An atomic force microscope was used to directly examine the physical state of nanometer-sized particles. The critical diameter of indium particles, where evidence of melting at room temperature was observed, was 7.8±1.2 nm. This conclusion is based on a method relying on the manipulation of particles in ambient air and at constant temperature. This method involves a simple set up that permits a combination of both manipulation and imaging of individual particles. To determine whether a particle is molten, three criteria are used: the merging of particles to form bigger spherical particles, a tip-induced shape change and the formation of nanofibres. All three criteria have been checked using other particle materials. The use of the atomic force microscope to determine whether a nanoparticle is molten, is however complicated by oxidation

We report on differential conductance measurements on a gold double-dot structure at 4.2 K. The two dots were connected in series by tunnel junctions formed by atomic force microscopy manipulation of nanodisks. The tunnel junctions were made strongly asymmetric. The characteristic honeycomb-shaped charging diagram separating different Coulomb blockade regions of well-defined occupancy of electrons was observed and the cells in the charging diagram were found to be skewed by the asymmetry of the tunnel junctions. In addition, a double-dot Coulomb staircase structure, with steps of varying width, was observed and was studied for varying gate voltage. The occupancy of electrons on the two dots was determined as a function of both drain source and gate voltages.

An atomic force microscope (AFM) was used to directly examine the physical state of nanometer-sized particles. The critical diameter of indium particles, where evidence of melting at room temperature was observed, was 7.8 ± 1.2 nm. This conclusion is based on a method relying on the manipulation of particles in ambient air and at constant temperature. This method involves a simple set-up that permits a combination of both manipulation and imaging of individual particles. To determine whether a particle is molten, three criteria are used: the merging of particles to form bigger spherical particles, a tip-induced shape change, and the formation of nanofibers. All three criteria have been checked using other particle materials. An attempt at 56°C revealed oxidation of the indium particles as the major problem for melting investigation. Manipulations under high-purity nitrogen atmosphere support the validity of the findings. The use of the AFM to determine whether a nanoparticle is molten is, however, complicated by the oxidation issue.

We report fabrication and measurements with two- and four-point probes with nanoscale dimensions, for high spatial resolution conductivity measurements on surfaces and thin films. By combination of conventional microfabrication and additive three-dimensional nanolithography, we have obtained electrode spacings down to 200 nm. At the tips of four silicon oxide microcantilevers, narrow carbon tips are grown in converging directions and subsequently coated with a conducting layer. The probe is placed in contact with a conducting surface, whereby the electrode resistance can be determined. The nanoelectrodes withstand considerable contact force before breaking. The probe offers a unique possibility to position the voltage sensors, as well as the source and drain electrodes in areas of nanoscale dimensions.

We report on the controlled manipulation of 5-20 nm-sized Au colloidal particles deposited on Si-based substrates using the tip of an atomic force microscope (AFM) operated at room temperature and under ambient conditions. This work is aiming at the step-by-step assembly of granular prototype nanometer-scale devices.For device fabrication and electrical transport measurements, respectively, different particle arrangements were assembled into a 10-40 nm wide gap region separating two Au nanoelectrodes.Decomposition of previously assembled devices allows to repeatedly synthesize new patterns of arbitrary shape using the same set of particles. This opportunity reflects the very high degree of flexibility of our approach in assembling novel functional devices.

We have fabricated gold single-electron transistors (SETs), operating up to 25 K, with tunnel gaps that could be individually tuned during fabrication. A combination of atomic-force-microscopy manipulation of nanodiscs and in situ electrical measurements was used to form statically stable tunnel gaps between the discs and lithographically defined electrodes. The gap resistances could be tuned to predetermined values over three orders of magnitude between ∼1 MΩ and ∼2 GΩ, corresponding to gap widths in the range of 3–10 Å. We report on SETs with symmetrically and asymmetrically coupled islands, i.e., with equal or different tunnel resistances. In the asymmetric SET a distinct Coulomb staircase was observed.

Single-electron transistors (SET) rely for their functionality on extreme control of lithography and lateral positioning as well as of properties of the building blocks from which the devices are built. BY an aerosol-based nanoparticle fabrication we can prepare nanocrystals down to sub-10nm dimensions with metallic or semiconducting character, as well as having a core + shell design for definition of tunnel-gaps. We present here results for a type of device that is based on the possibility to design functionality in the internal structure of the nanoparticles which are used as building blocks. We use such pre-fabricated building blocks to construct coulomb blockade devices and show that they operate at temperatures above 150K.

We describe a technique for the fabrication of lateral nanometer-scale devices, in which individual metallic nanoparticles are imaged, selected and manipulated into a gap between two electrical leads with the tip of an atomic force microscope. In situ, real-time monitoring of the device characteristics is used to control the positions of the particles down to atomic accuracy and to tune the electrical properties of the device during fabrication. Using this technique we demonstrate a nanomechanical switch as well as atomic-scale contacts that are stable at quantized conductance levels on the time scale of hours at room temperature.

