Name: scanning-probe single-electron capacitance spectroscopy
Uploaded: 2013-07-30T13:00:00
Description: Watch this Scientific Journal Video about Scanning-probe Single-electron Capacitance Spectroscopy at JoVE.com

The research discussed here was supported by the Michigan State University Institute for Quantum Sciences and the National Science Foundation DMR-0305461, DMR-0906939, and DMR-0605801. K.W. acknowledges support from a U.S. Department of Education GAANN Interdisciplinary Bioelectronics Training Program fellowship.

1. Protocol
<ol>
	<li>Initial setup of microscope and electronics.
	<ol>
		<li>Begin with a cryogenic-capable scanning probe microscope with associated control electronics. The microscopes used for the research described here use inertial translation to "walk" the sample towards and away from the tip along ramps13 (made from a conducting material such as copper, brass, or stainless steel to enable them to transmit bias voltage to the sample) as part of a Besocke design STM14, schematically shown i...

<ol>
	<li>Gasseller, M., DeNinno, M., Loo, R., Harrison, J. F., Caymax, M., Rogge, S., Tessmer, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-Electron+Capacitance+Spectroscopy+of+Individual+Dopants+in+Silicon.">Single-Electron Capacitance Spectroscopy of Individual Dopants in Silicon.</a> Nano Lett. 11, 5208-5212 (2011).</li><li>Kuljanishvili, I., Kayis, C., Harrison, J. F., Piermarocchi, C., Kaplan, T. A., Tessmer, S. H., Pfeiffer, L. N., West, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning-probe+spectroscopy+of+semiconductor+donor+molecules.">Scanning-probe spectroscopy of semiconductor donor molecules.</a> Nat. Phys. 4, 227-233 (2008).</li><li>Tessmer, S. H., Kuljanishvili, I., Kayis, C., Harrison, J. F., Piermarocchi, C., Kaplan, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanometer-scale+capacitance+spectroscopy+of+semiconductor+donor+molecules.">Nanometer-scale capacitance spectroscopy of semiconductor donor molecules.</a> Physica B. 403, 3774-3780 (2008).</li><li>Yoo, M. J., Fulton, T. A., Hess, H. F., Willett, R. L., Dunkleberger, L. N., Chichester, R. J., Pfeiffer, L. N., West, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+Single-Electron+Transistor+Microscopy:+Imaging+Individual+Charges.">Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges.</a> Science. 276, 579-582 (1997).</li><li>Urazhdin, S., Tessmer, S. H., Ashoori, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+low-dissipation+amplifier+for+cryogenic+scanning+tunneling+microscopy.">A simple low-dissipation amplifier for cryogenic scanning tunneling microscopy.</a> Rev. Sci. Instrum. 73 (2), 310-312 (2002).</li><li>Williams, C. C., Hough, W. P., Rishton, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+capacitance+microscopy+on+a+25+nm+scale.">Scanning capacitance microscopy on a 25 nm scale.</a> Appl. Phys. Lett. 55 (2), 203-205 (1989).</li><li>Tessmer, S. H., Glicofridis, P. I., Ashoori, R. C., Levitov, L. S., Melloch, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subsurface+charge+accumulation+imaging+of+a+quantum+Hall+liquid.">Subsurface charge accumulation imaging of a quantum Hall liquid.</a> Nature. 392, 51-54 (1998).</li><li>Tessmer, S. H., Kuljanishvili, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+single-+and+multiple-electron+resonances+for+electric-field-sensitive+scanning+probes.">Modeling single- and multiple-electron resonances for electric-field-sensitive scanning probes.</a> Nanotechnology. 19, 445503-445510 (2008).</li><li>Kuljanishvili, I., Chakraborty, S., Maasilta, I. J., Tessmer, S. H., Melloch, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+electric-field-sensitive+scanning+probe+measurements+for+a+tip+of+arbitrary+shape.">Modeling electric-field-sensitive scanning probe measurements for a tip of arbitrary shape.</a> Ultramicroscopy. 102, 7-12 (2004).</li><li>Martin, J., Akerman, N., Ulbricht, G., Lohmann, T., Smet, J. H., von Klitzing, K., Yacoby, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+electron-hole+puddles+in+graphene+using+a+scanning+single-electron+transistor.">Observation of electron-hole puddles in graphene using a scanning single-electron transistor.</a> Nat. Phys. 4, 144-148 (2008).</li><li>Ashoori, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrons+in+artificial+atoms.">Electrons in artificial atoms.</a> Nature. 379, 413-419 (1996).</li><li>Ashoori, R. C., Stormer, H. L., Weiner, J. S., Pfeiffer, L. N., Pearton, S. J., Baldwin, K. W., West, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-electron+capacitance+spectroscopy+of+a+few+electron+box.">Single-electron capacitance spectroscopy of a few electron box.</a> Physica B. 189, 117-124 (1993).</li><li>Frohn, J., Wolf, J. F., Besocke, K., Teske, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coarse+tip+distance+adjustment+and+positioner+for+a+scanning+tunneling+microscope.">Coarse tip distance adjustment and positioner for a scanning tunneling microscope.</a> Rev. Sci. Instrum. 60 (6), 1200-1201 (1989).</li><li>Besocke, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+easily+operable+scanning+tunneling+microscope.">An easily operable scanning tunneling microscope.</a> Surf. Sci. 181, 145-153 (1987).</li><li>Urazhdin, S., Maasilta, I. J., Chakraborty, S., Moraru, I., Tessmer, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-scan-range+cryogenic+scanning+probe+microscope.">High-scan-range cryogenic scanning probe microscope.</a> Rev. Sci. Instrum. 71 (11), 4170-4173 (2000).</li><li>Ashoori, R. C., Stormer, H. L., Weiner, J. S., Pfeiffer, L. N., Pearton, S. J., Baldwin, K. W., West, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-electron+capacitance+spectroscopy+of+discrete+quantum+levels.">Single-electron capacitance spectroscopy of discrete quantum levels.</a> Phys. Rev. Lett. 68 (20), 3088-3091 (1992).</li></ol>

