Nanowires: Properties, Preparation Routes, and Process Selection (Comprehensive Analysis of Top-Down and Bottom-Up Approaches with Recommended Aladdin Reagents)

Introduction: Why Nanowires?

The performance of conventional devices is often limited by the intrinsic properties of the underlying materials (such as intrinsic carrier concentration, bandgap, thermal conductivity, etc.). Once we enter the nanoscale, device performance is no longer determined solely by what the material is; it also depends strongly on what shape and what dimensions the material is engineered into.

Nanowires are a representative class of one-dimensional (1D) nanostructures, characterized by:

1. Diameter: On the order of ~1 to a few hundred nanometers

2. Length: Typically reaching tens to hundreds of micrometers

3. Morphology: Highly anisotropic, wire-like one-dimensional structures

4. Structure: Often single-crystalline or nearly single-crystalline, with defect densities that can be significantly lower than in bulk materials

Thanks to this unique morphology, nanowires combine high specific surface area, tailorable geometry, and excellent crystal quality. They provide an ideal platform for exploring and exploiting nanoscale effects, and show great promise in sensors, energy storage, biointerfaces, optoelectronic devices, and beyond.

Key Properties and Application Advantages of Nanowires

1. High Specific Surface Area and Interface Effects

Because of their extremely small diameter, nanowires possess a very high surface-to-volume ratio:

1. Surface states, surface adsorption, and surface functionalization exert a pronounced influence on overall properties.

2. For gas sensors and biochemical sensors, nanowires are highly sensitive to molecules or ions present in the environment.

3. Many nanowires are single-crystalline, with long axial conduction paths and few grain boundaries, which is favorable for rapid transport of electrons or ions.

Typical application examples:

1. Chemical/biological sensors:

By modifying receptor molecules on the nanowire surface, even minute concentration changes can induce marked variations in electrical conductivity.

2. Battery electrode materials:

(1) Axially, nanowires provide long, continuous electron transport pathways.

(2) Radially, they offer large interfacial areas in contact with the electrolyte, enabling fast charge and discharge.

2. Size-Dependent Optical, Thermal, and Mechanical Properties

When the nanowire diameter becomes comparable to or smaller than the wavelength of visible light (approximately 400–700 nm), and comparable to the phonon mean free path, a series of size effects arise:

1. Optical properties tunable by geometry

(1) In the visible range, nanowires operate in the so-called wave-optics regime.

(2) By varying diameter, length, and arrangement, one can select and tune the supported optical modes.

(3) This enables the design of highly absorbing photodetectors, low-reflectance surfaces, color filters, and related structures.

2. Reduced thermal conductivity

(1) When the nanowire diameter is smaller than or comparable to the phonon mean free path in the material,

(2) Phonons undergo strong scattering at interfaces → the thermal conductivity can be significantly lower than that of the bulk.

(3) This is highly relevant for thermoelectric materials and thermal management devices.

3. Enhanced mechanical flexibility

(1) Small dimensions and high surface area facilitate strain relaxation and redistribution at the surface.

(2) Provided there are no severe structural defects, many semiconductor or inorganic materials exhibit much higher elastic strain limits in the nanowire form.

4. Anisotropic transport

(1) Along the nanowire axis, long-range, directional charge or ion transport pathways can be established.

(2) In the radial direction, rapid injection or collection can be achieved via encapsulation or doping.

To fully harness these advantages, nanowires must first be synthesized in a stable and controllable manner. From a process perspective, nanowire fabrication methods can be broadly categorized into two classes:

1. Top-down: “Carving” nanowires out of bulk materials

2. Bottom-up: “Growing” nanowires step by step from atoms or molecules

In the following, we will introduce representative processes for both approaches, discuss their advantages and limitations, and outline suitable application scenarios.

Top-Down Nanowire Fabrication

1. Basic Concept

Top-down approaches can be likened to “carving a sculpture from a solid block of stone.” Starting from a wafer or bulk crystal, nanowires are formed by:

1. Patterning (photolithography, electron-beam lithography, nanoimprint, etc.)

2. Combining with wet or dry etching

to selectively remove excess material and leave behind wire-like structures.

