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A three-way few-electron switch is implemented using bidirectional electron pumps in silicon-on-insulator material. The switch consists of three branches defined by single-electron transistors, connected to a central node. Any combination of two single-electron transistors forms a bidirectional electron pump. At 4.2K, each cycle of an rf signal applied to the central node pumps electron packets approximately ten electrons in size through the circuit. It is possible to switch the electron packets in any direction through the branches. The switch may be used for the precise transfer of electrons, and as the basic element in few-electron logic applications.

High-density silicon nanopillar cathodes were fabricated using a self-assembling colloidal gold etch mask. Scanning tunneling microscopy experiments were performed to locate individual nanopillars and to investigate their field emission properties. Emission characteristics were obtained over a range of fixed separations from the nanopillar apex, allowing the empirical determination of the geometric field enhancement factors from the resulting Fowler–Nordheim plots. The geometric enhancement factors were found to increase dramatically for decreasing anode–cathode separation and the rate of increase is dependent on the nanopillar geometry.

Two Coulomb blockade devices connected in series and separated by a main island to which a rf signal was applied, are characterized electrically. The main island is large enough so that Coulomb phenomena in it can be neglected. Although no source–drain voltage is applied, the rf signal causes a current. The polarity of this current depends on the dc gate voltages, which control the two Coulomb blockade devices. The experimental data correspond closely to the simulations. Furthermore, it is evident from theoretical considerations that the circuit can pump electron packets against an applied potential.

We have observed the splitting of Coulomb oscillation peaks in coupled Si0.9Ge0.1 double quantum dots at 4.2 K. The quantum dots are formed by trench isolation, which means that the dots can be made much smaller than possible with the surface-gated approach. A dot diameter of 50 nm or less increases the charging energy and, therefore, the operating temperature of the device compared to previous approaches. A simulation of the results using parameters calculated from the lithographic dimensions of the device shows that a good fit to the experimental data can be achieved with a realistic interdot capacitance value.

Single-electron effects have been observed up to 60 K in a side-gated point contact device fabricated in nanocrystalline silicon films. The films were phosphorus-doped and deposited at 300 °C by plasma enhanced chemical vapor deposition. Using transmission electron microscopy and Raman spectroscopy, the grain size, crystalline volume fraction, and grain boundary thickness are determined. The single-electron effects are associated with islands formed by crystalline silicon grains ∼4 nm in size, isolated by amorphous silicon regions ∼0.5 nm in thickness. The structural characteristics of the nc-Si film are correlated to the electrical behavior. The electrical transport mechanism at high temperatures is attributed to percolation conduction across a distribution of tunnel barriers with a maximum height of 40 meV.

We report on measurements of hole transport through a double quantum dot structure formed by trench isolation from a SiGe:Si heterostructure. A period change in the Coulomb oscillations is observed upon changing a gate bias, which is attributed to the lowering of one of the tunnel barriers, effectively changing the device to a single quantum dot. Accompanying the period change is a significant change in the level of noise associated with the oscillations. This is explained by a carrier energy filtering effect in the double dot compared with the single dot, caused by the slight difference in energy level spacing in each quantum dot.

A polymer composed of ruthenium carbonyl and of the formula [Ru6C(CO)15Ph2PCCPPh2]n has been synthesized. It is found to behave as a negative electron-beam resist with a sensitivity of 400 C/m2. Upon exposure to the electron beam, the electrical conductivity of the patterned films is found to vary over seven orders of magnitude according to a power-law dependence on dose. Temperature dependence of the conductivity is studied, and the conduction is attributed to variable-range hopping between ruthenium superclusters in two dimensions.

A nanoscale electron tube with a field-emission cathode and a control gate (nanotriode) has been fabricated and characterized. Electrons are field emitted from metal nanopillars with radii of about 1 nm into a vacuum nanochamber, collected at the anode, and controlled by a gate electrode. The nanochamber is sealed by an integrated anode and has vertical and horizontal dimensions of 100 nm. The turn-on voltage is less than 10 V and is independent of ambient temperature. Currents of 10 nA and transconductances of up to 6 nS per device have been observed; this would yield a transconductance of 60 S cm−2 at the maximum packing density of 1010 nanotriodes cm−2 for these devices. The emission stability is better than 3% at room temperature and improves to 0.1% at 20 K.

We have observed single-electron charging effects in heavily doped polycrystalline silicon nanowires at 4.2 K. Wires of approximately 20 nm by 30 nm active cross section were defined by electron-beam lithography and thermal oxidation in standard polycrystalline silicon material. We have measured a Coulomb staircase and periodic current oscillations with gate bias, attributed to localized carrier confinement resulting from a statistical variation in the intergrain tunnel barriers. A sharp change in the current oscillation period is seen and we speculate that it is due to electrostatic screening of the gate bias by grain boundary defect states.

