RSC thanks the support of the National Science Council (NSC) of Taiwan under Project NSC 102-2112-M-011-001-MY3. YSH acknowledges the support of the NSC of Taiwan under Project NSC 100-2112-M-011-001-MY3.

1. Structural Characterization of MoSe2 Layer Crystals (See Step 1 in Figure 1)
<ol>
	<li>XRD Measurement Procedure
	<ol>
		<li>Mount a MoSe2 layer crystal (with the size range of 5 x 5 x 0.1-10 x 10 x 0.5 mm3) or crystal powder (which was mixed with quartz powder and binder and was smeared on the slide glass) on the holder.</li>
		<li>Press the holder by a slide glass to ensure layer crystal surface parallel to the holder surface.</li>
		<li>Load the sample holder into the diffractometer.</li>
		<li>Close the doors of diffractometer.</li>
		<li>Calibrate beam line accordingly to manufacturer&#8217;s instructions.</li>
		<li>Input measurement parameters such as the 2 scan range (10-80&#176;), the increment (0.004&#176;), and the dwell time (0.1 sec).</li>
		<li>Start the DIFFRAC.Measurement Center program on the computer attached to the diffractometer and then save data and name data file according to manufacturer&#8217;s protocol.</li>
		<li>Analyze the XRD pattern by identifying the positions of the diffraction peaks using the software and then compare with the standard data from JCPDS card database to confirm the single out-of-plane orientation and single-crystalline quality of the MoSe2 layer crystals32,33.</li>
	</ol>
	</li>
	<li>Micro-Raman Measurement Procedure
	<ol>
		<li>Perform the Raman equipment calibration using a silicon wafer as the standard sample. The measurement of the silicon wafer is the same as the procedure described below for the interested MoSe2 layer crystal.</li>
		<li>Mount a MoSe2 layer crystal on the slide glass.</li>
		<li>Load the slide glass on the holder of optical microscope and focus the sample surface with a white light source.</li>
		<li>Switch the light source from a white light to a laser beam (wavelength at 514 nm).</li>
		<li>Input measurement parameters such as the wavenumber scan range (150-500 cm-1), the integration time (10 sec), and the number of scan times (10-30 times).</li>
		<li>Start the program on computer attached to the Raman spectrometer and then save data and name data file according to manufacturer&#8217;s protocol.</li>
		<li>Analyze the Raman spectrum by identifying their peak widths and positions using the software and then compare with standard data from references to confirm the crystalline structure type and quality of the MoSe2 layer crystals34,35.</li>
	</ol>
	</li>
</ol>
2. Fabrication of MoSe2 Layer Nanocrystal Devices
<ol>
	<li>Mechanical Exfoliation of Layer Crystals
	<ol>
		<li>Clean tweezers with acetone and alcohol.</li>
		<li>Pick the MoSe2 layer crystals (4 to 8 pieces) with a shiny surface (i.e. mirror-like crystal face) and an area size larger than 0.5 x 0.5 mm2 with the tweezers and put them on the dicing tape with an area size of 20 x 60 mm2.</li>
		<li>Fold the tape in half to exfoliate the layer crystal and repeat the action approximately twenty times. Usually layer crystals can be stripped into many micrometer-sized crystals in width (see Step 2 in Figure 1).</li>
		<li>Load the dicing tape with the layer nanocrystal powder into the SEM chamber to observe the sizes and morphologies of these stripped MoSe2 layer microcrystal. If the width distributions of the layer nanocrystal are at 1-20 &#956;m, the nanocrystal powder can meet the criteria for the device fabrication.</li>
	</ol>
	</li>
	<li>Dispersion of the Layer Nanocrystals on the Device Template
	<ol>
		<li>Place the dicing tape with the layer nanocrystal powder upside-down on the device template. The template is SiO2 (300 nm)-coated silicon substrate with sixteen pre-patterned Ti (30 nm)/Au (90 nm) electrodes on the SiO2 surface (see Step 4 in Figure 1). The area size of the template is 5 x 5 mm2.</li>
		<li>Tap the dicing tape lightly to make some nanocrystals (roughly 10 to 100 pieces) fall on the template.</li>