A detailed explanation of the theoretical basis for this experimental method is given in References 8 and 9 and discussed with respect to the scenario of subsurface dopants in Reference 2; the overview presented here will therefore be brief and conceptual. The tip is treated as one plate of a capacitor, and the conducting layer underlying the sample comprises the other plate. If the DC voltage is applied such that electrons are pulled toward the tip, and if there is a dopant atom situated between the underlying conductin...

Subsurface Charge Accumulation (SCA) imaging is a low-temperature method capable of resolving single-electron charging events. When applied to the study of dopant atoms in semiconductors, the method can detect individual electrons entering donor or acceptor atoms, permitting characterization of the quantum structure of these minute systems. At its heart, SCA imaging is a local capacitance measurement6 well-suited for cryogenic operation. Because capacitance is based on electric field, it is a long-range effect that can resolve charging beneath insulating surfaces6. Cryogenic operation permits investigation of single-electron motion and quantum level spacing that would be unresolvable at room temperature1,2. The technique can be applied to any system in which electron motion below an insulating surface is important, including the charging dynamics in two-dimensional electron systems at buried interfaces7; for brevity, the focus here will be on studies of semiconductor dopants.
At the most schematic level, this technique treats the scanned tip as one plate of a parallel-plate capacitor, although realistic analysis requires a more detailed description to account for the curvature of the tip8,9. The other plate in this model is a nanoscale region of the underlying conducting layer, as shown in Figure 1. Essentially, as a charge enters a dopant in response to a periodic excitation voltage, it gets closer to the tip; this movement induces more image charge on the tip, which is detected with the sensor circuit5. Similarly, as the charge exits the dopant, the image charge on the tip is decreased. Hence the periodic charging signal in response to the excitation voltage is the detected signal - essentially it is capacitance; thus this measurement is often referred to as determining the C-V characteristics of the system.
During the capacitance measurement, the only net tunneling is between the underlying conductive layer and the dopant layer - charge never tunnels directly onto the tip. The lack of direct tunneling to or from the tip during the measurement is an important difference between this technique and the more familiar scanning tunneling microscopy, although much of the hardware for this system is essentially identical to that of a scanning tunneling microscope. It is also important to note that SCA imaging is not directly sensitive to static charges. For investigations of static charge distributions, scanning Kelvin probe microscopy or electrostatic force microscopy is appropriate. Additional cryogenic methods for examining local electronic behavior exist which also have good electronic and spatial resolution; for example, scanning single-electron transistor microscopy is another scanning probe method capable of detecting minute charging effects4,10. SCA imaging was originally developed at MIT by Tessmer, Glicofridis, Ashoori, and co-workers7; moreover, the method described here can be considered as a scanning probe version of the Single-Electron Capacitance Spectroscopy method developed by Ashoori and co-workers11. A key element of the measurement is an exquisitely sensitive charge-detection circuit5,12 using high electron mobility transistors (HEMT); it can achieve a noise level as low as 0.01 electrons/Hz&frac12; at 0.3 K, the base temperature of the cryostat in Reference 5. Such a high sensitivity allows observation of single-electron charging in subsurface systems. This method is suited for the study of electron or hole dynamics of individual or small groups of dopants in semiconductors, with typical dopant areal densities on the order of 1015 m-2 in a plane geometry2. An example of a typical sample configuration for this type of experiment is shown in Figure 1. The dopant layer is typically positioned a few tens of nanometers beneath the surface; it is important to know the precise distances between the underlying conducting layer and the dopant layer and between the dopant layer and the sample surface. In contrast to tunneling, capacitance does not fall off exponentially but instead essentially decreases in inverse proportion to the distance. Hence, the dopant depth could in principle be even deeper than tens of nanometers beneath the surface, as long as some reasonable fraction of electric field lands on the tip. For all of the aforementioned cryogenic local probes of electronic behavior, including the technique described here, spatial resolution is limited by the geometric size of the tip and by the distance between the subsurface feature of interest and the scanning probe tip.

