在本論文中，先沉積三氧化鎢薄膜，再利用爐管通入硫化氫在高溫環境中將三氧化鎢薄膜硫化，形成二硫化鎢薄膜，並嘗試藉由精準控制三氧化鎢薄膜的厚度，獲得不同層數的二硫化鎢薄膜。此外，對二硫化鎢薄膜進行光學及分析，以了解二硫化鎢薄膜的詳細特性，以便追蹤薄膜的製造品質。此外，也研究二硫化鎢相關元件的製作與特性。
實驗中，首先要先製作出穩定且可控制的二硫化鎢薄膜。在本研究的實驗流程中，首先利用射頻濺鍍機在基板上鍍上一層三氧化鎢薄膜，接著再利用高溫爐管中通入硫化氫，反應後即可得到二硫化鎢薄膜。薄膜品質的要點在於生長的三氧化鎢品質與厚度，因此，三氧化鎢的鍍率是首要的考量。由於需要精確的控制三氧化鎢的厚度，實驗中盡可能在穩定的情況中降低射頻濺鍍機的功率，並且監控每次使用時的偏壓，已達成實驗中成長薄膜的一致性。在本實驗中，使用了藍寶石基板與具有200奈米二氧化矽的矽基板，並且在生長時，藉由控制三氧化鎢沉積的時間，達到單層、雙層及塊材薄膜等等的不同厚度。再使用拉曼光學儀、橢圓偏光儀等光學儀器，以及高解析電子穿透式顯微鏡、原子力顯微鏡等等儀器做進一步的量測。由分析結果顯示，我們成功做出了不同厚度的二硫化鎢薄膜。其中，將單層薄膜與雙層薄膜進行比較，可以得知雙層薄膜的薄膜品質較好。生長於藍寶石基板上的薄膜品質也較生長於二氧化矽基板上的薄膜品質好。
在實驗的第二部分中，我們嘗試使用二硫化鎢薄膜製作相關的元件，其中有二硫化鎢酸鹼感測器、氣體感測器以及光感測器等等。在這個部分的實驗中，光感測的部分，雙層薄膜是唯一有穩定光響應的元件。對於單層薄膜元件，雖然可以觀察到反應，但我們沒辦法完成一個光-暗響應週期。多層薄膜中，我們也沒有辦法觀測到光響應。
對於氣體感測，單層薄膜雖然電流較小，但是可以有完整的反應-還原週期。單層薄膜的響應大約為70 %，而響應時間及回復時間則分別為75秒及200秒。雙層薄膜雖然有較大的響應，但是他的反應速度及還原速度相對較慢，大約為150秒及400秒，且在有限時間內，無法回復至原本的狀態。我們也藉由氣體感測的結果，推論薄膜屬於P型半導體。此外，提升溫度也可以加速單層薄膜的響應速度與還原速度。
對於酸鹼感測，單層薄膜的感應也是最好的，可以觀察到在不同酸鹼度的情況下，單層薄膜的電流差異最大。我們也有將薄膜重複來回浸泡在pH值為2及12的溶液中，觀察響應的穩定性，發現這些感測器都有重複性，而單層薄膜的響應最迅速。我們也觀察到生長於二氧化矽基板上的薄膜在經過浸泡之後，有缺損的情況。這也進一步驗證了我們認為它生長品質不佳的猜測。
由於單層元件感測表面積與總體積之間的比例是最大的，對於氣體感測及酸鹼感測上，單層元件有一定的優勢。這也是為何二維材料感測器受到重視的原因。相較之下，由於薄膜是透光的，在進行光感測時，單層材料的優勢就消失了。相對的，單層薄膜因為缺陷及表面完整度造成的電流較小且不穩定等因素，會使他相較於雙層薄膜沒有那麼好的特性。
二維二硫化鎢薄膜做出的感測器對特定頻率的光、氣體及酸鹼度有所響應，在實驗中也成功製作出相關的元件。經過我們的實驗，我們認為二為二硫化鎢也有製作更小尺度的元件以及薄膜電晶體的潛力。另外，使用我們的製程也可以成功製作出其他二維過度金屬硫化物。

In this work, a tungsten trioxide film is deposited first, and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high temperature environment to form a tungsten disulfide film. We try to precisely control the thickness of the tungsten trioxide film to obtain different layers of tungsten disulfide film. In addition, optical and analysis of the tungsten disulfide film are carried out to understand the detailed characteristics of the tungsten disulfide film in order to track the manufacturing quality of the film. In addition, the manufacture and characteristics of tungsten disulfide related devices are also studied.