The main advantage is their high compatibility with existing microelectronics manufacturing processes. However, they typically require:

1. Cleanroom environments

2. Expensive, high-precision equipment (lithography tools, etching systems, etc.)

2. Nanowire Fabrication by Lithography + Etching

1. Photolithography and Electron-Beam Lithography (E-beam Lithography)

1. Spin-coat a photoresist layer, such as PMMA, on the surface of a silicon or other semiconductor wafer.

2. Use a mask (photomask) or direct-write electron beam for exposure and development to obtain a patterned resist layer.

3. Vertical nanowires: the pattern consists of arrays of circular dots/holes.

4. Lateral (in-plane) nanowires: the pattern consists of lines/trenches (e.g., on SOI substrates).

5. The resolution of photolithography is limited by the light source wavelength and optical system. As the target feature size shrinks below several tens of nanometers, more advanced techniques such as electron-beam lithography and extreme ultraviolet (EUV) lithography are required. In current industrial practice, mainstream EUV technology is used at nodes in the tens-of-nanometers range, while e-beam lithography is mostly employed for research and mask fabrication rather than high-volume production.

2. Wet Etching and Dry Etching

1. Typical wet etchants such as KOH solution show dramatically different etch rates for different Si crystal orientations (e.g., {100}, {110}, {111}); among these, the {111} planes etch the slowest, leading to strongly anisotropic structural features.

2. Using photoresist or metals (such as Au) as an etch mask, the exposed regions are etched away to form pillar-like or wire-like structures.

3. Wet etching often leads to lateral undercutting beneath the mask, causing the nanowires to become tapered rather than ideal cylinders.

4. To obtain more vertical sidewalls, highly anisotropic dry etching processes such as deep reactive ion etching (DRIE) are commonly used, enabling vertical nanowire arrays with lengths of up to tens of micrometers.

3. Metal-Assisted Chemical Etching (MACE)

1. First, form metallic patterns (such as nanopores or dot arrays) on substrates like silicon.

2. In specific chemical solutions, local micro-electrochemical corrosion reactions occur between the metal and silicon, causing the silicon beneath the metal to be preferentially etched “downwards.”

3. This allows fabrication of nanowire/nanopore arrays with high aspect ratios and well-controlled morphology.

3. Lithography Alternatives: Nanosphere Lithography and Nanoimprint

To achieve higher resolution and higher throughput while reducing cost, several alternative patterning strategies have been developed:

1. Nanosphere Lithography (NSL)

1. Polymer nanospheres such as polystyrene self-assemble into close-packed monolayer arrays on the substrate surface.

2. The nanosphere array is then used as a mask for metal deposition or etching. After removing the spheres, large-area, periodic nanodot or nanopore arrays are obtained.

2. Nanoimprint Lithography (NIL)

1. A high-resolution master mold is first fabricated using more expensive techniques (e.g., electron-beam lithography).

2. The master mold is then mechanically pressed into a deformable photoresist or polymer layer to transfer the pattern.

3. This method is suitable for large-area replication of high-resolution structures, with low per-cycle cost, making it attractive for batch production.

4. Advantages and Limitations of Top-Down Methods

Advantages:

1. Straightforward fabrication of highly ordered nanowire arrays.

2. Easy integration with metal electrodes and interconnects, facilitating circuit-like routing.

3. Most processes are compatible with existing semiconductor manufacturing flows, enabling industrial-scale implementation.

Limitations:

1. As the target feature size decreases to tens of nanometers or below, conventional photolithography becomes increasingly complex and expensive.

2. Direct-write techniques such as electron-beam lithography and scanning-probe methods have low throughput and are not suitable for large-scale production.

3. Composition engineering and multi-segment structures in nanowires (e.g., axial heterojunctions, superlattices) are difficult to realize and require:

1. Pre-design during wafer growth using methods such as molecular beam epitaxy (MBE), or

2. Secondary processing such as ion implantation.

4. Overall process complexity and material costs are relatively high.

Bottom-Up Nanowire Synthesis

1. Basic Concept

Bottom-up approaches are closer to a chemist’s way of thinking: starting from atoms, molecules, or ions, the target structure is “grown” according to thermodynamic and kinetic principles. This is analogous to “growing a tree from a seed”:

1. Using gas-phase or solution-phase precursors

2. Controlling growth direction and morphology with catalysts or templates

3. Directly “writing in” compositional and structural information during growth

2. Vapor-Phase Synthesis: VLS/VSS, Templates, and Selective Epitaxy

2.1 Vapor–Liquid–Solid (VLS) Mechanism

VLS is one of the most common vapor-phase routes for nanowire growth:

1. Disperse metal nanoparticles (typically noble metals such as Au) on the substrate surface.

2. In a chemical vapor deposition (CVD) reactor, introduce gas-phase precursors containing the target elements (e.g., SiCl₄, organometallic precursors containing Ga or As, etc.).

