Causes, Diagnosis, and Control Strategies for Elevated Off-State Current in Semiconducting Single-Walled Carbon Nanotube Transistors

1. Why is off-state current a key metric for semiconducting single-walled carbon nanotube transistors?

1.1 What are off-state current and on/off ratio?

In a field-effect transistor (FET), the device regulates the channel current between the source and drain electrodes through the gate voltage. When the device is in the on state, the channel should carry a relatively high current, known as the on-state current, or Ion. When the device is in the off state, the channel current should be as low as possible; this current is known as the off-state current, or Ioff.

The ratio of on-state current to off-state current is called the on/off ratio, expressed as Ion/Ioff. If Ioff is high, the Ion/Ioff ratio will be limited even when Ion is high, leading to reduced switching capability of the device.

1.2 Why is s-SWCNT suitable as a gate-tunable channel?

Single-walled carbon nanotubes (SWCNTs) have high carrier mobility, excellent current-carrying capability, solution processability, and mechanical flexibility. They are therefore considered important candidate materials for high-performance thin-film transistors, flexible electronics, and sensor devices.

Among them, semiconducting single-walled carbon nanotubes, or s-SWCNTs, are suitable as FET channel materials because their conductance can be modulated by the gate voltage. The gate can regulate the carrier concentration in the channel, allowing the device to switch between the on and off states.

Whether s-SWCNTs can form a channel that is effectively controlled by the gate is the foundation for evaluating the performance of this type of transistor.

1.3 What are the main sources of elevated off-state current?

The factors affecting the off-state current of s-SWCNT FETs mainly include material purity, thin-film network structure, device interfaces, and nanotube density control.

Factor	Effect on off-state current
Residual metallic single-walled carbon nanotubes, or m-SWCNTs, in the material	Form conductive pathways that are difficult to turn off with the gate
Uncontrolled conductive networks in the thin film	Local percolating pathways increase off-state current
Unstable device interfaces and contacts	Introduce leakage, hysteresis, or device-to-device variation
Excessively high nanotube density or local aggregation	Increase abnormal conductive pathways and channel nonuniformity

These factors correspond respectively to three experimental stages: material purity, thin-film structure, and device interfaces.

1.4 Which device properties are affected by elevated off-state current?

For logic circuits, low-power electronic devices, and sensor readout circuits, elevated off-state current directly affects signal discrimination, power consumption, and device uniformity.

Phenomenon	Effect on device performance
Elevated off-state current	Reduced on/off ratio and poorer signal discrimination
Presence of leakage pathways	Difficulty achieving low-power operation
Large device-to-device variation	Unstable array circuits and sensor readouts

In multi-device arrays or sensor readout systems, elevated off-state current can further amplify device-to-device variation, reducing the stability of the output signal.

1.5 Why is on-state current alone insufficient?

When evaluating s-SWCNT FETs, one should not focus only on on-state current or mobility. A high Ion can be achieved by increasing nanotube density or improving the conductivity of the thin film. However, if the nanotube density is too high, or if the channel contains non-switchable pathways formed by m-SWCNTs, Ioff may also increase at the same time.

Therefore, even if a device exhibits high Ion, it cannot be considered to have good transistor switching characteristics if Ioff is also high. The optimization goal for s-SWCNT FETs should be to reduce Ioff while maintaining a high Ion, so that the channel exhibits stable and gate-controllable switching behavior.

2. Why can raw SWCNTs lead to elevated off-state current?

2.1 Origin of metallic and semiconducting behavior in SWCNTs

The electronic properties of SWCNTs are determined by their chiral indices, (n,m). SWCNTs with different chiralities have different diameters, bandgaps, and electronic structures, and can therefore behave as either metallic or semiconducting materials.

The raw or unsorted SWCNTs used in experiments are usually not a single material with identical electronic properties. Instead, they consist of carbon nanotubes with different diameters, chiralities, and electronic types. Typical as-synthesized samples usually contain both metallic and semiconducting SWCNTs, with a ratio that can approach 1:2. Therefore, for an FET channel, this mixed composition creates a direct problem: the sample contains not only gate-tunable s-SWCNTs, but also m-SWCNTs that are difficult to turn off using the gate.