In the experiment, a stable and controllable tungsten disulfide thin film must first be produced. In the experimental process of this research, a layer of tungsten trioxide film is first deposit on the substrate by radio frequency (RF) sputtering, and then hydrogen sulfide is injected into the high-temperature furnace tube, and the tungsten disulfide film can be formed after the reaction. The thickness and quality if tungsten trioxide is very important. Therefore, the deposit rate of tungsten trioxide is the primary consideration. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment, and the bias voltage during each process was monitored, and the consistency of the growth film in the experiment has been achieved. In this experiment, a sapphire substrate and a silicon substrate with 200 nm silicon dioxide are used, and during growth, by controlling the time of deposition of tungsten trioxide, different thicknesses of single layer, double layer, and bulk film are achieved. And then use optical instruments such as Raman optics, ellipsometers, and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Among them, comparing the single-layer film and the double-layer film, it can be seen that the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.
In the second part of this work, we tried to use tungsten disulfide thin films to make related devices, including tungsten disulfide pH sensors, gas sensors, and photodetectors. In the photodetector part, the double-layer film is the only component with stable photo response. For single-layer thin-film devices, although the response can be observed, we cannot complete a light-dark response cycle. In the multilayer film, we can not observe the light response, either.
For gas sensing, although the current of a single-layer film is small, it can have a complete reaction-recovery cycle. The response of the single-layer film is about 70%, and the response and recovery time are 75 seconds and 200 seconds, respectively. Although the double-layer film has a relatively large response, its reaction and recovery speed are relatively slow, about 150 seconds and 400 seconds, and within a limited time, current cannot return to the original state. We also deduced that the film is a P-type semiconductor based on the results of gas sensing. In addition, increasing the temperature can also accelerate the response speed and reduction speed of the single-layer film.
For pH sensing, the single-layer film has the best sensing. It can be observed that the current difference of the single-layer film is the largest under different pH conditions. We have also repeatedly immersed the film back and forth in solutions with pH values of 2 and 12, and observed the stability of the response, and found that these sensors have repeatability, and the single-layer film has the fastest response. We have also observed that the thin film grown on the silicon dioxide substrate is defective after being immersed. This also further verified our guess that it is of poor growth quality.
Since the ratio between the sensing surface area of the single-layer device and the total volume is the largest, the single-layer device has certain advantages for gas sensing and acid-base sensing. This is why two-dimensional material sensors are valued. In contrast, since the film is light-transmissive, the advantage of a single-layer material disappears when performing light sensing. In contrast, single-layer films have relatively small and unstable currents due to defects and surface integrity, which will make them have worse characteristics than double-layer films.
Two-dimensional tungsten disulfide thin film have response to light, gas, and pH, and related devices have been successfully fabricated in experiments. Through our experiments, we believe that tungsten disulfide has the potential to make smaller-scale devices and thin-film transistors. In addition, other two-dimensional transition metal sulfides can be successfully produced using our process.

[1] Novoselov, K. S., et al. "Electric Field Effect in Atomically Thin Carbon Films" Science. 306.5696 (2004): 666-669
[2] Sang, J. K., et al. "Materials for Flexible, Stretchable Electronics: Graphene and 2D Materials" Annual Review of Materials Research 45 (2015):63-84
[3] Shengxuan, X., et al. "Plasmonically induced transparency in in-plane isotropic and anisotropic 2D materials" OSA Optics 28.6 (2020):7980-8002
[4] Matthew, J. A., et al. "Honeycomb Carbon: A Review of Graphene" ACS Chemical Review 110.1 (2010):132-145
[5] Aamar, F. K., et al. "2D Hexagonal Boron Nitride (2D-hBN) Explored for the Electrochemical Sensing of Dopamine" ACS Publications 88.19 (2016):9729-9737
[6] Joshua, B, S., et al. "Growth of 2D black phosphorus film from chemical vapor deposition" IOP Science 27.215602 (2016)
[7] Sajedeh, M., et al. "2D transition metal dichalcogenides" Nature Review Materials 17033 (2017)
[8] Desheng, K., et al. "Synthesis of MoS2 and MoSe2 Films with Vertically Aligned Layers" ACS Nano 13.3 (2013):1341-1347
[9] Hui, F., et al. "High-Performance Single Layered WSe2 p-FETs with Chemically Doped Contacts" ACS Nano 12.7 (2012):3788-3792
[10] Drew, W. L., et al. "Electronic structure, spin-orbit coupling, and interlayer interaction in bulk MoS2 and WS2" APS Physics 91.235202 (2015)
[11] Vishakha, K. et al. "Charge Transport in 2D MoS2, WS2, and MoS2–WS2 Heterojunction-Based Field-Effect Transistors: Role of Ambipolarity" ACS Publications 124.42 (2020):23368-23379