3. The precursors decompose, and the resulting atoms dissolve into the metal droplets. Once supersaturation is reached, single-crystalline nanowires start to grow from the droplet–substrate interface.

4. As the reaction proceeds, the metal droplet can remain at the nanowire tip, and the nanowire continues to extend along its axial direction.

Features and advantages:

1. Growth parameters such as temperature, pressure, and gas flow rates can be precisely controlled.

2. By switching dopant sources on or off (e.g., phosphine PH₃, borane, dopant-containing precursors), doping can be tuned in situ during growth.

3. By varying the ratio of different precursors in multicomponent systems (e.g., GaAsₓP₁₋ₓ), axial superlattice and quantum-well structures with tailored bandgaps can be constructed.

In some material systems containing low-melting-point metals (such as GaAs), Ga itself can form droplets and act as a self-catalyst for VLS growth.

2.2 Vapor–Solid–Solid (VSS) Mechanism

VSS is similar to VLS, but the catalyst particles remain solid at the growth temperature:

1. Precursors diffuse and deposit at the solid catalyst/nanowire interface.

2. The growth rate is generally slower than in VLS.

3. However, because the interface is more stable, many systems can achieve sharper compositional transitions than with VLS, making VSS suitable for nanowire designs that demand high-quality heterointerfaces.

2.3 Template-Assisted and Catalyst-Free Growth

For applications where metal catalyst incorporation into nanowires is undesirable, template or selective epitaxy strategies can be adopted:

1. Template-assisted growth (e.g., AAO templates)

(1) Prepare anodic aluminum oxide (AAO) films with nanopore arrays; pore diameter and spacing are tunable.

(2) Use CVD, sputtering, or related methods to deposit/fill the target material into the nanopores.

(3) After removing the template, vertically aligned nanowire arrays are obtained.

2. Selective Area Epitaxy (SAE)

(1) Cover the substrate surface with a mask layer (e.g., SiO₂, Si₃N₄), and open only small holes or stripes to expose the underlying crystal surface.

(2) Under epitaxial growth conditions, crystal growth occurs only in the exposed regions, while almost no deposition occurs on the mask.

(3) This allows catalyst-free growth of nanowires or nanopillars directly at predefined locations.

3. Screw-dislocation-driven growth

(1) Screw dislocations present in certain materials can provide the driving force for spiral or one-dimensional growth.

(2) Long axial one-dimensional structures can thus be formed without additional catalysts.

In addition, variants such as aerotaxy suspend catalyst particles in a gas flow, enabling high-throughput nanowire production.

3. Solution-Phase Synthesis: SLS, Template Electrodeposition, and Seed-Mediated Growth

3.1 Solution–Liquid–Solid (SLS)

SLS is the solution-phase analogue of VLS:

1. Choose a high-boiling organic solvent (such as certain alkanes or oils) as the reaction medium.

2. Disperse metal nanoparticles in the solvent, where they form liquid droplets at the reaction temperature.

3. Precursors in solution decompose and diffuse into the droplets; once supersaturation is reached, crystals precipitate along the droplet interface, forming nanowires.

This method is suitable for synthesizing certain semiconductor or alloy nanowires at relatively low temperatures.

3.2 Template Electrodeposition

Templates such as AAO can also be used in solution-phase processes:

1. Place an AAO template on a conductive substrate.

2. Under electrochemical conditions, metal or semiconductor ions are reduced and deposited inside the nanopores.

3. By controlling potential, deposition time, and precursor concentration, nanowire length and composition can be tuned.

4. After removing the template, arrays of metallic/alloy/semiconductor nanowires are obtained.

3.3 Seed-Mediated, Surfactant-Controlled Nanowire Growth

For noble metal nanowires (such as Au and Ag), a “fast nucleation + slow growth + surface-directed control” strategy is commonly employed:

1. Use a strong reducing agent (e.g., sodium borohydride) to rapidly reduce metal salts and generate a large number of small seed particles.