Electronic type	Role in the FET channel
s-SWCNT	Serves as the main gate-tunable channel material
m-SWCNT	May form conductive pathways that cannot be effectively controlled by the gate

Raw SWCNTs should not be simply regarded as semiconducting channel materials suitable for FETs. To obtain low off-state current and a high on/off ratio, it is first necessary to reduce the proportion of m-SWCNTs and improve the electronic-type purity of s-SWCNTs.

2.2 How do m-SWCNTs form non-switchable conductive pathways?

The main effect of m-SWCNTs on FETs is that they compromise the turn-off capability of the channel. When an m-SWCNT directly bridges the source and drain electrodes, or when it connects with other nanotubes in a random network to form a percolating pathway, the gate voltage has difficulty cutting off this portion of the current pathway.

Form of m-SWCNT presence	Possible consequence
A single m-SWCNT bridges the source and drain electrodes	Forms a direct leakage pathway
Multiple m-SWCNTs interconnect within the network	Forms a local percolating conductive channel
m-SWCNTs and s-SWCNTs form a mixed film	Raises off-state current and lowers the on/off ratio

This is why raw SWCNTs usually require sorting before being used in FETs. The core purpose of sorting is not merely to improve material purity, but to reduce the non-switchable pathways caused by m-SWCNTs, so that the channel current is mainly controlled by s-SWCNTs.

3. How does polymer sorting improve s-SWCNT purity?

3.1 Selective dispersion by PFO and PFO-BPy

After recognizing that m-SWCNTs compromise the turn-off capability of the channel, the primary task in the material preparation stage is to improve the electronic-type purity of s-SWCNTs. Polymer sorting is an important method for this purpose, and polyfluorene-based conjugated polymers are among the most widely used systems.

The basic principle of polymer sorting is to use selective interactions between polymers and different SWCNTs, allowing SWCNTs with specific electronic types, diameters, or chiralities to be more stably dispersed in solution and enriched in the supernatant after centrifugation. Common polymer systems include:

Polymer	Full name or description	Main function
PFO	poly(9,9-dioctylfluorene), poly(9,9-dioctylfluorene-2,7-diyl)	Selectively disperses certain s-SWCNTs
PFO-BPy	poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(2,2′-bipyridine-6,6′-diyl)], a polyfluorene-bipyridine copolymer	Shows relatively high selectivity for s-SWCNTs within certain chirality and diameter ranges

Compared with conventional surfactant dispersion, polymer sorting is characterized by its ability to exhibit electronic-type, diameter, or chirality selectivity during the dispersion process. For example, PFO can selectively disperse specific (n,m) s-SWCNTs. Surfactants such as sodium cholate are commonly used for aqueous dispersion and can also participate in separation processes when combined with density-gradient ultracentrifugation or aqueous two-phase separation. However, simple surfactant dispersion generally does not exhibit strong electronic-type or chirality selectivity as directly as conjugated polymer-wrapping systems such as PFO or PFO-BPy.

3.2 What problems does polymer sorting solve?

Polymer sorting mainly addresses material-level issues related to electronic-type purity and dispersion state. Through polymer wrapping, sonication, and centrifugation, poorly dispersed bundles, particulate impurities, and some unstable dispersed components can be sedimented, leaving polymer-wrapped s-SWCNTs enriched in the supernatant. Its effects can be summarized in three aspects:

Effect	Significance for FETs
Enrichment of s-SWCNTs	Improves the electronic-type purity of the channel material
Improved individual nanotube dispersion	Reduces the impact of bundles and aggregation on channel uniformity
Regulation of diameter and chirality distribution	Helps achieve more consistent electronic structures

Previous studies have shown that specific PFO-BPy sorting systems can produce s-SWCNTs with extremely high semiconducting purity. It should be noted that such results are closely related to polymer structure, the source of the raw SWCNTs, solvent, dispersion conditions, and characterization methods. They should not be simply generalized to all polymer sorting systems.

3.3 What problems can polymer sorting still not solve?

Polymer sorting mainly improves material purity, dispersion state, and partial chirality selectivity, but it cannot directly replace thin-film formation and device-structure optimization.

Problems that polymer sorting cannot directly solve	Effect on the device
Whether the nanotube density in the thin film is appropriate	Affects both on-state and off-state current
Whether nanotubes are aligned along the source-drain direction	Affects carrier transport efficiency
Whether local aggregation or bundles are present	Affects device uniformity and leakage
Whether electrode contact is good	Affects on-state current and mobility
Whether the dielectric interface is stable	Affects hysteresis and off-state leakage

Polymer sorting addresses material purity and dispersion state. To obtain stable FET performance, it is still necessary to further control thin-film structure, nanotube density, degree of alignment, electrode contact, and dielectric interface.

