Field emission from single-walled carbon nanotubes aligned on a gold plate using a self-assembly monolayer

Field emission from single-walled carbon nanotubes (SWNTs) aligned on a patterned gold surface is reported. The SWNT emitters were prepared at room temperature by a self-assembly monolayer technique. SWNTs were cut into sub-micron lengths by sonication in an acidic solution. Cut SWNTs were attached to the gold surface by the reaction between the thiol groups and the gold surface. The field-emission measurements showed that the turn-on field was 4.8 V/μm at an emission current density of 10 μA/cm². The current density was 0.5 mA/cm² at 6.6 V/μm. This approach provides a novel route for fabricating CNT-based field-emission displays. Received: 3 May 2002 / Accepted: 6 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +82-54/279-8298, E-mail: ce20047@postech.ac.kr     

Low-threshold field electron emission of Si micro-tip arrays produced by laser ablation

Low-threshold field electron emission (FEE) is reported for periodic arrays of micro-tips produced by laser ablation of Si wafers. The best samples show emission at threshold fields as low as 4–5 V/μm for n-type Si substrates and of 1–2 V/μm for p-doped Si substrates, as measured with a flat-screen technique. Auger electron spectroscopy and X-ray electron spectroscopy reveal island-like deviation of the SiO₂ stoichiometry on the tip surfaces, with lateral dimensions of less than 100 nm. Microscopic studies using a special field-emission STM show that the emission originates from well-conducting regions of sub-micron size. The experimental data suggest FEE from the tip arrays by a geometric field enhancement of both the individual micro-tip and the narrow conducting channels in the tip body. Received: 3 May 2002 / Accepted: 1 July 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +7-095/135-82-34, E-mail: shafeev@kapella.gpi.ru     

Nanoscale effects in focused ion beam processing

Focused ion beams with diameters of 8 to 50 nm are used for material processing in the nanoscale regime. In this paper, effects of the ion beam–solid interaction determining the formation of small structures by ion-beam sputtering and chemically assisted material deposition and etching are investigated. In the case of decreasing feature size, angle-dependent sputtering, a non-constant sputter rate, and scattered ions play an important role. The impact on side-wall angle, aspect ratio, and shape of the bottom of the etched structures is discussed. In beam tail regions, these effects will be especially pronounced, leading to material swelling instead of material removal. Ion beam assisted etching and deposition will face additional effects. For small structures, gas depletion becomes a significant drawback. The impact on gas depletion and the competition with sputtering are discussed. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-9131/761360, E-mail: frey@iis-b.fhg.de     

Integration of ZnO nanowires in gated field emitter arrays for large-area vacuum microelectronics applications

Addressable field emitter arrays (FEAs) have important applications in vacuum electronic devices. However, it is important to integrate nanowire emitters into a gated structure without influencing the device structure and maintain the excellent field emission properties of nanowire emitters in the FEAs after the fabrication process. In this study, gate-structure ZnO nanowire FEAs were fabricated by a microfabrication process. The structure combines a planar gate and an under-gate, which is compatible with the preparation of ZnO nanowire emitters. The effect of electrode materials on the field emission properties of ZnO nanowires was studied using a diode structure, and it was found that ZnO nanowire pads on indium-tin-oxide (ITO) electrode showed better field emission performance compared with chromium (Cr) electrode. In addition, effective emission current modulation by the gate voltage was achieved and the addressing capability was demonstrated by integrating the ZnO nanowire FEAs in a vacuum-encapsulated field emission display. The reported technique could be a promising route to achieve large area addressable FEAs.     