2. In a system containing a weaker reducing agent (e.g., ascorbic acid), metal ions are reduced slowly and preferentially grow on existing seeds rather than forming new particles.

3. Add surfactants (such as CTAB) that selectively adsorb on specific crystal facets, thereby altering surface energy and growth rates along different directions.

4. Ultimately, one-dimensional preferential growth occurs along certain crystallographic directions (such as {111} or {100}), yielding nanowires with high aspect ratios. (For example, differences in CTAB adsorption on {100}/{110} and other facets lead to anisotropic growth rates and hence 1D growth.)

This method offers mild solution conditions, scalability, and morphology control via formulation and process tuning.

4. Advantages and Challenges of Bottom-Up Methods

Advantages:

1. Complex composition, doping profiles, and structural information can be directly “written in” during growth, enabling construction of:

(1) Axial or radial heterojunctions

(2) Superlattice structures

(3) Quantum wells and quantum dot–quantum wire hybrid structures, etc.

2. They provide highly designable structural platforms for photodetectors, light-emitting devices, memory devices, photonic crystals, and more.

3. Certain solution-based methods offer low cost and good scalability.

Challenges:

1. Many growth methods yield randomly oriented “nanowire forests” or colloidal dispersions.

2. For device-level applications, it is necessary to:

(1) Align nanowires in well-defined orientations at designated locations.

(2) Integrate them with electrodes and interconnects with high precision.

(3) Ensure compatibility with existing planar process flows and packaging technologies.

3. “How to transition from nanowire powders/suspensions to ordered, large-area, integrable arrays” remains one of the key engineering challenges at present.

Top-Down vs Bottom-Up: Comparison and Complementarity

From an engineering perspective, Top-down and Bottom-up are not meant to replace each other. Instead, they each have different strengths and are highly complementary:

1. Key Comparisons

1. Control over structure and position

(1) Top-down: Starts from a full wafer; positions, spacing, and patterns can be defined with high precision. This is well suited for large-area ordered arrays and electrode routing.

(2) Bottom-up: Positions are often determined by catalysts or templates. Without additional guiding strategies, it is usually difficult to achieve precise placement.

2. Composition and heterostructure design

(1) Top-down: Spatial modulation of composition and doping must be realized during wafer growth or post-processing, which makes the process complex and costly.

(2) Bottom-up: By switching precursors or dopant sources during growth, axial/radial heterojunctions and superlattices can form naturally, offering high flexibility.

3. Process compatibility and maturity

(1) Top-down: Highly compatible with CMOS and standard microelectronics processes, and can be readily introduced into existing production lines.

(2) Bottom-up: Integration with planar process flows is still a major engineering challenge and typically requires additional transfer, self-assembly, or alignment techniques.

4. Cost and throughput

(1) Top-down: At the nanoscale, high-end lithography and etching tools are required, leading to significant upfront investment.

(2) Bottom-up: Laboratory-scale costs are often lower, but achieving controlled, large-area, ordered integration still demands complex processing.

2. Complementary Strategies

The widespread industrial deployment of nanowires will very likely rely on a combination of both approaches. For example:

1. First, use Bottom-up methods to grow nanowires with complex heterostructures and tailored functionalities.

2. Then apply Top-down processes to:

(1) Achieve ordered alignment and precise positioning

(2) Precisely register electrodes and interconnect patterns

(3) Integrate the nanowires with existing chip or device platforms

Overview of Representative Aladdin Products for Nanowire Synthesis (Classified by Function)