4. Why do high-purity s-SWCNTs still require control of film structure?

Even after the material has been sorted, an unsuitable thin-film structure can still cause FETs to exhibit elevated off-state current, insufficient on-state current, or large device-to-device variation. The channel performance of an FET is not determined solely by the intrinsic properties of individual nanotubes. It also depends on the density, alignment, connection mode, and spatial uniformity of carbon nanotubes in the channel.

4.1 Random networks: simple to fabricate but difficult to control

Random-network films are relatively simple to prepare and are suitable for large-area processing. However, their conductive pathways are formed by the random overlap of many carbon nanotubes, making it difficult to precisely control each transport path.

If the nanotube density is too low, the on-state current will be insufficient. If the nanotube density is too high, a complex percolating network can easily form, increasing the risk of leakage. In network-type channels, even a small amount of non-switchable components or local high-density regions may alter the overall conductive pathways. Therefore, random networks require careful optimization of deposition concentration, number of deposition cycles, and network density.

4.2 Aligned arrays: improving transport efficiency and device uniformity

For FETs that require high conductance per unit width and good device uniformity, aligned s-SWCNT arrays offer clear advantages. When nanotubes are aligned along the source-drain direction, the carrier transport path is more direct, which helps improve conductance per unit width. Compared with random networks, aligned arrays can reduce unnecessary intertube hopping transport and improve channel transport efficiency.

Studies have shown that high-purity, aligned, individually dispersed s-SWCNT arrays can simultaneously achieve high on-state conductance and high on/off ratio. The performance improvement mainly arises from three factors: high semiconducting purity, high degree of alignment, and good individual nanotube dispersion during deposition.

4.3 Nanotube density: balancing on-state and off-state current

Nanotube density should be optimized according to the target device requirements. If the density is too low, conductive pathways are insufficient and the on-state current is low. If the density is too high, intertube coupling, local electrostatic screening, and incomplete depletion may become stronger, increasing the residual off-state current. If m-SWCNT residues, local aggregation, or bundles are also present, leakage pathways that are difficult to fully turn off with the gate are more likely to form. Nanotube density optimization should therefore be considered together with film uniformity and alignment control.

Nanotube density state	Possible result
Too low	Low on-state current and unstable mobility extraction
Optimized nanotube density	Helps balance on-state and off-state current
Too high	Enhanced intertube coupling, increased leakage pathways, and greater difficulty in turning off the channel

4.4 FESA film formation: improving channel structure through controlled deposition

Floating evaporative self-assembly, or FESA, is a method used to construct aligned s-SWCNT arrays. In this method, an organic ink containing polymer-wrapped SWCNTs is spread on the water surface, allowing the ink to form a thin layer at the gas-liquid interface. As the solvent evaporates, the contact line moves, and the substrate is withdrawn, s-SWCNTs are deposited on the substrate as aligned stripes.

The advantage of FESA is that deposition parameters can be used to regulate stripe spacing and nanotube density, thereby improving the structural uniformity of the film. For FETs, the significance of this type of film-formation method is not simply to increase coverage, but to make the conductive pathways in the channel more controllable.

5. How can FET metrics be used to identify the source of problems?

For semiconducting single-walled carbon nanotube field-effect transistors, or s-SWCNT FETs, a single metric is insufficient to evaluate device quality. On-state current, off-state current, on/off ratio, mobility, hysteresis, and device uniformity should be analyzed together to determine whether the problem originates from material purity, film structure, contact interfaces, or gate dielectric leakage.

It should be noted that Ion, Ioff, and Ion/Ioff should be reported together with the testing conditions, such as VDS, VG sweep range, off-state voltage point, sweep direction, sweep rate, ambient atmosphere, channel length, and channel width. When comparing these metrics across different devices or different studies, direct comparison without considering the testing conditions should be avoided.

5.1 Off-state current Ioff: determining whether abnormal leakage pathways exist

Elevated off-state current, or Ioff, usually indicates the presence of current pathways in the device that are not effectively controlled by the gate. However, its source is not necessarily limited to residual metallic single-walled carbon nanotubes, or m-SWCNTs.

