Nanoscale Electrocrystallization Research Articles

Investigation of copper nanoscale electro-crystallization under directed and non-directed electrodeposition from dilute electrolytes

In situ and ex situ atomic force microscopy was used to investigate crystal growth in copper electro-crystallization localized and directed by a moving nanoelectrode in close proximity to a gold substrate in a highly dilute electrolyte.

(Invited) Nanoscale Electrocrystallization: A Site-Selective Electrochemical π-Figuration of Nanocrystals for Electronic Devices

Efficient nanofabrication is still the problem awaiting solution in the nanotechnology field. Such nanofabrication should involve both economy and ecology-friendly process which produces high performance materials or devices. As seen in semiconductor industry, these fabrication technologies generally consume a large amount of energy under high-vacuum and/or high-temperature conditions. There is a strong need to switch to processes which are both eco-friendly and low-cost. Therefore pinpoint nanofabrication via eco-friendly process seems to be most promising. From the viewpoint, we have developed nanoscale electrocrystallization for nanodevice fabrication.1 This method allows everyone to grow nanocrystals, which consist of π-conjugated molecules, site-selectively within a gap between two electrodes fabricated on a substrate. In addition, this method also allows for the gap between the two electrodes to be bridged by the formed nanocrystals. · Magnetic field effect devices Magnetic field effect devices were designed by using dicyanoiron(III)phthalocyanine ([Fe(Pc)(CN)2]-) tetraphenylphosphonium (TPP+) salt as a starting material of nanoscale electrocrystallization. The electrolysis gave nanocrystals that exhibited a strong correlation between the localized spin and conduction electrons, TPP·[Fe(Pc)(CN)2]2 was obtained. A negative giant magnetoresistance was first observed as an organic nanocrystal.2 Moreover, an angular dependence of the negative giant magnetoresistance that originates from the highly oriented growth of the nanocrystals was also observed. · Electronic field effect devices Electronic field effect devices such as field-effect transistors (FETs) were designed by using materials for organic conductors. A bottom-gate type FET structure was simply obtained when a silicon substrate with oxide layer was used for an electrode substrate. The two electrochemical electrodes were reused as source and drain electrodes. FET characteristics showed current enhancement in some kinds of samples.3 The device fabrication was also demonstrated via an eco-friendly and non-vacuum process using a material printer.4 Further details of fabrication, materials, and physical properties will be reported.

Inkjet printing and nanoscale electrocrystallization: Complete fabrication of organic microcrystals-based devices under ambient conditions

We report the first successful attempt at complete device fabrication under ambient conditions using inkjet printing and nanoscale electrocrystallization. Three different electrode patterns—parallel-type, multiparallel, and multitip patterns—are prepared using inkjet patterning. The printed electrodes, which have gaps of ∼20μm, are produced using a material printer. Indium tin oxide and gold inks are used for printing, and the electrodes are printed on silicon and glass substrates. Next, using these printed electrodes, micro- or nanocrystals are synthesized through nanoscale electrocrystallization. Owing to the surface roughness of the electrodes, the manner of crystal growth is slightly different from that in the case of lithographically formed electrodes; however, the morphology of the grown crystals is similar. In addition, the nanocrystals-based bridge structure formed between the two electrodes by AC electrolysis is similar to that obtained using lithographically formed electrodes. Further, the two-terminal device shows ohmic characteristics, indicating that there is good contact between the electrode and obtained crystal.

Current-dependent formation of Bechgaard salt nanocrystals using nanoscale electrocrystallization for the fabrication of organic nanodevices

Herein, the nanocrystal formation of tetramethyltetraselenafulvalene (TMTSF)-based nanocrystals based on nanoscale electrocrystallization is reported. Whereas direct current electrolysis produced nanocrystals over the entire anode surface, nanocrystals were only formed in the gap between the two electrodes using alternating current (AC) electrolysis. Consequently, a two-terminal device where nanocrystals bridge the source and drain electrodes was simply prepared via this one-step electrolysis process. The prepared nanocrystal had the same structure as the bulk crystal of (TMTSF)2·ClO4, which is known as a superconducting Bechgaard salt. Although the nanocrystal exhibited a metallic nature, weak gate-voltage-dependent characteristics were observed in the current-voltage characteristics measurements. Facile fabrication of organic nanodevices was thus enabled using this AC electrolysis method.

Tetrathiafulvalene-based nanocrystals: site-selective formation, device fabrication, and electrical properties

A tetrathiafulvalene (TTF)-based nanocrystal was selectively synthesized only in the gap between two electrodes using a nanoscale electrocrystallization. A two-terminal TTF-based device and an FET could be readily obtained via an eco-friendly nanofabrication process.