Morphologies and optical properties of poly(2,5-diethoxyphenylene) nanofibril arrays

An anodic aluminum oxide (AAO) membrane can be used as a template for the synthesis of nanostructures. In this paper, we have fabricated poly(2,5-diethoxyphenylene) (EtO-PPP) nanofibril arrays by oxidative coupling polymerization of 1,4-diethoxybenzene (DEB) within the pores of an AAO template. The detailed molecular structure of the polymer nanofibrils was characterized by using the infrared spectrum and the ¹H-NMR spectrum. We have used transmission electron microscopy, scanning electron microscopy, and atomic force microscopy to confirm the morphologies and images of the template and the fabricated nanometer scale of poly(2,5-diethoxyphenylene)nanofibril arrays. The experimental results demonstrate that the pores of the AAO membrane are regular and uniform, and parallel to each other. Furthermore, the EtO-PPP chains in the narrowest template-synthesized fibrils were oriented parallel to the pore axes of the AAO membrane, and perpendicular to the surface of the aluminum substrate. The polymer chain orientation is partially responsible for the enhanced conductivity. The ultraviolet absorption maximum shows that the polymer contains a better extended π-conjugation system along the poly(p-phenylene) backbone, which results in a longer-wavelength shift of the absorption band. The photoluminescence (PL) spectrum of nanofibril arrays exhibits a 5-nm blue shift of the emission in comparison with the unordered molecules. Received: 3 January 2002 / Accepted: 7 January 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-931/891-1100, E-mail: lihl@lzu.edu.cn     

Transient-diffusion effects

Transient effects on diffusion and activation during post-implantation anneals are a major obstacle for the further miniaturization of ultra-large-scale integrated semiconductor devices. The article reviews recent developments in the simulation of such phenomena with particular emphasis on models for the kinetics of self-interstitial agglomerates and boron–interstitial clusters. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-9131/761-212, E-mail: pichler@iis-bfhg.de     

Copper nanowire arrays for infrared polarizer

A micropolarizer of copper nanowire arrays within anodic alumina membrane (AAM) was fabricated by anodization of pure Al foil and electrodeposition of Cu, respectively. X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations reveal that the ordered Cu nanowires are essentially single crystal, and have an average diameter of 90 nm. Spectrophotometer measurements show that the copper nanowire arrays embedded in AAM can only transmit polarized light vertical to the wires. An extinction ratio of 24 to 32 dB and an average insertion loss of 0.5 dB in the wavelength range of 1 to 2.2 μm were obtained, respectively. Therefore Cu nanowire/AAM can be used as a wire grid type micropolarizer. Received: 28 January 2002 / Accepted:17 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: ytpang@263.net     

Photofabrication of periodic microstructures in azodye-doped polymers by interference of laser beams

Volume holographic gratings and two-dimensional periodic microstructures in azodye-doped polymethylmethacrylate were fabricated, respectively, by interference of two coherent beams of a femtosecond laser and by interference of three coherent beams of a nanosecond laser. The dependence of the first-order Bragg diffraction efficiency and the photoinduced refractive-index modulation of the gratings on the intensity of the writing light was investigated. The measurements of the absorption spectra before and after irradiation with the writing light suggest that the photoinduced gratings were refractive-index-modulated gratings, which arose from a photoinduced decomposition reaction of the azodye molecules through multiphoton absorption. In the experiments involving the interference of three beams, the period of the two-dimensional periodic microstructures was changed by adjusting the angle between the three writing beams. Received: 10 July 2002 / Revised version: 5 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-774/955206, E-mail: jhsi@photon.jst.go.jp     

Enhanced field emission from ZnO nanopencils by using pyramidal Si(1 0 0) substrates

Zinc oxide nanopencil arrays were synthesized on pyramidal Si(1 0 0) substrates via a simple thermal evaporation method. Their field emission properties have been investigated: the turn-on electric field (at the current density of 10 μA/cm²) was about 3.8 V/μm, and the threshold electric field (at the current density of 1 mA/cm²) was 5.8 V/μm. Compared with similar structures grown on flat Si substrates, which were made as references, the pyramidal Si-based ZnO nanopencil arrays appeared to be superior in field emission performance, thus the importance of the non-flat substrates has been accentuated. The pyramidal Si substrates could not only suppress the field screening effect but also improve the field enhancement effect during the field emission process. These findings indicated that using non-flat substrates is an efficient strategy to improve the field emission properties.     