		<li>Check the number density and dispersion condition of the nanocrystal on the template by optical microscope or sometimes by SEM if the dispersed nanocrystals can be not observed by optical microscope. Usually 2 to 5 pieces of nanocrystals (area size larger than 2 x 2&#160;&#956;m2) dispersed on the center square (with area of 80 x 80 &#956;m2) of the template without overlapping to each other are the better condition for the next FIB processing.</li>
	</ol>
	</li>
	<li>Electrode Fabrication by FIB
	<ol>
		<li>Mount templates on the FIB holder using conducting copper foil tape. Typically, the area of conducting tape of 3 x 2.4 cm2 was required for mounting 6-8 templates.</li>
		<li>Load the holder into the FIB chamber.</li>
		<li>Evacuate the chamber to the vacuum degree down to 10-5 mbar by clicking the button &#8220;Pump&#8221;.</li>
		<li>Set the electron beam current (41 pA) and acceleration voltage (10 kV) for the SEM mode.</li>
		<li>Set the ion beam current (0.1 nA) and acceleration voltage (30 kV) for the FIB mode.</li>
		<li>Warm up the ion beam system and gas-injection-system (GIS) by clicking the button &#8220;beam on&#8221; and the button &#8220;Cold&#8221; in the &#8220;Gas Injection&#8221; block, respectively.</li>
		<li>Turn on the electron-beam by clicking the button &#8220;Beam On&#8221; and focus the image at a low magnification of 100X.</li>
		<li>Set the z-axial working distance (WD) at 10 mm for SEM mode.</li>
		<li>Set the magnification at 5,000X and focus.</li>
		<li>Set the tilt angle of the holder to 52 degrees by clicking the button &#8220;Navigation&#8221; and input the tilt angle &#8220;52&#8221;.</li>
		<li>Select a MoSe2 layer nanocrystal with a certain thickness (ranging from 5 to 3,000 nm) and a rectangular and square shape for the electrode fabrication.</li>
		<li>Take the SEM images at different magnifications (from 1,000X to 10,000X) of the targeted pristine material before electrode fabrication by clicking the button &#8220;Snapshot&#8221;.</li>
		<li>Switch to FIB mode and take an FIB image by the snapshot mode to reduce the exposure time of the targeted material under ion beam bombardment.</li>
		<li>Define the electrode deposition area, select the &#8220;Pt deposition&#8221; mode, and input the thickness (0.2-1.0 &#956;m) value of the deposited Pt electrode.</li>
		<li>Introduce the capillary of GIS into the chamber by clicking the box &#8220;Pt dep&#8221; in the &#8220;Gas Injection&#8221; block.</li>
		<li>Take an image by the snapshot mode again and modify the position of the electrodes if the originally defined pattern shifts slightly.</li>
		<li>Turn on the FIB deposition by clicking the button &#8220;Start Patterning&#8221;.</li>
		<li>After deposition, draw the capillary of GIS back by unclicking the box &#8220;Pt dep&#8221; in the &#8220;Gas Injection&#8221; block.</li>
		<li>Switch to SEM mode and check the result of the deposited Pt electrodes on the layer nanocrystal.</li>
		<li>Take the SEM images at different magnifications of the completed devices with two or four electrodes (see Step 3 in Figure 1).</li>
		<li>Set the tilt angle of the holder return to 0 degrees by clicking the button &#8220;Navigation&#8221; and input the tilt angle &#8220;0&#8221;.</li>
		<li>Take the top-viewed SEM images at different magnifications for the estimations of the material width and electrode inter-distance by clicking the button &#8220;Snapshot&#8221;.</li>
		<li>Turn off the electron-beam and ion beam systems and cool down GIS system by clicking the button &#8220;Beam Off&#8221; and the button &#8220;Warm&#8221; in the &#8220;Gas Injection&#8221; block, respectively.</li>
		<li>Vent the chamber by introducing nitrogen gas by clicking the buttons &#8220;Vent&#8221; and then take the holder out of the chamber. It typically takes 5 to 10 min to finish the venting process.</li>
		<li>Close the chamber door and evacuate the chamber.</li>
	</ol>
	</li>
</ol>