<table border="1">
		<tbody>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Equipment</td>
		 </tr>
		 <tr>
			<td>Besocke-design STM</td>
			<td>Custom</td>
			<td></td>
			<td>References 14 and 15</td>
		 </tr>
		 <tr>
			<td>Control electronics for STM</td>
			<td>RHK Technology</td>
			<td>SPM 1000 Revision 7</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Lock-in amplifier</td>
			<td>Stanford Research Systems</td>
			<td>SR830</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Curve tracer</td>
			<td>Tektronix</td>
			<td>Type 576</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Oscilloscope</td>
			<td>Tektronix</td>
			<td>TDS360</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Multimeter</td>
			<td>Tektronix</td>
			<td>DMM912</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Wire bonder</td>
			<td>WEST&middot;BOND</td>
			<td>7476D</td>
			<td>with K~1200D temperature controller</td>
		 </tr>
		 <tr>
			<td>Soldering iron</td>
			<td>MPJA</td>
			<td>301-A</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Cryostat</td>
			<td>Oxford Instruments</td>
			<td>Heliox</td>
			<td></td>
		 </tr>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Material</td>
		 </tr>
		 <tr>
			<td>Pt/Ir wire, 80:20</td>
			<td>nanoScience Instruments</td>
			<td>201100</td>
			<td></td>
		 </tr>
		 <tr>
			<td>GaAs wafer</td>
			<td>axt</td>
			<td>S-I</td>
			<td>For the mounting chip</td>
		 </tr>
		 <tr>
			<td>99.99% Au wire, 2 mil diameter</td>
			<td>SPM</td>
			<td></td>
			<td>For the mounting chip</td>
		 </tr>
		 <tr>
			<td>99.99% Au wire, 1 mil diameter</td>
			<td>K&amp;S</td>
			<td></td>
			<td>For wire bonding</td>
		 </tr>
		 <tr>
			<td>Indium shot</td>
			<td>Alfa Aesar</td>
			<td>11026</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Silver epoxy</td>
			<td>Epo-Tek</td>
			<td>EJ2189-LV</td>
			<td>Any low-temperature-compatible conductive epoxy is acceptable</td>
		 </tr>
		 <tr>
			<td>HEMT</td>
			<td>Fujitsu</td>
			<td>Low Noise HEMT</td>
			<td></td>
		 </tr>
		</tbody>
 </table>

scanning-probe single-electron capacitance spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

The chief indicator of a successful measurement is reproducibility, much as in other scanning probe methods. Repeated measurements are very important for this reason. For point capacitance spectroscopy, taking many measurements in succession at the same location helps to increase the signal-to-noise ratio and identify spurious signals.
Once a feature of interest has been identified within the charge accumulation image and capacitance spectroscopy has been performed, interpretation of the C-V d...

Watch this Scientific Journal Video about Scanning-probe Single-electron Capacitance Spectroscopy at JoVE.com

Scanning-probe Single-electron Capacitance Spectroscopy

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

scanning-probe-single-electron-capacitance-spectroscopy

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Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

A protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. Procedures and examples to determine the adhesion force and free energy of these molecules on solid supports and bio-interfaces are provided.

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single ...

Surface Enhanced Raman Spectroscopy Detection of Biomolecules Using EBL Fabricated Nanostructured Substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

We describe the fabrication and characterization of nano-biological systems interfacing nanostructured substrates with immobilized proteins and aptamers. The relevant experimental steps involving lithographic fabrication of nanostructured substrates, bio-functionalization, and surface-enhanced Raman spectroscopy (SERS) characterization, are reported. SERS detection of surface-immobilized proteins, and probing of protein-ligand and aptamer-ligand binding is demonstrated.

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

The paper describes a method for producing extreme nanowires by melt infiltration into carbon nanotubes and how 1D systems may be characterized and investigated using Resonance Raman Spectroscopy to determine vibrational and optical excitation energies.

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the ...

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we demonstrate an optical spectroscopy method that is capable of resolving spectral features beyond that of the spin fine structure and homogeneous linewidth of single quantum dots (QDs) using a standard, easy-to-use spectrometer setup. This method incorporates both laser and photoluminescence spectroscopy, combining the advantage of laser line-width limited resolution with multi-channel photoluminescence detection. Such a scheme allows for considerable improvement of resolution over that of a common single-stage spectrometer. The method uses phonons to assist in the measurement of the photoluminescence of a single quantum dot after resonant excitation of its ground state transition. The phonon&#39;s energy difference allows one to separate and filter out the laser light exciting the quantum dot. An advantageous feature of this method is its straight forward integration into standard spectroscopy setups, which are accessible to most researchers.

The manuscript describes a method of phonon-assisted quasi-resonant fluorescence spectroscopy that incorporates both laser-limited resolution and photoluminescence (PL) spectroscopy. This method utilizes optical phonons to provide linewidth-limited resolution spectra of atom-like semiconductor structures in the energy domain. The method is also easily realized with a single spectrometer optical spectroscopy setup.

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young&#39;s modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level.

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The ...

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.