The formation of self-assembled InAs and InAsxP1−x dots on InP has been studied, in particular with deposition conditions under which mainly coherent dots are developed. The samples were grown by metalorganic vapour phase epitaxy. Morphological investigations were performed by atomic force microscopy, with the instrument working in the contact mode as well as in the noncontact mode. Surface densities and height distributions were extracted, as a function of growth conditions. In addition, photoluminescence was used for investigations of the optical properties of capped InAs dots, formed under equivalent conditions. Comparisons between the two characterization techniques show a qualitative agreement with respect to the density of dots as well as their size homogeneity. It is also indicated that dots of binary InAs can be formed at deposition temperatures not higher than about 500°C. Elevated deposition temperatures in this process result in an unintentional alloying mechanism due to exchange reactions at the interface, leading to the formation of ternary InAsxP1−x dots, which can be seen as a simultaneous increase in the energy of the light emission and the average dot size, indicating the widening of the energy gap in the quantum dots, which counteracts the decreased energy quantization in the larger dots formed at higher temperatures.

We report a novel approach for the realization of quantum devices which require device structures of sub-10 nm dimensions and position control better than 1 nm. In this approach we combine three methods from nano-technology: (i) an aerosol technique for the fabrication of metallic and semiconducting nano-crystals or nano-particles with diameters in the range 5-50 nm, (ii) extreme electron beam lithography to define contact gap geometries with dimensions of 10-50 nm and (iii) a manipulation technique based on atomic-force microscopy, combined with in situ electrical measurements of the device characteristics, by which pre-fabricated nano-structures can be positioned with high accuracy. We present details of room-temperature measurements on quantized conductance devices, formed in the neck structures between neighbouring gold particles. These necks or wires have a cross-section of only one or a few gold atoms, leading to quantized conductance of , with values of n between 1 and 10 having been observed. Such lateral quantum resistor devices are found to be remarkably stable, frequently maintaining the conductance levels on the time scale of hours. We also discuss the prospect for novel devices in which a single nano-particle or a single molecule is controllably positioned with high accuracy, with tunnel gaps surrounding the island.

Quantum dots in the materials systems InP/GaAs and InP/Ga0.5In0.5P were grown at 600 degrees C by low pressure MOVPE in the Stranski-Krastanow growth mode and annealed under PH3/H-2 at growth temperature. AFM investigations of free standing islands (InP/GaAs) show a continuous decrease in height from 19 to 7 nm after 30 min annealing. Photoluminescence measurements on the overgrown dot samples (InP/Ga0.5In0.5P) show a shift of the quantum dot emission peak towards higher energies with an increase in annealing time. The proposed explanation relies on exchange reactions between the islands and the wetting layer, as well as alloying between the wetting layer and the underlying substrate due to interdiffusion. (C) 1998 Elsevier Science B.V. All rights reserved.

We have produced metallic nanowires by manipulating Au nanodiscs with the tip of an atomic force microscope in between electron beam defined Au electrodes. During the process we continuously monitored the electrical characteristics of the wire formation, and observed steps in the conductance in units of integer values of the conductance quantum G(0)=2e(2)/h. We also let the fabricated nanowires self-develop, and found wires stable at a certain conductance plateau N.G(0) for 30 minutes at room temperature.

Abstract : We have developed a new way to build extremely small scale and accurate structures for contacting of nano-objects. The principle is based on the use of the atomic force microscope (AFM) for very accurate movement of pre-fabricated nano-objects, such as lift-off defined metal discs, aerosol fabricated nano-particles and colloidal gold particles. The assembly procedure consists of moving selected nanometer sized objects into a small gap between two metal electrodes.

We have studied the formation of strained InAs and InP island structures on GaP surfaces grown by chemical beam epitaxy. InP grows pseudomorphically for 3 ML before island crystallization is observed by reflection high-energy electron diffraction, following a typical Stranski–Krastanov growth mode. For the growth of InAs on GaP, three-dimensional diffraction peaks are observed after 0.9 ML of InAs have been deposited, indicating a Volmer–Weber growth mode. Atomic force microscopy studies of these structures are presented and the optical properties are discussed.

Quantum dots in the materials system InP/GaAs were grown by low pressure MOVPE in the Stranski–Krastanow growth mode. Two basically different approaches were used to control the dot sizes: (i) Variations in temperature and deposition rate and (ii) post growth annealing under PH3/H2 at growth temperature. AFM investigations show a decrease in dot height from 17nm to 12 and 5nm (bimodal height distribution) by changing the deposition rate from 0.5 to 3.5ML/s. For the annealed samples we observe a continuous decrease in height from 19 to 7nm after 30min annealing.

Presently, there is a rapid growing interest in quantum devices based on single-electron-tunneling (SET)-effects. Such SET-devices are possible candidates for single electron memories that might allow room temperature operation. The focus of possible room temperature SET-devices is towards fabrication of lateral tunnel structures. We have during the last years developed a new way to fabricate lateral quantum devices. The principle is based on the use of the atomic force microscope (AFM) for very accurate movement of pre-fabricated nano-objects into a small gap between two metal electrodes. In this way a unique technique to build extremely small scale and accurate structures for contacting of nano-objects is realized, making hitherto unachievable devices to be formed.