3. Characterizations of the MoSe2 Layer Nanocrystal Devices
<ol>
	<li>Thickness Measurement of the Layer Nanocrystals by AFM
	<ol>
		<li>Install the AFM cantilever to the probe holder.</li>
		<li>Turn on AFM program and select &#8220;ScanAsyst&#8221; mode.</li>
		<li>Load the probe holder and connect it with the laser diode head of AFM station.</li>
		<li>Perform the calibration to align the incident laser beam position and the cantilever according to manufacturer&#8217;s protocol.</li>
		<li>Mount the sample (the template chip with FIB-fabricated layer nanocrystal devices) on the sample holder by Cu foil tape.</li>
		<li>Load the sample holder to the AFM station.</li>
		<li>Move the sample holder to the position approximately underneath the laser beam or AFM cantilever.</li>
		<li>Lower down AFM cantilever to the focus position by focusing the optical microscope image of the layer nanocrystal.</li>
		<li>Input scan parameters such as the scan area (6 x 6-30 x 30 &#956;m2), the frequency (0.5-1.5 Hz), and the resolution (256-512 lines).</li>
		<li>Start the program and save data according to the manufacturer&#8217;s protocol.</li>
		<li>Raise the AFM cantilever and take the sample holder out.</li>
		<li>Load the second sample and repeat the measurement procedure described above if need.</li>
		<li>Estimate the thickness of layer nanocrystals by analyzing the AFM image and height profile using the software &#8220;NanoScope Analysis&#8221;. Select a lateral height profile from the AFM image and determine the average thickness value by the flatten area of the profile. (See Figure 2d and 2e)</li>
	</ol>
	</li>
	<li>Current versus voltage (I-V) measurement of the layer nanocrystals
	<ol>
		<li>Mount the sample (the template chip with FIB-fabricated layer nanocrystal devices) on the mica substrate by Cu foil tape.</li>
		<li>Bond the enameled wires or Cu wires on the electrodes of the chip by Ag paste. (See Step 4 in Figure 1.)</li>
		<li>Load the completed sample in the probe station chamber and fix it on the sample holder by Cu foil tape. The cryogenic probe station was located in the dark environment. (See Step 5 in Figure 1.)</li>
		<li>Solder the electrical wires of the sample and the metal electrodes of the probes one by one.</li>
		<li>Cap the chamber top and evacuate the chamber down to 10-4 mbar. Cool down sample to the 77 K by introducing liquid nitrogen into the probe station. Set the temperature range (usually from 80 to 320 K), interval, and dwell time for the temperature control. (Necessary only for temperature-dependent measurement).</li>
		<li>Set the applied voltage sweeping range (typically from -1 to 1 V), voltage interval (0.01 V), and the limited maximal current (10 or 100&#160;&#956;A) in an ultrahigh-impedance multifunctional electrometer for the two-terminal I-V measurement. For four-terminal measurement, set the applied current sweeping range (typically from -100 to 100 &#956;A) and current interval (1 &#956;A).</li>
		<li>Start the program and save the I-V data at room temperature or at different temperatures.</li>
		<li>Open the chamber cap if necessary and take the sample out of the chamber.</li>
		<li>Load the second sample if need and repeat the procedure described above.</li>
		<li>Analyze the I-V curve by plotting the measured current versus applied voltage data using the software. Fit the I-V curve by selecting the Linear Fitting function. Check the linearity of the I-V curve and obtain the slope value (i.e. conductance value). (See Step 6 in Figure 1.)</li>
		<li>Repeat the Step 3.2.10 for the I-V curves measured at different temperatures if need.</li>
		<li>Calculate the conductivity (&#963;) value according to the equation &#963;= G(t/tw) by adopting the parameters obtained by I-V, SEM, and AFM measurements including conductance (G), thickness (t), width (w) and length (l) of the layer nanocrystal.</li>
		<li>Plot the curves of the conductance and conductivity values versus thickness of layer nanocrystals.</li>
	</ol>
	</li>
</ol>

