles.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Modeling the effect of subsurface interface defects on contact stiffness for ultrasonic atomic force microscopy

A. F. Sarioglu, A. Atalar, and F. L. Degertekin

Appl. Phys. Lett. 84, 5368 (2004); http://dx.doi.org/10.1063/1.1764941 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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We present a model predicting the effects of mechanical defects at layer interfaces on the contact stiffness measured by ultrasonic atomic force microscopy (AFM). Defects at subsurface interfaces result in changes at the local contact stiffness between the AFM tip and the sample. Surface impedance method is employed to model the imperfections and an iterative algorithm is used to calculate the AFM tip-surface contact stiffness. The sensitivity of AFM to voids or delaminations and disbonds is investigated for film-substrate combinations commonly used in microelectronic structures, and optimum defect depth for maximum sensitivity is defined. The effect of contact force and the tip properties on the defect sensitivity are considered. The results indicate that the ultrasonic AFM should be suitable for subsurface detection and its defect sensitivity can be enhanced by adjusting the applied force as well as by judicious choice of the AFM tip material and geometry.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.37.Tj Acoustic force microscopy

Atomic-scale characterization of perovskite superlattice using chemical lattice imaging and spatially resolved electron energy-loss spectroscopy

K. Kimoto, Y. Matsui, H. Yamada, M. Kawasaki, X. Yu, Y. Kaneko, and Y. Tokura

Appl. Phys. Lett. 84, 5374 (2004); http://dx.doi.org/10.1063/1.1767279 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2004

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The layered structure of a perovskite tricolor superlattice {SrTiO3(STO)/LaAlO3(LAO)/La0.6Sr0.4MnO3(LSMO)}n on an STO substrate is investigated using transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Conventional TEM imaging is not effective for thickness evaluation, in which both LAO and LSMO layers show the same image contrast because of the similarity in their mean atomic numbers. We observe 001 lattice fringes, which are chemically sensitive in the case of the perovskite structure ABO3, since the 001 structure factor is proportional to the difference between A- and B-site atomic scattering factors. The thickness of each layer is evaluated with an accuracy of one unit cell. We also apply spatially resolved EELS to analyze the depth profile of Ti, Mn, and La contents.
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68.65.Cd Superlattices
79.20.Uv Electron energy loss spectroscopy

Percolation network of growing V2O5 nanowires

Yu Jin Chang, Byung Hyun Kang, Gyu Tae Kim, Sung Joon Park, and Jeong Sook Ha

Appl. Phys. Lett. 84, 5392 (2004); http://dx.doi.org/10.1063/1.1767284 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2004

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Percolation network of the growing V2O5 nanowires was demonstrated by devising a simple but practical method to investigate the percolation phenomena. As the reaction proceeded in the ammonium(meta)vanadate solution at room temperature, the lengths of V2O5 nanowires increased at a speed of 0.13 μm/day at an early stage of the growth and 0.03 μm/day on the average up to 3 months. Percolation network was made by abruptly freezing the homogeneously dispersed aqueous solutions of V2O5 nanowires in liquid nitrogen. After 7 h of aging time, an abrupt increase of the conductance was observed, revealing the satisfaction of the percolation threshold (pc ∼ 0.17) at the average wire length of 40 nm.
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61.46.-w Structure of nanoscale materials
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
73.61.Ng Insulators

Chemistry-mediated two-dimensional to three-dimensional transition of In thin films

H. L. Wei, Hanchen Huang, C. H. Woo, X. X. Zhang, and L. G. Zhou

Appl. Phys. Lett. 84, 5401 (2004); http://dx.doi.org/10.1063/1.1767595 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2004

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This letter reports a mechanism of chemistry-mediated two-dimensional to three-dimensional (2D–3D) transition during In thin film deposition, and the corresponding evolution of nanoscale islands. Using magnetron sputtering technique, we deposit In on Au substrate. Despite the fact that In wets on Au, In islands prevail over the uniform film soon after the deposition starts. The 2D–3D transition is found to be a result of the formation of Au3In on the Au substrate. The alloy formation leads to nonwetting of In, thereby the high mobility of In atoms and In clusters, and eventually well-separated In islands. The structures of In and Au are characterized by scanning electron microscopy, transmission electron microscopy, and electron diffraction.
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64.70.K- Solid-solid transitions
81.15.Cd Deposition by sputtering
82.30.Nr Association, addition, insertion, cluster formation
81.05.Bx Metals, semimetals, and alloys
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
82.33.Hk Reactions on clusters
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.46.-w Structure of nanoscale materials

Formation of Ge nanocrystals in HfAlO high-k dielectric and application in memory device

Ying Qian Wang, Jing Hao Chen, Won Jong Yoo, Yee-Chia Yeo, Sun Jung Kim, Rohit Gupta, Zerlinda Y. L. Tan, Dim-Lee Kwong, An Yan Du, and N. Balasubramanian

Appl. Phys. Lett. 84, 5407 (2004); http://dx.doi.org/10.1063/1.1767597 (3 pages) | Cited 29 times