3-D microstructuring inside photosensitive glass by femtosecond laser excitation

We show that a femtosecond laser enables us to produce true three-dimensional (3-D) microstructures embedded in a photosensitive glass, which has superior properties of transparency, hardness and chemical and thermal resistances. The photosensitivity arises from the cerium in the glass. After exposure to a focused laser beam, latent images are written. Modified regions are developed by a post-baking process and then preferentially etched away in a 10% dilute solution of hydrofluoric acid at room temperature. We have measured the critical dose for modification of the photosensitive glass, and fabricated 3-D microstructures with microcells and hollow microchannels embedded in the glass based on the critical dose. Received: 12 August 2002 / Accepted: 13 August 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-48/468-4682, E-mail: mmasudaw@postman.riken.go.jp     

Spectroscopy of cesium atoms adsorbing and desorbing at a dielectric surface

We use evanescent waves in a counterpropagating beams configuration to study the adsorption/desorption processes at a Cs vapor/dielectric interface in a sealed cell. Atoms close to the surface are velocity-selectively spin-polarized before adsorption by an amplitude-modulated pump beam. We subsequently observe the contribution of the desorbed atoms to the probe-beam absorption by way of phase-sensitive detection. We measure the number of desorbing polarized Cs atoms as a function of the surface temperature. The analysis of results is done through a simple thermodynamical model for the atomic desorption and we discuss its validity to infer the adsorption energy of the cesium atoms on a fused-quartz surface. Received: 15 May 2002 / Revised version: 7 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +55-83/216-7513, E-mail: martine@otica.ufpb.br     

Deterministic coupling of single ions to an optical cavity

By combining the technologies of ion trapping and cavity QED, we have achieved deterministic coupling of single ions to an optical field. By Doppler cooling, the spread of the ion’s wavepacket was reduced to 42 nm, corresponding to Lamb–Dicke localization. As an application, we have measured the three-dimensional structure of cavity eigenmodes with sub-wavelength precision. The setup presented is suited for the controlled coherent processing of atomic and photonic quantum information. Examples include the triggered generation of single photons and two-ion quantum gates. Received: 20 August 2002 / Revised version: 16 December 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: keller@mpq.mpg.de     

Preparation of one-dimensional porous silicon photonic quantum-well structures

One-dimensional porous silicon (PSi) photonic quantum-well structures have been electrochemically fabricated and spectroscopically characterized. The photonic well in the structure is a photonic crystal (PC) consisting of alternately stacked high- and low-refractive-index PSi layers. Discrete states are observed in both reflectance and transmission spectra. It is found that the number of confined states appearing in the photonic bandgap of the photonic barrier depends on the number of periods adopted in the well PC. Thus, increased confined photonic states can be created simply by increasing the number of periods of the well PC in the structures. Received: 26 February 2002 / Accepted: 17 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6510-4949, E-mail: xyhou@fudan.edu.cn     

Electrochemical synthesis of ordered CdTe nanowire arrays

Semiconductor CdTe nanowire arrays embedded in the nanochannels of the porous anodic alumina (PAA) template have been prepared by using a potentiostatic electrochemical deposition method. The morphology and structure of the CdTe nanowire arrays have been characterized by X-ray powder diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. It is found that the CdTe nanowires with diameters and lengths of about 60 nm are single-crystalline with cubic phase structure, uniformly and continuously embedded in the nanochannels of the PAA template. X-ray energy-dispersion analysis and X-ray photoelectron spectroscopy analysis indicate that stoichiometric CdTe was formed. The growth mechanism of the CdTe nanowires is also discussed. Received: 11 June 2002 / Accepted: 2 July 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: aiwuzhao@yahoo.com.cn     

Nanoscale domain switching mechanism in Pb(Zr,Ti)O<Subscript>3</Subscript> thin film

Pb(Zr,Ti)O₃ (PZT) ferroelectric thin film was prepared by the sol-gel technique and crystallized with a (111) preferred orientation. The domain structure and polarization reversal behavior were investigated by using scanning force microscopy (SFM) piezoresponse mode at the nanometer scale. A step structure of approximately 30 nm in width was directly observed, which was formed during the polarization reversal process. The presence of the step structure reveals that the forward domain-growth mechanism is the dominant domain-switching process in our PZT thin films. Received: 6 August 2002 / Accepted: 9 August 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/5241-3122, E-mail: huarongzeng@163.net     