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H., Merlin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Raman Scattering in Materials Science. , (2000).</li><li>Tonndorf, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoluminescence+emission+and+Raman+response+of+monolayer+MoS2,+MoSe2,+and+WSe2.">Photoluminescence emission and Raman response of monolayer MoS2, MoSe2, and WSe2.</a> Opt. Express. 21 (4), 4908-4916 (2013).</li><li>Hu, S. Y., Liang, C. H., Tiong, K. K., Lee, Y. C., Huang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+characterization+of+large+niobium-doped+MoSe2+single+crystals.">Preparation and characterization of large niobium-doped MoSe2 single crystals.</a> J. Crystal Growth. 285 (3), 408-414 (2005).</li><li>Hu, S. Y., Liang, C. H., Tiong, K. K., Huang, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Re+dopant+on+the+electrical+and+optical+properties+of+MoSe2+single+crystals.">Effect of Re dopant on the electrical and optical properties of MoSe2 single crystals.</a> J. Alloys Compounds. 442 (1-2), 1-2 (2007).</li><li>Bougouma, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+and+characterization+of+large,+high+quality+MoSe2+single+crystals.">Growth and characterization of large, high quality MoSe2 single crystals.</a> J. Crystal Growth. 363, 122-127 (2013).</li></ol>

The authors have nothing to disclose.

The accurate determination of the &#963; value and its dimension dependence in the layer nanocrystals is highly dependent on the quality of the electrical contacts. The FIB deposition method used for metal electrode deposition played a crucial role throughout the study. According to electrical, structural, and composition analyses, the fabrication of stable and highly reproducible ohmic contacts, using FIB deposition method, in the MoSe2 or MoS2 devices was facilitated by the formation of t...

Transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2, and WSe2, have an interesting two-dimensional (2D) layer structure and semiconducting properties1-3. Scientists have recently discovered that the monolayer structure of MoS2 shows a substantially enhanced light-emitting efficiency because of the quantum confinement effect. The finding of the new direct-bandgap semiconductor material has attracted substantial attention4-7. In addition, the easily stripped layer structure of TMDs is an excellent platform for studying the fundamental properties of 2D materials. Unlike metallic graphene without the bandgap, TMDs have inherent semiconducting characteristics and have a bandgap in the range of 1-2 eV1,3,8. The 2D structures of the ternary compounds of TMDs9 and the possibility of the integration of these compounds with graphene provide an unprecedented opportunity to develop ultrathin and flexible electronic devices.
Unlike graphene, the room temperature electron mobility values of 2D TMDs are at a moderate level (1-200 cm2V&#8722;1sec&#8722;1 for MoS210-17; approximately 50 cm2V&#8722;1sec&#8722;1 for MoSe218). The optimal mobility values of graphene have been reported to be higher than 10,000 cm2V&#8722;1sec&#8722;1.19-21 Nevertheless, semiconducting TMD monolayers exhibit excellent device performance. For instance, the MoS2 and MoSe2 monolayers or multilayer field-effect transistors exhibit extremely high on/off ratios, up to 106-109 10,12,17,18,22. Therefore, it is crucial to understand the fundamental electrical properties of the 2D TMDs and their bulk materials.
However, studies of the electrical properties of the layer materials have been partially hampered because of the difficulty in forming good ohmic contact on the layer crystals. Three approaches, shadow mask deposition (SMD)23, electron beam lithography (EBL)24,25, and focused-ion beam (FIB) deposition,26,27 have been used to form electrical contacts on nanomaterials. Because SMD typically involves the use of a copper grid as the mask, the spacing between two contact electrodes is mostly larger than 10 &#956;m. Unlike EBL and FIB deposition, metal deposition of electrode arrays on a substrate is performed without targeting or selecting nanomaterials of interest in the SMD method. This approach cannot guarantee that the metal patterns are correctly deposited on individual nanomaterials as the electrodes. The result of the SMD method has an element of chance. The EBL and FIB deposition methods are used in the scanning electron microscope (SEM) system; nanomaterials can be directly observed and selected for electrode deposition. In addition, EBL can be used to easily fabricate metal electrodes with a line width and a contact electrode spacing smaller than 100 nm. However, the residual resist on the nanomaterial surface left during lithography inevitably results in the formation of an insulating layer between the metal electrode and the nanomaterial. Thus, EBL leads to high contact resistance.
The main advantage of electrode fabrication through FIB deposition is that it leads to low contact resistance. Because metal deposition is performed by the decomposition of an organometallic precursor by using an ion beam at the defined area, metal deposition and ion bombardment occur simultaneously. This could destroy the metal&#8211;semiconductor interface and prevent the formation of Schottky contact. Ion bombardment can also eliminate surface contaminants such as hydrocarbons and native oxides, which decreases contact resistance. Ohmic contact fabrication through FIB deposition has been demonstrated for different nanomaterials27-29. In addition, the entire fabrication procedure in the FIB deposition approach is simpler than that in EBL.
As layer semiconductors typically show highly anisotropic electrical conduction, the conductivity in the layer-to-layer direction is several orders of magnitude lower than that in the in-plane direction30,31. This characteristic increases the difficulty of fabricating ohmic contacts and determining electrical conductivity. Therefore, in this study, FIB deposition was used for studying the electrical properties of layer semiconductor nanostructures.

