Growth of Gold Dendritic Nanoforests on Titanium Nitride-coated Silicon Substrates

Summary

This study presents a feasible procedure for synthesizing gold dendritic nanoforests on titanium nitride/silicon substrates. The thickness of gold dendritic nanoforests increases linearly within 15 min of a synthesis reaction.

Abstract

In this study, a high-power impulse magnetron sputtering system is used to coat a flat and firm titanium nitride (TiN) film on silicon (Si) wafers, and a fluoride-assisted galvanic replacement reaction (FAGRR) is employed for the rapid and easy deposition of gold dendritic nanoforests (Au DNFs) on the TiN/Si substrates. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy patterns of TiN/Si and Au DNFs/TiN/Si samples validate that the synthesis process is accurately controlled. Under the reaction conditions in this study, the thickness of the Au DNFs increases linearly to 5.10 ± 0.20 µm within 15 min of the reaction. Therefore, the employed synthesis procedure is a simple and rapid approach for preparing Au DNFs/TiN/Si composites.

Introduction

Gold nanoparticles have characteristic optical properties and localized surface plasmon resonances (LSPRs), depending on the size and shape of the nanoparticles^1,2,3,4. Moreover, gold nanoparticles can significantly enhance plasmonic photocatalytic reactions⁵. Dendritic nanoforests stacked using gold nanoparticles have received considerable attention because of their noteworthy specific surface areas and robust LSPR enhancement^{6,7,8,9,10,11,12,13}.

TiN is an extremely hard ceramic material and has remarkable thermal, chemical, and mechanical stability. TiN has distinctive optical properties and can be used for plasmonic applications with visible-to-near-infrared light^14,15. Research has demonstrated that TiN can produce electromagnetic field enhancements, similar to Au nanostructures¹⁶. The deposition of copper¹⁷ or silver^18,19,20 on TiN substrates for applications has been demonstrated. However, few studies have been performed on Au/TiN composite materials for applications. Shiao et al. have recently demonstrated potential applications of Au DNFs/TiN composites for photoelectrochemical cells²¹ and chemical degradation²².

Au can be synthesized on a TiN substrate by using a FAGRR²³. The deposition condition of Au DNFs on TiN is crucial in the performance of applications. This study examines the growth of Au DNFs on a TiN-coated Si substrate.

Protocol

1. Sample preparation

1. TiN substrate preparation using a high-power impulse magnetron sputtering system
   1. Cut a 4 inch n-type silicon wafer into 2 cm x 2 cm samples.
   2. Wash the samples using acetone, isopropanol, and deionized water.
   3. Dry them using an N₂ spray for 5 min.
   4. Place the washed Si samples in a sample holder and place the sample holder into a high-power impulse magnetron sputtering (HiPIMS) chamber.
   5. Place a titanium target with a diameter of 4 inches on a sputtering cathode.
   6. Reduce the chamber pressure to less than 8 x 10^-6 Torr by using a mechanical pump and cryopump.
   7. Use HiPIMS to deposit a Ti layer on a silicon wafer and deposit a TiN layer on the Ti layer. See Table 1 for the deposition parameters of Ti and TiN layers in HiPIMS.
2. Au DNF preparation on TiN/Si substrates
   1. Place 24 mL of a reactant solution comprising 10 mM chloroauric acid (HAuCl₄) and buffered oxide etchant solution comprising 11.4% NH₄F and 2.3% HF into a Teflon container measuring 5 cm x 5 cm x 5 cm.
   2. Dip the substrates into the mixture solution for 3 min.
   3. Remove the sample and wash it using deionized water.
   4. Dry the sample using the N₂ spray and then incubate it at 120 °C for 5 min to obtain Au DNFs/TiN/Si samples.
   5. Repeat the Au DNF preparation 10x.

2. Sample examination

1. Scanning electron microscopy analyses
   1. Cut the sample into 0.4 cm x 0.8 cm with a tungsten pen, and clean it using the N₂ spray.
   2. Coat a thin Pt film on the sample by an ion sputter coater for 50 s.
   3. Place the prepared sample into a scanning electron microscopy (SEM) instrument.
   4. Obtain SEM images by the scanning electron microscope and conduct element analysis^21,22.
2. X-ray diffraction analyses
   1. Place the sample into an X-ray diffraction (XRD) instrument.
   2. Obtain XRD patterns^21,22.

Results

Figure 1 depicts images of the Au DNFs/TiN/Si sample preparations. The silicon wafer was silvery white (Figure 1a). TiN/Si was golden yellow and had a homogeneous surface (Figure 1b), which indicated the uniform TiN coating on the silicon wafer. Au DNFs/TiN/Si was yellowish brown and less homogeneous on the surface (Figure 1c) because of the random distribution of Au DNF...

Discussion

In this study, Au DNFs with multiple branch sizes were decorated on the surface of TiN/Si by using FAGRR. The deposition of the Au DNFs could be directly identified by a significant change in color. The thickness of the Au DNFs on TiN/Si increased to 5.10 ± 0.20 µm within 15 min, and this increase in thickness can be expressed using the following linear equation: y = 0.296t + 0.649, where the time varied from 1 to 15 min.

In FAGRR, the metal deposition is affected b...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone	Dinhaw Enterprise Co. Ltd.,Taipei, Taiwan
Isopropanol	Echo Chemical Co. Ltd., Miaoli, Taiwan	TG-078-000000-75NL
Buffered Oxide Etch	Uni-onward Corp., Hsinchu, Taiwan	UR-BOE-1EA
Chloroauric Acid	Alfa Aesar., Heysham, United Kingdom	36400.03
N-Type Silicon Wafer	Summit-Tech Company, Hsinchu, Taiwan
High-Power Impulse Magnetron Sputtering System (HiPIMS)	Melec GmbH, Germany		SPIK2000A
Scanning Electron Microscope (SEM)	JEOL, Japan		JSM-7800F
Ion Sputter Coater	Hitachi, Japan		E-1030
X-Ray Diffractometer (XRD)	PANalytical, The Netherlands		X'Pert PRO MRD