Site-selectively fabricated phthalocyanine neutral radical nanocrystals: structure and electrical properties

Phthalocyanine neutral radical nanocrystals were site-selectively synthesized by nanoscale electrocrystallization. These nanocrystals were found to have a three-dimensional π–π stacking structure. In addition, a bottom-gate-type field-effect transistor (FET) structure could be readily fabricated by reusing two electrochemical electrodes employed during the electrocrystallization process as the source and drain electrodes. We found that the nanocrystals exhibited properties similar to that of a weak p-type material. The weakened Mott-insulating nature of the nanocrystals, owing to the three-dimensional π–π interactions, may mitigate the field effect in the crystals. We believe that nanoscale electrocrystallization can also be applied to obtain crystals of various organic molecules and that further enhancements of this method will lead to the development of environmentally friendly, next-generation nanofabrication processes.

Giant negative magnetoresistance in an organic nanocrystal: site-selective device fabrication by nanoscale electrocrystallization

Herein, we report the fabrication of an organic spintronic device by a one-pot process called nanoscale electrocrystallization, that allows for the site-selective growth of organic nanocrystals on a substrate between two electrodes. Axially substituted iron phthalocyanine was used to constitute the nanocrystals that exhibited a strong correlation between the localized spin and conduction electrons. In addition, the nanocrystals exhibited a negative giant magnetoresistance ([R(B) − R(0)]/R(0)) of around −56%. Moreover, the spintronic device exhibited an angular dependence of its negative giant magnetoresistance, which confirmed the highly oriented growth of the nanocrystals by the nanoscale electrocrystallization method. In summary, our method enables the easy fabrication of organic spintronic devices based on such spin interactions.

Fabrication of sodium phthalocyanine nanocrystals using nanoscale electrocrystallization

Sodium phthalocyanine-based nanocrystals were selectively grown in the gap between two electrodes using a nanoscale electrocrystallization method. They had a width of approximately 100 nm and a length of several microns. Surprisingly, these nanocrystals exhibit weak n-type electrical characteristics during current–voltage measurements, even though they are p-type materials.

Microscopic and Electronic Structure of Semimetallic Sb and Semiconducting AlSb Fabricated by Nanoscale Electrodeposition: An in Situ Scanning Probe Investigation

The nanoscale electrocrystallization of pure Sb and the compound semiconductor AlSb on Au(111) has been studied by in situ scanning probe techniques (STM and STS) employing an ionic liquid electrolyte, {AlCl3-[C4mim]+Cl-} (1:1) containing SbCl3. The characteristic changes of the electronic structures with varying potentials have been probed for the first time by normalized differential conductance spectra, (dI/dU)/(I/U). In the underpotential deposition range of Sb the formation of two layers is observed. For the first monolayer a (square root 3 x square root 3)R30 degrees structure is determined from atomically resolved STM images. During the deposition and dissolution of the Sb monolayers characteristic wormlike or spinodal structures appear indicating surface alloying of antimony with the gold substrate. Under overpotential conditions two different Sb structures have been observed. If the deposition potential is continuously stepped to -0.1 V, Sb nanostripes form. On the other hand, randomly dispersed small clusters occur if the potential is jumped from 0.0 to -0.3 V vs Al/Al(III). Both modifications exhibit typical semimetallic behavior as shown by the STS spectra. At -1.1 V the cyclic voltammogram shows a clear reduction wave that is assigned to AlSb compound formation. Deposits in this potential range are characterized by a homogeneous distribution of clusters with diameters of approximately 20 nm. Conductance spectra of these clusters exhibit the main features of the electronic structure of the bulk semiconductor AlSb, with a band gap of 2.0 +/- 0.2 eV. Electrodeposition experiments on both sides of the compound deposition potential show a strong doping effect that is manifest in the corresponding conductance spectra.

Multiple simultaneous fabrication of molecular nanowires using nanoscale electrocrystallization

We carried out a multiple simultaneous fabrication based on the nanoscale electrocrystallization to simultaneously construct molecular nanowires at two or more positions. This substrate-independent nanoscale electrocrystallization process enables nanowires fabrication at specific positions using AC. We also succeeded in multiple fabrications only at each gap between the electrode tips. We found that π-stack was formed along the long axis of the nanowires obtained by analyzing the selected-area electron diffraction. We believe this technique has the potential for expansion to the novel low-cost and energy-saving fabrication of high-performance nanodevices.

Site-selective fabrication of conducting molecular nanowires based on electrocrystallization

We have grown nanowires in a selective position by using an electrochemical process and alternating current. Nanoscale electrocrystallization was carried out in an axially substituted phthalocyanine solution using substrates with two electrodes formed by photolithography. The growth area was limited to the narrowest part of the gap between the tips of the electrodes by using tapered electrodes. The nanowires obtained had a width of approximately 100 nm and a length of more than 1 μm. Analysis of the selected-area electron diffraction pattern showed that the nanowire structure was identical to that of bulk crystal.

Fabrication of molecular nanowire using an electrochemical method

Nano-crystal growth based on an electrochemical method was carried out to construct self-assembling molecular nanowires. For nanoscale electrocrystallization, an axially-substituted phthalocyanine solution and substrates with two electrodes formed by deposition were used. During our process, nanowires with a width of approximately 100 nm and a length of several microns were obtained. We were also able to control the growing area by using alternating current.