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ohmic contact fabrication using a focused-ion beam technique and electrical characterization for layer semiconductor nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

The determined values of the electrical conductance (G) and conductivity (&#963;) of layer nanomaterials with different thicknesses are highly dependent on the quality of the electrical contacts. The ohmic contacts of the FIB-deposition-fabricated two-terminal MoSe2 devices are characterized by measuring the current&#8211;voltage (I&#8211;V) curve. The room temperature I&#8211;V curves for the two-terminal MoSe2 nanoflake devices with different t...

Watch this Scientific Journal Video about Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures at JoVE.com

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

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12.2K Views.  National Taiwan University of Science and Technology. We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described. 

Video: Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

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 ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

Use of Sacrificial Nanoparticles to Remove the Effects of Shot-noise in Contact Holes Fabricated by E-beam Lithography

Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has been attributed to statistical fluctuations in the number of photons/electrons arriving at a given nano-region arising from shot-noise (SN). The SN varies inversely to the square root of a number of photons/electrons. For a fixed dosage, the SN is larger in EUV and E-beam lithographies than for traditional (193 nm) optical lithography. Bottom-up and top-down patterning approaches are combined to minimize the effects of shot noise in nano-hole patterning. Specifically, an amino-silane surfactant self-assembles on a silicon wafer that is subsequently spin-coated with a 100 nm film of a PMMA-based E-beam photoresist. Exposure to the E-beam and the subsequent development uncover the underlying surfactant film at the bottoms of the holes. Dipping the wafer in a suspension of negatively charged, citrate-capped, 20 nm gold nanoparticles (GNP) deposits one particle per hole. The exposed positively charged surfactant film in the hole electrostatically funnels the negatively charged nanoparticle to the center of an exposed hole, which permanently fixes the positional registry. Next, by heating near the glass transition temperature of the photoresist polymer, the photoresist film reflows and engulfs the nanoparticles. This process erases the holes affected by SN but leaves the deposited GNPs locked in place by strong electrostatic binding. Treatment with oxygen plasma exposes the GNPs by etching a thin layer of the photoresist. Wet-etching the exposed GNPs with a solution of I2/KI yields uniform holes located at the center of indentations patterned by E-beam lithography. The experiments presented show that the approach reduces the variation in the size of the holes caused by SN from 35% to below 10%. The method extends the patterning limits of transistor contact holes to below 20 nm.