Ordered thin films of alkyloxy-substituted benzaldehydes on a graphite surface studied by scanning tunneling microscopy

The molecular assembly of three different trialkyloxy-substituted benzaldehydes on graphite has been studied using scanning tunneling microscopy (STM). It is found that these benzaldehydes, which do not have intermolecular hydrogen bonding, could form a lamella arrangement in which the headgroups are aligned side by side. The effect due to the alkyl chain length on the lamella structure is also presented. Received: 21 January 2002 / Accepted: 22 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-10/6255-7908     

Quantum interference spectra at the difference-frequency generation in four-level atomic systems

Analytical expressions of the spectral functions have been derived for a number of induced excitations that occur near the difference-frequency generation in a four-level atomic system interacting with three laser fields. The spectral heights and subnatural line widths of the induced peaks depend on the intensities of the laser fields involved. The maximum heights of the induced peaks take positive, zero and negative values, indicating that the processes of absorption (attenuation), dark resonance and stimulated emission (amplification) are likely to occur near the difference-frequency generation, respectively. Received: 15 March 2002 / Revised version: 17 June 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +1-613-954-5242     

Axial non-uniformity of longitudinal hollow-cathode discharges for laser applications: numerical modeling and comparison with experiments

It is demonstrated by means of numerical modeling that longitudinal hollow-cathode discharges (HCDs) typically used for laser applications are strongly non-uniform in the axial direction. Two kinds of HCDs are investigated; those having one anode ring and those having two anode rings at opposite ends of the HCD tube. The HCD under study was made of copper and operated in a mixture of helium and argon. The calculated potential varied considerably in the axial direction. The densities of the major plasma species showed no maxima in the middle of the HCD, but rather at the anode side(s). The same applied to the sputtering rate at the cathode and the electron-impact ionization and excitation rates in the plasma. The calculation results for both configurations have been compared with measured data, i.e. with the electric current and the optical emission intensities of He (I) and Cu (I) lines as a function of axial position, and reasonable agreement has been reached. Received: 25 June 2002 / Revised version: 29 August 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +32-3/820-23-76, E-mail: annemie.bogaerts@ua.ac.be     

Extended defects in shallow implants

Extended defects are often found after ion implantation and annealing of silicon and they are known to affect dopant diffusion. The article reviews the structure and energetics of the most often found extended defects and describes the mechanisms by which all these defects grow in size and transform during annealing. Defects grow by interchanging the Si atoms they are composed of and thus maintain large supersaturations of free Si interstitials in the region. A model has been developped to describe such an evolution in presence of a free surface. It is shown that after low energy implantation, the surface of the wafer may recombine large amounts of these free Si interstitials, driving defects into dissolution before transformation into more stable forms. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +33-56/2257-999, E-mail: claverie@cemes.fr     

Fabrication and characterization of photonic crystals with well-controlled thickness and stop-band attenuation

Photonic crystals with stop bands located in the visible region have been fabricated by crystallizing monodispersed spherical colloids (made of polystyrene or silica) into cubic-close-packed lattices within specially designed packing cells. These crystals were oriented with their (111) planes parallel to their solid supports, and the number of these planes could be conveniently controlled from 13 to 127 layers by varying the thickness of packing cells. In accordance, the stop-band attenuation of these crystals monotonically increased from 1 to 21 dB. Our transmission spectral measurements indicated that there exists a non-linear dependence between the stop-band attenuation and the total number of (111) planes, and this dependence could be quantitatively simulated using the dynamic light scattering model or the photonic analogy to KKR method. The colloidal crystals presented here should find use as components in fabricating optical devices that include sensors, mirrors, filters, switches and waveguides. Received: 17 May 2002 / Accepted: 25 July 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-206/685-8665, E-mail: xia@chem.washington.edu