Novel field emission devices with electron path lengths an order of magnitude less than the elastic mean free path of electrons in air have been fabricated and tested at atmospheric pressure. The nanoscale-tip field emission system consisted of multiple emitter tips of radii about 1 nm within an extractor aperture of diameter 50 nm. The extractor turn-on voltage was approximately 7.5 V; field-emitted currents of up to 10 nA were collected at extractor voltages of less than 10 V. Maximum current densities of over 1011 A m−2 have been observed, and the emission stability in air at atmospheric pressure is better than 3%.

We report the evolution of the magnetoresistance (MR) and magnetization behavior of Ni80Fe20 wire arrays as the width (w) is reduced from 200 to 0.3 μm. At around 1.5 μm width, the hysteretic behavior seen in continuous films shows the near reversible behavior characteristic of spin rotation processes. At low field (H Ms), the linear MR response to the in-plane perpendicular hard axis field suggests a bulklike transverse MR effect.

Isothermal electron beam heating combined with in situ optical measurements has been used to measure the temperature dependence of the spectral emissivity of lightly doped silicon in the range 345–723 °C for wavelengths between 1 and 9 μm. The absorption coefficient was deduced from the spectral emissivity and compared with the predictions of a model including phonon‐assisted processes involved in interband transitions, free‐carrier absorption, and lattice absorption. The experimental data agree well with the model’s results.

The Coulomb blockade region was measured directly in an experimental single‐electron memory device. The device was constructed with multiple‐tunnel junctions (MTJ) formed by making a sidegated constriction in δ‐doped GaAs. The Coulomb blockade region is defined by electron transfer rates of less than 10 electrons per second. At low values of sidegate voltages in the MTJ an enhancement of the Coulomb blockade is observed and explained by the formation of a nonuniform electrostatic potential in the semiconductor tunnel junctions.

We have studied focused electron beam induced deposition from W(CO)6 at beam primary energies between 20 and 0.06 keV. Submicrometer resolution with 4 nA beam current was maintained at very low primary energies using a retarding field configuration. Decomposition cross sections of W(CO)6 for primary energies below about 1 keV were found to be about a factor of 4 larger than those at 20 keV. Depending on the scan conditions, the resistivity of the deposits formed using low primary energies was found to be up to about a factor of 4 lower than at 20 keV implying a higher metallic content. These results form the basis of an improved method for repairing clear defects on x‐ray masks and for making conducting tracks on semiconducting materials.

We have fabricated constrictions in δ‐doped GaAs using implanted gates to provide the lateral confinement. Large conductance oscillations are observed when the gate voltage is varied. The drain‐source current‐voltage characteristics are highly nonlinear; as many as 30 peaks are present, and peak‐to‐valley ratios greater than 100 have been measured. These results are explained in terms of resonant tunneling through the random potential distribution in the point contact. Using a simple model for the potential distribution we are able to simulate qualitatively the structure in the conductance.

We report the fabrication of high aspect ratio, sub‐10 nm size, structures in silicon without involving any wet chemical etching. A 50 nm thick double layer of low and high molecular weight polymethylmethacrylate resist was exposed with an 80 kV electron beam of diameter smaller than 5 nm. After exposure the resist was developed in 3:7 cellusolve: methanol with ultrasonic agitation during development. A 5 nm thick AuPd film was deposited by ionized beam evaporation and a metal pattern was obtained by liftoff. Sub‐10 nm AuPd dots were recorded with a scanning electron microscope. The AuPd pattern was then used as a mask on the Si substrate which was etched with reactive ion etching. Silicon nanocolumns with diameters ranging from 5 to 7 nm and an aspect ratio of height to diameter of about 7:1 were obtained.

We studied the change in electrical conductivity of deposits from focused electron beam induced dissociation of W(CO)6 for different exposure conditions. Lines were deposited by scanning repeatedly to build up the same total electron dose; with different electron doses per scan, resistance differences of more than one order of magnitude resulted. The lines with lower deposited thicknesses also have lower resistances, and so cannot be explained in terms of constant resistivity and different cross‐sectional areas. A theoretical description involving an intermediate and a final product is proposed and compared to the experimental results.

We report on the fabrication and electron transport in a novel heterostructure in which layers of AlGaAs and GaAs have been grown after a submicron free‐standing GaAs wire has been formed. Electronic conduction at low temperatures in this material is shown to be consistent with three‐dimensional hopping conduction with a transition to one‐dimensional hopping at temperatures below 1 K.

Side‐gated point‐contact structures in delta (δ)‐doped layers have been used to form single‐electron tunnel junctions with variable resistance. Clear Coulomb‐blockade effects have been observed in the current‐voltage characteristics. The measured characteristics are described in terms of a series of single‐electron transistors formed by microsegments within the point contact. The effective tunnel capacitance and side‐gate capacitance are estimated to be 10 and 1 aF, respectively, which are both one order of magnitude smaller than the reported capacitance of tunnel junctions made from Al or GaAs/AlGaAs heterostructures.