Category	Cat. No.	CAS No.	Name	Grade / Purity	Function / Description
Reducing agents / co-reducing agents	L432790	50-81-7	L-Ascorbic acid	UltraBio™, ultrapure grade, ≥99.5% (RT)	Mild reducing agent for solution-phase growth of metal nanowires/nanoparticles; used together with NaBH₄ for seed growth.
Reducing agents / co-reducing agents	A103533	50-81-7	Ascorbic acid	AR, ≥99% (T)	General analytical-grade ascorbic acid for metal nanostructure synthesis and antioxidant protection.
Reducing agents / co-reducing agents	A656912	50-81-7	Ascorbic acid	Moligand™, animal-free, low endotoxin, for cell culture, ≥98%	Biograde ascorbic acid suitable for biocompatible nanomaterials and cell-related experiments.
Strong reducing agents	S108355	16940-66-2	Sodium borohydride (explosive precursor)	≥98%	Strong reducing agent for solution-phase synthesis of metal nanowires/nanoparticles; used for rapid nucleation.
Strong reducing agents	S432203	16940-66-2	Sodium borohydride solution	~12 wt.% in 14 M NaOH	Pre-formulated alkaline NaBH₄ solution, suitable for continuous or scaled-up synthesis; reduces errors from on-site preparation.
Strong reducing agents	S432205	16940-66-2	Sodium borohydride solution	2.0 M in triethylene glycol dimethyl ether	Organic-phase NaBH₄ solution for metal nanostructure synthesis in organic/biphasic systems.
Surfactants / morphology control agents	H108983	57-09-0	Cetyltrimethylammonium bromide (CTAB)	≥99%	Classic cationic surfactant used to control one-dimensional anisotropic growth of gold nanowires/nanorods.
Surfactants / morphology control agents	H108985	57-09-0	Cetyltrimethylammonium bromide	Molecular biology grade, ≥99%	High-purity CTAB suitable for nanostructures or biological systems that are highly sensitive to impurities.
Vapor-phase precursors (for VLS growth)	H755911	10026-04-7	Silicon tetrachloride	AR, ≥99.5%	Classic Si precursor for VLS vapor-phase growth of Si nanowires.
Vapor-phase precursors (for VLS growth)	S104669	10026-04-7	Silicon tetrachloride	PrimorTrace™ Ultra, ≥99.9999% metals basis	Ultra-high-purity SiCl₄ for Si nanowire/epitaxy processes extremely sensitive to impurities.
Vapor-phase precursors (for VLS growth)	S431131	10026-04-7	Silicon tetrachloride	Packaged for deposition systems	SiCl₄ packaging tailored for CVD/ALD systems, convenient for direct connection and use.
Vapor-phase precursors (for MOCVD/VLS)	T282558	1445-79-0	Trimethylgallium	≥99%	Organometallic Ga source for GaAs and other III–V semiconductor nanowires and thin films.
Vapor-phase precursors (for MOCVD/VLS)	T283549	1445-79-0	Trimethylgallium	PrimorTrace™ Ultra, electronic grade, ≥99.9999% metals basis	High-purity electronic-grade TMGa for high-performance optoelectronic nanowire/quantum-structure epitaxy.
Vapor-phase precursors (for MOCVD/VLS)	T432113	1445-79-0	Trimethylgallium	Packaged for deposition systems	TMGa packaging compatible with deposition systems, facilitating process integration.
High-boiling solvents (SLS growth media)	S141335	111-01-3	Squalane	≥98%	Typical high-boiling organic solvent for SLS solution-phase nanowire synthesis.
High-boiling solvents (SLS growth media)	S141278	111-01-3	Squalane	≥95%	General-grade squalane for dispersing organic-phase precursors and use in high-temperature reaction systems.
High-boiling solvents (SLS growth media)	S420613	111-01-3	Squalane	10 mM in DMSO	Pre-formulated squalane solution for composite systems or bio-related studies.
Etchants / bases	P112284	1310-58-3	Potassium hydroxide	AR, ≥85%	Conventional KOH reagent for anisotropic wet etching of Si in top-down nanowire fabrication.
Etchants / bases	P112281	1310-58-3	Potassium hydroxide	Electronic grade, ≥99.99% metals basis, Purity excludes sodium content	High-purity electronic-grade KOH for semiconductor etching/cleaning processes requiring strict control of metallic impurities.
Developers	P1492633	1310-58-3	Potassium hydroxide developer	Electronic grade	Ready-to-use KOH developer for development or etching of specific photoresists/inorganic materials.