Cause of elevated Ioff	Possible mechanism
Residual m-SWCNTs	Form non-switchable conductive pathways
Excessively high nanotube density	Percolating pathways appear in the random network
Dielectric leakage	Gate dielectric defects introduce additional current
Local aggregation	Forms nonuniform conductive regions
Environmental adsorption or interface traps	Causes residual carriers and hysteresis

If the on-state current, or Ion, is high but Ioff is also high, priority should be given to checking for residual m-SWCNTs, excessive nanotube density, local aggregation, and dielectric leakage.

5.2 On-state current Ion: evaluating channel conduction capability

Ion reflects the conductivity of the device in the on state. A low Ion does not necessarily indicate poor electronic-type purity of the material; it may also arise from film formation, alignment, or contact problems.

Cause of low Ion	Possible mechanism
Insufficient nanotube density	Too few effective conductive pathways in the channel
Insufficient degree of alignment	Carrier transport paths are not direct
High source-drain contact resistance	Inefficient contact between the electrodes and s-SWCNTs
Many bundles or defects	Reduced effective transport capability
Unsuitable channel length or pattern design	Increased transport resistance or reduced effective channel utilization

If Ioff is low but Ion is also low, the problem is usually not a leakage pathway. It is more likely related to insufficient nanotube density, high contact resistance, insufficient alignment, or an unreasonable channel-structure design.

5.3 On/off ratio Ion/Ioff: comprehensively evaluating switching performance

The on/off ratio, Ion/Ioff, is affected by both Ion and Ioff. A low on/off ratio should not be attributed only to material purity; it should be analyzed based on the relative changes in Ion and Ioff.

Test observation	Main issue
Ion is high and Ioff is also high	Significant channel leakage or non-switchable pathways
Ioff is low and Ion is also low	Insufficient channel conduction capability
Both Ion and Ioff fluctuate significantly	Insufficient film uniformity or device fabrication consistency
Poor switching slope and obvious hysteresis	Interface traps, environmental adsorption, or gate dielectric issues are prominent

When analyzing the on/off ratio, one should not focus only on a single numerical value. The shape of the transfer curve, Ion, Ioff, hysteresis, and device structure should also be considered. For s-SWCNT FETs, the optimization direction should be to increase Ion while controlling Ioff, rather than simply increasing nanotube density to obtain high on-state current.

5.4 Mobility, hysteresis, and uniformity: evaluating transport, interfaces, and process stability

Mobility reflects the carrier transport capability of the channel. However, in network-type or array-type s-SWCNT FETs, mobility is often affected by nanotube density, degree of alignment, contact resistance, channel geometry, and model assumptions. Mobility should be analyzed together with Ion, Ioff, Ion/Ioff, and device statistics.

Hysteresis usually appears as a mismatch between forward and reverse gate-voltage sweep curves. Its sources may include water and oxygen adsorption, dielectric traps, residual polymer, and interface charge trapping. Device uniformity reflects the stability of the film-formation and fabrication processes.

Test metric	Main meaning	Abnormal behavior	Priority checks
Off-state current Ioff	Residual current in the off state	Elevated Ioff	Residual m-SWCNTs, leakage pathways, dielectric leakage, local aggregation
On-state current Ion	Channel current in the on state	Low Ion	Insufficient nanotube density, high contact resistance, poor alignment
On/off ratio Ion/Ioff	Difference between on-state and off-state current	Low on/off ratio	Excessively high Ioff or excessively low Ion
Apparent mobility	Overall channel transport capability	Large numerical variation	Nonuniform network, contact variation, unsuitable model
Hysteresis	Difference between forward and reverse sweep curves	Obvious hysteresis	Water/oxygen adsorption, dielectric defects, residual polymer, interface traps
Device uniformity	Performance distribution across multiple devices	Large dispersion	Nonuniform film formation, local aggregation, patterning errors

6. How can a material-film-device inspection workflow be established experimentally?

To improve the reproducibility of s-SWCNT FETs, experimental design should avoid optimizing only one stage. A more reasonable workflow is to verify the process step by step from material sorting to film structure and then to device testing.

6.1 Material stage: confirming purity and chirality distribution

At the material stage, it is necessary to confirm whether the s-SWCNTs have sufficiently high electronic-type purity, and whether the chirality and diameter distributions are suitable for the target device. Applicable characterization methods include:

Characterization method	Main function
Ultraviolet-visible-near infrared spectroscopy, or UV-Vis-NIR	Identifies different electronic transition features and evaluates sorting effectiveness
Raman spectroscopy	Analyzes radial breathing modes, G band, and metallic component features
Electrical statistical testing	Directly evaluates the effect of small amounts of m-SWCNTs on device off-state current

Spectroscopy can reflect the electronic-structure features of sorted samples, while electrical testing can more directly reveal the effect of small amounts of m-SWCNTs on off-state current and on/off ratio.