Online Publication Date: 17 June 2004

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Formation of Ge nanocrystals embedded in HfAlO high-k dielectric by co-sputtering of HfO2, Al2O3, and Ge, followed by rapid thermal annealing was demonstrated. Analysis by transmission electron microscopy and x-ray photoelectron spectroscopy confirmed the formation of nonoxidized Ge nanocrystals with a minimum size of about 5 nm embedded in HfAlO dielectric. We also demonstrated the application of such nanocrystals in nonvolatile memory devices, achieving a 2.2 V memory window as obtained from the C–V characterization of the memory device.
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61.46.-w Structure of nanoscale materials
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces
84.30.Sk Pulse and digital circuits
61.72.Cc Kinetics of defect formation and annealing

Coulomb blockade in suspended Si3N4-coated single-walled carbon nanotubes

H. B. Peng and J. A. Golovchenko

Appl. Phys. Lett. 84, 5428 (2004); http://dx.doi.org/10.1063/1.1765733 (3 pages) | Cited 9 times

Online Publication Date: 17 June 2004

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Uniform coaxial coating of suspended single-walled carbon nanotubes with high-quality dielectric silicon nitride has been obtained by low-pressure chemical vapor deposition. A three-terminal device has been demonstrated by coating a suspended metallic nanotube grown directly on contacting metal electrodes with subsequent patterning of a top gate electrode. Large charging energies have been observed in the suspended nanotubes and the conversion factor from gate voltage to the electrostatic potential in the nanotube approaches unity, which can be attributed to the device geometry.
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73.23.Hk Coulomb blockade; single-electron tunneling
81.07.De Nanotubes

Carbon nanotube electron source based ionization vacuum gauge

Changkun Dong and Ganapati R. Myneni

Appl. Phys. Lett. 84, 5443 (2004); http://dx.doi.org/10.1063/1.1767956 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2004

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The results of fabrication and performance of an ionization vacuum gauge using a carbon nanotube electron source are presented. The electron source was constructed with multiwall nanotubes, which were grown using thermal chemical vapor deposition. The electron emission of the source was stable in vacuum pressure up to 10−7 Torr, which is better than the metal field emitters. The measurement linearity of the gauge was better than ±10% from 10−6 to 10−10 Torr. The gauge sensitivity of 4 Torr−1 was achieved under 50 μA electron emission in nitrogen. The gauge is expected to find applications in vacuum measurements from 10−7 Torr to below 10−11 Torr.
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85.35.Kt Nanotube devices
07.30.Dz Vacuum gauges
07.77.Ka Charged-particle beam sources and detectors

Electron field emission from SiC/Si heterostructures by high temperature carbon implantation into silicon

Y. M. Xing, J. H. Zhang, W. W. Yang, Y. H. Yu, Z. R. Song, Z. X. Lin, and D. S. Shen

Appl. Phys. Lett. 84, 5461 (2004); http://dx.doi.org/10.1063/1.1767958 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2004

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A high-intensity electron field emission was obtained from a SiC/Si heterostructure, which was formed by high temperature carbon implantation into silicon. Densely distributed sharp tips were easily obtained at the interface of the SiC/Si heterostructure by post-implantation etching off the top Si. A low turn-on field of 2.6 V/μm was observed with samples formed by 160 keV carbon implantation with a dose of 8.0×1017 cm−2. The existence of the densely distributed small protrusions was considered as the main reason for efficient emission.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
61.72.uf Ge and Si

Electromechanical stiffening of rods and tubes

Roya Zandi, Ramin Golestanian, and Joseph Rudnick

Appl. Phys. Lett. 84, 5467 (2004); http://dx.doi.org/10.1063/1.1757018 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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Electrostatic interactions are shown to exert a significant effect on the buckling instability of a rod. In particular, the threshold value of the compressional force needed to induce buckling is found to be independent of rod length for long charged rods. In the case of rods of intermediate length, the critical buckling force crosses over from the classic inverse-square length dependence to asymptotic length-independent form with increasing rod length. It is suggested that this effect leads to the possibility of electromechanical stiffening of nanotubes, which would allow relatively long segments of them to be used as atomic force probes. © 2004 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems

Hexagonal-to-cubic phase transformation in GaN nanowires by Ga+ implantation

S. Dhara, A. Datta, C. T. Wu, Z. H. Lan, K. H. Chen, Y. L. Wang, C. W. Hsu, C. H. Shen, L. C. Chen, and C. C. Chen

Appl. Phys. Lett. 84, 5473 (2004); http://dx.doi.org/10.1063/1.1760593 (3 pages) | Cited 14 times

Online Publication Date: 17 June 2004

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Hexagonal to cubic phase transformation is studied in focused ion beam assisted Ga+-implanted GaN nanowires. Optical photoluminescence and cathodoluminescence studies along with high-resolution transmission electron microscopic structural studies are performed to confirm the phase transformation. In one possibility, sufficient accumulation of Ga from the implanted source might have reduced the surface energy and simultaneously stabilized the cubic phase. Another potential reason may be that the fluctuations in the short-range order induced by enhanced dynamic annealing (defect annihilation) with the irradiation process stabilize the cubic phase and cause the phase transformation. © 2004 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.55.Cr III-V semiconductors
61.46.-w Structure of nanoscale materials
78.60.Hk Cathodoluminescence, ionoluminescence
68.37.Lp Transmission electron microscopy (TEM)
68.35.Md Surface thermodynamics, surface energies
81.40.Gh Other heat and thermomechanical treatments
61.80.Jh Ion radiation effects
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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