We have carried out magnetoresistance measurements on a mesoscopic cross formed from two split gates on a GaAs/AlGaAs 2DEG and have observed anomalous peaks in the bend resistance before the electron collimation is finally destroyed by the magnetic field. We have considered two possible explanations for this effect, and have rejected the possibility of quantum mechanical effects in favor of a classical one in which we postulate the presence of an impurity close to the center of the active region.

We have studied the quantized conductance of a one‐dimensional ballistic channel in the two‐dimensional electron gas of a back‐gated GaAs/AlGaAs heterostructure. A standard Schottky split‐gate fabricated with electron‐beam lithography techniques is used to define the one‐dimensional channel, but we incorporate an epitaxially grownin situ back‐gate, situated ∼1 μm below the electron gas, to provide additional control of the carrier density. Quantized conductance steps can be induced by changing the bias on either gate, highlighting the self‐consistent nature of the electrostatics involved. We show that we can, in principle, achieve independent control of the one‐dimensional carrier density and channel width.

Beryllium implants have been used to form p‐n junctions which confine electrons laterally in a GaAs/AlGaAs heterostructure to make high‐mobility quasi‐one‐dimensional wires whose electrical width can be varied by biasing the implanted regions. Incorporation of an additional surface Schottky gate enables the electron density within the wires to be controlled independently. Magnetoresistance measurements have been performed at 1.7 K and the weak‐field boundary‐scattering maxima used to determine the width as a function of both the bias applied to the implanted regions and to the surface gate. The mobility is also calculated and is comparable to that reported for wires of similar dimensions fabricated using high energy ion damage.

Electron focusing has been observed in single‐ and double‐grid structures. The magnetoresistance shows strong maxima and minima with values both above and below the zero field resistance. These are interpreted in terms of electron trajectories which are either backscattered from or transmitted through the grids, with a good match between the measured and calculated magnetic field values for the position of these peaks. The difference in magnetoresistance between the two structures is explained by an internal scattering mechanism which is present only for the double‐grid system.

A novel microthermopile for CO2 laser radiation detection with a fast response time has been fabricated for the first time. The microthermopile is fabricated by high‐resolution e‐beam lithography and isotropic plasma etching of the substrate resulting in free‐standing hot junctions which are thermally isolated from the substrate. The good thermal isolation and small heat capacity of the hot junctions resulted in a responsivity of 60 V/W and a time constant of 20 μs. The device operates over the entire CO2 laser wavelength range from 9.4 to 10.6 μm. Detailed measurements are presented for 10.6 μm operation.

A time‐resolved reflectivity (TRR) technique has been developed for dynamic studies of swept beam heating of silicon‐on‐insulator (SOI) materials. The method exploits the temperature dependence of the reflectivity of SOI films to allow noncontact temperature measurement with high spatial and temporal resolution. This technique is of considerable practical importance for beam processing, since it allows the temperature distribution induced by a beam being scanned across a specimen to be determined. The temperature distribution produced by a line electron beam swept across a SOI specimen was experimentally measured and found to be consistent with a theoretical prediction. The TRR technique can also be used to study melting and will prove useful for characterizing zone melting recrystallization, where thermal modeling is often inadequate for the complex structures involved.

Shallow (Rp∼20 nm) As and B‐doped layers in (100) silicon, formed by low‐energy ion implantation, have been investigated using conventional and high resolution transmission electron microscopy before and after either electron beam or furnace annealing. After annealing residual defects were observed in the region beyond the original amorphous/crystalline interface for both As and B implants and the nature of these defects and their stability was found to be relatively insensitive to a variety of annealing conditions. Lattice images of 10‐keV As‐implanted material indicated that a continuous amorphous layer was formed after implantation which regrew into perfect single crystal following electron beam processing for 1 s with a peak temperature of 900 °C.

Micron‐sized loops of high‐mobility two‐dimensional electron gas have been made on GaAs‐AlGaAs heterostructures using a novel split‐gate technique. Aharonov–Bohm oscillations of amplitude up to 20% of the device resistance have been observed at very low temperatures (T

Fine structures can be fabricated in silicon dioxide layers by a two‐stage process in which localized ion implantation enhances the rate at which the oxide can be etched chemically. This process has been investigated as a technique for maskless microfabrication using a scanning ion beam lithography system.

A fabrication process for free-standing single-crystal silicon wires of submicrometer cross-sectional dimensions and lengths in excess of 40 µm is reported. The starting material is silicon-on-insulator that has been recrystallized using a dual electron beam recrystallizing system. The wires are then fabricated in the recrystallized layer by a combination of electron beam lithography and plasma etching. Electrical measurements have been performed and the fabrication limits of the process are discussed.