6.2 Film-formation stage: confirming alignment, density, and aggregation state

At the film-formation stage, it is necessary to confirm whether the film is uniform, whether the nanotube density is appropriate, whether the degree of alignment meets the device requirements, and whether local aggregation or bundles are present. Applicable morphological characterization methods include:

Characterization method	Main function
Scanning electron microscopy, or SEM	Observes large-area film uniformity, alignment, and local aggregation
Atomic force microscopy, or AFM	Observes individual nanotube dispersion, bundle height, and surface morphology
Optical microscopy	Rapidly checks large-scale deposition nonuniformity or pattern defects

Particular attention should be paid to the presence of local aggregation, overly dense regions, bundles, and abnormal conductive pathways bridging the source and drain.

6.3 Device stage: confirming electrical metrics and statistical distribution

At the device stage, mobility or on-state current should not be reported alone. Ion, Ioff, Ion/Ioff, transfer-curve hysteresis, number of devices, and performance distribution should also be reported. For thin-film network devices, statistical results are often more representative of process reliability than the best individual device. At minimum, the following information should be considered:

Information type	Function
Transfer curve of an individual device	Evaluates switching behavior and hysteresis
Performance distribution across multiple devices	Evaluates process uniformity
Comparison of different nanotube densities	Determines the balance point between Ion and Ioff
Blank device or dielectric leakage test	Excludes leakage from non-channel sources
Electrical comparison before and after bending	Evaluates the stability of flexible devices

7. Common abnormal phenomena and verification methods

Experimental phenomenon	Possible cause	Suggested verification method
Off-state current remains consistently high	Residual m-SWCNTs, excessive nanotube density, dielectric leakage, or local aggregation	Strengthen sorting-purity verification; reduce deposition concentration or number of deposition cycles; test leakage in a blank dielectric structure; observe morphology by SEM/AFM
Low on/off ratio but very high on-state current	Excessive nanotube density, local percolating network, or non-switchable pathways	Reduce deposition concentration; compare devices with different nanotube densities; observe the channel region by SEM/AFM
Both on-state current and off-state current are low	Insufficient s-SWCNT quantity, insufficient alignment, or high source-drain contact resistance	Increase the number of deposition cycles; optimize alignment-based film-formation conditions; compare different electrode materials or annealing conditions
Large device-to-device variation	Nonuniform film, local aggregation, patterning errors, or contact variation	Expand the morphology characterization area; collect statistics from multiple devices; compare device performance across different regions
Obvious hysteresis in the transfer curve	Interface traps, water/oxygen adsorption, residual polymer, or unstable dielectric surface state	Improve dielectric surface treatment; perform vacuum annealing; test after encapsulation; compare forward and reverse sweep curves
Performance degradation after bending of flexible devices	Electrode cracking, dielectric damage, channel slippage, or interface contact failure	Test Ion, Ioff, Ion/Ioff, and hysteresis before and after bending; observe the electrode and channel regions morphologically

8. From FETs to flexible electronics: a controllable channel remains the foundation

8.1 Why do flexible applications still require low off-state current?

The unique value of s-SWCNTs lies in their combination of electrical performance, solution processability, and mechanical flexibility. This makes them suitable for flexible transistors, wearable sensors, flexible display drivers, and low-temperature processed electronic devices.

However, flexible applications do not change the basic requirements of FETs. Even if a device can be bent or stretched, the channel still needs to be controllable, the off-state current must remain sufficiently low, and device-to-device uniformity must be maintained. If the off-state current is high, flexible devices will still be limited in low-power circuits and sensor readout applications.

8.2 Which electrical metrics should be monitored before and after bending?

Flexible s-SWCNT FETs should not emphasize only “bendability” or “stretchability”; key electrical metrics should also be compared before and after bending.