Element standard solutions	A105851	7429-90-5	Aluminum standard solution	Analytical standard, 1000 μg/mL in 1.0 mol/L HNO₃	For aluminum content calibration by ICP/atomic absorption; relevant to quality control of aluminum substrates and AAO templates.
Element standard solutions	G115387	7440-57-5	Gold standard solution	1000 μg/mL in 1.5 mol/L HCl	Gold elemental standard solution for content analysis and recovery-rate assessment of gold catalysts/gold nanostructures.
Alumina-based substrates	A420217	1344-28-1	Aluminum oxide	≥99.9% metals basis	High-purity Al₂O₃ powder for ceramic substrates or porous structure preparation.
Alumina-based substrates	A140802	1344-28-1	Aluminum oxide	PrimorTrace™, ≥99.99% metals basis	Ultra-high-purity alumina powder for optical/electronic-grade materials or high-quality templates.
Nano alumina	A431930	1344-28-1	Aluminum oxide	Nanopowder, <50 nm (TEM)	Nanoscale Al₂O₃ powder for thin films, porous materials, or nanostructure fabrication.
Nano alumina	A119404	1344-28-1	Nano alumina aqueous dispersion	5–10 nm, 20 wt.% in water	Nano alumina aqueous dispersion that can be readily coated into films; usable as a template or functional layer.
Nano alumina	V1375751	1344-28-1	Fumed nano alumina	Hydrophilic, ≥98%, BET specific surface area: 100 m²/g; particle size: 10–30 nm	Hydrophilic fumed nano Al₂O₃ with high specific surface area, suitable as template, filler, or catalyst support.
Nano alumina	A431931	1344-28-1	Aluminum oxide	Nanowires, diameter × L: 2–6 nm × 200–400 nm	Preformed alumina nanowires as model nanowire systems or reinforcement phases in composites.
Activated alumina beads	A1492666	1344-28-1	Activated alumina beads	General-purpose desiccant	Common desiccant for drying gases/solvents in nanowire synthesis environments.
Activated alumina beads	A1492668	1344-28-1	Activated alumina beads	Catalyst support	Catalyst support for loading metal particles for vapor-phase reactions or subsequent catalytic applications.
Alumina reference materials	A119405	1344-28-1	α-Phase nano alumina dispersion slurry	α-phase, 30 nm, 20 wt.% in water	Reference material for specific surface area/particle size measurements; related to characterization of porous alumina templates.
Alumina reference materials	A489899	1344-28-1	Aluminum oxide specific surface area reference material	Specific surface area: 5.78 m²/g	Standard material for BET specific surface area calibration.
Aluminum substrates / AAO parent materials	A433419	7429-90-5	Aluminum	PrimorTrace™, ≥99.999% metals basis, foil	High-purity aluminum foil, a typical starting material for preparing anodic aluminum oxide (AAO) porous membranes.
Aluminum substrates / AAO parent materials	A434751	7429-90-5	Aluminum	PrimorTrace™, ≥99.99% metals basis, pellets, 3–12 mm	High-purity aluminum pellets for melting/rolling, suitable for AAO preparation.
Aluminum substrates / AAO parent materials	A105846	7429-90-5	Aluminum sheet	PrimorTrace™, ≥99.99% metals basis, 0.1 mm	High-purity aluminum sheets suitable for direct anodization into AAO templates.
Aluminum powders	A105854	7429-90-5	Aluminum powder (explosive precursor)	≥99.95% metals basis, <10 μm	High-purity, fine aluminum powder for sintering, powder metallurgy, or alumina preparation.
Aluminum powders	A293601	7429-90-5	Aluminum powder (explosive precursor)	≥99.8%, spherical, D50: 2–3 μm	Spherical aluminum powder suitable as a high-specific-surface aluminum source or for special combustion systems.
Polystyrene resins	P107085	9003-53-6	Polystyrene (PS)	General-purpose type I, for general injection molding	General-purpose PS resin for use as a matrix material or for in-house preparation of microspheres/films.
Polystyrene resins	P434447	9003-53-6	Polystyrene (PS)	Mw ~400,000 (GPC)	PS with known molecular weight for research and use as a molecular weight standard.