Uniformly sized nanoparticles can remove fluctuations in contact hole dimensions patterned in poly(methyl methacrylate) (PMMA) photoresist films by electron beam (E-beam) lithography. The process involves electrostatic funneling to center and deposit nanoparticles in contact holes, followed by photoresist reflow and plasma- and wet-etching steps.

Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different materials show variability in resistive switching properties due to the intrinsic nature of the material used, leading to discrepancies in the field because of underlying operation mechanisms. This highlights a need for a reliable technique to understand mechanisms using nanostructural observations. This protocol explains a detailed process and methodology of in&#160;situ nanostructural analysis as a result of electrical biasing using transmission electron microscopy (TEM). It provides visual and reliable evidence of underlying nanostructural changes in real time memory operations. Also included is the methodology of fabrication and electrical characterizations for asymmetric crossbar structures incorporating amorphous vanadium oxide. The protocol explained here for vanadium oxide films can be easily extended to any other materials in a metal-dielectric-metal sandwiched structure. Resistive switching crossbars are predicted to serve the programmable logic and neuromorphic circuits for next-generation memory devices, given the understanding of the operation mechanisms. This protocol reveals the switching mechanism in a reliable, timely, and cost-effective way in any type of resistive switching materials, and thereby predicts the device&#39;s applicability.

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Presented here is a protocol for analyzing nanostructural changes during in&#160;situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different ...

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar energy and fuel generation, and electrochemical energy storage. Nanoscale characterization of such interfaces has recently been achieved using cryogenic electron microscopy, thereby providing a new path to advancing our fundamental understanding of interface processes.
This contribution provides a practical guide to mapping the structure and chemistry of solid-liquid interfaces in materials and devices using an integrated cryogenic electron microscopy approach. In this approach, we pair cryogenic sample preparation which allows stabilization of solid-liquid interfaces with cryogenic focused ion beam (cryo-FIB) milling to create cross-sections through these complex buried structures. Cryogenic scanning electron microscopy (cryo-SEM) techniques performed in a dual-beam FIB/SEM enable direct imaging as well as chemical mapping at the nanoscale. We discuss practical challenges, strategies to overcome them, as well as protocols for obtaining optimal results. While we focus in our discussion on interfaces in energy storage devices, the methods outlined are broadly applicable to a range of fields where solid-liquid interface play a key role.

Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar ...

Focused Ion Beam Lithography to Etch Nano-architectures into Microelectrodes

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of sophisticated microelectrodes with greater resolution and expanded capabilities. The progress in fabrication technology has supported the development of biomimetic electrodes, which aim to seamlessly integrate into the brain parenchyma, reduce the neuroinflammatory response observed after electrode insertion and improve the quality and longevity of electrophysiological recordings. Here we describe a protocol to employ a biomimetic approach recently classified as nano-architecture. The use of focused ion beam lithography (FIB) was utilized in this protocol to etch specific nano-architecture features into the surface of non-functional and functional single shank intracortical microelectrodes. Etching nano-architectures into the electrode surface indicated possible improvements of biocompatibility and functionality of the implanted device. One of the benefits of using FIB is the ability to etch on manufactured devices, as opposed to during the fabrication of the device, facilitating boundless possibilities to modify numerous medical devices post-manufacturing. The protocol presented herein can be optimized for various material types, nano-architecture features, and types of devices. Augmenting the surface of implanted medical devices can improve the device performance and integration into the tissue.

We have shown that the etching of nano-architecture into intracortical microelectrode devices may reduce the inflammatory response and has the potential to improve electrophysiological recordings. The methods described herein outline an approach to etch nano-architectures into the surface of non-functional and functional single shank silicon intracortical microelectrodes.

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

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Chapters in this video

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Writing and Low-Temperature Characterization of Oxide Nanostructures

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

Atomically Traceable Nanostructure Fabrication

Use of Sacrificial Nanoparticles to Remove the Effects of Shot-noise in Contact Holes Fabricated by E-beam Lithography

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VO_x

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Focused Ion Beam Lithography to Etch Nano-architectures into Microelectrodes