Metric	Change to monitor before and after bending
Ion	Determines whether channel conduction capability decreases
Ioff	Determines whether new leakage pathways are generated
Ion/Ioff	Determines whether switching performance is maintained
Mobility	Determines whether carrier transport is impaired
Hysteresis	Determines whether the interface state deteriorates
Device uniformity	Determines whether array stability is maintained after mechanical deformation

Mechanical flexibility is an important advantage of s-SWCNTs, but electrical stability determines whether the device is truly usable.

9. Representative Materials and Reagents Related to Semiconducting Carbon Nanotube Transistor Research

Table 1. Core Carbon Nanotube Materials and Control Samples

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Semiconducting single-walled carbon nanotubes	308068-56-6	C434657	Single-Walled Carbon Nanotubes	≥98% Semiconducting	Used for constructing semiconducting carbon nanotube channels; relevant to studies of off-state current, on/off ratio, and channel gate controllability.
Metallic single-walled carbon nanotube control	308068-56-6	C434658	Single-Walled Carbon Nanotubes	≥98% Metallic	Used as a metallic carbon nanotube residue control; relevant to studies of non-switchable conductive pathways and elevated off-state current.
Unsorted single-walled carbon nanotube raw material	308068-56-6	C124534	Single-Walled Carbon Nanotubes	≥95%, single-walled, dia. <2 nm, length 5–30 μm, Moving Catalyst	Used as a pre-sorting raw-material control; relevant to studies of the need for sorting mixed-electronic-type carbon nanotubes.
Semiconducting single-walled carbon nanotube dispersion	—	C141008	Semiconducting HiPCO Single-Walled Carbon Nanotube Dispersion in Toluene	≥99.9%	Used for high-purity semiconducting carbon nanotube film formation; relevant to organic dispersion systems, thin-film deposition, and FET channel fabrication.
Semiconducting single-walled carbon nanotube dispersion	—	C141009	Semiconducting Arc Single-Walled Carbon Nanotube Dispersion in Toluene	≥99.9%	Used for comparing semiconducting carbon nanotubes from different sources; relevant to studies of diameter distribution, chirality differences, and film-forming performance.
Metallic single-walled carbon nanotube dispersion control	—	C141010	Metallic HiPCO Single-Walled Carbon Nanotube Dispersion in Water	≥90%	Used as a metallic carbon nanotube dispersion control; relevant to analysis of leakage pathways, low on/off ratio, and sources of off-state current.
Chiral single-walled carbon nanotubes	308068-56-6	C434641	Single-Walled Carbon Nanotubes	≥90% carbon basis, ≥77% as carbon nanotubes, (7,6) chirality, 0.83 nm average diameter	Used for chirality- and diameter-related studies; relevant to bandgap, electronic structure, and differences in carbon nanotube channel performance.
Mixed-type single-walled carbon nanotube dispersion	—	C141004	Mixed-Type HiPCO Single-Walled Carbon Nanotube Dispersion in Water	≥98%	Used as a mixed-type carbon nanotube dispersion control; relevant to studies of changes in material electrical behavior and on/off ratio before and after sorting.