PS microsphere templates	P107772	9003-53-6	Polystyrene microspheres	Diameter 0.05–0.1 μm, 2.5% w/v	Sub-100 nm PS microspheres suitable for preparing fine-scale nanosphere lithography templates.
PS microsphere templates	P107775	9003-53-6	Polystyrene microspheres	Diameter 1.0–1.9 μm, 5% w/v	Micrometer-scale PS microspheres for micro-periodic structure templates.
PS microsphere templates	P107780	9003-53-6	Polystyrene microspheres	Diameter 6.0–6.9 μm, 5% w/v	Large PS microspheres for optical structures or macroscopic periodic arrays.
Functionalized PS microspheres	P107786	9003-53-6	Amino polystyrene microspheres	Diameter 0.05–0.1 μm, 2.5% w/v	Amino-functionalized nanospheres for subsequent chemical modification or bioconjugation.
Functionalized PS microspheres	P107790	9003-53-6	Amino polystyrene microspheres	Diameter 1.0–1.9 μm, 2.5% w/v	Micrometer-scale amino-functionalized PS microspheres for functional templates or particle arrays.
Functionalized PS microspheres	P107802	9003-53-6	Carboxyl polystyrene microspheres	Diameter 0.05–0.1 μm, 2.5% w/v	Carboxyl-functionalized nanospheres for coupling with amine-containing molecules in bio/sensing templates.
Functionalized PS microspheres	P107808	9003-53-6	Carboxyl polystyrene microspheres	Diameter 4.0–4.9 μm, 5% w/v	Micrometer-scale carboxyl PS microspheres for large-size functional templates or particle assemblies.
PMMA resins (photoresist matrix)	P434522	9011-14-7	Poly(methyl methacrylate) (PMMA)	Mw ~350,000 (GPC)	High-molecular-weight PMMA for e-beam resists or custom film preparation.
PMMA resins (photoresist matrix)	P434521	9011-14-7	Poly(methyl methacrylate) (PMMA)	Mw ~120,000 (GPC)	Medium-molecular-weight PMMA for films of different thicknesses and formulation tuning.
PMMA resins (photoresist matrix)	P141444	9011-14-7	Poly(methyl methacrylate) (PMMA)	General injection grade	Engineering-plastic-grade PMMA usable as a substrate or structural component.
Metallic gallium	G130123	7440-55-3	Gallium metal	PrimorTrace™, ≥99.99% metals basis	High-purity Ga for self-catalyzed VLS growth of GaAs/GaP nanowires.
Metallic gallium	G105131	7440-55-3	Gallium metal	PrimorTrace™ Ultra, ≥99.9999% metals basis	Ultra-high-purity Ga for high-end optoelectronic/nanowire epitaxy processes.
Metallic gallium	G493405	7440-55-3	Gallium	General grade	General-grade gallium for alloys, precursor synthesis, or teaching experiments.
III–V semiconductor materials	G119227	1303-00-0	Gallium arsenide	PrimorTrace™, ≥99.999% metals basis, pieces	High-purity GaAs for substrates, sputtering targets, or crushed as nanowire seeds; directly corresponds to GaAs nanowires discussed in the text.
Gold metal powders	G434758	7440-57-5	Gold	≥99.9% metals basis, powder, <10 μm	High-purity fine gold powder for nanogold catalysts or noble metal electrodes.
Gold metal powders	G434760	7440-57-5	Gold	≥99.99% metals basis, powder, <850 μm, ≥99.99% trace metals basis	Ultra-high-purity gold powder for evaporation targets or as a gold source.
Gold nanoparticles	S359068	7440-57-5	Spherical gold nanoparticles	30 nm, 0.03 mg/mL, solvent: ultrapure water	30 nm spherical gold nanoparticles for optical and sensing applications, or as precursors for VLS catalyst seeds.
Gold nanoparticles	G359129	7440-57-5	Gold nanoparticles	10 nm, 1 OD, supplied in 0.1 mM citrate buffer	Small citrate-stabilized gold nanoparticles for functionalization and labeling.
Gold nanoparticles	G486048	7440-57-5	Gold nanoparticles	Diameter 200 nm, stable suspension in citrate buffer	Large gold nanoparticles for scattering experiments or as templates.
Gold nanorods	G359095	7440-57-5	Gold nanorods	10 nm diameter, λmax 780 nm, dispersion in H₂O	Near-infrared-absorbing gold nanorods, closely related to CTAB-based morphology control systems; suitable for photothermal and optical device studies.

Note: Products labeled as “explosive precursor” are classified as hazardous chemicals. Their purchase and use must comply with relevant local regulations and safety management requirements.

Aladdin: https://www.aladdinsci.com/