During this time, researchers began using CNTs in other applications that benefit from their 1-D geometry, for example, using CNTs as field-emission electron sources. In 1998, CNT-tipped atomic force microscopy (AFM) probes were reported, demonstrating the potential of CNTs in enhancing scanning probe microscopy capabilities owing to their inherent high-aspect-ratio geometry. An innovative example of this is the use of carboxyl groups present on partially oxidized ends of the CNT AFM tips as attachment points for other chemical moieties, thereby forming AFM probes that are sensitive to the chemical functionality present on a sample surface. The ability to explore the use of CNTs in a wide variety of applications was enabled by advances in CNT synthesis in the 10 years following their discovery. In 1992, by optimizing the conditions of the arc-discharge process, particularly the helium pressure, Ebbesen and Ajayan were able to generate and isolate gram-scale quantities of MWCNTs. Subsequently, a group at Rice University led by Richard Smalley developed a process based on laser ablation of metal/graphite composite targets to produce SWCNTs with high yield. Another major development around this time was the development of chemical vapor deposition (CVD) methods to synthesize CNTs. In CVD, a carbon-containing precursor gas (benzene and acetylene in these early studies) flows over a substrate at elevated temperatures. Reactions between the precursor and surface then lead to the growth of CNTs from the surface. The degree of morphological control, adaptability, and scalability of CVD has led to it being the most common synthesis route for CNTs today. An example of the control and scalability of CNT CVD is the ability to generate aligned 'forests' of CNTs on a substrate consisting of catalytic iron nanoparticles embedded in silica. A total count of the CNT-related journal and patent publications between 1992 and 2023 is shown in Figure . Research in this field grew rapidly between 1991 and 1999, to roughly 1,000 publications per year by 2000. Between 2000 and 2013, an approximately linear, ten-fold increase in the number of journal publications is observed. Between 2013 and 2017, growth in journal publications appear to have plateaued and remain more or less constant at 10,000 publications per year, while the frequency of patent publications continued to grow, eventually leveling off at ~7,000 per year in 2018 (Figure ). Since 2016, the number of publications generally increased again, driven by diverse, emerging applications including electrochemical CO2 reduction, flexible sensors, and others that will be discussed in more detail in the "Applications of carbon nanotubes" section. Geographical distribution of publications indicates that commercial and non-commercial entities from China (CHN) appear to dominate in the field of CNT-related research with the total number of publications exceeding those from the United States (US), South Korea (KOR) and Japan (JPN) combined (Figure ). Other key countries/regions include India (IND), Iran (IRN), Germany (DEU), Russia (RUS), Taiwan (TWN), France (FRA), United Kingdom (GBR), Italy (ITA), Canada (CAN), Spain (ESP) and Brazil (BRA). The patent-to-journal ratios for these countries/regions indicates that most of them have a higher proportion of journal publications, the exceptions being South Korea and Japan which have a slightly higher proportion of patent publications. India and Iran on the other hand, have an overwhelming number of journal publications as compared to patent publications suggestive of minimal/lack of commercial efforts by organizations in those countries.