Table 2. Polymer Sorting Agents, Surfactants, and Separation Media

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Polymer sorting agent	123864-00-6	P290349	Poly(9,9-dioctylfluorene-2,7-diyl) (PFO)	Sublimed grade, ≥99%	Used for conjugated-polymer wrapping and sorting; relevant to enrichment of semiconducting carbon nanotubes and reduction of metallic components.
Polymer sorting agent	1423043-97-3	P1505006	Poly[2,2′-bipyridine]-6,6′-diyl(9,9-dioctyl-9H-fluorene-2,7-diyl)]	Mw > 50000	Used for selective dispersion of semiconducting carbon nanotubes; relevant to high-purity sorting, chirality selection, and channel material preparation.
Polymer sorting agent	19456-48-5	P1504868	Poly(9,9-dioctylfluorene-2,7-diyl) (PF8/PFO)	—	Used in polyfluorene-based wrapping and sorting systems; relevant to semiconducting carbon nanotube dispersion, purity enhancement, and organic-phase processing.
Anionic surfactant	151-21-3	S432157	Sodium Dodecyl Sulfate (SDS)	Anhydrous grade, ACS, ≥99%	Used for aqueous dispersion of carbon nanotubes and as a separation control; relevant to dispersion stability, bundle exfoliation, and aqueous processing.
Bile-salt surfactant	302-95-4	S274361	Sodium Deoxycholate	High purity	Used in aqueous carbon nanotube dispersion and density-based separation systems; relevant to bundle dispersion, surface wrapping, and auxiliary electronic-type separation.
Bile-salt surfactant	361-09-1	S161419	Sodium Cholate	Moligand™, ≥98%	Used as an aqueous carbon nanotube dispersion control; relevant to studies of the co-dispersion behavior of semiconducting and metallic carbon nanotubes.
Bile-salt surfactant	206986-87-0	S104205	Sodium Cholate Hydrate	≥98%	Used in aqueous dispersion and separation systems; relevant to carbon nanotube surface stabilization and comparison of sorting conditions.
Biomolecular sorting material	9007-49-2	D1501340	Deoxyribonucleic Acid Sodium Salt from Salmon Sperm	BioReagent, ≥80% (HPLC)	Used for nucleic-acid-assisted carbon nanotube sorting; relevant to chirality recognition, selective wrapping, and aqueous separation.
Two-phase separation polymer	9004-54-0	D400730	Dextran	Mw 6000	Used in aqueous two-phase separation systems; relevant to electronic-type separation of carbon nanotubes and dispersion-phase regulation.
Density-gradient medium	92339-11-2	I342725	Iodixanol	Moligand™, ≥98%	Used in density-gradient separation systems; relevant to fractionation of carbon nanotubes by electronic type or diameter.
Two-phase separation polymer	25322-68-3	P103724	Polyethylene Glycol (PEG)	Average Mn 4000	Used in aqueous two-phase separation systems; relevant to carbon nanotube phase partitioning, dispersion stability, and sorting-condition control.

Table 3. Solvents, Dispersion Media, and Film-Formation-Related Media

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Siloxane film-formation medium	63148-62-9	S433164	Silicone Oil	Viscosity 5 cSt (25°C)	Used for siloxane-related film formation and flexible-system processing; relevant to flexible device interfaces, coating, and wettability adjustment.
Organic dispersion solvent	67-66-3	C1506328	Chloroform (regulated precursor chemical)	Anhydrous grade, ≥99%, contains ethanol as stabilizer	Used for carbon nanotube organic inks and dissolution of conjugated materials; relevant to aligned deposition, thin-film formation, and device processing.
Organic dispersion solvent	109-99-9	T120775	Tetrahydrofuran (THF)	Anhydrous grade, ≥99.9%, contains 250 ppm BHT stabilizer	Used for dissolving polymers and organic semiconductors; relevant to sorting-polymer processing, solution processing, and thin-film preparation.
Organic dispersion solvent	108-90-7	C431386	Chlorobenzene	Anhydrous grade, ≥99.8%	Used for solution processing of conjugated polymers and optoelectronic materials; relevant to organic-phase film formation and active-layer fabrication.
Organic dispersion solvent	108-88-3	T399633	Toluene (regulated precursor chemical)	Anhydrous grade, ≥99.8%	Used in polyfluorene-based sorting systems and semiconducting carbon nanotube dispersions; relevant to organic dispersions, thin-film deposition, and channel preparation.
Polar dispersion solvent	872-50-4	M119668	N-Methyl-2-pyrrolidone (NMP)	Anhydrous grade, ≥99.5%	Used in carbon nanotube dispersion and slurry systems; relevant to dispersion stability, ink preparation, and thin-film processing.
High-boiling organic solvent	95-50-1	D119675	o-Dichlorobenzene	Anhydrous grade, ≥99%	Used for processing poorly soluble conjugated materials and carbon nanomaterials; relevant to film-formation windows, drying processes, and adjustment of film uniformity.
Aqueous medium	7732-18-5	W119424	Deionized Water	Deionized	Used for aqueous dispersion, surfactant systems, and floating self-assembly processes; relevant to water-surface deposition, dispersion preparation, and cleaning steps.

Table 4. Materials Related to Device Structure, Interfaces, and Flexible Systems

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Silicon-related material	7440-21-3	S108981	Silicon Powder	PrimorTrace™, ≥99.99% metals basis, 40–200 mesh	Used for silicon-related material research or control systems; relevant to the background of silicon-based substrates, back-gate structures, and semiconductor device fabrication.
Silicon dioxide-related material	7631-86-9	S118568	Silicon Dioxide	PrimorTrace™, ≥99.99% metals basis, 1–3 mm	Used for silicon dioxide-related material research or insulating-material controls; relevant to the background of gate dielectrics, interface traps, leakage control, and hysteresis analysis.
Polyester-related material	25038-59-9	P303204	Poly(ethylene terephthalate)	Granular, 30% glass particles as reinforcer	Used for polyester composite materials or control studies related to flexible electronics; relevant to substrate material selection, low-temperature processing, and mechanical stability discussions.
Flexible siloxane material	9016-00-6	P195721	Poly(dimethylsiloxane), trimethylsiloxy terminated	Average M.W. 115,000	Used in elastomer and flexible-device systems; relevant to stretchable substrates, interface buffering, and mechanical deformation testing.
Metal-contact-related material	7440-57-5	G112793	Gold Nanopowder	≥99.9% metals basis, ≤500 nm	Used for research related to metal contacts, conductive fillers, or electrode materials; relevant to source-drain electrodes, contact resistance, and flexible conductive structures.
Metal-contact-related material	7440-05-3	P106012	Palladium Powder	≥99.9% metals basis, ≤1 μm	Used for research related to palladium contact materials; relevant to source-drain contacts in carbon nanotube transistors, contact resistance, and on-state current optimization.
Metal-contact-related material	7440-47-3	C141222	Chromium Powder	≥99.5% metals basis, ≤10 μm	Used for research related to chromium adhesion layers or composite metal contacts; relevant to electrode stability, interfacial bonding, and device processing.

Table 5. Optoelectronic Extension Materials and Organic Semiconductor Acceptor/Donor Materials

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Fullerene acceptor material	99685-96-8	F434635	Fullerene-C₆₀	Sublimed grade, ≥99.9%	Used for carbon nanotube optoelectronic heterojunction research; relevant to exciton dissociation, charge transfer, and photovoltaic device extensions.
Polymer donor material	104934-50-1	P431318	Poly(3-hexylthiophene-2,5-diyl) (P3HT)	Regioregular, average Mw 85000–100000	Used in organic semiconductor and optoelectronic active-layer research; relevant to donor materials, heterostructure construction, and photoresponse analysis.
Polymer donor material	156074-98-5	P475798	Poly(3-hexylthiophene-2,5-diyl) (P3HT)	Regioregular	Used in organic semiconductor thin-film research; relevant to donor polymers, thin-film morphology, and optoelectronic device performance.
Fullerene acceptor material	160848-22-6	P400139	[6,6]-Phenyl-C₆₁-butyric Acid Methyl Ester	≥99.5%	Used in organic optoelectronic acceptor systems; relevant to charge separation, electron transport, and carbon nanotube optoelectronic device extensions.
Fullerene acceptor material	609771-63-3	P135215	[6,6]-Phenyl-C₇₁-butyric Acid Methyl Ester	≥97%, contains BHT stabilizer, mixture of isomers	Used in organic photovoltaic and photodetector acceptor systems; relevant to near-infrared absorption matching, charge extraction, and heterojunction active-layer research.

Note: The above are representative Aladdin products. More product specifications can be searched on the Aladdin website by “product name / CAS / catalog number.”

References

[1] Shea M. J., Brady G. J., Zhao J., Wu M.-Y., Evensen H. T. Polymer-Sorted Semiconducting Carbon Nanotubes for Transistors and Solar Cells. Sigma-Aldrich Technical Article.

[2] Brady G. J., Joo Y., Wu M., Shea M. J., Gopalan P., Arnold M. S. Polyfluorene-Sorted, Carbon Nanotube Array Field-Effect Transistors with Increased Current Density and High On/Off Ratio. ACS Nano, 2014, 8(11): 11614–11621. DOI: 10.1021/nn5048734.

[3] Joo Y., Brady G. J., Arnold M. S., Gopalan P. Dose-Controlled, Floating Evaporative Self-Assembly and Alignment of Semiconducting Carbon Nanotubes from Organic Solvents. Langmuir, 2014, 30(12): 3460–3466. DOI: 10.1021/la500162x.

[4] Wang J., Lei T. Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping. Polymers, 2020, 12(7): 1548. DOI: 10.3390/polym12071548.

[5] Wang H., Bao Z. Conjugated Polymer Sorting of Semiconducting Carbon Nanotubes and Their Electronic Applications. Nano Today, 2015, 10(6): 737–758.

[6] Tang D.-M., Cretu O., Ishihara S., et al. Chirality Engineering for Carbon Nanotube Electronics. Nature Reviews Electrical Engineering, 2024, 1: 149–162. DOI: 10.1038/s44287-023-00011-8.

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